Using Trunk Groups

BRI, PRI, and CAS interfaces and FXO, FXO, and Ear and Mouth (E&M) voice ports can be combined into trunk groups. When you create a trunk group, you can add configuration to control path selection. Create a trunk group with the global trunk group name command. This puts you in trunk group configuration mode. You can then add commands that will apply to all the circuits in the group. The max-call voice number command limits the number of incoming and outgoing calls that the trunk group will accept. By default, the least-used trunk is selected when the gateway hunts through a trunk group. You can change this with the hunt-scheme command. This command has the following options:

• least-idle [even | odd | both] Looks for the most recently released channel.
• least-used [even | odd | both [up | down]] Is the default hunt method for a trunk group. It looks for the trunk member with the most unused channels.
• longest-idle [even | odd | both] Looks for the trunk member that has been idle the longest amount of time.
• Random Chooses a trunk member at random and a random channel within that trunk member.
• round-robin [even | odd | both[up | down]] Looks at trunk group members in a round robin fashion, one after the other.
• sequential [even | odd | both[up | down]] Always starts looking for a free channel with the highest priority trunk.

In each command, even selects even-numbered channels within a trunk member first, odd selects odd-numbered channels within a trunk member first, and both considers all channels for selection. The option up hunts through the channels in ascending order, whereas the option down hunts through them in descending order.

Add an interface or voice port to a hunt group with the trunk group name [preference] command. The preference value indicates the priority of the trunk within the group. A lower preference value equates to a higher priority trunk. You can then assign multiple trunk groups to dial peers, with a priority value to determine their use by the dial peer.