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SETTING
S TANDARDS
FOR
COMPUTER COmUNICATION
THE CASE OF X.25
Marvin
Laurence
A.
E.
Sirbu
Zwimpfer
September 1984
CISR WP #117
Sloan WP ^/s^^^'g^
_DEWEy LIBRARY
Center for Information Systems Research
Massachusetts
Institute of
Sloan School of
Technology
Management
77 Massachusetts Avenue
Cambridge, Massachusetts, 02139
S TANDARDS
SETTING
FOR
COMPUTER COmUNICATIQN
:
THE CASE OF X.25
Marvin
Laurence
A.
E.
Sirbu
Zwimpfer
September 1984
CISR WP #117
Sloan WP -^/^"^/^y-g^
©
n,
A.
Sirbu.
L.
E.
Zwimpfer
1984
Center for Information Systems Research
Sloan School of Management
Massachusetts Institute of Technology
standards Setting for Computer Communication:
The Case of X.25
Marvin
A.
Laurence
and
Zwimpfer
Sirbu
E.
Introduction
1
The
to
first
international meeting to set standards for data
discuss interconnection
of
to
computers and communications technology
economic environment
of
in
in
of the
2.
of
particular.
the 1970s, coupled with
in
1865,
these changes, and
illustrate
The convergence
changes
these industries have forced dramatic changes
standards, and the processes by which standards are developed,
broad directions
Paris
coordinate the development of standards for
general and data communications
in
in
telegraph systems. Since that time, an elaborate network of institutions
and procedures have grown up which attempt
telecommunications
communications was held
in this
in
them with a detailed examination
the political and
both the role of
in
paper,
of
we
shall outline the
of the
development
packet switching standard, X.25.
The Nature and Function
Standards are
of
many
types:
of
Standards
the IBM Personal
standard for personal computers.
Bell
Computer Technical Reference defines a de
Communications Research procurement specifications
represent another type of standards document. More typically, however,
v/e think of formal
documents
facto
certified by a self-defined
when we
think of standards
standards making body. Groups engaged
in
formal standards setting include international agencies, national standards bodies, professional
associations, trade associations, government regulatory agencies and cabinet departments and
bureaus. Standards may, but usually do not, have the force of law; generally they represent voluntary
agreements among producers.
Massachusetts
Institute of
New Zealand
Post Office
Technology
While a
Firms
can be tliouyht
staiKJcird
may
of
as a documenl.
compatible devices though v^hat
build
it
is
also involves a set of behaviors and a process.
required for compatibility
down. Conversely, because a standard has been reduced
agreed
to
abide by
Standardization
it.
the patterns of behavior which
will
is
is
nowhere
does not mean
to writing
the process of developing the consensus
written
that firms
among
have
firms
and
achieve the ultimate goals of a standard, not just the production
of
a document.
the area of computers
In
and communications there are two
compatibility and variety reduction V
Compatibilitv or interchanqeabilitv standards are necessary for
complementary products, manufactured by
and boxcar axles,
equipment (DCE)
light
will
Variety reduction
work together.
Railroad
gauges
not work together unless they are compatible.
number
achieve potential economies of scale.
induce chipmakers
different producers, to
bulbs and sockets, data terminal equipment (DTE) and data circuit-terminating
limiting the
,
principal functions of standards:
to invest in
of versions of a product,
A
local area
VLSI implementations
may be
essential for producers to
network (LAN) standard may be necessary
of a local
to
network protocol. Without a standard,
they would be skeptical of achieving sufficient production volumes to justify the front end investment
in
chip design.
Variety reduction can also lead to
The absence
reduced inventory holdings^.
software dealers must stock programs
in
of a
economies
of stocking
and
distribution through
standard for 5 1/4 inch floppy disks means that
multiple versions for
each possible system.
While the compatibility and variety reduction functions are often closely related, they are not the
same.
Maximum
economies
of
compatibility would require a single local area network protocol; but available
scale
in
chip manufacturing
two different protocols. This
Mirlan
In
LANs
with the
same
is
may be achievable where
precisely what Intel proposes to
do
the
in
same chip can be used
for
supporting both Ethernet and
chip set^.
the information and communications arenas, compatibility has two aspects:
1.
the functions or services provided by the tv/o devices must be compatible; and
2.
the procedures used to provide the functions or services must be compatible.
procedures can often be made compatible
Identical functions provided using different
simple softwate conversion
the functions provided are different, an exact translation
If
means
Additional functionality usually
possible.
tiigfier
research and development. Functionality may also be
end
As a consequence, arguments over
user.
costs, either for the
critical to
tiiroucjh a
may
not be
end equipment
or for
achieving market acceptance by the
v;hat functionality to include
in
a standard are usually
the most contentious.
3.
Economic Theory
The economic motivation
•-
Standards
of
standards
for
compatibility or variety reduction -
be different depending upon the goal
will
and depending upon the economic positions
of the
standard
of the participants
the standards process.
in
In
the absence of economies of scale
in
production or of inventory, there
variety reduction standards. Similarly, there will
be a demand
for compatibility
is
no incentive to seek
standards only
wish to communicate or share information with a wide range of other users, and
translation, or multiple basic
The market structure
standardization.
equipment
of
sets,
Users often pay dearly
users
the costs of
significant.
buyers and
both
sellers
is
absence
for the
clearly
relevant
to
the
incentives
of standards, thus, they should
for
be the
Buyers may be fragmented, however, and unable
supporters of standardization.
principal
is
if
if
to
coordinate their demands. Where buyers are few and powerful, they can more easily exert pressure
on
sellers
to
Concentration
standardize,
increased
Where
with,
demand
standardize
in
force
among buyers should
Communications
communicate
or
networks
the
for
have
standards by coordinating
significant
is
externalities:
it
total size of the
may be
the
more other people one can
Where these
the network.
equipment which can access a larger
sellers are fragmented,
purchase specifications.
thus favor standardization.
more valuable
order to increase the
their
externalities translate into
portfolio, sellers
have an incentive
to
market.
difficult
to
coordinate the development
of
standards.
Where
there
is
one dommcmt
firdi
and many small ones.
v;e
can expect de facto standards
be set by
to
the dominant firm (absent patent, trade secret or copyright protection which inhibits copying the
dominant
Where
firm)'*.
sellers are few but of equal size, compatibility
standards would act
to
reduce
market power, and thus may be resisted. Integrated sellers v;ho produce both primary and secondary
products
may
resist standardization
since
allows entry to competitors
it
who produce
one
only
of
two
conjoint products.
The coalescence
of firms
around a standard
positive externalities of adopting the standard
of other users.
Thus, smaller firms are led to
is
a positive feedback process which results from the
which allows communications with the largest number
fall in
behind the standard of v/hichever
firm or
group
of
firms establishes the largest early following.
Standards Setting Processes
4.
in
Computers and
Telecommunications
the mid 1970s, the structures of the telecommunications and computer industries differed greatly.
