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

[Bruce B]

Got it. Thanks. Makes sense to keep an extra two in mind for conference
etc....

Off topic - what is top post? I am using gmail + chrome - no ugly Outlook.

On Fri, Jan 14, 2011 at 3:33 PM, Danny Nicholas <danny at debsinc.com> wrote:

>  Hurray for Microsoft Outlook (for creating this whole top-post thread).
> Just my .02;  The other two ports must have been a remnant of another
> channel;  as for the 4 ports – I think that the 4 port requirement is
> probably for “niceties” like conferencing and transfers.
>
>
>  ------------------------------
>
> *From:* asterisk-users-bounces at lists.digium.com [mailto:
> asterisk-users-bounces at lists.digium.com] *On Behalf Of *Bruce B
> *Sent:* Friday, January 14, 2011 2:15 PM
>
> *To:* Asterisk Users Mailing List - Non-Commercial Discussion
> *Subject:* Re: [asterisk-users] Why are 4 ports used for a single call?
>
>
>
> Thanks guys. I am not sure whether that call was asymmetric or not but I
> saw 4 ports open. It could be that the other two ports were remnant of
> another channel even though I doubt it.
>
>
>
> Now, when I tried again, it is only 2 ports that is opened like you
> mentioned, even RTP port, and RTP port +1. So, does Asterisk usually use
> the symmetric method or is the asymmetric method used as well by some media
> servers?
>
>
>
> The reason why I am asking is because there are many many
> online responses that there is 4 ports needed per call and make sure you
> keep enough ports open, blah blah...
>
>
>
> Thanks again
>
> On Fri, Jan 14, 2011 at 2:57 PM, Gary Allen <solstars1 at gmail.com> wrote:
>
> RTP always uses a random even numbered port, then RTCP will use the next
> port, which will always be odd numbered.  Symmetric RTP only needs two
> ports, while asymmetric RTP uses four.
>
> http://www.armware.dk/RFC/rfc/rfc4961.html
>
>
>   On Fri, Jan 14, 2011 at 12:44 PM, Bruce B <bruceb444 at gmail.com> wrote:
>
>  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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