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.