Category Archives: Lync

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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Lync Server 2013 Databases

Lync Server 2013 use SQL Server 2012 Express Edition (64 bit) for servers where Lync server role require local configuration database and SQL Server 2008 R2/2012 (64 bit) for Lync Back End, Archiving, Monitoring, and Persistent Chat and Persistent Chat Compliance databases. You can configure SQL mirror to achieve High Availability for Lync Back End, Archiving, Monitoring, and Persistent Chat and Persistent Chat Compliance databases.

So, now we will have a look into the databases and their uses.

Lync Back End Server databases: Lync Back End (SQL) Server maintains Lync Central Management Store, users & applications databases. You can also use the same database server for archiving, monitoring, persistent chat and persistent chat compliance databases. For more information about the collocation of database please go through

SQL Back End server store Central Management Store, users & applications databases for Lync Enterprise Edition FE pool.

Below is the list of backend server databases:

xds: xds is the main database of Lync Server and part of central management store which maintain the topology information, polices, configuration etc. and replicate a read only copy to every subsequent lync server.

lis: lis stand for Location information service and maintains the location information service data.

rtcxds: rtcxds maintains the backup for user data

rtcshared: rtcshared hosts the conferencing directory

rtcab: rtcab stands for real time communication address book and maintain the address book service information

cpsdyn: cpsdyn maintains the dynamic information database for Call Park application.

rgsconfig: rgsconfig maintains the response group configuration service data file.

rgsdyn: rgsconfig maintains the runtime data for response group configuration service data file.

Lync Front End Server Local databases: Lync FE server uses SQL express edition to store databases under database instance name RTC Local. There are three databases (xds, rtc & rtcdyn) under RTC Local which created at the time of Lync Installation on each Front End server and maintain the replica from Lync Bank End Server. In lync 2013 Front End & Back End are loosely coupled and use lazy writes to update the databases. Therefore, Lync 2013 maintains presence information on Lync Front End Servers.

Below is the list of frontend server databases:

xds: xds on Lync frontend server maintain a read only copy of xds database which is part of central management store and resides in SQL backend database server.

rtc: rtc store persistent users data such as contact list, schedule conferences and ACL’s etc.

rtcdyn: rtcdyn maintains dynamic user data such as presence.

lyss: lyss stands for Lync Storage Service and used to maintain HA within a FE pool. It is a blob database and abstract writes to backend database. It maintains a copy of the data within Front End servers in the pool temporarily, and delete that data once it has been delivered to the final database server. It is a replacement for MSMQ which was used in previous version of Lync. Therefore, it is part of the Front End servers and it is located under LYNCLOCAL named instance. It is also used for Archiving integration and Unified Contact Center. Currently, it supports Exchange and SQL for archiving.

Lync Archiving database: Lync 2013 provides two options for archiving. You can use either SQL Server or Exchange Server for archiving purpose. If you use SQL server as an option for archiving it creates LcsLog database for the same.

lcslog: lcslog maintains data file for the retention of instant messaging and conferencing data on an Archiving Server.

Lync Monitoring databases: Lync 2013 maintain call detail recording and quality of service data if you deploy Lync Monitoring Server role in you deployment.

cdr: cdr stands for call detail recording and maintains the call detail recording data.

QoE: QoE stands for quality of Experience and maintains the QoE data to provide best experience to Lync users.

Lync Persistent Chat database: Lync 2013 has new server role called Persistent Chat which is replacement of Group chat server and to maintain user persistent chat data Lync uses mgc database.

Lync Persistent Chat Compliance database: In Lync 2013 as Persistent Chat is a part of Lync Servers role, so to maintain compliance data for this user service Lync uses mgccomp database.

