High VPN router CPU utilization with voice traffic

[dgoswick]

I posted this question on the VPN forum, but no one responded...

I have two 2620 routers each with an AIM-VPN/BP hardware encryption module. They both have a T1 to an ISP, and we have a VPN tunnel set up between them. We are using single DES, not 3DES between these sites. I can send data through without any problem and I get the desired T1 speed that I want. However, if I send 6 or 7 g.729 (without cRTP) voip calls over that same link, the CPU utilization starts to peg out at 99%. This of course results in poor quality calls. Any idea why this is happening? I can change the codec to g.711 and it looks almost identical as far as CPU utilization. I have tested with 2 calls at both codecs, and they both put the same load on the CPU. What is causing this?

[a.wells]

I dont have an answer ,though we experience simillar problem with the same routers under the same type of load 5 calls cpu hits 99%

[dgoswick]

I wonder if bug CSCdu89643 has anything to do with this. The bug states "AIM-VPN performance is different for IP and UDP traffic" This would make sense being that voice traffic is RTP.