Browse Prior Art Database

Maintaining Fairness With Priority Tokens in ECL Environment

IP.com Disclosure Number: IPCOM000046488D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 25K

Publishing Venue

IBM

Related People

Sy, KK: AUTHOR

Abstract

This article describes a procedure which allows stations with different types of priorities to be connected to a ring-type local area network, hereinafter called an established communication link (ECL). The procedure further insures that low priority stations are not shut out from transmitting on the ring by other low priority stations.

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 57% of the total text.

Page 1 of 3

Maintaining Fairness With Priority Tokens in ECL Environment

This article describes a procedure which allows stations with different types of priorities to be connected to a ring-type local area network, hereinafter called an established communication link (ECL). The procedure further insures that low priority stations are not shut out from transmitting on the ring by other low priority stations.

Fig. 1 shows a schematic for an established communication link network. Data is transmitted in the direction shown by the arrow. A and B represent normal nodes, C represents an asynchronous node, D represents a synchronous server, and E and F represent synchronous nodes.

The order of node priorities is as follows:

(a) Synchronous (sync) node

(b) Asynchronous (async) node

(c) Normal node

Fig. 2 shows the structure or format of a frame called the physical controlled field (PCF). This frame traverses the loop and informs each station (based on priority) when a slot is available to transmit data. The bits in the PCF are interpreted as follows: P1, P2 = priority bits

T = token

C = monitor count

R1R2 = reservation bits

X = reserved

S = signaling

In operation, a sync node will transmit only if it sees a sync- free token (P1, P2 = 1,1). An async node will transmit if it sees the following: (a) A normal free token (P1, P2 = 0,0). In this case

the async node will act like a normal node.

(b) An async-free token (P1, P2 = 0,1).

A normal node will transmit only if it sees a normal-free token (P1, P2 = 0,0).

Assume A and B are normal nodes, C is an async node, D is a sync server, and E and F are sync nodes. Assume also that A is transmitting and the normal node B is waiting to transmit. Without priority capabilities after A completes transmission, the token is passed to B for transmission. However, assume that C is a priority node and requires service. C will intercept the busy token frame (Fig.
2), and will turn on the priority reservation request as follows...