Subject: Re: Encoding of multiple levels

From: Tony Li <[email-masked]>
Date: Fri, 30 Apr 1999 22:51:17 -0700 (PDT)

|  Also, does anyone remember why version is there twice in the fixed part
|  of the header? I got to make a joke about it in the book, which is nice,
|  but how did it happen? Was one field intended as a major version number and
|  the other a minor version number? That would have been useful. I think
|  it was that way in DECnet Phase V (major/minor version
|  number, where minor was bumped for compatible changes). Doesn't matter, but I'm 
|  just curious.

My guess was that one field was always intended as the protocol version
number, the other was the PDU format version number.

Well, at least that sorta made sense.  ;-)

Tony

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From: Henk Smit <[email-masked]>
Date: Mon, 3 May 1999 15:05:28 +0200 (MET DST)

> Rather than having a zillion packet types (level 7 CSNP, level5 Hello, etc),
> perhaps the packet type field should be divided into level/type.

  That would be nice.

> So then you can just put in "level" in 3 bits, and the type into 3 bits
> (pt-to-pt Hello, LAN Hello, CSNP, PSNP, LSP). Right now that octet has
> 3 reserved bits and 5 bits for PDU type.

  Exactly. Unfortunately we are stuck with the PDU types for L1 and L2,
 which seems to be assigned randomly. So what we could do is:
 if (level <= 2) then PDU type = old random PDU type
 if (level >= 3) then PDU type = 3 bits for the level + 5 bits for PDU type
                                                        (only need 2 bits)

  Another issue would be the p2p hello. We only need one p2p PDU for
 all levels. The p2p hello PDU type wouldn't even fit in a perfect
 scheme of 3 bits per level, and 2 bits for PDU type.

      Henk.