🚀 go-pugleaf

In article <1992Dec31.023213.21653@magnus.acs.ohio-state.edu> sgururaj@magnus.acs.ohio-state.edu (Sanjay R Gururaj) writes:
>Hi!
>
>Does anyone know what the difference is between SDLC (synchronous data
>link protocol) and HDLC (????)
>Any pointers to documentation on the above protocol would be appreciated.
>Thanks in advance.

Well, for a rough first cut, SDLC is mostly a subset of HDLC.  ISO
HDLC specifications include 3 general operating modes for HDLC,
NRM (Normal Response Mode), ARM (Asynchronous Response Mode) and
ABM (Asynchronous Balanced Mode), together with numerous options
within those modes.  Ignoring some of the bizarre varients of SDLC
(like ring mode operation), SDLC is a NRM subset of HDLC. HDLC/LAPB
which is one of the most common flavors of HDLC (used by X.25) is
an ABM version of HDLC.  In NRM HDLC (or SDLC) there is one "Primary"
Station and one or more "Secondary" stations.  The HDLC address is
used to identify the secondary involved in a transaction.  Commands
are always to a secondary and Responses are always from a secondary.
A secondary is only allowed to send responses when "polled" by the primary.
This means a command frame with the "Poll" bit set.  When the secondary
is finished talking to the primary, it sets the "Final" bit in the
last response frame sent to the primary.  The primary can now move on
to some other secondary.  In contrast, in an ABM version (like LAPB)
either end can issue a command or response frame at any time.  But
ABM HDLC is usually limited to point-to-point operation.

As for documents, there is an IBM document describing SDLC.  There
are a series of ISO documents for HDLC (sorry I'm at home and don't have
the references).

>sanjay gururaj

Art Berggreen

In article <1992Dec31.023213.21653@magnus.acs.ohio-state.edu>, sgururaj@magnus.acs.ohio-state.edu (Sanjay R Gururaj) writes:
>Hi!
>
>Does anyone know what the difference is between SDLC (synchronous data
>link protocol) and HDLC (????)

This is a basic data comm question.  The bigest difference off  the bat is
that SDLC can poll multible remote stations.   HDLC is used in point to point
connections.   In an HDLC connect both a Primary and secondary station exist
at both ends.  In SDLC One station is a Primary and all the rest are secondarys.
 



>Any pointers to documentation on the above protocol would be appreciated.
>Thanks in advance.

If you are writting a driver you will need to get a hold of 
ANSI X3.66-1979, "American National Standard fo advanced data 
communications protocol procedures (ADCCP).    This document will 
cover the standards for both HDLC and SDLC.

ISO has specific document on HDLC.  

IBM has has a General ref on SDLC, sorry I don't have the numbers right
off but they are easy to find.  


If you just need general information, most basic Data comm books cover 
bitsync.

  Don't Let the bits byte,

        Louis

>
>sanjay gururaj
>
>Please send reply to sgururaj@magnus.acs.ohio-state.edu