Network Working Group J. Winett
Request for Comments: 109 MIT Lincoln Laboratory
NIC: 5805 24 March 1971 Level III Server Protocol for the Lincoln Laboratory
This material has not been reviewed for public release and is
intended only for use with the ARPA network. It should not be quoted
or cited in any publication not related to the ARPA network.
The Lincoln Laboratory IBM 360/67 is connected to the ARPA network
and acts as a serving host providing access to the CP-67 virtual
machine operating system. Upon completion of the Login procedure,
users have control of a 360 virtual machine through a virtual 1052
online console. Attached to the virtual machine is a virtual card
reader, card punch and line printer, and a number of disk storage
devices. The 360 virtual machine can be either a virtual 360/67 with
dynamic address translation hardware or a standard System/360. Most
users run a standard 360 with 256K bytes of virtual memory and
operate the CMS conversational monitor system. CMS provides
facilities for file creation, maintenance and manipulation, program
development, debugging and execution, and a number of other useful
utility functions. The section in the Network Notebook on the
Lincoln Laboratory 360/67 more fully describes the facilities
Network Control Program
All communication with the 360/67 through the IMP are processed by a
Network Control Program (NCP). The NCP operates with the Host-Host
Protocol described in the Network Working Group Document No. 1 dated
3 August 1970.
Initial Connection Protocol
To create a virtual machine from the network, a pair of connections
must be made with the LOGGER. The sockets to be used are assigned
following the Initial Connection Protocol (ICP). The LOGGER is
enabled and waiting for an RTS control command for socket X'0A 0000
01'. This ICP socket corresponds to home X'0A', user X'0000', and
tag X'01' (send gender). Requests for connection on the ICP socket
are stacked until it becomes free. If the LOGGER is willing to
service another network user, a 32 bit socket ID of a receive socket
will be sent over this initial connection and the ICP socket will
then be closed. If the LOGGER is not willing to service another
network user, it will not complete the initial connection for the ICP
socket and will refuse the request by closing the connection without
Once a pair of user sockets have been assigned, the connection
protocol should be completed on these sockets. The LOGGER then
expects to receive (on the receive socket) one 8-bit byte indicating
the data type which characterizes the transmission code used to
communicate with the network user over this pair of sockets. A code
of X'01' implies 7 bit ASCII code in 8-bit bytes with the leading bit
zero. A code of X'02' implies 8-bit EBCDIC code. When the data type
code is received, the LOGGER will echo back the data type code over
the send socket followed by the message:
LINCOLN LABORATORY CP-67 ONLINE NL
in the appropriate code. (In ASCII, NL is transmitted as CR LF).
The procedure continues according to the normal CP-67 login protocol
with the LOGGER performing an additional function of mapping network
userids and passwords into valid CP-67 userids and passwords. This
mapping is specified by entries in a file (the LOGGER FILE) which the
LOGGER accesses. If a network userid does not match an entry in the
file or if the password given does not match the corresponding
network password, the usual CP responses will be sent to the users.
Thus network access to the Lincoln Laboratory system is restricted to
those accounts for which an appropriate entry has been made in the
It should be noted that CP transmits a BYP code (Bypass) to suspend
the printing of characters keyed while a password is being entered.
After the password has been entered, CP transmits a RES code
(Restore) to resume the printing when characters are keyed. When
communicating in ASCII, these character codes are converted to X'FF'
since no corresponding ASCII code is defined. Refer to the Network
Resource Notebook for more details on CP-67 and on CMS.
The NET Account
Lincoln Laboratory is providing one account which can be used by
network users to familiarize themselves with our time-sharing system.
The userid of this account is NET and the password is ARPA. This
account has 900 records of storage, which can store approximately
720,000 characters. NET users are free to ERASE any file on this
account since many different people may use this account.
The SERVER Protocol
CP-67 operates on a line at a time, i.e., a group of characters are
processed as a line and not as a sequence of individual characters.
Also, the system does normally buffer input lines, that is, input is
not normally entered until requested by a read from the system. With
IBM 2741 or 1052 terminals, the keyboard is locked until a read is
requested. The virtual terminals through which network users have
access to the CP-67 system have been designed to support either a
line oriented terminal or a character oriented terminal. When CP
requests a line of input, the SERVER transmits a prompting code
X'80'. This character can be used to signal a user process to change
transmission modes and to transmit an input line. Characters
received by the SERVER are buffered until a NL character is received.
Lines received can then be used to satisfy CP requests for an input
CP may send out lines which may or may not end with a NL character.
If a line does not end with a NL character, the prompting character
will naturally be sent following the output line to request input to
a CP process.
