RFC 0080
Protocols and Data Formats
Network Working Group E. Harslem Request for Comments: 80 J. Heafner NIC: 5608 RAND 1 December 1970 PROTOCOLS AND DATA FORMATS Because of recent discussions of protocols and data formats we issue this note to highlight our current attitudes and investigations in those regards. We first discuss some specific sequences, and then offer some thoughts on two general implementation approaches that will handle these and other specifics. We wish to place emphasis on the _general solutions_ and not on the specifics. INITIAL CONNECTION PROTOCOLS We wish to make two points concerning specific Initial Connection Protocols (IPCs). Firstly, the IPC described in NEW/RFC #66--its generality and a restatement of that ICP. Secondly, a proposal for a variant ICP using basically the same logic as NWG/RFC #66. I. NWG/RFC #66 The only technical error in this IPC is that as diagrammed both the Server and User send ALL messages before the connections are established which is inconsistent with Network Document No. 1. This can easily be remedied as will be shown in the restatement below. In terms of generality, any ICP that is adopted as a standard should apply to more situations than a process calling a logger. That is, some Network service processes that hook directly to a user process, independent of logger action, could perhaps use a standard ICP. Thus, as is shown below, the process name field of the server socket should be a parameter with a value of zero being a special case for loggers. Restatement of NWG/RFC #66 (using the same wording where appropriate) 1. To initiate contact, the using process attaches a receive socket (US) and requests connection to process SERV socket #1 in the serving HOST. (SERV = 0 for ICP to the logger.) As a result the using NCP sends:
1 4 3 1 1
+-----+---------------------+---------------+-----+-----+
| RTS | US | SERV | 1 | P |
+-----+---------------------+---------------+-----+-----+
over link 1, where P is the receive link.
2. The serving process (SERV) may decide to refuse to the call, in
which case it closes the connection. If it accepts the call,
the serving process completes the connection (via an INIT
system call, hence an STR).
1 3 1 4
+-----+----------------+-----+--------------------+
| STR | SERV | 1 | US |
+-----+----------------+-----+--------------------+
3. When the connection is completed, the user process allocates a
nominal amount of space to the connection, resulting in the NCP
sending:
1 1 4
+-----+-----+--------------------+
| ALL | P | SPACE |
+-----+-----+--------------------+
where SPACE is the amount.
4. The serving process then selects the socket pair it wishes to
assign this user. It sends exactly an even 32 bit number over
the connection. This even 32 bit number (SS) is the receive
socket in the serving HOST. This socket and the next higher
numbered socket are reserved for the using process.
5. It then closes the connection. The serving NCP sends (step 4):
4
+---------------------+
| SS |
+---------------------+
on link P, and (step 5):
1 3 1 4
+-----+----------------+-----+--------------------+
| CLS | SERV | 1 | US |
+-----+----------------+-----+--------------------+
on the control link (which is echoed by the using NCP).
6. Now that both server and user are aware of the remote socket
pair for the duplex connection, <STR, RTS>s can be exchanged.
_Sever sends User_
1 4 4
+-----+--------------------+--------------------+
| STR | SS + 1 | US |
+-----+--------------------+--------------------+---+
| RTS | SS | SS + 1 | Q |
+-----+--------------------+--------------------+---+
where Q is the Server's receive link.
_User sends Server_
1 4 4
+-----+--------------------+--------------------+
| STR | US + 1 | SS |
+-----+--------------------+--------------------+---+
| RTS | US | SS + 1 | R |
+-----+--------------------+--------------------+---+
where R is the User's receive link.
ALLocates may then be sent and transmission begun.
II. A Variation of NWG/RFC #66
This variation reduces Network messages and eliminates duplication of
information transfer.
Steps 3 and 4 above are deleted. The user process is not notified
directly which of the Server's sockets it will be assigned. The user
process, however, will listen on sockets US and US + 1 for calls from
SERV after step 5 above. It can reject any spurious calls. In
accepting the calls from SERV, the connection is established.
