Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wasatch!haas
From: haas@wasatch.utah.edu (Walt Haas)
Newsgroups: comp.protocols.misc
Subject: Re: IEEE 802.2 Standard
Keywords: IEEE 802.2
Message-ID: <1727@wasatch.utah.edu>
Date: 3 May 89 23:07:33 GMT
References: <1955@umbc3.UMBC.EDU> <1702@wasatch.utah.edu> <6048@pdn.paradyne.com>
Organization: University of Utah CS Dept
Lines: 19

In article <6048@pdn.paradyne.com>, larry@pluto.paradyne.com (Larry Swift) writes:
> In article <1702@wasatch.utah.edu> haas@wasatch.utah.edu (Walt Haas) writes:
> >Type 1 LLC is trivial.  Type 2 is very similar to LAPB, as used by X.25,
> >so any good X.25 implementation should serve as a suitable starting point.
> 
> This is very surprising, since LAPB is a connection-oriented,
> flow-controlling protocol and Ethernet is a connectionless,
> free-flowing medium.  Can you explain the differences and similarities
> between Type 2 & LAPB?

Well, referring to Chapter 5 of IEEE 802.2, we see that the 802.2 LLC PDU
control fields are 16 bits long with 7 bits allocated to sequence numbers,
whereas LAPB control fields are 8 bits long with 3 bits allocated to
sequence numbers.  XID is as far as I know unique to 802.2.  802.2 frames
begin with a DSAP/SSAP pair which do not exist in LAPB.  Other differences
seem to be mostly terminology.  Type 2 LLC does indeed establish a reliable,
flow-controlled path between two hosts on a[n] 802.[345] network[s].

Cheers  -- Walt Haas    haas@cs.utah.edu    utah-cs!haas