3 networking evolution
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Data Communication Network Evolution
Motivation
SNA
DNA
TYMNET
ARPANET
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Layered communications protocol used by IBM forcommunications between IBM mainframes and devices
Uses token ring as the access method (IEEE 802.5)
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Physical Units on an SNA Network
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Provide reliable and tested communications withIBM systems
Disadvanta e requires special devices and complex training to
configure, manage and troubleshoot
Still used in some networks of Banks in USA
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DNA
Di italNetwork
Architecture
Developed for use on networks using DEC computers
Architecture used by Digital Equipment Corporation computers (nowCompaq)
DNA Structured Model
Has eight layers
Man hardware latforms need to communicate
Protocols
Digital Data Communication Message Protocol (DDCMP)
X.25
erne
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TYMNET
TYMNET was a commercial network
eve ope y are n .
TYMNET I, was designed to interface low-speed (10-30 character/s)
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The data rate was low, the size of the network was small (less than100 nodes),
The log-on rate low (less than 10 new users/min).
nteracte w t u up ex term na s on a c aracter y c aracter
basis.
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Mechanisms for data transmission in TYMNET
TYMNET was acket switched network
A tree structure for supervisory control of the original network
A virtual circuit approach for user data transmission andmu p ex ng over s ng e p ys ca n .
v rtua
c rcu t
sc eme
supports
no es
w t
sma u ers
memory.
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Terminal-oriented
Interactive, Duplex system
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ou ng n
routin is centralized virtual circuits
Uses adaptive shortest path routing algorithm (Dijkstras &
Bellman Fords)
The supervisory node computes the shortest path and sends a
needle packet to source that contains the routing information.
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routin is centralized virtual circuits
Uses adaptive shortest path routing algorithm (Dijkstras &
Bellman Fords)
The supervisory node computes the shortest path and sends a
needle packet to source that contains the routing information.
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vers ons
TYMNET-I :the supervisory node explicitly sets the routing tables at the nodes.
twas mp emente n 1 tm n computers.
TYMNET-II : routing tables are set by a set-up packets that precedes the
transmission of data.
.
Supports high density network
o e: ot vers ons use rtua rcu t pproac
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erence w -
In TYMNET-I the supervisor maintains an image of theinternal routing tables of all the nodes and explicitly reads
and writes the tables in the nodes,
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there is much less interaction between node and
supervisor.
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in 1957Seen as a defeat by the US
Spurred on by President Kennedy and his
vision to ut man on the moon b the end
of the decade, two new agencies were formed
NASA and ARPA in the DoD (Department
SPUTNIK
ARPA was the founding agency of ARPANET
which eventually led to the Internet
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ARPANET EVENTS
Build a minicomputer in each site as an interface betweennetwork & mainframe nodes
Processors
-corporation
By 1973, E-mail was 75% of all ARPANET Traffic
Also in 1973, TCP/IP was conceived by Vinton Cerf of Standford & BobKahn of DARPA
-is safely received at the following node (a store and forward system)
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Layout of the ARPANET Hosts and terminals
"talk" with each other via the IMP-subnet.
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ARPANET
message switched network.
received at the following node (a store and forwards stem
identical processors - kept at each node connect these processors to leased common-carrier
circuits to form a subnet
Research computers at each node are connected to these,
Processors (IMPs).
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Growth of the ARPANET (a)December 1969, (b)July 1970,
, . .
The Evolution of ARPANET