Key network requirements for audio/video in an Office Communications Server deployment include the following:

• In any location with multiple Edge Servers deployed behind a load balancer, the external firewall cannot function as a network address translator (NAT). However, in a site with only a single Edge Server deployed, the external firewall can be configured as a NAT. For details about this requirement, see Firewall Requirements for External User Access.
  
  
• If your organization uses a Quality of Service (QoS) infrastructure, the media subsystem is designed to work within this existing infrastructure. For details, see Requirements for a QoS Environment.
  
  
• 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, Office 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 Office 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 Office 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 Office 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. For details about the user model and other capacity planning considerations, including bandwidth considerations, see Capacity Planning.