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Lecture #5: Reference Models Lecture #5: Reference Models
and Example Networks and Example Networks
C o n t e n t s C o n t e n t s
The ISO OSI Reference Model The ISO OSI Reference Model
The TCP Reference Model The TCP Reference Model
Example Networks: Example Networks:
Novell Novell ™ ™ NetWare NetWare
®® From ARPANET to Internet From ARPANET to Internet
Gigabit projects Gigabit projects
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Reference Models - Basics Reference Models - Basics
Reference models, ISO Reference models, ISO
OSI = OSI = Open Systems Open Systems Interconnection Interconnection
Layers: Layers:
Perform similar functions Perform similar functions
Process similar data Process similar data
Respect internationally standardized protocols Respect internationally standardized protocols
Minimize the information flow though the interfaces Minimize the information flow though the interfaces
Their number is the smallest possible to mach all Their number is the smallest possible to mach all different levels of protocol abstraction
different levels of protocol abstraction
• Examples Examples : ISO 7 layers; internet 5 layers : ISO 7 layers; internet 5 layers
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Reference Models - the Reference Models - the
OSI Model OSI Model
The The OSI OSI model: model:
7 layers 7 layers
Points out the set of functions of each Points out the set of functions of each layer
layer
Establishes international standard for all Establishes international standard for all of the layers but not protocols
of the layers but not protocols
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Protocol stacks Protocol stacks
OSI protocol stack OSI protocol stack
OSI-protocols are specified in seven layers. The lower OSI-protocols are specified in seven layers. The lower layers are more hardware and transmission oriented. The layers are more hardware and transmission oriented. The
upper layers are oriented to presentation and upper layers are oriented to presentation and
synchronization purposes. The middle layers handle network synchronization purposes. The middle layers handle network
quality, addressing and routing.
quality, addressing and routing.
Layers Layers with example OSI protocols are with example OSI protocols are : :
Application Presentation Session Transport Network Data link Physical
FTAM, ACSE, ROSE OSI Presentation
OSI Session BSS, BSC, BAS OSI Transport Class 0,..,4 OSI Network, X.25
HDLC
Voltages as X.24 7
6 5 4 3 2 1
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Communication Communication Functions according to Functions according to
the OSI Model the OSI Model
User applications ..
Encryption/
decryption
compression/
expansion
Choice of syntax Session
control
Session to transport mapping
Session management Session
synch.
Layer and flow control
Error recovery
Multiplexing
Connection control
Routing Addressing
Error control
Flow control Data link
establishment
Synch Framing
Access to transm. media
Physical and electrical interface
Activation/
deactivation of con.
Application layer Presentation layer
Session layer Transport layer
Network layer Link layer Physical layer
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The OSI Model - The The OSI Model - The
Physical Layer Physical Layer
Bit-slice transmission via some Bit-slice transmission via some communication channel e.g.
communication channel e.g.
Method of bit coding 0/1 Method of bit coding 0/1
Physical parameters: Physical parameters:
voltage/amperage etc.
voltage/amperage etc.
Timing: frequency/period, shape of Timing: frequency/period, shape of signal front, etc.
signal front, etc.
Direction[s] of transmission Direction[s] of transmission
Establishment and canceling of the Establishment and canceling of the connection
connection
Physical/mechanical interfaces to Physical/mechanical interfaces to the connection medium (e.g.
the connection medium (e.g.
