Network Working Group F. Andreasen Request for Comments: 3435 B. Foster Obsoletes: 2705 Cisco Systems Category: Informational January 2003 Media Gateway Control Protocol (MGCP) Version 1.0 Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. IESG Note This document is being published for the information of the community. It describes a protocol that is currently being deployed in a number of products. Implementers should be aware of RFC 3015, which was developed in the IETF Megaco Working Group and the ITU-T SG16 and which is considered by the IETF and ITU-T to be the standards-based (including reviewed security considerations) way to meet the needs that MGCP was designed to address. Abstract This document describes an application programming interface and a corresponding protocol (MGCP) which is used between elements of a decomposed multimedia gateway. The decomposed multimedia gateway consists of a Call Agent, which contains the call control "intelligence", and a media gateway which contains the media functions, e.g., conversion from TDM voice to Voice over IP. Media gateways contain endpoints on which the Call Agent can create, modify and delete connections in order to establish and control media sessions with other multimedia endpoints. Also, the Call Agent can instruct the endpoints to detect certain events and generate signals. The endpoints automatically communicate changes in service state to the Call Agent. Furthermore, the Call Agent can audit endpoints as well as the connections on endpoints. Andreasen & Foster Informational [Page 1] RFC 3435 MGCP 1.0 January 2003 The basic and general MGCP protocol is defined in this document, however most media gateways will need to implement one or more MGCP packages, which define extensions to the protocol suitable for use with specific types of media gateways. Such packages are defined in separate documents. Table of Contents 1. Introduction.................................................5 1.1 Relation with the H.323 Standards............................7 1.2 Relation with the IETF Standards.............................8 1.3 Definitions..................................................9 1.4 Conventions used in this Document............................9 2. Media Gateway Control Interface.............................10 2.1 Model and Naming Conventions................................10 2.1.1 Types of Endpoints..........................................10 2.1.2 Endpoint Identifiers........................................14 2.1.3 Calls and Connections.......................................16 2.1.4 Names of Call Agents and Other Entities.....................22 2.1.5 Digit Maps..................................................23 2.1.6 Packages....................................................26 2.1.7 Events and Signals..........................................28 2.2 Usage of SDP................................................33 2.3 Gateway Control Commands....................................33 2.3.1 Overview of Commands........................................33 2.3.2 EndpointConfiguration.......................................36 2.3.3 NotificationRequest.........................................37 2.3.4 Notify......................................................44 2.3.5 CreateConnection............................................46 2.3.6 ModifyConnection............................................52 2.3.7 DeleteConnection (from the Call Agent)......................54 2.3.8 DeleteConnection (from the gateway).........................58 2.3.9 DeleteConnection (multiple connections from the Call Agent) 59 2.3.10 AuditEndpoint...............................................60 2.3.11 AuditConnection.............................................65 2.3.12 RestartInProgress...........................................66 2.4 Return Codes and Error Codes................................69 2.5 Reason Codes................................................74 2.6 Use of Local Connection Options and Connection Descriptors..75 2.7 Resource Reservations.......................................77 3. Media Gateway Control Protocol..............................77 3.1 General Description.........................................78 3.2 Command Header..............................................79 3.2.1 Command Line................................................79 3.2.2 Parameter Lines.............................................82 3.3 Format of response headers.................................101 3.3.1 CreateConnection Response..................................104 3.3.2 ModifyConnection Response..................................105 Andreasen & Foster Informational [Page 2] RFC 3435 MGCP 1.0 January 2003 3.3.3 DeleteConnection Response..................................106 3.3.4 NotificationRequest Response...............................106 3.3.5 Notify Response............................................106 3.3.6 AuditEndpoint Response.....................................106 3.3.7 AuditConnection Response...................................107 3.3.8 RestartInProgress Response.................................108 3.4 Encoding of the Session Description (SDP)..................108 3.4.1 Usage of SDP for an Audio Service..........................110 3.4.2 Usage of SDP for LOCAL Connections.........................110 3.5 Transmission over UDP......................................111 3.5.1 Providing the At-Most-Once Functionality...................112 3.5.2 Transaction Identifiers and Three Ways Handshake...........113 3.5.3 Computing Retransmission Timers............................114 3.5.4 Maximum Datagram Size, Fragmentation and Reassembly........115 3.5.5 Piggybacking...............................................116 3.5.6 Provisional Responses......................................117 4. States, Failover and Race Conditions.......................119 4.1 Failover Assumptions and Highlights........................119 4.2 Communicating with Gateways................................121 4.3 Retransmission, and Detection of Lost Associations:........122 4.4 Race Conditions............................................126 4.4.1 Quarantine List............................................127 4.4.2 Explicit Detection.........................................133 4.4.3 Transactional Semantics....................................134 4.4.4 Ordering of Commands, and Treatment of Misorder............135 4.4.5 Endpoint Service States....................................137 4.4.6 Fighting the Restart Avalanche.............................140 4.4.7 Disconnected Endpoints.....................................143 4.4.8 Load Control in General....................................146 5. Security Requirements......................................147 5.1 Protection of Media Connections............................148 6. Packages...................................................148 6.1 Actions....................................................150 6.2 BearerInformation..........................................150 6.3 ConnectionModes............................................151 6.4 ConnectionParameters.......................................151 6.5 DigitMapLetters............................................151 6.6 Events and Signals.........................................152 6.6.1 Default and Reserved Events................................155 6.7 ExtensionParameters........................................156 6.8 LocalConnectionOptions.....................................157 6.9 Reason Codes...............................................157 6.10 RestartMethods.............................................158 6.11 Return Codes...............................................158 7. Versions and Compatibility.................................158 7.1 Changes from RFC 2705......................................158 8. Security Considerations....................................164 9. Acknowledgments............................................164 Andreasen & Foster Informational [Page 3] RFC 3435 MGCP 1.0 January 2003 10. References.................................................164 Appendix A: Formal Syntax Description of the Protocol.............167 Appendix B: Base Package..........................................175 B.1 Events.....................................................175 B.2 Extension Parameters.......................................176 B.2.1 PersistentEvents...........................................176 B.2.2 NotificationState..........................................177 B.3 Verbs......................................................177 Appendix C: IANA Considerations...................................179 C.1 New MGCP Package Sub-Registry..............................179 C.2 New MGCP Package...........................................179 C.3 New MGCP LocalConnectionOptions Sub-Registry...............179 Appendix D: Mode Interactions.....................................180 Appendix E: Endpoint Naming Conventions...........................182 E.1 Analog Access Line Endpoints...............................182 E.2 Digital Trunks.............................................182 E.3 Virtual Endpoints..........................................183 E.4 Media Gateway..............................................184 E.5 Range Wildcards............................................184 Appendix F: Example Command Encodings.............................185 F.1 NotificationRequest........................................185 F.2 Notify.....................................................186 F.3 CreateConnection...........................................186 F.4 ModifyConnection...........................................189 F.5 DeleteConnection (from the Call Agent).....................189 F.6 DeleteConnection (from the gateway)........................190 F.7 DeleteConnection (multiple connections from the Call Agent).......................................190 F.8 AuditEndpoint..............................................191 F.9 AuditConnection............................................192 F.10 RestartInProgress..........................................193 Appendix G: Example Call Flows....................................194 G.1 Restart....................................................195 G.1.1 Residential Gateway Restart................................195 G.1.2 Call Agent Restart.........................................198 G.2 Connection Creation........................................200 G.2.1 Residential Gateway to Residential Gateway.................200 G.3 Connection Deletion........................................206 G.3.1 Residential Gateway to Residential Gateway.................206 Authors' Addresses................................................209 Full Copyright Statement..........................................210 Andreasen & Foster Informational [Page 4] RFC 3435 MGCP 1.0 January 2003 1. Introduction This document describes an abstract application programming interface (MGCI) and a corresponding protocol (MGCP) for controlling media gateways from external call control elements called media gateway controllers or Call Agents. A media gateway is typically a network element that provides conversion between the audio signals carried on telephone circuits and data packets carried over the Internet or over other packet networks. Examples of media gateways are: * Trunking gateways, that interface between the telephone network and a Voice over IP network. Such gateways typically manage a large number of digital circuits. * Voice over ATM gateways, which operate much the same way as voice over IP trunking gateways, except that they interface to an ATM network. * Residential gateways, that provide a traditional analog (RJ11) interface to a Voice over IP network. Examples of residential gateways include cable modem/cable set-top boxes, xDSL devices, and broad-band wireless devices. * Access gateways, that provide a traditional analog (RJ11) or digital PBX interface to a Voice over IP network. Examples of access gateways include small-scale voice over IP gateways. * Business gateways, that provide a traditional digital PBX interface or an integrated "soft PBX" interface to a Voice over IP network. * Network Access Servers, that can attach a "modem" to a telephone circuit and provide data access to the Internet. We expect that in the future, the same gateways will combine Voice over IP services and Network Access services. * Circuit switches, or packet switches, which can offer a control interface to an external call control element. MGCP assumes a call control architecture where the call control "intelligence" is outside the gateways and handled by external call control elements known as Call Agents. The MGCP assumes that these call control elements, or Call Agents, will synchronize with each other to send coherent commands and responses to the gateways under their control. If this assumption is violated, inconsistent behavior should be expected. MGCP does not define a mechanism for synchronizing Call Agents. MGCP is, in essence, a master/slave protocol, where the gateways are expected to execute commands sent by the Call Agents. In consequence, this document specifies in great Andreasen & Foster Informational [Page 5] RFC 3435 MGCP 1.0 January 2003 detail the expected behavior of the gateways, but only specifies those parts of a Call Agent implementation, such as timer management, that are mandated for proper operation of the protocol. MGCP assumes a connection model where the basic constructs are endpoints and connections. Endpoints are sources and/or sinks of data and can be physical or virtual. Examples of physical endpoints are: * An interface on a gateway that terminates a trunk connected to a PSTN switch (e.g., Class 5, Class 4, etc.). A gateway that terminates trunks is called a trunking gateway. * An interface on a gateway that terminates an analog POTS connection to a phone, key system, PBX, etc. A gateway that terminates residential POTS lines (to phones) is called a residential gateway. An example of a virtual endpoint is an audio source in an audio- content server. Creation of physical endpoints requires hardware installation, while creation of virtual endpoints can be done by software. Connections may be either point to point or multipoint. A point to point connection is an association between two endpoints with the purpose of transmitting data between these endpoints. Once this association is established for both endpoints, data transfer between these endpoints can take place. A multipoint connection is established by connecting the endpoint to a multipoint session. Connections can be established over several types of bearer networks, for example: * Transmission of audio packets using RTP and UDP over an IP network. * Transmission of audio packets using AAL2, or another adaptation layer, over an ATM network. * Transmission of packets over an internal connection, for example the TDM backplane or the interconnection bus of a gateway. This is used, in particular, for "hairpin" connections, connections that terminate in a gateway but are immediately rerouted over the telephone network. For point-to-point connections the endpoints of a connection could be in separate gateways or in the same gateway. Andreasen & Foster Informational [Page 6] RFC 3435 MGCP 1.0 January 2003 1.1 Relation with the H.323 Standards MGCP is designed as an internal protocol within a distributed system that appears to the outside as a single VoIP gateway. This system is composed of a Call Agent, that may or may not be distributed over several computer platforms, and of a set of gateways, including at least one "media gateway" that perform the conversion of media signals between circuits and packets, and at least one "signaling gateway" when connecting to an SS7 controlled network. In a typical configuration, this distributed gateway system will interface on one side with one or more telephony (i.e., circuit) switches, and on the other side with H.323 conformant systems, as indicated in the following table: ------------------------------------------------------------------ | Functional| Phone | Terminating | H.323 conformant | | Plane | switch | Entity | systems | |-----------|------------|-----------------|-----------------------| | Signaling | Signaling | Call agent | Signaling exchanges | | Plane | exchanges | | with the Call Agent | | | through | | through H.225/RAS and| | | SS7/ISUP | | H.225/Q.931. | |-----------|------------|-----------------|-----------------------| | | | | Possible negotiation | | | | | of logical channels | | | | | and transmission | | | | | parameters through | | | | | H.245 with the call | | | | | agent. | |-----------|------------|-----------------|-----------------------| | | | Internal | | | | | synchronization| | | | | through MGCP | | |-----------|------------|-----------------|-----------------------| | Bearer | Connection| Telephony | Transmission of VoIP | | Data | through | gateways | data using RTP | | Transport | high speed| | directly between the | | Plane | trunk | | H.323 station and the| | | groups | | gateway. | ------------------------------------------------------------------ In the MGCP model, the gateways focus on the audio signal translation function, while the Call Agent handles the call signaling and call processing functions. As a consequence, the Call Agent implements the "signaling" layers of the H.323 standard, and presents itself as an "H.323 Gatekeeper" or