Manual

71
In a typical codec applicaon, Codec X will send a packet from Address A Port B, to Address C Port D on the Desnaon
Codec Y. A codec that has mulple applicaons running (like streaming audio while simultaneously serving a
conguraon web page) would deliver these applicaons from, and to, dierent port numbers, but perhaps to the same
IP address. Port numbers are also used by NAT routers in segmenng applicaons owing through them and they may
change source port numbers at will.
Network Address Translaon (NAT) refers to the ability of a router to translate requests from computers (or codecs)
within its LAN onto the public Internet. On its most basic level, this involves replacing the private “source” or return
IP address in each packet with the true public IP and remembering where that packet was sent. This insures that any
response can be forwarded back to the proper device.
A good way to think of this is that an outgoing packet “punches a hole” in the router, through which authorized reply
packets may be returned to the codec for a limited me.