The following sample sequence illustrates this ICP. (The notation is
as above).
1. User --> Server
1 4 3 1 1
+-----+--------------------+----------------+-----+-----+
| RTS | US | SERV | 1 | P |
+-----+--------------------+----------------+-----+-----+
2. Server --> User
If accepted:
1 3 1 4
+-----+----------------+-----+---------------------+
| STR | SERV | 1 | US |
+-----+----------------+-----+---------------------+
| CLS | SERV | 1 | US |
+-----+----------------+-----+---------------------+
If rejected:
1 3 1 4
+-----+----------------+-----+---------------------+
| CLS | SERV | 1 | US |
+-----+----------------+-----+---------------------+
3. If accepted, user listens on US and US + 1.
4. Server --> User
1 4 4
+-----+--------------------+---------------------+
| STR | SS + 1 | US |
+-----+--------------------+---------------------+---+
| RTS | SS | US + 1 | Q |
+-----+--------------------+---------------------+---+
5. User accepts the calls, hence:
User --> Sender
1 4 4
+-----+---------------------+--------------------+
| STR | US + 1 | SS + 1 |
+-----+---------------------+--------------------+---+
| RTS | US + 1 | SS | R |
+-----+---------------------+--------------------+---+
and the connection is established.
This reduces the number of network messages by two and only passes
the information regarding the Server's sockets once via RTS and STR.
PRE-SPECIFIED DATA FORMATS
We would like to adopt those suggestions for data formats in NWG/RFC
#42 and #63. We subscribe to multiple standards as solutions to
particular problem classes.
AN ADAPTABLE MECHANISM
We would like to adapt to Network use, problem programs that were
not planned with the Network in mind, and which, no doubt, will
not easily succumb to Network standards existing at the time of
their inclusion. This incompatibility problem is just as
fundamental a part of the research underlying the Network as is
different Host hardware. To require extensive front-ends on each
such program is not a reasonable goal. We view the Network as an
amalgamation of a) Hosts that provide services; b) parasite Hosts
that interface terminals to the services, and c) a spectrum of
Hosts that behave as both users and providers of services. To
require that each parasite Host handle different protocols and
data formats for all services that its users need is not a
reasonable goal. The result is programs and terminals that wish
to communicate but do not speak the same language.
One approach to the protocol and data format problems is to
provide an adaptable mechanism that programs and terminals can use
to easily access Network resources. ARPA is sponsoring the
Adaptive Communicator Project at Rand which is a research effort
to investigate a teachable front-end process to interface man to
program. The variety of terminal devices being explored include
voice, tablets, sophisticated graphics terminals, etc.
The Adaptive Communicator looks very encouraging but it will not
be ready for some time. The Network Project at Rand chose to take
the adaptable approach (_not_ adaptive, i.e., no heuristics, no
self-learning). Our problem is to get Rand researchers onto the
Network easily, assuming that they have different simultaneous
applications calling for different program protocols and data
configurations.
Protocols and data formats will be described separately to
illustrate what we mean by adaptation. Protocols are sequences of
"system calls" that correspond to (and result in NCP's issuance
of) NCP commands. Data formats are the descriptions of regular
message contents and are not meaningful to an NCP.
The Form Machine (adapting to data formats)
To put the reader in context, the Form Machine is of the class of
finite state machines that recognize a form of _regular_
expressions_ which, in our case, describe data formats. The
notation, however, is aimed at particular descriptions and
therefore can be more succinct, for our purposes, than the
language of regular expressions.
The Form Machine is an experimental software package that couples
a variety of programs and terminals whose data format requirements
are different. We envision Form Machines located (to reduce
Network traffic) at various service providing Hosts.
To test the Form Machine idea, we are implementing two IBM OS-
callable subroutines; a compiler that compiles statements which
describe forms of data formats; and an executor that executes a
compiled form on a data stream.
