Megaco WG J. Bouwen Internet Draft Alcatel Bell Document: November 2000 Category: Informational Extensions to Megaco to support Data in an ISDN D-channel Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 1. Abstract In ISDN interfaces the D-channel is used to transport the Q.931 signalling messages. In addition, the D-channel can transport packet data for user-to-user communication. The Megaco protocol specification has to be extended to support data in an ISDN D- channel. More specifically, ephemeral terminations on top of physical ISDN terminations have to be allowed, and support for the ISDN addressing scheme has to be added to refer to the data streams in the D-channel. This draft defines the required additional functionality, that could be part of the second version of the Megaco protocol. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [2]. 3. Introduction In ISDN interfaces the D-channel is used to transport the Q.931 signalling messages. But the D-channel can be used for more than that. In addition to Q.931 signalling, it can be used to transport Bouwen Informational û Expires May 2001 1 Megaco Extensions for Data in D-channel November 2000 packet for user-to-user communication. Examples of packet data in the D-channel include: * Always on ISDN. An internet connection over the D-channel can be used to signal the arrival of new messages in the user's mailbox. A B-channel will be opened for download of the packet data. * Credit card verification * Exchange of data between shops and a central database, for instance for Lotto shops and petrol stations. The current Megaco specification doesnÆt contain the required functionality to support packet data in D-channels in ISDN access gateways. The necessary extensions are twofold: 1. The possible presence of multiple data flows in the D-channels implies that the D-channel can be considered as a packet interface, that can support multiple ephemeral terminations. The consequence for the Megaco is that the protocol should allow that ephemeral terminations are created on top of physical terminations of the Switched Circuit Network. 2. Ephemeral terminations on an IP interface are identified with the use of the transport address (IP address and port). In the case of ISDN, the Data Link Connection Identifier (DLCI) serves this purpose. Support for the ISDN addressing scheme of the DLCI has to be included in the Megaco protocol, i.e. in SDP in the case of the text version. (The binary version of the Megaco protocol is currently not discussed in this draft). The following paragraphs explain the ISDN addressing scheme (DLCI), and shows how a message of the extended Megaco protocol would look like. 4. Data Link Connection Identifier The D-channel uses a layered protocol according to ITU-T recommendations Q.920, Q.921, Q.930 and Q.931. The Q.921 Data Link uses the DLCI to identify a connection. Figure 1 shows the use of the DLCI. DLCI Data Link Connection Identifier An address conveyed in a Q.921 message which indicates the source and destination of an intended instance of communication at the data link layer The DLCI is the combination of the TEI and the SAPI SAPI Service Access Point Identifier Portion of the DLCI associated with the service access point on the network side or the user side of the user- network interface. The Service Access Point is the point at which the Q.921 data link layer provides services to layer 3 (Q.931). Bouwen Informational û Expires May 2001 2 Megaco Extensions for Data in D-channel November 2000 TEI Terminal Endpoint Identifier Portion of a DLCI associated with one (point-to-point data link) or more than one (broadcast data link) terminal equipment. The TEI is used to identify a specific connection endpoint within a Service Access Point. ########################### ########################### C P # Terminal 1 # # Terminal 2 # U R # # # # S E # +--------+ +--------+ # # +---------+ # T M # | Packet | | Q.931 | # # | Q.931 | # O I # | Data | | Sign. | # # | Sign. | # M S # +--------+ +--------+ # # +---------+ # E E # | | # # |...| # R S # /|\ SAPI /|\ SAPI # # /| |\ SAPI # ' # \|/ 16 \|/ 0 # # \|...|/ 0 # S # | | # # | | # ######|###########|######## ###########|###|########### | | | | |TEI88 |TEI88 TEI3| |TEI8 | | | | | +--------+ +------------+ | +------------------+ | | +--------------+ | | | | | | | | -->| | | |<--D-Channel | | | | | | | +---------------+ N +-----------+ | +-------------+ | E | +-----------+ | | T | | | | W / \ SAPI /|'''|'''|\ SAPI O \ / 16 \|...|...|/ 0 R | | | | K +--------+ +---------+ | Packet | | Q.931 | | Data | | Sign. | +--------+ +---------+ DLCI = SAPI + TEI Figure 1 - Relationship between SAPI, TEI and DLCI (based on [5]) The Q.921 SAPI differentiates between Q.931 signaling and packet data. The SAPI has the value of 0 for Q.931, and 16 for packet data. Bouwen Informational û Expires May 2001 3 Megaco Extensions for Data in D-channel November 2000 5. Extensions to Megaco and SDP The following example message shows a Megaco message that creates an ephemeral termination on top of the D-channel for a data stream that is used for connection to the Internet. MEGACO/1 [123.123.123.4]:55555 Transaction = 10003 { Context = $ { Add = ISDNTerm/BA17/D/$ { Media { Stream = 66 { LocalControl { Mode = SendReceive}, Remote { v=0 c=ISDN DLCI 88 m=data 16 ppp } } }, Add = $ { Media { Stream = 66 { LocalControl { Mode = SendReceive}, --Remote and Local descriptors for IP network data session-- }} } } } 5.1 New Megaco functionality The message contains the following new items: Add = ISDNTerm/BA17/D/$ The command requests the Media Gateway to create an ephemeral termination within the D-channel (indicated by the $ after the name of the D-channel). The Media Gateway will indicate in its response the assigned termination identifier. Stream = 66 A value different from 1 has been selected, as this one is reserved for audio An ephemeral termination on top of the D-channel is specified with the use of ISDN addressing information. This implies that a æRemoteÆ descriptor is required. The Remote descriptor contains SDP. 5.2 New SDP functionality The SDP part in the Remote descriptor for the ephemeral termination on to of the D-channel has the form: c=ISDN DLCI 88 Bouwen Informational û Expires May 2001 4 Megaco Extensions for Data in D-channel November 2000 m=data 16 ppp The components of this description are (modelled on the current use of the parameters for IP networks): c=ISDN DLCI 88 The network is the ISDN, Q.921 DLCI is the addressing scheme The Terminal Equipment Identifier is 88. m=data 16 ppp A data stream is set up to Service Access Point 16, (packet data in the D-channel) over PPP. The creation of an ephemeral termination on the IP side is basically no different from dial-in connections from analogue lines, and is not further discussed. 6. Conclusion This draft defined the necessary new functionality for the Megaco protocol in order to support packet data streams in an ISDN D- channel. Extensions to the Megaco syntax and SDP have been described. It is proposed that the described extensions are taken into consideration for inclusion in version 2 of the Megaco protocol. 8. Security Considerations 9. References 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 10. Acknowledgments 11. Author's Addresses Jan Bouwen Alcatel Bell Bouwen Informational û Expires May 2001 5 Megaco Extensions for Data in D-channel November 2000 F. Wellesplein 1 B-2000 Antwerpen Belgium Email: jan.bouwen@alcatel.be Bouwen Informational û Expires May 2001 6 Megaco Extensions for Data in D-channel November 2000 Full Copyright Statement "Copyright (C) The Internet Society (date). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implmentation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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