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Lecture 1: OverviewEE450: Introduction to Computer Networks

Professor A. Zahid

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Administrative Information I• EE450: Introduction to Computer Networks• Lecture Hours: TTH 7:30 ~ 8:50 AM (Studio D)• Discussion Session: W 8:30 ~ 9:20 AM• Instructor: A. Zahid• Office: EE102, (213)-740-2221• Office Hours: TTH 7:00 ~ 7:25 AM, 9:00 ~ 10:45

AM, 1:00 ~ 3:00 PM• E-Mail : zahida54@yahoo.com, azahid@usc.edu• Voice Messages: (213)-382-7768• URL: http://www-classes.usc.edu/engr/ee-s/450z/

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• Course Prerequisites: – Junior/Senior Standing– Passion and dedication to the course

• Course Textbook:– Computer Networks: A System Approach, 2nd

edition, L. Peterson and B. Davie, Morgan Kaufmann Publishing, 2000

– ISBN: 1-55860-514-2

Administrative Information II

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EE450 Team Members I• Teaching Assistant: Mr. Karim Seada• Email: seada@usc.edu• Office: EEB201• Office Hours: W 10:00-12:00 PM• Responsibilities include

– Conducting a weekly discussion session– Maintaining the course web site– Conducting office hours– Assisting students with their homeworks

• All e-mails concerning the homeworks should be addressed to the TA and CCed to me.

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EE450 Team Members II• Grader: Ms. Deniz Gurkan (dgurkan@usc.edu)• Office: EEB533• Office Hours: F 11:00-1:00 PM• Grader: Ms. Jieyu Zheng (jieyuzhe@usc.edu)• Office: EEB201• Office Hours: M 3:30-5:30 PM• Graders Responsibilities:

– Grading homeworks and answering questions regarding the grading

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• Midterm, October 17, 7:30 ~ 8:50 AM • Final, December 12, 4:30 ~ 6:30 PM• There is absolutely no make-up exams no matter

what your reasons are.• Roughly 6~7 Homeworks . Homeworks must be

submitted during the lecture they are due or before that. No late Homeworks shall be accepted. No electronic Homeworks shall be accepted. Solutions to Homeworks shall be posted.

• For DEN students, please contact DEN office for a FAX number or an e-mail address for submitting your Homeworks.

Course Workload

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Grading Policy/Scale

• There is absolutely No curve in this course • You will get the Maximum of the following two

options– {40% M, 50% F, 10% H} or – {30% M, 60% F, 10% H}

• Grading Scales:– 85% ~ 100%, A- to A+– 70% ~ 84%, B- to B+– 55 ~ 69%, C- to C+– 45% ~ 54%, D- to D+

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Reference Textbooks

• Data and Computer Communications, W. Stallings• Networks for Computer Scientists/Engineers, Y. Zheng• Communications Networks, L. Garcia• Computer Networking, J. Kurose & K. Ross• Computer Networks, A. Tanenbaum• Data Communications and Networking, B. Forouzan• Internetworking with TCP/IP, D. Comer

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Important Notes !• All Students are required to e-mail our TA their e-

mails for him to form a group address for the class. Any announcements relevant to the course (meetings/seminars/etc…) shall be broadcasted

• Lecture charts, homework solutions and other announcements shall be posted on the site. So please do check the site regularly

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Course Overview• Part 1: Data Communications & Networking• Part 2: Computer Networking Protocols (TCP/IP)• Part 3: Wide Area Networks (WANs)• Part 4: Local Area Networks (LANs)• Part 5: Internetworking• Part 6: Transport Layer Protocols• Part 7: Network Applications

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Simple Data Communications Model

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Components of the Model• Source

– Generates data to be transmitted• Transmitter

– Converts data into transmittable signals• Transmission System/Media

– Carries the transmitted signal• Receiver

– Converts received signal into data• Destination

– Takes incoming data

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Key Communications Tasks• Transmission System Utilization• Interfacing• Signal Generation• Synchronization• Exchange Management• Error detection and correction• Addressing and routing• Recovery• Message formatting• Security• Network Management

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Computer Networks

• A computer network is a set of nodes such as routers, switches, hosts, etc.. interconnected via transmission facilities such as copper, cable, fiber, satellite, radio, microwave, etc.. for the purpose of providing services to end systems/users

• Do we need networking? Yes we do! • Point-to-point communication is not practical!

