RFC681 - Network UNIX

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　　NWG/RFC# 681 JBP 14-MAY-75 14:38 32157
3/18/75 NETWORK UNIX S. Holmgren

NETWORK UNIX 1

RFC681 NIC 32157 2

INTRODUCTION 3

THE UNIX TIME-SHARING SYSTEM [1] PRESENTS SEVERAL INTERESTING

CAPABILITIES AS AN ARPA NETWORK MINI-HOST. IT OFFERS POWERFUL
LOCAL PROCESSING FACILITIES IN TERMS OF USER PROGRAMS, SEVERAL
COMPILERS, AN EDITOR BASED ON QED, A VERSATILE DOCUMENT
PREPARATION SYSTEM, AND AN EFFICIENT FILE SYSTEM FEATURING
SOPHISTICATED ACCESS CONTROL, MOUNTABLE AND DE-MOUNTABLE
VOLUMES, AND A UNIFIED TREATMENT OF PERIPHERALS AS SPECIAL FILES. 3a

THE NETWORK CONTROL PROGRAM (NCP), IS INTEGRATED WITHIN THE
UNIX FILE SYSTEM. NETWORK CONNECTIONS ARE TREATED AS SPECIAL
FILES WHICH CAN BE ACCESSED THROUGH STANDARD UNIX I/O CALLS; VIZ.
READ, WRITE, OPEN, CLOSE. SPECIAL FILES HAVE DIRECTORY ENTRIES
SIMILAR TO NORMAL FILES EXCEPT THAT CERTAIN FLAG BITS ARE SET.
THESE FLAG BITS CAUSE SYSTEM I/O ROUTINES TO TAKE SPECIAL ACTION.
IN UNIX, SPECIAL FILES SIGNIFY PERIPHERAL DEVICES. FOR EXAMPLE,
I/O TRANSACTION WITH MAGTAPE ZERO WOULD BE ACCOMPLISHED BY
ACCESSING THE SPECIAL FILE, "/DEV/MT0". FOR THE UNIX NETWORK
SYSTEM, ADDITIONAL SPECIAL FILES WERE CREATED EACH OF WHICH
SPECIFIES A HOST ON THE ARPA NETWORK. FOR EXAMPLE
"/DEV/NET/HARV" REPRESENTS THE PDP-10 AT HARVARD. THIS SIMPLE
ACCESS MECHANISM, THROUGH THE FILING SYSTEM, ALLOWS STANDARD ARPA
PROTOCOLS SUCH AS TELNET AND FTP TO BE IMPLEMENTED AS
SWAPPABLE USER PROGRAMS, RESIDENT ONLY WHEN NEEDED. FURTHERMORE,
A USER MAY WRITE HIS OWN PROGRAMS TO COMMUNICATE WITH THESE
SPECIAL FILES JUST AS THE TELNET PROGRAM DOES. THE SAMPLE
PROGRAM FOUND BELOW DEPICTS THE ESSENTIALS OF NETWORKING FROM
UNIX. 3b

STANDARD I/O 4

TO PRESENT THE BASIC PROPERTIES OF UNIX I/O, THE READ, WRITE,
OPEN, AND CLOSE FUNCTION CALLS ARE SUMMARIZED BELOW. EACH CALL
MAY RESULT IN AN ERROR CODE OF MINUS ONE. 4a

TO MANIPULATE AN EXISTING FILE WITH READS OR WRITES, IT MUST
FIRST BE OPENED WITH THE FOLLOWING CALL: 4b
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FILEDES = OPEN( "ANYFILENAME",FLAG ) 4b1

WHERE "ANYFILENAME" IS THE ARBITRARY NAME OF THE FILE TO BE
OPENED. THE SECOND PARAMETER INDICATES WHETHER THE FILE IS TO BE
READ, WRITTEN, OR UPDATED. THE RETURNED VALUE "FILEDES", IS
CALLED A FILE DESCRIPTOR. IT IS AN INTEGER USED TO IDENTIFY THE
FILE IN SUBSEQUENT CALLS TO READ AND WRITE. 4c