When a user wishes to interrupt a CP process, i.e., to change modes,
an interrupt code X'80' should be sent to the SERVER. This code will
result in an asynchronous interrupt being sent to the running
process, stimulating the pressing of the 'attention' button on a 2741
terminal. Together with the transmission of the interrupt code, the
user should cause an INS to be sent over the send link. This signal
will be synchronized with the interrupt code. If the interrupt code
has not yet been received and processed, all characters buffered and
those received before the receipt of the interrupt code will be
flushed, i.e., deleted. When the interrupt code is received, it will
be paired with the previously received INS. If an INS is received
after an interrupt code has been received and processed, the INS will
be paired with this previously received interrupt code.
If CP has a line to send to a user after it has requested an input
line but before it has received any input, the SERVER will transmit
an INS on the user's receive link to notify the user that previously
sent prompting character should be retracted and that a line has been
or will be sent to the user. This message line is called a
Graphic and Control Codes
Figure 1 gives the 8-bit codes for the EBCDIC graphics and controls.
Figure 2 gives the 7-bit codes for the ASCII graphics and controls.
The controls are tabulated and compared in Figure 3. The standard
interpretation of the ASCII controls are given in Figure 4.
There are 4 ASCII codes which do not have a corresponding graphic or
control in the EBCDIC code. The EBCDIC codes given to these codes
are as follows:
| Hex Code
Symbol | ASCII | EBCDIC
DC3 | 13 | 3A
` | 60 | 70
\ | 5C | 71
^ | 5E | 72
There are 29 EBCDIC graphics codes and 19 EBCDIC control codes which
do not have a corresponding graphic or control in the ASCII code. In
addition, there are 84 other EBCDIC codes whose interpretation is
unspecified. Four of these codes have been chosen to correspond to
the ASCII control and ASCII graphics which do not have a
corresponding EBCDIC code. When converting EBCDIC codes to ASCII
codes, the remaining 80 codes plus the 29 EBCDIC graphics and 18
EBCDIC controls (not counting NL) are converted into the code X'FF'.
The NL character is treated specially. The NL character, EBCDIC code
X'15', is converted into the two character sequence CR LF, i.e.,
ASCII X'0D 0A'. As stated above, the code X'80' is transmitted as a
prompting character whenever CP requests an input line.
On converting from ASCII to EBCDIC, if any code other than the 128
ASCII codes, or the interrupt codem X'80', is received, it is
converted to the code X'FF'. In addition , whenever the two ASCII
characters CR LF are found sequentially in the input stream, they are
converted into the single EBCDIC character NL.
[In Figure 1, positions shown as "[?]" cannot be printed in ASCII.]
CAT EBCDIC ASCII TTY PTTC FUNCTION
NUL NUL NULL Null
CC SOH SOH SOM Start of Heading
CC STX STX EOA EOA (D) Start of Text
CC ETX ETX EOM End of Text
DC PF PF Punch Off
FE HT HT H.TAB TAB Horizontal Tab
GR LC LC Lower Case
DEL DEL RUBOUT DEL Delete
SMM Start of Manual Message
FE VT VT V.TAB Vertical Tab
FE FF FF FORM Form Feed
FE CR CR RETURN Carriage Return
GR SO SO SO Shift Out
GR SI SI SI Shift In
CC DLE DLE DC0 Data Link Escape
DC DC1 DC1 X-ON Device Control 1
DC DC2 DC2 TAPE ON Device Control 2
TM Tape Mark
DC RES RES Restore
FE NL NL New Line
FE BS BS BS Backspace
IL IL Idle
CAN CAN FE0 CAN Cancel
EM EM S1 End of Medium
CC Cursor Control
CU CU1 Customer Use 1
IS IFS FS S4 Info. Field Separator
IS IGS GS S5 Info. Group Separator
IS IRS RS S6 Info. Record Separator
IS IUS US S7 Info Unit Separator
ED DS Digit Select
ED SOS Start of Significance
ED FS Field Separator
DC BYP BYP Bypass
FE LF LF LF LF Line Feed
CC ETB ETB LEM EOB (B) End of Text Block
ESC ESC S3 PRE Escape
SM Set Mode
CU CU2 Customer Use 2
CC ENQ ENQ WRU Enquiry
CC ACK ACK RU (Y) Acknowledge
BEL BEL BELL Bell
CC SYN SYN SYNC Synchronous Idle
DC PN PN Punch On
DC RS RS Reader Stop
GR UC UC Upper Case
CC EOT EOT EOT EOT (C) End of Transmission
CU CU3 Customer Use 3
DC DC4 DC4 TAPE OFF Device Control 4
CC NAK NAK ERROR (N) Negative Acknowledge
SUB SUB S2 Substitute
DC DC3 X-OFF Device Control 3
Control Functions Compared
CC (Communication Control). A functional character intended to
control or facilitate transmission of information over
FE (Format Effector). A functional character which controls the
layout or positioning of information in printing or display
IS (Information Separator). A character which is used to separate
and qualify information in a logical sense. There is a group
of four such characters, which are to be used in a hierarchical
DC (Device Control). A functional character used for the control
of ancillary devices associated with data processing of
telecommunication systems, more especially switching devices
"on" and "off".
