One way voice

[Brendan Marmont]

We have an issue where an external call coming into our SIP GW will establish a call, however the caller can't hear audio, this happens to about 6% off all incoming calls at random times and on random IP 6xxx/7xxx Phones.

We have 2 remote sites reporting an issue, both use SIP. Working sites use PRI.

When we divert a problem site DDI (via a translation pattern in the CUCM) to terminate on a working site extension, the problem is replicated, proving the remote sites LAN and the GWS WAN configurations are not at fault.

We have zero errors on the core switch SIP facing interface.

Both SIP Router and CUCM sit in the same VLAN,

Since the problem is intermittent we don't believe there to be a routing related issue, otherwise it would occur all of the time?

We use a telco managed cisco 2800 router trunked to our CUCM 7.1.3. local Publisher

Phone load images have been updated to the latest release SCCP69xx.9-2-1-0

Any pointers would be appreciated. Finger points the SIP router likely at fault.

Cheers

Brendan

[Yufang Zhou]

Starting with identifying the acutal media path by:

1. Made test call using simlar call flow as the problem calls.

2. Browse into the the IP phones and identify the RTP remote/local ip addresses.

3. With above result, you should be able to identify if MTP are inserted or not in the media path.

Routing/Networking issue can not be eliminated yet as RTP UDP port numbers for any established call are dynamically negoiated on per call basis and there could be some ports are not openning and RTP packets not getting through.

Locate a nearest point to the SIP gateway to use packet capture to capture the problem streams are the best way to isolate the issue.

[Brendan Marmont]

Thanks for your input, we think we have found the issue, the telco SIP router had a defaulting route to the wrong IP. Fingers crossed, it's been a day so far without error.