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Token-Ring Reservation Enhancer for Early Token Release

IP.com Disclosure Number: IPCOM000102647D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 5 page(s) / 166K

Publishing Venue

IBM

Related People

Lee, JK: AUTHOR [+3]

Abstract

Disclosed is a scheme which relieves the token reservation deficiency caused by the Early Token Release (ETR) protocol in the IEEE 802.5 LAN standard. One of the characteristics of the ETR ring is that token reservations may be lost if carried by a short frame.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Token-Ring Reservation Enhancer for Early Token Release

       Disclosed is a scheme which relieves the token
reservation deficiency caused by the Early Token Release (ETR)
protocol in the IEEE 802.5 LAN standard.  One of the characteristics
of the ETR ring is that token reservations may be lost if carried by
a short frame.

      Fig. 1 shows a block diagram of the Token Reservation Enhancer
(TRE).  Its main function is to save the reservation bits (bits 5, 6,
7 in the Access Control Field (ACF)) in the token whenever a station
uses the token to transmit.  When the transmit station releases its
token at the end of its last transmitted frame, it will release the
token with the saved reservation.  This allows the requested priority
token to be released to the requesting station.

      During a normal frame transmit or token release operation, all
the transmit data, namely delimiters, information field data, and ACF
of tokens, are multiplexed through the PMUX and parallel loaded into
the Transmit Data Serializer (TX Serializer).  The TX Serializer
changes the parallel data stream into a serial data stream and feeds
through the Input Data Selector (I-SEL) into the normal serial
transmit data path.  Path-1 is the normal repeat path.  Path-2 is the
priority delay path.  Path-3 is the monitor delay path.  The Output
Selector (O-SEL) will select one of the three paths depending on
which mode the transmitter is being configured.  The output of the
O-SEL will be converted from Transitional code to Differential
Manchester code by the Manchester Encoder (T/M).  The output of the
T/M will go through the front-end ring driver into the ring.

      The normal incoming ring data, after being converted from
Differential Manchester code to Transitional code by T/M, is fed back
to the serial input of the TX Serializer. The 16-bit TX Serializer
will shift out the parallel transmit data and, at the same time,
shift in the feedback ring data behind the transmit data.  This makes
up a storage element for the ring input data and also enables the
hardware to save the token reservation bits to perform the TRE
function.  The timing is arranged in such a way that when the
Transmit State Machine (TXSM) sees a usable token and gets ready to
transmit, the token reservation bits are in the TX Serializer.  In
order to save the reservation bits, the PH hardware loads the
necessary bits from the TX Serializer to the Fire Token Register
(FTOK REG).  At the end of the frame transmit ope ration, when the
transmitter is ready to release the next token, the TXSM will
multiplex the contents of the FTOK REG to form the ACF of the next
token.  In this way, the original reservation of the used token is
preserved and the priority control algorithm will eventually generate
the reserved priority token to honor the reserving station.

      Fig. 2 illustrates the operation of the TRE in a ring with
three stations (STA-1, STA-2, and STA-3).

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