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RFC 51: Proposal for a Network Interchange Language

  • M. Elie
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Page 1: Network lflo.rking Grou.'"P M. Elie ~ . '!'Jes t for Ccnment.s #51 4 Hay .70 L C A- Proposal for a Net"iOrk InterChange Language IntreXiuction . In this paper 04"1 attempt is made to specify a high level programning Lanquaqe for co:nputer networks , and rrore specifically the l\.RPA network, The main con cept introduced. is t.he one of an abstrract; Netv;ork iV.L3chine, which is conai.st.ent; with the idea of a HOST ask.inq a service fran the o::roputer netvork considered as an overall canputinJ facility. The dial~e is always between a HCST ar.r1 the Nebvork Ma&.ine ~;Jhich language is always the same, though itS configuration may va:ry accordir.g to the real remote nOST. . . Fran a prcqranrrdnq langu'3.ge po.int; .of vi.ew, this concept is similar to the mX:OL . proposed in 1958 [STR05S] but never implemented, oo'J..'E!Ver,· the applicati.on to a o.::mputer network implies a real time interaction between programs. Also, ::'~e possibility for the user to use ~'IL either in a standard rnode or in an exten:1ed mode where he defines himself hi,s own entities shoul.d give to NIT. a maxinum of flexibility. 1. Basic concepts introduced in NTh 1.1 Aim of NIL The u..'O main objectives of NIL are: a) to describe the enviror.ment in which a prcqzam is executed (its conplemerrc ); this involves the description of: data formats am data structures excharqes with input and out~t devices and characcerd.stdcs -- expected =;:.uu fhen - - interface ~rlth operating system b) . to express the front end part of an interactive system: The data flcM rhrouqh an interactive systxsn g( 'nerally decreases as the data. zeaches the kern el of the syst.sm: it is assumed that in ma...'1y interactive systems a separable rroduLe exists or can be defLned vzhi.ch involves a great errount, of data exchanqed with the user, and much less exchanqed vath the rest of the systrm, This modul,e is called Front-End. It is Impor -tant; th~t the zesponse time of the syst.em is affected as little as poss.ibl. e by additional trar:.smission delays. Also, it is desirable to keep the data rates as 10;" as possdbl,e on the n etvork. It is assumed t.hat fhe trar.sfer of a Front Ern do es r.ot imply to solve the whole problem of p:o.:;sT<li.11 trC.!'1Sfer &l1i.1 ity •
Page 2: , . Netwo:~:k Working Group M. Elie Request for Ccmrents #51 4 May 70 1.2 NIL subcategorization As pointed out by S. Volansky [ ] it's convenient to divide J.an:ruages in several sublanguages cozresponddrq to their main functdons , NIL is thus . subdivided in: a oontrol sublanguage an operation sublanguage a data declaration sublanguage - an environment sublanguage ! .1 1.2.1 COntrol sublanguage I The control sublanguage states WHEN a ccmputatzion is done: It describes the flOtl of control or orderinj of the canputations. ~lith sane infor mation contained frcrn the other sections of the language, it also states WHERE the canputations are to be executed. As a canputer netvork introduces loose connections between several systems, the control language of the Neb-x:lrk r-1achine should be able ,in an elaborate version/of assigning canputations to available processors, taking into account the time delays and resource allocation problems involved. It is not our purpose to consider this level at the m:ment. 1.2.2 Operation ' sublanguage The operation sublanguage describes the operations to be perfonned on the data without indication of the sequencing between operations, it answer's to the question of Hal] an operation is performed. The operat.ions are sub divided into u.x:> groups. . . - a canputation group - a data manipulation group The later is the most irnp:>rtant part of NIL since its main purpose is the transfonration of data structures and patterns. 1.2.3 Data declaration sublanguage The data declaration sublanguage is necessary to declare the variables and data structures on which operations are perfonned. The possibility is given to build structures of atonic e Iementis called beads. NIL provides a stan:1ard set of beads used in the "standard rncde" ; in the "ext.ended IIDc1e " a user may defi ne new beads and new structures of them. 2
