[asterisk-users] Why are 4 ports used for a single call?

[Bruce B]

I mean part of RTP RFC?

On Fri, Jan 14, 2011 at 2:41 PM, Bruce B <bruceb444 at gmail.com> wrote:

> Hi Everyone,
>
> I am just tweaking a pfSense router and learning lots about NAT etc....I
> noticed that each call uses four UDP port for RTP. Here is an example of
> port for a call I made:
>
> 10200
> 10201
> 10504
> 10505
>
> Seems like they are random in pair. I have a restriction of 10000-11000 in
> my rtp.conf so that makes sense. But why use 4 ports per call? is that part
> of SIP RFC?
>
> Thanks
>
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