User's Manual 370 Document #: LTRT-42060
Mediant 2600 E-SBC
adjacent (below) rule in the table that is configured as 'Alt Route Ignore/Consider
Inputs' are used. The alternative routes rules can be set to enforce the input matching
criteria or to ignore any matching criteria. Alternative routing occurs upon one of the
following conditions:
• A request sent by the device is responded with one of the following:
♦ SIP response code (i.e., 4xx, 5xx, and 6xx SIP responses) configured in the
SBC Alternative Routing Reasons table (see ''Configuring SIP Response
Codes for Alternative Routing Reasons'' on page 378).
♦ SIP 408 Timeout or no response (after timeout).
• The DNS resolution includes IP addresses that the device has yet to try (for the
current call).
Messages are re-routed with the same SIP Call-ID and CSeq header fields (increased
by 1).
Note: If the Proxy Set (see Configuring Proxy Sets on page 269) associated with the
destinat
ion of the call is configured with multiple IP addresses, the device first
attempts to route the call to one of these IP addresses, starting with the first listed
address. Only when the call cannot be routed to any of the Proxy Set’s IP addresses
does the device search the IP-to-IP Routing table for an alternative routing rule for the
call.
Re-routing of SIP requests: This table enables you to configure "re-routing" rules of
requests (e.g., INVITEs) that the device sends upon receipt of SIP 3xx responses or
REFER messages. These rules are configured for destinations that do not support
receipt of 3xx or REFER and where the device handles the requests locally (instead of
forwarding the 3xx or REFER to the destination).
Least cost routing (LCR): If the LCR feature is enabled, the device searches the
routing table for matching routing rules and then selects the one with the lowest call
cost. The call cost of the routing rule is done by assigning it a Cost Group. For
configuring Cost Groups, see ''Least Cost Routing'' on page
195. If two routing rules
have identical costs, then the rule appearing higher up in the table (i.e., first-matched
rule) is used. If a selected route is unavailable, the device uses the next least-cost
routing rule. However, even if a matched rule is not assigned a Cost Group, the device
can select it as the preferred route over other matched routing rules with Cost Groups,
according to the settings of the LCR parameter, LCRDefaultCost (see ''Enabling LCR
and Configuring Default LCR'' on page 224).
Call Forking: The IP-to-IP Routing table can be configured to route an incoming IP
call to multiple destinations (call forking). The incoming call can be routed to multiple
destinations of any type such as an IP Group or IP address. The device forks the call
by sending simultaneous INVITE messages to all the specified destinations. It handles
the multiple SIP dialogs until one of the calls is answered and then terminates the
other SIP dialogs.
Call forking is configured by creating a Forking group. A Forking group consists of a
main routing rule ('Alternative Route Options' set to Route Row) whose 'Group Policy'
is set to Forking, and one or more associated routing rules ('Alternative Route
Options' set to Group Member Ignore Inputs or Group Member Consider Inputs).
The group members must be configured in contiguous table rows to the main routing
rule. If an incoming call matches the input characteristics of the main routing rule, the
device routes the call to its destination and all those of the group members.
An alternative routing rule can also be configured for the Forking group. The
alternative route is used if the call fails for the Forking group (i.e., main route and all its
group members). The alternative routing rule must be configured in the table row
immediately below the last member of the Forking group. The 'Alternative Route
Options' of this alternative route must be set to Alt Route Ignore Inputs or Alt Route
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