After an engineer implements load balancing in the Cisco CMS cluster, they observe that shortly after the second Call Bridge is added to the cluster, call into a space randomly disconnect when the…

Question

Options

• AEnable "Accept Unsolicited Notification" on the SIP Trunk security profile.
• BEnable "Accept Presence Subscription" on the SIP Trunk security profile on Cisco UCM.
• CEnable "Accept Out-of-dialog REFER" on the SIP Trunk security profile".
• DEnable "Accept Replaces Header" on the SIP Trunk security profile on Cisco UCM.

• A
  15% (6)
• B
  8% (3)
• C
  3% (1)
• D
  74% (29)

Explanation

When CMS load balances calls across multiple Call Bridges, it may need to move a call leg from one Call Bridge to another. This is accomplished using the SIP 'Replaces' header, which instructs the remote end (UCM in this case) to replace an existing call dialog with a new one. By default, Cisco UCM's SIP Trunk security profile does not accept the Replaces header, causing the call to fail/disconnect when CMS attempts the load-balancing transfer. Enabling 'Accept Replaces Header' on the SIP Trunk security profile in Cisco UCM allows UCM to process these requests correctly. Options A, B, and C address different SIP behaviors (unsolicited NOTIFYs, presence subscriptions, and out-of-dialog REFERs) that are unrelated to the load-balancing disconnect scenario.

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