> -----Original Message-----
> From: Guy Harris [mailto:guy@xxxxxxxxxxxx]
> Sent: Wednesday, October 08, 2003 12:11 AM
> To: Michael Lum
> Cc: packet steve; ethereal-dev@xxxxxxxxxxxx; Jeff Morriss
> Subject: Re: [Ethereal-dev] Questions about Connection Oriented SCCP
>
>
> On Tue, Oct 07, 2003 at 01:37:41PM -0700, Michael Lum wrote:
> > OK, a given MTP3 point code pair, SSN=142 (RANAP), and the associated
> > SLR/DLR defines a conversation. We can associate a dissector with that
> > conversation.
>
> Why would the SSN be needed to define the conversation? Can there be
> more than one SSN used in a connection? If so, how do you know how to
> dissect the payload of packets lacking an SSN?
>
The SSN is only available with the SCCP Connection Request and is required
to know what type the payload is. There is only one SSN for a connection.
I was trying to say that if the SCCP CR is for SSN=142 then we know what
dissector is required for the payload (RANAP). Any subsequent SCCP messages
in the connection will also contain a RANAP payload (if any) and I am
assuming that means for the conversation.
For example SSN=142 would imply RANAP, SSN=252 would imply IOS, SSN=254
could be GSM BSSAP or IS-634 or IOS.
I suppose you could rely on heuristics but I have found that doesn't work
all of the time.
> > SCCP Release Complete MTP3 [OPC=X, DPC=Y, SLR=A, DLR=B] or
> [OPC=Y, DPC=X,
> > SLR=B, DLR=A]
> > end of conversation
>
> Note that, currently, conversations have no notion of a beginning or
> end; we could add one, along the lines of what we do for "circuits".
The notion of 'end' is important because xLRs will eventually be reused.
One would normally expect a given OPC/DPC pair to use one SSN but you
never know.