<div>I have a couple of customers who are experiencing poor audio using an IAD to connect their PBX to our h.323 PSTN GW.</div>
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<div>Basic Layout.</div>
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<div>Customer PBX PRI > IAD PRI (Network-emulate) converted to VoIP > MPLS enabled T1 > Core > AS5850 (VoIP converted to TDM) > PSTN.</div>
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<div>The customer reports that poor audio is experienced inbound into their PBX. They say their outbound audio is okay. This doesnt happen on every call but we do have more than one customer reporting the issue.</div>
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<div>The audio can be described anywhere from echo, cutting out or distorted audio. The problem has also been reported by users who have 38xx series gateways so i dont think the problem is IAD specific. The AS5850 is a shared device used by many different customers, the majority of which connect using Cisco IP phones and this demographic of customers are not reporting the problem.</div>
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<div>I have done packet captures on the AS5850 and there is no packet loss reported, the packets arrive in sequence and the jitter is very low.</div>
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<div>In my testing, I have found double-talk to cause the far end audio (AS5850) to cut-out. All the packets arrive but they contain a payload value of 7F. Some improvement can be made to this condition by disabling non-linear progression. </div>
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<div>My questions for the community are related to experiences or lessons learned from using PRI network emulate.</div>
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<div>Can there be too many echo cancellers in the call flow? (i.e. Customer PBX UC500 with Cisco PRI, IAD PRI, AS5850 PRI all with echo cancellers)</div>
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<div>Does the cable length command have any bearing on voice quality?</div>
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<div>Are there any special commands i should enter when connecting back to back wth a T1 cable (echo-cancel coverage, nlp, etc)?</div>
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<div>Is a 2 pair sheilded T1 cable necessary for the PRI back to back connection of less than 20 ft?</div>
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<div>Any insight or suggestions would be greatly appreciated. </div>
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<div>Thanks,</div>
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<div>Jeff </div>
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