There are 3 ISDN channel connect VP8000 terminal, when they call the far end, the video stay still or blue screen of death, and last some time and recover themselves, the audio is OK.
Turn on the CRC of the H221 the bit error will be large than 90% at this situation.
1,Let 2 terminal make point to point call by ISDN(2B+D), they are OK. So in the switch office that ISDN connected was out of sync with other switch office.
2,Add the terminal software that can test the change of delay to orient this problem and we find the delay had changed before they are out of sync, it can not happen to the circuit switch network.
The test show that the wider bandwidth (the more B channels) the more frequent to change the delay.
The result of using the test instrument: we use SUNSET ISDN test instrument to call other test instrument of other office in BONDING and do loopback to the instrument, we find the 2B channel (on the same line) delay changed, we get it when we call out but can not get it from the local calling. When we make local call, the fault also has the chance to come out, because the test instrument can test only 2 B channel.
The change of the delay is mainly caused by the follow reasons:
1,The change of timeslot in time division switching, such as reconnecting network chip.
2,The the I/O clock on the delay circuit out of sync and slip.
3,Some hardware reset and clear the buffer and shake the clock.
4,Sevial BRI clocks are out of sync.