[sctp-dev] Using SctpMultiChannel

[Chris]

Hi Chris,

I guess I need to read that draft to see if I can get my head around it. But it would have been really nice if one could use the connect() type of model with the SctpServerChannel so one doeesn't have to re-implement a lot of stuff when going to the MultiChannel; I just want multiple associations that are can be either incoming or outgoing from a single socket.

Regarding your question:
I'd like to use branch() to get "out of" the SctpMultiChannel if only I could get to that point. 
Since before, I have implementations that use the SctpChannel and SctpServerChannel API for server/client behavior and those are interopping fine with other SCTP implementations (so those shouldn't be broken).

I can get the multi-channel to create an outgoing connection to my "server" implementation, but I can't get my "client" to successfully connect to the multi-channel implementation. When I try to do finishConnect() on the SctpChannel, I just get "connection refused" from the multi-implementation, which seems strange since it didn't seem to mind the initial connect(). I'm probably doing something wrong, so I need to debug this more. I can't find any example code anywhere on the net for how SctpMultiChannel is to be used, and sicne the API seems to be very different from the other nio classes, it is difficult to get it working.

BR,
  Chris

--- On Fri, 8/12/11, Chris Hegarty <chris.hegarty at oracle.com> wrote:

> From: Chris Hegarty <chris.hegarty at oracle.com>
> Subject: Re: [sctp-dev] Using SctpMultiChannel
> To: "Chris" <devnullaccount at yahoo.se>
> Cc: "Johan Lübcke" <johan.lubcke at symsoft.com>, "sctp-dev at openjdk.java.net" <sctp-dev at openjdk.java.net>
> Date: Friday, August 12, 2011, 2:50 PM
> The SCTP package provides two
> programming model styles. ( below taken 
> partly from the package description ):
> 
>    The one-to-one style supported by
> SctpChannel and SctpServerChannel,
>    and the one-to-many style supported by
> SctpMultiChannel. The
>    semantics of the one-to-one style
> interface are very similar to TCP (
>    like ServerSocketChannel and
> SocketChanel). An SctpChannel can only
>    control one SCTP association. The
> semantics of the one-to-many style
>    interface are very similar to UDP (like
> DatagramChannel). An
>    SctpMutliChannel can control multiple
> SCTP associations.
> 
> These two styles are taken from the Sockets API Extensions
> for SCTP [1]. 
> I see that the one-to-many style does support a connect
> function, we 
> could expose this through the SCTP API, in a similar way to
> how it is 
> done in DatagramChannel.
> 
> I am curious about your need to use SctpMultiChannel. I do
> get the fact 
> that you want the association to use the same local
> IP/port, but it is 
> not correct to think that a branched (sctp_peeloff in
> native terms) will 
> not incur additional OS resources. Taken from [1]:
> 
>   "After an association is established on a
> one-to-many style socket,
>    the application may wish to branch off
> the association into a
>    separate socket/file descriptor."
> 
> -Chris.
> 
> 
> [1] http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-31
> 
> On 11/08/2011 14:30, Chris wrote:
> > I see now that my reading comprehension isn't so good.
> So the multi-channel does create new associations also for
> incoming connections :)
> >
> > But what I think I would really be after is a
> connect() method on SctpServerChannel that spawned a new
> SctpChannel. If so I wouldn't have to go to the multichannel
> and its somewhat different way of working.
> >
> > BR,
> >    Chris
> >
> > --- On Thu, 8/11/11, Chris<devnullaccount at yahoo.se> 
> wrote:
> >
> >> From: Chris<devnullaccount at yahoo.se>
> >> Subject: Re: [sctp-dev] Using SctpMultiChannel
> >> To: "Johan Lübcke"<johan.lubcke at symsoft.com>,
> "Chris Hegarty"<chris.hegarty at oracle.com>
> >> Cc: "sctp-dev at openjdk.java.net"<sctp-dev at openjdk.java.net>
> >> Date: Thursday, August 11, 2011, 3:13 PM
> >> Hi Chris and Johan
> >>
> >> big thanks for the replies.
> >>
> >> I guess I could try send(), but I won't have any
> data to
> >> send initially but would like to have the
> conneciton up so
> >> it sounds a bit messy compared to my current code.
> But with
> >> lack of other options, I'll try it.
> >> Would the association change be a COMM_UP event
