Dynamic ISDN Data Link Control/Synchronous Data Link Control Protocol Protocol Recognition and Initialization for the ISDN B-CHL
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Fisher, ME: AUTHOR [+3]
A method is disclosed for dynamically recognizing the Synchronous Data Link Control (SDLC) or the ISDN Data Link Control (IDLC) protocol on an ISDN B-channel. The method further describes how one side of the B-channel protocol can begin communicating with the recognized protocol.
Dynamic ISDN Data Link Control/Synchronous Data Link
Protocol Recognition and Initialization for the ISDN B-CHL
A method is
disclosed for dynamically recognizing the
Synchronous Data Link Control (SDLC) or the ISDN Data Link Control
(IDLC) protocol on an ISDN B-channel. The method further describes
how one side of the B-channel protocol can begin communicating with
the recognized protocol.
this invention attempts to solve is how to add
support for SDLC or IDLC to a device that currently supports only one
of these protocols, but with minimal changes to the upper layers of
software and minimal or no customer configuration.
is to create a software layer under, or inside of,
the existing IDLC or SDLC layer that will do the following:
recognize whether the protocol is primary SDLC,
negotiable SDLC, secondary SDLC or IDLC.
2. If the
recognized protocol is not directly supported, provide
appropriate conversions. For example:
protocol is SDLC, but software supports only IDLC,
then automatically convert received SDLC frames to IDLC
primitives before sending the data to the higher layer software;
automatically send SDLC frames when given IDLC primitives. (The
details of this step are not addressed here.)
recognition procedure will now be described in
detail, using the example of a device with software that supports
distinguish a new IDLC entity that has implemented the
protocol recognition algorithm described here, the term IDLC is
For an IDLC'
entity to recognize the protocol to which it is
attached, it must do the following:
I -- Recognize if the Remote is an IDLC' Entity
o The local IDLC'
entity must first send a frame that can only be
recognized by another IDLC' entity. This frame will be called
the IDLC' recognition frame and the local IDLC' entity should
start the IDLC response timer after it sends the frame. The
frame may be a two-byte "SDLC" frame with an address of zero,
X'00', (the "no stations" SDLC address) and a second byte that
will arbitrarily be defined as an IDLC Unnumbered Information
(UI) command control byte, X'13', (an invalid SDLC control byte).
o If the remote
protocol is SDLC, it should discard the frame
because '00'X is the "no stations" address.
o If the remote
protocol is IDLC, the frame will be too short and
will also be discarded.
o Only if the
remote protocol is IDLC', will it recognize the
frame. If the remote protocol is IDLC', it will also have sent
an IDLC' recognition frame. The receipt of an IDLC' recognition
frame immediately before or after having sent an IDLC'
recognition frame may be interpreted as the the correct IDLC'
response. Recognition is now c...