Page 3: ! I I .' Network Working Group M. Elie Request for Canrents #51 , 4 May 70 I 1 i 1.2.4 Envirorroent sublanguage ' The environment sub).anguage expresses the context in whi.ch a pregram expects to operate; ex.pecte:1 characteristics of the peripherals, semantics of the excharqes with the outside \A.orld through a particular I ~operating system. , ! I Thus a canplete "projrem descriptor" will contain, four distinct sections: 'enviro nn en t section data declaration section control section operation section The identification section is anitted because it corresponds to the leg in and socket grabbing port of the initialization procedure. ---- --- --- 1 , 1.3 ' '!he Network Hachine One fundanenta'l concept in NIL is that of an abstrac ·t Net\'1Ork r-1achine which ' ha s the follo;.7ing characteristics: - an infinite memory: there is no problem of memory allccation or garbage collection in this machine. But as an item must be accessible, it must still have an address. - variable word length: a word may be considered as the snallest intelligible and addressable item of data. The atanic element called bead is in fact the machine word, The structure and 1eI"X]th of each type of beads are expressed in the data. defini tion sublanguage. ~ As presented on figure 1.9.1, one HOST r=:-=-l(--3 Network only carmunicates with a Net\olOrk Mach- ~ Machine ine which may operate in bX) medea, , figure 1.9.1 starrlard mode where the beads ..f-4:('H:i~a . their structuresI am the all&',ed -' transforrna tions on them are standard and need not to be redefined: standard beads and structures are known of every HOST - - _ ... -- .. . , ' . --- .,. ", , ' .. . " .. . .. . . . - : . extended rrode where in addition to or instead of the standard data defini lions and ' manipulation, a HOST may specify new beads structures and transformations. The extended rrode. al.Icws ::-1l.e. user to defi ne his aim ma chi.ne as the Net work Machi.ne , Tlu.S 15 then equivalent to the mcdes HY LCCcIL, YOUR LOCAL proposed in RFC #42 by Ancona. If the d efinition of a narre has not been altered the st.andard definition is assumed. 3
Page 4: Network vlorking Group M. Elie Request for Carments #51 4 May 70 The data definition sublanguage is as wel.L used for the purpose of documenb ing the set of s'candard beads. The instruction set of the Net\'.Drk Machine stands at a high level per mitting global transfonnations of data structures. The ' envirorment of the Neu-x:>rk Machine is detennined by the subset; of the environuent of the server I s HOST \'mch is used by the program in execution; the systen HOST-Netv..-ork Naclllne can take bo-:o main configura tions shown in figure 1. 3.2. . • a) The Neuvork Hach.ine · stands for the user of a pro:;ram provided by t;he HOST (server HOST) ' b) The HOST machine is the user of a proqram ~f-(--/f~=~~ provided by the Neb-lOrk Machine. ~ ~server) The server machine assigns its hardware .environ ment to the user machine. This choice is made so tf'l.at prcgrams can be ranotely used without Network Machine (user) bei.ng- mcx1if ied; it is up to the user of a remote program to adapt himself and his own environnent. Thus, when the Network Machine is server, it defines the Data Definition and Environrrent sections.figure 1. 3.2 4
Page 5: .' ~ Network ~'Jorking Group M. E1ie Request for Caments #51 4 May 70 "1.4 Irnplenentation The data and environment definition sublanguages should be able to describe as wel.L envirorment and data in HOSTs as data in Net ,,"ork Machine. At the limit it should enable .two programs written in different languages to a:mnunicate r . as long as the data representation they use are expressible in the data de scription sublanguage. In each HOST will be implenented a "generator" which will accept rules describing the HOST data structures arrl environ ment and will generate an adequate translator to translate than in Netv.;ork Nachine format, as sbown in the figure 1.4.1. once the network machine stanc1a.rds wi.Ll, be settled . it seans valuable to think about anulatin:] the tran slator using a micropro gramed unit which would be either added to the Host or rather to the nIP" thus avoiding the load of a translation whi.ch may involve lengthy operations on the bit level - (Figure 1.4.2. ) HOST description Neu\:ork Hac1'ine • (description standard mcx1e)non r Netv.ork Hachin~ starrlard mode I/ I i I GENERATOR/ I I / / I I I I rata is J,. ~ Data in \ TRANSLATOR I-------~ HOST for Neh?Ork Mach±ile mat format figure 1.4.1 HOOT Figure 1. 4. 2 5
