There have been many discussions within the Lync community regarding how many conferences Lync Server 2013 on-premise can support and \ or handle. Ironically these are two different topics in their own rights with regards to supported and what will technically work especially with the adjusted supported number of users per Lync 2013 Front-End server (which is 6660 users, if you didn’t know). In this article, I will explore the suggested conferencing meeting size limit of 250 users and take a look into some additional numbers that might affect conferencing and the quantity of Front End servers you have in your pool or the amount users you have in your organization assigned to a particular pool. For additional information on Front End servers and sizing, read through the article where I discussed that information: Determining How Many Front-End Servers to Deploy in Lync Server 2013.
How the numbers add up:
So, maybe you’ve heard about the number of 250 users per conference and 1250 users per Front End server in a conference before, but how did those numbers come about? 250 users per conference is not a hard limit, but a limit that is recommended by the Microsoft Lync Server team based on how often would and organization host conferences where there are 250+ users in size in a particular meeting. Now could this happen? The majority of Lync ad-hoc conferences are between 4-6 users.
Only a small percentage that is hosted on Lync Server would be in an excess of 250+ users, so we can actually say that less than 5% of conferences would be that large. So to put in perspective we are talking between 1-5% conferences would need to be 250 users are over; so this is where the recommendation of 250 users comes into the picture.
The Microsoft Lync Server team recommends an on-premise conferencing limit not to exceed 250 users in a single conference. Anything larger than that should have its own dedicated Lync Front End server pool. The Lync user model states that 5% of an organizations user base would be in a conference in a given time for a typical organization that has moderate conferencing needs. There will always be organizations that require more, but for the sake of the topic, let’s stick with the average. Keep in mind that there are some hard limits such as the following:
• 12 Front End Servers per pool
• 80,000 users per pool
So when we go back to the 5% of users are in a conference at any point in time and do the math with numbers beside the typical 80,000 users for not everybody’s organizations has that many users, you can see how the numbers turn out. For the example, we’ll use 7,500 users based on a medium size organization that has users spread across the organization. So now we have (5% / 7,500) = 375 concurrent users in a conference for that pool. (375 users / 3 Front End servers) gets us to approximately 125 users per Front End server in a conference.
Now we take the average number of users for an ad hoc conference, which is about 4 taken from the (4-6) users in an ad hoc conference profile. That gives us (125 users per FE / 4 users per conference) = 31 concurrent conferences per Front End server is the number conferences each Front End server can handle safely.
Lync Server 2013 User Models
Users per Conference:
The 125 conferencing users per Front-end server is considerably lower than the actual limit of what a Front End server can handle which is approximately 333 conferencing users per Front End server taken from the model of 5% users in a conference and the Microsoft max capacity of users in a pool of 80,000 users; (5% / 80,000) = 4,000 users in a pool in a conference at the same time. Then we take (4,000 users / 12 max front-end servers in a pool) = 333 conferencing users per Front End server; (4 avg users in a conference/ 333 conferencing users per front-end server) = 83 concurrent meetings per Lync Front End server.
Conferences per Front End server:
The 31 concurrent conferences per Front End server in our example earlier is also considerably lower than the estimated number of conferences that Lync Server 2013 can handle which is approximately 83 concurrent conferences averaging 4-6 users per conference.
Lync 2013 Conferencing Reaching Capacity
Lync 2013 on-premise conferencing with the inclusion of Audio, Video, IM, and Application Sharing has come a long way in the past few versions (OCS 2007 R2 to Lync 2013).
The key concept to remember is Lync Server 2013 can hold many different types of conferences and users such as remote, federated, and even anonymous ones as well. Scaling Lync Server 2013 out to meet organizations conferencing requirements will vary with each implementation, but based on the technical and business requirements of the deplorer will dictate the number of users and Front End servers that are ultimately deployed for the Lync pool. There’s talk with future editions of Lync having the ability to host large standing meetings that would scale far beyond what Lync is handling today, but that waits to be seen.