At>5tra~t
Mik.Wilbur 920 Dennis Drive Palo Alto CA 94303
This paPer describeS a teleco~mun1cation network Or1ented specificallY to_ard personal ~omputer
uSels. The e~phasls IS on technicdl aSPects of the network, tne paper also briefly discusses the motlvatino co~s1detatlons and some economic, social and legal aspects of su~h a net. Profit by mi experience with computer communicat10n and my thouontb on hOw we coula brlng Some of 1ts faCilities into the world ot perSOnal computers.
The motlvatln? l~eas were the subject of my Byte article and are brletly summarized here. GOOd
Communl~ation can tacilltate tree prOqram Sharing, al10wlno a community at ~sers to build on the work Of an authOr and then become authors themselves.
~oOd co~~unlcation can also let a product"S prOSpective buyerS profit by the experience of tne product"s former buyers. If the ~ommunlcatlon
tacllitles are decentrallzed, then 1t IS nard for a PeOPle have opened time sharing serv1ces oriented to.ard perSchal COmputer users. Traditionally, these time sh~rlnu houses have offered strictly computatinnal services, sucn as games, cross Comptlers ari microProcessor sl~ulatlon Proqrams.
Add1tionally, thoUqh, these COncerns could otter a
CI~ss Of services ~hlch ~e ~ould call a "eom~unity 'ntorm~tion ~xchanoe·, a computeriZed vers10n Of bulletin hOards, yelloN pages and mailboxeS. (The feasibllltv netor. attempting to enlist the support Of the peo~le runnln~ tne host.
The ld~~ ot Inter~st nere 15 an outgrowth of the Dasic notion at ~ CI~: since the perSOnal comPuter
community is wideli d1spersed geOgraPhiCally, It can greatlY Denet1t from a dispersed CommUnication tacilitv. The mailbOx aspect at the CIE idea" can be
expande~ to inclUde the not10n Of moVing messages from one CIF to another. In fact, CIE"S can be 11 nk ed toqetner In a network to move a meSSage frOm the source elL through several 1ntermediate CIE"s Until It tinall~ reaches the desired destination
elE.
that"S an expensiVe proposition: phone lines cost money, and it ~ould be foollsn to have them Call betweeO eIL"s, each could" determine Which trafftc is aolng in the general direction of the the cOnc~lvable tmplementatlons, this paper
~onsiderS those that are communic-ation bet.een programs. the mast UsefUl of thOSe pr09raOlS, hOWeVer, 1s one ",hose pOtential was autOmatiCallY construct a response, and to autOmatiCallY forward messages from One computer to another as a person rooves around. That IS a meaSure Of the Iffiportant role tne program Plays in connecting peOPle to peoole.
The facjlity has evolved into a verY useful form select1velY print Out entire messageS or one-line SummarieS Of messaoe headers; it Will also, on Command, Call the mess~ge-sendin~ progra~, perhaps Initiallzino it to tOrw~rd or respond to tne message
FIRST COMPUTER FAIRE PROCEEDINGS BOX 1579, PALO ALTO CA 94302 PAGE 150 netWork oriented to personal computer peOple.
FortunatelY, they wOUld De the easiest to dUplicate ComputerS oriented SpeCificallY tONard terminals, they were located tn about 70 dlfterent places. In interpreted 8S <living a more p·recise Specification Of the Inte~ded destination. Thus, the Precision With which an adoress neej be Interpreted increases as the mesSage approaenes its destJ.nation, ane:! so a iarge address space can De handled withOut requiring anY partlcipant to possess the information required to Precisely Interpret more than a few addresseS. prObably·a quOd Idea to incorporate SUch fleXibility into a elF net. both to aecomodate sYstems already Co.puter and the servin9 computer being operational limUltaneouslY. In fact. the net dependS on the Communication bet~een speCial purpose PrOgrams. It Is PerhaPS more indicative to conSider messages betweeri people: Metcalfe found that their averag.
lenqth was more liKe a hundred words. and the averaqe Of the last 219 I receiVed was bOO
chara~ters (inCluding rieaders). No_. lilY messaoel arrived at an avpra~e rate of two a daY and include Programs in connected computers. and then messages refer to it. The motivating assumptiOn is that many messages Will be sent down a connectiOn during itl life. Jt would De mUch more appropriate in a CIE net for eaCh meSSage to be self contained, inclUding in itself the intended destination and the source to whieh an aCknOwledgment Should be returned.
