Browse Prior Art Database

Unconditional Link Reset for Remote LAPB-Stations

IP.com Disclosure Number: IPCOM000106439D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 6 page(s) / 159K

Publishing Venue

IBM

Related People

Gervais, G: AUTHOR [+4]

Abstract

Remote stations connected to a host processor via a communication link based on the International Telegraph and Telephone Consultative Committee (CCITT) data link access procedure (LAPB), suffer from the constraint that there are no means for resetting the hardware in the station when its communications protocol controller is no longer operational. For example, a remote station such as a modem cannot be reset by the host processor when the modem's communications controller is in a hang condition. An example host interface to a remote station is shown in Fig. 1.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 44% of the total text.

Unconditional Link Reset for Remote LAPB-Stations

      Remote stations connected to a host processor via a
communication link based on the International Telegraph and Telephone
Consultative Committee (CCITT) data link access procedure (LAPB),
suffer from the constraint that there are no means for resetting the
hardware in the station when its communications protocol controller
is no longer operational.  For example, a remote station such as a
modem cannot be reset by the host processor when the modem's
communications controller is in a hang condition.  An example host
interface to a remote station is shown in Fig. 1.

      The mechanism and apparatus described herein provides a low
cost and simple method of using the existing point-to-point data link
signals and bypassing the communication protocol controller in the
remote station to achive an unconditional reset.

      The primary design goal was to define a remote link protocol
and associated generation and detection logic to perform a remote
Reset that was independent of the state of the remote link protocol
controller in the remote station.  The basic principle involves using
the abort and the idle data patterns as defined by the CCITT
recommendations to establish the remote reset controls.

      The remote station and host station shall use similar circuits
for generating and detecting remote reset events.  The usage of the
remote reset generator/detector is fully symmetrical.  The same logic
circuits can be used in both the host station and the remote station.
A block diagram of the remote reset generator/detector 'black box'
interconnect is shown in Fig. 2.  This is only one example of the
several possible implementations of the remote reset
generator/detector.

      A remote reset is initiated by a generator on the host station
which will send abort data frames to the remote station.  An abort
data frame is a data pattern which contains seven or more consecutive
binary '1' bits terminated by a binary '0' bit.  For the purpose of
remote reset, seven binary '1' bits shall be used.  To distinguish
the abort data frame used for remote reset from a normal abort frame,
the data pattern shall be sent a minimum of eight consecutive times.

      The remote reset is decoded on the remote station by a detector
circuit.  Once the remote station detects a remote reset it also
starts transmitting abort patterns to the host station.  This
feedback path is provided for two reasons:

1.  To indicate to the remote reset has been received by the remote
    station.

2.  To provide a simple remote link wrap mechanism to verify that the
    remote interface is operational.

When the host station detects eight consecutive abort frames, it
notifies the processor via an interrupt.  To reset the remote reset
latch on the remote station, a series of eight consecutive flag
patterns (B'01111110') must be transmitted by the host station.  The
generator on the host...