Those of us that use Cisco 7940/7960 sip phones know that we've been
impacted by two very different changes that have occurred over the last
couple of months.
First, when cisco created sip v6.x code, they implemented a new DSP (as
well as other software changes) that effectively drops any incoming rtp
packet that does not have even timestamps within the rtp packets. The
dropped packets cause choppy audio and significantly impacts quality.
The issue is unrelated to which codec one might use.
Second, an ongoing programming effort has been happening within * to
tie the rtp timestamps together when the rtp traffic crosses channel
types (iax/gsm to sip/rtp, isdn/capi to sip/rtp, etc). It would appear
the iax->sip timestamps are now functional, however Vic just found
where isdn->sip is creating the same type of problem. I'm not sure
why handling the timestamps in this way is needed, however only those
users of Cisco phones are actually impacted by the irregular timestamps.
In searching the Cisco TAC problem list, it would appear the timestamp
issue has not been reported. (A search based on "timestamp" turned up
nothing, and a search on "rtp" found nothing relevant.)
If someone that has experienced these problems has a SmartNet service
agreement could open a TAC case, it would help all 7960 users. (Now I
wish I had a SmartNet agreement!)
Rich
