How to create an SCTP association

[Bernd Walter]

On Thu, May 01, 2014 at 11:06:09PM +0200, Michael Tuexen wrote:
> On 01 May 2014, at 22:42, Bernd Walter <ticso at cicely7.cicely.de> wrote:
> 
> > On Thu, May 01, 2014 at 08:07:19PM +0200, Michael Tuexen wrote:
> >> On 01 May 2014, at 14:49, Bernd Walter <ticso at cicely7.cicely.de> wrote:
> >> 
> >>> I have an SOCK_SEQPACKET socket and want to setup an association
> >>> without sending a message.
> >> Just call connect() or sctp_connectx().
> > 
> > Cool - I wasn't sure about using *connect*() because tutorials only
> > mention it for 1to1 sockets.
> You might want to take a look at
> http://tools.ietf.org/html/rfc6458#section-3.1.6
> http://tools.ietf.org/html/rfc6458#section-9.9
> sctp_connectx() also provides you a way to get the association id,
> which is needed for 1-to-many style sockets.

Ah - there it is.
So many sources to get things running, SCTP still is too new to
easily find good sample code beyound basics.
About the association id - so far I'm always using socket_addr.
I may be able to track association IDs, but are they really unique?
E.g. association shuts down and a new one gets the ID?
I also use it to get the RTT, which is untested code so far.

> >>> The background is that I want to keep the round-trip times of peer
> >>> servers.
> >>> I've enabled regular heartbeat and can use SCTP_GET_PEER_ADDR_INFO
> >>> to get the RTT.
> >>> But in case a host is down or services are restarted I don't have
> >>> an association to ask, so I will need some way to (re)establish
> >>> associations.
> >>> This is done in a different thread as the normal socket operation,
> >>> which uses EOR to write.
> >>> If I send a (dummy)message to the socket I would have to add a mutex
> >>> to not disturb the sending thread.
> >> Does the above solve your issue?
> > 
> > Yes.
> > 
> > But I have another question.
> > Which resources will connecting an unreachable peer use on my one to
> > many socket?
> Basically the resources for an association and it will run a timer for
> retransmitting the INITs.

Great - that's what I was hoping for.
I may have enough troubles already with data for down hosts stuck in
socket buffer, but this is a one time thing until the data times out.

Thank you

-- 
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.