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.


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?


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

CS332 - Computer Networks 4

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


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)


• Spirit's West Valley Panorama – original size, 5.8 MB – roughly 1 hour transmission time

• Engineering challenges:– Compression– Error correction– Lag time


How do we connect computers?

• 2 computers is pretty easy



• Where does # 3 connect?

?




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Interconnection strategies

• Point-to-point: Internet, phone network



• Multipoint – shared channel.

• Example – original Ethernet

…


Interconnection stragegies

• Ring: examples – FDDI, SONET



• Star or switched hub – examples: various Ethernet versions

Hub


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)


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?


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


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


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


Evolution: Migration of services

As Packet Switching technology matured, former circuit-switched applications migrated to packet-switched networks

• Voice-over-IP

• Audio/Video broadcast


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


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


Medium: Copper

• Coaxial cable (Cable TV, old Ethernet)

• Unshielded Twisted Pair (UTP) - phone wire

• Shielded Twisted Pair

• 10 - 3000 Megabit/sec data rate


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


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.)


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


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)


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


Evolution of Protocols

• Proprietary networks

• ARPAnet

• Ethernet

• Unix and the Open Systems movement

• Network standardization

• The Internet


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.


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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overview cs 332 – computer networks 1cs332 - computer networks

Documents

separated computers

phone network

connection setup

endtoend connection

earth data rate

wide area network wan

example original ethernet

examples fddi