We have a Cisco CallManager 3.1(2c) with a pair of DT-24+ gateways providing PRI access to the DMS-100 class 5 telco switch. The DT-24+ gateways are running the latest general release loads that we can get from TAC. We get echo at the IP phone end on approximately 5% of calls into or out of the DT-24+ gateway. We are confident that the problem is caused by poorly balanced analog hybrids at the PSTN end of the call, exacerbated by the IP packetization/dejitter delays. We have been able to determine that the problem shows up most commonly on PSTN calls that are long distance, but not long enough for the telco inter-switch trunks to have echo cancellers.
We have messed around with the addition of padding in the DT-24+ cards and are currently sitting with 6 db of padding in the IP Telephony to PSTN direction. This has reduced the echo somewhat, but hasn't eliminated it. As well, we are starting to have "can't hear" complaints from PSTN connected parties.
Is anyone out there having the same issue with the DT-24+? Would any other Cisco PRI gateways perform any better or do I have to tell my customer to live with it?
We have messed around with the addition of padding in the DT-24+ cards and are currently sitting with 6 db of padding in the IP Telephony to PSTN direction. This has reduced the echo somewhat, but hasn't eliminated it. As well, we are starting to have "can't hear" complaints from PSTN connected parties.
Is anyone out there having the same issue with the DT-24+? Would any other Cisco PRI gateways perform any better or do I have to tell my customer to live with it?