ONCE A FILE HAS BEEN OPENED, THE FOLLOWING CALLS MAY BE USED: 4d

NBYTES = READ( FILEDES,BUFFER,COUNT );
NBYTES = WRITE( FILEDES,BUFFER,COUNT ); 4d1

COUNT IS THE NUMBER OF BYTES TO BE TRANSMITTED BETWEEN THE
FILE REPRESENTED BY 'FILEDES' AND THE BYTE ARRAY REPRESENTED BY
'BUFFER'. NBYTES IS THE NUMBER ACTUALLY TRANSMITTED. FOR THE
READ CALL, 'NBYTES' MAY BE ZERO TO INDICATE THE END OF FILE; IN
EITHER CASE, MINUS ONE WILL BE RETURNED IF THERE WAS AN ERROR. 4e

FOR EACH OPEN FILE, THE SYSTEM MAINTAINS A POINTER TO THE NEXT
BYTE TO BE READ OR WRITTEN. IF N BYTES ARE TRANSMITTED, THE
POINTER ADVANCES N BYTES. DATA WRITTEN TO A FILE AFFECT ONLY
THOSE BYTES IN THE FILE WHICH ARE INDICATED BY THE POSITION OF
THE WRITE POINTER AND THE COUNT; NO OTHER PART OF THE FILE IS
CHANGED. IF THE SYSTEM POINTER INDICATES THAT ANY BYTES BEING
WRITTEN WOULD LIE BEYOND THE END OF THE FILE, THE FILE IS
ENLARGED AS NEEDED. 4f

ONCE THE USER HAS FINISHED PROCESSING A FILE, IT SHOULD BE
CLOSED. THIS IS AFFECTED WITH THE FOLLOWING CALL: 4g

CLOSE( FILEDES ); 4g1

ALTHOUGH IT IS NOT ABSOLUTELY NECESSARY TO DO A SPECIFIC CLOSE
ON A FILE WHEN FINISHED, (THE SYSTEM CLOSES ALL FILES WHEN A
PROGRAM EXITS), IT IS A GOOD PRACTICE, SINCE THE USER IS
ALLOWED ONLY SIXTEEN OPEN FILES. 4h

THERE ARE SEVERAL ADDITIONAL SYSTEM CALLS RELATED TO I/O WHICH
WILL NOT BE DISCUSSED IN DETAIL. A FEW OF THE MORE NOTABLE ONES
ALLOW THE USER TO: GET THE STATUS OF A FILE, CHANGE THE
PROTECTION OR OWNERSHIP OF A FILE, CREATE A FILE, CREATE A
DIRECTORY, MAKE A LINK TO AN EXISTING FILE, AND DELETE A

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FILE. FOR FURTHER INFORMATION CONCERNING THE DIFFERENT I/O
CALLS THE READER IS DIRECTED TO THE UNIX PROGRAMMER'S MANUAL,
FIFTH EDITION, K. THOMPSON, AND D. M. RITCHIE, JUNE 1974. 4i

THE USER COMMUNICATES WITH THE NETWORK VIA THESE SAME SYSTEM
CALLS. FOR EXAMPLE, IF ONE WISHED TO CONNECT TO THE THE PDP-10
AT HARVARD, THE FOLLOWING SEQUENCE OF CALLS MIGHT BE USED. 4j

FILEDES = OPEN( "/DEV/NET/HARV",2 );
IF( FILEDES < 0 )
PRINTF(" HARVARD IS DEAD");
ELSE
WHILE( (NBYTES=READ(FILEDES,BUF,80)) > 0 )
WRITE( 0,BUF,NBYTES ); 4j1

THE OPEN INSTRUCTS THE SYSTEM TO OPEN A TELNET CONNECTION TO
HARVARD, IF MINUS ONE IS RETURNED, THE PROGRAM PRINTS A MESSAGE
AND EXITS, OTHERWISE THE PROGRAM WILL READ ANY BYTES SENT BY
HARVARD AND PRINT THEM OUT ON THE CONTROLLING TELETYPE. THIS WILL
GO ON UNTIL HARVARD CLOSES THE CONNECTION (READ WILL RETURN
MINUS ONE WHEN THE CONNECTION IS CLOSED). 4k