as one or more "H.323 Endpoints" to the H.323 systems. Andreasen & Foster Informational [Page 7] RFC 3435 MGCP 1.0 January 2003 1.2 Relation with the IETF Standards While H.323 is the recognized standard for VoIP terminals, the IETF has also produced specifications for other types of multi-media applications. These other specifications include: * the Session Description Protocol (SDP), RFC 2327 * the Session Announcement Protocol (SAP), RFC 2974 * the Session Initiation Protocol (SIP), RFC 3261 * the Real Time Streaming Protocol (RTSP), RFC 2326. The latter three specifications are in fact alternative signaling standards that allow for the transmission of a session description to an interested party. SAP is used by multicast session managers to distribute a multicast session description to a large group of recipients, SIP is used to invite an individual user to take part in a point-to-point or unicast session, RTSP is used to interface a server that provides real time data. In all three cases, the session description is described according to SDP; when audio is transmitted, it is transmitted through the Real-time Transport Protocol, RTP. Andreasen & Foster Informational [Page 8] RFC 3435 MGCP 1.0 January 2003 The distributed gateway systems and MGCP will enable PSTN telephony users to access sessions set up using SAP, SIP or RTSP. The Call Agent provides for signaling conversion, according to the following table: ------------------------------------------------------------------ | Functional| Phone | Terminating | IETF conforming systems| | Plane | switch | Entity | | |-----------|------------|---------------|-------------------------| | Signaling | Signaling | Call agent | Signaling exchanges | | Plane | exchanges | | with the Call Agent | | | through | | through SAP, SIP or | | | SS7/ISUP | | RTSP. | |-----------|------------|---------------|-------------------------| | | | | Negotiation of session | | | | | description parameters | | | | | through SDP (telephony | | | | | gateway terminated but | | | | | passed via the call | | | | | agent to and from the | | | | | IETF conforming system)| |-----------|------------|---------------|-------------------------| | | | Internal syn- | | | | | chronization | | | | | through MGCP | | |-----------|------------|---------------|-------------------------| | Bearer | Connection| Telephony | Transmission of VoIP | | Data | through | gateways | data using RTP, | | Transport | high speed| | directly between the | | Plane | trunk | | remote IP end system | | | groups | | and the gateway. | ------------------------------------------------------------------ The SDP standard has a pivotal status in this architecture. We will see in the following description that we also use it to carry session descriptions in MGCP. 1.3 Definitions Trunk: A communication channel between two switching systems, e.g., a DS0 on a T1 or E1 line. 1.4 Conventions used in this Document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED, "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [2]. Andreasen & Foster Informational [Page 9] RFC 3435 MGCP 1.0 January 2003 2. Media Gateway Control Interface The interface functions provide for connection control and endpoint control. Both use the same system model and the same naming conventions. 2.1 Model and Naming Conventions The MGCP assumes a connection model where the basic constructs are endpoints and connections. Connections are grouped in calls. One or more connections can belong to one call. Connections and calls are set up at the initiative of one or more Call Agents. 2.1.1 Types of Endpoints In the introduction, we presented several classes of gateways. Such classifications, however, can be misleading. Manufacturers can arbitrarily decide to provide several types of services in a single package. A single product could well, for example, provide some trunk connections to telephony switches, some primary rate connections and some analog line interfaces, thus sharing the characteristics of what we described in the introduction as "trunking", "access" and "residential" gateways. MGCP does not make assumptions about such groupings. We simply assume that media gateways support collections of endpoints. The type of the endpoint determines its functionality. Our analysis, so far, has led us to isolate the following basic endpoint types: * Digital channel (DS0), * Analog line, * Announcement server access point, * Interactive Voice Response access point, * Conference bridge access point, * Packet relay, * ATM "trunk side" interface. In this section, we will describe the expected behavior of such endpoints. Andreasen & Foster Informational [Page 10] RFC 3435 MGCP 1.0 January 2003 This list is not final. There may be other types of endpoints defined in the future, for example test endpoints that could be used to check network quality, or frame-relay endpoints that could be used to manage audio channels multiplexed over a frame-relay virtual circuit. 2.1.1.1 Digital Channel (DS0) Digital channels provide a 64 Kbps service. Such channels are found in trunk and ISDN interfaces. They are typically part of digital multiplexes, such as T1, E1, T3 or E3 interfaces. Media gateways that support such channels are capable of translating the digital signals received on the channel, which may be encoded according to A-law or mu-law, using either the complete set of 8 bits per sample or only 7 of these bits, into audio packets. When the media gateway also supports a Network Access Server (NAS) service, the gateway shall be capable of receiving either audio-encoded data (modem connection) or binary data (ISDN connection) and convert them into data packets. +------- +------------+| (channel) ===|DS0 endpoint| -------- Connections +------------+| +------- Media gateways should be able to establish several connections between the endpoint and the packet networks, or between the endpoint and other endpoints in the same gateway. The signals originating from these connections shall be mixed according to the connection "mode", as specified later in this document. The precise number of connections that an endpoint supports is a characteristic of the gateway, and may in fact vary according to the allocation of resources within the gateway. In some cases, digital channels are used to carry signaling. This is the case for example for SS7 "F" links, or ISDN "D" channels. Media gateways that support these signaling functions shall be able to send and receive the signaling packets to and from a Call Agent, using the "backhaul" procedures defined by the SIGTRAN working group of the IETF. Digital channels are sometimes used in conjunction with channel associated signaling, such as "MF R2". Media gateways that support these signaling functions shall be able to detect and produce the corresponding signals, such as for example "wink" or "A", according to the event signaling and reporting procedures defined in MGCP. Andreasen & Foster Informational [Page 11] RFC 3435 MGCP 1.0 January 2003 2.1.1.2 Analog Line Analog lines can be used either as a "client" interface, providing service to a classic telephone unit, or as a "service" interface, allowing the gateway to send and receive analog calls. When the media gateway also supports a NAS service, the gateway shall be capable of receiving audio-encoded data (modem connection) and convert them into data packets. +------- +---------------+| (line) ===|analog endpoint| -------- Connections +---------------+| +------- Media gateways should be able to establish several connections between the endpoint and the packet networks, or between the endpoint and other endpoints in the same gateway. The audio signals originating from these connections shall be mixed according to the connection "mode", as specified later in this document. The precise number of connections that an endpoint supports is a characteristic of the gateway, and may in fact vary according to the allocation of resources within the gateway. A typical gateway should however be able to support two or three connections per endpoint, in order to support services such as "call waiting" or "three way calling". 2.1.1.3 Announcement Server Access Point An announcement server endpoint provides access to an announcement service. Under requests from the Call Agent, the announcement server will "play" a specified announcement. The requests from the Call Agent will follow the event signaling and reporting procedures defined in MGCP. +----------------------+ | Announcement endpoint| -------- Connection +----------------------+ A given announcement endpoint is not expected to support more than one connection at a time. If several connections were established to the same endpoint, then the same announcements would be played simultaneously over all the connections. Connections to an announcement server are typically one way, or "half duplex" -- the announcement server is not expected to listen to the audio signals from the connection. Andreasen & Foster Informational [Page 12] RFC 3435 MGCP 1.0 January 2003 2.1.1.4 Interactive Voice Response Access Point An Interactive Voice Response (IVR) endpoint provides access to an IVR service. Under requests from the Call Agent, the IVR server will "play" announcements and tones, and will "listen" to responses, such as DTMF input or voice messages, from the user. The requests from the Call Agent will follow the event signaling and reporting procedures defined in MGCP. +-------------+ | IVR endpoint| -------- Connection +-------------+ A given IVR endpoint is not expected to support more than one connection at a time. If several connections were established to the same endpoint, then the same tones and announcements would be played simultaneously over all the connections. 2.1.1.5 Conference Bridge Access Point A conference bridge endpoint is used to provide access to a specific conference. +------- +--------------------------+| |Conference bridge endpoint| -------- Connections +--------------------------+| +------- Media gateways should be able to establish several connections between the endpoint and the packet networks, or between the endpoint and other endpoints in the same gateway. The signals originating from these connections shall be mixed according to the connection "mode", as specified later in this document. The precise number of connections that an endpoint supports is a characteristic of the gateway, and may in fact vary according to the allocation of resources within the gateway. 2.1.1.6 Packet Relay A packet relay endpoint is a specific form of conference bridge, that typically only supports two connections. Packets relays can be found in firewalls between a protected and an open network, or in transcoding servers used to provide interoperation between incompatible gateways, for example gateways that do not support compatible compression algorithms, or gateways that operate over different transmission networks such as IP and ATM. Andreasen & Foster Informational [Page 13] RFC 3435 MGCP 1.0 January 2003 +------- +---------------------+ | |Packet relay endpoint| 2 connections +---------------------+ | +------- 2.1.1.7 ATM "trunk side" Interface ATM "trunk side" endpoints are typically found when one or several ATM permanent virtual circuits are used as a replacement for the classic "TDM" trunks linking switches. When ATM/AAL2 is used, several trunks or channels are multiplexed on a single virtual circuit; each of these trunks correspond to a single endpoint. +------- +------------------+| (channel) = |ATM trunk endpoint| -------- Connections +------------------+| +------- Media gateways should be able to establish several connections between the endpoint and the packet networks, or between the endpoint and other endpoints in the same gateway. The signals originating from these connections shall be mixed according to the connection "mode", as specified later in this document. The precise number of connections that an endpoint supports is a characteristic of the gateway, and may in fact vary according to the allocation of resources within the gateway. 2.1.2 Endpoint Identifiers Endpoint identifiers have two components that both are case- insensitive: * the domain name of the gateway that is managing the endpoint * a local name within that gateway Endpoint names are of the form: local-endpoint-name@domain-name where domain-name is an absolute domain-name as defined in RFC 1034 and includes a host portion, thus an example domain-name could be: mygateway.whatever.net Andreasen & Foster Informational [Page 14] RFC 3435 MGCP 1.0 January 2003 Also, domain-name may be an IP-address of the form defined for domain name in RFC 821, thus another example could be (see RFC 821 for details): [192.168.1.2] Both IPv4 and IPv6 addresses can be specified, however use of IP addresses as endpoint identifiers is generally discouraged. Note that since the domain name portion is part of the endpoint identifier, different forms or different values referring to the same entity are not freely interchangeable. The most recently supplied form and value MUST always be used. The local endpoint name is case-insensitive. The syntax of the local endpoint name is hierarchical, where the least specific component of the name is the leftmost term, and the most specific component is the rightmost term. The precise syntax depends on the type of endpoint being named and MAY start with a term that identifies the endpoint type. In any case, the local endpoint name MUST adhere to the following naming rules: 1) The individual terms of the naming path MUST be separated by a single slash ("/", ASCII 2F hex). 2) The individual terms are character strings composed of letters, digits or other printable characters, with the exception of characters used as delimiters ("/", "@"), characters used for wildcarding ("*", "$") and white spaces. 3) Wild-carding is represented either by an asterisk ("*") or a dollar sign ("$") for the terms of the naming path which are to be wild-carded. Thus, if the full local endpoint name is of the form: term1/term2/term3 then the entity name field looks like this depending on which terms are wild-carded: */term2/term3 if term1 is wild-carded term1/*/term3 if term2 is wild-carded term1/term2/* if term3 is wild-carded term1/*/* if term2 and term3 are wild-carded, etc. In each of these examples a dollar sign could have appeared instead of an asterisk. Andreasen & Foster Informational [Page 15] RFC 3435 MGCP 1.0 January 2003 4) A term represented by an asterisk ("*") is to be interpreted as: "use ALL values of this term known within the scope of the Media Gateway". Unless specified otherwise, this refers to all endpoints configured for service, regardless of their actual service state, i.e., in-service or out-of-service. 5) A term represented by a dollar sign ("$") is to be interpreted as: "use ANY ONE value of this term known within the scope of the Media Gateway". Unless specified otherwise, this only refers to endpoints that are in-service. Furthermore, it is RECOMMENDED that Call Agents adhere to the following: * Wild-carding should only be done from the right, thus if a term is wild-carded, then all terms to the right of that term should be wild-carded as well. * In cases where mixed dollar sign and asterisk wild-cards are used, dollar-signs should only be used from the right, thus if a term had a dollar sign wild-card, all terms to the right of that term should also contain dollar sign wild-cards. The description of a specific command may add further criteria for selection within the general rules given above. Note, that wild-cards may be applied to more than one term in which case they shall be evaluated from left to right. For example, if we have the endpoint names "a/1", "a/2", "b/1", and "b/2", then "$/*" (which is not recommended) will evaluate to either "a/1, a/2", or "b/1, b/2". However, "*/$" may evaluate to "a/1, b/1", "a/1, b/2", "a/2, b/1", or "a/2, b/2". The use of mixed wild-cards in a command is considered error prone and is consequently discouraged. A local name that is composed of only a wildcard character refers to either all (*) or any ($) endpoints within the media gateway. 2.1.3 Calls and Connections Connections are created on the Call Agent on each endpoint that will be involved in the "call". In the classic example of a connection between two "DS0" endpoints (EP1 and EP2), the Call Agents controlling the endpoints will establish two connections (C1 and C2): +---+ +---+ (channel1) ===|EP1|--(C1)--... ...(C2)--|EP2|===(channel2) +---+ +---+ Andreasen & Foster Informational [Page 16] RFC 3435 MGCP 1.0 January 2003 Each connection will be designated locally by an endpoint unique connection identifier, and will be characterized by connection attributes. When the two endpoints are located on gateways that are managed by the same Call Agent, the creation is done via the three following steps: 1) The Call Agent asks the first gateway to "create a connection" on the first endpoint. The gateway allocates resources to that connection, and responds to the command by providing a "session description". The session description contains the information necessary for a third party to send packets towards the newly created connection, such as for example IP address, UDP port, and codec parameters. 