H.221 Negotiation Timeout Problem

[nstwksp]

Hi,
When i dial the VTC via ISDN, I get H.221 negotiation timeout error. I tried both 64k and 128k. But when i restricted the call to 56k, the call was successful; i could see and hear the other end clear but they couldn't see and hear me properly. Only they could hear was background noise. I do have all three ISDN numbers serviceable. Reading through this forum, i saw that it could be D channel error. Could anyone explain me the detail about the possible error and cause? Please help

[Joe Vallender]

Sounds like the route your data calls for video are taking is not optioned for 64K clear channel data. It could be your (BRI) lines or your local switch providers trunks to the local tandem office or the tandem offices trunks to the long distance switched network. To isolate the problem, see if your LEC has a video test number to call to see if you can connect with 64K channels. You may need to get your LD carrier involved (assuming your video calls are LD).

[nstwksp]

Thanks for the information. Our data goes through VSAT and the exchange is Realitis DX. While the VTC is connected on restricted 56k, i traced the call on exchange. I could see that first two Directory Number were connected on 64k each but not the third DN which is voice or D channel. I am stuck and need help desperately.
Thanks

[Joe Vallender]

If you have a BRI, there are only two B-channels available for calls. The D-channel is used for signalling only (or data too if your ISDN device were to support that, but a video unit does not). It still sounds like there is a configuration or restriction on the channels that is not passing 64K data or data at all. The channels somewhere along the path appear to be configured as voice.
Are you receiving the call only on your VTC or originating it? How is your VTC connected to the (VSAT) network? Exactly what equipment is involved?

[nstwksp]

The problem occurs while i am receiving and originating both. The ISDN line goes to realitis exchange and to Promina(Multiplexer) node before going through VSAT. On the other side of the VTC, they will have mirror image of what i have. The aggregate Bandwidth on our VSAT is more than enough. I don't know if they have previlege to restrict the calls on the Promina.
Thanks