[OpenSIPS-Users] Why does NAT keepalive only work for UDP?

[Bogdan-Andrei Iancu]

Klaus Darilion wrote:
> Dan Pascu schrieb:
>   
>> Man, you have a lot of questions today... :P
>>
>> On Wednesday 12 November 2008, Iñaki Baz Castillo wrote:
>>     
>>> Hi, I wonder why SIP keepalive method (sending a NOTIFY/OPTIONS
>>> perdiodically) just works for UDP, this is: why the request is not sent
>>> via TCP?
>>>       
>> Mainly I guess it's because nobody did implement it, as none had a need 
>> for it yet? Add to that that the TCP stack is handled differently (inside 
>> opensips) and it's a complex beast which is not easy to tap into as it is 
>> with UDP. Also, I guess historical reasons was also a factor as it was 
>> meant as an improved replacement for the (UDP only) solutions in the 
>> nathelper and mediaproxy modules (which it is). While being improved it 
>> doesn't imply it has to be perfect, so if you need TCP support, you are 
>> wellcome to implement it and share it with us ;)
>>     
>
> and make it non-blocking ;-)
>   

Well, this is not difficult to do :) - because you do TCP connection 
re-usage and avoid opening and searching for TCP conns.

I think the question is not from technical point of view, but more a 
logical one. Like known issues not to do TCP ping; does TCP ping may 
help after all? how TCP ping and TCP keepalive work?

Regards,
Bogdan