High jitter levels with IP softphone on individual PCs

rigneydolphin used Ask the Experts™

I have a number of IP softphones setup connected back to an AVAYA pbx. I have ruled it out being a network issue as I have tried a number of different types of PC,s into the same port on a catalyst switch.

One particular model of PC works fine with the softphone and has an average Jitter level of zero.

Another model of PC works but has high Jitter resulting in bad conversation. Jitter can be as high as 21 average.

Bear in mind both these PC's have traveresed the same path back to the AVAYA, with me even trying both PC's into the same switch port.

The PC that works is a Lenovo Thinkcentre 8107.

The PC that does not work is a Fujitsu Siemens Esprimo E3510.

Both PC's have QOS enabled on the network card. I can't see any other difference but must be something PC related.

Any suggestions ??

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Reid PalmeiraTelecom Engineer
Top Expert 2005

I don't know the particulaar model or software revs but I know my old Fujitsu had really old network drivers and it was causing issues with QOS tagging as well as with the auto-speed setting on the ethernet port on the laptop. You might check the network drivers you have installed and try to update them.

might also be good if you can setup a mirror or span port on the switch and grab a couple of packets from the PC to make sure it's actually tagging the voip packets according to the ip pbx's qos settings.
It turned out to be an issue with the sound card in the PC's. When we used a USB headset the jitter disappeared. Problem sorted.

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