T.120 – one barrier broken down

“Those who cannot remember the past are condemned to repeat it.” George Santayana

Part of why video conferencing got sidetracked in the 1990s were the wasted, ultimately counter-productive, efforts associated with ITU-T Recommendation T.120, “Data protocols for multimedia conferencing”, an ambitious family of specifications, once seemingly essential to the industry, and now disdained.

I can both confess and disclaim roles in these efforts. It was important to integrate personal computers with (video) conferencing. However, data conferencing was not as important as many of us thought back then. There were and are lots of ways to have two-way data conferencing. Extending one or more of those to an asymmetrical multi-point paradigm would likely have met the real needs and survived. However, T.120 attempted much more, complex symmetrical multipoint data conferencing with many participants.

The primary requirement was and is for conference participants to view something a speaker wants to be seen. In physical conferences, this “something” is typically two dimensional, and might be letter sized paper, a marker board (“white” board), a flip-chart on an easel, a projection screen or a computer display. Though this “something” may be modified during the conference, and though more than one person may make modifications, the typical situation is that either there are no modifications or that the speaker is the only one making changes.

The seeming emphasis in the T.120 family of recommendations was in T.126, “Still Image Protocol Specification”. T.126, supported by the prerequisites in T.122-T.125, elaborately defines layers of two dimensional planes, a designated virtual pointer plane and multi-party annotation of the images. These capabilities are more than are needed in most situations, and more than most implementors want to provide.

T.120 was also over-reaching in defining file transfer protocols (T.127, “Multipoint Binary File Transfer Protocol Specification”), and program sharing implementation (T.128, “Multipoint application sharing”[1]).

In 1993-96, when T.120 emerged as a seeming necessity, there were many networking options, including ISDN, analog telephone lines, TCP/IP, IPX/SPX and others, all addressed by T.120, particularly T.123, “Protocol Stack for Audiographics and Audiovisual Teleconference Applications”.

There have been very few T.120 implementations, probably no successful implementations except for the one from DataBeam. DataBeam’s implementation was licensed by most companies that supported T.120, including Microsoft. Microsoft NetMeeting was the most prominent application supporting T.120, and often used in other conferencing products simply to profide T.120.

Microsoft abandoned NetMeeting and T.120 along with it. Conferencing vendors, especially more newly established companies, are avoiding and disparaging T.120.

In this decade, T.120 has been superceded by the simpler, sufficiently effective, notion of secondary video streams providing the “something a speaker wants to be seen”. Proprietary approaches have merged into the ITU-T Recommendation H.239 “Role management and additional media channels for H.300-series terminals”.

However, some see H.239 as not enough…

  1. Microsoft’s RDP is an extended version of T.128 a.k.a. T.Share: Understanding the Remote Desktop Protocol (RDP). It could be argued that RDP is also “overreaching”.

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