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New Member

QoS for VoIP


Setup is pretty simple. A c871 router with various devices (PCs and SIP phones) connected to LAN ports (all in one VLAN), and a trunk with two VLANs towards ISP backbone (two dot1q subi-fs on router). One VLAN is used for data-only, other is used to reach VoIP platform. Phones are marking their traffic with DSCP 46 (EF).

Task - grant a strict priority for voice traffic on uplink.

Question is - I can apply a policy-map on physical interface (in this case FastEthernet4), or I can apply policy-map on subinterfaces. In case I apply it on physical interface - it matches nothing, as traffic is routed on subinterfaces. Plus - I cant apply it on subinterfaces, as it makes no sense to apply it on data interface as there is no VOIP traffic, and it makes no sense to apply it to VOIP subinterface, as all traffic there is VOIP.

Any ideas where and how to configure, that marked traffic gets strict priority compared to non-marked?




Re: QoS for VoIP

Use this Cisco 800 Series Routers Configuration Guides for your configuration assitance.

New Member

Re: QoS for VoIP

No offence, but I dont think you understood the question. I'm not looking for Configuration Assistance in general, as I perfectly understand how QOS works in theory and how its configured. I need an advice for this specific box and this specific issue.



New Member

Re: QoS for VoIP


You typically need LLQ on WAN links. It appears that this is a MAN connection - very high speed. If you are already confident that your traffic is marked correctly and the ISP will route the traffic according to your settings then this interface may be good to go. If you want to make sure traffic is marked by passing it through ACLs and Class/Policy maps sure, you can.

This is a very high speed link, almost identical to an internal F/E link. If you look at the QOS SRND for Branch Routers, you will note that the only thing applied to such interfaces is marking/classification verification.

Now that being said. If you end up having congestion or for some reason fear you will fill up 100M or more pipe, then you may need to look at policing and rate limiting traffic.