ED (Edit and Mark). A control character used by the System/360
Edit and Mark (EDMK) instruction for the formatting of
GB (Graphic Control). A control character indicating that the code
combinations which follow are to be interpreted in a particular
code table, depending upon the particular control character.
CU (Customer Use). A character excluded from future assignment by
IBM. These "protected" codes are intended for use by customer
systems so that their use will not conflict with a possible
future IBM use.
Figure 3 (Continued)
Categories of Control Functions
NUL (Null). The all-zeros character which may serve to accomplish
time fill and media fill.
SOH (Start of Heading). A communication control character used at
the beginning of a sequence of characters which constitute a
machine-sensible address or routing information. Such a
sequence is referred to as the _heading_. An STX character has
the effect of terminating a heading.
STX (Start of Text). A communication control character which
precedes a sequence of characters that is to be treated as an
entity and transmitted through to the ultimate destination.
Such a sequence is referred to as _text_. SIX may be used to
terminate a sequence of characters started by SOH.
ETX (End of Text). A communication control character used to
terminate a sequence of characters started with STX and
transmitted as an entity.
EOT (End of Transmission). A communication control character used
to indicate the conclusion of a transmission, which may have
contained one or more texts and any associated headings.
ENQ (Enquiry). A communication control character used in data
communication systems as a request for a response from a remote
station. It may be used as a "Who Are You" (WRU) to obtain
identification, or may be used to obtain station status, or
ACK (Acknowledge). A communication control character transmitted by
a receiver as an affirmative response to a sender.
BEL (Bell). A character for use when these is a need to call for
human attention. It may control alarm or attention devices.
BS (Backspace). A format effector which controls the movement of
the printing position one printing space backward on the same
printing line (applicable also to display devices).
HT (Horizontal Tabulation). A format effector which controls the
movement of the printing position to the next in a series of
predetermined positions along the printing line (applicable
also to display devices and the skip function on punched
LF (Line Feed). A format effector which controls the movement of
the printing position to the next printing line (also
applicable to display devices).
VT (Vertical Tabulation). A format effector which controls the
movement of the printing position to the next in a series of
predetermined printing lines (also applicable to display
FF (Form Feed). A format effector which controls the movement of
the printing position to the first predetermined printing line
on the next form or page (also applicable to display devices).
CR (Carriage Return). A format effector which controls the
movement of the printing position to the first printing
position on the same printing line (also applicable to display
SO (Shift Out). A control character indicating that the code
combinations which follow shall be interpreted as outside of
the character set of the standard code table until a Shift In
Character is reached.
SI (Shift In). A control character indicating that the code
combinations which follow shall be interpreted according to the
standard code table.
DLE (Data Link Escape). A communication control character which
will change the meaning of a limited number of contiguously
following characters. It is used exclusively to provide
supplementary controls in data communication networks.
DC1, DC2, DC3, DC4 (Device Controls). Characters for the control of
ancillary devices associated with data processing or
telecommunication systems, more especially switching devices
"on" and "off". (If a single "stop" control is required to
interrupt of turn off ancillary devices, DC4 is the preferred
NAK (Negative Acknowledge). A communication control character
transmitted by a receiver as a negative response to a sender.
SYN (Synchronous Idle). A communication control character used by
a synchronous transmission system in the absence of any other
character to provide a signal from which synchronism may be
achieved or retained.
ETB (End of Transmission Block). A communication control character
used to indicate the end of a block of data for communication
purposes. ETB is used for blocking data where the block
structure is not necessarily related to the processing format.
CAN (Cancel). A control character used to indicate that the data
with which it is sent is in error or is to be disregarded.
EM (End of Medium). A control character associated with the sent
data which may be used to identify the physical end of the
medium, or the end of the used, or wanted, portion of
information recorded on a medium. (The position of this
character does not necessarily correspond to the physical end
of the medium.
SS (Start of Special Sequence). A control character used to
indicate the start of a variable length sequence of characters
which have special significance or which are to have special
ESC (Escape). A control character intended to provide code
extension (supplementary characters) in general information
interchange. The Escape character itself is a prefix affecting
the interpretation of a limited number of contiguously
FS (File Separator), GS (Group Separator), RS (Record Separator)
and US (Unit Separator). These information separators may be
used within data in optional fashion, except that the
hierarchical relationship shall be : FS is the must inclusive,
then GS, then RS, and US is least inclusive. (The content and
length of a File, Group, Record, or Unit are not specified.)
DEL (Delete). This character is used primarily to "erase" or
"obliterate" erroneous or unwanted characters in perforated
tape. (In the strict sense, DEL is not a control character.)
ASCII Control Functions
 - Cent sign
 - Logical not ("bent bar")
[?] - Graphics not in ASCII. See Postscript or PDF version of
[This RFC was put into machine readable form for entry]
[into the online RFC archives by Lorrie Shiota, 10/02]