D.37. rtp.conf
The rtp.conf
file controls the Real-time Transport Protocol (RTP) ports that
Asterisk uses to generate and receive RTP traffic. The RTP protocol
is used by SIP, H.323, MGCP, and possibly other protocols to carry
media between endpoints.
The default rtp.conf file uses the RTP port range of
10,000 through 20,000. However, this is far more ports than you're
likely to need, and many network administrators may not be
comfortable opening up such a large range in their firewalls. You
can limit the RTP port range by changing the upper and lower bound
limits within the rtp.conf
file.
For every bidirectional SIP call between two
endpoints, five ports are generally used: port 5060 for SIP
signaling, one port for the data stream and one port for the
Real-Time Control Protocol (RTCP) in one direction, and an
additional two ports for the data stream and RTCP in the opposite
direction.
UDP datagrams contain a 16-bit field for a
Cyclic Redundancy Check (CRC), which is used to verify the
integrity of the datagram header and its data. It uses polynomial
division to create the 16-bit checksum from the 64-bit header. This
value is then placed into the 16-bit CRC field of the datagram,
which the remote end can then use to verify the integrity of the
received datagram.
Setting rtpchecksums=no requests that
the OS not do UDP checksum creating/checking for the sockets used
by RTP. If you add this option to the sample rtp.conf file, it will look like this:
[general]
rtpstart=10000
rtpend=20000
rtpchecksums=no
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