Key network requirements for audio/video in a Communications Server 2010 deployment include the following:

• The external firewall can be configured as a NAT (whether the site has only a single Edge Server deployed or has multiple Edge Servers deployed). For details about this requirement, see Determining Firewall and 50k Port Range Requirements.
  
  
• 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 audio and video traffic. For details, see IPsec Exceptions.
  
  

To ensure optimal media quality, do the following:

• Provision your network links to support throughput of 45 kilobits per second (Kbps) per audio stream and 300 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, Communications 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, because this will reduce the ability of the Communications Server media endpoints to dynamically deal with varying network conditions, such as temporary high packet loss.
  
  
• For network links where provisioning is extremely costly and difficult, you may be forced to consider provisioning for a lower volume of traffic and let the elasticity of the Communications 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, but also of 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 Communications Server media components cannot reduce, and it is important to find and eliminate the weak points.
  
  

Bandwidth utilization for meeting content downloaded from the IIS server depends on the size of the content which is uploaded. The user model defines average content sizes that have been tested.