Page 6: · Network Working Group M. Elie Request for Ccmrents #51 4 May 70 2. Data definition sub1anguage 2.1 Fields All ccmnunications with the Network Hachine are done using strings of bits: these strings of bits, also referred to as messages are parsed by the receiving HOST to reconstruct inside its memory the data structures in its a.m rremory and cede. Bits are grouped into significant fields: a field is a group of bits having definite contents • . It may contain: a) an elarent of data (data field) b) sate bit pattern specifying' environrrent parameters c) .a pointer d) the identification of sane other fields. '!he method to describe the fonnats of beads is derived from the method of description of a binary message suggested in RFC 4/:31: a) each field is declared with its narre and length in number of bits. b) ccmnon1y used fixed values of a field that correspond .to a special meaning, may be given names. c) legal ways of concatenating fields are initiated by rules; men only certain fixed values of a field are allo.'led, they may be either specified by their value or by the corresponding narre. 2.2 Data beads. Data fields (type (a» are concatenaded to form data beads: a bead is an indivisible atomic unit of data .us ed as building element of any data structure to be transrni tted between HOSTs and Network Mach.ine , A bead is the smallest unit of data that can be referenced. The legal ways of forming a bead by concatenation of several fields are indicated in a construction rule. Beads have a fixed length and an unambiguous structure. In real machine beads are usually defined as an integer number of contiguous registers. This constraint does not apply here, though it may turn out to be more efficient to favor HOSTs with, for L instance, 32 b.i.cwords , and 4 bytes per word, which .a r e the most carmon ....rord structure on the ARPA n etwork. !.."" Data beads may be consd.dered as the operands of the Lanquaqe in which fields of type (b) and (c) would be operators. 6
Page 7: -, Nat\vork V\orking Group Request for Carrrents #51 M. Elie 4 May 70 2.3 Control fields '!be way data beads are linked ore to the other and the environ ment in which they operate are specified by additional control fields whi.ch cannot be referenced and are operators on or identifiers of the follo.ving string of beads, or linkage between individual beads. The scope of a control field may as well be all the beads or substructures of a structure, if it is specified at the level of the .he ad of the structure. To be more precise, two kinds of structures of beads must be defined: hcmogeneous and .heterogeneous structures • .A structure is defined as hanogeneous if both a unique type of bead and a fixed pararreter environrrent for the whole structure is specified at the head of the structure. A structure is defined as heterogeneous if at least one of the follcwing conditions i's true .. - different types of beads are used for building the structure . - the environrnent in which lie tile beads of the structure is changing within the structure. Five main control fields need to be defined. a) MODIFY b) . FLAG c) POINI'ER d) IDENI'IFlCATION e) PARAMETER 2.3.1 MODIFY field '!he HODIFY field is a one bit field preceding every bead of a heterogeneous structure: it is a flag set when follo. ~·ed by one or several control fields of type b, d, or e, which aim at modifying either the environment of data beads or their type. '!bis field has the value: 1 if the attached data bead type and its envi.romrant; do not change o . if t11e attached elernent is a control field or a ' seque nce of control fields of type b, d, or e specify ing a change in type/or environment of follo.ving data beads. 7
Page 8: · , Network Working Group M. Elie Request for Carrrents #:51 4 May 70 2.3.2 FIAG field \'ben set, the MODIFY field is imnediately follaved by an 8 bit FLAG field indicating which of the IDENTIFICATION and several possible PARAHEiI'ER fields are present; when set to one each individual bit means the follcwing: bit number o IDENTIFICATION field present . 1 first pararr.eter field present 2 second parameter field present - - -+-- - _.. , 6 siXth para:rreter field present . 7 next - fielq#- is another FLAG field , ' for sane more pararreters (in case ' \ rrore than 6 parameters may be I attarned to a bead environrrent) • \ -- - -- --- - - - - .. 2.3.3 POINTER field The number and nature of pointers to be att ached to each bead depends on the structure definition. A given list structure may need one forward pointer. A ring structure may use an ' additional pointer to the first element. 