Tag Archives: SBA

Collocated or Stand-alone Mediation Server

Most of the time, Lync Enterprise voice deployments need debate for collocated or stand-alone mediation server. Collocation of Mediation Server can reduce the TCO and data center footprints. Can Mediation server collocation be a wise option? To choose a wise option out of collocated or stand-alone mediation server depends on the following:

  1. Number of users enabled for UC-PSTN calls
  2. Number of UC-PSTN calls per user per hour
  3. Number of UC-PSTN calls at the time of peak load
  4. Connected gateway / SBC and mediation server
  5. Percentage of calls that support media bypass
  6. Branch sites configuration for UC-PSTN deployment

If I have missed any point here, please leave your comment so that I can add the same.

Any call which initiate from any Lync endpoint has two components signaling and media. For UC-PSTN calls, signaling always goes through Mediation server if stand-alone or Standard Edition / Front End server collocated with mediation server role.

No Media Bypass:

Media Bypass:

If your gateways, SBC or IP-PBX support media bypass, you can use collocated mediation server. But if you are planning for an option which do not support media bypass, I will advise you not to use collocated mediation server as collocated meditation server will increase load on front end servers which can cause of poor performance.

If you still want to use collocated meditation server, you can increase number of front end servers which can help you to distribute the load among front end servers.

A Stand-alone Mediation server deployment also depends on Branch sites which are connected to central site. If your branch sites don’t have dedicated PSTN connectivity then you should go with stand-alone mediation server pool. Again this topic requires more debate. As we know Lync 2013 use M:N trunk, in simple way it means if you have mediation server deployed in branch site and that can support media bypass you can still go with collocated option.

You can use Lync Planning tool to try all options and choose best out of that which provide you better ROI and best performance.


Lync 2013 Enterprise Edition Users and Servers Model

Lync designing & planning is intricate part and right decision can help organization to get better ROI. This article may help Solution Architects, Consultants and System Administrator to choose best Lync server/pool model. Number of Lync servers in a pool, collocated or distributed model of Lync roles typically depends on No. of Lync users, their activities and different geo locations.

Lync 2013 Server Pools Number of Servers Supported No. of End users Remarks
Lync 2013 Front End pool (Collocated with A/V conferencing, Mediation Server, A/M server) 12 80,000 Max. Conferences size is limited to 250 users, Media Bypass is required to support all users with condition of 60 % users are enable for EV and only 40% calls are UC-PSTN calls.
Lync 2013 Front End Pool (A/V only) 2 Large conferences b/w 250 – 1000 users
Lync 2013 Mediation Pool 12 80,000 100% users are enabled for EV and 80% calls are UC-PSTN calls. 12 servers are required if Media by pass in not enable/supported for deployed EV connectivity. No. of servers will reduce based on Media bypass configuration according to the %.
Lync 2013 Persistent Chat 8 (4 active & 4 Passive) 80,000 1, 50,000 users can be enabled for pChat and 80,000 users can use concurrent. Only pChat pool can be stretched b/w sites to achieve DR. For more details check Lync 2013 HA
Lync 2013 Edge Server 4 – 8 80,000 Depends on how many users will access Lync services simultaneously, 3-4 servers for 30-40% & 7-8 servers for 100%
Lync Director (optional) 3 – 8 80,000 Depends on remote users, 3 servers for 30% remote users and 8 servers for 100% remote users.
SQL Server 2* 80,000 *2 for each backend databases


Important: Above data has provided for physical servers, minor change can happen if you use virtualization as per MS guidelines. It does not take any accountability of DR plan/scenarios. If you are planning for DR also, please account overhead of DR users if available.

Branch Site Connectivity options for Lync

Good connectivity between sites is a basic requirement for every organization. To keep the same requirement in consideration Microsoft designed Lync with multiple branch connectivity options. Basically Lync 2013 supports four types of branch connectivity solutions to choose from which depends on your requirement. Branch sites can have few hundreds of users or few thousands of users. Therefore, solution also depends on usage, connectivity between the sites and number of users. Basically branch sites come into picture at the time of connectivity failure b/w central and branch site and provide resiliency to branch site users.

Only WAN connectivity: This solution is not called as a branch site connectivity option by Microsoft. Usually, it might be an option for small sites where organization has few users (1 – 25) but good WAN connectivity which can sustain the load of branch site users. Organization can have one or more sites which are directly connected to the central site with good WAN connectivity. All the users from this type of sites will directly login to central site and will use all the features including PSTN.

Survival Branch Appliance (SBA): SBA can have an option for those branch sites where organization has user’s b/w 25 to 1000 or maybe 2000 and don’t have local administrative support. SBA is an industry standard appliance which has Lync server registrar and mediation server component. SBA also contains PSTN Gateway for direct PSTN connectivity to branch sites. If you have users range b/w 25 to 1000 you can choose SBA accordingly or if you have more than 1000 users you can have two SBA, this is just an example but totally it depends on requirements and supported number of users by device. SBA provides resiliency to branch users at the time of WAN failure for Enterprise Voice but does not provide resiliency for other Lync features such as IM/Presence, conferencing etc.

Survival Branch Server (SBS): SBS can have an option for those branch sites where organization has more than 1000 users and have local administrative support. SBS is a Windows Server which has Lync server registrar and mediation server component installed on it. SBA does not contain PSTN Gateway for direct PSTN connectivity to branch sites. Therefore you need a separate PSTN gateway to connect PSTN service provider or you need SIP trunk connectivity with ITSP. Same like SBA, SBS provides resiliency to branch users at the time of WAN failure for Enterprise Voice but does not provide resiliency for other Lync features such as IM/Presence, conferencing etc.

Standard Edition Server: Standard Edition Server is an option to provide all the Lync functionality to branch site users or you can say that is a small central site. Standard Edition Server need a PSTN connectivity same as central site using a Media Gateway or SBC to connect ITSP/PSTN service provider. Standard Edition Server provides resiliency to branch users at the time of WAN failure for Enterprise Voice as well as for other Lync features such as IM/Presence, conferencing etc.

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