In
These differences included the
characteristics
employees.
of
All of
the
legal charter of the participants; their
technology;
and the characteristics
their
of
these differences contributed to quite different patterns
economic motivations; the
technical
of
and
behavior
managerial
v/ith
respect to
standards.
4.1
.
Telecommunications
Telecommunication services have
of
traditionally
Posts Telegraph and Telephone (PTTs)
-•,
been provided by government agencies
--
Ministries
by nationalized firms such as Nippon Telephone and
Telegraph, or by regulated private monopolies such as AT&T. Until quite recently, the focus
firms has
been on the extension
of basic
population. Thus, from 1976 to 1983, the
24
million.
In
telephone service
number
of
telephones
most countries there was an unmet backlog
of
to
in
of
these
an ever greater fraction of the
France increased from 7
demand
for basic service;
million to
consequently,
telephone authorities have been more concerned with increasing supply than designing and
marketing
ne-.v
products or services. Technological change
v.-as
confined primarily to the process of
providing telecommunication services and not to the service product.
Telecomiminication operations are characterized by large capital investments
in
highly reliable,
k
'
long-lived equipment.
years,
Telecommunications equipment
and thus new technologies are introduced
equipment continue
Because
to
work with the
most network operators,
would
for
in
fact
spend
all
working
promotion and therefore middle
As monopoly providers
own standards
International
of
life
the technical and
with the
for
its
levels
organization. Seniority
managers are
is
to
no voting power.
of
has been low; most
an important element
typically over 40.
At the international level, they
meet together as members
their
of the
decide on interconnection arrangements between
to the
telecommunication carriers also
Technical standards (or Recommendations as they are
set by the International Consultative
(CCITT), a permanent organ of the ITU. The
work
same
management
The manufacturers who supply equipment
known) are
an absolute requirement that new
telecommunication services, most have absolute authority to set
Telecommunication Union (ITU)
participate but they have
is
telecommunication systems and the monopoly position
level technical
at the national level.
national networks.
formally
of
staff mobility at
their
There
slowly.
old.
character
of the specialist
often depreciated over a period of 20-40
is
Committee
CCITT meets every
specialized study groups and approve
for
Telegraph and Telephone
four years to agree on a
new Recommendations.
program
Detailed technical
work
of
is
carried out by Working Parties or Special Rapporteurs.
Telecommunication standardization processes have
decades
defined
of first-hand
and
homogeneous
experience
understood
tight-knit
by
in
been very
international agreement-making.
participants^.
The
participants
group with a rather conservative outlook.
international standards to
motivating factor
the
in
traditionally
permit the interconnection of
national
stable,
based on many
The process has been
have also been a
well-
relatively
The absolute necessity
for
networks has been a strong
obtaining complete consensus on the standards developed, although there have
been cases when some participants have placed more value on national goals than international
ones,
(e.g.
color television standards®). Typically, standards have only been approved after they have
been implemented and
tested; that
is,
the standardization process has relied heavily on
compromises
Hov;ever. the process has not been able to cope
based on established de facto standards'
situations
m
which participants already have a substantial commitment
standard: for example, the divergent U.S. and European standards for
4.2.
to
v^ell
with
a particular de facto
PCM.
The Computer Industry
The computer industry
in
the mid 1970s presented a completely different picture.
Instead of stable,
conservative, national monopolies, the computer industry w/as a dynamic, rapidly changing industry
dominated by a few large multinationals.
changes
The industry has been highly innovative and
product mix. The industry's dominant
its
in
in
IBM rose
to
its
position through
its
Unlike the
telecommunication industry, the infrastructure required to support a computer system
The people involved are
also typically
(20-40 age group) and as a group have a
because they possess more marketable
Attempts
at
standards setting
in
much younger
much
encouraged
to
than
in
the telecommunication industry
higher mobility --partly because of their age but also
the computer industry have been diffused and largely ineffectual.
Institute
(ANSI)
been coordinated by a single organization
in
do the actual standards development work, including trade associations
and Electronic Engineers
(IEEE)).
(e.g.
The
the United States) but other organizations are
United States, the Electronic Industries Association (EIA)), and professional groups
of Electrical
is relatively
skills.
At the national level, standards have generally
American National Standards
life of
microelectronic miniaturization and the corresponding rapid decline
costs has created a pressure on users to regularly upgrade their equipment.
small.
emphasis
Most computer equipment has had a design
on marketing, rather than process technology.
5-10 years; the rapid advances
firm,
rapidly
Large computer users
(e.g.
(e.g.
the Federal
(e.g. in
the
the Institute
Government
in
the United States acting through the National Bureau of Standards) have also taken an active interest
in
the development of standards, and where necessary, have adopted their ov;n standards.
Because the computer industry has been so dominated by IBM, consensus standards-setting
procedures have been
(typically the
relatively unsuccessful.
Only when there has been pressure from a large user
government) has progress been made.'' Because IBM has been a
full line
producer
of
both basic aiul ccniplomentary products,
it
lias
had
little
incentive to support standards wtiicii would
piecemeal fashion.
have enabled smaller competitors
to attack
early years operated primarily as
standalone devices there
it
in
Also,
because computers
in
the
loss incentive for standardization.
vi^as
Users could achieve internal standardization by buying from a single vendor; standardization on a
larger scale brought few additional advantages. Rapid technological
For example,
at standardization.
in
1961 IBM was promoting
interchange code, but only four years later had changed
4.3.
Changing Industry Structure and
Ivlajor
changes
to
its
6
change also undermined
bit
support an
code (BCD) as a US standard
8-bit
code (EBCDIC).
Effect on Standardization
Its
both technology and regulation altered dramatically the industry structure
in
efforts
in
both
These changes affected the motivations
computers and communications during the 1970s.
for
achieving data communication standards, and had a profound impact on the development of X.25.
Beginning with the Carterphone decision
in
1968 and the Specialized
Common
1971, the U.S. began opening the telecommunications industry to competition.
literally
hundreds
of
companies would be
including computer terminals and
-•
services, including
dominance
of the U.S.'
anti-trust
suit
Within a few years
customer premises equipment
- while others would promise a host of
This influx of
new
new entrants challenged AT&T's
filed
also
in
was witnessing
1959,
minicomputer market, IBM had
a period of increased competition.
networks
of
of large
hundred
and because
lost
of
its
failure
to
computer
or
utilities
even thousands
technology.
in
threat of
foresee the importance of the
share to a new group of companies such as
possible by the spectacular successes
standards:
traditional
Under the
Digital
Corporation, Data General, and Prime. With continued growth, the industry also began to
from the model
netv/ork
telecommunication standards process.
The computer industry
an
modems
digital facilities.
all
offering a dazzling variety of
Carrier decision in
Equipment
shift
away
based on hand crafted mainframes towards interconnected
of
mass produced machines.
microelectronics,
This transformation,
made even more
made
imperative the need for
not only for compatibility, but to achieve the economies of scale offered by VLSI
8
VLSI
allows extremely complex devices to be manufactuied
tecliiiulocjy
challenge
is
a design
find
to
needed
in
change. Complex software - such as
characteristics:
based standards are easier
to
for
in silicon,
costs.
investments.
however, standards are more
computer networking
and low reproduction
large design costs
very low unit cost; the
sufficient quantity to justify the frdnt-end
Standards help create and define such needs. Once etched
difficult to
at
--
exhibits similar
economic
Unlike hardware, however, software
modify and evolve, posing problems
in
the stability of standards
once
they are codified.
