SIP User's Manual 288 Document #: LTRT-83310
Mediant 600 & Mediant 1000
The steps for configuring alternative Trunk Group routing based on Q.931 cause codes are
summarized below.
To configure alternative Trunk Group routing based on Q.931 cause codes:
1. Set the RedundantRoutingMode parameter to 1 so that the device uses the Inbound
IP Routing table for alternative routing.
2. Configure alternative routing rules in the Inbound IP Routing table with the same call
matching characteristics, but with different Trunk Group destinations.
3. Configure up to five Q.931 cause codes that invoke alternative IP-to-Tel routing:
a. Open the Reasons for Alternative Routing page (Configuration tab > VoIP menu
> GW and IP to IP submenu > Routing submenu > Alternative Routing
Reasons).
Figure 18-14: IP to Tel Reasons - Reasons for Alternative Routing Page
b. Under the 'IP to Tel Reasons' group, select the desired Q.931 cause codes.
c. Click Submit to apply your changes.
18.4.7.2 Alternative Routing to IP Destination upon Busy Trunk
You can configure the device to forward (i.e., call redirection) IP-to-Tel calls to an
alternative IP destination using SIP 3xx responses. This can be done upon the following
scenarios:
For digital interfaces: Trunk Group has no free channels (i.e., “busy”).
For analog interfaces: Unavailable FXS / FXO Trunk Group. This feature can be used,
for example, to forward the call to another FXS / FXO device.
This feature is configured per Trunk Group and is configured in the Forward on Busy Trunk
Destination page, as described later in this section.
The alternative destination can be defined as a host name (IP address with optional port
and transport type), or as a SIP Request-URI user name and host part (i.e., user@host).
For example, the below configuration forwards IP-to-Tel calls to destination user “112” at
host IP address 10.13.4.12, port 5060, using transport protocol TCP, if Trunk Group ID 2 is
unavailable:
ForwardOnBusyTrunkDest 1 = 2, 112@10.13.4.12:5060;transport=tcp;
When configured with user@host, the original destination number is replaced by the user
part.
The device forwards calls using this table only if no alternative IP-to-Tel routing rule has
been configured in the Inbound IP Routing table or alternative routing fails and one of the
following reasons included in the SIP Diversion header of 3xx messages exists:
For digital interfaces: “out-of-service” - all trunks are unavailable/disconnected
"unavailable":
• For digital interfaces: All trunks are busy or unavailable
• For analog interfaces: All FXS / FXO lines pertaining to a Trunk Group are busy
or unavailable
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