There are one CISCO2821 and one CISCO3845. Both of them are configured with SRTP. They can make calls to the third-party phone with SRTP. But both gateways can not accept any call if I set them to use SRTP only. Even if the 2 gateways call each other, the calls still can not work. If I set the gw to allow srtp falling back to rtp , the calls can be established. The attached file is the debugging log from the cisco2821 .
Cisco IOS Software, 2800 Software (C2800NM-ADVIPSERVICESK9-M), Version 12.4(15)T
6, RELEASE SOFTWARE (fc2)
Cisco IOS Software, 3800 Software (C3845-ADVIPSERVICESK9-M), Version 12.4(15)T5,
RELEASE SOFTWARE (fc4)
Thanks lot of for your help