The prOCedures in the ARPA net are rigorOUSly Uncooperative) time shar~ng'&erviee that has a BASIC View of the ~orld.
IMP's dO almost all the error cheeking that getl done in the ARPA net. once an IMp accePts a meSSage, It guarantees that the meSsage will be aCCUrately transmltted to its destination and that the source will get a reply saying that it arrived Intact. this increases the buffer storage required at each IMP and torees the IMP to expend a oreat
ResPonSibilitv for transmission between CIE', could be even more dlftuse when the halt time ,harin,
FIRST COMPUTER FAIRE PROCEEDINGS BOX 1519. PALO ALTO CA 94302 PAGE 151 indiVidually sendS them toward the destination. The destination iMP then reassemDles the meSsage before lending It on to the connected computer. rhat's not reqUirement of tranScontinental propagation In half a second. Much ot tile complexity Of the IMP progral1l comes fro~ the packetlzing logic. AS If that weren't enough, paCketizing qave the ARPA Community one of Its most amUsing bUQs In recent Year~: it one IMP Is the destinatiOn of a lot of traffiC, then it
~19ht Well till Its reassembly bufters with PartiallY 8ssewhled messages. Then, since the Imps guarantee deliver~ Of every messa~e they aCcept and SinCe tht'Y route Plckets around conqested partS of the net, all the transmission buffers IN THE REST OF THE NET fill u~ ~lth paCkets headed fof that IMP.
No~o~y usPS the net until somebOdy walkS over to the overstUffed aestlnation and t~eaks the buttonS on its front pariel. NO. the I~P progra~ II even Programs that prOvided the proper ISOlatIon between users: it would depend on its sUbS~rlbers to refrain dellendin" on VOlUntary contrioutions from its Participants. The Ho~ebre~ ~omputer CLUb prOvides a faVorable precedent. Its newsletter is financed entirely bY people occaSionally p-utt1ng a dOllar or waY. forelQn computer establishes contact with the faCility Via the net. It also defineS .the formats Of all the ~essaQes sent tnrough the net When the faCility Is ~sed as well as the CirCUmStances under WhiCh eaCh may, must, or must not be sen~. Some ARPA net protocolS also specify timing restrictions.
Each protOCol, however, is very stronglY fOCUsed on separate the protOCOlS between neighboring CIE's from the protocols between the source and destlnatiOIl ot a wessage. The interactions between a CIE and its SUbSCriber should De left COmpletely out of the deSign Of a CIE net: each CIE Will be hosted by a computer system that was cno.en for econowic or logistic reasons and will have Its own Idiosyncrasies that should be aCCOmOdated at the option ot its SUbScribers. Between CIE's, however,
acknowlpdge~ent or retransmission Of each line Of Characters. At the next level up, there Snould be a Protocol specityih~ the format ot meSsages between CIE's: sUch [essageS may be concerned With th~ retinement and thoU~r>tful definition Of Ideas. It alSO forces explicit definition ot the Inter~ctionl
bet1lieen thp levels ana the requirement.' and guarantees that gO along with them. FinallY, and perhaps most importantlY, it restricts the range o~
PoSSible interactiOnS In a ~ay that focuses attention in more worth~hile directions.