'Ihe necessary lin1(age between beads are defined in the structure definition thereafter the necessary pointer fields autanatically added to each data bead. A bead is referenced within a structure by an address relative to the head of the 5 tructure. 'Ihus a 16 bit pointer field should be fully sufficient to contain this address. 2.3.4 IDENTIFICATION field The IDENTIFICATION field is an 8 bit field which identifies a bead type arrong the list of defined bead 'type s . Standard bead types are nuubered from zero up and non-standard bead types are numbered from 255 dam. The non-standard types mrrnbering is special to each server program or to a set of server programs. The IDENTIFIC"\TIO~J fields ,f ol I a .., a HODIFY field of value 1 when ever the bead type has not been defined alloVer the structure in the structure root. Identification fields are also used at the level of the head of the structure to specify the type of identical elements (beads or structures) used wi, thin this structure. 2.3.5 P~~R field The' PARN1E.'TER field gives the list of the environment pararreters in whi.ch th e f cd. Lcwi.nq stri ng of d at a b eads li es. A PARi\HCTER field is specific of a bead type; it directly follolls the HODIY:{ field when there is no arrbiguity or the type of th e next data beads. 8
Page 9: Network Working Group .' ReqUest for Connents #51 Example: "the par~er field of the standard bead BEN-NVr will contain the follcMing fields. M. Elie 4 May 70 - a 2 bit field indicating the type of moverrent generated 00 01 10 11 do not display ". display final point display vector unused nove the beam point . vector - a 4 bit field indicating beam intensity, by a nun:ber fran 0 to 15, 0 meaning a null intensity, and 15 the maximum possible intensity. - a 1 bit field for blinking o off 1 an - a 1 bit field for light pen sensitivity o off 1 on 2.4 Metalanguage definition A COBOL - report like rreta language is used in the examples because of its readibility, as well in the beads as in the structure definitions. Symbol + Meaning concatanation { } [ ] choice optional choice repetition 1 - - --- - - - -- _. -- - -- ~ - - - - -- - _... ._ -- -_._ - _._ -- - ---- -_ ._._- --- - -- - - . _ -~ - - - - - ---- _._- - laver bound on the number of identical items; if anitted 1 is assumed to be O. u upper bound on the nurrber of identical iterns; if anitted u is ass umed to be 00 • .a number alone rreans: exact; nU1lber of repeti lion. 9
Page 10: " .. .' " Netw"Ork \'k>rking Group " M. Elie Request for eomtents *51 4 May 70 .. = = ::> ( " ) o G 2.5 2.5.1 label for further use within the same rule assignment condi tional alternati ve , grouping indicates a special value given to the folloong field narre plus minus Prcposed standard beads Alphanumeric beads Character: CHAR A character is canposed of one eight bit field (which has the same name). Many special patterns, corresponding to currently " used special characters are defined; they are indicated in table 2.5.1, as we l l, as sorre subsets of CHAR. The basic char acter code is declared as s tandard ASCII standard EBCDIC or by the name CODE follo. ...ed by the 128 characters in this code corresponding to the 128 ASCII charactars , If no code declaration is specified, the ASCII code is assumed by default. Nu:nber representation Normally the kernel of a proqrarn stays in the ' server's HOST and the user's HOsr should have no ari thrnetic operations to perform on the data. In this case, the principl es involved in the arithmetic unit conception of a HOST do not need to be described. But the format of fixed and floating point nunbers has to be described. in the " case when user and server Hosr' s have the same number representation,for instance the stiandard representation) the transmission of data in their nunber representation reduces the data flo..; between them. - if the server HOST has a different number representatioi1 than the standard representation, depending on the d ata transmitted, there are two alternatives: 10
