Trunks
,Trunk configuration in Lync Server 2010 is an object that administrators can use to define the connection between Lync Mediation servers and IP/PSTN gateways within the infrastructure. One important feature is that a trunk configuration can control how dial strings are passed to a specific IP/PSTN gateway.
In Office Communications Server 2007 R2, any outbound dialing rules had to be performed by the IP/PSTN gateway itself, which required organizations to maintain dialing rules in multiple locations. With Lync Server 2010, dial strings can be manipulated before being sent to an IP/PSTN gateway so that digits can be removed, added, or translated.
A common example is where an IP/PSTN gateway does not support the + prefix in E.164 and needs to be removed before being sent. In other cases, the PBX might require special prefixes for local, long distance, or international calls and these digits can be appended through the trunk configuration.
Note
When configuring a trunk, be sure to set up the translation rules on only one side or the other. Ideally, handle the translation rules within Lync Server and have the opposite IP/PSTN gateway perform no modification of the dial strings. If both sides are manipulating digits, it might become difficult to troubleshoot the calls.
Trunk configuration is also where Media Bypass features can be enabled or disabled. Media Bypass is a new feature that enables a Lync endpoint to bypass the Mediation server transcoding of RTAudio to G.711 and simply send G.711 directly to the IP/PSTN gateway. This removes the need for additional processing resources on the Mediation server and is the main reason support for collocating the Mediation server with the Front End is available in Lync Server 2010.
In addition to translation rules and Media Bypass features, the trunk configuration controls whether media encryption is required and whether a separate media termination point exists.
Trunk configuration exists at a global level by default, can be constrained to a site, or can be defined on a specific IP/PSTN gateway. This flexibility enables organizations to use Media Bypass on IP/PSTN gateways that support the feature and leave the feature disabled on others. It also accommodates situations where the IP/PSTN gateway expects different dial strings in different locations.
For example, Company ABC’s IP/PSTN gateways in Chicago might support a + in the dial string, but the San Francisco IP/PSTN gateway might require it to be removed before passing a call successfully. Because all the trunk configuration translation rules occur only after a number is normalized and routed, it is completely transparent to the end user and she can continue dialing the same patterns regardless of where the call is sent. This is especially useful in a failure scenario where calls are routed out a backup location, but the users have no idea that their calls are redirected to a different gateway.
Use the following steps when planning for trunk configuration to identify whether any changes should be made:
• Identify the appropriate dial string format for each IP/PSTN gateway in the topology.
• Identify which IP/PSTN gateways support Media Bypass.
• Create a trunk configuration for each unique group of settings, scoped appropriately to a site or IP/PSTN gateway.