2.21.4.1. Payload 
Depending on the board in use (HG 3500 or HG 3575), ports used are
taken from a certain port range defined by the parameter UDPPORT (AMO
SIPCO). The port range for RTP/RTCP is defined by the following interval:
[UDPPORT .. UDPPORT + 960].
Port 4007 is used for a path test in the case of poor payload quality.
See Section
2.9.1, “When is Payload Survivability Used?” in the
document "IP Distributed Architecture (IPDA)" - keyword "UDP-PINA".
Figure 39. Example: Port usage for payload
