How to use Route Lists

Symptom:
You wish to distribute incoming Dialogic IMG Integrated Media Gateway calls to multiple outgoing Channel Groups, or redirect calls when Outgoing channel groups are full or unavailable.

Background:
In simple configurations, an IMG routes calls from an Incoming Channel Group to an Outgoing Channel Group, which is relatively straightforward. 

Using IMG Route Lists provides much greater flexibility in routing and redirecting calls, but requires a better understanding of how Route Lists work, in order to achieve the desired results.

This article explains how IMG Route Lists work, using five example scenarios.  

In each scenario, the call comes into the IMG on the SIP Channel Group, JB_Cube - ID:1.  

The scenarios progress from simple to complex.

Scenario 1
Without using a Route List the IMG routes calls from one channel group to another, via a route table.  We will use the following shorthand to describe this call flow (abbreviations defined in Glossary below) :

ICG1(SIP) --> RT5 --> OCG0(SS7)

Scenario 2

This scenario results in exactly the same behavior as scenario 1, but uses a route list, RL1, with a single channel group entry.

ICG1 --> RT5 --> RL1 --> OCG0

Scenario 3
In this scenario, we start to use a route list, RL1, to distribute calls between to outgoing channel groups.  The route list is just a list of channel groups to which calls will be distributed.  In this case, the route list contains only two channel groups, for illustrative purposes, but there can be more.   Route list hunting options determine how the calls are distributed.  If one outgoing channel group is unavailable, calls will only be distributed to the remaining outgoing channel group(s).
 

Call 1: ICG1(SIP) --> RT5 --> RL1 --> OCG0(SS7)

Call 2: ICG1(SIP) --> RT5 --> RL1 --> OCG2(SIP)

NOTE: In the above scenario, if no circuits are available in OCG0 and OCG2, then a SIP 503 response is sent to the originating endpoint via ICG1

Scenario 4

In scenario 3, we know that a 503 will be sent to the originating endpoint if no outgoing channel group is available to complete the call.  It could be useful to redirect the call to another IMG for example, whose outgoing channel groups are available.  The Route List Redirect  feature makes the IMG send a 302 Redirect, with a contact address of an alternate gateway, rather than a 503.  Then, the originating endpoint will send the same call to the alternate IMG gateway.  

This is what the route list looks like in ClientView after adding the Redirect entry, which is highlighted with a red oval:

Call 1: ICG1(SIP) --> RT5 --> RL1 --> OCG0(SS7) (no circuits)

--> OCG3(SIP) (no response)

<-- 302, with Contact header of Alternate SIP gateway (OCG2)

Open

NOTE:  When using the Redirect feature, the route list hunting option must be set to 'Sequential.'

Scenario 5
As an alternate to redirecting calls, the route list hunting option can be set to use percentage routing.  For example, to distribute calls evenly to three channel groups, configure the percent allocation to 33, 33, and 34.  The percentage must always add up to 100 amongst the channel groups in the route list.  In addition, all channel group type entries must be set to 'Normal' and not redirect.

 
Product List
Dialogic IMG Integrated Media Gateway

Glossary of Acronyms / Terms
ICG: Incoming Channel Group
RT: Route Table
RL: Route List
OCG: Outgoing Channel Group