The RTP and SRTP base ports are configurable via the IpTransportRtpBasePort
parameters. The base port is usually set to an even number,
to follow the convention of having even ports for RTP/SRTP and odd ports for RTCP/SRTCP.
Both RTP and SRTP have a default base port of 5004. Using the same base port for RTP and SRTP
does not cause port range conflicts. For example, when the DefaultSecurityRtpMode
parameters are set to "Secure with fallback", the
audio streams in the outgoing offers would have a UDP port number of 5004 and 5006 for RTP and
The range of ports allocated for RTP and SRTP is from (base port) to (base port) +
(number of "usable endpoints" * 4).
The number of "usable endpoints" is the number of physical ports + (number of
DSPs * Number of conferences supported per DSP.). The number of conferences supported per DSP is 2.
Example: A unit has 2 T1 ports (23 channels each) and 8 FXS ports, and 4 DSPs able to handle 2 conferences each.
The number of "usable endpoints" is (23 * 2) + 8 + (4 * 2) = 62. The number of ports allocated is 62 * 4 = 248.
Therefore, if the RTP base port is configured with 65300, the range of reserved ports is from 65300 to 65548.