An administrator uses the Cisco Unified Real-Time Monitoring Tool to investigate recent calls on a Cisco UCM cluster. The SIP trace for an on-net. direct-media call shows two 180 Ringing and two 11…

Question

Options

• AThe source phone sends a 180 Ringing signal to the Cisco UCM, which sends a 180 Ringing
• BThe source phone must signal to the destination phone that it is ringing, and the destination
• CThe calls have an MTP in the call path due to different codec support. The calls are
• DThe destination phone signals back to the Cisco UCM that it is ringing, and the Cisco UCM

• A
  3% (1)
• B
  8% (3)
• C
  5% (2)
• D
  85% (34)

Explanation

In a Cisco UCM direct-media call, UCM acts as a back-to-back user agent (B2BUA) for signaling even though media flows directly between endpoints. This means every SIP message travels in two legs: one leg between the destination phone and UCM, and one leg between UCM and the source phone. When the destination phone rings, it sends a '180 Ringing' to UCM, and UCM then sends its own '180 Ringing' to the source phone - producing two 180 messages in the trace. The same applies to BYE: the terminating side sends a BYE to UCM, and UCM sends a BYE to the other party. This hairpin signaling is normal UCM behavior regardless of direct media.

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