To everyone who responded on last week’s Usage Poll, thank you! We already have quite a few responses. I’ll leave it open another week (go here if you haven’t voted yet).

In the meantime, I received an email from a reader. Jose was curious about Lync call transmission methods. He asked (in part):

“We are planning to deploy Lync on-cloud. But I wonder if the audio-call or video-call is established directly peer-to-peer or is it always depending of an internet connection?”

It’s a good question to ask before you deploy Lync – in any form! When I replied, I asked him what form of Lync deployment they were considering. This will become important in a moment.

How Lync Transmits Calls Across the Network and Out to Phones

But first, let me answer the question of call transmission method. There are three types of calls to consider here: Peer-to-peer Lync calls, PSTN/Enterprise Voice calls, and conferencing.

Peer-to-peer calls use existing network bandwidth. Internally, so do conferencing calls. They use different audio codecs to facilitate their connections, and they have specific bandwidth requirements for those codecs.Lync Call Transmission Methods

Here’s a list of those codecs and their requirements: Network Bandwidth Requirements for Media Traffic – TechNet

(Obviously, conferencing will require more bandwidth to transmit video!)

PSTN/Enterprise Voice calls are a bit trickier. Since these need to communicate with the worldwide phone network, they must be translated into a signaling medium compatible with our phones. To do this in Lync Server 2010 and 2013, you need two things: the Mediation Server Role, and either a PSTN gateway or SIP trunk.

Here’s an overview page on Mediation Server: Mediation Server Component – TechNet
There’s also some information PSTN gateways and SIP trunks.

Through configuration in your Lync topology and Mediation Server, you dictate how voice calls are transmitted to & from the PSTN. It takes some setup, and you must make sure you have enough bandwidth available! But the system works once it’s in place.

I communicated this to Jose. And I asked him a question of my own:

“You said on-cloud – do you mean a hosted Lync Server installation, or Lync Online with Microsoft? Lync Online does not include Mediation Server, the component which governs communication with PSTN gateways.”

Good thing I did. Jose responded by saying he was interested in Lync Online instead of a full on-premises Lync Server. He added:

“Is there any way to create some sort of hybrid environment to have Lync Online with the Mediation Server capabilities? I’m trying to get this scenario because Lync Online is cheaper than a full on premises implementation.”

This is also a very good question. It’s true that Lync Online is cheaper than on-premises Lync Server 2013. But you’re making a trade-off when you opt for Lync Online – its calling capabilities are severely limited. Why? Because Enterprise Voice is not included. No Mediation Server. No PSTN calling capability.

Lync Online requires an Internet connection? Yes, to start. But what about PSTN calls?

Now, let’s go back to Jose’s original question. He wanted to know if Lync Online required an Internet connection for direct peer-to-peer calls. I cannot answer this with complete certainty, as I don’t have Lync Online right in front of me to test. (Really need to get myself an account…)

However, after consulting Office 365 Help (Set up Microsoft Lync Online), I feel confident in saying that Lync Online requires Internet access to establish peer-to-peer calls. But it uses existing network bandwidth to facilitate them once established.

Lync Online runs off of Microsoft servers. It makes sense that the Lync client would store contacts on those servers, and need to call back to those servers when a Lync call or conference is started.

But what about PSTN calling?

It’s here that Lync Online stumbles. It has no Mediation Server component available. No Enterprise Voice capability. At least, not yet. Microsoft has recently stated that PSTN calling functionality is coming. Lync Online users are clamoring for its addition…but for now, they have to wait.

In the meantime, is there a hybrid solution like Jose asked? Yes. I do know of one option:
Telephony Support for Lync Online or Office 365 – Sangoma Express for Lync

Sangoma offers a Lync gateway to add VoIP to Lync Online. From the page:

“Express for Lync is the ONLY Lync server appliance with a built-in VoIP gateway and SBC, both of which are qualified and tested for Lync. It is the easiest and most convenient way to deploy Lync with telephony support for Office 365, for a branch office or for a complete PBX replacement using Lync for installations of less than 1,000 users.”

1,000 user limit…while I’d strongly recommend organizations with 1,000 users and up use on-premises Lync Server, it’s good that we have an option for smaller organizations.

I hope this helped Jose with his questions. And his future Lync rollout, whichever form it takes.

Did this post help you with understanding Lync calls? If so, please comment or email. Oh, and don’t forget to vote in the poll! We’ll return to it next week. See you then!

Reader Question: Call Transmission in Lync Server vs. Lync Online
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