Browse Prior Art Database

Concurrent Host Communication Link Status Change Handling

IP.com Disclosure Number: IPCOM000108660D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 94K

Publishing Venue

IBM

Related People

Manka, R: AUTHOR [+3]

Abstract

A method for the IBM 3174 Establishment Control Unit to inform a Distributed Function Terminal (DFT) device of status changes to one or more of the physical communications links to which the device may be attached in a Concurrent Host Communications environment is described. This method requires no microcode changes to the DFT, yet allows it to have multiple sessions with a multiplicity of SNA hosts.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Concurrent Host Communication Link Status Change Handling

       A method for the IBM 3174 Establishment Control Unit to
inform a Distributed Function Terminal (DFT) device of status changes
to one or more of the physical communications links to which the
device may be attached in a Concurrent Host Communications
environment is described.  This method requires no microcode changes
to the DFT, yet allows it to have multiple sessions with a
multiplicity of SNA hosts.

      The 3174-to-DFT interface specifies that communication (comm)
check reminders (e.g., idle line timeout, non-productive timeout,
etc.) are to be passed to the DFT with an identifier that addresses
the physical display rather than a particular logical terminal (LT).
In the Concurrent Host Communications environment, if one or more of
the physical communications links were to go into a check condition,
the 3174 could not use the standard technique of device notification.
The DFT (not knowing more than one link exists) would interpret the
standard status to mean that all LTs in the DFT are unable to
communicate, which is not necessarily true since the other links
could be operational.

      There are no existing Controller-to-DFT interface commands
which can be used to pass the same semantic meaning as a comm check.
The 3174 will map the comm check into a 3174-generated SNA Deactivate
Logical Unit (DACTLU).  The 3174 will also generate other SNA request
units (RUs) to keep the host up to date as concerns the DFT's status
once the communication link returns to normal.  Since the DACTLU will
deactive the SNA session and the comm check can be transient, the
3174 will not issue the DACTLU until the DFT initiates a sequence
which would result in the use of the communications link which is not
operational.

      The following finite state machine is defined for each LT on
each physical link to describe the action to take based on the
variety of input conditions.

      Table 1.  DACTLU_state FSM
      state number                  1         2         3
      state name                  RESET     DACTLU    DACTLU
      inputs                               pending     sent
comm check reminder               2(a)       --        --
Enter or PF key               ...