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Tenex NCP finite state machine for connections (RFC0689)

IP.com Disclosure Number: IPCOM000003736D
Original Publication Date: 1975-May-23
Included in the Prior Art Database: 2000-Sep-13
Document File: 5 page(s) / 13K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

R. Clements: AUTHOR

Abstract

TENEX NCP Finite State Machine for Connections Page 5

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 21% of the total text.

Request for Comments: 689 May 1975

NIC #32656

TENEX NCP Finite State Machine for connections

TENEX Memo Number 155

The attached figure describes the finite state machine used in TENEX

version 1.33 to implement the ARPANET Host to Host protocol. This

memo updates that of 27 August 1971, TENEX memo number 113, with

regard to the finite state machine. Other parts of that memo have

been incorporated into the JSYS manual and other documents.

TENEX NCP Finite State Machine for Connections Page 2

The components of a finite state machine (FSM) are States,

Events, and Actions. These are listed below:

States Events Actions

01 CLZD 00 RRFC 00 ANOP

02 PNDO 01 CLSR 01 AFNY

03 LSNG 02 CLSS 02 ACLS

04 RFCR 03 CLZR 03 ARFC

05 CLW1 04 CLZS 04 AOPB

06 RFCS 05 ACPT 05 AOPL

07 OPND 06 CONN 06 ACLL

10 CLSW 07 LISN 07 ACLO

11 DATW 10 RRFN 10 AEOR

12 RFN1 11 TIME 11 AEOS

13 CLZW 12 RRFB 12 AES1

16 FREE 13 AABT

14 ACKA

Note that there are two kinds of "close" events and actions: a close

at the JSYS level (CLOSF) and one at the host-to-host protocol level

(CLS). The names in the above list contain "CLS" if they are

concerned with host-to-host CLS, and CLZ if the are concerned with

CLOSF.

Each state will be briefly described below, along with events

which may occur while a connection is in that state, and actions which

are taken as the state is advanced.

A few overall notes: Actions are shown on the state diagram

following a "/''. Any transition without an action shown generates

"ANOP", a null action. The action "AFNY" means a "funny" event (i.e.,

one not expected in this state -- probably a bug) has occurred. The

result of this action is an IMPBUG error printout. Any event NOT

shown on the state diagram causes the state to loop back to itself and

an AFNY to be generated. These are not shown explicitly on the

diagram. Another "funny" event is the execution of an "accept" MTOPR

by the user program when the state is not RFCR. However, an errant

user program can do this, and no IMPBUG should be generated as a

result, so most states show a loop to self with no action (i.e., an

"ANOP") as a result of the ACPT event. The event "TIME" (also called

"HUNG") simply means that the socket has not changed state for a

specified time interval and may need to be prodded along. This time

is currently two minutes, except for connections in error states where

the FSM is stepped faster to clear the connection out.

State 16 - FREE - Free connection

A connection in this state has never existed, or is almost completely

deleted. No events are e...