> -----Original Message----- > From: Guy Harris [mailto:[EMAIL PROTECTED] > Sent: Wednesday, October 08, 2003 12:11 AM > To: Michael Lum > Cc: packet steve; [EMAIL PROTECTED]; 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.
