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October 1998

So You Say You Want A Standard?


What keeps IP telephony from growing faster? A few years ago the answer would have been a lack of standards. Today, it's no exaggeration to say the answer is too many standards. Standards groups and their proposed standards are bouncing around so fast, it takes a mighty quick eye just to follow the action.

The predecessor of today's International Telecommunications Union (ITU) was founded in 1865 to standardize international telecommunications (which, in 1865, meant telegraphy). When the telephone was put into international service, the ITU undertook standardizing telephony as well. The ITU is an agency of the United Nations and only national PTTs vote. In the case of the United States, which does not have a national PTT, the State Department represents the country. The ITU is large, formal, and bureaucratic. The work relating to IP telephony is done in the Telecommunications Standardization Sector (ITU-T), one of the ITU's three main sections Work is done in Study Groups, which are divided into Working Parties, which are composed of Expert Teams, which are divided into ad hoc groups. Note that the ITU calls their standards 'recommendations' because, technically, it is the responsibility of the member countries for formally adopting standards. Nevertheless, an ITU 'recommendation' is a standard.

ITU-T Study Group 16 (SG 16) gave us our first grounding in IP telephony standards when it approved H.323 as a standard for multimedia communications over LANs in 1996. H.323 builds upon work done by the International Engineering Task Force Audio Visual Transport (avt) working group, specifically in the area of the Real Time Protocol (RTP).

Among several technical specifications in H.323 is the all-important selection of a voice coder. H.323 requires that compatible endpoints support G.711, and provides options for several others, including G.723.1 and G.729.

H.323, it is important to note, is strongly related to H.324, the ITU-T standard for multimedia communication over the PSTN. Contemplating video conferencing, H.324 specifies G.723.1 as the baseline audio coder. G.723.1 is a good choice for audio coding in a video conference. Its relatively high compression factor saves bandwidth for the video, and its 30 millisecond frame size does not produce excessive latency in context of the relatively larger video frame size.

Whereas the ITU is organized, formal, and hierarchical, the Internet Engineering Task Force (IETF) is self-described (on the "Tao of the IETF") as "a loosely self-organized group of people who make technical and other contributions to the engineering and evolution of the Internet and its technologies." ITU develops new Internet standard specifications. There is no membership; anyone can register for and attend any meeting.

The IETF has eight functional areas, each with a set of working groups. The avt working group specifies experimental protocols for real-time transmission of audio and video over UDP and IP multicast.

As the ITU-T SG16 was developing standards for multimedia communication and the IETF was developing protocols for multimedia over IP, the frame relay community was adding voice to frame relay. The Frame Relay Forum (FRF) is an association of corporate members committed to implementing frame relay in accordance with national and international standards. The ITU-T SG 15 issues ITU standards for frame relay. The FRF spearheaded the standards effort for voice over frame relay. Among the many technical specifications for the standard is, of course, the choice of the voice coder. The FRF chose G.729a, technically a good choice. While consuming a bit more bandwidth than G.723.1 (8 Kbps versus 6.3 Kbps), G.729a has a smaller frame size (10 msec), leading to lower latency. It is also less complex than G.723.1.

With all these standards activities bouncing around, there was no single suitable standard for voice communication over wide-area IP networks in 1995 when the first commercial IP telephony products began appearing on the market from Vocaltec, followed quickly by others. To address this gap, a small group of vendors began meeting in 1996 to form the Voice Over IP (VoIP) Forum, which was later folded into the International Multimedia Teleconferencing Consortium (IMTC).

As the members of the VoIP Forum began considering a range of options for an IP telephony standard, market forces quickly zeroed in on a small range of options. In July 1996, Intel announced a free IP telephony client software product using H.323 and G.723.1. Microsoft soon followed with a similar product, NetMeeting. The prospects of millions of free IP telephony clients from Microsoft and Intel gave overwhelming momentum for the IMTC to adopt H.323 as the IP telephony call control standard, and, eventually, G.723.1 as the baseline voice coder. At first everyone seemed to accept H.323, but there was and is contention about G.723.1 from both service providers and vendors, particularly those vendors from a frame relay background.

