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Protocol experiment (RFC0700)

IP.com Disclosure Number: IPCOM000003746D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2000-Sep-13
Document File: 6 page(s) / 15K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

E. Mader: AUTHOR [+3]

Abstract

In early February, 1974 the main line printer on BBN's TENEX system failed and it was decided to use the PDP-11 line printer via the ARPANET both for the direct purpose of obtaining listings and also the indirect purpose of studying network protocols.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 19% of the total text.

NWG/RFC 700 August 1974

NIC 31020

INWG Experiments Note 1

A Protocol Experiment

Eric R. Mader

William W. Plummer

Raymond S. Tomlinson

I. Introduction

In early February, 1974 the main line printer on BBN's TENEX system

failed and it was decided to use the PDP-11 line printer via the ARPANET

both for the direct purpose of obtaining listings and also the indirect

purpose of studying network protocols.

II. The Basic Protocol

The design was based on the protocol described by Cerf and Kahn in INWG

Note #39. Familiarity with that document is assumed. The following is

a brief sketch of the protocol. Not all features described in this

section have been implemented. See Section VI.

At any instant, the sender has two pointers into the stream of bytes to

be sent. Bytes to the left of the LEFT pointer have already been sent

and acknowledged. Bytes in the "window" between the LEFT and RIGHT

pointers have been sent (zero or more times), but no indication of

successful transmission has been received. Bytes to the right of RIGHT

remain to be considered at some time in the future.

In operation the sender is constantly sending bytes from the input data

stream resulting in the RIGHT pointer advancing. Positive

acknowledgements produced by the receiver cause the LEFT edge of the

window to move towards the RIGHT edge.

LEFT and RIGHT are actually numerical byte positions within the data

stream. The low order 16 bits of RIGHT are sent with each message as a

sequence number so that the receiver can identify which part of the data

stream it is receiving in case messages are not received in the same

order they were transmitted. The receiver has a finite amount of buffer

space available in which it can reassemble an image of the data in the

transmitter's window. The receiver discards any messages which have

sequence numbers outside of its buffer area. However, messages to the

left of LEFT must be acknowledged even though they are discarded.

Otherwise, a lost ACK would cause the sender to retransmit (and the

receiver ingore) the message indefinitely. Messages received with bad

checksums are also discarded.

As "good" messages are received, the holes are filled in the receiver's

buffer and continuous segments at the left edge are passed to the

physical line printer (in our case). The receiver informs the sender of

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this action by sending an ACK (acknowledgement) message. This message

spe...