These changes
The
shift
technology and regulation have affected the standards process
in
from standards primarily
for
reasons
altered the motivations of the participants.
of compatibility
The need
to define
as opposed to interconnect two national markets leads
a standard
in
several ways.
for variety
reduction
order to create a market,
to:
accelerate the standards process for commercial reasons;
1.
pressures
2.
definition of standards in parallel with research
to
towards standards
in
and development on the underlying
technology;
3.
increased risks
4.
the
absence
of
of
problems
in
the resultant standards
market experience making
difficult
the appropriate level of functionality to incorporate
Finally,
the
to
hasty development; and
the resolution of controversies over
in
the standard.
deregulation and the convergence of computers and communications has vastly increased
number
standard
due
The
of players.
will
be agreed
to,
larger set of
or b)
some
needs
to
significant
be
satisfied increases the risk- that either: a)
group
of users will find the resulting
no
standard
unacceptable.
Thus, as a result
of
deregulation
in
production and increased competition
came under heavy pressure
just as
the telecommunications industry and a shift towards
in
computers, the standards processes
packet netv^orks were being developed.
in
mass
these industries
5.
Computer Communications and Packet Switching
Early
computer systetns were quite independent
was
industry
not constrained by the
with remote terminals
were
still
absence
of
of
each other and therefore the development
standards. Even early timesharing computer systems
relatively self-contained:
typically both the central
remote terminals would be supplied by the same manufacturer
manufacturers would copy the de facto standard
were required
to interface
need
critical
for
communications
line
of
was
at
the principal supplier). However,
between
interface
the
which linked remote terminals
to the
modems which
converted
digital
e.g.
some standards
modems. The
computer terminal
the
computer.
"foreign attachments" to the network, the telephone administrations
standards for the
processor and the
equipment supplied by other
(or
computers with the communications network,
standards
of the
Through
were
in
single
and
their control
the
over
a position to determine
bitstreams into analog signals suitable for the voice
network.
But voice telephone circuits are costly to the data communications user and
totally
inadequate for
high speed, error-free data communications. During the late 1960s, the concept of packet switching
emerged as a
"bursty"
solution to the problem of providing efficient, error-free service to computers sending
Packet sv^itching systems transmit data by means
traffic.
which include both data and
of binary digits
call
of
addressed packets,
control information.
available for use by packets being transferred
between
to create,
process, and switch packets
communications channels. Thus,
more
efficient
it
became
was
declining at a
much
of
computer processing
faster rate than that of
cost effective to use computer-based switching to
make
use of the channel.
There are two
distinctly different
ways
to'
organize the provision of packet switching service:
connection-oriented or connectionless, often referred to as
Datagram
address
The channel then
different data terminal equipment.
Packet switching became economically viable largely because the cost
needed
groups
These packets occupy the
transmission channel for the duration of the transmission of the packet only.
becomes
i.e.
service.
In
virtual circuits vs
datagrams.
a "connectionless" datagram network, each packet carries the
of the destination
and
is
full
routed independently from the origin to destination
10
terminal.
As a
be corrupted
is
packets may arrive out
in transit
by errors, or even
of
seciuence
lost altogether.
Others may
at
the dci^tinalion.
In
a connectionless network,
it
the responsibility of the endpolnts to resequence packets or request retransmission of
packets
•
result,
Virtual
damaged
in transit.
service
circuit
is
the logical equivalent of a physical circuit, or connection,
between the source terminal and destination terminal. An originating terminal starts by
sending a call origination packet which specifies the destination to which subsequent
data packets are to be sent. The call is assigned a short logical call number which can be
used to specify where to send subsequent packets. The network takes responsibility for
insuring that packets arrive
in
the correct
sequence
for requesting retransmission of lost packets.
packet takes
down
shall
see
later,
debates over
At the
As with leased
the virtual circuit.
customers can be assigned "permanent
As we
as they would on a "circuit" • and
virtual circuits"
virtual circuit
end
of
a
virtual call,
lines in the
a clearing
telephone network,
which are always
in
place.
versus datagram service played an important role
the development of packet netv,/ork standards.*
in
5.1
.
Standards
The exchange
for
Computer Networks
of
data over a computer network requires agreement
at
many
levels,
physical interconection of the computer to the communication line to agreements on the
the bits exchanged between computers at opposite ends of the network. Early
packet networks
it
was recognized
that a standard
terminal should connect to the netv;ork.
would be needed
This interface, between
boundary between equipment provided by the
carrier
in
to define
from the
meaning
of
the development of
how
a computer or
DTEs and DCEs, would mark
the
and equipment provided by the user, or the
computer manufacturer.
The development
of
standards
process and motivations
for this interface
for standardization in the
provides a dramatic illustration of the differences
computer and the telecommunications
•
For a further discussion of the merits
of virtual circuits
versus datagrams see
8 9 10 11
'
*
industries.
in
11
A Case Study
6.
The
revolution
in
X.25
of
computers and coinnuinications has been so rapid and computer communication
networks are today so widespread that
demonstrated the
possibilities of
seems
it
diflicuit
to
imagine that the
packet switching a mere 15 years ago. Indeed, v/hat
ARPANET
is
striking
first
about
the history of X.25 are the doubts which prevailed throughout the process as to the very need for
public packet networks, and
tiie possibilities of
developing a successful standard. While today X.25
can be viewed as a successful standard, there were, as we
6.1.
many rough spots along
the way.
X.25 gets on the standards agenda
The need
CCITT
systems and standards
for special
with the creation of a
Working Party
Transmission Working Party was elevated
had produced a
set of
in
to
for
data communications was
full
study group status, and by 1964, the
to
had outlined a program
should be standardized
of
to permit international
the discussion within
to investigate the possibilities of
Vli
(New Networks
23 points under the general Question:
NRD
prior to
new
for
Data Transmission) and
"What general characteristics
data communications over public data networks?"
1972 had concerned
between 1968 and 1972 several PTTs had announced
circuit
switched public data networks;
their intention to build
such networks.^** Only
23 points. Question C, dealt with packet switching: "Should the packet-mode of operation
be provided on public data netv;orks, and
if
so
how should
Special Rapporteur had been appointed for question
NRD
new study group
data transmission services.'^
By 1972, the Working Party had became Study Group
of the
recognized by the
the late 1950s. At the 1960 Plenary Assembly, the Data
Working Party' was created
networks that might be wholly dedicated
fvlost of
first
recommendations dealing with data transmission over the telephone network.
