Impact on cisco route load generated by voip traffic

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Apr 18th, 2007
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Hi guys,


What is the difference betwin voip traffic and normal data traffic such as internet and mail follow throught a cisco router ?


We have on 256K internet link and when we use a router cisco 805 and behind him we put a voip gateway, when this gateway estabilish 6 calls (~150k) the processor of router was 85/90% and we start to have packet lost and consequently degradated voice quality.

We try with a cisco 1721 and this problem not happen.


Why ?


Thanks.


Fred


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paolo bevilacqua Wed, 04/18/2007 - 10:48
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Hi,


voip traffic is generally 50 PPS bidirectional per call, unless a smalle sample size is configured. So your 6 calls calls in g279 were generating about 29 x 6 = 170 kbps bidir (close to your figure) and 300 pps, again bidir.

It is not much in absolute but the old 805 has shown it can't cope with that. Considering that when serial port maximum speed is only 512 kbps compared to 2 or 4 mbps for other routers. One could have looked why, if buffers, new software to diagnose, but all in all it appears very reasonable it was time to upgrade the router.


Hope this helps, if so please rate post!

fred_m Thu, 04/19/2007 - 06:14
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How can we see how many PPS our router or serial interface can handle ?


Thanks.


Fred

paolo bevilacqua Thu, 04/19/2007 - 07:09
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If the interface is not too fast, the router will be able to use it at line rate. A slower router with performance limitation could not keep up and drop packets. You can check that with "show proc" and "show buffers" ,etc.

stresspattern Thu, 04/19/2007 - 09:33
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We were having the same issue on the 7206vxr, see my posting "Edge router for VOIP".


We removed the bridge-group 1 command from our GigE interface and the CPU usage dropped by 50%.


Regards,


Marvin

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