Fresh from reading for my Support exam from Cisco Press CIT........ SDLC is
the granddaddy of them all......... created in the mid-1970's to transport
SNA. ISO modified SDLC to create HDLC. Then ITU-T modified HDLC to create
LAP, then later, LAPB. IEEE modified HDLC to get 802.2, which is also known
as LLC, of which there are 3 types: Type 1 a connectionless version, Type 2
a connection-oriented version, and Type 3 an acknowledged connectionless
version.
NetBEUI and SNA both need the reliability of LLC Type 2. I wouldn't say
"Because NetBEUI and SNA are legacy, the use of LLC Type 2 is
diminishing"......I would say "Because reliability is more frequently left
to higher layer protocols, such as TCP, the need for the reliable LLC Type 2
is diminishing".... hehe =)
I don't know if NetBEUI is a good choice to use in this example. Perhaps
NetBIOS would be a better choice...... Check out:
http://ourworld.compuserve.com/homepages/TimothyDEvans/intro.htm
http://www.geocities.com/SiliconValley/Monitor/3131/ne/osimodel.html
http://www.windowsitlibrary.com/Content/386/10/2.html
(watch for wrap)...... These pages have some info about NetBEUI/BIOS....
from the sounds of it NetBEUI *is* a Connection-Oriented transport layer
protocol, in which case it would NOT need the LLC Type 2 reliability, while
the older NetBIOS a Connectionless transport layer procotol that could
indeed benefit from the use of LLC Type 2........ But I can't say for sure
=)
Hope this helps! Good luck on your writing!
Mike W.
"Priscilla Oppenheimer" wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> I found myself writing this paragraph for a new writing project:
>
> When NetBEUI and SNA are used on Ethernet networks, they take advantage of
> the reliability of LLC Type 2. Because NetBEUI and SNA are legacy
> protocols, the use of LLC Type 2 is diminishing. However, it is still
> important to learn LLC Type 2 because WAN protocols, such as High-Level
> Data Link Control (HDLC) and Link Access Procedure on the D Channel
(LAPD),
> also known as ITU-T Q.921, are based on LLC Type 2. (Cisco's HDLC is
> non-standard and is not based on LLC Type 2, however. Cisco's HDLC is
> connectionless.)
>
> Do I have it backwards? Are HDLC and LAPD based on LLC2, or is it the
other
> way around? Any other lies you can pinpoint in my paragraph? I know it's a
> bit awkward still. I will polish it. ;-) Thanks for your help!
>
> Priscilla
>
> Thanks for your help!
>
> Priscilla
>
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
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