UNIX TELNET 5

IN ORDER TO COMMUNICATE WITH REMOTE HOSTS ON THE ARPA
NETWORK, ONE FIRST LOGS IN TO UNIX AS A NORMAL USER. THE USER
THEN RUNS A PROGRAM, TELNET, WHICH AFTER ANNOUNCING ITSELF LEAVES
HIM WITH SEVERAL OPTIONS. 5a

HE MAY CONTINUE WITH HIS NORMAL UNIX ACTIVITIES. WHEN TELNET
SEES A UNIX COMMAND, IT WILL INITIATE THE REQUEST AS A
PARALLEL TASK, IN THE SAME MANNER AS THE UNIX COMMAND PROCESSOR
(THE SHELL). SINCE THIS MAY BE DONE REGARDLESS OF WHETHER OR NOT
A NETWORK CONNECTION IS OPEN, THE USER MAY SIMULTANEOUSLY RECEIVE
OUTPUT FROM A FOREIGN HOST'S SERVER TELNET AND CONVERSE WITH THE
LOCAL UNIX SYSTEM. 5b

WHEN THE TELNET-USER OPENS A CONNECTION, TELNET ACCEPTS THE
HOST NAME AND ANY SPECIAL PARAMETERS, AND DOES AN OPEN ON THE
SPECIAL FILE CORRESPONDING TO THAT HOST. WHEN CONTROL IS
RETURNED, THE CONNECTION IS OPEN. ANY FURTHER DATA RECEIVED
FROM THE TERMINAL NOT CONTAINING ESCAPE CHARACTER IS SENT TO THE

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NETWORK FILE. ANY DATA RECEIVED IN RESPONSE TO A READ ON THE
NETWORK FILE, IS WRITTEN ON THE USER'S TYPEWRITER. 5c

COMMUNICATION CONTINUES WITH THE HOST UNTIL THE USER WISHES
TO CLOSE THE CONNECTION. THE USER SIMPLY MAKES THIS KNOWN TO
TELNET VIA A COMMAND, AND TELNET DOES A STANDARD CLOSE ON THE
NETWORK FILE. THE NEGOTIATION OF CLOSING THE NETWORK CONNECTION
IS LEFT TO THE SYSTEM, FREEING THE USER FOR OTHER COMPUTATIONAL
WORK. 5d

THERE IS SOME CHARACTER TRANSLATION AND INVISIBLE CONTROL
INFORMATION PASSED BACK AND FORTH BETWEEN THE FOREIGN HOST AND
THE TELNET PROCESS. THIS INVOLVES RECOGNITION OF TELNET IACS AND
THE TRANSLATION OF CARRIAGE RETURN(CR) AND LINE FEED(LF) TO LINE
FEED ON ALL DATA RECEIVED FROM THE NETWORK, AND THE INVERSE
TRANSLATION OF LF TO CR LF ON ALL DATA SENT TO THE NETWORK. 5e

NCP STRUCTURE 6

DUE TO THE STRUCTURE OF BOTH THE IMP TO HOST[2] AND HOST TO
HOST[3] NETWORK PROTOCOLS, DATA COMES FROM THE NETWORK
DESTINED NOT ONLY FOR ONE OF MANY ACTIVE PROCESSES, BUT FOR
THE INFORMATION OF THE LOCAL HOST AS A WHOLE. FOR EXAMPLE,
NETWORK TRAFFIC SUCH AS A HOST TO HOST RESET, WHICH GENERALLY
SIGNALS THAT A FOREIGN HOST HAS COME "ALIVE" MUST BE ACKNOWLEDGED
TO LET THAT HOST KNOW THAT THE LOCAL HOST ITSELF IS "ALIVE".
THEREFORE, THE LOCAL HOST MUST MONITOR DATA COMING FROM THE NET
TO PERFORM NOT ONLY A MESSAGE SWITCHING FUNCTION, WHICH IS THE
BULK OF NETWORK TRAFFIC, BUT TO PROVIDE A CONTROL AND STATUS
FUNCTION. 6a