At the 1968 Plenary a Joint
one
shall see,
Nouveau Reseau de Donnees
C and
it
be implemented?"^^ By July
a program of study established.
of
1974 a
12
switched networks
6.2. Early packet
By 1972, when the CCITT was
still
asking whether there should even be public packet switching
networks, there were numerous private or experimental net-.vorks already
the U.S.'^.
networks,
NPL
RETD
Spain and the Tymnet network
in
the U.S.^'' were also
Most telephone administrations, however, expected
demand
voice and data, to meet the
for
circuit
of traffic,
and data was
In
••
and the idea
as
it
still is -•
of
skeptics into believers.'^ Hov;ever, there
wisdom
be
networks, carrying both
more economical than
far
communications generated by
demonstrated
far
for carrying
the greater
both voice
still
the
first
International
manufacturers v;ould be reluctant
to
make
Conference on
Roberts, then head of
DARPA, converted many
a great deal of uncertainty
among PTTs concerning
to Larry
was
at
packet services: standards v/ould take too long
of establishing
public
viewed as speculative.
Computer Communications, and, according
the
digital
to
in
operation.
in
packet networks as the dominant technology
ARPANET was
October 1972, the
switched
data services and, ultimately,
building a separate packet network just for data. Voice
amount
Two
the UK, and the international airline reservation network, SITA.^^
in
in
ARPANET
operation;
in
to
develop and computer
the necessary changes to their products to support a
standard network interface.
Such skepticism had not deterred
ARPANET
builders, Bolt
first
Packet Communications Inc and then Telenet
Beranek and Newman) from seeking authority
in
US
the
(a subsidiary of
to establish public
packet networks. By April 1974, both had received approval, though PCI soon dropped out when
had trouble raising
In
capital.
France, a decision to build a public packet switched network
November
(TRANSPAC) was made
in
RCP.^
In
1973,^® based on experience gained with an experimental network called
Canada, a trans-continental
Communications Group
service
it
was recognized
all
of the
to
packet switched service,
digital private line service
was introduced
in
1973 by the Computer
Trans-Canada Telephone System (TCTS).^^ However,
be uneconomic
for
low volume users.
DATAPAC, which was announced
in
TCTS began
planning
October, 1974.^^
In
private line
in
1973
for a
the UK, the British
13
Post Office av;arded a contract to Ferranti Ltd.
August 1973
in
for
an experimental packet service.
EPSS.^^
There was also considerable interest
European Informatics Network
EURONET was
while
(EIN)
in
two packet networks being developed
in
at the
end
1971 Japan's
which was
a project of the PTTs, designed to
A contract
1973,
and tested by NTT
NTT
and attending
Commercial Pressure
November
circuit
for a
of 1974, at the third
meeting
netv/ork service would have to provide
to
the
end
of 1974.
switched networks.
use the network.
in
Needing a standard
particular
were anxious
into operation until 1975,
to
Rapporteur's meetings.
of the
Rapporteur's group, attention
finally
to the question of a standard for the interface
it.
custom software and hardware
for every
moved past
between the
of
packet
brand of computer
With such a standard, the computer vendors themselves might
see a standard defined. While
DATAPAC was
The Canadians
not scheduled to
come
to
bo made
ICCC
in
1974 suggested that there would be many networks
at
the second
in
1980.
in
If
1974. Moreover, the growing interest
in
a standard could not be agreed before
the 1976 Plenary, then by 1980, each network v;ould have been firmly committed to
unacceptable.
DTE/DCE
Without such a standard, a would-be vendor
by the end of the subsequent CCITT study period
of
in
design decisions had
packet switching exhibited
and the adoption
for
the v/ork of the Rapporteur's Group, eventually
eventually provide the necessary capability for their products to use packet networks.
in
and
successor, DDX-2, for which research began
of the
ail
network and the computers which would use
wanted
let at
Standard
whether there should be packet nets
that
It's
took an active interest
subfnitting 15 contributions,
In
EIN was
for
information databases
an integrated circuit/packet switching system, DDX-1,
1974.^^
in
was based on separate packet and
interface for DDX-2^^,
6.3.
make science
of 1975.
NTT had begun research on
installed
Europe: The
and EURONET. EIN was driven by the research community.^*
throughout Europe more easily accessible.
EURONET
jointly in
a new international standard would be both
politically
its
own
design,
and economically
14
Dave Norton,
Thus,
his
in
Communications Group
in
role
as
Assistant
TCTS began an
interface standard. Morton realized that
Vice-President
for
Planniny
Computer
the
of
international lobbying effort to press for the adoption of an
order to influence the CCITT, he would
in
support from other telecommunications administrations. A
joint contribution
first
have
to
would be more
obtain
likely to
gain acceptance than one submitted by a single administration. Horton began the process by issuing
a glossy-covered specification of the proposed
6.4. Virtual Circuits
The TCTS
there
was
was
to
service and circulating
it
widely.
^^
Versus Datagrams
draft called for a standard
was implementing a
DATAPAC
virtual circuit
be a standard,
it
was
based on a datagram mode
network, and the French
clear to Horton that
of operation.
RCP was
agreement on
However, Telenet
also a virtual circuit design.
this
If
fundamental design choice
imperative.
Roberts, by
now
President of Telenet, favored virtual circuit service, largely for economic reasons.
Simply routing packets represents only 10% of the value added of a packet network; providing
circuit service
interface, the
and other interface
computer processing
virtual circuit interface
facilities
to
would be the major contribution.
With a datagram
resequence packets could be provided by the end
would force the customer
to obtain
--
and pay
for
••
virtual
user.
A
these services from the
carrier.^
Technical arguments for choosing
that a
virtual circuit service
datagram network places the various netv;ork control
packet sequencing--in the hands of the end user. As a
situations only by throttling
all
traffic
were advanced as
well.
Roberts argued
functions--e.g. error control, flow control,
result, the
from an entire host, even
if
network can respond to overload
it
is
only
one
virtual circuit that is
generating the overload condition.
Datagrain proponents argued that the overhead involved
for
all
simple point-of-sale, or automatic
that
will feel
is
required,
teller
fvloreover, they argued,
in setting
up a
transactions where one packet
no matter how reliable the
virtual circuit
in
was wasted
each direction might be
virtual circuit service
is,
they must protect themselves against the possibility of network errors by duplicating
users
in
the
15
end computers much
of the error
virtual circuit service.
Finally,
a datagram network than
it
correctiny anil packet sequencing
packet voice suffers less from an occasional
does
provided as part of a
facilities
lost or
froin the uncertainties in delivery delay
damaged packet
in
associated with virtual
circuits.^
Faced with these arguments, and recognizing
committed
call
to their
respective implementations,
DATAPAC
Hov;ever.
service.
TCTS agreed
retained
the
and the French PTT were more
that Telenet
to align
DATAPAC
by providing
virtual
datagram mode as the underlying transport
mechanism."^
6.5.
In
Formal and informal processes
January
of 1975, a
counterparts
in
group from TCTS traveled
Table 6-1
London, Paris and Madrid
DATAPAC
the PTTs, and discuss the
informally.
