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Hardware transcoder and DiffServ

We've noticed that the router-based hardware transcoder/conference bridge platform does not support DiffServ. More specifically the SCCP code on the router only has options for IP Precedence.

Our entire network is setup to use DiffServ, and our carrier only supports Diffserv.

What options do we have to replace the ToS tagging with DiffServ? Place the transcoder behind an intelligent switch that can rewrite the tagging, or should we use Service Policies on the egress to rewrite the tagging?


Re: Hardware transcoder and DiffServ

Like you said, I see only two options. Placing a transcoder behind a switch will require you to redesign a part of the network. Easy one would be to classify the precedence set by sccp, and mark it to dscp using a policy-map, and apply the service-policy to the egress interface. You need to enable "ip cef" to set the dscp in policy-map.

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Re: Hardware transcoder and DiffServ

We have most of the configuraton in place to use policy-map and service-policy, so this seems the only workable solution.

The last remaining issue with it is that a rule to match IP precedence 5 also matches DSCP EF and

if the service-policy is set to rewrite the tagging we will be modifying packets that were already correctly tagged.

I doubt we will see any performance impact, as the router is only lightly loaded, but it does seem to be a waste of resources.



Re: Hardware transcoder and DiffServ

There is just a little difference between the precedence and dsscp mapping.

IP Precedence 5 -- 101000 (decimal 40)

DSCP EF -- 101110 (decimal 46)

Cisco recommends to use dscp value EF for voice bearer and AF31 for voice control traffic. So, if you follow these guidelines, you will find a difference.

And this will for sure use some resources, but that won't make much difference.



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