Strange Transcoder DSCP Markings

Unanswered Question
Aug 4th, 2008

I've had this problem for a while and finally figured out the cause but not the fix.

I have a pair of 2651XM voice gateways at my main site. They are used to access PRI circuits as well as performing g.711/g.729 transcoding services for Unity. Note that Unity is configured to only accept g.711 calls.

Here is the problem. Packets from the voice gateway to phones are marked 101110 (DSCP EF). Packets from the same device but using the transcoder service are marked 101100 (DSCP ??).

Packets from Unity to x-coder are marked 101110

Packets to Unity from x-coder are marked 101100 <==== BAD!

Packets from phone to x-coder are marked 101110

Packets to phone from x-coder are marked 101100 <==== BAD!

Packets from phone to PRI gateway are marked 101110

Packets to phone from PRI gateway are marked 101110

How do I change the transcoder to use the right EF DSCP value? I'm running CM 4.1.3.

Thanks,

Patrick

I have this problem too.
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hypnotoad Tue, 08/05/2008 - 10:40

I figured this out.

This is an IOS bug that effects 26xx platforms with NM-HDV modules. The BugID is CSCeh00460. I added the following to my config:

class-map match-all RTP-Traffic

match ip rtp 16383 16383

!

!

policy-map SET-RTP-TO-EF

class RTP-Traffic

set dscp ef

!

interface FastEthernet0/0

service-policy output SET-RTP-TO-EF

--Patrick

hypnotoad Thu, 08/07/2008 - 08:21

More information.

I've learned that this bug effects the older SCCP stack in IOS. Upgrading to 12.4.11T4 or greater upgraded the SCCP stack to 4.x. The bug is fixed in the newer SCCP stack. Use the 'show sccp' command to see the version.

--Patrick

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