Nortel Networks Telephone NN10033-111 Bedienungsanleitung PDF herunterladen (Seite 8)

8 Overview

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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

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Nortel Networks Telephone NN10033-111 Bedienungsanleitung Seite 8