Subject: Re: [AAA-WG]: Issue #67: How to deal with CER and CEA in the case of SCTP

From: Jonathan Wood <[email-masked]>
Date: Wed, 20 Jun 2001 15:49:21 -0700 (PDT)

Tony,

The situation is actually the same for TCP and SCTP -- both
will automatically merge two identical associations
initiated at the same time, and both may have some implementations
that permit listening and initiating connections from the
same port, while others do not permit it.

So I recommend forbidding listening and connecting from the
same port under SCTP as well as TCP, and using the same
resolution mechanism for SCTP as for TCP.

Jonathan

>
>All,
>
>The new text in section 8.0 Peer Sate Machine supports both the behavior of
>SCTP and TCP under the condition that the port on which a connection is
>initiated MUST NOT be the port Diameter listens for incoming connections.
>
>Form all of the previous mail discussions I think we all agree that this is
>the correct assumption in the TCP case, but what about SCTP? In the SCTP
>case you can use the same port to initiate connections as well as listening
>for incoming connections. Under these circumstances, the normal operation of
>SCTP will guarantee you only get one transport layer connection, even if
>both sides start to initiate the connection at the same time, and there is
>no need for the I- and R- connection functionality currently defined in the
>state machine. The drawback in this situation is that SCTP may not be able
>to tell you whether or not you are deemed the initiator- it ONLY guarantees
>that you get ONE connection. So, to allow SCTP to use the same port, would
>unfortunately require some additional handling of the CER and CEA :(,
>because as soon as the transport connection is established both peers may
>ending up issuing CER.
>
>I'm not sure how far we should go on this issue. I don't have any problems
>to reject and close this issue #67 if I'm the only one who sees any utility
>in allowing incoming and outgoing SCTP connection requests to use the same
>port.
>
>However, if we do see some advantages in this, we only need some additional
>text that deals with the case that a peer receives a CER instead of an CEA,
>like the following.
>
>In the case Diameter is configured over SCTP to initiate and listen for
>connection requests on the same port, SCTP will not make use of the I- and
>R- states defined in the state machine. Under these circumstances, in the
>event that two peers attempt to connect at the same time, SCTP will
>automatically resolve the connection requests into a single connection, and
>both peers may issue CER.  When both peers send the CER and then receive the
>CER from the other peer instead of a CEA, it MUST in these cases treat the
>received CER as a CEA.
>
>Comments, please.
>
>/Tony
>
>
>