A
By the end
of the year, Telenet
total of ten
this time, interest in
such informal meetings, some
and the
BPO
much
was followed by a
in
their
series of
CCITT meetings (See
the formal
of the drafting
lasting as long as a
were also drav/n
packet nets had grown
meet with
to
the French PTT, aimed at developing a
Although both groups were also participating
a chronology of working group meetings),
for
This
proposal.
TCTS and
informal meetings during 1975, mainly involving
draft standard.
to
in to
work was carried out
week were
held
in
1975.
these informal meetings. Also by
where Rapporteur's Group meetings were drawing
to
40-50 people.
The same
individuals
Subcommittee
Meetings
of
of
were also representing
the Data
the International Standards Organization's TC97, as well as
Communications
in
ANSI X3S37.
these groups provided additional settings for discussing X.25.
6.6. National Delegations
As a
their organizations in
treaty organization,
it
and Standing
is
States
•-
the US, the Departments of State and
national position for
in
the
CCITT
and not companies
Commerce
CCITT meetings. For
all its
•-
that
have
official
organize Study Groups
of
standing
US
in
the ITU.
In
firms to formulate a
enthusiasm, Telenet could not speak
for the
US, and
16
Table 6-1: Chronology
of
Formal CCITT Meetings
Related to X.25
Dote
Meeting
December 1972
5th
CCITT Plenary Assembly (Geneva)
January 1974
SG
VII First
Meeting
Rapporteur on Packet Switching
First
August 1974
Rapporteur on Packet Switching
Second Meeting
November 1974
Rapporteur on Packet Switching
March 1975
Rapporteur on Packet Switching
May 1975
Rapporteur on Packet Switching
SG
VII
-
Meeting
Third Meeting
Informal Meeting
•
Fourth Meeting
Second Meeting
September 1975
Rapporteur on Packet Switching
February 1976
SG
VII Final
September 1976
6th
CCITT Plenary Assembly (Geneva)
November 1976
Interim Rapporteur on Packet Switching
Fifth
Meeting
February 1980
SG
SG
SG
SG
VII Final
November 1980
7th
CCITT Plenary Assembly (Geneva)
April
1977
April
1978
April
1979
could not, on
its
VII
Second Meeting
VII
Third Meeting
FCC
1974 and 1975 the US
TCTS experienced
organization for the
Meeting
its
in April
official
development and approval
(CTCA).
Meeting
VII First
own, advance
public carrier from the
of
views
directly.
1974,
position
had no
it
--
problems
in
Indeed,
right
until
even
to
it
received approval as a recognized
attend
CCITT meetings. Throughout
dominated by the skeptical views
an interface standard
similar
CCITT
Meeting
in
for
of
AT&T
of a
was
that
packet switching was premature.
obtaining
support
from
the
official
representative
Canada, the Canadian Telecommunications Carriers Association
TCTS's proposals were opposed by a competitor, CNCP, who considered
development
•-
standard would not be
in
their
that the rapid
business interest; consequently, TCTS's views could
not be presented as the Canadian position. Thus, while Telenet and
TCTS
played key roles
in
drafting
the eventual standard, the drafts had to be submitted as national contributions from France and the
UK, whose positions were determined solely by
their respective
PTTs.
17
Ifi
1974
International
tlie
membership
CCITT meetings
A
•-
in
in
Processing was granted
information
that representatives of the IFIP Network'
an advisory capacity.
of a
IFIP did
datagram
quickly discovered that they were quite powerless
category
(d)
Working Group,
6.1,
submit a number
of
written
service, but representatives to the
the
in
CCITT forum.
(1976)
draft of X.25
first
CCITT
tlie
for
and strongly supported the inclusion
contributions,
6.7. X. 25
CCITT. This meant
in tlie
could participate
Federation
was
finally
prepared by an informal drafting party
work which was subsequently confirmed
informal meetings during the
summer
in
led to
the
May 1975
in
Ottawa
in
Ivlarch,
Numerous
formal Rapporteur's meeting.
8 written contributions
to the
1975
September Rapporteur's
meeting, the last scheduled meeting of the 1973-76 study period.
Although there were a
no opportunity
be translated
meeting
of
for further
for
full
any more meetings
into the three
SG
12 months remaining
Vil in
at
the study period after September there would be
in
the Rapporteur level.
The
results of the
meeting needed
working languages used by the CCITT and distributed before the
February 1976. After the February
change before formal
ratification at the
the final meeting of the Rapporteur's
Group was
SG
VII
of the
September 1976 CCITT Plenary Assembly. Thus
under
crucial:
traditional
September Rapporteur's meeting, however, there were
issues: e.g. packet lengths, packet length indicators, call progress
indicator for virtual calls,
datagram/virtual
datagram
call
datagram and
classification
be changed from
representatives from France and TCTS.
CTCA spoke
virtual call flow control
issue remained unresolved.
CCITT procedures,
made
it
seem
still
"essential"
to
in
1976.
signals,
"more data"
mechanisms. "^^ Furthermore, the
"additional."
to the
meeting that the
He was supported by
However, representatives from NTT, ISO, ECMA,
was
the
numerous unresolved
and advisory
Roberts had proposed
against hasty action; as a result the point
Rapporteur's meeting
final
meeting, there would be no opportunity
decisions of this meeting would determine whether or not a standard would be adopted
By the end
to
left
open.
The
final
USA and
report of the
doubtful that a standard would be ready for adoption by
SG
VII.
Immediately following the September 1975 Rapporteur's meeting (which had lasted two days),
18
TCTS. Ihe Fiencli PIT and Larry Roberts spent a
proposal.
mid-October,
In
TCTS
arid Telenet
met
A key issue
their
in
discussion was flow control.
significance only (DTE-DCE); Roberts supported an
Despres also supported an
attempts
control
of the draft
to
eventually reached by disguising
if
end
October,
of
Washington. D.C. While
local
flow control significance (DTE-DTE).
while Roberts supported
in
the Telenet and
e.g.
some
of the
RCP
window
networks.
differences of opinion
to
pay
in
was mandated but endto-end
local flow control
desired by individual network providers. Everyone
were prepared
all
thie
arrange a further X.25 meeting.
scheme
would create problems when attempts were made
the future, but
in
At
redrafting the X.25
Despres supported flow control with
endto-end
explicit credit flow control
recommendation;
was acceptable
specification
Geneva
resolving these differences failed, but with assistance from Anthony Rybczynski of
at
TCTS a compromise was
wording
in
ISO TC/97/SC6
This conflict arose because of different implementations
rotation.
Initial
of
Washington. Roberts seized on the opportunity
in
week
for furtfier discussions.
Remi Despres from the French PTT attended a meeting
Despres was
fiitllier
knew
that
flow
such a loose
to interconnect different
this price in the interests of getting the
the
networks
in
agreed portions of X.25
accepted.
The
BPO
an
result of this
v/ere prepared to support.
