Browse Prior Art Database

METHOD OF FLOW CONTROL RECOVERY FOR A DATA LINK LAYER

IP.com Disclosure Number: IPCOM000008672D
Original Publication Date: 1998-Jun-01
Included in the Prior Art Database: 2002-Jul-02
Document File: 2 page(s) / 94K

Publishing Venue

Motorola

Related People

Tim Spets: AUTHOR [+3]

Abstract

In connection oriented HDLC protocol, an endpoint notifies its peer of a change in local node flow control condition through the exchange of supervisory frames. Procedures mandate that is the responsibility of the local node to keep the remote node apprised of the changes.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 2

MOTOROLA Technical Developments

@

METHOD OF FLOW CONTROL RECOVERY FOR A DATA LINK LAYER

by Tim Spets, Ken Wollack and Karen Brailean

  In connection oriented HDLC protocol, an endpoint notifies its peer of a change in local node flow control condition through the exchange of supervisory frames. Procedures mandate that is the responsibility of the local node to keep the remote node apprised of the changes.

NORMAL FLOW CONTROL

  When the local node initially enters a change in flow control state, the local node sends either the RR or RNR frame to notify the peer. The local node can choose to use the poll/final mechanism to insure the receipt of this information. Additionally the local node may employ persistence, i.e. repetitive retransmissions with associated time-outs, over error prone mediums.

THE PROBLEM

  In a system where a data link layer transmission medium is over a shared RF resource (error prone medium), limiting unnecessary transmissions is critical to increasing throughput. The use of polling from the local node for changes in flow control state may cause extra messaging in the case where the remote peer has no data to send.

THE SOLUTION

  Rather than the local node being responsible for the notifications of flow condition changes the responsibility is shifted to the remote peer. This new approach uses a new frame called an 'IsRR' frame within the flow control mechanism. The remote peer will start an 'IsRR' timer only when receiving an RNR command. The IsRR timer upon expiration will ONLY poll the local node if there is data ready to send. Using an "Is your Receiver Ready (IsRR)" message, the remote peer will solicit an RR or RNR response from the local node so the transmitter

can stay in sync.

TRANSMllTlNG ENDPOINT (REMOTE PEER) PROCEDURES

1. If the Transmitting endpoint receives the RR command at any time, it will stop the IsRR timer (if it was previously in...