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Full-Memory Go-Back-N Protocol for Point-To-Multipoint Communication

IP.com Disclosure Number: IPCOM000042005D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 3 page(s) / 65K

Publishing Venue

IBM

Related People

Gopal, IS: AUTHOR [+2]

Abstract

A link protocol, designated the "Full-Memory Go-Back-N Protocol", is proposed for use in point-to-multipoint data communication operations. When any message in a sequence of messages is not successfully received by all intended recipients within a given time, as measured by a count of N successive messages in the transmitted sequence, there will be a retransmission of N messages, starting with the unsuccessful message, in the original order of transmission. This retransmission procedure is repeated as often as necessary until all messages originating at a transmitter are received without error by all receivers in the network. N is an arbitrarily selected number or "window size".

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Full-Memory Go-Back-N Protocol for Point-To-Multipoint Communication

A link protocol, designated the "Full-Memory Go-Back-N Protocol", is proposed for use in point-to-multipoint data communication operations. When any message in a sequence of messages is not successfully received by all intended recipients within a given time, as measured by a count of N successive messages in the transmitted sequence, there will be a retransmission of N messages, starting with the unsuccessful message, in the original order of transmission. This retransmission procedure is repeated as often as necessary until all messages originating at a transmitter are received without error by all receivers in the network. N is an arbitrarily selected number or "window size". The environment assumed herein consists of K+1 stations, one being the source station (transmitter) and the other K being destination stations (receivers). Data sent out by the transmitter is received simultaneously by all K receivers, which are constantly "listening" to the channel. All data is transmitted in the form of "messages" or clearly delimited blocks of information. Such messages have embedded in each of them a sequence number and a cyclic redundancy code (CRC). The sequence number uniquely identifies the message and its position in the sequence of messages being transmitted (the transmission sequence). The sequence number continually increases, and two consecutive messages in the transmission sequence always differ in sequence number by 1. The CRC enables each receiver to detect transmission errors. The transmitter expects to receive confirmation that every message has been correctly received by all K receivers, and a separate acknowledgement channel enables all receivers to provide this confirmation by transmitting acknowledgements back to the transmitter. Receiver operation is as follows: Upon receipt of a message, a receiver first checks the CRC to determine if any transmission errors have occurred. If they have, the receiver discards the message and waits for the next message transmission. If no errors are detected, the receiver sends a positive acknowledgement to the transmitter. Then it checks the message sequence number. If the sequence number is the one that it expects (l more than the sequence number of the last message accepted by it), it accepts the message and delivers it to the upper layers of the protocol. Otherwise, it discards the message and waits for the next message transmission. Fig. 1 is a flowchart of the receiver operation. It should be noted that a receiver may acknowledge some messages that it subsequently discards. This is important to ensure that the protocols do not get into deadlock situations. Transmitter operation is as follows: The transmitter sends messages...