Recursive Search, Hold, Retrieve | Nortel Networks NN10033-111

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include the audio codecs supported by the gateways. For the SDP that is received from the CS 2000, the MCP fills in the missing mandatory parameters as specified in RFC 2327. Details on the restrictions on SDP are specified in the SN03 IP Gateway InterOP Requirements document.

Recursive Search

The MCP Back-to-Back User Agent (BBUA) handles SIP 302 responses to an INVITE sent out because of a received INVITE from the CS 2000. The BBUA sends INVITEs for each contact in the SIP 302 response. The SIP 302 response will not be passed back to the CS 2000. The INVITES for each contact can be sent parallel or sequentially depending on the mode in which the BBUA processed the initial INVITE, which then resulted in the SIP 302 response.

Hold

SIP implements a Hold as a re-INVITE with the connection information in the SDP set to 0.0.0.0. In this release, Hold cannot be handled by all the CS 2000 media gateways. The MCP shields the CS 2000 from seeing Hold re-INVITE requests. The MCP, when equipped with an RTP Media Portal, can manage the RTP connections without affecting the connection to the CS 2000.

Retrieve

Retrieve is also implemented in SIP through a re-invite. To retrieve a party on hold the new invite contains valid SDP. The new SDP is used to restore the media connection between the two clients.

Long Call Audit Timers

In order to prevent hung calls between the two platforms, a long call audit timer is implemented between the two platforms. Both platforms use the INFO ping capability described in the SIP INFO message RFC2976. This involves sending an INFO message with no message body. Upon receipt of this message, a client should send a 200 OK if the call exists. If the response to the INFO is any of the following response codes, then the platform sending the message assumes that the call no longer exists and frees all resources associated with the call:

•404 Not Found

•408 Request Timeout

•410 Gone

•480 Temporarily Unavailable

•481 Transaction Does Not Exist

NN10033-111 Standard MCP 1.1 FP1 (02.02) April 2003