Packetizer Logo

The content on this page was written in about the year 2000 and is obviously quite dated. While it's likely many links are broken, it is retained since it might be of some value to some.

Synchronous V.34 Modems

Is my modem H.324 compatible?

To do standards-based videoconferencing over the PSTN ("POTS") using H.324, you must have an "H.324 compatible," or synchronous V.34 modem, such as those listed below. There are two types on the market, V.80 and Rockwell Video Mode (a.k.a. RVM and VRPI), although V.80 is by far the most prevalent. To determine whether you have one of these modems, use a program that allows you to enter AT commands to the modem directly, e.g., Terminal, HyperTerm, Procomm, or QuickLink III. Some modems support V.80 and VRPI. A V.80 modem will respond with "OK" to the following AT command:

AT command to query modem


and a VRPI modem will respond with "OK" to this command:

AT command to query modem


Note that some H.324 products will only work with V.80 modems and not VRPI modems. Smith Micro's VideoLink 324 and AudioVision products work with both. Also note that "V.80" and "VRPI" refer to the interface between the modem and the software--the DTE interface--and not between modems--the DCE interface. IOW, if you have a V.80 modem and your friend has a VRPI modem, you can still talk to each other because they produce the same bit stream.

Can I still somehow use my non-H.324-compatible modem for videoconferencing?

Yes, some products, such as VideoLink and AudioVision allow you to use just about any modem, even ancient 14.4kbps V.32bis and good-old V.34 modems, but both ends of the connection must use software from the same vendor. This is because there is no standard for this. As a matter of fact, I call this NCOM mode, "Non-Compliant Old-Modem mode." :-) I have noticed that some products from different vendors happen to be compatible with each other using this mode, but this is nothing on which you the consumer should depend.

What modems are H.324 compatible?

DISCLAIMER: This list is not complete--I will continue to add to it as I learn of other synchronous V.34 modems--but to the best of my knowledge, it is accurate. However, manufacturers can change the specs on modems at any time, so there is no guarantee that if you buy one of these modems that it will indeed by "H.324 compatible" or work with a specific H.324 terminal.