The SIP SRTP Fallback to Nonsecure RTP feature enables a Cisco IOS Session Initiation Protocol (SIP) gateway to fall back from Secure Real-time Transport Protocol (SRTP) to Real-time Transport Protocol (RTP) by accepting or sending an RTP/Audio-Video Profile (AVP) (RTP) profile in response to an RTP/SAVP (SRTP) profile. This feature also allows inbound and outbound SRTP calls with nonsecure SIP signaling schemes (such as SIP URL) and provides the administrator the flexibility to configure Transport Layer Security (TLS), IPsec, or any other security mechanism used in the lower layers for secure signaling of crypto attributes.
For more information about configuring SRTP fallback and negotiation, see the srtp, srtp negotiate, and voice-class sip srtp negotiate commands in the Cisco IOS Voice Command Reference.
Cisco Unified Border Element
•Cisco IOS Release 12.4(22)T or a later release must be installed and running on your Cisco Unified Border Element.
Cisco Unified Border Element (Enterprise)
•Cisco IOS XE Release 3.1S or a later release must be installed and running on your Cisco ASR 1000 Series Router.