levin@spam.istc.sri.com (05/06/89)
I am working on a LAP-B implementation and find the official
specification in the CCITT RED book, Rec X.25, to be difficult to
follow. The main problem is the ambiguity of some subtle exchange
sequences. Does anyone know where I can find a LAP-B description in
SDL format ? What I am looking for is something like the RED Book's
definition of LAP-D where the diagrams clarify the text.
As an example of the types of problems I am having, consider Sec
2.4.5.9, paragraph 8 of the X.25 spec on the REJ command. Since the P
and F bits are actually the same bit position with the name dependant
on the REJ being a command or a response, the statement
"..wait until the supervisory frame with the F bit set to 1 is
received" implies a very specific sequence of exchanges that
distinguish the above mentioned REJ from the one mentioned at the start
of the paragraph as "...a REJ with the P bit set to 1". I think I
have worked out the correct sequence in this case but would like to
verify it against someone else's interpretation of the spec.
Thank you.
Larry Levin
levin@spam.istc.sri.com
SRI, Menlo Park, CA.