RS234 connector)
RS234 connector)
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The OSI Model - The Data The OSI Model - The Data
Link Layer Link Layer
Maintains the Maintains the error-free error-free transmission transmission line line for for data frames data frames serving the serving the
requests of the upper Network requests of the upper Network
Layer.This includes:
Layer.This includes:
braking the upper level data into or braking the upper level data into or
packing the lower level bit stream into packing the lower level bit stream into
frames frames
keeping the data keeping the data sequence sequence by exchange by exchange of acknowledgement frames
of acknowledgement frames
create or recognize frame boundaries by create or recognize frame boundaries by bit patterns for beginning/end frame
bit patterns for beginning/end frame boundaries
boundaries
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The OSI Model - The Data The OSI Model - The Data
Link Layer Link Layer
retransmission of corrupted or erroneous retransmission of corrupted or erroneous frames
frames
manages problems of duplicate, corrupted or manages problems of duplicate, corrupted or lost frames depending on the service
lost frames depending on the service
(price/speed) level applied by the upper layers (price/speed) level applied by the upper layers
low level buffering between upper layers low level buffering between upper layers peers of different capacity
peers of different capacity
support of bi-directional communication: support of bi-directional communication:
incoming data frames share the line with incoming data frames share the line with
outgoing acknowledgement frames outgoing acknowledgement frames
for broadcast networks: medium access for broadcast networks: medium access sublayer for shared channel control
sublayer for shared channel control
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The OSI Model - The The OSI Model - The
Network Layer Network Layer
Subnet Subnet control layer i.e. control layer i.e. routing routing of of the of of the Data Link Layer packets from source to
Data Link Layer packets from source to destination. Routing might be:
destination. Routing might be:
static static - based on static tables - based on static tables
dynamic dynamic - new route for each session - new route for each session
turbo turbo - new revision of the route for each - new revision of the route for each packet
packet
Routing trends to solve problems with Routing trends to solve problems with temporarily bottlenecks
temporarily bottlenecks
Network layer also does the following: Network layer also does the following: 8
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The OSI Model - The The OSI Model - The
Network Layer Network Layer
counts (on demand of the upper layers) the counts (on demand of the upper layers) the number of packets/B/b produced by
number of packets/B/b produced by customer/network etc.
customer/network etc.
interprets addresses from another conventions interprets addresses from another conventions
adjusts the packet size according to the size of adjusts the packet size according to the size of peer network
peer network
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The OSI Model - The The OSI Model - The
Transport Layer Transport Layer
Exchange (“transport”) of data “ Exchange (“transport”) of data “ point-to- point-to- point
point ” providing the upper (session) layer with ” providing the upper (session) layer with error-free
error-free data messages. It cares for: data messages. It cares for:
effective communication - for high throughput it effective communication - for high throughput it might open >1 network connections -
might open >1 network connections -
“ “ multiplexing multiplexing ” ”
fault tolerance fault tolerance
opening/closing the connections with named opening/closing the connections with named parties in the network + support of naming parties in the network + support of naming
mechanism needed - “
mechanism needed - “ flow control flow control ” ”
different types of services: point-to-point channel; different types of services: point-to-point channel;
isolated messages; broadcasting.
isolated messages; broadcasting.
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The OSI Model - The The OSI Model - The
Session Layer Session Layer
Establishes sessions between network Establishes sessions between network
machines. The sessions are extensions over machines. The sessions are extensions over
the transport layer communication, that the transport layer communication, that
support:
support:
remote login remote login
file transfer file transfer
interactive exchange (dialogue): interactive exchange (dialogue):
bi-directional simultaneous bi-directional simultaneous
bi-directional alternative bi-directional alternative
uni-directional uni-directional
dialogue synchronization - by session brakes dialogue synchronization - by session brakes
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The OSI Model - The The OSI Model - The
Presentation Layer Presentation Layer
Interprets the exchanged data as Interprets the exchanged data as
information considering its syntax and information considering its syntax and
semantics. This includes:
semantics. This includes:
security coding/decoding security coding/decoding
presenting data as presenting data as text strings text strings , , formatted numbers
formatted numbers (integers, fixed, (integers, fixed, floating, double, etc.) according different floating, double, etc.) according different
formatting codes in both directions:
formatting codes in both directions:
– local computer standard local computer standard
– network standard network standard
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The OSI Model - The The OSI Model - The
Application Layer Application Layer
Set of protocols providing network-wide Set of protocols providing network-wide
compatibility of the user programs including:
compatibility of the user programs including:
full-screen terminal compatibility full-screen terminal compatibility
file- and directory- structure compatibility file- and directory- structure compatibility
remote procedure calls/remote evaluation remote procedure calls/remote evaluation
electronic mail electronic mail
………… ………… . .
Solution: network virtual standard to which to Solution: network virtual standard to which to translate local structures/objects
translate local structures/objects
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OSI reference model OSI reference model
(N)-SAP
(N-1)-SAP (N-1)-SAP (N-1)-SAP (N)-entity
(N+1)-level
(N-1)-level
(N)-level
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The OSI Model - example The OSI Model - example
Data Transmission Data Transmission
Sender transmits Data to Receiver Sender transmits Data to Receiver
The protocols implementing each OSI The protocols implementing each OSI layer add special header to the Data layer add special header to the Data
(header might be null) (header might be null)
The lower level deals with extended The lower level deals with extended Data (Data+Header) as a whole
Data (Data+Header) as a whole
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The OSI Model - The OSI Model -
Drawbacks Drawbacks
Late appearance (after widespread Late appearance (after widespread application of another models like application of another models like
TCP/IP) TCP/IP)
Heavy implementation Heavy implementation
– ignores less reliable but prompt ignores less reliable but prompt connectionless services
connectionless services
– multiplicates the layer functions multiplicates the layer functions throughout several layers
throughout several layers
Result: slow protocols Result: slow protocols
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Reference Models - the Reference Models - the
TCP/IP Model TCP/IP Model
Developed for ARPANET (70ties US Developed for ARPANET (70ties US
national military network) and inherited in national military network) and inherited in
the Internet the Internet
Features: Features:
flexible routing - tolerant to loss of network flexible routing - tolerant to loss of network nodes, subnets, route[r]s, connections, etc.
