Asterisk, DoorBell and Cisco SPA 112 and Lync 2010


In our company we using Microsoft Lync as a primary communication way between other user and external people.
Before deploying Lync we used an analog LG PBX. Our doorbell was connected to that PBX, and it was work flawless.
Now, when we get rid of analog PBX, I wanted to let the guest coming to office call directly Lync numbers form doorbell.

To do that, I deployed a new ver. of Asterisk , connected doorbell to SPA 112 also opened an addtitional PSTN gateway in Lync topology. And it works - it is possible to make calls from doorbell directly to chosen Lync extension via SIP Trunk.

But, the quality is not very good. It happens quite often, that girls in office cannot hear the guest at all, especially in first sec. of connection. Other time, it works perfect. it is random.

If I plugged a basic, simple desk phone instead of doorbell, everything works great everytime. No jitter, no delay etc.

So my questions is - doeas any of you know about some special settings need to be changed in Cisco SPA 112 configuration, to improve working with that doorbell ? At begining, I thougt that is no any different between desk phone and doorbel at all, form technical point of view, but maybe it is.