Media Gateways

If Direct SIP is not an option because the PBX does not support the feature or has no IP PBX capabilities, a third-party device called a media gateway can be used to complete the integration. Media gateways act as an intermediary between the PBX and Lync Server to help translate traditional PBX protocols to SIP traffic that Lync Server 2013 can understand. In some cases it may be preferable to use a media gateway instead of Direct SIP to handle additional number translation of transcoding features. Media gateways are produced by many vendors today and provide a wide array of integration options for businesses looking to implement the voice features of Lync Server 2013. They typically have traditional telephony ports for T1/E1 digital trunks or FXS/FXO ports, along with network adapters to communicate with Lync Server. Media gateways can be used to provide interoperability with an existing PBX, or connect directly to the PSTN. Figure 17.7 shows a logical layout of how a media gateway fits in the topology.

Figure 17.7. PBX Integration with media gateway.

Also like when a Direct SIP trunk link is being configured, some configuration of the PBX is necessary so that it knows to route calls for specific extensions to the media gateway, which will then deliver the calls to Lync Server. An additional layer of complexity is involved because the media gateway must also be configured to route calls appropriately, but on the other hand, the media gateway provides a degree of flexibility in call manipulation that sometimes is not possible natively with a PBX or Lync Server.

Depending on the media gateway and business requirements, it might make sense to terminate existing trunks at the media gateway and place it in front of an old PBX, as shown in Figure 17.8. This could potentially have a bigger impact on the organization, but can greatly simplify some of the routing configuration during a large migration. Some gateway vendors have software that can detect whether a user’s extension is Enterprise Voice or whether they have a legacy phone by reading specific Active Directory attributes. This might not seem like a big advantage up front during a pilot phase, but as users are migrated to Enterprise Voice it becomes advantageous not to have to constantly change routing rules on the PBX itself to indicate where an extension exists.

Figure 17.8. Media Gateway in front of PBX.

Regardless of the media gateway placement, it can provide a great deal of flexibility for organizations looking to move to or test Lync Server Enterprise Voice.