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:

 

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:

 

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:

 

• 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.