Enterprise Voice with Legacy Phone

In this scenario end users have full Enterprise Voice functionality, but also retain a legacy PBX phone on their desks like shown in Figure 17.11. This scenario is typical for migrations from a legacy PBX in which a period of coexistence is required while users become accustomed to the new Lync endpoints. Users have the choice of which system to use when placing or receiving calls through the use of simultaneous ringing. As the users grow more familiar Lync, they will rely less and less on the legacy phone until it becomes unnecessary and can be removed. As the migration ends and legacy devices are retired, the organization actually ends in the pure Enterprise Voice state. Although the idea of simultaneous ringing sounds attractive and it generally works well for basic calls, it’s important to work through all the possible use cases required to maintain two systems. For example, consider boss/admin scenarios, voice mail forwarding features, and any directory search attendants.

Figure 17.11. Enterprise Voice with a legacy phone.

Most implementations require a user to have two extensions during this period of coexistence. One extension is the user’s primary, or publicly known, extension that other users dial and that is associated with the user’s Lync account. The other is a secondary, or unpublished, extension that is associated only with the legacy phone.

When placing calls, users can choose whether to use Lync or the legacy phone. One caveat shown here in Figure 17.12 is that, when calling from Lync, the callees will see the call from the user’s primary, published number in the organization, but calls coming from the legacy phone will show as coming from the unpublished number. This can be mitigated slightly with PBXs that support sending a display name, but the extension might still appear as unrecognized to the callee. Again, as users begin to leverage Lync more and more, this becomes less of an issue.

Figure 17.12. Simultaneous ringing.

Receiving calls on both devices in this scenario can be accomplished by the users configuring simultaneous ringing within Lync. Inbound calls will be routed first to the Lync account, which determines what should happen to the call. Users generally set their Lync call forwarding options to simultaneously ring the secondary extension associated with their legacy PBX phone. This allows them to answer incoming calls either with a Lync endpoint or on the legacy phone without the caller’s noticing where the call was picked up. As the migration period goes on, users can adjust their simultaneous ringing to stop ringing the legacy phone altogether. The downside to this approach is that users won’t be able to use simultaneous ringing with a mobile number since Lync allows only a single number to be targeted for simultaneous ring.

Something to keep in mind is that depending on the current PBX, the simultaneous ringing might not scale well. Consider when a media gateway device is used to bridge a legacy PBX and Lync Server 2013. If inbound calls still flow through the PBX initially, and then are directed through the media gateway to Lync Server, each call requires one channel on the media gateway. If a user configures simultaneous ringing to a legacy phone, yet another channel is required on the media gateway and PBX to support the call.