High Availability in Lync 2013

Availability is the concern for any enterprise application. In Lync 2013 Microsoft took a step ahead and delivered better availability options. Lync 2013 is a next level enterprise communication and voice based solution which based on different Lync Server roles. In Lync 2013 Microsoft did a tremendous job to consolidate many Lync roles and reduced the number of Lync roles and their complexity. To know more about Lync roles click here

Lync Server Standard Edition and HA*

This is big question for all to know about HA option in Lync Server 2013 Standard Edition. Lync Server 2013 supports up to 5000 users and can be deployed in a single box but to achieve more availability (*not exactly High Availability) you can deploy Lync 2013 SE in paired pool. Paired pools means deploy two Lync SE Server and paired them in a pool. Failover In a paired pool is manual activity (can be automated by PowerShell scripting) and users will get limited functionality at the time of failover. HA can’t be achieved for Persistent Chat in Standard Edition.

Lync Server Enterprise Edition and HA

Lync Server Front End (Audio/Video, Archiving & Monitoring is collocated): High availability can be achieved by deploying Lync 2013 Enterprise Edition Server pool. In one Lync Server 2013 EE pool you can accommodate 80,000 users by deploying maximum of 12 servers. Lync 2013 Enterprise Edition is designed by using brick model which works on Windows Fabric to provide HA. In Lync 2013 EE need minimum three FE servers (MS recommendation) for one pool. For availability, Lync Server pool needs N/2, N/2+1 server in a pool to work.

Microsoft recommends if you have large conferences for more than 250 users, a separate A/V (FE) pool can be deployed.

Lync Server Back End: Lync Server uses SQL server for its backend databases. You need databases for Lync Server backend, archiving/monitoring and persistent chat which can be collocated in one SQL server or deployed on separate (MS recommended) SQL Server instances. Lync Server 2013 supports SQL mirror for its databases. It does not support SQL failover clustering (not recommended) or SQL always on feature. To configure automatic failover in SQL server mirror, you need SQL witness server which can be SQL Express edition or SQL Server instance.

Lync Mediation Server: In Lync 2013, Mediation server role can be collocated with FE server role or can be deployed separately as a pool.

Lync Persistent Chat: In Lync 2013, Persistent Chat is a new server role which replace Lync server 2010 Group Chat server component which was not part of the Lync 2010 server roles. You can deploy Lync Server Persistent Chat as a pool to achieve HA and can have maximum 8 servers in a pool (4 active and 4 passive) for 80,000 concurrent users and total 1, 50,000 users.

Lync Edge Server: Lync Edge server role can be deployed as a pool in a perimeter network to provide HA for external (outside your organization firewall) users.

Director: In Lync 2013, Director is an optional role and can be deployed in the same way as Lync Server 2010 Director pool.

Reverse proxy: Reverse Proxy is not part of any Lync Server role but required for external users. You can use Microsoft Reverse proxy solutions such TMG 2010 / UAG 2010 / IIS ARR or can have any third party solution.

Bandwidth Requirements for Lync 2013

Lync is a real-time communication platform to provide rich communication experience to end users. To accomplish rich experience for Lync users, Network assessment and planning is a most important phase of your overall design and implementation. This article can help architects, consultants and system administrators at the time of Network planning for Lync infrastructure.

Before going deep into the bandwidth requirements, I would like to explicate Lync call flow scenarios. Any IP based UC solution (here Lync), used diverse media paths for different scenarios such as Peer to Peer sessions, Conference sessions and PSTN/PBX sessions. During peer to peer and conference sessions, there is a possibility to share the content such as entire desktop or any specific application etc.

Lync uses different codecs/protocols for different modalities. Below are the tables which will demonstrate the bandwidth requirement for Lync 2013 infrastructure.

Audio Codec Bandwidth:

Audio codec Scenarios Maximum bandwidth (Kbps) w/o FEC Maximum bandwidth (Kbps) with FEC Typical bandwidth (Kbps)
RTAudio Wideband Peer-to-peer, default codec 62 91 39.8
RTAudio Narrowband Peer-to-peer, PSTN 44.8 56.6 30.9
G.722 Default conferencing codec 100.6 164.6 46.1
G.722 Stereo Peer-to-peer, Conferencing 159 73.1
G.711 PSTN 97 161 64.8
Siren Conferencing 52.6 68.6 25.5


Shown Bandwidth in exceeding table includes IP header, UDP header, RTP header, and SRTP headers. The stereo version of the G.722 codec is used by systems that are based on the Lync Server 2013 Meeting Room Edition, which enables stereo microphone capture so that listeners to can more easily distinguish between multiple talkers in the meeting room.