To describe the Form Machine test, it is necessary to mention
another program at Rand--the Network Services Program (NSP), which
is a multi-access program that interfaces the Network Control
Program both to arbitrary programs and to Video Graphics Consoles.
(We view a terminal as just another program with a different
interface, i.e., # characters/line, # lines/page, unique hardware
features, the application to which it is put, etc.) The Form
Machine subroutines are callable from NSP upon consoles or program
direction.
Operationally, a console user names and specifies the data forms
that he will use. The forms are compiled and stored for later
use. At some future time when the user wishes to establish
Network connections and transmit data, he dynamically associates
named forms with each side of a port--a symbolically named Network
full duplex connection. Data streams incoming or outgoing are
executed according to the compiled form and the transformed data
stream is then passed along to the console/program or to the
Network, respectively.
The details of the syntax of our Form Machine notation are
unimportant to the collective Network community. However, the
provisions of the notation are of interest. It will eventually
encompass the description of high performance CRT displays, TTY,
and arbitrary file structures. To test its viability, a subset of
such features is being implemented.
The current version is characterized by the following features:
1) Character code translation (viz., decimal, octal,
hexidecimal, 8 bit ASCII, 7 bit ASCII, EBCDIC, and
binary).
2) Multiple break strings (many terminals have multiple
termination signals).
3) Insertion of literals (used primarily for display
information presentation).
4) Skip or delete arbitrary strings (used to remove record
sequence numbers, etc., that are not to be displayed).
5) Record sequence number generation.
6) String-length computation and insertion.
7) _Arbitrary_ data string length specifications, e.g., "a
hex literal string followed by an _arbitrary_ number of
EBCDIC characters, followed by a break string, .....".
8) Concatenation of Network messages, i.e., the execution of
compiled forms on incomplete data strings.
9) Data field transposition.
10) Both explicit and indefinite multiplicative factors for
both single and multi-line messages.
Features that are not being implemented but will be added, if
successful, include:
1) Graphics oriented descriptions.
2) General number translations.
3) Conditional statements.
4) A pointer capability.
The Protocol Manager (adapting to NCP command sequences)
The NSP allows terminal users and programs to work at the NCP
protocol level; i.e., LISTEN, INIT, et al. It also allows them to
transmit and massage information meaningful only to themselves.
This "hands-on" approach is desirable from the systems
programmer's, or exploratory point of view. However, it is
desirable to eliminate the laborious "handshaking" for the
researcher who repeatedly uses a given remote program by allowing
him to define, store, retrieve, and execute "canned" protocol
sequences.
We are currently specifying a Protocol Manager as a module of NSP
that will allow the above operations on NCP command sequences.
Features of the module are:
1) The sequences may contain "break points" to permit the
console user to dynamically inject any contextually needed
information.
2) The parameters of a command may contain tokens whose values
are supplied by the remote party during the protocol dialog.
For example, in Note #66 the socket number provided by the
server is to be used by the user in subsequent RTS, STR
commands.
REQUEST
We would like to hear from anyone concerning the notion of
adaptation to data formats and protocol. Is this a reasonable
approach? What should it encompass?
JFH:EFH:hs
Distribution
Albert Vezza, MIT
Alfred Cocanower, MERIT
Gerry Cole, SDC
Bill English, SRI
Bob Flegel, Utah
James Forgie, LL
Peggy Karp, MITRE
Nico Haberman, Carnegie-Mellon
John Heafner, RAND
Bob Kahn, BB&N
Margie Lannon, Harvard
James Madden, Univ. of Ill.
Thomas O'Sullivan, Raytheon
Larry Roberts, ARPA
Robert Sproull, Stanford
Ron Stoughton, UCSB
Chuck Rose, Case University
Benita Kirstel, UCLA
[This RFC was put into machine readable form for entry]
[into the online RFC archives by Lorrie Shiota, 10/01]