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VOIP w/NEC phones and Cisco Catalysts

william.culver
Level 1
Level 1

An NEC phone switch with a VoIP starter package was recently introduced to the environment. We have Cisco switches (6500/2950/3750). Voice conversations can be choppy. Need to prioritize voice packets. Where can I look to get some info on this?

3 Replies 3

yshraybman
Level 4
Level 4

I think you might have a bigger issue. RTP stream is very small compared to 100Mb pipe. Unless there is a broadcast storm voice conversations should not be choppy even without QoS. Check if there is duplex mismatch between IP phone and switch port. Also check how much traffic is pushed thru switch ports.

Accross multiple switches you should check your COS you can set your ports to trust the cos or dscp being recieved from the NEC ip phones and then set up your queuing to prioritse what ever cos/dscp the nec phones are using.

An excellent book on Quality of services that will explain how to implement from multiple different types of switches to different ways of doing qos on routers is "End-toEnd QOS Network Design" by Tim Szigeti, and Cristina Hattingh from Cisco Press. http://www.ciscopress.com/title/1587051761

Patrick

Ohh and just because you have 100mb pipe does not mean that you will get perfect quality rtp streams. I've seen two 2950's connected to each other with some PCs on one side some phones on both and a server on the other give us problems with voice quality until we setup the priority queues on them.

Patrick

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