Video Codec Bandwidth:

Video codec Resolution and aspect ratio Maximum video payload bit rate (Kbps) Minimum video payload bit rate (Kbps) Typical bit rate (Kbps)
H.264 320×180 (16:9)212×160 (4:3) 250 15 200
H.264/RTVideo 424×240 (16:9))320×240 (4:3 350 100 280
H.264 480×270 (16:9)424×320 (4:3) 450 200 350
H.264/RTVideo 640×360 (16:9)640×480 (4:3) 800 300 640
H.264 848×480 (16:9) 1500 400 1200
H.264 960×540 (16:9) 2000 500 1600
H.264/RTVideo 1280×720 (16:9) 2500 700 2000
H.264 1920×1080 (16:9) 4000 500 3200
H.264/RTVideo 960×144 (20:3) 500 15 400
H.264 1280×192 (20:3) 1000 250
H.264 1920×288 (20:3) 2000 500


Forward error correction (FEC) for video is included in the video payload bit rate.

Neither in peer to peer nor in conference sessions, audio or video packets stream continuously. Only sessions activity define that how often packets are sent for a stream.

Streaming activity in a peer-to-peer scenario:

  • When the users speak in peer to peer call then only endpoints send audio streams.
  • Audio streams received by both participants.
  • In peer to peer video calls, both endpoints send and receive video streams during the entire call.
  • In peer to peer video call if there are little or no movement in video scenes, the actual bit rate may temporarily be very low, because the video codec skips encoding regions of the video with no changes.

Streaming activity in a conferencing scenario:

  • When the users speak in conference calls then only endpoints send audio streams.
  • In a conference call, all participants in conference receive audio streams.
  • In a conference call if video is used, all participants can receive up to five receive video streams and one panoramic (for example, aspect ratio 20:3) video stream. By default, the five receive video streams are based on active speaker history, but users can also manually select the participants from which they want to receive a video stream. Users also can fixed video by using pin option which they want to see without based on active participants.

The typical stream bandwidth for panoramic video is based on currently available devices that stream only up to 960×144 panoramic video. After devices with 1920.x.288 panoramic video become available, the typical stream bandwidth is expected to increase.

Network Bandwidth Requirements for Media Traffic:

Modality Description Maximum bandwidth Typical bandwidth
IM, presence, and signaling Nonmedia elements 2 Kbps 1.6 Kbps
Voice Default = RTAudio Wideband 62 Kbps 39 Kbps
Conference voice Default = G.722 100.6 Kbps 46.1 Kbps
Video – small Uses H.264 at 320×180 250 Kbps 200 Kbps
Video – medium Uses H.264 at 640×480 800 Kbps 640 Kbps
Video – high Uses H.264 at 1280×1080 4 Mbps 3.2 Mbps


  • All figures are based around the industry standard of 20ms packetization for UC applications, which is 50 packets per seconds.
  • Bandwidth figures include the protocol overheads for IP, UDP, RTP, and SRTP. This is why the Microsoft bandwidth figures for standard codecs are different from those quoted by other VoIP suppliers, who only state the raw codec figure, and not the entire packet overhead. For Microsoft, this figure includes encrypting all communications.
  • Figures in the following table for audio bandwidths do not include a Forward Error Correction (FEC) overhead. FEC is a mitigation technique that is enabled when the network suffers unusually high packet loss. The assumption is that, for planning, the network administrator will estimate traffic use without mitigations.
  • For video, the default codec is the H.264/MPEG-4 Part 10 Advanced Video Coding standard, coupled with its scalable video coding extensions for temporal scalability. To maintain interoperability with Lync 2010 or Office Communicator 2007 R2 clients, the RTVideo codec is still used for peer-to-peer calls between Lync Server 2013 and legacy clients. In conference sessions with both Lync Server 2013 and legacy clients, the Lync Server 2013 endpoint may encode the video by using both video codecs, and may send the H.264 bit stream to the Lync Server 2013, and send the RTVideo bit stream to Lync 2010 or to Office Communicator 2007 R2 clients.

