Asterisk as PSTN gateway for Microsoft Lync

Hello, I’m looking for a little guidance. We have been looking to adopt Microsoft Lync 2010 and I’ve been doing some research into how to get PSTN connectivity, as Lync is not capable of taking a trunk from a SIP provider that is not Lync certified. This means we have to purchase a (pricey) gateway to do the conversion, or get a SIP provider that is Lync certified.

My question is whether or not it is possible to bring SIP over a T1 connection into Asterisk and have it essentially send all calls over a SIP trunk to Lync without having to provision any users/extensions in Asterisk. We want to be able to handle all user provisioning in Lync, but just need to call out to the PSTN through asterisk and have incoming calls routed through Asterisk and over the SIP trunk to Lync. I know there are Lync-certified gateways to do this sort of thing, but am wondering whether Asterisk is capable, or if my thinking is flawed… I really don’t have much knowledge of telephony.

Thank you in advance,


Asterisk isn’t a Lync certified SIP trunk provider.

Asterisk is quite capable of doing this for a PABX that doesn’t have arbitrary restrictions on the provider of the SIP trunks to which it connects.

Yes , you can have sip trunk between asterisk and Microsoft lync . you can then register your PSTN gateways in asterisk and use them in your lync . I was involved in the same project for asterisk side configuration . you can simply have trunk between them just pay attention that Microsoft Lync use SIP Over TCP and you have to set this option in your asterisk sip trunk .

I’ve had Lync and Asterisk talking over a SIP trunk in the past, so I’m pretty sure it works to that extent. I had a small lab setup where I was using a non-Lync-certified IP phone connected to Asterisk to call Lync clients by dialing an extension associated with the trunk. My situation is a little different now, in that Asterisk wouldn’t be dealing with any of the incoming calls, it would just be sending to Lync… And, if that’s possible, what stops people from subscribing to a non-Lync SIP provider and just throwing an Asterisk box in between? I’m guessing maybe there’s more to being a Lync-certified trunk provider than the protocols/security you use?

Some non-certified providers will be using Asterisk themselves!