For VoIP over slow WAN links (<=T1), one can configure compressed RTP (cRTP) to reduce bandwidth usage. However, this will cause extra cpu load. I searched CCO all over, every relevant page says that the number of simultaneous calls a router can support will decrease due to cRTP processing, but it does not give any numbers.
Does anyone know how to estimate the impact of cRTP on cpu utilization? Specifically I'm looking at Cisco 7500 series routers and want to know how many T1 lines the router can support if I turn on the cRTP feature.
Thanks for the tips. For 7200 with NPE-300 its cpu could not handle more than 117 avtive calls when cRTP turned on. If each call on average carries 12 kbps traffic, this means the device could only deliver 1.4 mbps voice traffic, a pretty bad number. So I guess when you have enough bandwidth, you should never turn on cRTP! Use this feature only on slow links.
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