2) The Call Agent then asks the second gateway to "create a connection" on the second endpoint. The command carries the "session description" provided by the first gateway. The gateway allocates resources to that connection, and responds to the command by providing its own "session description". 3) The Call Agent then uses a "modify connection" command to provide this second "session description" to the first endpoint. Once this is done, communication can proceed in both directions. When the two endpoints are located on gateways that are managed by two different Call Agents, the Call Agents exchange information through a Call-Agent to Call-Agent signaling protocol, e.g., SIP [7], in order to synchronize the creation of the connection on the two endpoints. Once a connection has been established, the connection parameters can be modified at any time by a "modify connection" command. The Call Agent may for example instruct the gateway to change the codec used on a connection, or to modify the IP address and UDP port to which data should be sent, if a connection is "redirected". The Call Agent removes a connection by sending a "delete connection" command to the gateway. The gateway may also, under some circumstances, inform a gateway that a connection could not be sustained. The following diagram provides a view of the states of a connection, as seen from the gateway: Andreasen & Foster Informational [Page 17] RFC 3435 MGCP 1.0 January 2003 Create connection received | V +-------------------+ |resource allocation|-(failed)-+ +-------------------+ | | (connection refused) (successful) | v +----------->+ | | | +-------------------+ | | remote session | | | description |----------(yes)--------+ | | available ? | | | +-------------------+ | | | | | (no) | | | | | +-----------+ +------+ | +--->| half open |------> Delete <-------| open |<----------+ | | | (wait) | Connection |(wait)| | | | +-----------+ received +------+ | | | | | | | | | Modify Connection | Modify Connection | | | received | received | | | | | | | | | +--------------------+ | +--------------------+ | | | |assess modification | | |assess modification | | | | +--------------------+ | +--------------------+ | | | | | | | | | | |(failed) (successful) | (failed) (successful) | | | | | | | | | | +<---+ | | +-------------+-------+ | | | +<-------------------+ | | +-----------------+ | Free connection | | resources. | | Report. | +-----------------+ | V Andreasen & Foster Informational [Page 18] RFC 3435 MGCP 1.0 January 2003 2.1.3.1 Names of Calls One of the attributes of each connection is the "call identifier", which as far as the MGCP protocol is concerned has little semantic meaning, and is mainly retained for backwards compatibility. Calls are identified by unique identifiers, independent of the underlying platforms or agents. Call identifiers are hexadecimal strings, which are created by the Call Agent. The maximum length of call identifiers is 32 characters. Call identifiers are expected to be unique within the system, or at a minimum, unique within the collection of Call Agents that control the same gateways. From the gateway's perspective, the Call identifier is thus unique. When a Call Agent builds several connections that pertain to the same call, either on the same gateway or in different gateways, these connections that belong to the same call should share the same call-id. This identifier can then be used by accounting or management procedures, which are outside the scope of MGCP. 2.1.3.2 Names of Connections Connection identifiers are created by the gateway when it is requested to create a connection. They identify the connection within the context of an endpoint. Connection identifiers are treated in MGCP as hexadecimal strings. The gateway MUST make sure that a proper waiting period, at least 3 minutes, elapses between the end of a connection that used this identifier and its use in a new connection for the same endpoint (gateways MAY decide to use identifiers that are unique within the context of the gateway). The maximum length of a connection identifier is 32 characters. 2.1.3.3 Management of Resources, Attributes of Connections Many types of resources will be associated to a connection, such as specific signal processing functions or packetization functions. Generally, these resources fall in two categories: 1) Externally visible resources, that affect the format of "the bits on the network" and must be communicated to the second endpoint involved in the connection. 2) Internal resources, that determine which signal is being sent over the connection and how the received signals are processed by the endpoint. Andreasen & Foster Informational [Page 19] RFC 3435 MGCP 1.0 January 2003 The resources allocated to a connection, and more generally the handling of the connection, are chosen by the gateway under instructions from the Call Agent. The Call Agent will provide these instructions by sending two sets of parameters to the gateway: 1) The local directives instruct the gateway on the choice of resources that should be used for a connection, 2) When available, the "session description" provided by the other end of the connection (referred to as the remote session description). The local directives specify such parameters as the mode of the connection (e.g., send-only, or send-receive), preferred coding or packetization methods, usage of echo cancellation or silence suppression. (A detailed list can be found in the specification of the LocalConnectionOptions parameter of the CreateConnection command.) Depending on the parameter, the Call Agent MAY either specify a value, a range of values, or no value at all. This allows various implementations to implement various levels of control, from a very tight control where the Call Agent specifies minute details of the connection handling to a very loose control where the Call Agent only specifies broad guidelines, such as the maximum bandwidth, and lets the gateway choose the detailed values subject to the guidelines. Based on the value of the local directives, the gateway will determine the resources to allocate to the connection. When this is possible, the gateway will choose values that are in line with the remote session description - but there is no absolute requirement that the parameters be exactly the same. Once the resources have been allocated, the gateway will compose a "session description" that describes the way it intends to send and receive packets. Note that the session description may in some cases present a range of values. For example, if the gateway is ready to accept one of several compression algorithms, it can provide a list of these accepted algorithms. Andreasen & Foster Informational [Page 20] RFC 3435 MGCP 1.0 January 2003 Local Directives (from Call Agent 1) | V +-------------+ | resource | | allocation | | (gateway 1) | +-------------+ | | V | Local | Parameters V | Session | Description Local Directives | | (from Call Agent 2) | +---> Transmission----+ | | (CA to CA) | | | V V | +-------------+ | | resource | | | allocation | | | (gateway 2) | | +-------------+ | | | | | V | | Local | | Parameters | Session | Description | +---- Transmission<---+ | | (CA to CA) V V +-------------+ | modification| | (gateway 1) | +-------------+ | V Local Parameters -- Information flow: local directives & session descriptions -- Andreasen & Foster Informational [Page 21] RFC 3435 MGCP 1.0 January 2003 2.1.3.4 Special Case of Local Connections Large gateways include a large number of endpoints which are often of different types. In some networks, we may often have to set-up connections between endpoints that are located within the same gateway. Examples of such connections may be: * Connecting a call to an Interactive Voice-Response unit, * Connecting a call to a Conferencing unit, * Routing a call from one endpoint to another, something often described as a "hairpin" connection. Local connections are much simpler to establish than network connections. In most cases, the connection will be established through some local interconnecting device, such as for example a TDM bus. When two endpoints are managed by the same gateway, it is possible to specify the connection in a single command that conveys the names of the two endpoints that will be connected. The command is essentially a "Create Connection" command which includes the name of the second endpoint in lieu of the "remote session description". 2.1.4 Names of Call Agents and Other Entities The media gateway control protocol has been designed to allow the implementation of redundant Call Agents, for enhanced network reliability. This means that there is no fixed binding between entities and hardware platforms or network interfaces. Call Agent names consist of two parts, similar to endpoint names. Semantically, the local portion of the name does not exhibit any internal structure. An example Call Agent name is: ca1@ca.whatever.net Note that both the local part and the domain name have to be supplied. Nevertheless, implementations are encouraged to accept call agent names consisting of only the domain name. Reliability can be improved by using the following procedures: * Entities such as endpoints or Call Agents are identified by their domain name, not their network addresses. Several addresses can be Andreasen & Foster Informational [Page 22] RFC 3435 MGCP 1.0 January 2003 associated with a domain name. If a command or a response cannot be forwarded to one of the network addresses, implementations MUST retry the transmission using another address. * Entities MAY move to another platform. The association between a logical name (domain name) and the actual platform is kept in the domain name service. Call Agents and Gateways MUST keep track of the time-to-live of the record they read from the DNS. They MUST query the DNS to refresh the information if the time to live has expired. In addition to the indirection provided by the use of domain names and the DNS, the concept of "notified entity" is central to reliability and fail-over in MGCP. The "notified entity" for an endpoint is the Call Agent currently controlling that endpoint. At any point in time, an endpoint has one, and only one, "notified entity" associated with it. The "notified entity" determines where the endpoint will send commands to; when the endpoint needs to send a command to the Call Agent, it MUST send the command to its current "notified entity". The "notified entity" however does not determine where commands can be received from; any Call Agent can send commands to the endpoint. Please refer to Section 5 for the relevant security considerations. Upon startup, the "notified entity" MUST be set to a provisioned value. Most commands sent by the Call Agent include the ability to explicitly name the "notified entity" through the use of a "NotifiedEntity" parameter. The "notified entity" will stay the same until either a new "NotifiedEntity" parameter is received or the endpoint does a warm or cold (power-cycle) restart. If a "NotifiedEntity" parameter is sent with an "empty" value, the "notified entity" for the endpoint will be set to empty. If the "notified entity" for an endpoint is empty or has not been set explicitly (neither by a command nor by provisioning), the "notified entity" will then default to the source address (i.e., IP address and UDP port number) of the last successful non-audit command received for the endpoint. Auditing will thus not change the "notified entity". Use of an empty "NotifiedEntity" parameter value is strongly discouraged as it is error prone and eliminates the DNS- based fail-over and reliability mechanisms. 2.1.5 Digit Maps The Call Agent can ask the gateway to collect digits dialed by the user. This facility is intended to be used with residential gateways to collect the numbers that a user dials; it can also be used with Andreasen & Foster Informational [Page 23] RFC 3435 MGCP 1.0 January 2003 trunking gateways and access gateways alike, to collect access codes, credit card numbers and other numbers requested by call control services. One procedure is for the gateway to notify the Call Agent of each individual dialed digit, as soon as they are dialed. However, such a procedure generates a large number of interactions. It is preferable to accumulate the dialed numbers in a buffer, and to transmit them in a single message. The problem with this accumulation approach, however, is that it is hard for the gateway to predict how many numbers it needs to accumulate before transmission. For example, using the phone on our desk, we can dial the following numbers: ------------------------------------------------------ | 0 | Local operator | | 00 | Long distance operator | | xxxx | Local extension number | | 8xxxxxxx | Local number | | #xxxxxxx | Shortcut to local number at| | | other corporate sites | | *xx | Star services | | 91xxxxxxxxxx | Long distance number | | 9011 + up to 15 digits| International number | ------------------------------------------------------ The solution to this problem is to have the Call Agent load the gateway with a digit map that may correspond to the dial plan. This digit map is expressed using a syntax derived from the Unix system command, egrep. For example, the dial plan described above results in the following digit map: (0T|00T|[1-7]xxx|8xxxxxxx|#xxxxxxx|*xx|91xxxxxxxxxx|9011x.T) The formal syntax of the digit map is described by the DigitMap rule in the formal syntax description of the protocol (see Appendix A) - support for basic digit map letters is REQUIRED while support for extension digit map letters is OPTIONAL. A gateway receiving a digit map with an extension digit map letter not supported SHOULD return error code 537 (unknown digit map extension). A digit map, according to this syntax, is defined either by a (case insensitive) "string" or by a list of strings. Each string in the list is an alternative numbering scheme, specified either as a set of digits or timers, or as an expression over which the gateway will attempt to find a shortest possible match. The following constructs can be used in each numbering scheme: Andreasen & Foster Informational [Page 24] RFC 3435 MGCP 1.0 January 2003 * Digit: A digit from "0" to "9". * Timer: The symbol "T" matching a timer expiry. * DTMF: A digit, a timer, or one of the symbols "A", "B", "C", "D", "#", or "*". Extensions may be defined. * Wildcard: The symbol "x" which matches any digit ("0" to "9"). * Range: One or more DTMF symbols enclosed between square brackets ("[" and "]"). * Subrange: Two digits separated by hyphen ("-") which matches any digit between and including the two. The subrange construct can only be used inside a range construct, i.e., between "[" and "]". * Position: A period (".") which matches an arbitrary number, including zero, of occurrences of the preceding construct. A gateway that detects events to be matched against a digit map MUST do the following: 1) Add the event code as a token to the end of an internal state variable for the endpoint called the "current dial string". 2) Apply the current dial string to the digit map table, attempting a match to each expression in the digit map. 3) If the result is under-qualified (partially matches at least one entry in the digit map and doesn't completely match another entry), do nothing further. If the result matches an entry, or is over-qualified (i.e., no further digits could possibly produce a match), send the list of accumulated events to the Call Agent. A match, in this specification, can be either a "perfect match," exactly matching one of the specified alternatives, or an impossible match, which occurs when the dial string does not match any of the alternatives. Unexpected timers, for example, can cause "impossible matches". Both perfect matches and impossible matches trigger notification of the accumulated digits (which may include other events - see Section 2.3.3). The following example illustrates the above. Assume we have the digit map: (xxxxxxx|x11) and a current dial string of "41". Given the input "1" the current dial string becomes "411". We have a partial match with "xxxxxxx", but a complete match with "x11", and hence we send "411" to the Call Agent. Andreasen & Foster Informational [Page 25] RFC 3435 MGCP 1.0 January 2003 The following digit map example is more subtle: (0[12].|00|1[12].1|2x.#) Given the input "0", a match will occur immediately since position (".") allows for zero occurrences of the preceding construct. The input "00" can thus never be produced in this digit map. Given the input "1", only a partial match exists. The input "12" is also only a partial match, however both "11" and "121" are a match. Given the input "2", a partial match exists. A partial match also exists for the input "23", "234", "2345", etc. A full match does not occur here until a "#" is generated, e.g., "2345#". The input "2#" would also have been a match. Note that digit maps simply define a way of matching sequences of event codes against a grammar. Although digit maps as defined here are for DTMF input, extension packages can also be defined so that digit maps can be used for other types of input represented by event codes that adhere to the digit map syntax already defined for these event codes (e.g., "1" or "T"). Where such usage is envisioned, the definition of the particular event(s) SHOULD explicitly state that in the package definition. Since digit maps are not bounded in size, it is RECOMMENDED that gateways support digit maps up to at least 2048 bytes per endpoint. 