– Devices are too far apart– Large set of devices would need impractical number

of connections. See illustration next chart

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Example: Telephone Network

Fully-Connected Mesh# of FDX links = N(N-1)/2e.g., N=6; 6(5)/2=15 linksTotal # ports = N(N-1)e.g., N=6; 6(5)=30 ports

CentralOffice(CO)

With Central Office# of FDX links = Ne.g., N=6; 6 linksTotal # of ports = Ne.g. N=6, 6 ports

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Multimedia Convergence

Network Telephone companies (telco)Internet Service Providers (ISP)Networking

Computer Hardware/SoftwareTelco/wireless Hardware

Video- pre-recorded / on-demand

(e.g., MPEG, RealNet)- live (video phone,

video teleconference)

Broadcast TVFilm

Data- e-mail- files-- executables-- source code-- data-- html-- image

Computer SoftwareFinancial, eCommerce, etc.

Major industries

RecordingBroadcast RadioVoice / Audio

- pre-recorded /on-demand(streaming or file [mp3])

- live (RealNet, VoIP)

PDA

Cellphone

Pager

Wireless

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Networking Architecture Models I

• Client/Server Model

Client Server

Request

Response

Network

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Illustration of Client/Server Architecture

Client(web browser)

-source-

Network

Server(web server)-destination-

html file image file

Example: World Wide Web

Request(GET index.html)

Response(HTML filegif, jpeg, png file[s])

Http://www.yahoo.com

<html>

</html>

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Networking Architecture Models II

• Peer-to-Peer– Each host has both client and server functionalities– CPU cycle sharing

Client

Server

Request

ResponseNetwork

Server

Client

Server

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Networking Perspectives• Application Programmer / End User

– Guaranteed timely, reliable and recognizable delivery of message/information

• Network Designer– Cost-effective design. Resources (Bandwidth,

Memory and CPUs) must be used efficiently and are fairly allocated

• Network Provider– Administration & management effort, fault

detection/fault isolation, easy to account for usage

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The Public Internet

local ISP

companynetwork

regional ISP

router workstationserver

mobile

• Millions of connected computing devices: hosts, end-systems– PC’s, Workstations, Servers– PDA’s, Phones, Toasters!– Running network applications

• Communication links– Fiber, Copper, Radio, Satellite

• Routers: forward packets (chunks) of data across the network

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The Public Internet (Continued)

• Protocols are used to control sending & receiving of messages– e.g., TCP, IP, HTTP, FTP, PPP

• Internet: “Network of networks”– Loosely hierarchical topology– Public Internet versus private

Intranet

• Internet standards– RFC: Request for comments– IETF: Internet Engineering Task

Force

local ISP

companynetwork

regional ISP

router workstationserver

mobile

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The Internet Infrastructure

NBP A

NBP B

NAP NAP

Regional ISP

Regional ISP

LocalISP

localISP

• Hierarchical• National/international

backbone providers (NBPs)– e.g. BBN/GTE, Sprint,

AT&T, IBM, UUNet– Interconnect (peer) with

each other privately, or at public Network Access Point (NAPs)

• Regional ISPs• Local ISPs

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National Backbone Provider

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Networking Performance Measures

• The two most important network performance measures are Delay/Latency & Throughput

• End-to-end delay consists of several components– Transmission time– Propagation delay– Nodal processing– Queuing delay (Random, depends on network

loading, link capacities, disciplines, etc.. ee465)

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Transmission Time• Transmission Time (ttrans)

– The time it takes to transmit a group of bits (e.g., a Message/Packet/Frame) of bits into a network

ttran = Number of message bitsData rate [bps]

t trans vs. Frame Size vs. Data Rate

1.00E-071.00E-061.00E-051.00E-041.00E-031.00E-021.00E-01

1.00E+001.00E+011.00E+021.00E+03

1 10 100 1000 10000 100000 1000000

Frame Size (bits)

t tran

s (s

ec) 1000

10000100000100000010000000

Data Rate (bps)

