Toll Bypass in Lync Enterprise Voice

In order to explain something in a future article, I need to take a "Back to the Future" approach in this article. I'm going to talk about a capability that has been around since Microsoft Office Communications Server (OCS) 2007: toll bypass. However, depending on where organizations are in their Lync Server 2013 deployment, they could still be using toll bypass in the present day.

With the toll bypass capability, calls can hop off a Public Switched Telephone Network (PSTN) gateway closest to the location of the person being called. The best way to see how this works is by looking at an example of what happens without and with toll bypass.

The Scenario

Suppose an organization in Texas has two offices: Houston (specifically, in the calling area beginning with the area code 713) and Dallas (specifically, in the calling area beginning with the area code 214). User A works in the Houston office and has a Direct Inward Dialing (DID) number (713-xxx-xxxx). User B works in the Dallas office and has a DID number (214-xxx-xxxx).

Related: Lync Server 2013 M:N Routing

When User A calls User B, the call is handled entirely within the Lync network (i.e., doesn't egress to the PSTN). However, when User A needs to call a person in Dallas who isn't on the Lync network, the call must egress to the PSTN. The Lync administrator would like to avoid having to pay long-distance charges for calls that travel out the Houston PSTN gateway when calls are made to people in Dallas outside the organization. Calls from Houston that egress through the Houston PSTN gateway to the PSTN incur long-distance phone charges. If the calls were to hop off the Dallas PSTN gateway instead of the Houston PSTN gateway, they'd appear as a local call leaving the Dallas PSTN gateway and not incur any long-distance charges.

Without Toll Bypass

Without toll bypass, the following steps occur when User A (in Houston) calls a person in Dallas who isn't in the organization:

1. User A dials 214-123-4567.
2. Normalization is attempted on 214-123-4567, which is translated to + 1-214-123-4567.
3. Reverse number lookup fails to find a Session Initiation Protocol (SIP) Uniform Resource Identifier (URI) match to the dialed number. As a result, outbound routing logic takes place.
4. A route is determined based on the number that begins with the area code 214, originating from the Houston location.
5. User A's call is routed to the local (Houston) Mediation Server and PSTN gateway.
6. User A's call egresses through the local (Houston) PSTN gateway to the PSTN.
7. The call recipient in Dallas receives the call sent from the Houston PSTN gateway. The call incurs long-distance charges.

Figure 1 graphically depicts these steps.

Toll Bypass in Action

Now let's see what happens when toll bypass is used. To implement toll bypass, there needs to be a dial plan that specifies the route calls should take. In this case, the dial plan needs to state that calls originating in Houston with a destination of 214.xxx.xxx must hop out of the Lync network using the Dallas Mediation Server and PSTN gateway.

Related: Media Bypass in a Lync Enterprise Voice Deployment

When toll bypass is implemented, the following steps occur when User A (in Houston) calls a person in Dallas who isn't in the organization:

1. User A dials 214-123-4567.
2. Normalization is attempted on 214-123-4567, which is translated to + 1-214-123-4567.
3. Reverse number lookup fails to find a SIP URI match to the dialed number. As a result, outbound routing logic takes place.
4. A route is determined based on the destination phone number and voice policy associated with the caller.
5. User A's call will be routed across the network to the Dallas Mediation server and PSTN gateway.
6. User A's call egresses through the Dallas PSTN gateway to the PSTN.
7. The call recipient in Dallas receives the call sent from the Dallas PSTN gateway. The call won't incur any long-distance charges.

Figure 2 graphically depicts these steps.

Strategic Routing to Avoid Costly Long-Distance Charges

Toll bypass is a nice capability to have when you're trying to avoid costly long-distance charges for calls made to destinations in which there's an existing Lync infrastructure. However, this capability comes at a price—the time and effort needed to figure out your existing dial plan and create a new one. When creating dial plans for locations outside the United States, you must also take into consideration that some countries have strict laws on where calls can leave and enter the country.