From: [email protected] List-Post: [email protected] Date: 9 May 1997 14:34:50 EDT
>In 99% of the cases there will be a protocol message that indicates >the call has "left ISDN" or is not "ISDN end-to-end" and at this >point the data transmission can automatically be switched to 56Kbps >and the end user does not have to make any adjustments except to >wait longer for the data Actually, in North America & Japan, the call will typically fail to set up if the originator has requested a 64kbps B-channel, and one is not available end-to-end. The originating ISDN device will send a Q.931 SETUP packet to start the call, and the local ISDN switch will typically respond with a Q.931 RELease COMplete packet (rather than a Q.931 CALL PROCeeding packet). The REL COM packet should tyically contain a "cause" of "Incompatible Destination". This is rather misleading, since the destination may well be compatible, but there is a 56kbps "choke point" somewhere _in-between_ the originating and terminating locations. Unfortunately, when we were trying to make 64kbps B-channel connections via AT&T's long distance network to some destinations, we got even more confusing responses from the network, rather than the "Incompatible Destination"! ________________________________________________________________ John Combs, Senior Project Engineer, ITS/TestMark Laboratories Email: [email protected] URL: http://www.testmark.com