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Propagation Delay• Propagation time (tprop)

– The time it takes for a bit to traverse the link

tprop = link length[m]vprop [m/s]

• Example propagation velocities:Air/Free space: c = 3x108 meters/sec Cat 5 UTP: 2~2.5x108 meters/sec Optical Fiber: 2~2.5x108 meters/sec

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Propagation Delay (Cont.)tprop vs. Velocity vs. Length

1.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-021.00E-011.00E+00

1 10 100 1000 10000 1E+05 1E+06 1E+07 1E+08

length (m)

tpro

p (s

ec)

0.67c0.8c1.0c

GEOMEO

LA-LondonLA-NY

systemroom

buildingcampus city country

continentInternet

space

WAN

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Nodal Processing/Queuing Delay

• Nodal processing: – Check bit errors– Determine output link (Routing decision)

• Queuing– Time waiting at output link for transmission – Depends on congestion level of router

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Message Transfer Time

• Message Transfer Time (txfr) = Message latency– Time for sender to transmit message to the

receiver and for the receiver to receive the entire message. Also known as the end-to-end delay

txfr = ttrans + tprop + tqueuing/processing

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Summary of Delay Components

A

B

propagation

transmission

nodalprocessing queueing

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Round Trip Time (RTT)• Round Trip Time: The time to send a message

from a sender to the receiver and receive a response back

• RTT depends on message size, length of link, direction of propagation, propagation velocity, network node processing, network loading, etc…

• For simplicity, RTT is normally assumed to be twice the end-to-end propagation delay although this might not be true if the message and the response traverses different links

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Network Throughput• The Throughput is defined as the number of

information bits that can be transmitted reliably over a certain period of time. It is measured in “bps”

• The throughput is the carried load and it is notequal to the offered load

• Protocols add overhead bits and time delays in addition to the transmission time of the actual information bits. That would result in reduced throughput.

• Link errors are result in reduced throughput

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Bandwidth/Capacity• The bandwidth or the data rate is the

number of bits that can be transmitted over a certain period of time.– For example, 10 Mbps means that 10 million

bits are transmitted every seconds. • Link Capacity is the maximum data rate

possible on the link with negligible error rate (Shannon Theorem, to be discussed later)

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“Bandwidth x Delay” Product• Pipe Size: The maximum amount of data present

on the line• Example: If the line bandwidth /data rate is 10

Mbps and the end-to-end delay is 30 msec, the amount of data found on the line is 300 Kbps or 37.5 Kbytes. For RTT, it is 75Kbytes

Figure 3.20 in text

Bandwidth

Delay

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Network Topologies• Network topology is the physical arrangement

of the network nodes and the links interconnecting them– Mesh topology– Star/Hub topology– Bus topology– Tree Topology– Ring topology

• A fully connected network is one in which every node is connected to every other node

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Mesh/Fully Connected Topology

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Star/Hub Topology

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Bus Topology

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Tree Topology

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Ring Topology

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Network Classifications

• Networks can be classified based on Coverage into– LANs: Local Area Networks– WANs: Wide Area Networks– Others including MAN (Metropolitan Area

Networks, PAN (Personal Area Networks), Home Networks, etc…

• Networks could also be classified as Switched or Shared (Broadcast) networks

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Local Area Networks (LANs)

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Metropolitan Area Networks (MANs)

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Wide Area Networks (WANs)

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Home NetworksTypical home network components• ADSL or cable modem• Router/firewall• Ethernet• Wireless access point

WirelessAccess Point

WirelessLaptops

Router/Firewall

CableModem

to/fromcable

headend

Ethernet(Switched/Shared)

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Internetwork

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Link Topology

• Point-to-point– Direct link – Only 2 devices share link

• Multipoint– More than two devices share the link

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Link Duplicity• Simplex

– One direction– e.g. Radio/Television broadcasting

• Half duplex (HDX)– Either direction, but only one way at a time– e.g. Police radio

• Full duplex (FDX)– Both directions at the same time– e.g. Telephony

or

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Transmission Modes

Unicast Multicast Broadcast

One-to-one One-to-selected group

One-to-all