Network Working Group J. Bouknight
Request for Comments: 76 J. Madden
NIC 5180 G. Grossman
 University of Illinois
 28 October 1970
 Connection-By-Name: User-Oriented Protocol
I. Introduction
 Shortly after the first of the year, 1971, the Center for Advanced
 Computation (CAC) at the University of Illinois will begin to use the
 facilities of the ARPA network. We are the first of a small class of
 network nodes whose chief characteristic is that the node is a port
 to the network only. All computational power for these nodes will be
 taken from other nodes on the network, ILLIAC IV for example.
 An important characteristic of most of the users at our Center is a
 lack of sophistication about data communication techniques and
 practices. The user will eventually be in the majority of those
 using the network from all nodes but the problem is ours, almost from
 the start.
 In our discussions with our prospective users of the network as we
 designed our port facility, we found that the greatest confusion and
 consternation arose over having to deal with network protocol at the
 "nitty-gritty" level of sockets, links, etc. While most of them have
 been acclimated to computer systems at the file and device-by-name
 level where the software system handles details, here on the current
 version of the network, the user handles all details.
 Thus, we were compelled to seek a user level interface to network
 protocol where all user protocol is handled symbolically with system
 procedures making the translation into host-to-host protocol.
 Currently, connections are established by exchange of known socket
 numbers for the four loose ends of the connection. This requires
 either that the user or process always know all socket numbers he
 will use at his or other installations OR that his NCP (and/or
 related software) remember them for him, allowing him to reference
 them symbolically.
 We propose a more general solution to the "telephone book" approach
 of obtaining socket numbers for user or processes. Only the host, at
 each site, knows its socket number space at any given instant in time
 as well as the status of the user or process to which a socket number
 assigned. Additionally, most permanently assigned devices and/or
 processes are known by standard mnemonic labels such as DSK (disk),
 LP (line printer), CR (card reader), TECO (PDP-10 text editor), etc.
 In most systems, all other communications are done through files or
 pseudo files, known only to the user by their names and not by their
 internal mechanism. In other words, most intrasystem communication
 at the user level is by symbolic reference to both devices and
 process.
 We propose facilities, by extension of the current protocol, that
 will allow users to use the network on a connection-by-name basis as
 they already do in their host system. In the remainder of this paper
 we will present the suggested extensions to the current protocol and
 give an example of its usage in a dialogue between a user at CAC,
 controlling two processes; one at UTAH, and one at PAOLI (ILLIAC IV
 construction site).
II. Proposed Extensions to Protocol
 Let us define a class of syntax elements for use in our proposed
 extensions to the protocol. (This syntax is expressed in the
 metalanguage of the ALGOL-60 report.)
 <label> ::= <usercode>/<filename>|<device name>
 <devicename> ::= <string>
 <usercode> ::= <string>
 <filename> ::= <string>|<filename>/<string>
 <string> ::= <char>|<char> <string>
 <char> ::= A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z|0|1|2|
 3|4|5|6|7|8|9|.|,
 A standard set of <devicenames> should be established to reference
 line printers, card readers, etc. - those hard peripherals with fixed
 processing tasks. A beginning set of <labels> might be:
 LP line printer
 CR card reader
 CP card punch
 PTR paper tape recorder
 PTP paper tape punch
 MT magnetic tape
 DSK disk
 TTY teletype compatible terminal
 The format of <usercode> is that of the responding host for the
 current discussion. Future discussions about foreign-user usage of
 host facilities may result in a standard format for the entire
 network.
 Most systems can identify files by one <string> plus the <usercode>.
 Others, such as the Burroughs B6500 use multifile identifiers where
 many <strings> may be used in the <label>. The set of <char> is that
 proposed in RFC 66, i.e., ASCII.
 The proposed extensions involve a "request" for information and
 several variants of a "response" to the request.
 A. Request for Socket Number for this Label
 <RFSNL> <my socker #> <0> <label>
 The RFSNL is sent on the control link to the destination host
 requesting the socket number of the attached <label>.
 B. Acknowledgement of Request
 Upon receipt of an <RFSNL>, the destination host returns one of three
 responses:
 <AORP> <desired socket#> <your socket #>
 <AORN> <desired socket#> <your socket #>
 <AORN> <0> <your socket #>
 The first response returns the requested socket number and signifies
 that the user, device, or process exists. The second response
 returns the requested socket number but signifies that the user,
 device, or process is not currently available for connection. The
 last response signifies that no such user, device, or process exists.
