Transcript CSCI 344 Notes 3

Approaches to Network Communications
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Circuit-Switched
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Connection Oriented
Form dedicated connection between 2 points
U.S. Telephone System
Packet_Switched
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Connectionless
Data to be transferred broken into small packets
Multiplexed onto high capacity systems
Carries a few hundred(s) data usually
Advantage: Multiple communications occur concurrently
Disadvantage: Network overload causes throughput decrease
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WAN/LAN
Fundamental difference between large and
small spanning geographical distance
networks
 2 Categories, no formal split
 Wide Area Networks, long haul networks
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 Slower
speeds, greater delays
 Typical speeds 56Kbps to 155 Mbps
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WAN/LAN
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Local Area Network
 Highest
speed, sacrifice long distance
 Single building, small campus
 Typical speeds 10 Mbps to 2 Gbps
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LAN - Each computer connects directly to
physical transport medium via network
interface device
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WAN/LAN
WAN - Network usually consists of a series
of interconnected intermediate node routers
interconnected by communication lines and
modems
 Extending network means adding another
packet switch
 Connect a new computer to WAN means
connecting it to a packet switch
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WAN/LAN
Adding a new switch adds delay along route
 Software hides details of hardware on different
packet switches
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 Hardware
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independent transport
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Network Hardware Addresses
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Each hardware technology has an addressing
mechanism
Specifies destination of packet
Every computer on a network is assigned a unique
address
 Usually an integer
Destination address field contained in each packet
 Same location in all packets
Sender must know destination address
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Ethernet Technology
Packet-switched LAN technology
 Xerox Palo Alto Research Center (PARC) in
early ‘70s
 Connection between computer and co-axial
(coax) called a transceiver
 Pin hole in ether = tap
 Connections to Ethernet have 2 major
components
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Transceiver/Host Interface
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Host Adapter
Transceiver
 Connects to center wire and braided shield
 Sensing and sending signals on the ether
Host Interface
 Plugs into the computer’s bus on motherboard
 Connected to transceiver by cable called Attachment
Unit Interface (AUI)
Oldest form of Ethernet technology (Thick-Wire Ethernet)
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Thin-Wire Ethernet
First improvement, better access, lower cost
 Thinnet
 Thinner coax cable, less expensive, more
flexible
 Thinner cable more susceptible to electronic
interference (noise), shorter distances, fewer
computers
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Thinnet
Replace high cost transceivers with digital
circuitry inside of host interfaces
 Direct connection from computer to ether
 Connects direction from one computer to
another
 BNC Connectors, T’s in the back plugged
into host adapter
 Show on board
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Twisted Pair Ethernet
No longer need for shield of coax
 Ethernet access with pair of unshielded
copper wires similar to telephone wires
 Further reduces cost, protects other users on
network when someone disconnects
 10Base-T wiring connects computers via an
Ethernet Hub
 See Figure 2.1 on page 17
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Hub
Electronic device that simulates signals of
Ethernet
 Computers must be < 100m away
 Requires power
 Intelligent vs. Dumb Hub
 Connection to hub acts same as host adapter
to transceiver
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