2.1.6 Packages MGCP is a modular and extensible protocol, however with extensibility comes the need to manage, identify, and name the individual extensions. This is achieved by the concept of packages, which are simply well-defined groupings of extensions. For example, one package may support a certain group of events and signals, e.g., off-hook and ringing, for analog access lines. Another package may support another group of events and signals for analog access lines or for another type of endpoint such as video. One or more packages may be supported by a given endpoint. MGCP allows the following types of extensions to be defined in a package: * BearerInformation * LocalConnectionOptions * ExtensionParameters Andreasen & Foster Informational [Page 26] RFC 3435 MGCP 1.0 January 2003 * ConnectionModes * Events * Signals * Actions * DigitMapLetters * ConnectionParameters * RestartMethods * ReasonCodes * Return codes each of which will be explained in more detail below. The rules for defining each of these extensions in a package are described in Section 6, and the encoding and syntax are defined in Section 3 and Appendix A. With the exception of DigitMapLetters, a package defines a separate name space for each type of extension by adding the package name as a prefix to the extension, i.e.: package-name/extension Thus the package-name is followed by a slash ("/") and the name of the extension. An endpoint supporting one or more packages may define one of those packages as the default package for the endpoint. Use of the package name for events and signals in the default package for an endpoint is OPTIONAL, however it is RECOMMENDED to always include the package name. All other extensions, except DigitMapLetter, defined in the package MUST include the package-name when referring to the extension. Package names are case insensitive strings of letters, hyphens and digits, with the restriction that hyphens shall never be the first or last character in a name. Examples of package names are "D", "T", and "XYZ". Package names are not case sensitive - names such as "XYZ", "xyz", and "xYz" are equal. Andreasen & Foster Informational [Page 27] RFC 3435 MGCP 1.0 January 2003 Package definitions will be provided in other documents and with package names and extensions names registered with IANA. For more details, refer to section 6. Implementers can gain experience by using experimental packages. The name of an experimental package MUST start with the two characters "x-"; the IANA SHALL NOT register package names that start with these characters, or the characters "x+", which are reserved. A gateway that receives a command referring to an unsupported package MUST return an error (error code 518 - unsupported package, is RECOMMENDED). 2.1.7 Events and Signals The concept of events and signals is central to MGCP. A Call Agent may ask to be notified about certain events occurring in an endpoint (e.g., off-hook events) by including the name of the event in a RequestedEvents parameter (in a NotificationRequest command - see Section 2.3.3). A Call Agent may also request certain signals to be applied to an endpoint (e.g., dial-tone) by supplying the name of the event in a SignalRequests parameter. Events and signals are grouped in packages, within which they share the same name space which we will refer to as event names in the following. Event names are case insensitive strings of letters, hyphens and digits, with the restriction that hyphens SHALL NOT be the first or last character in a name. Some event codes may need to be parameterized with additional data, which is accomplished by adding the parameters between a set of parentheses. Event names are not case sensitive - values such as "hu", "Hu", "HU" or "hU" are equal. Examples of event names can be "hu" (off hook or "hang-up" transition), "hf" (hook-flash) or "0" (the digit zero). The package name is OPTIONAL for events in the default package for an endpoint, however it is RECOMMENDED to always include the package name. If the package name is excluded from the event name, the default package name for that endpoint MUST be assumed. For example, for an analog access line which has the line package ("L") as a default with dial-tone ("dl") as one of the events in that package, the following two event names are equal: Andreasen & Foster Informational [Page 28] RFC 3435 MGCP 1.0 January 2003 L/dl and dl For any other non-default packages that are associated with that endpoint, (such as the generic package for an analog access endpoint-type for example), the package name MUST be included with the event name. Again, unconditional inclusion of the package name is RECOMMENDED. Digits, or letters, are supported in some packages, notably "DTMF". Digits and letters are defined by the rules "Digit" and "Letter" in the definition of digit maps. This definition refers to the digits (0 to 9), to the asterisk or star ("*") and orthotrope, number or pound sign ("#"), and to the letters "A", "B", "C" and "D", as well as the timer indication "T". These letters can be combined in "digit string" that represents the keys that a user punched on a dial. In addition, the letter "X" can be used to represent all digits (0 to 9). Also, extensions MAY define use of other letters. The need to easily express the digit strings in earlier versions of the protocol has a consequence on the form of event names: An event name that does not denote a digit MUST always contain at least one character that is neither a digit, nor one of the letters A, B, C, D, T or X (such names also MUST NOT just contain the special signs "*", or "#"). Event names consisting of more than one character however may use any of the above. A Call Agent may often have to ask a gateway to detect a group of events. Two conventions can be used to denote such groups: * The "*" and "all" wildcard conventions (see below) can be used to detect any event belonging to a package, or a given event in many packages, or any event in any package supported by the gateway. * The regular expression Range notation can be used to detect a range of digits. The star sign (*) can be used as a wildcard instead of a package name, and the keyword "all" can be used as a wildcard instead of an event name: * A name such as "foo/all" denotes all events in package "foo". * A name such as "*/bar" denotes the event "bar" in any package supported by the gateway. Andreasen & Foster Informational [Page 29] RFC 3435 MGCP 1.0 January 2003 * The name "*/all" denotes all events supported by the endpoint. This specification purposely does not define any additional detail for the "all packages" and "all events" wildcards. They provide limited benefits, but introduce significant complexity along with the potential for errors. Their use is consequently strongly discouraged. The Call Agent can ask a gateway to detect a set of digits or letters either by individually describing those letters, or by using the "range" notation defined in the syntax of digit strings. For example, the Call Agent can: * Use the letter "x" to denote" digits from 0 to 9. * Use the notation "[0-9#]" to denote the digits 0 to 9 and the pound sign. The individual event codes are still defined in a package though (e.g., the "DTMF" package). Events can by default only be generated and detected on endpoints, however events can be also be defined so they can be generated or detected on connections rather than on the endpoint itself (see Section 6.6). For example, gateways may be asked to provide a ringback tone on a connection. When an event is to be applied on a connection, the name of the connection MUST be added to the name of the event, using an "at" sign (@) as a delimiter, as in: G/rt@0A3F58 where "G" is the name of the package and "rt" is the name of the event. Should the connection be deleted while an event or signal is being detected or applied on it, that particular event detection or signal generation simply stops. Depending on the signal, this may generate a failure (see below). The wildcard character "*" (star) can be used to denote "all connections". When this convention is used, the gateway will generate or detect the event on all the connections that are connected to the endpoint. This applies to existing as well as future connections created on the endpoint. An example of this convention could be: R/qa@* where "R" is the name of the package and "qa" is the name of the event. Andreasen & Foster Informational [Page 30] RFC 3435 MGCP 1.0 January 2003 When processing a command using the "all connections" wildcard, the "*" wildcard character applies to all current and future connections on the endpoint, however it will not be expanded. If a subsequent command either explicitly (e.g., by auditing) or implicitly (e.g., by persistence) refers to such an event, the "*" value will be used. However, when the event is actually observed, that particular occurrence of the event will include the name of the specific connection it occurred on. The wildcard character "$" can be used to denote "the current connection". It can only be used by the Call Agent, when the event notification request is "encapsulated" within a connection creation or modification command. When this convention is used, the gateway will generate or detect the event on the connection that is currently being created or modified. An example of this convention is: G/rt@$ When processing a command using the "current connection" wildcard, the "$" wildcard character will be expanded to the value of the current connection. If a subsequent command either explicitly (e.g., by auditing) or implicitly (e.g., by persistence) refers to such an event, the expanded value will be used. In other words, the "current connection" wildcard is expanded once, which is at the initial processing of the command in which it was explicitly included. The connection id, or a wildcard replacement, can be used in conjunction with the "all packages" and "all events" conventions. For example, the notation: */all@* can be used to designate all events on all current and future connections on the endpoint. However, as mentioned before, the use of the "all packages" and "all events" wildcards are strongly discouraged. Signals are divided into different types depending on their behavior: * On/off (OO): Once applied, these signals last until they are turned off. This can only happen as the result of a reboot/restart or a new SignalRequests where the signal is explicitly turned off (see later). Signals of type OO are defined to be idempotent, thus multiple requests to turn a given OO signal on (or off) are Andreasen & Foster Informational [Page 31] RFC 3435 MGCP 1.0 January 2003 perfectly valid and MUST NOT result in any errors. An On/Off signal could be a visual message-waiting indicator (VMWI). Once turned on, it MUST NOT be turned off until explicitly instructed to by the Call Agent, or as a result of an endpoint restart, i.e., these signals will not turn off as a result of the detection of a requested event. * Time-out (TO): Once applied, these signals last until they are either cancelled (by the occurrence of an event or by not being included in a subsequent (possibly empty) list of signals), or a signal-specific period of time has elapsed. A TO signal that times out will generate an "operation complete" event. A TO signal could be "ringback" timing out after 180 seconds. If an event occurs prior to the 180 seconds, the signal will, by default, be stopped (the "Keep signals active" action - see Section 2.3.3 - will override this behavior). If the signal is not stopped, the signal will time out, stop and generate an "operation complete" event, about which the Call Agent may or may not have requested to be notified. If the Call Agent has asked for the "operation complete" event to be notified, the "operation complete" event sent to the Call Agent SHALL include the name(s) of the signal(s) that timed out (note that if parameters were passed to the signal, the parameters will not be reported). If the signal was generated on a connection, the name of the connection SHALL be included as described above. Time-out signals have a default time-out value defined for them, which MAY be altered by the provisioning process. Also, the time-out period may be provided as a parameter to the signal (see Section 3.2.2.4). A value of zero indicates that the time-out period is infinite. A TO signal that fails after being started, but before having generated an "operation complete" event will generate an "operation failure" event which will include the name of the signal that failed. Deletion of a connection with an active TO signal will result in such a failure. * Brief (BR): The duration of these signals is normally so short that they stop on their own. If a signal stopping event occurs, or a new SignalRequests is applied, a currently active BR signal will not stop. However, any pending BR signals not yet applied MUST be cancelled (a BR signal becomes pending if a NotificationRequest includes a BR signal, and there is already an active BR signal). As an example, a brief tone could be a DTMF digit. If the DTMF digit "1" is currently being played, and a signal stopping event occurs, the "1" would play to completion. If a request to play DTMF digit "2" arrives before DTMF digit "1" finishes playing, DTMF digit "2" would become pending. Signal(s) generated on a connection MUST include the name of that connection. Andreasen & Foster Informational [Page 32] RFC 3435 MGCP 1.0 January 2003 2.2 Usage of SDP The Call Agent uses the MGCP to provide the endpoint with the description of connection parameters such as IP addresses, UDP port and RTP profiles. These descriptions will follow the conventions delineated in the Session Description Protocol which is now an IETF proposed standard, documented in RFC 2327. 2.3 Gateway Control Commands 2.3.1 Overview of Commands This section describes the commands of the MGCP. The service consists of connection handling and endpoint handling commands. There are currently nine commands in the protocol: * The Call Agent can issue an EndpointConfiguration command to a gateway, instructing the gateway about the coding characteristics expected by the "line-side" of the endpoint. * The Call Agent can issue a NotificationRequest command to a gateway, instructing the gateway to watch for specific events such as hook actions or DTMF tones on a specified endpoint. * The gateway will then use the Notify command to inform the Call Agent when the requested events occur. * The Call Agent can use the CreateConnection command to create a connection that terminates in an "endpoint" inside the gateway. * The Call Agent can use the ModifyConnection command to change the parameters associated with a previously established connection. * The Call Agent can use the DeleteConnection command to delete an existing connection. The DeleteConnection command may also be used by a gateway to indicate that a connection can no longer be sustained. * The Call Agent can use the AuditEndpoint and AuditConnection commands to audit the status of an "endpoint" and any connections associated with it. Network management beyond the capabilities provided by these commands is generally desirable. Such capabilities are expected to be supported by the use of the Simple Network Management Protocol (SNMP) and definition of a MIB which is outside the scope of this specification. Andreasen & Foster Informational [Page 33] RFC 3435 MGCP 1.0 January 2003 * The Gateway can use the RestartInProgress command to notify the Call Agent that a group of endpoints managed by the gateway is being taken out-of-service or is being placed back in-service. These services allow a controller (normally, the Call Agent) to instruct a gateway on the creation of connections that terminate in an "endpoint" attached to the gateway, and to be informed about events occurring at the endpoint. An endpoint may be for example: * A specific trunk circuit, within a trunk group terminating in a gateway, * A specific announcement handled by an announcement server. Connections are logically grouped into "calls" (the concept of a "call" has however little semantic meaning in MGCP itself). Several connections, that may or may not belong to the same call, can terminate in the same endpoint. Each connection is qualified by a "mode" parameter, which can be set to "send only" (sendonly), "receive only" (recvonly), "send/receive" (sendrecv), "conference" (confrnce), "inactive" (inactive), "loopback", "continuity test" (conttest), "network loop back" (netwloop) or "network continuity test" (netwtest). Media generated by the endpoint is sent on connections whose mode is either "send only", "send/receive", or "conference", unless the endpoint has a connection in "loopback" or "continuity test" mode. However, media generated by applying a signal to a connection is always sent on the connection, regardless of the mode. The handling of the media streams received on connections is determined by the mode parameters: * Media streams received through connections in "receive", "conference" or "send/receive" mode are mixed and sent to the endpoint, unless the endpoint has another connection in "loopback" or "continuity test" mode. * Media streams originating from the endpoint are transmitted over all the connections whose mode is "send", "conference" or "send/receive", unless the endpoint has another connection