Network requirements for audio/video (A/V) in a Lync Server 2010 deployment include the following:

• The external firewall can be configured as a NAT (that is, whether the site has only a single Edge Server deployed or has multiple Edge Servers deployed). The internal firewall cannot be configured as a NAT. For details about these requirements, see Determining External A/V Firewall and Port Requirements in the Planning documentation.
  
  
• If your organization uses a Quality of Service (QoS) infrastructure, the media subsystem is designed to work within this existing infrastructure.
  
  
• If you use IPsec, we recommend disabling IPsec over the port ranges used for A/V traffic. For details, see IPsec Exceptions in the Planning documentation.
  
  

To ensure optimal media quality, do the following:

• Provision your network links to support throughput of 65 kilobits per second (Kbps) per audio stream and 500 Kbps per video stream, if enabled, during peak usage periods. A bidirectional audio or video session consists of two streams.
  
  
• To cope with unexpected spikes in traffic above this level and increased usage over time, Lync Server media endpoints can adapt to varying network conditions and support loads of three times the throughput (see previous paragraph) for audio and video while still retaining acceptable quality. However, do not assume that this adaptability will support an under-provisioned network. In an under-provisioned network, the ability of the Lync Server media endpoints to dynamically deal with varying network conditions (for example, temporary high packet loss) is reduced.
  
  
• For network links where provisioning is extremely costly and difficult, you may need to consider provisioning for a lower volume of traffic. In this scenario, you let the elasticity of the Lync Server media endpoints absorb the difference between that traffic volume and the peak traffic level, at the cost of some reduction in the voice quality. Also, there is a decrease in the headroom otherwise available to absorb sudden peaks in traffic.
  
  
• For links that cannot be correctly provisioned in the short term (for example, a site with very poor WAN links), consider disabling video for certain users.
  
  
• Provision your network to ensure a maximum end-to-end delay (latency) of 150 milliseconds (ms) under peak load. Latency is the one network impairment that Lync Server media components cannot reduce, and it is important to find and eliminate the weak points.
  
  
• For servers running antivirus software, include all servers running Lync Server 2010 in the exception list in order to provide optimal performance and audio quality. For details, see Specifying Anti-Virus Scanning Exclusions in the Security documentation.
  
  

The bandwidth that is used to download conference content from the Internet Information Services (IIS) server depends on the size of the content that is uploaded.