The Cll protOCOlS shOUld be rigorOuSlY definedj number of wi1ely usea protocol implementations In the net; peDPle ~IIl be more likelf to use someone else's Implp~pntatlon than to write on~ ot their Own. It one Of the popular implementations contairis an undetpcted bUg, then many people can be' inconv.enienced ~hen some other pOpUlar program SUPPlies it the .inputs i t needs to miSbehave. Un the ot~pr hand, it informality characterizes the CI~
net las it rrot'1:bly "ould), the.n the buggY program's
auth~r may well not be available to fix it. AIS0#
the posslblp rise Of mutually unintelliqlole local dialects would be a great inconvenience to peopie WhO want t,o <lse ,t.neir t ;\Vor i te sfstem in sevet'al
difterent ie?lOns.
-While the CI~ p~rticlPants ShoUld abide bV their agreements as de~inea in the protOColS, that stance
FIRST COMPUTER FAIRE PROCEEDINGS BOX 1579, PALO ALTO CA 94302 PAGE 152 ShOUld not preclude experimentation. The protocols
snOUld inClude within themselves metnodl for allowing People to experiment witn neW ideas. ror
Experimental protocol extenSions Should be cOmpatible, no~ever. ror example, the ARPA net deClare the transmisston a failure.
keliabtlitY techniques can be apPlied at several different levelS. At least," they can be it has unsuccessfUllY tried some reasonable number Of alternatives. SimilarlY, the source CIE could delayed out still delivered.
Damage to a message can be detected Dy including some redundant infOrmation along With it. The cyCliC redundanCY chec~sum is sensitive to Permutations of its input and is a Candidate for meSSage trarswisslon, tne participants shOUld taKe reasonable precautiOns to detect errors at lower levelS and shOUld taKe reasonable stePs to Cope with PreVenting interlopers from altering the encryption Program itself, discovering a subscriber"S keY or reading the clear text version Of the infOrmation before encrvption or after decryption. Subscribers communicatlnQ with tne crE via their own Personal computerS Ca~ encrypt their entire communication With their CIE, with the exception Of just certain control inforroation, sUCh as the dddreS$es of any meSSages they send through the"CIE. In order to allow for inCreasingly sophisticated intrUders, It
see~s wise to use Diffie and Hellman"s modificat10n to the N~S encryption algorithm.
The Idea of a CIE net intrOdUceS a new prOblem in the genera} area of access protection: SUbscribers must have so~e protection trom 1unK mail, but that a relativelY inaCtive subscriber incapable Of reCeiving mall trom triends.
The conflict cah be resolved bY allowin9 the CIE forWarding the message to its destination: however, the possibillty of letting a SUbscriber limit the communicate ~ith a neignDoring Cl~ withOut requiring the cooperation of both of their host computers.
SinCe SUCh a medium Should be Droadly accessible, allow cnea P eXperimentation and permit the transmisSiOn ot encrYpted data, the telephone is a logical ChOIce. M~demS that can handle 300 baud are commonly aVailable on tne personal computer market, and that bandwidth will transmit 50 pageS Of,
~esSaoes In dbout 2S roinutes, .hich is probably reaSonable tor a CIF that is just ~etting started.
(I Presume tnat, once a Cl~ gets enoUgh"momentu m to have a nioner vOlu~e, its operators will have SUCceeded tn cOhvlncing the host computer"s management to orerate the CIE, ~~lng a more serious
com~unication uediu~.)
FIRST COMPUTER FAIRE PROCEEDINGS BOX 1579. PALO ALTO CA 94302 PAGE 153 Amateur radio 15 probably not an appropriate
initial mediu~ for three reasons. First, it is markedly less aenerallY available, although it could CertainlY be available to link any two particular Prohibited trom handling encrypted data. While ASCII cOuld be tranSlated to ~audot the translation transmitted: the limit Is marginal for telephones, but the Cheaper long distance capaoility of amateur ShOUld they become aVailable.