in "loopback" or "continuity test" mode. * In addition to being sent to the endpoint, a media stream received through a connection in "conference" mode is forwarded to all the other connections whose mode is "conference". This also applies Andreasen & Foster Informational [Page 34] RFC 3435 MGCP 1.0 January 2003 when the endpoint has a connection in "loopback" or "continuity test" mode. The details of this forwarding, e.g., RTP translator or mixer, is outside the scope of this document. Note that in order to detect events on a connection, the connection must by default be in one of the modes "receive", "conference", "send/receive", "network loopback" or "network continuity test". The event detection only applies to the incoming media. Connections in "sendonly", "inactive", "loopback", or "continuity test" mode will thus normally not detect any events, although requesting to do so is not considered an error. The "loopback" and "continuity test" modes are used during maintenance and continuity test operations. An endpoint may have more than one connection in either "loopback" or "continuity test" mode. As long as there is one connection in that particular mode, and no other connection on the endpoint is placed in a different maintenance or test mode, the maintenance or test operation shall continue undisturbed. There are two flavors of continuity test, one specified by ITU and one used in the US. In the first case, the test is a loopback test. The originating switch will send a tone (the go tone) on the bearer circuit and expects the terminating switch to loopback the tone. If the originating switch sees the same tone returned (the return tone), the COT has passed. If not, the COT has failed. In the second case, the go and return tones are different. The originating switch sends a certain go tone. The terminating switch detects the go tone, it asserts a different return tone in the backwards direction. When the originating switch detects the return tone, the COT is passed. If the originating switch never detects the return tone, the COT has failed. If the mode is set to "loopback", the gateway is expected to return the incoming signal from the endpoint back into that same endpoint. This procedure will be used, typically, for testing the continuity of trunk circuits according to the ITU specifications. If the mode is set to "continuity test", the gateway is informed that the other end of the circuit has initiated a continuity test procedure according to the GR specification (see [22]). The gateway will place the circuit in the transponder mode required for dual-tone continuity tests. If the mode is set to "network loopback", the audio signals received from the connection will be echoed back on the same connection. The media is not forwarded to the endpoint. If the mode is set to "network continuity test", the gateway will process the packets received from the connection according to the transponder mode required for dual-tone continuity test, and send the processed signal back on the connection. The media is not forwarded Andreasen & Foster Informational [Page 35] RFC 3435 MGCP 1.0 January 2003 to the endpoint. The "network continuity test" mode is included for backwards compatibility only and use of it is discouraged. 2.3.2 EndpointConfiguration The EndpointConfiguration command can be used to specify the encoding of the signals that will be received by the endpoint. For example, in certain international telephony configurations, some calls will carry mu-law encoded audio signals, while others will use A-law. The Call Agent can use the EndpointConfiguration command to pass this information to the gateway. The configuration may vary on a call by call basis, but can also be used in the absence of any connection. ReturnCode, [PackageList] <-- EndpointConfiguration(EndpointId, [BearerInformation]) EndpointId is the name of the endpoint(s) in the gateway where EndpointConfiguration executes. The "any of" wildcard convention MUST NOT be used. If the "all of" wildcard convention is used, the command applies to all the endpoints whose name matches the wildcard. BearerInformation is a parameter defining the coding of the data sent to and received from the line side. The information is encoded as a list of sub-parameters. The only sub-parameter defined in this version of the specification is the bearer encoding, whose value can be set to "A-law" or "mu-law". The set of sub-parameters may be extended. In order to allow for extensibility, while remaining backwards compatible, the BearerInformation parameter is conditionally optional based on the following conditions: * if Extension Parameters (vendor, package or other) are not used, the BearerInformation parameter is REQUIRED, * otherwise, the BearerInformation parameter is OPTIONAL. When omitted, BearerInformation MUST retain its current value. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). Andreasen & Foster Informational [Page 36] RFC 3435 MGCP 1.0 January 2003 2.3.3 NotificationRequest The NotificationRequest command is used to request the gateway to send notifications upon the occurrence of specified events in an endpoint. For example, a notification may be requested for when a gateway detects that an endpoint is receiving tones associated with fax communication. The entity receiving this notification may then decide to specify use of a different type of encoding method in the connections bound to this endpoint and instruct the gateway accordingly with a ModifyConnection Command. ReturnCode, [PackageList] <-- NotificationRequest(EndpointId, [NotifiedEntity,] [RequestedEvents,] RequestIdentifier, [DigitMap,] [SignalRequests,] [QuarantineHandling,] [DetectEvents,] [encapsulated EndpointConfiguration]) EndpointId is the identifier for the endpoint(s) in the the gateway where the NotificationRequest executes. The "any of" wildcard MUST NOT be used. NotifiedEntity is an optional parameter that specifies a new "notified entity" for the endpoint. RequestIdentifier is used to correlate this request with the notifications that it triggers. It will be repeated in the corresponding Notify command. RequestedEvents is a list of events, possibly qualified by event parameters (see Section 3.2.2.4), that the gateway is requested to detect and report. Such events may include, for example, fax tones, continuity tones, or on-hook transition. Unless otherwise specified, events are detected on the endpoint, however some events can be detected on a connection. A given event MUST NOT appear more than once in a RequestedEvents. If the parameter is omitted, it defaults to empty. To each event is associated one or more actions, which can be: * Notify the event immediately, together with the accumulated list of observed events, Andreasen & Foster Informational [Page 37] RFC 3435 MGCP 1.0 January 2003 * Swap audio, * Accumulate the event in an event buffer, but don't notify yet, * Accumulate according to Digit Map, * Keep Signal(s) active, * Process the Embedded Notification Request, * Ignore the event. Support for Notify, Accumulate, Keep Signal(s) Active, Embedded Notification Request, and Ignore is REQUIRED. Support for Accumulate according to Digit Map is REQUIRED on any endpoint capable of detecting DTMF. Support for any other action is OPTIONAL. The set of actions can be extended. A given action can by default be specified for any event, although some actions will not make sense for all events. For example, an off-hook event with the Accumulate according to Digit Map action is valid, but will of course immediately trigger a digit map mismatch when the off-hook event occurs. Needless to say, such practice is discouraged. Some actions can be combined as shown in the table below, where "Y" means the two actions can be combined, and "N" means they cannot: -------------------------------------------------------------- | | Notif | Swap | Accum | AccDi | KeSiA | EmbNo | Ignor | |--------------------------------------------------------------| | Notif | N | Y | N | N | Y | Y* | N | | Swap | - | N | Y | N | N | N | Y | | Accum | - | - | N | N | Y | Y | N | | AccDi | - | - | - | N | Y | N | N | | KeSiA | - | - | - | - | N | Y | Y | | EmbNo | - | - | - | - | - | N | N | | Ignor | - | - | - | - | - | - | N | -------------------------------------------------------------- Note (*): The "Embedded Notification Request" can only be combined with "Notify", if the gateway is allowed to issue more than one Notify command per Notification request (see below and Section 4.4.1). If no action is specified, the Notify action will be applied. If one or more actions are specified, only those actions apply. When two or more actions are specified, each action MUST be combinable with all Andreasen & Foster Informational [Page 38] RFC 3435 MGCP 1.0 January 2003 the other actions as defined by the table above - the individual actions are assumed to occur simultaneously. If a client receives a request with an invalid or unsupported action or an illegal combination of actions, it MUST return an error to the Call Agent (error code 523 - unknown or illegal combination of actions, is RECOMMENDED). In addition to the RequestedEvents parameter specified in the command, some MGCP packages may contain "persistent events" (this is generally discouraged though - see Appendix B for an alternative). Persistent events in a given package are always detected on an endpoint that implements that package. If a persistent event is not included in the list of RequestedEvents, and the event occurs, the event will be detected anyway and processed like all other events, as if the persistent event had been requested with a Notify action. A NotificationRequest MUST still be in place for a persistent event to trigger a Notify though. Thus, informally, persistent events can be viewed as always being implicitly included in the list of RequestedEvents with an action to Notify, although no glare detection, etc., will be performed. Non-persistent events are those events that need to be explicitly included in the RequestedEvents list. The (possibly empty) list of requested events completely replaces the previous list of requested events. In addition to the persistent events, only the events specified in the requested events list will be detected by the endpoint. If a persistent event is included in the RequestedEvents list, the action specified will replace the default action associated with the event for the life of the RequestedEvents list, after which the default action is restored. For example, if "off-hook"was a persistent event, the "Ignore off-hook" action was specified, and a new request without any off-hook instructions were received, the default "Notify off-hook" operation would be restored. The gateway will detect the union of the persistent events and the requested events. If an event is not included in either list, it will be ignored. The Call Agent can send a NotificationRequest with an empty (or omitted) RequestedEvents list to the gateway. The Call Agent can do so, for example, to a gateway when it does not want to collect any more DTMF digits. However, persistent events will still be detected and notified. The Swap Audio action can be used when a gateway handles more than one connection on an endpoint. This will be the case for call waiting, and possibly other feature scenarios. In order to avoid the Andreasen & Foster Informational [Page 39] RFC 3435 MGCP 1.0 January 2003 round-trip to the Call Agent when just changing which connection is attached to the audio functions of the endpoint, the NotificationRequest can map an event (usually hook flash, but could be some other event) to a local swap audio function, which selects the "next" connection in a round robin fashion. If there is only one connection, this action is effectively a no-op. If there are more than two connections, the order is undefined. If the endpoint has exactly two connections, one of which is "inactive", the other of which is in "send/receive" mode, then swap audio will attempt to make the "send/receive" connection "inactive", and vice versa. This specification intentionally does not provide any additional detail on the swap audio action. If signal(s) are desired to start when an event being looked for occurs, the "Embedded NotificationRequest" action can be used. The embedded NotificationRequest may include a new list of RequestedEvents, SignalRequests and a new digit map as well. The semantics of the embedded NotificationRequest is as if a new NotificationRequest was just received with the same NotifiedEntity, RequestIdentifier, QuarantineHandling and DetectEvents. When the "Embedded NotificationRequest" is activated, the "current dial string" will be cleared; however the list of observed events and the quarantine buffer will be unaffected (if combined with a Notify, the Notify will clear the list of observed events though - see Section 4.4.1). Note, that the Embedded NotificationRequest action does not accumulate the triggering event, however it can be combined with the Accumulate action to achieve that. If the Embedded NotificationRequest fails, an Embedded NotificationRequest failure event SHOULD be generated (see Appendix B). MGCP implementations SHALL be able to support at least one level of embedding. An embedded NotificationRequest that respects this limitation MUST NOT contain another Embedded NotificationRequest. DigitMap is an optional parameter that allows the Call Agent to provision the endpoint with a digit map according to which digits will be accumulated. If this optional parameter is absent, the previously defined value is retained. This parameter MUST be defined, either explicitly or through a previous command, if the RequestedEvents parameter contains a request to "accumulate according to the digit map". The collection of these digits will result in a digit string. The digit string is initialized to a null string upon reception of the NotificationRequest, so that a subsequent notification only returns the digits that were collected after this request. Digits that were accumulated according to the digit map are reported as any other accumulated event, in the order in which they occur. It is therefore possible that other events accumulated are Andreasen & Foster Informational [Page 40] RFC 3435 MGCP 1.0 January 2003 found in between the list of digits. If the gateway is requested to "accumulate according to digit map" and the gateway currently does not have a digit map for the endpoint in question, the gateway MUST return an error (error code 519 - endpoint does not have a digit map, is RECOMMENDED). SignalRequests is an optional parameter that contains the set of signals that the gateway is asked to apply. When omitted, it defaults to empty. When multiple signals are specified, the signals MUST be applied in parallel. Unless otherwise specified, signals are applied to the endpoint. However some signals can be applied to a connection. Signals are identified by their name, which is an event name, and may be qualified by signal parameters (see Section 3.2.2.4). The following are examples of signals: * Ringing, * Busy tone, * Call waiting tone, * Off hook warning tone, * Ringback tones on a connection. Names and descriptions of signals are defined in the appropriate package. Signals are, by default, applied to endpoints. If a signal applied to an endpoint results in the generation of a media stream (audio, video, etc.), then by default the media stream MUST NOT be forwarded on any connection associated with that endpoint, regardless of the mode of the connection. For example, if a call-waiting tone is applied to an endpoint involved in an active call, only the party using the endpoint in question will hear the call-waiting tone. However, individual signals may define a different behavior. When a signal is applied to a connection that has received a RemoteConnectionDescriptor, the media stream generated by that signal will be forwarded on the connection regardless of the current mode of the connection (including loopback and continuity test). If a RemoteConnectionDescriptor has not been received, the gateway MUST return an error (error code 527 - missing RemoteConnectionDescriptor, is RECOMMENDED). Note that this restriction does not apply to detecting events on a connection. Andreasen & Foster Informational [Page 41] RFC 3435 MGCP 1.0 January 2003 When a (possibly empty) list of signal(s) is supplied, this list completely replaces the current list of active time-out signals. Currently active time-out signals that are not provided in the new list MUST be stopped and the new signal(s) provided will now become active. Currently active time-out signals that are provided in the new list of signals MUST remain active without interruption, thus the timer for such time-out signals will not be affected. Consequently, there is currently no way to restart the timer for a currently active time-out signal without turning the signal off first. If the time- out signal is parameterized, the original set of parameters MUST remain in effect, regardless of what values are provided subsequently. A given signal MUST NOT appear more than once in a SignalRequests. Note that applying a signal S to an endpoint, connection C1 and connection C2, constitutes three different and independent signals. The action triggered by the SignalRequests is synchronized with the collection of events specified in the RequestedEvents