Voice Lag on transferred calls - UCM6308


We are using a UCM6308 and experiencing a voice lag with incoming external SIP calls that are being transferred to another internal number. The transfers are both manual and automatic.

We are able to replica the issue by calling from a cell phone to a SIP DID that is routed to an UCM extension. The conversation with the initial extension is fine and there no delay or lag with the voice. The problem occurs when the call is transferred to another internal number then we are experiencing a delay or lag in the voice.

This calls are either manually transferred or transferred automatically via a forwarding setup.


Firmware version on the UCM and what make/model are the phones?


Two UCM6308 on firmware using HA. Using over 600 Grandstream 2615 and 1760 all on WiFi.


Hello. I am having similar issues also on a newly set up UCM6308 and GXP2170 phone where when a call comes in, IVR answers very quickly, caller makes a selection, call is transferred to an extension and there is often (estimate 70% of the time) a 5-6 second delay from when the call is answered on the destination extension and the audio connects. I have checked everything I can think of, including codecs and connections. Carrier states they are sending PCMU codec, so I have tried to retain that throughout the system. Any suggestions? Firmware is on the UCM and on the GXP. Thank you.


lacks scenery and details,
activated codecs for example?


Sorry, just updated the post with codec details as you were typing probably. Anything else that would be helpful?


insert only one codec, example only PCMU might be a thing to try,
checking if you have internet connectivity issues related to latency and jitter might be another thing to try,
there is no immediate solution,
for that the more details you give, the more someone might have advice to give you


damiano70, I’ll remove all codecs except PCMU. I had G.722 and GSM as options.

SIP line is dedicated, no other devices/usage and is provided by our legacy phone carrier, Consolidated Communications so there should be no congestion/jitter problems.


when there is a problem, anything could be the problem, there is no “shouldn’t” or “I guess not” situation.
It is not always easy to arrive at the solution, each situation has circumstances that are different from others.
So don’t underestimate anything.


You are correct, there are always definite solutions to problems. Hopefully I have asked the right question and have implemented the correct solution. We’ll see, thanks for your help.


UCM and phones on the same network delay can be caused on layer 2 at the switch level. maybe doing a packet capture can show more but this happening at packet forwarding not routing. I with test switch ports make a model of switch VLANs etc. Just an idea


Telecomsolutions thanks for your suggestion.

The system and phones are on dedicated, single switch LAN (phones) and WAN (SIP) networks, no VLANS and very lightly loaded. I’ll keep this in mind if the problems continue though.


I am having similar issues w/ our ucm6308 & gxp2170 sets. It seems a reboot to the UCM helps for a week or so. But then the problem returns. Have you had any luck with your issues? If so, what changes were mad?

Thanks… Doug


please note the Outbound DOD on UCM :slight_smile:

…and it’s not a WIFI problem


Sorry for the delay getting back to you. It appears in this case the solution was to choose one codec and stick with it in all configurations throughout the equipment. Our SIP provider was handing us PCMU, so all devices were configured with that codec and all others deleted from the available option list. It seems to have solved the codec negotiation that (we think) may have been going on and appeared to be causing a delay before before the audio was passed through. No problems for several months and many thousands of calls later.