I have a Call Manager 4.01 Sr1a implementation with approximately 55 7940/7960 IP Phones. They are connected with 2 3560 48 port inline power phones, a 3550 24 port and then a 3750 24 Port Gigabit switch. I have a voice and data vlan with all the voice servers and phones in the voice vlan. I recently upgraded to the 6.05 firmware load on the phone and noticed a strange thing. For off-net and on-net calls sometimes, maybe 3 out of 10 calls users will hear a delay in the audio. Once a call is established you try to speak and hear nothing for 3 seconds. After the 3 seconds you can hear the other caller. Some delay in the RTP stream. I've opened a TAC case and they helped me take the firmware back to 6.04 but I am still hearing the same delays. They've wanted me to gather packet traces but since this is so random it is difficult to track down. I essentially have to do a port span and be right at the phone to capture the traces correctly. Wondering if anybody has seen this before?
I've swapped switch ports, ethernet cables, phones. I'm using auto qos voip cisco-phone on the switch ports for the QOS features. There's no inter-vlan routing going on for the voice traffic.
The switches are in a hub-and-spoke design with all the switches hanging off the gigabit switch. They're uplinked with each other via copper gigabit.