Moving forward, the IMTC drafted an interoperability agreement that augmented H.323 to better address needs for communicating over wide-area IP networks.

ITU-T SG16, in revising H.323 for wide area use (which culminated in H.323 Rev 2, approved this year), 'recommended' G.723.1 as the preferred voice coder in applications that also include video, and G.729a as the preferred voice coder in applications without video.

Meanwhile, the European Telecommunication Standards Institute (ETSI) began its project TIPHON (Telephone and Internet Protocol Harmonization over Networks) to address end-to-end interoperation between circuit switched networks and IP networks. Moving beyond the connectivity issues that are the IMTC's major focus, ETSI also addresses issues like accounting, security, authentication, non-repudiation, and law enforcement. ESTI is a regional standards body for the European Union, and also the driving force behind GSM standard for wireless telephony. Not surprisingly, its standards include provisions for GSM voice coding, which helps enable interoperation of wireless and IP networks.

None of these standards yet included provisions for fax. The IETF Fax working group proposed a simple mode store-and-forward protocol based on Enhanced Simple Mail Transport Protocol (ESMTP), which was used as a basis for T.37. Meanwhile, the ITU-T SG8 worked on a real-time fax-over-IP protocol. In June of this year, ITU-T approved T.38 real-time fax-over-IP and T.37 simple mode store-and-forward protocol. The IETF Fax working group is now working on a full mode store-and-forward fax standard that includes provisions for things like confirmation.

Just as the IP telephony world was resigned to H.323 for the control standard, along came the Session Initiation Protocol (SIP), in development by the Multiparty Multimedia Session Control (mmusic) working group of the IETF. The mmusic working group is chartered to develop standard protocols to support Internet teleconferencing sessions. SIP has gained favor in some segments of the IP telephony industry for its simplicity and compactness. The momentum for H.323 seems all but overwhelming, but as you are probably beginning to sense, the standards have not yet coalesced to a point where anything can be considered final.

Over the last several months, another spate of standards activities has emerged. The IETF PSTN and Internet Internetworking working group (Say that three times fast!) has begun to "address connection arrangements through which Internet applications can request and enrich PSTN … telephony service." IETF IP Telephony working group (iptel) is initially focused on gateway discovery and call processing syntax. At least four recent IETF drafts have proposed different ways to split call control from the media stream, most notably the Simple Gateway Control Protocol proposed by Cisco and Bellcore. A Birds-of-a-Feather meeting is planned at the August IETF meeting to discuss SS7 and the Internet. Level 3 is leading the Technical Advisory Council (TAC) to develop a set of technical standards to bridge between current circuit-based public switched telephone networks (PSTN) and emerging Internet Protocol (IP) based networks. Pulver.com is leading the IP Telephony Memorandum of Understanding (MOU) to define requirements for commercial peering of gateways and gatekeepers. The Enterprise Computer Telephony Forum (ECTF) has thrown its hat in the fray to "begin facilitating interoperability for the convergence of PSTN and IP network communications." CableLabs is leading the PacketCable effort to identify, qualify, and support IP-based voice and video products over cable systems. The Intelligent Network Forum (INF) is also addressing PSTN-IP network convergence. And rest assured, more is coming.

It's time to do something about all this confusion. That is why today, I am announcing a new group for Standard Taxonomy of Protocols -- also known as STOP(!).

Laurence J. Fromm is vice president, new business development for Dialogic Corporation. Dialogic is a leading manufacturer of high-performance, standards-based computer telephony components. Dialogic products are used in voice, fax, data, voice recognition, speech synthesis, and call center management CT applications. The company is headquartered in Parsippany, New Jersey, with regional headquarters in Tokyo and Brussels, and sales offices worldwide. For more information, visit the Dialogic Web site at www.dialogic.com.

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