There’s been many discussions within the Lync community regarding how many conferences Skype for Business Server 2015 on premise can support and \ or handle; ironically enough these are two different topics in their own rights with regards to supported and what will technically work; specially with the adjusted supported number of users per Skype 2015 Front-End server, which is 6660 users if you didn’t know. We 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, check out the article where we discussed that information; Determining How Many Front-End Servers to Deploy in Lync Server 2015.
How the numbers add up.
We’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? So let’s ease that initial shock of hearing about such a number; 250 users per conference is not a hard limit, but a limit that is recommended by the Microsoft Skype 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? Yes, but it’s, but not very practical, and again we are talking about a typical meeting on the Skype Front-End Pool; keep in mind there will always be exceptions but we are going to focus on the majority of conferences that take place. The majority of Lync ad-hoc conferences are between 4-6 users. Only a small percentage that are hosted on Skype 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 Skype 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 Skype Front End server pool. Now the Skype 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 we are going to stick with the average. Keep in mind that there are some hard limits out there 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 besides the typical 80,000 users for not everybody’s organizations has that many users, we will see how the numbers turn out. We will use for the example to follow 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. Then 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. So now we have (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.
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 Skype 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 Skype Server 2015 can handle which is approximately 83 concurrent conferences averaging 4-6 users per conference.
Skype 2015 Conferencing Reaching Capacity
Skype 2015 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 Skype 2013). The key concept to remember is Skype Server 2013 can hold many different types of conferences and users such as remote, federated, and even anonymous ones as well. Scaling Skype 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 quantity of users and Front End servers that are ultimately deployed for the Skype pool. There’s talk with future editions of Skype having the ability to host large standing meetings that would scale far beyond what Skype is handling today, but that waits to be seen.
Byron Spurlock's Teams, Skype, & Exchange Tidbits 