Page 11: » , ". Network Working Group M. Elie Request for Ccmnents #51 4 May 70 + the nunerical data is exchan:jed as decimal nUI1'lters in the standard code + the fixed and floating po.int; fonnat are defined to the _Neuvork Machine and the user HOST performs ei ther a ' direct transco:1.ing fra-n the server binary representation to decimal representation and vice . versa. or a transcoc1ing f ran the server binarY representation to its own binary representation an::l vice versa. As most of the numbers exchanged are to be printed in decilnal or are given as decimal input, it is felt that when there is incanpati bility between binary represe..T1te"ltions of corresrx::mc1irrg HOSTs, exchanges in decimal representation would te the easiest. Thus are defined: a) .Number in decimal r~presentati.on whi.ch is not a bead but a string of characters (see 2.3.1) b) Fixed poirrt numbers single preci.sion FXP1.'illMl double precision FXPNUH2 Field defi.nition BYTE 8 SIGN 1 SBYTE 7 FXP NThU~SIGN + SBY'I'E + {BYTE}3 FXP NUM2 <-FXP!-'TQM i + .: {BYTE} 4 c) Floating point numbers single precision FLPNUMI double precision FLPl'-JG'M2 FLP NUHl ~ SIGN + SBYTE + {BYTE}3 FLP. NUM2 ~ FLPNUr'-U + {BYTE} 4 This only ~presses the syntax of t..;e floating po.int; number. The sanantics should say: in FLPNUI\'l1 SIGN is the sign of the number of fonnat {BY'I'E}3 vlhich is the mantissa SBi.'TE is the exponent, ard its value is based by a value to insure positive exponents. In fact, FXPNu'H1of 401 6 and FLP ~·;(JMl di f f er by their s emant.i.cs , 11
Page 12: Network vbrkir.g Group M. E1ie Request for Carments #51 '4 Nay 70 These prop=rties will be expressed by specd.al, field definition: EXP .(_ SBYTE (±) I 400 I SBYTE rW1r <_,. SIGN G1 {BY"TE} 3 and a floating point number is defined as: FLP "= !v1ANT .pp 12
Page 13: : Nebvork Harking Group r-1. E1ie Request for Crnroents #51 4 r-1ay 70 1. Special Characters Transnission Control Characters SOH STX ETX Ear ENQ ACK DLE NAK SYN EI'B ESC Printer Control Characters horizontal tabulation HT 1- 'OXl' CHAR vertical tabulation VT 1- 'OBX' CHAR new line NL 1- 'OAX' OlAR end of message ID-1 1- '08X' CHAR - _. Te1e otype Control Characters Carriage return CR 1- "ODX' oOIAR shift out SO 1- 'OEX' OIAR shift in 81 1 'OFX' OlJ-R BS 1 Device Control Characters OC1 OC2 OC3 OC4 Tabl e 2.3.1 13
Page 14: .: Neu..urk \,]orki!'B Group M. Elie Request for Carrnents if5l 4 May 70 2. Subsets of Characters Numeric characters 1 2 NUM + aJAR 9 Printable characters PRCHAR + Intennediate characters 'J~acters "I' ITCHAR + \n~l= ) OIAR Final Ch3.rac ·ters FIN CHAR + CHAR e ITCHAR Transnission Control<, Characters* CHAR TRACHA..~ + t~}Derra Control Characters DEL Teletype control character OCQIAR + CHAR' (OCl I' TYCOIAR {CR ~ S1 r,t~~ ) SO " BSJ Alphabetic characters M:l?H + Printer Control Characters ~HAR + Table 2.3.1: Special ASCII characters and groups of ASCII characters. *see USACII standards 14
Page 15: - <, Netwurk ~vorking Group r.1. Elie Request for Ccrrments #51 4 Hay 70 2.5.2 ' Graphic Beads As proposed in RFC #5 by J. Rulifson, the screen of any graphical display is taken to be a square; the coordinates of points are normalized fran -1/2 to +1/2 on roth axes. The pos.i lion of the first podrit; of a structure is determined by the deflection fran the origin whi.ch is the rest po.int; of the beam; fol1m"d.ng points are detennined by their deflections (AX,AY) fran the last beam pos.i.tdon • . Thus, only u.o data fields need to be defined: DEFLECl'ION which is a 12 bit field: the deflection is defined by a mmber between - 1 and +1 with the precision usual to the server. ANGLE which is a 15 bit field defining an angle fran 0 to 211 in radians between the horizontal axis and an axis passing through the origin. The first bit of it indicates if the angle must be taken clock wise or counterclock.\vise. The data beads are: MOVE Deperrling on the parameters which are set when this bead appears, MOVE may specify: - an invisible movement of the beam; in this case the beam intensity is null a new point: in this case the team intensity is on only when the team has reached the new point. - a vector: in this case thebearn intensity is set to a certain non zero value MOVE + {DEFIECl'ION}2 Arc of circle: ARC An arc of circle is defined vJ its center, fo'l.Lowed by its start ing point and fhe angle of its ending axis. ARC + {DEFI.ECrrCN} 4+liJ."\"l(;I.E 15
