Videoconferencing Buzzword Alert

Here are some videoconferencing buzzwords, most of which relate to low-bit-rate videoconferencing and telecommunications, that are generally misunderstood and therefore constantly misused. They will continue to be (mis)used, so we'll just have to learn to understand them within the context they are used.

POTS stands for Plain Old Telephone Service; however, it is not a synonym for, or an adjective to be applied to, analog phone lines, a.k.a. regular phone lines. POTS is what is done over the line, not a description of the line itself. POTS includes such basic services as dial-tone, busy signal, ring-back, and local and long-distance dialing. For example, one uses POTS over regular and ISDN phone lines on the GSTN but not typically over a leased T1 line. The GSTN is what the public telephone network is called. It stands for General Switched Telephone Network. You may have also seen PSTN (P as in Public), which is a synonym for GSTN.

Intel knows the difference. This is from their online ISDN glossary: "POTS (Plain Old Telephone Service): The basic telephone service - standard single line telephones, telephone lines, and access to the public switched network. There are no added features, such as call waiting or call forwarding, with POTS." Other references include Anatomy of Telecommunications by Tom Smith and a recent column in Wired magazine by Nicholas Negroponte.

The bottom line is this: When someone uses the acronym, "POTS," he or she is usually referring to either the GSTN or analog phone lines and not really to POTS itself.

In the context of synchronous V.34 modems, you really shouldn't call regular modems asynchronous modems. This is because all modems are asynchronous and synchronous simultaneously, at different levels. Neophytes won't have a clue either way as to what you're talking about, and people who know modems will either misunderstand you or won't know that you really do understand the technology after all. In lieu of a precise name (there isn't one), may I suggest calling them simply "regular modems" or work into what you're saying that they are not the "synchronous V.34 modems" that are required by H.324.

And be careful about using the term, synchronous modem. This is because there have been synchronous modems and synchronous V.34 modems for many years now. Always say synchronous V.34 modem and make it clear that you are referring to the modem that is required by H.324. I've noticed some vendors calling them video-ready modems, videoconferencing-ready modems, and Video Phone-ready modems, none of which are accurate because modems don't know that they are being used for video, but at least an existing term is not being high-jacked. These are just simple names invented by marketing to describe to the end-user what is really a subtle, very technical difference between regular modems and synchronous V.34 modems.

The low-bit-rate standard for multimedia, e.g., videoconferencing, over the GSTN is H.324. It requires a synchronous V.34 modem, and V.80 is the most common interface between an H.324 videoconferencing system and its synchronous V.34 modem. Another interface is the Rockwell video mode. I'll address related issues in a question-and-answer format:

Isn't V.80 required for H.324? No, V.80 is not mentioned in or required by H.324; however, H.324 is mentioned in the V.80 Recommendation, but only once and then only as an example. As far as compatibility goes, the end-user only has to make sure that if his or her videoconferencing system requires a specific interface such as V.80, he or she better be using a modem that supports it.

Is V.80 beneficial? The practical reason for using a V.80 modem is that you need a synchronous V.34 modem for H.324, which will likely also be a V.80 modem, because H.324 requires you to have one to be able to talk to other H.324 terminals. :-) however, the ostensible reason for having a synchronous V.34 modem, with V.80 coming along for the ride, is that it

performs better over a noisy line,
can get marginally better performance due to possibly reduced packet overhead, and
allows the terminals to communicate with each other about the transmission while the same line is carrying user data such as video, providing better control over the flow of data. However, we have products that use regular and synchronous V.34 modems and haven't noticed that much difference.

Do both modems need to be using V.80? V.80 is not an interoperability issue because it is not necessarily something that comes out of the modem onto the line. It is how your videoconferencing program talks to the modem. Therefore, while two terminals must either be both regular or, in the case of H.324, synchronous V.34 modems, they could have different internal interfaces, e.g., one uses V.80 and the other uses Rockwell video mode. However, in answer to the question, "Do both sides have to operate as synchronous V.34 modems to get any advantage?," the answer is yes.

Do I also have to have a V.80 modem for H.323? H.323 is an ITU-T Recommendation for LANs, so it does not require any specific kind of modem, or a modem at all. How you connect to your first LAN segment is your own business. For example, you could dial into your ISP using a V.34 or V.32bis modem or connect to your intranet with an Ethernet card. However, since H.324 is for the GSTN, all H.324 terminals must have a modem because it is so central in accessing the GSTN.

Will a V.80 modem work with the communication software I already have such as HotFax and HyperTerminal? A V.80 modem can be used without the V.80 stuff. Likewise, a synchronous V.34 modem can be used like a regular V.34 modem, so you don't loose anything by buying a V.80 or synchronous V.34 modem. Besides, pretty soon, all modems will have these features, so you won't have a choice.

Will a synchronous V.34 modem make cruising the Internet faster? No, only software that is written specifically for these modems can take advantage of their features. It's not like adding another, faster DCE transmission rate.

Here are the major ITU-T documents relating to interactive multimedia over communications channels, of which videoconferencing is a prime application. Look out for these "H-dots" when talking to vendors, reading literature, etc. about standards-based videoconferencing. Interoperability between these standards is provided by gateways. IOW, there is not a single videoconferencing standard.

For communicating directly over the GSTN, the ITU-T Recommendation (standard) is H.324;

for non-guaranteed-quality-of-service LANs including the Internet, H.323;

for guaranteed-quality-of-service LANs, H.322;

for ATM, H.310, although a "flavor" of H.323 can be used over ATM networks;

for B-ISDN, H.321;

for N-ISDN, H.320, although there is a version of H.324 for ISDN, sometimes called H.324I, which, by the way, will be the future of videoconferencing over ISDN--H.320 is a dead-end-street;

likewise, there is a version of H.324 for wireless, mobile networks, H.324M.