[Freeswitch-users] OT: Apple goes to great lengths to defeat NAT and firewalls with new Facetime

[Steven Ayre]

>
> What you're after is probably something like
> http://tools.ietf.org/html/rfc5761 - patches welcome ;)


... that wasn't the document I was after. I think I had seen a draft about
multiplexing SIP+RTP, but I may be mistaken.



On 20 September 2013 14:49, Steven Ayre <steveayre at gmail.com> wrote:

> Wondering why the FS developers default to not including rtpmap lines
>> for statically defined RTP payload types?
>
>
> Because SIP over UDP doesn't play well with fragmentation. SDP can make
> packets large than the PMTU, leading to fragmented packets, which leads to
> devices ignoring the packet. Removing the unnecessary rtpmap lines means
> smaller SDP so smaller packet so less likelihood of that being an issue.
>
> It shouldn't be such an issue over TCP.
>
> Devices *should* support it since the standard explicitly say the rtpmap
> isn't required for static types, but there are some manufacturers who
> ignored that part so there's the verbose_sdp=true compatibility option for
> them.
>
> Wonder why SIP signalling over TCP or TLS is much more reliable
>
> through various NAT and firewall devices?
>
>
> That's not necessarily a given.
>
> In general though because the TCP connection explicitly signals the
> connection closing the mapping will stay in the firewall. With UDP it is
> removed after a long period of inactivity. That can cause problems with
> signalling during a phone call unless the endpoints send keepalive packets
> often enough.
>
> TLS will prevent the router helping with SIP ALG - you must have endpoints
> capable of doing NAT traversal themselves (STUN). Though that's a good idea
> in all cases anyway.
>
>  I wonder if FS could multiplex SIP and RTP over the same port someday?
>
> Maybe support deflate encoding?
>
>
> That wouldn't automatically work. It would need support by both ends and
> protocol changes to support it.
>
> What you're after is probably something like
> http://tools.ietf.org/html/rfc5761 - patches welcome ;)
>
>
>
>
>
> On 20 September 2013 14:07, Kristian Kielhofner <kris at kriskinc.com> wrote:
>
>> Somewhat off-topic but because it comes up here regularly.
>>
>> Wondering why the FS developers default to not including rtpmap lines
>> for statically defined RTP payload types?
>>
>> Wonder why SIP signalling over TCP or TLS is much more reliable
>> through various NAT and firewall devices?
>>
>> Apple has put a significant amount of effort into redesigning Facetime
>> to better handle NAT and firewall devices.  More details here:
>>
>> http://blog.krisk.org/2013/09/apples-new-facetime-sip-perspective.html
>>
>> I wonder if FS could multiplex SIP and RTP over the same port someday?
>>  Maybe support deflate encoding?
>>
>> --
>> Kristian Kielhofner
>>
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