3.2.8. TOpology connectiOns from berKeley, stanford and Cupertino.
~ach IMP continually monitors its connections to the other IMP'S and eaCh tells the others what it sees, So, when a new I~P is added to the net, all others find out within secondS and are then prepared to Send meSsages to it. Conversely, when a circuit il diSconnected, messages are automatically routed arOUnd it. SpeCifying the location pro~ressivelY more PreCiselY, then eaCh CIE handling a message need only fOrWard it in the general direction of its destlnatioh and need not require that it go via any Particular intermediate CIE. SUCh an addressing Scheme permit a (IE to have only a vague notiOn Of test the Programs Implementin~ the basic protocols.
for examPle, a program may request that its messages their purported imple~entations of the basic networK ProtOCOlS. they should be prOVided both at the level Of communiCation between elK's and communication between a subscriber and a CIE • . If each of these levels is further diVided into levels inVOlving proqressivelY more parts Of the hardware and software involved, then bugs can be isolated Promptly. [hat Can be of great help in getting PeOPle (and Cl~'s) initially connected and In the normal prOCess ot eVOlving their programs.
All this also impinges on the design of the baSic ProtOCOlS tnemselves. A program Should be able to detect accidental and unintentional invocation of at least the eChoing facility. If, say, a modem connected to a CIE were aCCidentally lOOped bacK to itSelf, then the CIE coUld send a message via the modem, and, on getting the echo, it could acKnowledge the message it had JUSt received and then count the message as successfUlly transmitted When it heard the acKnowledge~ent. One way to avoid that rather e~barrassing scenario -ould be to have eaCh meSSaqe contain the current transmitter's address in a fixed place. Then, anY incoming
ineffiCiency that actuallY occurs onlY rarely.
It is not immediatelY ObViouS JUSt what kind Of PerfOrmance should be monitored, and there are two waYs to cope with that situation: anticipation and fleXibility. Probably the most useful parameters that an 1ndividual CIE COUld monitor are the number eXPonentiallY increaSing bucKet sizes, then all this Information can be stored qUite comPactlv~ Just additional measurements may be useful to PinPoint the flaws 1n the design or implementatiOn of a
eIE
net. The fleXibility required to adapt the measuremeAt facility to changing needS may be Patterned after the measurement faCilities of the ARPA net. A few fake user names (e.g., STATS) could be reserVed at eaCh CIE: a message to STATS could be interpreted bY the meaSurement faCility, whiCh could then respond with messages from the fake user STATS.The meSSageS themselVes COUld be in a simple free format, With the individual fields preceded by short deSCriPtive identifiers, so "THRUSIZES=" COUld PreCede tht length histoqram of meSSages palSing thrOUgh the ClEo Yinally, the fake" user name
eIE
information, like PrOgrams, the sharemost
technical valuable
~IRSTCOMPUTER FAIRE PROCEEDINGS BOX 1579, PALO ALTO CA 94302 PAGE 154
Many cowputer no~biists currently attend meetingS Of the local l"oN'vlst Club just to eXchange verbal information ~ith one otner person. 'rhat Is exactly What a eIE net ~ould dO best. IhuS a CIe net could help redUCe the 1ecompOSition Of anCient fossils that accowpanies the usudl attendance of people at hObbyist CIU~ meetings. HOObYist clubs serve many otner valuable servlc~s to the community of people PerSonal Iv uslno Computers, out a functional erE net
coul~ belP people communicdte withOut without transpOrtatl011 lro sO"'e cones.
3.3;3. [n~lvidualism Very looSely orOdnlzed cooperative etfort, it WoUld not benefit from a prewature or Unanticipated intrUSion Of lne la~. lneretore, its participants ShOUld be ~.are of the legal aspects of What they are ~oing ana take SOme nominal care to keep them as Innocuous as poss!Ole until they are prepared to handle a someWhat formalized relatiOnShip with
~overnmenta) bOdies.
