7960 (8.2 SIP) Requesting Configuration under heavy call volume

Question

I have a group of 7960 phones, connected to asterisk (1.2.10) acting as part of a ring group.
13 phones altogether. Periodically, mostly under heavy volume, but occasionally with only one call, the phones will drop active calls and display "Requesting Configuration"
The phones are each configured with 5 identical lines/registrations, and one Intercom registration.
Has anybody experienced this before, or know what might cause a SIP loaded phone to suddenly drop and Request Config?

Answer 1

Hi Ahmed,
Sorry for being late.
Actually i solved the problem about week ago. It was a black hole in the packets path. actually it was an MTU configuration needed to be edited to solve the issue. below the details:
1- GW sends SIP INVITE message successfully to CVP
2- CVP replies successfully with ACK
3- CVP should be sending a SIP INVITE to the GW (which includes the VRU label+corr ID)
4- GW proceeds then to initialize the vxml services and starts vxml part
after checking debugs and outputs from "debug ccsip messages", i noticed that message number 3 is never received by the GW. So i used wireshark on CVP to check if the message is being sent, and yes the message was sent successfully using 2 frames (fragmantation is there, as the whole packet is more than 1900 byte size), but fragmantation was done to 1500+400 from CVP, which should be passing though our network with no problems
I ran more debugs and logging on the routers in the path, and then i decided to use the hero command (not recommended to use ) "debug ip packet" on the voice GW, and here i found that the GW received only one frame with size 280 byte and in the packet detail the fragmantation offset is about 1620!!
I understood then that the problem was in the middle, in Cisco ASR1002 which probably reframed the packets according to its MTU configured on its uplink interface, so i decreased its MTU a little, and voila, the problem was solved (packet received correctly)