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For Media Anti-Tromboning

• When Media Anti-Tromboning media path mode is activated, Cisco UBE does not perform supplementary services such as handling REFER-based call transfers or media services such as Secure Real-Time Transport Protocol (SRTP) and SNR.
• Anti-Tromboning does not work if one call leg is media flow-through and the other call leg is Media Flow-Around. Similarly, Anti-Tromboning does not work if one call leg is Session Description Protocol (SDP) pass-through and another call leg is SDP normal.
• H.323 is not supported.

Media Flow-Through is a media path mode where media and signaling packets terminate and originate on CUBE. As CUBE is an active participant of the call, this mode is recommended when connected outside an enterprise (untrusted endpoints).

Figure 1. Media Flow-Through Mode

The media flow-through command is used to configure this feature in global VoIP configuration mode (config-voi-serv), dial-peer configuration mode (config-dial-peer) and voice-class configuration mode (config-class). Refer to Modes for Configuring Dial Peers to enter these modes and configure this feature.

Media Flow-Around is a media path mode where signaling packets terminate and originate on CUBE. As media bypasses CUBE and flows directly between endpoints, this mode is recommended when connected within an enterprise (trusted endpoints). Media Flow-Around is supported for both audio and video calls.

Figure 2. Media Flow-Around

The media flow-around command is used to configure this feature in global VoIP configuration mode (config-voi-serv), dial peer mode (config-dial-peer) and voice class configuration mode (config-class). Refer to Modes for Configuring Dial Peers to enter these modes and configure this feature.

Media Anti-Tromboning is a media path mode that allows CUBE to detect and avoid loops created by call transfers or call forwards. Loops are restricted to the SIP signaling path and removed from the RTP media path.

The user agent may initiate call forwards and call transfers that are sent towards CUBE as a new SIP INVITE dialog. CUBE considers the original call and the forwarded call as separate unrelated calls. Media anti-tromboning allows CUBE to detect the relation between the calls and resolve the media loop by sending SDP packets back to the sender.

The figure below illustrates how CUBE needlessly loops RTP packets towards the User Agent because it fails to detect the loop.

Figure 3. Tromboning - Needless looping of Media Packets

The figure below illustrates how CUBE detects and avoids the loop with the anti-tromboning feature.

Figure 4. Anti-Tromboning - Avoiding Media Loops

The media anti-trombone command is used to configure this feature in global VoIP configuration mode (config-voi-serv), dial-peer configuration mode (config-dial-peer) and voice-class configuration mode (config-class). Refer to Modes for Configuring Dial Peers to enter these modes and configure this feature.