Overview CS 332 – Computer Networks 1CS332 - Computer Networks.
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Transcript of Overview CS 332 – Computer Networks 1CS332 - Computer Networks.
Overview
CS 332 – Computer Networks
1CS332 - Computer Networks
How did we get here?• 1950 - 1968 The golden age of the
mainframe/data center• 1968 Initial ARPAnet deployment• 1970 First 16-bit minicomputer• 1976 Ethernet introduced• 1979 Initial USENET news
deployment• 1980 IBM PC introduced
4.0BSD Unix with integrated (inter)networking
• 1980-presentPopularization of "workstations"• 1990s Explosion of the Internet/Web
Peer to Peer networkingetc.
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TrendsMainframe - Terminal Isolated PC - SneakerNet
Networked PCsClient/Server
Hosted Apps/Web Apps
Trending toward applications on central servers with relatively "dumb" PCs?
Difference between web-app paradigm and old mainframe/terminal?
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Sun/Oracle "Network Computer"
• Late 1990's, small footprint, no disk, ran Java apps hosted on an application server.
• Image found on the GlobalNerdy blog by Joey DeVilla
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Applications
• SSH, E-mail, file transfer• Business: electronic funds transfer, electronic
data interchange (EDI), point-of-sale, e-commerce, reservation systems, telepresence
• Control: factory floor, HVAC, automotive, avionics
• Entertainment: Web, DVR, streaming media• Science: I2, deep space communication
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Example: Mars Rover
• Rover can communicate directly with earth or with orbiters
• Direct-to-earth data rate: 3.5 – 12 kilobits per second, for 3 hours per day (power and thermal limitations) – max 130 Megabits per day (CD – 700 megabytes)
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• Spirit's West Valley Panorama – original size, 5.8 MB – roughly 1 hour transmission time
• Engineering challenges:– Compression– Error correction– Lag time
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How do we connect computers?
• 2 computers is pretty easy
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How do we connect computers?
• Where does # 3 connect?
?
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How do we connect computers?
• Where does # 3 connect?
?
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How do we connect computers?
• Where does # 3 connect?
??
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Interconnection strategies
• Point-to-point: Internet, phone network
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Interconnection strategies
• Multipoint – shared channel.
• Example – original Ethernet
…
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Interconnection stragegies
• Ring: examples – FDDI, SONET
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Interconnection strategies
• Star or switched hub – examples: various Ethernet versions
Hub
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Datacom Evolution
• Early data networks used a technique called circuit switching– Large, widely separated computers establish
an end-to-end connection through a point-to-point switching network for each conversation
– The connection reserves bandwidth for communication between the two computers
Referred to as Wide Area Network (WAN)
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Data conversations are bursty.
• During quiet periods, reserved bandwidth is wasted.
• Connection setup and teardown take time
• Utilization of bandwidth can be quite poor
How can we do better?
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Data Comm Evolution: Packet Switching
• Bundle data that needs to be transmitted into a "packet" with all the information needed to route it to its destination
• No connection setup/teardown
• Channel can be shared more efficiently by many bursty data sources
• Routing info in each packet is overhead
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Data Comm Evolution: PCs
• Companies with many PCs wanted to network them
• WAN solutions were too complex to be used on simpler, less capable machines
• Large scale networking technologies are optimized for situations that don't hold on small networks
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Data Comm Evolution: Local Area Networks
• Use shared communication medium to reduce cost
• Simplify addressing
• Boost speed
• Use packet switching for efficient sharing of communication channel
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Evolution: Migration of services
As Packet Switching technology matured, former circuit-switched applications migrated to packet-switched networks
• Voice-over-IP
• Audio/Video broadcast
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Evolution: mobility
• Unplug a laptop from the internet in one location and plug back in somewhere else
• Communication without wires
• Communication while on the move - cellular
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Transmission media: Copper wire
• Good conductor of electricity
• Signals attenuate as they propagate
• Susceptible to electromagnetic interference unless carefully shielded
• Good conductor of (harmful) electricity such as power spikes or lightning strikes
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Medium: Copper
• Coaxial cable (Cable TV, old Ethernet)
• Unshielded Twisted Pair (UTP) - phone wire
• Shielded Twisted Pair
• 10 - 3000 Megabit/sec data rate
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Medium: Unguided Broadcast
• No wire to pull
• Allows portability
• Attenuation is worse than copper, so range is limited
• Walls block and reflect signals
• Some varieties require unobstructed line of sight
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Medium: Unguided Broadcast
• Radio (UH Alohanet, PRnet, Cellular communication)
• Microwave• Satellite• Infrared• Laser• 300 Megabit/sec maximum data rate
(802.11N with channel bonding. 130 Mbps is more common.)
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Medium: Optical Fiber
• Very high bandwidth
• Low attenuation
• Impervious to electromagnetic interference
• Inexpensive compared to copper
• Driver hardware is more expensive than corresponding electronic equipment
• Difficult to “tap,” so topologies are limited
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Medium: Optical Fiber
• Multimode• Graded Index Multimode• Single Mode• Typical data rates range from 45 Mbps to
40 Gigabits/sec. per channel, up to 80 multiplexed channels per fiber (3.2 Tbps)
• Data rate record: 155 multiplexed 100 Gbps connections over 7000 km (Bell Labs in Villarceaux, France)
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Protocols
A protocol is a set of rules which allows the transfer of information between two or more entities.
Examples:
Two-way radio communication
Human communication
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Evolution of Protocols
• Proprietary networks
• ARPAnet
• Ethernet
• Unix and the Open Systems movement
• Network standardization
• The Internet
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Layered Protocol Stacks
• The accepted general architecture for the design of complex network protocols calls for a series of software layers. Characteristics of this approach:– Sets of related objectives are isolated into a single layer of the
network software.– A given layer only needs to know how to interact with the layers
directly above and below it, simplifying each layer.– The interface between layers is well defined, improving
interoperability of differing implementations.– The layer interface is designed to hide the details of how the
services offered by the layer are actually carried out (abstraction).
– As long as the specified interfaces between layers are preserved, lower layers can be changed without affecting higher layers.
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Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Presentation
Session
Transport
Network
Data Link
Physical
Process A Process B
Machine 1 Machine 2
Application Protocol
Presentation Protocol
Session Protocol
Transport Protocol
Network Protocol
Data Link Protocol
Physical ProtocolSub
net l
ayer
s
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