CC Notes Lecture 01

7/29/2019 CC Notes Lecture 01

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Data Communication Networks

Lecture # 01Introduction

Course Instructor:

Engr. Ghulam Shabbir

Assistant Professor, TED UET Taxila


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Grading Policy

As per policy of CASE


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Quizzes may be announced or unannounced.

Exams are closed-book and extremely time

limited.

Exams consist of design questions,

numerical, maybe true-false and short

answer questions.


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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

Data and Computer Communication by WilliamStallings (7th Edition) Prentice Hall.


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Data Communications

The term telecommunication means

communication at a distance. The word data

refers to information presented in whatever

form is agreed upon by the parties creatingand using the data. Data communications are

the exchange of data between two devices

via some form of transmission medium suchas a wire cable.


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Fundamental Characteristics

The effectiveness of a data communication

system depend on four fundamental

characteristics:

Delivery

Accuracy

Timelines

Jitter


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Five Components of Data

Communication

1. Message

2. Sender 3. Receiver

4. Medium

5. Protocol


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Direction of data flow

Simplex

Half Duplex

Full Duplex


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Network design

Before looking inside a computer

network, first agree on what acomputer network is


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Computer network ?

Set of serial lines toattach terminals to

mainframe ? Telephone network

carrying voice traffic ?

Cable network to

disseminate videosignals ?

Specialized tohandle:

Keystrokes

Voice

Video


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What distinguishes a

Computer network ?

Generality

Built from general purposeprogrammable hardware

Supports wide range of applications

Not optimized for special purposeapplication like making phone calls ordelivering television signals


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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 accessto every other node in the

network

Connectivity is the magic needed to communicate ifyou 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 nodewith every other node ?

Number of computers that can beconnected 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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A Network

A network can be defined recursively as

two or more nodes connected by aphysical link

Or

two or more networks connected by one ormore nodes


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Switched Networks

two or more nodesconnected by a link

white nodes(switches)implement thenetwork

colored nodes(hosts) use thenetwork

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 clouddenotes any

type of independentnetwork

A network can be defined recursively as...


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Switching Strategies

Circuit switching:carry bit streams

a. establishes a dedicatedcircuit

b. links reserved for useby communicationchannel

c. send/receive bit streamat constant rate

d. example: originaltelephone network

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

blocks of data

b. utilizes resourcesaccording to trafficdemand

c. send/receive messagesat 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 itwants 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

nestingof networks

An address is required for each node

that is reachable on the network

Address is used to routemessagestoward 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-effectiveresource 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 betweenapplication expectations and hardwarecapabilities


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Networks: key issues

Network criteria

Performance

Throughput

Delay

Reliability

Data transmitted are identical to data received.

Measured by the frequency of failure

The time it takes a link to recover from a failure Security

Protecting data from unauthorized access


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Terminology

The throughputorbandwidthof a channel is

the number of bits it can transfer per second

The latencyordelayof a channel is the time

that elapses between sending information and

the earliest possible reception of it


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Network topologies

Topology defines the way hosts are

connected to the network


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Network topology issues

1. highthroughput (bandwidth)

2. low latency

a goal of any topology


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Bandwidth and Latency

1.telecommunications: range of radio frequencies: a range of radiofrequencies used in radio or telecommunications transmission and

reception

2. computing:communications capacity: the capacity of acommunications channel, for example, a connection to the Internet, often

measured in bits per second

3. a data transmission rate; the maximum amount of information(bits/second) that can be transmitted along a channel

Latency

A synonym fordelay, is an expression of how much time it takes

for transmission from one designated point to another

Bandwidth


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Categories of Topology


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Mostly used network topologies

mesh

star

bus

ring


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A hybrid topology: a star backbone with three bus networks


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Hierarchical organization of the Internet


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LAN, WAN & MAN

Network in small geographical Area (Room, Building or a

Campus) is called LAN (Local Area Network)

Network in a City is call MAN (Metropolitan Area Network)

Network spread geographically (Country or across Globe) is

called WAN (Wide Area Network)


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Layering & Protocol Stacks


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Whats a protocol?

human protocols:

whats the time?

I have a question

introductions

specific msgs sent

specific actions taken when msgs received, or other events

network protocols:

machines rather than humans

all communication activity in Internet governed by protocols


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Protocol

protocols define format, order of msgs sent

and received among network entities, and

actions taken on msg transmission, receipt

a human protocol and a computer network protocol:

Hi

Hi

Got thetime?

2:00

TCP connectionreq.

TCP connection

reply.

Get http://gaia.cs.umass.edu/index.htm

time


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Standard

Essential in creating and maintaining an open

and competitive market for equipment

manufacturers

Guaranteeing national & internationalinteroperability of data & telecommunication

technology & process.


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Layered Tasks

An example from the everyday life

Hierarchy?

Services


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Why layered communication?

To reduce complexity of communication task

by splitting it into several layered small tasks

Functionality of the layers can be changed as

long as the service provided to the layerabove stays unchanged

makes easier maintenance & updating

Each layer has its own task

Each layer has its own protocol


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Reference Models

OSI reference model

TCP/IP


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OSI Reference model

Open System Interconnection

7 layers

1. Crate a layer when different abstraction is needed2. Each layer performs a well define function

3. Functions of the layers chosen taking internationally

standardized protocols

4. Number of layers large enough to avoid

complexity


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Seven layers of the OSI model


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Exchange using OSI Model


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Issues, to be resolved by the layers

Larger bandwidth at lower cost

Error correction

Flow control

Addressing

Multiplexing Naming

Congestion control

Mobility

Routing

Fragmentation Security

....


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Applications

E-mail

Searchable Data (Web Sites)

E-Commerce

News Groups

Internet Telephony (VoIP)

Video Conferencing

Chat Groups

Instant Messengers

Internet Radio


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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

Chapter 1 (B. A Forouzan)

Section 1.1, 1.2, 1.3,1.4

Chapter 2 (B.A Forouzan) Section 2.1


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Documents

CC Notes Lecture 01