 C. Discussion
 The above extensions to the protocol are intended to enhance user
 acclimation to network usage. The element of strangeness is subdued
 and, in fact, for user of the B6500 erased. Attached to this RFC is
 an appendix containing a preliminary description of the user language
 of the network port facility being brought up at the CAC. We now
 present a sample user session on the CAC facility and detail how the
 protocol is used to establish the proper communication paths.
III. Example of User Dialogue
 Assume a user residing at CAC, whose site code is URBANA. His
 terminal is an alphanumeric CRT terminal and we assume solution of
 code conversion problems for network communications.
 The sample user session will involve the setting up of two processes
 at two host sites with control from the third host site. All
 operations can be accomplished with the current protocol plus the
 proposed extensions.
 In addition, we also assume that some form of standard user code is
 in use for all host sites uniquely identifying every network user
 when he is present.
 Output keyed by systems will be underlined. Comments are offset to
 the right for legibility. All statements about the UTAH system are
 purely hypothetical.
 User Dialogue Comments
 The user moves to the terminal, applies
 power and types:
 HELLO
 The CAC system responds for login
 purposes with:
 USER= GROSSMAN
 ------
 for the user's code.
 1437 TR7/GROSSMAN LOGGED IN
 ___________________________
 LINE PRINTER DOWN TILL 1600
 ___________________________
 This acknowledges proper usercode and
 sends any appropriate notes on system
 status.
 ! LINK TO ILLIAC
 The exclamation point (!) is the escape
 character which flags direct input to
 the PDP-11 OS:
 User requests connection to the ILLIAC
 IV node. NCP operations establish link
 from user terminal to B6500 MCP.
 1437 TR7/GROSSMAN LINKED ILLIAC
 -------------------------------
 Completes response.
 ? EXECUTE DISK/PRINT; FILE DISK = ALPHA@UTAH REMOTE QUEUE; END
 1. DISK/PRINT lists text files from
 disk to B6500 line printer.
 2. REMOTE files on the B6500 will refer
 to files going to/coming from the
 network.
 3. ALPHA@UTAH specifies that a
 connection is to be made via the
 network to a file GROSSMAN/ALPHA from
 the UTAH node.
 4. QUEUE specifies periodic attempt to
 complete the connection.
 The B6500 will ask for the socket
 number associated with GROSSMAN/ALPHA
 until an AORP is received.
 The language is that of the monitor for
 the B6500
 ! FLAG ILLIAC =#
 All data received or sent on the link
 to ILLIAC must now be prefaced by the #
 character.
 ! LINK TO UTAH
 1441 TR7/ GROSSMAN LINKED UTAH
 ------------------------------
 User now links into UTAH PDP-10 system.
 #1410: DISK/PRINT BOJ 1441
 --------------------------
 System message stating beginning-of-job
 for DISK/PRINT on B6500.
 ^C
 . R PIP
 -
 User will run PIP on a listing file.
 * NETWKR:ALPHA@ILLIAC <- DSK:FIL.TMP
 -
 NETWRK is network file type for UTAH
 system. Mechanism for file control
 basically same as for B6500 system.
 Since PIP will be sending to the
 network, it does not request a socket #
 from the B6500 NCP but instead
 instructs its NCP to acknowledge any
 request for GROSSMAN/ALPHA from ILLIAC
 with the socket number PIP will send
 from. As soon as the B6500 NCP tries
 again to find GROSSMAN/ALPHA from UTAH,
 success occurs and the socket numbers
 are exchanged with subsequent
 connection establishment.
 *
 -
 PIP completes the task and terminates
 the connection to the B6500.
 #14: DISK/PRINT EOJ 1448
 B6500 acknowledges completion of task.
 #? TO SPO: SAVE LIST GROSSMANHA FOR MAIL(U OF I/GROSSMAN)
 User sends message to B6500 operator.
 User logs out of UTAH.
 JOB 10, USER GROSSMAN@URBANA TY68 AT 1448 ON 22-NOV-70
 ------------------------------------------------------
 FILES DELETED: 0, FILES SAVEDL RUNTIME 0 MIN 12 SEC
 ---------------------------------------------------
 System logout listing.
 ! END UTAH
 1449 TR7/GROSSMAN DELINKED UTAH
 -------------------------------
 Link to UTAH system now dropped.
 # FROM SPO: LISTING MAILED
 --------------------------
 B6500 operator response.
 ! LEAVE
 User desired to log out of CAC system.
