Two Dial Plans... Sometimes Less is (not) More

Some PBX professionals familiar with Cisco or Avaya phone systems are under the impression that if you add Lync voice to the environment, the administrative complexities could outweigh the benefits. "You'd have to create and maintain two dial plans," they often say. Less is more, oftentimes, but before dismissing the notion, consider the benefits of adding Lync to an existing PBX environment.

Lync is connected to existing PBXs for two reasons:

1) To enable callers from external phones and employees on PBX phones to join Lync audio conferences. Lync can support conferences of up to 1,000 participants. Anyone can join from an IP-connected PC, Mac, or tablet. By establishing a DID associated with the conference bridge, traditional phones may join via audio as well. Companies who do so save money compared to traditional audio conferencing services like Intercall or Webex.

2) To enable some users to use their PCs, Macs, tablets, SIP phones, or smartphones as their enterprise telephony device. Mobile workers like road warriors, telecommuters, field reps and managers have been the typical first foray into Lync for most companies.

To enable Lync audio conferencing, network the IP PBX to Lync with a PRI through a SIP Media gateway or natively through a SIP trunk. The PBX needs a new trunk group associated with this new trunk. Establish a new externally available DID and route that extension to the new trunk group to Lync. When the call leaves the PBX or gateway, its route is to the Lync mediation server, which handles all inbound calls to the Lync environment. Lync realizes the DID is bound for the audio conferencing MCU (which is often on the same virtual machine as the mediation server). Now, external and PBX phones can call into the Lync audio bridge, and the enterprise pays only for the inbound PSTN trunk or SIP trunk bandwidth. Compare this to all internal (and external) users calling out to a bridge service and paying by the minute. Many companies are leveraging Lync to lower such costs.

Most people agree up until this point. But the impression is that there's a lot involved with having some users set up for Lync enterprise voice and others remaining on the PBX. Fact is, once Lync is set up for dial-in audio conferencing, it's already set up for Enterprise Voice, too.

Once the trunk to from the PBX is configured and tested for dial in conferencing, Lync is already able to make outbound calls through the PBX, for its conferencing callback feature. Callback allows attendees to specify a number for Lync to call them. To enable all possible outbound callback rules, a Lync dial plan is created with normalization rules for local, national, international, and service calls.

That same dial plan is used for outbound calls from users. In short, the Lync dial plan is already set up.

So then what's left to move a user from the PBX to Lync to enable benefit number 2 above?

a) Ensure the user's phone # is in Active Directory in E.164 format

b) Enable them for Enterprise Voice in the Lync Management Console

c) Remove the extension from CUCM

d) Ensure the route pattern for that phone # routes to the trunk to Lync

These steps enable the inbound routing for the user to take the call from their preferred Lync device.

So while there is some up-front programming for dial in conferencing, the remaining four steps involved is less maintenance of two dial plans than most PBX professionals realize. Considering the benefits to the users and the organization, in some cases, more really is more.

Christian Stegh is the VP of Strategy at Enabling Technologies. In this role, he leads the partnerships and strategic decisions of the company, works with key customers on their UC roadmaps, and represents Enabling within the UC industry.