parameter. For example, if the NotificationRequest mandates "ringing" and the RequestedEvents asks to look for an "off-hook" event, the ringing SHALL stop as soon as the gateway detects an off-hook event. The formal definition is that the generation of all "Time Out" signals SHALL stop as soon as one of the requested events is detected, unless the "Keep signals active" action is associated to the detected event. The RequestedEvents and SignalRequests may refer to the same event definitions. In one case, the gateway is asked to detect the occurrence of the event, and in the other case it is asked to generate it. The specific events and signals that a given endpoint can detect or perform are determined by the list of packages that are supported by that endpoint. Each package specifies a list of events and signals that can be detected or performed. A gateway that is requested to detect or perform an event belonging to a package that is not supported by the specified endpoint MUST return an error (error code 518 - unsupported or unknown package, is RECOMMENDED). When the event name is not qualified by a package name, the default package name for the endpoint is assumed. If the event name is not registered in this default package, the gateway MUST return an error (error code 522 - no such event or signal, is RECOMMENDED). The Call Agent can send a NotificationRequest whose requested signal list is empty. It will do so for example when a time-out signal(s) should stop. If signal(s) are desired to start as soon as a "looked-for" event occurs, the "Embedded NotificationRequest" action can be used. The embedded NotificationRequest may include a new list of RequestedEvents, SignalRequests and a new Digit Map as well. The embedded NotificationRequest action allows the Call Agent to set up a Andreasen & Foster Informational [Page 42] RFC 3435 MGCP 1.0 January 2003 "mini-script" to be processed by the gateway immediately following the detection of the associated event. Any SignalRequests specified in the embedded NotificationRequest will start immediately. Considerable care must be taken to prevent discrepancies between the Call Agent and the gateway. However, long-term discrepancies should not occur as a new SignalRequests completely replaces the old list of active time-out signals, and BR-type signals always stop on their own. Limiting the number of On/Off-type signals is encouraged. It is considered good practice for a Call Agent to occasionally turn on all On/Off signals that should be on, and turn off all On/Off signals that should be off. The Ignore action can be used to ignore an event, e.g., to prevent a persistent event from being notified. However, the synchronization between the event and an active time-out signal will still occur by default (e.g., a time-out dial-tone signal will stop when an off-hook occurs even if off-hook was a requested event with action "Ignore"). To prevent this synchronization from happening, the "Keep Signal(s) Active" action will have to be specified as well. The optional QuarantineHandling parameter specifies the handling of "quarantine" events, i.e., events that have been detected by the gateway before the arrival of this NotificationRequest command, but have not yet been notified to the Call Agent. The parameter provides a set of handling options (see Section 4.4.1 for details): * whether the quarantined events should be processed or discarded (the default is to process them). * whether the gateway is expected to generate at most one notification (step by step), or multiple notifications (loop), in response to this request (the default is at most one). When the parameter is absent, the default value is assumed. We should note that the quarantine-handling parameter also governs the handling of events that were detected and processed but not yet notified when the command is received. DetectEvents is an optional parameter, possibly qualified by event parameters, that specifies a list of events that the gateway is requested to detect during the quarantine period. When this parameter is absent, the events to be detected in the quarantine period are those listed in the last received DetectEvents list. In addition, the gateway will also detect persistent events and the events specified in the RequestedEvents list, including those for which the "ignore" action is specified. Andreasen & Foster Informational [Page 43] RFC 3435 MGCP 1.0 January 2003 Some events and signals, such as the in-line ringback or the quality alert, are performed or detected on connections terminating in the endpoint rather than on the endpoint itself. The structure of the event names (see Section 2.1.7) allows the Call Agent to specify the connection(s) on which the events should be performed or detected. The NotificationRequest command may carry an encapsulated EndpointConfiguration command, that will apply to the same endpoint(s). When this command is present, the parameters of the EndpointConfiguration command are included with the normal parameters of the NotificationRequest, with the exception of the EndpointId, which is not replicated. The encapsulated EndpointConfiguration command shares the fate of the NotificationRequest command. If the NotificationRequest is rejected, the EndpointConfiguration is not executed. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). 2.3.4 Notify Notifications with the observed events are sent by the gateway via the Notify command when a triggering event occurs. ReturnCode, [PackageList] <-- Notify(EndpointId, [NotifiedEntity,] RequestIdentifier, ObservedEvents) EndpointId is the name for the endpoint in the gateway which is issuing the Notify command. The identifier MUST be a fully qualified endpoint identifier, including the domain name of the gateway. The local part of the name MUST NOT use any of the wildcard conventions. NotifiedEntity is a parameter that identifies the entity which requested the notification. This parameter is equal to the NotifiedEntity parameter of the NotificationRequest that triggered this notification. The parameter is absent if there was no such parameter in the triggering request. Regardless of the value of the NotifiedEntity parameter, the notification MUST be sent to the current "notified entity" for the endpoint. Andreasen & Foster Informational [Page 44] RFC 3435 MGCP 1.0 January 2003 RequestIdentifier is a parameter that repeats the RequestIdentifier parameter of the NotificationRequest that triggered this notification. It is used to correlate this notification with the request that triggered it. Persistent events will be viewed here as if they had been included in the last NotificationRequest. An implicit NotificationRequest MAY be in place right after restart - the RequestIdentifier used for it will be zero ("0") - see Section 4.4.1 for details. ObservedEvents is a list of events that the gateway detected and accumulated. A single notification may report a list of events that will be reported in the order in which they were detected (FIFO). The list will only contain the identification of events that were requested in the RequestedEvents parameter of the triggering NotificationRequest. It will contain the events that were either accumulated (but not notified) or treated according to digit map (but no match yet), and the final event that triggered the notification or provided a final match in the digit map. It should be noted that digits MUST be added to the list of observed events as they are accumulated, irrespective of whether they are accumulated according to the digit map or not. For example, if a user enters the digits "1234" and some event E is accumulated between the digits "3" and "4" being entered, the list of observed events would be "1, 2, 3, E, 4". Events that were detected on a connection SHALL include the name of that connection as in "R/qa@0A3F58" (see Section 2.1.7). If the list of ObservedEvents reaches the capacity of the endpoint, an ObservedEvents Full event (see Appendix B) SHOULD be generated (the endpoint shall ensure it has capacity to include this event in the list of ObservedEvents). If the ObservedEvents Full event is not used to trigger a Notify, event processing continues as before (including digit map matching); however, the subsequent events will not be included in the list of ObservedEvents. ReturnCode is a parameter returned by the Call Agent. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). Andreasen & Foster Informational [Page 45] RFC 3435 MGCP 1.0 January 2003 2.3.5 CreateConnection This command is used to create a connection between two endpoints. ReturnCode, [ConnectionId,] [SpecificEndPointId,] [LocalConnectionDescriptor,] [SecondEndPointId,] [SecondConnectionId,] [PackageList] <-- CreateConnection(CallId, EndpointId, [NotifiedEntity,] [LocalConnectionOptions,] Mode, [{RemoteConnectionDescriptor | SecondEndpointId}, ] [Encapsulated NotificationRequest,] [Encapsulated EndpointConfiguration]) A connection is defined by its endpoints. The input parameters in CreateConnection provide the data necessary to build a gateway's "view" of a connection. CallId is a parameter that identifies the call (or session) to which this connection belongs. This parameter SHOULD, at a minimum, be unique within the collection of Call Agents that control the same gateways. Connections that belong to the same call SHOULD share the same call-id. The call-id has little semantic meaning in the protocol; however it can be used to identify calls for reporting and accounting purposes. It does not affect the handling of connections by the gateway. EndpointId is the identifier for the connection endpoint in the gateway where CreateConnection executes. The EndpointId can be fully-specified by assigning a value to the parameter EndpointId in the function call or it may be under-specified by using the "any of" wildcard convention. If the endpoint is underspecified, the endpoint identifier SHALL be assigned by the gateway and its complete value returned in the SpecificEndPointId parameter of the response. When the "any of" wildcard is used, the endpoint assigned MUST be in- service and MUST NOT already have any connections on it. If no such endpoint is available, error code 410 (no endpoint available) SHOULD be returned. The "all of" wildcard MUST NOT be used. The NotifiedEntity is an optional parameter that specifies a new "notified entity" for the endpoint. Andreasen & Foster Informational [Page 46] RFC 3435 MGCP 1.0 January 2003 LocalConnectionOptions is an optional structure used by the Call Agent to direct the handling of the connection by the gateway. The fields contained in a LocalConnectionOptions structure may include one or more of the following (each field MUST NOT be supplied more than once): * Codec compression algorithm: One or more codecs, listed in order of preference. For interoperability, it is RECOMMENDED to support G.711 mu-law encoding ("PCMU"). See Section 2.6 for details on the codec selection process. * Packetization period: A single millisecond value or a range may be specified. The packetization period SHOULD NOT contradict the specification of the codec compression algorithm. If a codec is specified that has a frame size which is inconsistent with the packetization period, and that codec is selected, the gateway is authorized to use a packetization period that is consistent with the frame size even if it is different from that specified. In so doing, the gateway SHOULD choose a non-zero packetization period as close to that specified as possible. If a packetization period is not specified, the endpoint SHOULD use the default packetization period(s) for the codec(s) selected. * Bandwidth: The allowable bandwidth, i.e., payload plus any header overhead from the transport layer and up, e.g., IP, UDP, and RTP. The bandwidth specification SHOULD NOT contradict the specification of codec compression algorithm or packetization period. If a codec is specified, then the gateway is authorized to use it, even if it results in the usage of a larger bandwidth than specified. Any discrepancy between the bandwidth and codec specification will not be reported as an error. * Type of Service: This indicates the class of service to be used for this connection. When the Type of Service is not specified, the gateway SHALL use a default value of zero unless provisioned otherwise. * Usage of echo cancellation: By default, the telephony gateways always perform echo cancellation on the endpoint. However, it may be necessary, for some calls, to turn off these operations. The echo cancellation parameter can have two values, "on" (when the echo cancellation is requested) and "off" (when it is turned off). The parameter is optional. If the parameter is omitted when creating a connection and there are no other connections on the endpoint, the endpoint SHALL apply echo cancellation initially. If the parameter is omitted when creating a connection and there are existing connections on the endpoint, echo cancellation is unchanged. The endpoint SHOULD subsequently enable or disable echo Andreasen & Foster Informational [Page 47] RFC 3435 MGCP 1.0 January 2003 cancellation when voiceband data is detected - see e.g., ITU-T recommendation V.8, V.25, and G.168. Following termination of voiceband data, the handling of echo cancellation SHALL then revert to the current value of the echo cancellation parameter. It is RECOMMENDED that echo cancellation handling is left to the gateway rather than having this parameter specified by the Call Agent. * Silence Suppression: The telephony gateways may perform voice activity detection, and avoid sending packets during periods of silence. However, it is necessary, for example for modem calls, to turn off this detection. The silence suppression parameter can have two values, "on" (when the detection is requested) and "off" (when it is not requested). The default is "off" (unless provisioned otherwise). Upon detecting voiceband data, the endpoint SHOULD disable silence suppression. Following termination of voiceband data, the handling of silence suppression SHALL then revert to the current value of the silence suppression parameter. * Gain Control: The telephony gateways may perform gain control on the endpoint, in order to adapt the level of the signal. However, it is necessary, for example for some modem calls, to turn off this function. The gain control parameter may either be specified as "automatic", or as an explicit number of decibels of gain. The gain specified will be added to media sent out over the endpoint (as opposed to the connection) and subtracted from media received on the endpoint. The parameter is optional. When there are no other connections on the endpoint, and the parameter is omitted, the default is to not perform gain control (unless provisioned otherwise), which is equivalent to specifying a gain of 0 decibels. If there are other connections on the endpoint, and the parameter is omitted, gain control is unchanged. Upon detecting voiceband data, the endpoint SHOULD disable gain control if needed. Following termination of voiceband data, the handling of gain control SHALL then revert to the current value of the gain control parameter. It should be noted, that handling of gain control is normally best left to the gateway and hence use of this parameter is NOT RECOMMENDED. * RTP security: The Call agent can request the gateway to enable encryption of the audio Packets. It does so by providing a key specification, as specified in RFC 2327. By default, encryption is not performed. * Network Type: The Call Agent may instruct the gateway to prepare the connection on a specified type of network. If absent, the value is based on the network type of the gateway being used. Andreasen & Foster Informational [Page 48] RFC 3435 MGCP 1.0 January 2003 * Resource reservation: The Call Agent may instruct the gateway to use network resource reservation for the connection. See Section 2.7 for details. The Call Agent specifies the relevant fields it cares about in the command and leaves the rest to the discretion of the gateway. For those of the above parameters that were not explicitly included, the gateway SHOULD use the default values if possible. For a detailed list of local connection options included with this specification refer to section 3.2.2.10. The set of local connection options can be extended. The Mode indicates the mode of operation for this side of the connection. The basic modes are "send", "receive", "send/receive", "conference", "inactive", "loopback", "continuity test", "network loop back" and "network continuity test". The expected handling of these modes is specified in the introduction of the "Gateway Control Commands", Section 2.3. Note that signals applied to a connection do not follow the connection mode. Some endpoints may not be capable of supporting all modes. If the command specifies a mode that the endpoint does not support, an error SHALL be returned (error 517 - unsupported mode, is RECOMMENDED). Also, if a connection has not yet received a RemoteConnectionDescriptor, an error MUST be returned if the connection is attempted to be placed in any of the modes "send only", "send/receive", "conference", "network loopback", "network continuity test", or if a signal (as opposed to detecting an event) is to be applied to the connection (error code 527 - missing RemoteConnectionDescriptor, is RECOMMENDED). The set of modes can be