FURTHER, WHEN A PERSON ASSOCIATED WITH THE LOCAL HOST WISHES
TO CARRY ON A CONVERSATION WITH A NETWORK SERVER, THE INITIAL
CONNECTION PROTOCOL[4] MUST BE USED TO PROVIDE A LOGICAL PORT
AT EACH SITE FOR SUCCEEDING INFORMATION FLOW. 6b

EXPERIENCE WITH THE ANTS MARK I[5] AND ANTS MARK II[6] SYSTEMS
HAS SHOWN THAT THE ABOVE CLASSES OF NETWORK EVENTS ARE
RELATIVELY INFREQUENT, AND THAT MOST NETWORK TRAFFIC IS IN TERMS
OF USER DATA FLOW AND THE ASSOCIATED FLOW CONTROL( HOST TO HOST
ALLOCATES AND IMP TO HOST RFNMS). IT IS ALSO THE CASE THAT THE
SOFTWARE REQUIRED TO IMPLEMENT THE STATUS AND CONTROL FUNCTION IS
THE BULKIEST PART OF AN NCP. 6c

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IN UNIX, THE KERNEL OF THE OPERATING SYSTEM IS CORERESIDENT
AND NON-SWAPPABLE. A LARGE KERNEL REDUCES THE MEMORY AVAILABLE
FOR USER PROGRAMS. THUS IT IS DESIRABLE TO MINIMIZE THE
AMOUNT OF CODE ADDED TO THE BASIC UNIX KERNEL FOR THE NCP. FOR
THIS REASON, THE NCP IS IMPLEMENTED IN TWO PARTS. ONE PART IS
ROOTED IN THE KERNEL AND MAKES UP THE NON-SWAPPABLE SECTION,
ABOUT 3.5K WORDS OF CORE. THE OTHER SECTION (CALLED THE NCP
DAEMON) DEALS WITH USER REQUESTS TO OPEN AND CLOSE CONNECTIONS
AND HANDLES THE STATUS TRAFFIC DESCRIBED ABOVE. THE NCP DAEMON
RUNS AS A SWAPPABLE USER PROCESS OF ABOUT 8.5K WORDS IN SIZE, AND
COMMUNICATES WITH THE KERNEL VIA A SPECIAL FILE. 6d

HARDWARE AND SOFTWARE REQUIREMENTS 7

THE NETWORK SOFTWARE FOR UNIX WAS DEVELOPED ON A
PDP-11/50, WITH MEMORY MANAGEMENT, TWO RK05 DISK PACKS, TWO NINE
TRACK MAGTAPE DRIVES, FOUR DECTAPE DRIVES, 32K WORDS OF CORE, AND
THREE TERMINALS. PRESENTLY THIS HAS BEEN EXPANDED TO ENCOMPASS A
DH11 TERMINAL MULTIPLEXOR, AN RP03 MOVING HEAD DISK, A TWIN
PLATTER RF11 FIXED HEAD DISK, FLOATING POINT, AND 48K OF CORE.
USER FILES ARE STORED ON THE RP03. THE RF11 IS USED AS A SWAP
DISK AND FOR TEMPORARY FILE STORAGE; ONE RK05 PLATTER CONTAINS
THE SYSTEM FILES, AND THE SECOND CONTAINS LOGIN AND ACCOUNTING
INFORMATION. IN THE NEAR FUTURE, THE SYSTEM WILL BE EXPANDED TO
128K WORDS OF CORE MEMORY WITH 10 DIAL IN AND 10 HARD WIRED
TERMINAL LINES. 7a

THE BASE OPERATING SYSTEM OCCUPIES 24.5K WORDS OF MEMORY. THIS
SYSTEM INCLUDES A LARGE NUMBER OF DEVICE DRIVERS, AND ENJOYS A
GENEROUS AMOUNT OF SPACE FOR I/O BUFFERS AND SYSTEM TABLES. A
MINIMAL SYSTEM WOULD REQUIRE 40K WORDS OF HARDWARE MEMORY. IT
SHOULD BE NOTED THAT UNIX ALSO REQUIRES THE MEMORY MANAGEMENT
OPTION OFFERED BY DEC TO RUN AT ALL. 7b