 1450 TR7/GROSSMAN DELINKED ILLIAC
 ---------------------------------
 Link to ILLIAC system new dropped.
 1450 TR7/GROSSMAN LOGGED OUT
 ----------------------------
 Session over.
 Syntax and Semantics for the Terminal User Control Language
 for the Proposed PDP-11 ARPA Network Terminal System
 by
 G. R. Grossman
Prefatory Notes
 The following document represents a first attempt at providing a
 control language for the terminal user of the PDP-11 network terminal
 system. This language is deemed sufficiently powerful to provide the
 user with a minimal facility for attaching to remote host computers
 over the ARPA network, initiating processes, and routing data flow to
 local peripheral devices.
 The hardware system as envisioned will comprise a PDP-11/20 with a
 least 8k of core, a small disk (512 kilobytes of storage), a console
 teletype, and optional card readers, line printers, DECtapes, User
 terminals, card punches, storage scopes, etc.
 The executive system will consist of a basic driver system which will
 control autonomous processes and interrupt-driven device service
 routines. The system will keep tables in core and on the small disk
 for logging peripheral usage, keeping track of connections on the
 network, queuing up of tasks that cannot be immediately performed,
 storing attributes of remote hosts, etc.
 Since network hosts handle communications in character-at-a-time or
 message modes, and may or may not echo characters over the network,
 the system takes this into account when handling connections to
 specific hosts. If the connection is in message mode, minimal line-
 by-line editing facility (character and line deletion) is provided.
 A means for the user to change flag and message transmit characters
 is provided to prevent incompatibilities which may arise between the
 PDP-11 and other hosts.
 This document does not describe control card syntax for card reader
 usage, nor does it describe the operator's control language. These
 will be described in later documents.
Character Set
 <character> ::= <letter> | <digit> | <special> | <space>
 <letter> ::= A | B | ... | Y | Z
 <digit> ::= 0 | 1 | ... | 8 | 9
 <special> ::= ! | " | # | $ | % | & | ' | ( | ) | * | + | , | - |
 . | / | : | : | < | = | > | ? | @ | [ | | ] | ^ |
 |` | { | <bar> | }
Identifiers
 <identifiers> ::= <letter> | <identifier> <letter> |
 <identifier> <digit>
 Semantics: Identifiers are used to designate peripheral units,
 host computers, etc. No identifier may exceed 8 characters in
 length.
Numbers
 <integer> ::= <digit> | <integer> <digit>
 Semantics: <integer> are the only form of number allowed in the
 control language. They must not exceed 2^15-1.
Peripheral Designator
 <peripheral designator> ::= <device class> <device number> | OPR
 <device number> ::= <digit> | <digit> <digit> |
 <device class> ::= CR | CP | LP | DT | TR | SS
 Semantics: Peripheral designators name specific peripheral
 devices. Device lasses designate classes of peripherals.
 OPR designates the operator's console teletype. The classes of
 peripherals corresponding to the device classes are given on the
 following table:
 <device class> type of peripheral
 CR card reader
 CP card punch
 LP line printer
 DT DECtape
 TR terminal
 SS storage scope
File Label
 <file label> ::= <tape label> | <tape label> / <tape file name>
 <tape label> ::= <identifier>
 <tape file name> ::= <identifier>
 Semantics: File labels provide the means for designating tape
 files symbolically. If the <tape label> form is used, the
 designated file is assumed to occupy the entire tape.
Flagged Control Statement
 <flagged control statement> ::= <flag> <control statement>
 <flag> ::= <special>
 Semantics: <Flagged control statement>s arc the user's names of
 communicating with the PDP-11 system. The <flag> must be the
 system default flag (!) or a substitute which the user provides
 by means of the <flag statement>. Input to the system which
 does not begin with a <flag> will be passed on to the process to
 which the user is connected, if any.
Control Statements
 <control statement> ::= <link statement> |
 <copy statement> |
 <end statement> |
 <user statement> |
 <status statement> |
 <out statement> |
 <to statement> |
 <escape statement> |
 <back statement> |
 <delete statement> |
 <transmit statement> |
 <lock statement> |
 <unlock statement> |
 <assign statement> |
 <label statement> |
 <create statement> |
Link Statement
 <link statement> ::= LINK TO <host> <q>
 <q> ::= <empty> |
 QUEUE |
 QUEUE <integer>
 Semantics: The Link statement directs the system to set up a
 connection between the user's unit and a remote host. The <q>
 construct allows the user to specify that, if the connection
 cannot be set up immediately, the system is to keep trying. If
 the QUEUE form is used, the system will keep trying
 indefinitely. If the QUEUE integer form is used, the system
 will try for integer minutes.