extended. The gateway returns a ConnectionId, that uniquely identifies the connection within the endpoint, and a LocalConnectionDescriptor, which is a session description that contains information about the connection, e.g., IP address and port for the media, as defined in SDP. The SpecificEndPointId is an optional parameter that identifies the responding endpoint. It is returned when the EndpointId argument referred to an "any of" wildcard name and the command succeeded. When a SpecificEndPointId is returned, the Call Agent SHALL use it as the EndpointId value in successive commands referring to this connection. The SecondEndpointId can be used instead of the RemoteConnectionDescriptor to establish a connection between two endpoints located on the same gateway. The connection is by definition a local connection. The SecondEndpointId can be fully- specified by assigning a value to the parameter SecondEndpointId in Andreasen & Foster Informational [Page 49] RFC 3435 MGCP 1.0 January 2003 the function call or it may be under-specified by using the "any of" wildcard convention. If the SecondEndpointId is underspecified, the second endpoint identifier will be assigned by the gateway and its complete value returned in the SecondEndPointId parameter of the response. When a SecondEndpointId is specified, the command really creates two connections that can be manipulated separately through ModifyConnection and DeleteConnection commands. In addition to the ConnectionId and LocalConnectionDescriptor for the first connection, the response to the creation provides a SecondConnectionId parameter that identifies the second connection. The second connection is established in "send/receive" mode. After receiving a "CreateConnection" request that did not include a RemoteConnectionDescriptor parameter, a gateway is in an ambiguous situation. Because it has exported a LocalConnectionDescriptor parameter, it can potentially receive packets. Because it has not yet received the RemoteConnectionDescriptor parameter of the other gateway, it does not know whether the packets that it receives have been authorized by the Call Agent. It must thus navigate between two risks, i.e., clipping some important announcements or listening to insane data. The behavior of the gateway is determined by the value of the Mode parameter: * If the mode was set to ReceiveOnly, the gateway MUST accept the media and transmit them through the endpoint. * If the mode was set to Inactive, Loopback, or Continuity Test, the gateway MUST NOT transmit the media through to the endpoint. Note that the mode values SendReceive, Conference, SendOnly, Network Loopback and Network Continuity Test do not make sense in this situation. They MUST be treated as errors, and the command MUST be rejected (error code 527 - missing RemoteConnectionDescriptor, is RECOMMENDED). The command may optionally contain an encapsulated Notification Request command, which applies to the EndpointId, in which case a RequestIdentifier parameter MUST be present, as well as, optionally, other parameters of the NotificationRequest with the exception of the EndpointId, which is not replicated. The encapsulated NotificationRequest is executed simultaneously with the creation of the connection. For example, when the Call Agent wants to initiate a call to a residential gateway, it could: Andreasen & Foster Informational [Page 50] RFC 3435 MGCP 1.0 January 2003 * ask the residential gateway to prepare a connection, in order to be sure that the user can start speaking as soon as the phone goes off hook, * ask the residential gateway to start ringing, * ask the residential gateway to notify the Call Agent when the phone goes off-hook. This can be accomplished in a single CreateConnection command, by also transmitting the RequestedEvents parameters for the off-hook event, and the SignalRequests parameter for the ringing signal. When these parameters are present, the creation and the NotificationRequest MUST be synchronized, which means that both MUST be accepted, or both MUST be refused. In our example, the CreateConnection may be refused if the gateway does not have sufficient resources, or cannot get adequate resources from the local network access, and the off-hook NotificationRequest can be refused in the glare condition, if the user is already off-hook. In this example, the phone must not ring if the connection cannot be established, and the connection must not be established if the user is already off-hook. The NotifiedEntity parameter, if present, defines the new "notified entity" for the endpoint. The command may carry an encapsulated EndpointConfiguration command, which applies to the EndpointId. When this command is present, the parameters of the EndpointConfiguration command are included with the normal parameters of the CreateConnection with the exception of the EndpointId, which is not replicated. The EndpointConfiguration command may be encapsulated together with an encapsulated NotificationRequest command. Note that both of these apply to the EndpointId only. The encapsulated EndpointConfiguration command shares the fate of the CreateConnection command. If the CreateConnection is rejected, the EndpointConfiguration is not executed. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). Andreasen & Foster Informational [Page 51] RFC 3435 MGCP 1.0 January 2003 2.3.6 ModifyConnection This command is used to modify the characteristics of a gateway's "view" of a connection. This "view" of the call includes both the local connection descriptor as well as the remote connection descriptor. ReturnCode, [LocalConnectionDescriptor,] [PackageList] <-- ModifyConnection(CallId, EndpointId, ConnectionId, [NotifiedEntity,] [LocalConnectionOptions,] [Mode,] [RemoteConnectionDescriptor,] [Encapsulated NotificationRequest,] [Encapsulated EndpointConfiguration]) The parameters used are the same as in the CreateConnection command, with the addition of a ConnectionId that identifies the connection within the endpoint. This parameter was returned by the CreateConnection command, in addition to the local connection descriptor. It uniquely identifies the connection within the context of the endpoint. The CallId used when the connection was created MUST be included as well. The EndpointId MUST be a fully qualified endpoint identifier. The local name MUST NOT use the wildcard conventions. The ModifyConnection command can be used to affect parameters of a connection in the following ways: * Provide information about the other end of the connection, through the RemoteConnectionDescriptor. If the parameter is omitted, it retains its current value. * Activate or deactivate the connection, by changing the value of the Mode parameter. This can occur at any time during the connection, with arbitrary parameter values. If the parameter is omitted, it retains its current value. * Change the parameters of the connection through the LocalConnectionOptions, for example by switching to a different coding scheme, changing the packetization period, or modifying the handling of echo cancellation. If one or more LocalConnectionOptions parameters are omitted, then the gateway Andreasen & Foster Informational [Page 52] RFC 3435 MGCP 1.0 January 2003 SHOULD refrain from changing that parameter from its current value, unless another parameter necessitating such a change is explicitly provided. For example, a codec change might require a change in silence suppression. Note that if a RemoteConnectionDescriptor is supplied, then only the LocalConnectionOptions actually supplied with the ModifyConnection command will affect the codec negotiation (as described in Section 2.6). Connections can only be fully activated if the RemoteConnectionDescriptor has been provided to the gateway. The receive-only mode, however, can be activated without the provision of this descriptor. The command will only return a LocalConnectionDescriptor if the local connection parameters, such as RTP ports, were modified. Thus, if, for example, only the mode of the connection is changed, a LocalConnectionDescriptor will not be returned. Note however, that inclusion of LocalConnectionOptions in the command is not a prerequisite for local connection parameter changes to occur. If a connection parameter is omitted, e.g., silence suppression, the old value of that parameter will be retained if possible. If a parameter change necessitates a change in one or more unspecified parameters, the gateway is free to choose suitable values for the unspecified parameters that must change. This can for instance happen if the packetization period was not specified. If the new codec supported the old packetization period, the value of this parameter would not change, as a change would not be necessary. However, if it did not support the old packetization period, it would choose a suitable value. The command may optionally contain an encapsulated Notification Request command, in which case a RequestIdentifier parameter MUST be present, as well as, optionally, other parameters of the NotificationRequest with the exception of the EndpointId, which is not replicated. The encapsulated NotificationRequest is executed simultaneously with the modification of the connection. For example, when a connection is accepted, the calling gateway should be instructed to place the circuit in send-receive mode and to stop providing ringing tones. This can be accomplished in a single ModifyConnection command, by also transmitting the RequestedEvents parameters, for the on-hook event, and an empty SignalRequests parameter, to stop the provision of ringing tones. When these parameters are present, the modification and the NotificationRequest MUST be synchronized, which means that both MUST be accepted, or both MUST be refused. Andreasen & Foster Informational [Page 53] RFC 3435 MGCP 1.0 January 2003 The NotifiedEntity parameter, if present, defines the new "notified entity" for the endpoint. The command may carry an encapsulated EndpointConfiguration command, that will apply to the same endpoint. When this command is present, the parameters of the EndpointConfiguration command are included with the normal parameters of the ModifyConnection with the exception of the EndpointId, which is not replicated. The EndpointConfiguration command may be encapsulated together with an encapsulated NotificationRequest command. The encapsulated EndpointConfiguration command shares the fate of the ModifyConnection command. If the ModifyConnection is rejected, the EndpointConfiguration is not executed. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). 2.3.7 DeleteConnection (from the Call Agent) This command is used to terminate a connection. As a side effect, it collects statistics on the execution of the connection. ReturnCode, ConnectionParameters, [PackageList] <-- DeleteConnection(CallId, EndpointId, ConnectionId, [NotifiedEntity,] [Encapsulated NotificationRequest,] [Encapsulated EndpointConfiguration]) The endpoint identifier, in this form of the DeleteConnection command, SHALL be fully qualified. Wildcard conventions SHALL NOT be used. The ConnectionId identifies the connection to be deleted. The CallId used when the connection was created is included as well. The NotifiedEntity parameter, if present, defines the new "notified entity" for the endpoint. Andreasen & Foster Informational [Page 54] RFC 3435 MGCP 1.0 January 2003 In the case of IP multicast, connections can be deleted individually and independently. However, in the unicast case where a connection has two ends, a DeleteConnection command has to be sent to both gateways involved in the connection. After the connection has been deleted, media streams previously supported by the connection are no longer available. Any media packets received for the old connection are simply discarded and no new media packets for the stream are sent. After the connection has been deleted, any loopback that has been requested for the connection must be cancelled (unless the endpoint has another connection requesting loopback). In response to the DeleteConnection command, the gateway returns a list of connection parameters that describe statistics for the connection. When the connection was for an Internet media stream, these parameters are: Number of packets sent: The total number of media packets transmitted by the sender since starting transmission on this connection. In the case of RTP, the count is not reset if the sender changes its synchronization source identifier (SSRC, as defined in RTP), for example as a result of a ModifyConnection command. The value is zero if the connection was always set in "receive only" mode and no signals were applied to the connection. Number of octets sent: The total number of payload octets (i.e., not including header or padding) transmitted in media packets by the sender since starting transmission on this connection. In the case of RTP, the count is not reset if the sender changes its SSRC identifier, for example as a result of a ModifyConnection command. The value is zero if the connection was always set in "receive only" mode and no signals were applied to the connection. Number of packets received: The total number of media packets received by the sender since starting reception on this connection. In the case of RTP, the count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was always set in "send only" mode. Andreasen & Foster Informational [Page 55] RFC 3435 MGCP 1.0 January 2003 Number of octets received: The total number of payload octets (i.e., not including header, e.g., RTP, or padding) transmitted in media packets by the sender since starting transmission on this connection. In the case of RTP, the count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was always set in "send only" mode. Number of packets lost: The total number of media packets that have been lost since the beginning of reception. This number is defined to be the number of packets expected less the number of packets actually received, where the number of packets received includes any which are late or duplicates. For RTP, the count includes packets received from different SSRC, if the sender used several values. Thus packets that arrive late are not counted as lost, and the loss may be negative if there are duplicates. The count includes packets received from different SSRC, if the sender used several values. The number of packets expected is defined to be the extended last sequence number received, as defined next, less the initial sequence number received. The count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was always set in "send only" mode. Interarrival jitter: An estimate of the statistical variance of the media packet interarrival time measured in milliseconds and expressed as an unsigned integer. For RTP, the interarrival jitter J is defined to be the mean deviation (smoothed absolute value) of the difference D in packet spacing at the receiver compared to the sender for a pair of packets. Detailed computation algorithms are found in RFC 1889. The count includes packets received from different SSRC, if the sender used several values. The value is zero if the connection was always set in "send only" mode. Average transmission delay: An estimate of the network latency, expressed in milliseconds. For RTP, this is the average value of the difference between the NTP timestamp indicated by the senders of the RTCP messages and the NTP timestamp of the receivers, measured when the messages are received. The average is obtained by summing all the estimates, Andreasen & Foster Informational [Page 56] RFC 3435 MGCP 1.0 January 2003 then dividing by the number of RTCP messages that have been received. When the gateway's clock is not synchronized by NTP, the latency value can be computed as one half of the round trip delay, as measured through RTCP. When the gateway cannot compute the one way delay or the round trip delay, the parameter conveys a null value. For a detailed definition of these variables, refer to RFC 1889. When the connection was set up over a LOCAL interconnect, the meaning of these parameters is defined as follows: Number of packets sent: Not significant - MAY be omitted. Number of octets sent: The total number of payload octets transmitted over the local connection. Number of packets received: Not significant - MAY be omitted. Number of octets received: The total number of payload octets received over the connection. Number of packets lost: Not significant - MAY be omitted. A value of zero is assumed. Interarrival jitter: Not significant - MAY be omitted. A value of zero is assumed. Average transmission delay: Not significant - MAY be omitted. A value of zero is assumed. The set of connection parameters can be extended. Also, the meaning may be further defined by other types of networks which MAY furthermore elect to not return all, or even any, of the above specified parameters. The command may optionally contain an encapsulated Notification Request command, in which case a RequestIdentifier parameter MUST be present, as well as, optionally, other parameters of the NotificationRequest with the exception of the EndpointId, which is not replicated. The encapsulated NotificationRequest is executed simultaneously with the deletion of the connection. For example, when a user hang-up is notified, the gateway should be instructed to delete the connection and to start looking for an off-hook event. Andreasen & Foster Informational [Page 57] RFC 3435 MGCP 1.0 January 2003 This can be accomplished in a single DeleteConnection command, by also transmitting the RequestedEvents parameters, for the off-hook event, and an empty SignalRequests parameter. When these parameters are present, the DeleteConnection and the NotificationRequest must be synchronized, which means that both MUST be accepted, or both MUST be refused. The command may carry an encapsulated EndpointConfiguration command, that will apply to the same endpoint. When this command is present, the parameters of the EndpointConfiguration command are included with the normal parameters of the DeleteConnection with the exception of the EndpointId, which is not replicated. The EndpointConfiguration command may be encapsulated together with an encapsulated NotificationRequest command. The encapsulated EndpointConfiguration command shares the fate of the DeleteConnection command. If the DeleteConnection is rejected, the EndpointConfiguration is not executed. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). 2.3.8 DeleteConnection (from the gateway) In some rare circumstances, a gateway may have to clear a connection, for example because it has lost the resource associated with the connection, or because it has detected that the endpoint no longer is capable or willing to send or receive media. The gateway may then terminate the connection by using a variant of the DeleteConnection command: ReturnCode, [PackageList] <-- DeleteConnection(CallId, EndpointId, ConnectionId, ReasonCode, Connection-parameters) The EndpointId, in this form of the DeleteConnection command, MUST be fully qualified. Wildcard conventions MUST NOT be used. Andreasen & Foster Informational [Page 58] RFC 3435 MGCP 1.0 January 2003 The ReasonCode is a text string starting with a numeric reason code and optionally followed by a descriptive text string. The reason code indicates the cause of the DeleteConnection. A list of reason codes can be found in Section 2.5. In addition to the call, endpoint and connection identifiers, the gateway will also send the connection parameters that would have been returned to the Call Agent in response to a DeleteConnection command. ReturnCode is a parameter returned by the Call Agent. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). Note that use of this command is generally discouraged and should only be done as a last resort. If a connection can be sustained, deletion of it should be left to the discretion of the Call Agent which is in a far better position to make intelligent decisions in this area. 2.3.9 DeleteConnection (multiple connections from the Call Agent) A variation of the DeleteConnection function can be used by the Call Agent to delete multiple connections at the same time. Note that encapsulating other commands with this variation of the DeleteConnection command is not permitted. The command can be used to delete all connections that relate to a Call for an endpoint: ReturnCode, [PackageList] <-- DeleteConnection(CallId, EndpointId) The EndpointId, in this form of the DeleteConnection command, MUST NOT use the "any of" wildcard. All connections for the endpoint(s) with the CallId specified will be deleted. Note that the command will still succeed if there were no connections with the CallId specified, as long as the EndpointId was valid. However, if the EndpointId is invalid, the command will fail. The command does not return any individual statistics or call parameters. Andreasen & Foster Informational [Page 59] RFC 3435 MGCP 1.0 January 2003 It can also be used to delete all connections that terminate in a given endpoint: ReturnCode, [PackageList] <-- DeleteConnection(EndpointId) The EndpointId, in this form of the DeleteConnection command, MUST NOT use the "any of" wildcard. Again, the command succeeds even if there were no connections on the endpoint(s). Finally, Call Agents can take advantage of the hierarchical structure of endpoint names to delete all the connections that belong to a group of endpoints. In this case, the "local name" component of the EndpointId will be specified using the "all of" wildcarding convention. The "any of" convention SHALL NOT be used. For example, if endpoint names are structured as the combination of a physical interface name and a circuit number, as in "X35V3+A4/13", the Call Agent may replace the circuit number by the "all of" wild card character "*", as in "X35V3+A4/*". This "wildcard" command instructs the gateway to delete all the connections that were attached to circuits connected to the physical interface "X35V3+A4". After all the connections have been deleted, any loopback that has been requested for the connections MUST be cancelled by the gateway. This command does not return any individual statistics or call parameters. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). 2.3.10 AuditEndpoint The AuditEndPoint command can be used by the Call Agent to find out the status of a given endpoint. Andreasen & Foster Informational [Page 60] RFC 3435 MGCP 1.0 January 2003 ReturnCode, EndPointIdList,|{ [RequestedEvents,] [QuarantineHandling,] [DigitMap,] [SignalRequests,] [RequestIdentifier,] [NotifiedEntity,] [ConnectionIdentifiers,] [DetectEvents,] [ObservedEvents,] [EventStates,] [BearerInformation,] [RestartMethod,] [RestartDelay,] [ReasonCode,] [MaxMGCPDatagram,] [Capabilities]} [PackageList] <-- AuditEndPoint(EndpointId, [RequestedInfo]) The EndpointId identifies the endpoint(s) being audited. The "any of" wildcard convention MUST NOT be used. The EndpointId identifies the endpoint(s) being audited. The "all of" wildcard convention can be used to start auditing of a group of endpoints (regardless of their service-state). If this convention is used, the gateway SHALL return the list of endpoint identifiers that match the wildcard in the EndPointIdList parameter, which is simply one or more SpecificEndpointIds (each supplied separately). In the case where the "all of" wildcard is used, RequestedInfo SHOULD NOT be included (if it is included, it MUST be ignored). Note that the use of the "all of" wildcard can potentially generate a large EndPointIdList. If the resulting EndPointIdList is considered too large, the gateway returns an error (error code 533 - response too large, is RECOMMENDED). When a non-wildcard EndpointId is specified, the (possibly empty) RequestedInfo parameter describes the information that is requested for the EndpointId specified. The following endpoint info can be audited with this command: RequestedEvents, DigitMap, SignalRequests, RequestIdentifier, QuarantineHandling, NotifiedEntity, ConnectionIdentifiers, DetectEvents, ObservedEvents, EventStates, BearerInformation, RestartMethod, RestartDelay, ReasonCode, PackageList, MaxMGCPDatagram, and Capabilities. Andreasen & Foster Informational [Page 61] RFC 3435 MGCP 1.0 January 2003 The list may be extended by extension parameters. The response will in turn include information about each of the items for which auditing info was requested. Supported parameters with empty values MUST always be returned. However, if an endpoint is queried about a parameter it does not understand, the endpoint MUST NOT generate an error; instead the parameter MUST be omitted from the response: * RequestedEvents: The current value of RequestedEvents the endpoint is using including the action(s) and event parameters associated with each event - if no actions are included, the default action is assumed. Persistent events are included in the list. If an embedded NotificationRequest is active, the RequestedEvents will reflect the events requested in the embedded NotificationRequest, not any surrounding RequestedEvents (whether embedded or not). * DigitMap: The digit map the endpoint is currently using. The parameter will be empty if the endpoint does not have a digit map. * SignalRequests: A list of the; Time-Out signals that are currently active, On/Off signals that are currently "on" for the endpoint (with or without parameter), and any pending Brief signals. Time- Out signals that have timed-out, and currently playing Brief signals are not included. Any signal parameters included in the original SignalRequests will be included. * RequestIdentifier: The RequestIdentifier for the last NotificationRequest received by this endpoint (includes NotificationRequests encapsulated in other commands). If no NotificationRequest has been received since reboot/restart, the value zero will be returned. * QuarantineHandling: The QuarantineHandling for the last NotificationRequest received by this endpoint. If QuarantineHandling was not included, or no notification request has been received, the default values will be returned. * DetectEvents: The value of the most recently received DetectEvents parameter plus any persistent events implemented by the endpoint. If no DetectEvents parameter has been received, the (possibly empty) list only includes persistent events. * NotifiedEntity: The current "notified entity" for the endpoint. * ConnectionIdentifiers: The list of ConnectionIdentifiers for all connections that currently exist for the specified endpoint. * ObservedEvents: The current list of observed events for the endpoint. Andreasen & Foster Informational [Page 62] RFC 3435 MGCP 1.0 January 2003 * EventStates: For events that have auditable states associated with them, the event corresponding to the state the endpoint is in, e.g., off-hook if the endpoint is off-hook. Note that the definition of the individual events will state if the event in question has an auditable state associated with it. * BearerInformation: The value of the last received BearerInformation parameter for this endpoint (this includes the case where BearerInformation was provisioned). The parameter will be empty if the endpoint has not received a BearerInformation parameter and a value was also not provisioned. * RestartMethod: "restart" if the endpoint is in-service and operation is normal, or if the endpoint is in the process of becoming in-service (a non-zero RestartDelay will indicate the latter). Otherwise, the value of the restart method parameter in the last RestartInProgress command issued (or should have been issued) by the endpoint. Note that a "disconnected" endpoint will thus only report "disconnected" as long as it actually is disconnected, and "restart" will be reported once it is no longer disconnected. Similarly, "cancel-graceful" will not be reported, but "graceful" might (see Section 4.4.5 for further details). * RestartDelay: The value of the restart delay parameter if a RestartInProgress command was to be issued by the endpoint at the time of this response, or zero if the command would not include this parameter. * ReasonCode: The value of the ReasonCode parameter in the last RestartInProgress or DeleteConnection command issued by the gateway for the endpoint, or the special value 000 if the endpoint's state is normal. * PackageList: The packages supported by the endpoint including package version numbers. For backwards compatibility, support for the parameter is OPTIONAL although implementations with package versions higher than zero SHOULD support it. * MaxMGCPDatagram: The maximum size of an MGCP datagram in bytes that can be received by the endpoint (see Section 3.5.4). The value excludes any lower layer overhead. For backwards compatibility, support for this parameter is OPTIONAL. The default maximum MGCP datagram size SHOULD be assumed if a value is not returned. Andreasen & Foster Informational [Page 63] RFC 3435 MGCP 1.0 January 2003 * Capabilities: The capabilities for the endpoint similar to the LocalConnectionOptions parameter and including packages and connection modes. Extensions MAY be included as well. If any unknown capabilities are reported, they MUST simply be ignored. If there is a need to specify that some parameters, such as e.g., silence suppression, are only compatible with some codecs, then the gateway MUST return several capability sets, each of which may include: - Compression Algorithm: A list of supported codecs. The rest of the parameters in the capability set will apply to all codecs specified in this list. - Packetization Period: A single value or a range may be specified. - Bandwidth: A single value or a range corresponding to the range for packetization periods may be specified (assuming no silence suppression). - Echo Cancellation: Whether echo cancellation is supported or not for the endpoint. - Silence Suppression: Whether silence suppression is supported or not. - Gain Control: Whether gain control is supported or not. - Type of Service: Whether type of service is supported or not. - Resource Reservation: Whether resource reservation is supported or not. - Security: Whether media encryption is supported or not. - Type of network: The type(s) of network supported. - Packages: A list of packages supported. The first package in the list will be the default package. - Modes: A list of supported connection modes. The Call Agent may then decide to use the AuditConnection command to obtain further information about the connections. If no info was requested and the EndpointId refers to a valid endpoint (in-service or not), the gateway simply returns a positive acknowledgement. Andreasen & Foster Informational [Page 64] RFC 3435 MGCP 1.0 January 2003 ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. Note that PackageList MAY also be included with error code 518 (unsupported package). 2.3.11 AuditConnection The AuditConnection command can be used by the Call Agent to retrieve the parameters attached to a connection. ReturnCode, [CallId,] [NotifiedEntity,] [LocalConnectionOptions,] [Mode,] [RemoteConnectionDescriptor,] [LocalConnectionDescriptor,] [ConnectionParameters,] [PackageList] <-- AuditConnection(EndpointId, ConnectionId, RequestedInfo) The EndpointId parameter specifies the endpoint that handles the connection. The wildcard conventions SHALL NOT be used. The ConnectionId parameter is the identifier of the audited connection, within the context of the specified endpoint. The (possibly empty) RequestedInfo describes the information that is requested for the ConnectionId within the EndpointId specified. The following connection info can be audited with this command: CallId, NotifiedEntity, LocalConnectionOptions, Mode, RemoteConnectionDescriptor, LocalConnectionDescriptor, ConnectionParameters The AuditConnection response will in turn include information about each of the items auditing info was requested for: * CallId, the CallId for the call the connection belongs to. * NotifiedEntity, the current "notified entity" for the Connection. Note this is the same as the "notified entity" for the endpoint (included here for backwards compatibility). Andreasen & Foster Informational [Page 65] RFC 3435 MGCP 1.0 January 2003 * LocalConnectionOptions, the most recent LocalConnectionOptions parameters that was actually supplied for the connection (omitting LocalConnectionOptions from a command thus does not change this value). Note that default parameters omitted from the most recent LocalConnectionOptions will not be included. LocalConnectionOptions that retain their value across ModifyConnection commands and which have been included in a previous command for the connection are also included, regardless of whether they were supplied in the most recent LocalConnectionOptions or not. * Mode, the current mode of the connection. * RemoteConnectionDescriptor, the RemoteConnectionDescriptor that was supplied to the gateway for the connection. * LocalConnectionDescriptor, the LocalConnectionDescriptor the gateway supplied for the connection. * ConnectionParameters, the current values of the connection parameters for the connection. If no info was requested and the EndpointId is valid, the gateway simply checks that the connection exists, and if so returns a positive acknowledgement. Note, that by definition, the endpoint must be in-service for this to happen, as out-of-service endpoints do not have any connections. ReturnCode is a parameter returned by the gateway. It indicates the outcome of the command and consists of an integer number optionally followed by commentary. PackageList is a list of supported packages that MAY be included with error code 518 (unsupported package). 2.3.12 RestartInProgress The RestartInProgress command is used by the gateway to signal that an endpoint, or a group of endpoints, is put in-service or out-of- service. ReturnCode, [NotifiedEntity,] [PackageList] <-- RestartInProgress(EndPointId, RestartMethod, [RestartDelay,] [ReasonCode]) Andreasen & Foster Informational [Page 66] RFC 3435 MGCP 1.0 January 2003 The EndPointId identifies the endpoint(s) that are put in-service or out-of-service. The "all of" wildcard convention may be used to apply the command to a group of endpoints managed by the same Call Agent, such as for example all endpoints that are attached to a specified interface, or even all endpoints that are attached to a given gateway. The "any of" wildcard convention SHALL NOT be used. The RestartMethod parameter specifies the type of restart. The following values have been defined: * A "graceful" restart method indicates that the specified endpoints will be taken out-of-service after the specified delay. The established connections are not yet affected, but the Call Agent SHOULD refrain from establishing new connections, and SHOULD try to