Default aspect ratio for Lync Server 2013 has been changed to 16:9. The 4:3 aspect ratio is still supported for webcams that don’t allow capture in 16:9 aspect ratio.

The network bandwidth numbers in all preceding tables represent one-way traffic only, and include 5 Kbps for RTCP traffic overhead for each stream.

For all bandwidth tables, the maximum bandwidth figures should generally be used in network planning. Lync Server depends entirely on the underlying network for the user-perceived quality of its communications, particularly voice. In addition, sites with fewer than 100 users should always use the maximum figures because, statistically, the network peaks for Lync Server occur more frequently. For sites with more than 100 users, the typical figures can be used.


Disclaimer: In this article data has taken form Microsoft Lync Server Networking guideline which has been modified a bit to understand better instead of going through a more than 100 page document.

Lync Enterprise Voice Connectivity

World is changing and moving towards rich collaboration and corporates can’t avoid these changes. As well as, we also can’t neglect our traditional way of communication. It means still we need phone to communicate with people. Microsoft did excellent job in this field as earlier only mailing solution was the key application for formal communication. But to understand better, we were using traditional phone. Microsoft Lync as an application can cater all your corporate needs. Microsoft Lync is a rich communication medium and easily can be integrated with other business applications such as Exchange & SharePoint.

Lync provides many options to enable Enterprise Voice. Usually organization uses traditional PBX or IP PBX which involves lots of cost and need distinct administration to manage the whole solution. Lync provides an Enterprise solution which can be deployed with or without your traditional PBX’s. In general there are three ways to enable enterprise voice with Lync.

1. Traditional PBX connectivity with Lync mediation server using media gateway.

2. Direct SIP, Advance IP PBX connectivity directly with Lync mediation server.

3. Direct SIP/PSTN Gateway/VOIP only deployment option directly with Lync mediation server.

4. SIP Trunk, Direct connectivity to Lync Mediation server from ITSP using SBC.

What’s New in Lync Server 2013…?

Microsoft is playing a major role in Unified Communication market. Lync Server 2013 is a 6th release in last one decade. Enterprise voice was started with OCS 2007 R2 and Lync server 2010 became a major release in Enterprise voice space. Lync 2013 is a major release after Lync 2010 and now cumulative updates are also available to download.

In Lync 2013, Microsoft came up with few tremendous features in terms of voice which changed the overall Lync deployment as well as fit into those countries where government has regulation for VOIP. Now, you are thinking which that tremendous feature is; I am talking about Location based routing (LBR) which can provide room for Lync implementation with Enterprise voice in those countries where government has regulated or they have some specific concerns with regards to VOIP roll out.

I will start with basic features of Lync Server 2013 which differentiate it from previous releases. To start with Lync Server 2013 server roles, I am providing table with comparison which can help you to understand better.

Lync Server 2013 Lync Server 2010
Front End & Back End (A/V is collocated) Front End & Back End
A/V Conferencing (Can be collocated with Front End)
Archiving (Can be deployed separately) Archiving (Can be collocated with Front End)
Monitoring (Can be deployed separately) Monitoring (Can be collocated with Front End)
Mediation (Can be collocated with Front End) Mediation (Can be collocated with Front End)
Director (Optional & Can’t be collocated with Front End) Director (Can’t be collocated with Front End)
Edge (Can’t be collocated with Front End) Edge (Can’t be collocated with Front End)
Persistent Chat (Can’t be collocated with Front End) Group Chat (Can’t be collocated with any Lync Server role)
Standard Edition Server (All above roles combined) Standard Edition Server (All above roles combined except group chat)


To get a better understanding, have a look into the images:

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