CoS on Serial interface - 1841

Unanswered Question
Sep 22nd, 2009

Hello,

I have a question.

We recently deployed a solution that involves VoIP. The VoIP isn't a cisco solution, but we are using a Cisco 1841. We are configuring QoS on the router. ISP says that we need to tag voice traffic with Class of Service 4.


This is my policy map:

policy-map voice_cos

class voice_cos

set cos 4

priority percent 60



However, when I went to apply the service-policy output voice_cos command to the serial interface, it said this:

Router(config-if)#service-policy output voice_cos

Process 'set' action associated with class-map voice_cos failed:

Set cos supported only with IEEE 802.1Q/ISL interfaces


So, my question is, can I not set a CoS on a serial interface?


It's my understanding that I need to set CoS on the serial interface so that routers later down the line knows to prioritize the traffic. I know that there are other ways of marking traffic - such as DSCP, but the ISP specifically said that it should have Class of Service 4.


Any suggestions or feedback would be appreciated.


I attached the config. 192.168.2.240 is my internal VOIP PBX. The pbx is hybrid. Internal phones talk to it trough traditional lines. It talks to ISP through VoIP.


Thanks,

Ben



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Benjamin Waldon Wed, 09/23/2009 - 16:39

Thanks, That is helpful.


But, it won't take the :service-policy inbound voice_cos" command on the fa port.


I just reread you comment, maybe your suggesting on the switch itself? I guess that would work too. Thanks.

Joseph W. Doherty Wed, 09/23/2009 - 19:14

"But, it won't take the :service-policy inbound voice_cos" command on the fa port. "


It won't if the policy contains queuing configuration commands, e.g. priority, bandwidth. Inbound policies are more restricted in their support of command configuration.

Joseph W. Doherty Wed, 09/23/2009 - 03:28

"It's my understanding that I need to set CoS on the serial interface so that routers later down the line knows to prioritize the traffic. I know that there are other ways of marking traffic - such as DSCP, but the ISP specifically said that it should have Class of Service 4."


It would be best to confirm what your ISP meant by a "Class of Service 4" marking. They might have meant a DSCP class selector 4 (DSCP CS4) or an IP Precedence 4 marking. (They might have also meant a particular "class of service" within their QoS framework, which might use a marking, usually DSCP, unique to it.) Both DSCP CS4 and IP Prec 4 are L3 IP header markings.


As the error message indicates, "Set cos supported only with IEEE 802.1Q/ISL interfaces ", the cos your attempting to use only exists in L2 Ethernet frames with VLAN tags.


PS:

If you are in fact dealing with a vendor class of services, you should find out from the vendor what all it does. For instance how much bandwidth is guaranteed per class and what happens if you oversubscribe the class bandwidth, etc.

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