[asterisk-users] how many UDP ports is required for 1 call

[Gilles]

On Tue, 21 Feb 2012 19:00:48 +0530, virendra bhati
<virbhati at gmail.com> wrote:
>how many UDP ports is required for 1 call. and why .

If you mean a voice call, it appears that each host must open three
UDP sockets:

- One to send/receive SIP commands
- Two to receive sound (one for RTP, one for RTCP; The first port is
even, the other is odd)

http://www.cs.columbia.edu/~hgs/rtp/faq.html#ports

www.freecode.com/articles/nat-traversal-for-the-sip-protocol
(great article, but missing images)

"Understanding the relationship between SIP and RTP"
http://blog.lithiumblue.com/2007/07/understanding-relationship-between-sip.html