Browse Prior Art Database

Link Access D-Channel Protocol Processor for Integrated Service Digital Network Data Link Control

IP.com Disclosure Number: IPCOM000107622D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 6 page(s) / 282K

Publishing Venue

IBM

Related People

Farrell, JK: AUTHOR [+4]

Abstract

Described is an implementation of a link access D-channel protocol (LAP-D) processor for the integrated service digital network (ISDN) for incorporation into integrated data link controller (IDLC) designs. The LAP-D processor is designed to improve subsystem performance by reducing microcode path length and interrupt processing at the data link control (DLC) layer. (Image Omitted)

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 25% of the total text.

Link Access D-Channel Protocol Processor for Integrated Service Digital Network Data Link Control

       Described is an implementation of a link access D-channel
protocol (LAP-D) processor for the integrated service digital network
(ISDN) for incorporation into integrated data link controller (IDLC)
designs.  The LAP-D processor is designed to improve subsystem
performance by reducing microcode path length and interrupt
processing at the data link control (DLC) layer.

                            (Image Omitted)

      The LAP-D processor is designed to off-load a microprocessor by
providing DLC functions of the LAP-D protocol, as follows:
       . Manage and update own stations link state variables (Vs, Va
and Vr).
       . Acknowledge (ACK) PEER I frames without microcode
intervention.
       . Manage own stations transmit window using a programmable K
value.
       . Suppress microcode interrupts for the S-frames received with
no new ACKs.
       . Manage T200 timer - enable/disable and reset.
       . Automatic issue 'REJECT' on detected NS error in I-Frame
from peer.
       . Timer recovery action - issue automatic poll to peer on T200
timeout and inhibit new I-Frame transmission.
       . Detect receiver buffer overflow - move to own station busy
state and transmit receiver not ready (RNR) to peer.
       . Supports clearing of own station busy state - TX RR to peer.
       . Detects peer station busy condition - inhibits new I-Frame
transmission.
       . Detects peer station busy condition clear - allows new
I-Frame transmission.

      Functions which are detected by the protocol processor but
require microcode management actions by the hardware and the next
actions expected to be taken by the microcode are listed and
described as follows:
       . Detection of NR error in either S-Frame or I-Frame - In the
case of an NR error, the hardware will not check for an NR error in
an I-Frame received.  The following actions will occur in the
hardware as a result of this error being detected.
        1. The microcode will be notified of this event by an
interrupt with the NR ERROR bit set.
        2. The T200-Timer will be disabled.
        3. The receivers hardware assist function will be disabled.
        4. The link state variables will not be updated.
        5. The transmitter will not be disabled since microcode could
re-enable it again prior to handling the NR error interrupt.
       . Unnumbered frame received while the receiver is in normal
mode - The same actions will take place as when an NR error is de
tected, as described above, except the microcode will be noti  fied
of this event by an interrupt with the un-numbered frame received bit
set which will occur before the microcode notifica  tion of item 1
above.
       . Timer recovery failure - The same actions will tak...