Page 16: . . ". NeUt.Drk ~Alorking- Group ·M. Elie Request for Colments #51 4 May 70 2.6 Proposed parameter fields. 2.6.1 Character str.i.nqs. In character strings sane of the control characters are really parameter fields: they act as an operator on the folloftTing strin:; of characters. Le. : 10\'1er shift upper shift new line escape But as the code and use of these characters are detiemtined in the standard codes, they are not included in parameter definition. I ,t may be taken advantage that these characters are in the Ut70 left columns of ti'e ASCII or EBCDIC standard code: they cor.respond to codes with the first three bits Jll..lll in EBCDIC ard the ' first two bits null in ASCII. 2.6. 2 Graphics parameters The follOt.-,.i.nq parameter fields are defined: scale SCALE 4 beam intesity I~"T 4 light pen sensivity SENS + SV·iTrCH blinkim BLINK + S"I"1I'ICH beam B.E1J'1 + SWITCH ~~rDCH is . a 1 bit field Which may take the values: 00<-'1' S\"1I'ICH OFF <.- '0' S"I'1I'I'CH A switch parameter stays ON, as long- as it is not reset to OFF. The beam intensity is expressed. by a number' fran 0 to 1. 0 is black and 1 as light as the display can go. .Numbers in between specify the relative log of the intensity difference. BEAM permits to swi.tch the BEAM on or off without chancJing the Current INT parameter. 2.7 StructLrres 2.7.1 Structure definition. The struc tur e de f in i ·t i on con sit s main l y i n t.he speci f i ca t i on of thetor.olcgical relation..s between data beads: sequential relations; DO r:ointer field nec essary link.s through a mmber of p:>inters. 16
Page 17: '" . Netv..urk v.larking' Group M. Elie Request for 'Cannents #51 4 May 70 2.7.2 Standard structure type. 'l\-x) basic standard structure types are chosen VECIOR to represent 's eque nc e of data beads (strings, arrays, tables ••• ) ' ' PLEX to represent any kind of directed graph, tree, ring .•. ) VECTOR (CiN, ••• N +- VECroRIIDR + VEX:TOP.BODY C) VECrORBODY+(=C+l:{defi.r!ed bead}Ni + [VEC'IOPBODY] VECTOPJIDR +'VECTOR' IDEN"TIFICATION + C + N + N2 + ••• -tN l cC is the number of parts (co.limns) in the vector, each part hav :in:J ~:TC elsuents. It is also probably interesting to define a canpressed vector CCMPVECTOR in whi.ch sequence of the identical elErnents ~are trans rni tted as 1 elanent + .a special bead + the number of identical eleuents in sequence. ' PLEX (H) The first bit of a podrrter field indicates if the p::>inter po.irrcs to a tenninal el.ement; or not. If it is the case, forward p?inter fields are not added to the data element. M is the nunber of data elsuents in the ' structure. 2.8 Objects 2.8.1 object 'definition. An object is defined by a semantic rule including, on the right hand side r a name to identify the object 'La set of parameters of the object definition. (operands: name of tie beads used as data e'lemenbs on the left: : , -- hand side loperators: parameter fields structure of the data beads . Le. The definition of a new object called SQUARE is: SQUARE ';,- (A,L~Ae) RYI'lh(ANGLE:Z,) (VECrOR (l, 4) (OCl\!'1' OFF' + MOVE (A) + B.EJ..I-I 'ON' + f.'lOVE (O,L) + r..:OVE (1.,0) + HOVE (0 ,~L) + NOVE (e.L, 0) ) v.]here Rar refers to a transformation def i.ned in the data rnani.oul,« ation Lanjuaqe , aril. VECTOR is def i.n ed as a atardard structure: 17
Page 18: ·" Neu.~"'Ork \'Iorking Group M. Elie Request for Ccmnents #51 4 May 70 The identifier of the le\" structure is SQUAnE .The structure type used is VECTOR wi.th dimension 1 and 4 el.enents The elerrents of the VECTOR are standard beads HOVE . ' The parameters are A, L , ard A G Parameter fields BEAH ,IOFF ' and EEAH ION' are used , 2.8.2 Alphanumeric standard objects. Ccrnpressed character string (CQ."1STRmG) , "t\. ~NlJi'll ) . V!'+}.,"'tJM I EOF) :C+CHAJJR a::JMSTRING ~ VECIOR (1) ( [PRCHAR] n + EOP A canpressed string of characters is any mmber of times a strin:3' of any number of printable characters fo'l.Lcwed by one of the follcMing characters . horizontal tabulation fo l.Iowed by the mmber of correspond- . in:; blan.1.::.s to be added - vertical tabulation fo Llrwed by the nurnber of lines to be ski.pped, - escape fo'l Lowed by any character - new line - end of page The canpr-essed string is ended by an EOF character. Co1e table (CODE) CODE.(-VECroR (1; 128) [~28 CODE is the name of the translation table assumErl for a given program. When definErl by the user I he must give fran column 1 to column 8 the 8 bit pattern equdvaLent; to the correspor.ding ]lEerr cede. 18
Page 19: . . ~ . . Netv.:ork ~·;orkilXJ Group Request for Ccmnents #51 H. Elie 4 .I-1a y 70 " Binary card image B CARD (-VEX:TOR (1; 120) {CHAR}120 packed dec.irrB.l number ffiU ·1 4 bits field X X HNUH PN1JI·1 f- HNUH x .::~~'X X X 1£.n.:31 . PDNUH f-- ~NL"r-t} + DSIGN _ . Decimal mmber (unpacked or zoned _ lL..n<31 DNU1 f-- {i-roi.1] + D SIGN+ PNUM - I 19
RFC 51: Proposal for a Network Interchange Language
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