Cisco VOIP and QoS

Unanswered Question
Jan 26th, 2009

Hello - we have a CallManager 5.1(1) installation with several VG224 for analog phone/fax/modems. We've been having some problems with the faxes and modems and also an occasional problem dialing out where the recipent cannot hear us (on our Cisco VOIP phones - 7941/7960's). I feel like I may need to do some QoS setup which we really haven't done much with prior to now. A little about our set up...we have a core 4510 switch with 4 other wiring closets with 3560s. Like I said we also have 4 VG224s. We have fiber out to two 2811 routers and T1s from there to the local phone company. I am not familiar (much) with configuring QoS. Can someone point me in the right direction (either for reading material to get up to speed) or other information to find out how I can start configuring QoS. Thanks in advance.

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Nicholas Matthews Mon, 01/26/2009 - 10:17

Unless you have a congested LAN core, you will really only need to apply QoS to your WAN links.

I'm attaching a sample QoS configuration for WAN links you may find useful.

hth,

nick

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CHRIS CHARLEBOIS Mon, 01/26/2009 - 11:37

I agree with Nick. While QoS/CoS should be considered at every level, it probably would not cause the problems you describe on a LAN.

The fax/modem issue sounds like a codec selection problem. Have you confirmed that you are using G.711 on all fax/modem lines? QoS is not going to help a fax on G.729.

As for the one-way audio... I haven't heard of QoS causing one-way audio issues. That is probably a routing or a firewall/access list problem.

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