computer communication & networks

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Computer Communication & Networks

Lecture 1

Introduction

http://web.uettaxila.edu.pk/CMS/coeCCNbsSp09/index.asp

Waleed Ejazwaleed.ejaz@uettaxila.edu.pk

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Overview

Administrative Networking: An Overview of Ideas and

Issues

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Who’s Who

Instructor Engr. Waleed Ejaz

2006 -2008 MS (Computer Engineering) from NUST Area of Specialization: Communication & Computer

Networks 2003-2006 BE (Computer Engineering) from UET Taxila

Lab Engineer Engr. Noshina Ishaq

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Web Resources

Course web• http://web.uettaxila.edu.pk/CMS/coeCCNbsS

p09/index.asp

• This website and email will serve as a communication medium between you and me besides the lecture timing.

Do visit the course website regularly and see Recent Announcements for updates.

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Grading Policy

Final Exam: 100 Grand Quiz 10 Assignments 5 Quizzes: 10 Labs 25

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Answers to FAQs

All home works are due at the beginning of the class indicated on the course calendar After that 10% penalty: only if submitted before solutions

are posted.

Exams are closed-book and extremely time limited. Exams consist of design questions, numerical,

maybe true-false and short answer questions. More about Exams you can see Past Exams from

WEB.

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Reading Text book:

Data Communications and Networking, 4/e B.A. Forouzan,

McGraw-Hill, 2003, ISBN 0-07-292354-7.

Reference books: Computer Networking, a top-down approach

featuring the Internet (3rd edition), J.K.Kurose, K.W.Ross,

Addison-Wesley, 2005, ISBN 0-321-26976-4.

Computer Networks, A Systems Approach

L. Peterson & Davie

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Required Skills

The course does not assume prior knowledge of networking.

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My Requirement from YOU

I require YOU to take active part during lectures

Which means Lot of Questioning in the class – (Interactive session)

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Aim of the Course

Aim of the course is to introduce you to the world of computer networks, so that you could know the science being used in running this

network Use this knowledge in your professional field

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Network design

Before looking inside a computer network, first agree on what a computer network is

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Computer network ?

Set of serial lines to attach terminals to mainframe ?

Telephone network carrying voice traffic ?

Cable network to disseminate video signals ?

Specialized to handle:

Keystrokes

Voice

Video

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What distinguishes a Computer network ?

Generality Built from general purpose

programmable hardware Supports wide range of applications

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Information, Computers, Networks Information: anything that is represented in bits

Form (can be represented as bits) vs Substance (cannot be represented as bits)

Properties: Infinitely replicable Computers can “manipulate” information Networks create “access” to information

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Networks

Potential of networking: move bits everywhere, cheaply, and with desired

performance characteristics Network provides “connectivity”

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What is “Connectivity” ?

Direct or indirect access to every other node in the network

Connectivity is the magic needed to communicate if you do not have a direct pt-pt physical link. Tradeoff: Performance characteristics worse than true physical

link!

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Building Blocks

Nodes: PC, special-purpose hardware… hosts switches

Links: coax cable, optical fiber… point-to-point

multiple access…

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Why not connect each node with every other node ? Number of computers that can be

connected becomes very limited Number of wires coming out of each

node becomes unmanageable Amount of physical hardware/devices

required becomes very expensive Solution: indirect connectivity using

intermediate data forwarding nodes

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Switched Networks

two or more nodes connected by a link

white nodes (switches) implement the network

colored nodes (hosts) use the network

A network can be defined recursively as...

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Switched Networks

two or more networks connected by one or more nodes: internetworks

white nodes (router or gateway) interconnects the networks

a cloud denotes “any type of independent network”

A network can be defined recursively as...

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A Network

A network can be defined recursively as

two or more nodes connected by a physical link

Or

two or more networks connected by one or more nodes

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Switching Strategies

Circuit switching: carry bit streams

a. establishes a dedicated circuit

b. links reserved for use by communication channel

c. send/receive bit stream at constant rate

d. example: original telephone network

• Packet switching: store-and-forward messagesa. operates on discrete

blocks of datab. utilizes resources

according to traffic demand

c. send/receive messages at variable rate

d. example: Internet

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What next ?

Hosts are directly or indirectly connected to each other Can we now provide host-host connectivity ?

Nodes must be able to say which host it wants to communicate with

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Addressing and Routing

Address: byte-string that identifies a node usually unique

Routing: forwarding decisions process of determining how to forward messages

to the destination node based on its address Types of addresses

unicast: node-specific broadcast: all nodes on the network multicast: some subset of nodes on the network

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Wrap-up

A network can be constructed from nesting of networks

An address is required for each node that is reachable on the network

Address is used to route messages toward appropriate destination

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What next ?

Hosts know how to reach other hosts on the network

How should a node use the network for its communication ?

All pairs of hosts should have the ability to exchange messages: cost-effective resource sharing for efficiency

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Multiplexing Physical links and nodes are shared among users

(synchronous) Time-Division Multiplexing (TDM) Frequency-Division Multiplexing (FDM)

L1

L2

L3

R1

R2

R3Switch 1 Switch 2

Multiple flows on a single link

Do you see any problem with TDM / FDM ?

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What Goes Wrong in the Network?

Reliability at stake

Bit-level errors (electrical interference) Packet-level errors (congestion)

distinction between lost and late packet Link and node failures

distinction between broken and flaky link distinction between failed and slow node

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What Goes Undesirable in the Network?

Required performance at stake

Messages are delayed Messages are delivered out-of-order Third parties eavesdrop

The challenge is to fill the gap between application expectations and hardware capabilities

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Research areas in Networking Routing Security Ad-hoc networks Wireless networks Protocols Quality of Service …

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Readings

Chapter 1: 1.1, 1.2 Computer Networks, A Systems Approach

L. Peterson & Davie

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