Video conferencing will not work over a 1720 ISDN link. Since 1720 is not a gateway, H.320 systems cannot dial into the ISDN interface. If you had H.323 in mind, not enough bandwidth is available to account for video + IP overhead + PPP overhead which I assume would be used for ISDN connect.
I read your answer...I would like to know how much bandwidth to I need to have voice calls between two routers or gateways.
We are thinking to have a 7822 in a city and an isdn router with Iphones in an other city connecting them ON DEMAND by an isdn Link.
Do you think it is a suitable solution?
Greets from Italy.
Voice-only is a much easier proposition than video. Bandwidth used on a voice call is dependant upon which audio codec you use. Typically, mostapps use G.711 (3 khz @ 64k) or G.729 (3 khz @ 8k). Remember to add roughly 10% for IP overhead. So for your particular application, I don't see the ROI of doing IP voice over a dial-up ISDN link. Whether you compress voice or not, you must still dial up at least 1 bearer channel to do voice. To the extent that you already have active channels for data traffic, you may be able to route some voice calls over that path as well using G.729. Not sure of the pitfalls of using routers. Presumably, you will use PPP between routers adding even more overhead to the voice packets. Look at a permanent connection of some sort between your offices for both voice and video, this may cost justify your desired application