(BPO)
this
February they described the draft standard as a
in
Thus, by the end
of 1975, with the
years and
interface.
of
its
Spain
supporting
it
standard was reflected
fait
their
paper even before the
in
RETD
network had been
the development of X.25
in their
network.
who had
to
do so was prepared
in
operation for almost
national traffic continued to increase without the benefit of a standard
felt
SG
accompli.
network or had made a commitment
support the proposed X.25 standard. The Spanish
five
to a
exception of Spain, every administration and carrier
either already established a public packet
to
agreement was tantamount
1976 AFIPS National Computer Conference. Submitting
for the
meeting
That
by Rybczynski (TCTS), Wessler (Telenet), Despres (French PTT) and Wedlake
article drafted
VI!
meeting was a draft recommendation that TCTS, Telenet, the French PTT and the
DTE/DCE
was an "unstable study" and therefore had no
intention
19
Despite acceptance by the leading earners, the draft
SG
from 20 countries represented
in
probleins surfaced. The
US
official
still
needed
to
be
ratified
many
During debate on the draft proposal
VII.
delegation was a particularly vocal
critic:
the
US
of the
position
no standard should be accepted which had obvious technical flaws. The technical points
were not resolved, but a document was agreed
US
to after the
French cooperation on unrelated issues
the eleven
recommendations
of
SG
at the Plenary.
--
VII
In
was understood
September 1976
X.25
including
known
was
that
of conflict
delegation, under pressure from
France, agreed to stop challenging the proposal. Consent by the U.S.
for
members
by the 200
at
the
to
be
CCITT
in
return
Plenary,
were adopted unanimously, thus
-•
completing the formal process.
6.8.
Problems and Revisions
Some saw
Adoption of X.25( 1 976) by the CCITT did not bring about immediate widespread support.
it
as
little
more than an "advertisement
for
were many ambiguities and unresolved
alignment of the
link level of
a standard."** The participants themselves
Tv/o
issues.
X.25 with the
HDLC
of
these were
of
knew
there
particular importance:
standard being developed by ISO; and datagram
service.
X.25 had been developed using a draft ISO
HDLC
procedure was subsequently rejected when put
By early 1977, the ISO had
still
procedure
to letter ballot
at
the
link level.
The
draft
ISO
and a modified proposal developed.
not reached agreement on the portion of
HDLC
dealing with
symmetrical and balanced classes of procedures which v;ere of most interest to X.25
In
the unbalanced class of procedure, one station (designated the primary) has total responsibility
for control of the link.
This class had been strongly supported by
IBM whose Systems Network
Architecture was, at that time, designed to rely on a large central mainframe controlling dependent
Over the opposition
terminals.
response
mode (ARM)
the primary.
potential
The LAP
in v>^hich
in X. 25(1
of
IBM, this class had been extended to permit an asynchronous
a secondary
may
transmit without receiving explicit permission from
976) had been based on the
deadlock problems were detected
v;ith
ARM
proposal. However, during balloting
the proposaP^,
and a new balanced class
of
20
i_
procetlures -vas developed.
For
nu
this class,
made between
dii^tinction is
primary and secondary
i
A version
stations, thus giving both stations equal control over the link.
asynchronous balanced mode (ABM) was proposed as a revised
link
mode, known as
of this
access procedure
for X.25, or
LAPS.
To avoid the
meeting
risk of further
CCITT SG
of
Eventually a
experts and ISO
VII
TC/97 met
compromise "mutually objectionable
Despite the compromise, the earlier
There was a danger
protocol.
LAP
implementing the old
had adopted LAP
implementing
its
the
in
that both
to reviev; their differences.
v;as on the books as the official X.25 link access
DTE vendors would
camps with incompatible
continue
standards. Already
network and by early 1977 had proceeded much too
a newly adopted CCITT
Approval
Recommendations"
joint
was reached.
both parties,"
netv;ork to convert immediately to
Draft
1977
April
in
network developers and
protocol, leading to two
DATAPAC
to
LAP standard
preferred standard,
of
CCITT and ISO standards making, a
inconsistencies between
procedure
ballot
letter
between
To make clear
LAPB.
LAPS was
obtaining
for
was used
Plenaries
that
ratify
to
TCTS
far in
the
new
"Provisional
LAPB;
fifteen
administrations approved and three abstained.^
At the February 1976
At the
first
meeting
of
'*^
fast-select service.'^'
and
call
facility
select
SG
VII
SG
The
meeting
VII
in
it
had been agreed
still
Support
and ANSI
for a
hold datagrams over for further study.^
1977, the participants examined a proposal from Japan for a
fast-select facility
would allow the inclusion
disconnect packets. Thus for small quantities
would provide
to
data
of
simple two packet exchange,
much
--
e.g.
like
of user
data
in
the call set up
transaction data - the fast select
a datagram service. However, fast
requires the netv;ork to incur the overhead of virtual circuit set-up.
for inclusion of a
X3S37.'*^'
'*'*
service that provided
IFIP
datagram service
in
X.25
came
primarily from IFIP
Working Group
represented the scientific community and their interest
maximum
flexibility
to
the user.
The ANSI
position
in
economic terms:
i.e.
that
a network
was formulated by a
subgroup whose members represented ARPA, NCR, Xerox and Western Union.
datagram service v;as couched
in
6.1,*^
Their support for
datagram service would be
far
more cost
21
effective for shoit transactioti type traffic than v/uuld
conducted and publisfied a survey
and
rallied
permanent
additional support
virtual circuits
February 1960.
In
SG
as a
Vli
be
users and vendors on
of
ISO TC97/SC5.
in
means
to
To buttress
virtual circuits.
countered
position ttiey
a datagram interface,''^
ttie desirability of
Tlie Frencti
ttieir
witfi
a proposal to use
provide a low-overfiead data exciiange capability.
adopted a revised version
X.25 (X.25(1980))
of
v;hicfi
included datagram
service and fast select as "additional," or optional services as opposed to "essential" parts of the
standard.
Inclusion of a datagram specification has turned out to be an empty gesture.
absence
any obligation
of
has done so.
the
In
implement datagram service, not a single public packet netw^ork operator
to
X.25(1984) calls for the datagram option to be dropped altogether.'*® The fast select
option has been implemented only by NTT."*
Lessons From X.25
7.
Louis Pouzin has described the X.25 standardization process as a "well engineered political
_
__
coup
,
.
A
48
II
.
small, highly motivated
group
of
packet sv;itching carriers developed a new/ standard
breaking time and persuaded a very conservative standards organization, the CCITT,
The process was
proposal.
informal processes used.
of a
In
engineered' with respect
'well
1975, there were a
standard before implementation seemed
that the
most important issues
number
to
stake had
at
of
to
its
compatible
with
the
emerging
networks.
telecommunication network providers could secure
communication market. X.25 was a 'coup'
Rapporteur's group) seemed
draft
proposal
supported
to
by
in
the
A
DTE/DCE
manufacturers
standard
their claim for a
sense
X.25 was
do with technical
computer terminal
packet
accept
its
timing and the mix of formal and
sense.
motivation for international telecommunication standardization. A
persuade computer mainframe and
record-
imminent public packet networks; adoption
make good
little
to
to
in
that just
was
share
when the
in
'political' in
the sense
compatibility, the usual
standard was needed to
to
produce equipment
also
required
so
that
the rapidly growing data
institutional
processes (the
be foundering, the informal group suddenly produced a completed
a
Furthermore, the group succeeded
number
in
of
telecommunication
administrations
gaining the approval of the CCITT.
and
carriers.
