CS2105An Awesome Introduction to

Computer Networking

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OoiWei TsangAS6 05-14

ooiwt@comp.nus.edu.sg

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Office HourMonday 4-6pm

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2 programming assignments1 written assignment

9 problem sets4 practical exercises

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Important DatesMidterm: 10March 2014Final Exam: 30 April 2014

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Midterm& Final areSemi-Open Book

(one double-sided A4 crib sheetallowed)

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Slides to be posted 1-2 daysbefore the lecture

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Slides ̸=Notes

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You are expected to take notesduring lecture

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You are expected to read theassigned readings

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Nomodel answer will beposted

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``Nomercy''policy againstplagiarism

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``Nomercy''policy againstvoilation of naming

convention

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http://blog.nus.edu.sg/cs2105

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Check for updates frequentlyand

subscribe via email or RSS

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Use your real namewhencommenting online

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Screencast will be posted

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You need an SoCUNIX account.Get one here:

https://mysoc.nus.edu.sg/~newacct/

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Questions?

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CS2105 Lecture 1

Introduction14 January, 2014

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CS2105 Lecture 1

Introduction14 January, 2014

After this class, you are expected to:

• understand the basic terms, including host, packet, protocol,throughput, bottleneck link, store-and-forward, and autonomoussystem.

• know about the logical (the five layers) and physical architecture (as anetwork of ASes) of the Internet.

• know about the pros and cons of packet switching versus circuitswitching.

• understand the different components of end-to-end delay and theirrelations to bandwidth, packet size, distance, propagation speed, andqueue size.

The complexity involved inengineering the Internet willmake your head explode, butthis one incredibly simple trickkeeps the complexitymanageable.

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What is CS2105about?

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Concepts andprinciplesbehind computer networking

Introduction to networkedapplication programming

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The Internet is a network ofconnected computing devices.

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Hostsorend systems

996,230,757as of July 2013

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996,230,757as of July 2013

Data obtained from Internet SystemsConsortium: http://www.isc.org/solutions/survey/history

The hosts rundistributedapplications

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Web: browsers, Web serversWoW: clients, game serversSkype: clients, supernodesBitTorrent: peers, trackers

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Applicationsexchangemessages andcommunicate according to

protocols

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Protocol: the type andorderofmessages exchanged and theactions taken aftermessages

are sent or received

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Examples:HTTP, SMTP, FTP, TCP

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The hosts access the Internetthroughaccess network

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WiFi, Ethernet, 3G, LTE, DSL,Cable, Fiber, Dial-Up, Satellite

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WiFi, Ethernet, 3G, LTE, DSL,Cable, Fiber, Dial-Up, Satellite

You can read upmore about these differentaccess network technologies in Section 1.2.1.Wewill cover Ethernet andWiFi inmoredetails in CS2105.

Hosts can communicate overdifferentphysicalmedia

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twisted pair

coaxial cablefiber optic

fiber optic

Consider two hosts connecteddirectly through a physical medium

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The hosts communicate by sendinginformation to each other.

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Information can be represented by asequence of bits -- 0 or 1.

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Modulation/Demodulation:Conversion between bits and

signals

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Error Detection/Correction:Ensuring that bits are received

correctly

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Packetization/Segmentation:Dividing data into chunks(called packets) so that only

errornous packets need to beretransmitted.

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Considermultiple hosts connectedthrough a shared physical medium

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Addressing:Identify the source and

destination

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Mediumaccess control:Regulate who sends

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Considermultiple hosts connectedthrough intermediate packetswitches, which store and forwardthe packets.

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The Internet is apacketswitchingnetwork

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Packet switching:Resources used on demand;

best effort services

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Circuit switching:Resources are reserved,guaranteeing services

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Packet vs. Circuit Switching:Which ismore efficient?

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Packet vs. Circuit Switching:Which ismore efficient?

Details about packet switching and circuitswitching is explained in Sections 1.3.1 and1.3.2

Who owns the intermediatepacket switches on the

Internet?

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The Internet is a``network-of-networks'',

organized into autonomoussystems (AS), each is owned by

an organization.

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The Internet is a``network-of-networks'',

organized into autonomoussystems (AS), each is owned by

an organization.

To learnmore about the architecture of theInternet, read Section 1.3.3. The Internettopology figure is taken fromhttp://www.caida.org/research/topology/as_core_network/

traceroute

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traceroute

You can also try to traceroute from otherlocations on the Internet athttp://www.traceroute.org

Routing: Decidewhichpath/route to take

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Reliability: Recover frompacket losses

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Link Rate/Bandwidth:Howmany bits can be

``pushed'' onto a link per unittime.

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Delay:Time between send and

receive

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To send a packet in a packet switchnetwork, for each link in the path1. transmit packet onto the link as

bits2. propagate bits to next node3. store and process the packet4. wait to be transmitted

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End-to-end packet delay consists of:1. transmission delay2. propagation delay3. processing delay4. queueing delay

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.

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Throughput:Howmany bits can be

communicated per unit time.

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Multiple applications can run on eachhost

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Demultiplexing: Determinewhich packet belongs towhich

application

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Many issues to consider, to supportdifferent applications running onlarge number of hosts throughdifferent access technology and

physical media.

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Layering:Common CS trick to deal withlarge and complex systems

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Each layer provides a service;Simple interfaces btwn layers;Hide details from each other.

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Each layer provides a service;Simple interfaces btwn layers;Hide details from each other.

The five layers of the Internet are described inSection 1.5.

..Application.

Transport

.

Network

.

Link

.

Physical

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Applications (or processes)treat the Internet as ablackbox, sending and receivingmessages through a socket.

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Transport layerprovides process-to-processmessage delivery services.

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TCPreliable, in-order delivery, withcongestion and flow control

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UDPbest-effort delivery

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Network layerhost-to-host delivery

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Link layernode-to-node delivery

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Physical layer``bits over physical media''

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