In Lync Server 2013, Microsoft has made some significant enhancements to Enterprise Voice (Lync's VoIP functionality). One of those enhancements is resulting in better integration with IP-PBXs from a routing point of view. When it comes to routing media traffic to and from the Lync Server 2013 environment by way of PBXs, the more paths for the media to travel, the better. With this in mind, I'll discuss:

  • Legacy routing
  • The new type of routing in Lync Server 2013
  • The benefits of the new type of routing

Legacy Routing

Back in the days of Microsoft Office Communications Server 2007 R2 (OCS 2007 R2), you were limited to using one-to-one (1:1) routing when routing traffic from the Mediation Server. With this type of routing, you can connect a single Mediation Server to a single Public Switched Telephone Network (PSTN) gateway, as Figure 1 shows.

Figure 1: OCS 2007 R2 Routing from the Mediation Server to the PSTN Gateway

There are several significant drawbacks with this type of routing:

  • There are few possible redundancy scenarios.
  • It isn't cost effective if you have multiple PSTN gateways and multiple Mediation Servers at a location.
  • It allows only a single trunk. According to Microsoft, "A trunk is a logical association between a Mediation Server FQDN and listening port and a PSTN gateway FQDN and listening port." In simpler terms, it's the path associations made from the Mediation Server to the PBX.

In Microsoft Lync Server 2010, things changed for the better when it introduced one-to-many (1:M) routing for routing traffic from the Mediation Server. With 1:M routing, you can connect a single Mediation Server to multiple PSTN gateways, as Figure 2 shows. With 1:M routing, the number of possible redundancy scenarios increases. However, it still only allows a single trunk between the Mediation Server and the PSTN gateways.

Figure 2: Lync 2010 Routing from the Mediation Server to Multiple PSTN Gateways

Routing in Lync Server 2013

In Lync Server 2013, many-to-many (M:N) routing was introduced. It's a huge step forward in Microsoft's vision to have Lync Server be commonly used as a replacement application for PBX software.

With M:N routing, the Mediation Server can handle multiple paths from a PBX on multiple different ports. This means that multiple PSTN gateways can be associated with the same Mediation Server pool, as Figure 3 shows. It also means that PSTN gateways can be associated with multiple Mediation Server pools or the same Mediation Server pool on multiple ports.

Figure 3: Lync Server 2013 Routing from Multiple Mediation Server Pools to Multiple PSTN Gateways

Lync Server 2013 supports multiple trunks between Mediation Servers and PSTN gateways. As a result, a Mediation Server can have multiple trunks to different gateways, and a gateway can have multiple trunks to different Mediation Servers. Although it can be a bit confusing, it's great for redundancy.

The Benefits

You might be wondering, "How does this new type of routing help me?" For starters, the additional trunks provided by M:N routing give you more flexibility when setting up Enterprise Voice in your Lync Server 2013 environment. They also give you the ability to configure redundancy into the media paths when connecting to PSTN gateways. Finally, they allow you to set up Session Initiation Protocol (SIP) trunk configurations, where Mediation Servers are connecting to Internet Telephony Service Providers (ITSPs).

More Interoperability with Telephony

The gap between Microsoft and other PBX software vendors is narrowing. With M:N routing, Lync Server 2013 can now meet the needs of deployments that rely on Lync Server as a PBX replacement.

Personally speaking, I'm pleased to see that this subtle but much needed feature has been added to Lync Server 2013. Too many times in the past I've encountered the roadblock of too few available redundancy scenarios when designing Enterprise Voice implementations. With M:N routing, the redundancy roadblock has been removed—and it's been a long time coming.