nodes, subnets, route[r]s, connections, etc.
flexible architecture - tolerant to different flexible architecture - tolerant to different throughput and application services (off-line, throughput and application services (off-line,
on-line, real-time) on-line, real-time)
4-layer structure 4-layer structure 1/18
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Protocol stacks Protocol stacks
TCP/IP stack TCP/IP stack
• Internet networks are based on TCP/IP protocols, so Internet networks are based on TCP/IP protocols, so the TCP/IP model and protocol stack have a growing the TCP/IP model and protocol stack have a growing
importance.
importance.
• TCP/IP is based on TCP/IP is based on five five protocol layers instead of protocol layers instead of seven. The OSI model session and presentation layers seven. The OSI model session and presentation layers
can be considered empty in TCP/IP context.
can be considered empty in TCP/IP context.
• TCP/IP stack with example protocols is shown TCP/IP stack with example protocols is shown below:
below:
Application Transport Network Data link
Telnet, FTP, SMTP, SNMP, HTTP TCP, UDP
IP
HDLC or LAN frames Voltage levels
Physical
7 4 3 2 1
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TCP/IP Layered communication TCP/IP Layered communication
Client Server
Router Telnet request
TCP segment IP datagram Ethernet frame
Voltage
Telnet request TCP segment
IP datagram Ethernet frame
Voltage IP datagram
Ethernet frame
Voltage
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The TCP/IP Model - The The TCP/IP Model - The
“Host/Network Layer”
“Host/Network Layer”
Corresponds to OSI Physical+Data Link Corresponds to OSI Physical+Data Link Layers
Layers
Unspecified strictly as protocol Unspecified strictly as protocol
implementations vary in different implementations vary in different networks and even hosts
networks and even hosts
only restriction: serving upper (internet) only restriction: serving upper (internet) layer in transmission of data packets
layer in transmission of data packets
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The TCP/IP Model - The The TCP/IP Model - The
Internet Layer Internet Layer
Connectionless layer (in order to provide the Connectionless layer (in order to provide the flexibility needed)
flexibility needed)
Implementation: Implementation: IP IP
free independent exchange of packets (IP free independent exchange of packets (IP datagrams) transparently to the sender and datagrams) transparently to the sender and
receiver
receiver routing routing is a key issue in IP is a key issue in IP
standard standard packet format packet format (strictly (strictly supported) for proper routing
supported) for proper routing
corresponds to OSI Network Layer corresponds to OSI Network Layer
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The TCP/IP Model - The The TCP/IP Model - The
Transport Layer Transport Layer
Supports “point-to-point” connectivity between Supports “point-to-point” connectivity between the source and destination (like OSI transport the source and destination (like OSI transport
layer) layer)
Implemented by two protocols: Implemented by two protocols:
TCP TCP (Transmission Control Protocol) - connection (Transmission Control Protocol) - connection oriented, delivers the byte stream from source to oriented, delivers the byte stream from source to
destination by fragmentation into discrete messages destination by fragmentation into discrete messages for transmission by IP. Receiving TCP assembles the for transmission by IP. Receiving TCP assembles the incoming messages to output stream
incoming messages to output stream
UDP UDP (User Datagram Protocol) - connectionless, (User Datagram Protocol) - connectionless, unreliable, non-sequential, for prompt delivery unreliable, non-sequential, for prompt delivery (multimedia applications)
(multimedia applications)
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The TCP/IP Model - The The TCP/IP Model - The
Application Layer Application Layer
Top level protocols (session and presentation Top level protocols (session and presentation layer functions are performed by the
layer functions are performed by the application when needed) like:
application when needed) like:
TELNET TELNET
FTP FTP
SMTP SMTP
DNS DNS
HTTP HTTP
…… …… ... ...
