So You Say You Want A Standard?
BY LAURENCE J. FROMM
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.
FIRST, THERE WAS THE ITU
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.
THEN, THERE WAS THE IETF
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.
MEANWHILE, OVER ON THE FRAME RELAY SIDE
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.
INTO THE VOID
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.
THEN, THINGS GOT COMPLICATED
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.
WHERE'S THE FAX?
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.
CALL CONTROL GETS CONTENTIOUS
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.
THINGS HEAT UP
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. |