sccp ip precedence value

Unanswered Question
Feb 8th, 2009

I know IP Prec is a bit old school BUT I need something clarified.

The command sccp ip precedence 'value' is an optional command you can use when you are configuring media resources within terminal configuration window.

According to Cisco documenation it sets the IP precedence value for SCCP. A more specific explaination continues...

•This command enables you to increase the priority of voice packets over connections controlled by SCCP.

•value-Range is 1(highest) to 7 (lowest). Default is 5.

Now the wording is a little vague - or is it?,

SCCP = signaling, voice packets = rtp. SCCP = TCP 2000, RTP = UDP 16384-32767 etc.

Default 5 sounds like media as per description, is this correct or is this old school TOS bits field used for signaling?

I only ask because I see a lot of SCCP configurations on the net that have this set to 3.

Any help appreciated!

I have this problem too.
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Nicholas Matthews Sun, 02/08/2009 - 15:46

I checked this in the lab, and it's fairly easy to check.

access-list 101 permit tcp any any eq 2000 precedence 5

access-list 102 permit tcp any any eq 2000 precedence 3

access-list 103 permit tcp any eq 2000 any precedence 5

access-list 104 permit tcp any eq 2000 any precedence 3

There are SCCP keepalives every 30 seconds, and more traffic if you have active SCCP MTP/Conferencing.

'debug ip packet 101' shows that by default signaling is sent with precedence 5. 'debug ip packet 102' shows that we don't use precedence 3.

'debug ip packet 103' shows that CUCM doe not send us precedence 5 SCCP traffic. 'debug ip packet 104' shows that CUCM sends us SCCP traffic with IP precendence 3.

So yes - the 'sccp ip precedence' command is for signaling. I tried to find out why we use a default of 5, but didn't get any history.

hth,

nick

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