THE BASE OPERATING SYSTEM WAS DEVELOPED BY BELL LABORATORIES
IN MURRAY HILL, NEW JERSEY. THE BELL INSTALLATION SUPPORTS A
HIGH SPEED PAPER TAPE READER-PUNCH, NINE-TRACK MAGNETIC TAPE,
AND DECTAPE. BESIDES THE CONSOLE TERMINAL, THERE ARE 14
VARIABLE SPEED COMMUNICATION DATASETS, AND A 201 SERIES DATASET
FOR SPOOLING PRINTOUT TO A COMMUNAL LINE PRINTER. THERE ARE ALSO
SEVERAL ONE-OF-A-KIND DEVICES INCLUDING A VOICE RESPONSE UNIT, A
VOICE SYNTHESIZER, A PHOTOTYPESETTER, A DIGITAL SWITCHING

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NETWORK, AND A SATELLITE PDP-11/20 WHICH GENERATES VECTORS,
CURVES, AND CHARACTERS FOR A TEKTRONIX 611 STORAGE-TUBE DISPLAY. 7c

RELIABILITY 8

AS OF THIS WRITING, NETWORK UNIX HAS BEEN RUNNING ON A FULL
TIME BASIS FOR ABOUT FOUR WEEKS. DURING THAT PERIOD, THERE WERE
BETWEEN THREE AND FOUR CRASHES A DAY. THIS IS NOT A VALID
INDICATOR BECAUSE MANY OF THE FAILURES WERE DUE TO HARDWARE
COMPLICATIONS. MORE RECENTLY THE HARDWARE HAS BEEN RE-CONFIGURED
TO IMPROVE RELIABILITY AND THE CRASH RATE HAS BEEN REDUCED TO ONE
A DAY WITH A DOWN TIME OF 2-3 MINS. THIS IS EXPECTED TO
CONTINUE, BUT THE SAMPLING PERIOD HASNT BEEN LONG ENOUGH FOR ANY
DEPENDABLE ANALYSIS. 8a

AVAILABILITY 9

ALTHOUGH THE UNIX NETWORK SOFTWARE WAS DEVELOPED WITHOUT ARPA
SUPPORT, THE CENTER FOR ADVANCED COMPUTATION IS WILLING TO
PROVIDE IT GRATIS TO THE PEOPLE OF THE ARPA COMMUNITY. 9a

HOWEVER BELL LABORATORIES MUST BE CONTACTED FOR A LISCENSE TO
THE BASE SYSTEM ITSELF. BELL'S POLICY IN THE PAST HAS BEEN TO
LISCENSE THE SYSTEM TO UNIVERSITIES FOR A NOMINAL FEE,
$150.00, AND UNFORTUNATELY FOR A COST OF $20,000.00 TO
"NONUNIVERSITY" INSTITUTIONS. 9b

IN THIS LIGHT BELL WAS APPROACHED TO SEE WHAT THEIR REACTION
WOULD BE TO AN ARPA NETWORK WIDE LISCENSE, THEY SAID THEY WERE
OPEN TO SUGGESTIONS IN THAT AREA. SO SHOULD ENOUGH PEOPLE
BECOME INTERESTED, PERHAPS A LESS EXPENSIVE FEE CAN BE
NEGOTIATED. 9c

INTERESTED USERS WHO HAVE EITHER SOURCE LISTINGS OR SOURCE
FILES INCLUDE: 9d

THE RAND CORPORATION WHICH IS USING OUR IMPLEMENTATION AS A BASIS
FOR THEIR OWN VERSION. 9e

LINCOLN LABORATORIES WHICH HAS A SOURCE LISTING TO BE USED AS
AN AID IN EVALUATION OF THE UNIX SYSTEM. 9f

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THE INCO CORPORATION OF MC LEAN VIR. HAS A LISTING TO HELP IN
THE INSTALLATION OF AN NCP INTO DEC'S RSTS OPERATING SYSTEM. 9g