Copy Statement
 <copy statement> ::= COPY <source> TO <dest> <q>
 <source> ::= NETWORK |
 <file label> |
 <source class> |
 <source device>
 <source class> ::= CR | TR | SS |
 <source device> ::= <source class> <device number>
 <dest> ::= NETWORK
 <file label> |
 <dest class> |
 <dest device>
 <dest class> ::= CP | LP | TR | SS
 <dest device> ::= <dest class> <device number>
 Semantics: The <copy statement> directs the system to set up a
 connection between the <source> and <dest> and copy records of
 information between them. If the <device class> or <device>
 form is used for either <source> or <dest>, the copy process
 cannot begin until a unit is assigned to the user. If the <file
 label> form is used, the copy process can likewise not proceed
 until the system has access to a properly labeled tape. if the
 NETWORK form is used, a connection to a remote process must be
 pending.
 The <q> construct has the same meaning as for the <link
 statement>, with the additional provision that the condition
 that caused the process to be incomplete may be the lack of a
 device assignment.
End Statement
 <end statement> ::= END
 Semantics: The <end statement> causes the current connection to
 be terminated.
User Statement
 <user statement> ::= USER = <identifier>
 Semantics: The <user statement> is used during the log in
 process to allow the user to identify himself.
Status Statement
 <status statement> ::= STATUS <device class> |
 STATUS <peripheral designator>
 Semantics: The <status statement> allows the user to interrogate
 the system as to the status of a device or class of devices.
Out Statement
 <out statement> ::= OUT|LEAVE
 Semantics: The <out statement> allows a user to log out of the
 system. If the OUT form is used, all queued process initiated
 by the user are terminated. The LEAVE from does not terminate
 such pending queued processes so long as these processes do not
 directly involve the user's terminal.
To Statement
 <to statement> ::= TO CON :<text> | TO <user> : <text>
 Semantics: The <to statement> allows the user to send a message
 to the operator or another logged-in user.
Flag Statement
 <flag statement> ::= FLAG = <special>
 Semantics: The <flag statement> allows the user to define the
 character which the system recognizes as preceding a control
 statement as distinguished from a message to a remote process to
 which he may be attached. The default flag character is "|".
Back Statement
 <back statement> ::= BACK ? {ascii special or control character}
 Semantics: The <back statement> allows the user to define the
 character which, in control or message mode, causes the system
 to "forget" the previous input character. The default backspace
 character is RUBOUT (ASCII 1778).
Delete Statement
 <delete statement> ::= DELETE = {ASCII special or control character}
 Semantics: The <delete statement> allows the user to define the
 character which, in control or message mode, causes the system
 to "forget" the previous line of input. The default delete
 character is ASCII VT (control K).
Transmit Statement
 <transmit statement> ::= TRANSMIT = {ASCII special or
 control character}
 Semantics: The <transmit statement> allows the user to define
 the character which, in control or message mode, causes the
 system to begin interpreting the control statement or to
 transmit the message. The default transmit character is
 carriage return.
Lock Statement
 <lock statement> ::= LOCK
 Semantics: The <lock statement> causes the system to prevent any
 user or process but the process to which the user is currently
 attached from sending messages to the user's terminal.
Unlock Statement
 <unlock statement> ::= UNLOCK
 Semantics: The <unlock statement> reverses the action of a
 previous <lock statement>.
Assign Statement
 <assign statement> ::= ASSIGN <assign device> <q>
 <assign device> ::= LP | DT | CP
 Semantics: The <assign statement> causes the system to attempt
 to assign a device not currently in use to the user. The <q>
 construct has the same meaning as for the <link statement>.
Label Statement
 <label statement> ::? LABEL DT <device number> <tape label>
 Semantics: The <label statement> causes the system to write a
 new label on the DEC tape specified.
Create Statement
 <create statement> ::= CREATE <tape file name> ON <tape label>
 Semantics: The <create statement> causes the system to create a
 new file named <tape file name> on the DEC tape labeled <tape
 label>.
Purge Statement
 <purge statement> ::= PURGE <tape label> |
 PURGE <tape file name> ON <tape label>
 Semantics: The <purge statement> causes the system to delete all
 tape directory information on the DEC tape or tape file
 specified.
 [ This RFC was put into machine readable form for entry ]
 [ into the online RFC archives by Gottfried Janik 2/98 ]