If you use the port range registry key settings to reduce the ports that can be used for media, it is recommended that you do so according to the minimums described in this section.

For client endpoints, the port range should not be reduced to the point where it can compromise the ability of the media stack to negotiate audio, video, and desktop sharing communication ports during session setup or during a call. More specifically, for an Office Communicator 2007 R2 client, the minimum port range is 40. A smaller range of ports can result in errors during call transfer and conference escalation scenarios.

By configuring a minimum of 40 ports, you enable the client to evaluate the candidate transport addresses that it can use to stream audio, video, and desktop sharing to another client, as described in the Internet Engineering Task Force (IETF) Interactive Connectivity Establishment (ICE) protocol. Candidate addresses include a local address and an address on the A/V Access Edge server. A minimum of 40 ports in the port range will also accommodate any escalations from a peer-to-peer call to a conference.

Note:
An escalation of a peer-to-peer call to a conference triggers a temporary doubling of the ports in use.

Different call scenarios can dictate whether to deliver by using User Datagram Protocol (UDP) or Transmission Control Protocol (TCP). However, whenever UDP can be used to deliver media, it will be used instead of TCP.

Note:

Secure Real-Time Transport Protocol (SRTP) and Secure Real-Time Transport Control Protocol (SRTCP) streams are multiplexed over TCP but are delivered separately in the case of UDP. UDP connections are more resilient to packet loss than TCP. When a UDP packet is lost, there is no transport impact to subsequent packets. When packet loss occurs over TCP, all subsequent packets are held at the transport level to ensure a reliable stream of data. As a result, overall latency in the media delivery chain may increase over TCP.

The following set of tables show the detailed port requirements for call setup:

Table 1.0 Port Requirements for Call Setup

Table 1.1 Port Requirements for Call Setup

Table 1.2 Port Requirements for Call Setup

The following set of tables show the detailed port requirements for escalation during a call:

Table 2.0 Port Requirements for Escalation During a Call

Table 2.1 Port Requirements for Escalation During a Call

Table 2.2 Port Requirements for Escalation During a Call

The following set of tables show the detailed overall requirements for ports:

Table 3.0 Overall Requirements for Ports

Table 3.1 Overall Requirements for Ports

Table 3.2 Overall Requirements for Ports

Note:
* 8 additional ports required to accommodate any third party applications. At least 40 ports needed for allocating ports in the same range at the same time.

As described in the tables, the minimum number of ports that must be allocated on a client platform is 40. During a normal call, the number of ports used will not exceed 2, 4, or 5 depending on whether audio, audio/video, or audio/video/Desktop sharing are streamed.

Changing the default port range on the server is not recommended. However, if your organization has a need to establish port ranges on the server, you can use the following WMI settings to configure the port range:

• MSFT_SIPPoolConfigSetting
  
  
• MSFT_SIPDataMCUSetting
  
  
• MSFT_SIPMediationServerConfigSetting
  
  

For an A/V Conferencing Server as well as all other server components terminating Audio/Video media (for example, Front-Ends hosting Conferencing Attendant, Response Group Service), the port range must be at least six times the maximum number of concurrent call legs that can be supported on the server (that is, two ports for the RTP and RTCP traffic for each modality – audio, video, and panoramic video).

For an A/V Access Edge server, the port range must be at least twelve times the maximum number of outside user calls that can be supported on the server (two ports for the RTP and RTCP traffic for each modality – audio, video and panoramic video, or audio, video, and desktop sharing for ICE v6 and ICE v19.

For a Mediation Server, the port range must be at least eight times the maximum number of concurrent calls that can be supported on the server (that is, two ports for the RTP and RTCP traffic for audio multiplied by two because the Mediation Server is a back-to-back User Agent for ICE v6 and also for ICE v19).