22
7.1
.
Evaluating X.25
Before
we can draw any conclusions
from the case
X.25 for other standards efforts,
of
first,
by the extent
of
use
of the
first
Success can be measured
establish vWiether or not X.25 can be judged a "successful" standard.
two ways:
we must
in
standard; and second, by a more subjective assessment of
"technical quality".
Over 30 countries have public packet switching services
-- all
X.25 compatible - while only a dozen
countries offer circuit switched digital services."*^ Most administrations were able to take advantage of
the revised X.25 proposals developed during the 1977-1980
implemented the 1976 version
An important goal
manufacturers
to
of the
of X.25,
and
it
took
until
network providers was
develop X.25 compatible products:
60 computer and terminal manufacturers made by
supporting
been
X.25'*^.
1981
,
IBM
finally
joined in^
by Telenet as conforming
certified
vendor.
In
1983
CCITT study
for Telenet to fully convert to X.25 (1980).
induce terminal and computer equipment
to
in this
TCTS
A survey
of
1978 showed 25 already committed
to
they have been successful.
in
and by 1983, more than 100 software packages had
to X.25(1980), including
software for every major computer
Another two dozen vendors supply standalone interface boxes
Some 57%
of the hosts
connected
to
Thus X.25
is
question
now
is
X.25 internally.
more ambiguous. Only a few
The public packet networks struggled
and Tymnet began
Telenet did not
of the uncertainties
to
facilities.
billion
profit until 1983.''^, the
of its
own.
On
for
number
same year
of
in
the other hand, the
TRANSPAC
characters per month.
^'
services
is
it
used? The answer
to
customers between 1976 and 1980.
traffic
sessions quadrupling
v/hich
AT&T
finally
in
volume on Telenet
three years.
began
many users over
more than 8000 X.25 connections and
Still,
offering an X.25
European PTTs, by adjusting the
leased lines versus packet services, are gradually forcing
France's
key users,
network operators have adopted
surrounding X.25 resolved by 1980,
increase rapidly with the
show a
based packet service
tariffs of
of the largest private
Finally,
for internal networks.
widely available to the data communications user - but
However, with many
for host-to-X.25 support.
Telenet have user-supplied X.25 interfaces'*^.
such as the U.S. Federal Government have adopted X.25 as a standard
this
period: only four networks
relative
to public
data
carries traffic of 100
23
X.25
Fioni a teclinical perspective.
still
both
lias
defenders and detractors.
its
ambiguities of X.25(t976) were resolved by X.25(1980). but
multiple options or interpretations. As
of X.2.5
has presented somevWiat
"^^
alike.
7-
1 ).
particularly scathing critique by
moving
target to
and revisions proposed
expensive for transaction
traffic
for
in
1976
1984
As noted
will
to fault
for the
X.25
AT&T
for
its
for
development
packet switched networks based on the ISO
protocol by
IBM put
it.
was
the
to ratify
"The evolution
network implementors and terminal designers
to
significantly
differ
between
videotex service
earlier,
in
to support
HDLC
common
at
the packet level. Pouzin
terminal interface for both circuit
standard^.
The introduction
further evidence of the
is
is
packet voice.
unv/arrented complexity
of a
a
no public network has offered datagram
eliminate datagrams from X.25 altogether. Thus, X.25
and cannot be used
such as Pouzin continue
argued strenuously
solution
which was resolved by defining a datagram "option," ended
service,
clear defeat for datagram proponents.
Critics
tfie
of
This poses continuing problems for those writing X.25 host software.
datagram
battle over
service,
many cases
As a consequence, packet network services continue
countries (Table
The
of a
one
in
Most
need
of a
and
new LAPD
a simpler terminal
for
protocol.
On
balance, X.25 (1976) must be seen as a technically
but by no
means
ideal.
Revisions scheduled for adoption
weak standard,
in
1984 should
with X.25 (1980) as better,
permit X.25 to be used
finally
by microcomputers over the dial-up network.
7.2.
Lessons
X.25 represents only one of the
much
to read too
standards setting
Lesson
V.
many standards
into a single case.
activities to
was
computer communications;
Nevertheless,
draw several lessons from
An Imperfect Standard
X.25 (1976)
for
is
Better Than
hurriedly adopted with
known
implemented the 1976 version were obligated
to
we
believe
it
may be
it
is
risky to
attempt
instructive for future
this history of X.25.
None
ambiguities.
modify
their
Networks - and
implementations
their
customers
••
to align with the
who
1980
24
Table
7-
1
:
Comparison
of Differences in
X.25 Public Networks
Country
Germany
France
U.K.
Japan
Network
Datex-P
Transpac
PSS
DDX
Packet Level:
25
version •
at significant
success.
From
their
succeeded
perspective, X.25
equipment manufacturers
to
in
its
same networks as
most important objective:
it
a great
induced
take packet networks seriously and to begin designing compatible
By 1975, Tymnet,
equipment.
Yet X.25 has been hailed by these
expense.
RETD and
Telenet had been established without an international
TCTS, the EEC, the BPO and the French PTT had committed themselves
standard interface.
establish networks with or without a
CCITT approved standard.
If
to
these networks had been allowed to
evolve independently, the chances of reaching agreement later would have been drastically reduced.
X.25 suggests that economic and competitive pressures are forcing the rapid implementation of
computer communications and
standards.
If
standards are
to
that these
make
new
applications
will
a contribution to these technologies they must be developed on a
compatible time scale. The typical eight year development cycle
The
the current competitive environment.
the standard's rigour
in
abberation: rather,
if,
alternative, as
revision.
We
refined,
is
Lesson
revisions.
The
direct
The
in
the
future,
alternative, to delay the benefits of
in
is far
is
too slow
in
some
of
to sacrifice
is
consequence
from a commercial perspective, an imperfect standard
perceived to be too costly
2:
ISO and CCITT
would argue that the imperfections
can expect more hurriedly developed standards
subsequent
of
suggested by X.25,
favour of more rapid approval.
sucsequent changes and
be implemented with or without
of
is
a need for
X.25 were not an
better than none,
we
expended
in
and more
new technology
effort
while standards are
a competitive marketplace.
Build a coalition in private meetings with other vendors
and submit
a joint proposal to
formal institutional standards meetings
The Rapporteur's group on packet switching
involving
carriers
full
reach agreement whereas an informal group
TCTS, Transpac, Telenet, BPO and NTT succeeded. This smaller group, containing those
committed
to the
implementation
motivation for agreement, met
the
failed to
more than
of
packet switching, and thus with the greatest economic
ten times
in
1975, sometimes for as
much
as a week, while
Rapporteur's group was meeting only three times. The informal group then presented the
Study Group with a complete draft
of
a standard
at
the February 1976 meeting.
full
26
Our economic theory
of
standards suggested a positive feedback model
unit eventually forces the standard.
economic
momentum.