IN ANY CASE WE ARE WILLING TO HELP ANY GROUP WITH ACQUISITION
OF A SYSTEM. 9h

FOR FURTHER INFORMATION CONCERNING THE SYSTEM CONTACT: 9h1

STEVE HOLMGREN
210 ADVANCED COMPUTATION BLDG.
UNIVERSITY OF ILLINOIS
URBANA ILLINOIS 61801

(217)-333-8469
OR
HOLMGREN AT BBN

OUTLOOK AND FUTURE PLANS 10

WITH THE ADVENT OF TELNET IN UNIX, CURRENT PLANS ARE TO RUN THE
SYSTEM OVER THE NEXT ONE OR TWO MONTHS AND WORK OUT ANY
REMAINING BUGS. WHILE THIS IS GOING ON, EXTENSIVE BANDWITH AND
LOAD TESTING IS GOING TO TAKE PLACE AND ANY REASONABLE
IMPROVEMENTS MADE. 10a

AFTER TELNET HAS PROVED ITSELF RELIABLE, THE OPEN SYSTEM CALL
WILL BE EXPANDED TO INCLUDE FURTHER PARAMETERIZATION. THIS
PARAMETERIZATION WILL ENCOMPASS CONNECTIONS TO SPECIFIC SOCKETS,
SIMPLEX CONNECTIONS BASED ON A SOCKET ALREADY IN USE, AND THE
ABILITY TO LISTEN ON A LOCAL SOCKET. 10b

AFTER THOSE EXTENSIONS, NET MAIL, THEN NETWORK FTP AND FINALLY
NETWORK RJE WILL BE IMPLEMENTED. ALL WILL RUN AS USER
PROGRAMS SO THE KERNEL SYSTEM SIZE WILL NOT INCREASE. 10c

THERE IS ALSO INTEREST IN IMPLEMENTING SOME OF THE PROCEDURE
CALL PROTOCOL BEING DEVELOPED BY THE NATIONAL SOFTWARE WORKS,
BUT NO DEFINATE PLAN HAVE BEEN MADE. 10d

ACKNOWLEDGEMENTS 11

I AM MUCH INDEBTED TO GARY GROSSMAN WHO PARTICIPATED IN THE
DESIGN AND WROTE THE NCP DAEMON; AND TO STEVE BUNCH WHO WAS THE

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THE THIRD MEMBER OF OUR DESIGN GROUP AND WROTE THE KERNEL
MESSAGE SOFTWARE. 11a

THE THREE OF US ARE PARTICULARLY APPRECIATIVE OF THE CRITICISM
AND SUPPORT OF DR. HUGH FOLK, DR. PETER ALSBERG, GREG
CHESSON, JOHN MULLEN, KARL KELLEY AND DAVE HEALY. 11b

REFERENCES 12

1. UNIX TIME-SHARING SYSTEM
KEN THOMPSON AND DENNIS RITCHIE
COMMUNICATIONS OF THE ACM
JULY 1974, VOL 17, NUMBER 7 12a

2. SPECIFICATIONS FOR THE INTERCONNECTION OF A
HOST TO AN IMP
REPORT NO. 1822 BOLT BERANEK AND NEWMAN INC.
CHAPTER 3, SYSTEM OPERATION 12b

3. HOST/HOST PROTOCOL FOR THE ARPA NETWORK
ALEX MCKENZIE, BBN
NIC DOCUMENT 8246 12c

4. OFFICIAL INITIAL CONNECIION PROTOCOL
DOCUMENT #2
J. POSTEL, UCLA-NMC
NIC DOCUMENT 7101 12d

5. ANTS MARK I USER'S GUIDE
KARL KELLEY
CENTER FOR ADVANCED COMPUTATION 2/1/74 12e

6. ANTS MARK TWO SYSTEM
KARL KELLEY
CENTER FOR ADVANCED COMPUTATION 1/10/74 12f

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