Configuring RTP Base UDP Port

You can configure the range (pool) of local UDP ports from which the device allocates ports to media (RTP, RTCP, and T.38) channels (legs). The range limit of UDP ports is from 6,000 through to 65,535.

The consecutive port offset from the RTP port for RTCP and T.38 traffic is one and two, respectively (i.e., RTCP port = RTP port + 1; T.38 port = RTP port + 2). For example, if the voice session uses RTP port 6000, the device allocates port 6001 for RTCP and port 6002 for T.38. However, you can configure the device to use the same port for RTP and T.38 packets, by configuring the [T38UseRTPPort] parameter to 1.

Within the port range, the device allocates the UDP ports per media channel (leg) in "jumps" (spacing) of 2 (see below note), 4, 5, or 10, which is configured by the [UdpPortSpacing] parameter. For example, if the port range starts at 6000 and the UDP port spacing is 10, the available ports are 6000, 6010, 6020, 6030, and so on. Within the port range, the device assigns these ports randomly to the different media channels. For example, it allocates port 6000 to leg 1, port 6030 to leg 2, and port 6010 to leg 3.

You can configure the starting port (lower boundary) of the port range (default is 6000), using the 'RTP Base UDP Port' [BaseUDPPort] parameter. Once configured, the port range is according to the following equation:

<'RTP Base UDP Port' parameter value> to 65,535

For example: If you configure the 'RTP Base UDP Port' parameter to 6000, the port range is 6000 to 65,535.

You can also configure specific port ranges for specific SIP user agents (UAs), using Media Realms (see Configuring Media Realms). You can configure each Media Realm with a different UDP port range and then assign the Media Realm to a specific IP Group, for example. However, the port range of the Media Realm must be within the range configured by the 'RTP Base UDP Port' parameter.

The following procedure describes how to configure the RTP base UDP port through the Web interface.

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To configure the RTP base UDP port:

1.

Open the RTP/RTCP Settings page (Setup menu > Signaling & Media tab > Media folder > RTP/RTCP Settings).

2.

In the 'RTP Base UDP Port' field, configure the lower boundary of the UDP port range.

3.

Click Apply, and then restart the device with a save-to-flash for your settings to take effect.