Tiie coalition of Xerox.
DEC and
AT&T
network standard, and the moves by
American Presentation Level Protocol Syntax
Lesson
has
there
Standards agreements
3:
been some
X.25 (1976)
to
were
of creating sufficient
adoption
If
The leading
new technologies
with
are
CBS
for its
North
be most easily reached after
likely to
and
technology,
the
role in the
•-
to benefit
those
15,
it
in
when
a
number
of
had
ARPANET
to
many
as 15 under
for the
1976 CCITT
operation, but as
to
be developed
development was taken by TCTS, Transpac and the BPO. The three
RETD,
Telenet,
and Tymnet
spearhead the development
--
while agreeing to eventually conform,
effort.
Conversely, without the experience of the three networks already
packet networks
the Ethernet local area
videotex are examples of similar coalition formation.
there were only 3 networks
a standard was
operation
in
less motivated to
publicized
of
support by Canada and
to solicit
for
for the
one means
Organizations whose implementations are imminent are the ones
was approved when
networks already
push
is
which the dominant
develop standards.
discussion for 1980.
Plenary.
Intel to
experience
practical
implementations are imminent.
most motivated
lor
Coalition formation
in
experience,
it
would not have been possible
develop a standard.
The
rooted
firmly
to
in
operation, plus the widely
generate sufficient interest
circuit
switching tradition
in
in
the
telecommunications industry had caused some reluctance during the early 1970s on the part of the
PTTs and
to the
carriers to establish public packet networks. But by 1975
technology to recognize
its
potential.
The
fact that
four year intervals forced the proponents of a standard
to
most had had
sufficient
exposure
CCITT Plenary sessions are held only
move
quickly
in
at
1975 or face an additional
four years delay.
The best time
some
the
to
develop a standard thus appears to be a during a very narrow window after there
operating experience, and
field,
The need
but before these
for
some
when
there has been a
commitment by other organizations
same organizations have committed themselves
operating experience before the standard
is
to
is
to enter
divergent approaches.
developed means that the leading
27
may have
innovators
to
British Prestel videotex
4:
RETD and Tymnet have been
been forced on Ungermann-Bass. a pioneer
(Similar redesign has
Lesson
redesign their systems as Telenet.
system
•-
both pioneers
Managers who can commit
who
got ahead
in
of the
their organizations will
obliged to do.
and the
local area networks,
standards making process.)
be more successful
in
securing
adoption of a standard than technical experts without decision-making responsibility
CCITT processes have
from the more
political
must check with
led
been characterized by a separation
The usual CCITT
Plenary meetings.
participant
of technical
only an intermediary
is
agreeing to any proposal. However, the effort
his chiefs before
study groups
to
who
develop X.25 was
by top management from the key organizations: Norton was Assistant Vice-President (Planning)
of the
the
traditionally
Computer Communications Group
BPO, Roberts was President
Precisely because of the
managers took a
of
TCTS, Kelley was Head
of Telenet,
and Picard became Directeur General
economic importance
direct interest.
Data Systems Division
of the
They had the
of
of
in
Transpac.
standards to these fledgling netv;orks, these
authority to
make commitments on
behalf of their
organizations which greatly accelerated the process.
Lesson
interfaces
5;
Standards agreements are more
where there
is
likely to
be reached
for
a natural division in responsibility lor the supply of
"natural" interfaces,
i.e.,
equipment or services.
Recotnmendation X.25 defines the interface between customer terminal equipment and the
communications network. For public data services, customer equipment
is
generally provided by the
user rather than the network provider, thus creating a division of responsibility and a "natural"
interface.
For "natural" interfaces, both sides can further their
Network operators are freed from providing multiple interfaces
extent that qsers
demand data
self interest
to
by adopting a standard.
many equipment
providers.
To the
terminal equipment capable of being used on public netv.'orks,
equipment providers gain a larger market
if
their
devices can be used interchangeably
in
many
different countries without modification.
By contrast, host-to-host standards
division of responsibility
and were not
--
e.g.
finally
the ISO's Transport Protocol
agreed
to until 1983.
••
do
not define a natural
28
Lesson
The layered approach speeds the development of standards.
6:
k
Recommendafion X.25 separates
DTE/DCE
the various network functions at the
physical layer, a link layer and a packet layer.
developed by separate working groups, and
theory, layering allows standards for each layer to be
In
is
interface info a
expected
changes
to facilitate
standards as they
to the
evolve.
The
history of X.25 suggests that layering
except that the Study Group adopted a
the ISO
HDLC
proposals.
link
does
help.
X.25 (1976) might not have been ready
access procedure and a physical
and included
in
the revised version of X.25 published
physical level or the packet level.
The speed
with
in
1978.
which
jointly
HDLC
this revision
link
by ISO and the CCITT
No changes were
was
time
standard based on
the event. ISO subsequently rejected the proposed
In
A compromise procedure (LAPS) was developed
procedure.
level
in
access
in
1977
required at either the
possible
was due
largely to
the layered structure of the standard.
The success
of
Interconnection, and
The cooperation
Lesson
7:
the
in
layering
concept
is
reflected
in
the
ISO's
model
Open Systems
for
the activities of the IEEE's Local Area Network group, 802.
with ISO leads us to our final observation, namely:
Standards of higher quality and greater generality are
settings organizations cooperate with
likely to
be produced
each other during the development and
if
standard-
drafting of
new
standards.
The HDLC standard was
bit-oriented data link control
been a strong overlap
CCITT SG
VII
in
the result of considerable effort aimed at developing a
procedure
the
for
membership
to
of related
committees, the 1977
and the ISO working party charged with developing
HDLC
joint
set a
under pressure from the EEC, the ISO and the CCITT were able
develop transport protocols
in
1982.
efficient
synchronous communications. Although there has often
session between
precedent
cooperation between the these two standards organizations. Efforts to institutionalize
failed until,
more
to
this
harmonize
for formal
precedent
their efforts
29
8.
Conclusion
The need
demands on
to
develop new computer communications standards has placed
traditional standards setting processes.
reflected this stress,
changes
to
and
the process.
standard rushed
to
in
Economic
agreement.
for the first time,
priorities
The
among
on the meetings and committed
employed
of
Recommendation X.25
the course of developing a standard, the key participants
in
through informal meetings
The development
were allowed
to override technical
formal, plodding procedures of the
the key parties.
Top managers
their organizations to
in
such areas as videotex,
services can be expected to exhibit
many
of the
same
made
significant
concerns and a weak
CCITT were circumvented
rather than technical specialists sat
an agreement. The principal
as well as an unusual degree of cooperation betv/een
Current standards efforts
unprecedented
of layering
CCITT and
local area networks, or electronic
patterns of decision-making.
was
the ISO.
message
30
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