Experiencing distorted phone calls

[stps]

Product Details
Server: Avaya S8710, CM 5.2.1
Media Gateway: MG 430, FW Version/HW Vintage: 30 .12 .1 /1
Phones: 9630G, 9640G IP

Problem Clarification
Issue: Voice quality on an established call is garbled or clipped – ~ every third word – on both internal or external calls; appears to be QoS issue

Troubleshooting & Testing Performed:
· Network tech applied QoS on all-PBX-related ports on the Cisco Catalyst Switch & checked the ports’ traffic
· Monitored phones to ascertain amount of jitter – quite a lot at first – lessened when QoS applied & when MEDPROs reset
· Tested all PBX IP-related cards (9) – all cards passed all tests
· Looked for errors & alarms on all 9-cards – none discovered
· Checked, tested 4-primary trunk groups (20, 70, 76, & 80) DS1s to networks – found no alarms, no errors, plus all cards passed all tests
· Reset the 2-MEDPRO cards – had high discard rates - this past Sunday night to preclude disrupting service