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Service to protocol Service to protocol
-mapping -mapping
Ethernet header
Encapsulation between protocol layers
IP header
“Connect”
Telnet request: “Connect
”
TCP segment: TCP header
IP datagram: TCP header “Connect”
IP header TCP header “Connect”
Ethernet frame:
Voltages:
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The TCP/IP Model - The TCP/IP Model -
Drawbacks Drawbacks
Tightly specified, non-general model, Tightly specified, non-general model,
oriented to the suspected set of protocols oriented to the suspected set of protocols
The lowest “host/network” layer is The lowest “host/network” layer is
practically unspecified and this makes practically unspecified and this makes
difficulties applying new communication difficulties applying new communication
media and technologies media and technologies
freeware protocols: freeware protocols:
wide application but bad documentation, wide application but bad documentation,
bad quality of some and bad quality of some and
security security problems (big possibilities for problems (big possibilities for hackers)
hackers)
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Reference Models - OSI vs.
Reference Models - OSI vs.
TCP/IP TCP/IP
Similarities: Similarities:
– structure structure : stack of protocols : stack of protocols
– functionality functionality : routing + point-to-point : routing + point-to-point
connectivity + application supporting functions connectivity + application supporting functions
Dissimilarities ( Dissimilarities ( OSI OSI )/(TCP): )/(TCP):
– conceptuality conceptuality /applicability /applicability
– hidden, transparent, replaceable protocols hidden, transparent, replaceable protocols / / conservative, non-conceptual approach
conservative, non-conceptual approach
– mostly connection oriented mostly connection oriented / pure connectionless / pure connectionless oriented
oriented
– 7 layers 7 layers / 4 layers / 4 layers
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Example Networks - The Example Networks - The
ARPANET ARPANET
[Defense] [Defense] Advance Research Project Agency Advance Research Project Agency - - consists of subnet and hosts
consists of subnet and hosts
Subnet is based Interface Message Processors Subnet is based Interface Message Processors ( ( IMP IMP ) connected by communication lines. ) connected by communication lines.
– Software: IMP/IMP- Host/IMP- and Host/Host- Software: IMP/IMP- Host/IMP- and Host/Host- protocols
protocols
Development - chiefly US universities: 1969, 70, Development - chiefly US universities: 1969, 70, 72, 73
72, 73
Extensions: Terminal Interface Processors ( Extensions: Terminal Interface Processors ( TIP TIP ) ) (Terminal Complexes), LANs, TCP/IP (protocol (Terminal Complexes), LANs, TCP/IP (protocol
stack and model -1974), DNS (1981) stack and model -1974), DNS (1981)
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Example Networks - The Example Networks - The
ARPANET ARPANET
[Defense] Advance Research Project Agency - first [Defense] Advance Research Project Agency - first to adopt
to adopt packet-switching packet-switching replacing traditional replacing traditional circuit-switching. Advantages:
circuit-switching. Advantages:
– multiple routes rise fault-tolerance (dated) multiple routes rise fault-tolerance (dated) – dense communication channels (actual) dense communication channels (actual)
Structure: Structure: subnet subnet and and hosts hosts
Subnet structure: Interface Message Processors Subnet structure: Interface Message Processors (IMP) connected by communication lines;
(IMP) connected by communication lines;
Alternative connections for each IMP Alternative connections for each IMP
– Software: IMP/IMP- Host/IMP- and Host/Host- Software: IMP/IMP- Host/IMP- and Host/Host-
protocols based on datagram exchange; rerouting protocols based on datagram exchange; rerouting
algorithms for lost datagrams.
algorithms for lost datagrams.
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Example Networks - The Example Networks - The
ARPANET ARPANET
Development - chiefly US universities: 1969, 70, 72, Development - chiefly US universities: 1969, 70, 72, 73 73
Extensions: Extensions:
– Terminal Interface Processors (TIP) (Terminal Terminal Interface Processors (TIP) (Terminal
Complexes) - multiple host per TIP, multiplexed access Complexes) - multiple host per TIP, multiplexed access
of one host to several TIPs of one host to several TIPs – LANs LANs
– TCP/IP (protocol stack and model -1974) suitable for TCP/IP (protocol stack and model -1974) suitable for mobile networks where a host can be switched to
mobile networks where a host can be switched to
different networks of the subnet; since 1983 the only different networks of the subnet; since 1983 the only
protocol stack of ARPANET protocol stack of ARPANET
– DNS (1981) organization of host domains, namind all DNS (1981) organization of host domains, namind all the hosts and mapping onto list of IP addresses
the hosts and mapping onto list of IP addresses
Early 90’s ARPANET melted in arising Internet space Early 90’s ARPANET melted in arising Internet space
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Internet – a brief prehistory Internet – a brief prehistory
ARPANET ARPANET was the first. was the first.
