Echo on VOIP calls!

In this environment there are 5 sites which share network connectivity between each other via an IPSs Ethernet Handoff/WAN, with the Internet connection all traveling through one main site.  The ISP honors QoS packet markings of DSCP=46/EF between sites.  All Layer 3 routers (Adtran NetVanta) implement QoS on the egress of their WAN connections (low latency queuing).  The voice codec between sites is G.729a and the G.711u codec is used for local internal calls.  The main site has a PRI circuit (also where the only/main Internet connection resides) and the 4 remote sites have local copper trunks.

Users complain of echoing on VOIP calls between sites& maybe 1 or 2 instances every couple of days.  The Layer 3 routers interfaces, QoS queues (no drops) are running clean yet users occasionally experience echo on VOIP calls, even sometimes when the call is using a local copper and/or PRI circuit.    I have tested the VOIP quality with NetIQ and when I saturate the WAN inter-site connection.  The MOS scores for using a G.729a codec is 4.02.  When I switch the Inter-site codec to G.711u the MOS scores increased to 4.35.  Of course the G.711u is more resilient to network latency, jitter, etc. but it also requires more bandwidth (from mid30s Kbps to mid 90s Kbps).  If everything is running clean would it be fair to say that the echoing/latency are attributable to the ISP?  Oh yeah, the IP Telephony system is  a ShoreTel.

Please let me know if you need any information and/or have questions.

Thanks,
-Jon
Start Free Trial