~ CIg can opel ate as a very informal aSSociation Of Its subscribers, It probablY will nOt come under Puslness la~. However, if it were to make a prOfit, employ peOple or accept legal responsibilities, it would prObably need a license to operate and need to
computation Is not regulated. The c~mmuntcation
SerVices ot ~ CI~ (and a CII net) have a pronounced computational flavor, especially to the extent that they Include services tnat, for examPle, help a SubScriber sort throUqh large CollectionS Of meSSaQes. The arguments 6h both sides are confusing Without haVlno its pOsition clarified.
4. Future Development computer. ~nat dedicated hacker could Im~lement
many (perhapS aliI ot the critical proqrams for a
Further staqes ot implementation reqUire that our friend have acce$s to a time sharing Service that nost comPuter. rhen, this hard-WOrking hobbyist Will actually nave TwO Crg's (one on the Personal computer) an1 can -ake sure all the prOgrams work.
rhat is the time to start forming a com~unltYJ
extrewelY sympathetic friends are the most approoriate people to recruit first. when most Of the more Obvious bugs have neen worked out, then more people can be attracted to the community.
When SeVeral CI~"s are operational, then theY c~n
link tnemselves tOgether without yet requiring coOPeration (or even a~areness) trom tneir host
~sinq all the appropriate low-level protocols, Which the intermediary would copy to SOme nUrnber Of cassettes. ~nen tne mail had been tranSferred, then our comwitted computerist would close tne cOnnection and Dhone the otner CIE, telling it to prepare beCOme a"condult tor the reimbursement for telephone company charoes. In addition, It would gain a uler communitY t6at it had not needed to build Up, so It
mig~t oe strongly attracted to forming a cooperative relationShip ~lth the CIE.
FIRST COMPUTER FAIRE PROCEEDINGS BOX 1679. PALO ALTO CA 94302 PAGE 166
4.1.2. Other Ct~ Services
ThiS paper isn"t reallY about Clr."s themselves but rather acout their interconnection. still, Community InformatiOn· ~xChanges themselves are not too commOn (I know ot none th~t are currentlY in operation.), ana so tne previous SubSeCtion assumed that formlnq a CJ~ would be part ot connectinq Its communlty tu a networK of CIE"s. The Sjme reason jUltlfles mY spendln; a bit ~ore space just
·mentloninq a feW tnings a Cl~ COUld be qood tor in itselt • • irst ot all, it could inClude a community Qulletin board, whicn its sUbscribers could selectivelY read bY means of a sopnisticated
eo~puter PrOgram. It (or in fact, its nost) co~ld
Provlde a nara-copy output service that woul~ free itl Subscribers trom neeainq to deal WIth an expensive, bulKy and unreliable device that stands idle most of the time. (A sUbscriber could inform the CJE that a certain tile should be Printed; the
CI~ would do so and send the result bY U.S. ~ail.)
~f COurle, the host computer WOUld probaDIY provide
• Wide range ot more Convention~l computational
*erv1ces, sUCh as qames. cross Compilers and non-tiny languaq~s.
4.2. RelationShip to Otner NetworKs
NO current compUter net Is suitable for the PerSonal COmPuter user: they are all set up for the exclus1ve use ot a library sYstem, a sChOOL System, ARPA, a bank, etc., or else tney are strictly commerctal and oriented to highly capitalized, ldr~e
Volume customers. A CIE net COUld edsily ~row up as the first computer net oriented specifically to.ard the IndiVidual. In tact, since personal comPuter users comprise less tnan 0.1% ot tne countrY"s POPUlation, the first commercially operated comPuter nets that appear Will also not De oriented tO~ard
PerSonal comPuter users. ThuS, even thouqh comPuter nets are currently in operation and ~ill grow fantasticallY more numerous in the near future, there 15 nO immediate prospect for any commercial Operation t~at would resemble the CIE net discussed here. that Delng the case, any cr~cial parts of its deSign Should be thought out ratner carefully
beca~se theY will be rather less than amenable to Change ohce they are codified in widely dispersed
beca~se theY will be rather less than amenable to Change ohce they are codified in widely dispersed