User`s manual

Version 5.4 209 May 2008
SIP User's Manual 3. Web-Based Management
3.4.5.4.6 Reasons for Alternative Routing
The 'Reasons for Alternative Routing' page includes two groups - IP to Tel Reasons and
Tel to IP Reasons. Each group allows you to define up to four different release reasons. If
a call is released as a result of one of these reasons, the device tries to find an alternative
route for that call. The release reason for IP-to-Tel calls is provided in Q.931 notation. The
release reason for Tel-to-IP calls is provided in SIP 4xx, 5xx, and 6xx response codes. For
Tel-to-IP calls, an alternative IP address is provided; for IP-to-Tel calls an alternative Hunt
(Mediant 1000 analog modules) or Trunk (digital modules) Group is provided. Refer to ''Tel
to IP Routing Table'' on page 200 for information on defining an alternative IP address;
refer to ''IP to Trunk Group Routing'' on page 204 for information on defining an alternative
Trunk Group.
You can use the 'Reasons for Alternative Routing' page for the following example
scenarios:
 Tel-to-IP calls: when there is no response to an INVITE message (after INVITE
retransmissions), the device issues an internal 408 'No Response' implicit release
reason.
 IP-to-Tel calls: when the destination is busy and release reason #17 is issued or for
other call releases that issue the default release reason (#3). Refer to
DefaultReleaseCause in ''Advanced Parameters'' on page 166.
Notes:
• The reasons for alternative routing for Tel-to-IP calls only apply when a
Proxy isn't used.
• For Tel-to-IP calls, the device sends the call to an alternative route only
after the call has failed and the device has subsequently attempted twice
to establish the call unsuccessfully.
• You can also configure alternative routing using the ini file table
parameters AltRouteCauseTel2IP and AltRouteCauseIP2Tel (refer to
''Number Manipulation and Routing Parameters'' on page 364).