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

[Bruce B]

Also, to get the SIP very well as well, SIP uses both TCP/UDP 5060 right?
and why are there recommendations of opening 5000-5082 UDP for SIP along
with 5060 TCP? Are there any "niceties" to that as well? maybe video
transmission stuff?

Thanks again,

On Fri, Jan 14, 2011 at 4:12 PM, Bruce B <bruceb444 at gmail.com> wrote:

> 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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>> _____________________________________________________________________
>> -- Bandwidth and Colocation Provided by http://www.api-digital.com --
>> New to Asterisk? Join us for a live introductory webinar every Thurs:
>>               http://www.asterisk.org/hello
>>
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>
>
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