Jim Breen's HDLC (High-Level Data-link Control protocol) Server
This server uses a program I wrote back in 1991 as a teaching aid to
demonstrate the operation of the Asynchronous Balanced Mode (ABM)
version of the HDLC communications protocol. ABM is the mode of HDLC
that is used in many areas
of communications. It is the basis for LAP-B in X.25, IS8802 in
LANs, LAP-D in ISDN, LAP-M in GSM, HDLC framing in PPP, etc. The basic
concepts are closely related to the recovery and flow control mechanisms
My original program was called ABMDEMO and was released as a DOS
executable. Copies are still hanging around freeware archives. The
server simply wraps CGI operation around the ABMDEMO program. Click here for an explanation of the fields in the
The server simulates the exchange of frames between DTE-A and DTE-B on a
full-duplex synchronous link. The user provides the basic parameters for
each DTE and the length of the simulation.
Note: The value of the ACK timer is set to 30 clock ticks.