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0 pointskragen1y ago0 comments

Not only isn't that an accurate summary of Graham's book, it isn't even a topic discussed in the first half of the book, which is all I've read so far. I suspect it isn't a topic discussed in the book at all; can you back up your assertion with some quotes?

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OhMeadhbh1y ago

Yes, but the book also has enough inaccuracies as to make it... I don't know what. For example, in the first chapter the author says "no one knows what a session is," which is patently false. I myself implemented control logic in telco equipment to respond to X.225 compliant messages to change the state of an abstract state machine used on either side of the connection. And while I'm sure it's possible to use CONS or CLNP to communicate with a CEEFAX terminal, that is far from the only use to which the various OSI compliant protocols were put.

Just because you don't understand something, that doesn't mean it's bad.

kragenOP1y ago

I think he means to be saying that, in the context of TCP/IP, nobody knows what a “session” in the OSI sense would correspond to—not that nobody has ever implemented X.225. Presumably Graham knows that people have written X.225 implementations and isn't trying to convince his readers otherwise?

I don't know enough to judge his assertion that the session layer exists to solve problems created by half-duplex terminals. (He doesn't seem to specifically call out Ceefax.)

OhMeadhbh1y ago

From page 11: "OSI was designed primarily around the dumb terminal connected to a mainframe."

Also from page 11: "'session' meant something related to attaching videotex terminals to mainframes."

And yes, all Ceefax terminals were Videotex terminals, but not all Videotex terminals were Ceefax terminals.

I might recommend that instead of guessing what the session layer is, you (or more appropriately, Mr. Graham) go and look at what the specs say it is and what it's used for. The X.225 spec is available for download at https://www.itu.int/rec/T-REC-X.225-199511-I/en. X.215 is available at https://www.itu.int/rec/T-REC-X.215-199511-I/en.

The OSI session layer is not related to HTTP session cookies as the original author proposes.

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OhMeadhbh1y ago

Just because you don't understand something, that doesn't mean it's bad.

kragenOP1y ago

I don't know enough to judge his assertion that the session layer exists to solve problems created by half-duplex terminals. (He doesn't seem to specifically call out Ceefax.)

OhMeadhbh1y ago

From page 11: "OSI was designed primarily around the dumb terminal connected to a mainframe."

Also from page 11: "'session' meant something related to attaching videotex terminals to mainframes."

And yes, all Ceefax terminals were Videotex terminals, but not all Videotex terminals were Ceefax terminals.

The OSI session layer is not related to HTTP session cookies as the original author proposes.

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