CSNET CSNET ("Computer Science Network“, 1980- ("Computer Science Network“, 1980-
1989) – a non-military alternative to ARPANET.
1989) – a non-military alternative to ARPANET.
Running TCP/IP over X.25.
Running TCP/IP over X.25.
NSFNET NSFNET (“National Science Foundation (“National Science Foundation
Network”, 1985) – provides open access to Network”, 1985) – provides open access to
supercomputer centers for researchers.
supercomputer centers for researchers.
Started from
Started from 56 kbps 56 kbps speed. speed.
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Example Networks - The
Example Networks - The Internet Internet
The Internet arises on base of ARPANET after The Internet arises on base of ARPANET after joining of another regional networks - NSFNET, joining of another regional networks - NSFNET,
BITNET, EARN, …, thousands of LANs; early 90’
BITNET, EARN, …, thousands of LANs; early 90’
the term “internet” widely accepted as net name the term “internet” widely accepted as net name
“The Internet”
“The Internet”
Internet machine is each machine that Internet machine is each machine that
(1) (1) inter-communicates with others under TCP/IP and inter-communicates with others under TCP/IP and (2) (2) has a specific IP address. has a specific IP address.
Classic applications: mail, news, remote login and Classic applications: mail, news, remote login and file transfer
file transfer
“ “ New wave” New wave” applications: from gophers to WWW applications: from gophers to WWW surfing
surfing
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Example Networks -
Example Networks - Novell Novell ™ ™ NetWare
NetWare ® ®
Client-server model based LANs, basically Client-server model based LANs, basically connecting user PCs and server-PCs
connecting user PCs and server-PCs
Special protocol stack - 5 layers, closer to Special protocol stack - 5 layers, closer to TCP TCP / / IP than OSI: IP than OSI:
– Phys./Data layer: different industry standards Phys./Data layer: different industry standards
– Network layer: Network layer: Internet Packet Xchange Internet Packet Xchange (IPX) prototcol: (IPX) prototcol:
connectionless
connectionless (like IP), IPX packet has (like IP), IPX packet has 12-byte 12-byte Source/Destination Address (IP datagram : 4 bytes) Source/Destination Address (IP datagram : 4 bytes) – Transport layer Transport layer : :
• Network Core Protocol Network Core Protocol (NCP) - user data transport + (NCP) - user data transport + numerous distributed file system services or
numerous distributed file system services or
• Sequenced Packet Xchange Sequenced Packet Xchange (SPX)- simple, compact (SPX)- simple, compact transport protocol or
transport protocol or
• option: option: TCP TCP
4B network # IP Number
6B machine # LAN 802 addr.
2B local addr. machine socket
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Example Networks - Example Networks -
Novell
Novell ™ ™ NetWare NetWare ® ®
– Application layer: includes File system + Application layer: includes File system + SAP SAP (Service Advertising Protocol: (Service Advertising Protocol:
broadcasts information about the server broadcasts information about the server
data and services to routers) data and services to routers)
3-component client-server model 3-component client-server model : client : client machine (user workstation), network
machine (user workstation), network server (local router) and remote server server (local router) and remote server
negotiable IPX packet length (i.e. data negotiable IPX packet length (i.e. data field varies)
field varies)
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Example Networks - Gigabit Example Networks - Gigabit
Implementations Implementations
Next step after 100 Mbps Internet backbones Next step after 100 Mbps Internet backbones
Specific Applications: Specific Applications: Teleservices Teleservices (on-line (on-line transmission of huge data arrays) especially transmission of huge data arrays) especially
televideoservices, cable TV to net, etc.
televideoservices, cable TV to net, etc.
Note Note : not always faster, but better bandwidth : not always faster, but better bandwidth - for mass communications
- for mass communications
Implementations: mainly Ethernet LANs and Implementations: mainly Ethernet LANs and ATM switches: 3Com
ATM switches: 3Com
®®(1000 megabits per second (Mbps) (1000 megabits per second (Mbps)
Gigabit Ethernet networking infrastructure around eleven 3Com CoreBuilder Gigabit Ethernet networking infrastructure around eleven 3Com CoreBuilder
9000 enterprise switches).
9000 enterprise switches).
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ARPANET growth: 12.1969 – 09.1972
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