> with a
> >> newly-created Association? And I guess that means
> the
> >> "attachment" will be null when reaching the
> handler...
> >>
> >> Chris Hegarty said:
> >>> It would appear that you want SctpChannel
> semantics
> >> but not
> >>> the overhead
> >>> of creating a new socket for each association.
> But
> >> once
> >>> branched the
> >>> returned SctpChannel will be assigned its own
> socket.
> >>>
> >>
> >> Does it? As far as I understood RFC4960, you use
> the same
> >> *socket* (since I'm using the same local IP/port)
> that
> >> handles multiple different associations. So I'd
> like a new
> >> association, which I guess is an SctpChannel but
> still bound
> >> to the same socket. But maybe that's what you mean
> and I'm
> >> just twisting words :)
> >>
> >> I'm very surprised by the difference between the
> >> SctpServerChannel and SctpMultiChannel since they
> are very
> >> similar in what they do. Could I pervert the
> >> SctpMultiChannel to do channel.register(OP_ACCEPT)
> and
> >> channel.accept() in a similar way as to using
> "send()" to
> >> create a connect()?
> >> I will need to run a single socket with that can
> do both
> >> accept() and connect() on the same port, and
> currently I'm
> >> not sure of which of these classes supports that.
> >>
> >> BR,
> >>    Chris
> >>
> >>
> >>
> >> --- On Thu, 8/11/11, Chris Hegarty<chris.hegarty at oracle.com>
> >> wrote:
> >>
> >>> From: Chris Hegarty<chris.hegarty at oracle.com>
> >>> Subject: Re: [sctp-dev] Using
> SctpMultiChannel
> >>> To: "Johan Lübcke"<johan.lubcke at symsoft.com>
> >>> Cc: "Chris"<devnullaccount at yahoo.se>,
> >> "sctp-dev at openjdk.java.net"
> >> <sctp-dev at openjdk.java.net>
> >>> Date: Thursday, August 11, 2011, 2:59 PM
> >>>
> >>>
> >>> On 08/11/11 01:25 PM, Johan Lübcke wrote:
> >>>> I had the same problem and I ended up
> doing a
> >> "send"
> >>> call to the remote address. That way I get a
> >>> AssociationChangeNotification with an
> association id
> >> that
> >>> can be passed to "branch".
> >>>
> >>> Yes, this would be the best way to achieve
> what you
> >> are
> >>> looking for.
> >>>
> >>> SctpMultiChannel is a little like a datagram
> socket,
> >> in
> >>> that it can send
> >>> and receive messages to/from remote peers
> without
> >>> explicitly setting up
> >>> an association, i.e. no connect is required.
> The
> >> class
> >>> description and
> >>> send method describe this:
> >>>
> >>>     "The channel will
> implicitly setup a new
> >>> association whenever it
> >>>      sends or receives a
> message from a remote
> >>> peer if there is not
> >>>      already an association
> with that peer."
> >>>
> >>> It would appear that you want SctpChannel
> semantics
> >> but not
> >>> the overhead
> >>> of creating a new socket for each association.
> But
> >> once
> >>> branched the
> >>> returned SctpChannel will be assigned its own
> socket.
> >>>
> >>> -Chris.
> >>>
> >>>
> >>>> This seems a bit awkward but it works.
> >> (Especially
> >>> since I need to have some actual data to send
> already
> >> when I
> >>> want to connect to the remote side). Doing a
> "connect"
> >> would
> >>> have been more natural.
> >>>
> >>>
> >>>
> >>>>
> >>>> If there is a better way I am equally
> >> interested!
> >>>>
> >>>>      / Johan
> >>>>
> >>>>
> >>>> 11 aug 2011 kl. 14.03 skrev Chris:
> >>>>
> >>>>> Hi,
> >>>>>
> >>>>> I'm trying to use SctpMultiChannel to
> get
> >> multiple
> >>> associations on the same socket (same local
> port/IP
> >> but
> >>> different remote endpoints), but I can't for
> the life
> >> of me
> >>> figure out the API (http://openjdk.java.net/projects/sctp/javadoc/com/sun/nio/sctp/SctpMultiChannel.html)
> >>>>>
> >>>>> I get that I should do
> >> SctpMultiChannel.open() to
> >>> create an instance and that I should bind it
> to my
> >> local
> >>> address(es).
> >>>>> But then I want to use something like
> >> connect()
> >>> (like on a regular SctpChannel), but there's
> no such
> >> method,
> >>> or anything similar as far as I can see. And
> the only
> >> way to
> >>> get a regular SctpChannel out of this class
> seems to
> >> be
> >>> branch(Accociation), but that's not either an
> option
> >> since
> >>> I  need to have an association to call
> that.
> >>>>>
> >>>>> What am I missing?
> >>>>>
> >>>>> TIA,
> >>>>>     Chris
> >>>>
> >>>
> >>
>