[Users] OpenSER and transport selection (SRV and NAPTR)

[Joachim Fabini]

Hi,

Initially I intended to submit a feature request for
OpenSER functionality similar to t_relay_to_udp, 
t_relay_to_tcp but WITHOUT the need to specify the 
destination IP address and port.
My reasoning was to let the new functions do exactly 
what t_relay() does but in addition force the DNS SRV 
query for a specific transport (udp, tcp, or tls). 

Seeing the roadmap for 1.1 I realized that NAPTR solves 
part of this problem. Is there already any estimation 
when NAPTR implementation will be available in OpenSER?

I intentionally said "part of the problem" because 
NAPTR delegates the decision on the transport to the
destination DNS. But: our own proxy might also be
required to control the selected transport.
It seems to me quite flexible to implement a 
proxy-hosted NAPTR emulation and specify the list 
of requested protocols, e.g. 
t_relay_to_transport("tls","tcp",0) 
specifies that t_relay should firstly generate a 
SRV DNS query for _sips._tcp.mydomain.org, if this 
fails to query for _sip._tcp.mydomain.org and then 
give up - if I don't want UDP. 

This saves one DNS query (NAPTR) and enables a proxy
to control what protocols it uses for contacting the 
next hop.

Finally, I believe that the interface to t_relay_naptr() 
(or whatever the naptr relaying will be called) should 
support selection of desired protocols, e.g.
t_relay_to_naptr("tls", "tcp", "udp") where entries
can be left empty to indicate that this transport is
not desired. The argument order might even overrule 
the NAPTR response transport ranking - finally we
connect and thus decide on what transport we prefer... ;)  

Any comments warmly welcome,
best regards
--Joachim