Understanding Data Communications and Telecommunications: A Comprehensive Guide, Lecture notes of Computer Networks

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COMPUTER NETWORKS

Ubaid Bin Zafar

NCBA&E

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DATA COMMUNICATIONS DATA COMMUNICATIONS

The term The term telecommunicationtelecommunication means communication at ameans communication at a

distance. The word distance. The word datadata refers to information presentedrefers to information presented

in whatever form is agreed upon by the parties creating in whatever form is agreed upon by the parties creating

and and usingusing thethe data.data. DataData communicationscommunications areare thethe

exchange of data between two devices via some form of exchange of data between two devices via some form of

transmission medium such as a wire cable. transmission medium such as a wire cable.

Components

Data Representation

Data Flow

Topics discussed in this section: Topics discussed in this section:

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Figure 1.1 Five components of data communication

Components

Message

Sender

Receiver

Transmission Media

Protocol

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Transportation vs. Computer Networks

Transportation Network Computer Network

Vehicles/People Packets/Payload

Street address IP address

Intersection Bridge/router

Street, highway, path Link/broadband/path

Traffic jam Network congestion

Stop and go traffic light Flow control

Taking alternative path Alternative route

Collision Collision of packets

HOV lane Flow Priority

Following a route to school Routing algorithm

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Biggest Internet Challenge

Scale

How to manage such a large system,

growing rapidly and uncontrollably,

consisting of heterogeneous devices,

managed by multiple entities

having limited resources

Let’s take things one at a time

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Network Design

The task of connecting nodes via links , so that nodes can exchange

information, reliably, timely, efficiently, safely, privately, “greenly”,

and with low cost.

Need to define the network architecture, protocols, applications,

interfaces, policies, usages.

Let’s start with the architecture

Directly connected networks

Circuit-switched networks

Packet-switched Networks

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What Drives Network Design?

Applications

WWW, email, chat, videoconferencing, e-commerce, audio/video streaming,

VOIP, file sharing

Who deploys the network

Enterprise, government, end-user

Where is the network deployed

Home, building, campus, state, country, continent, globe

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Directly-Connected Networks

Point-to-point links : Each node is directly connected to other with a

link

Multiple access : All nodes share the same physical medium

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point-to-point

multiple access

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Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

Half Duplex Mode

In half-duplex mode, each station can both

transmit and receive, but not at the same

time. When one device is sending, the other

can only receive, and vice versa. The half-

duplex mode is used in cases where there is

no need for communication in both direction

at the same time. The entire capacity of the

channel can be utilized for each direction.

Example: Walkie- talkie in which message is

sent one at a time and messages are sent in

both the directions.

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Full Duplex Mode

In full-duplex mode, both stations can transmit

and receive simultaneously. In full duplex

mode, signals going in one direction share the

capacity of the link with signals going in other

direction, this sharing can occur in two ways:

Either the link must contain two physically

separate transmission paths, one for sending

and other for receiving.

Or the capacity is divided between signals

travelling in both directions.

Full-duplex mode is used when communication

in both direction is required all the time.

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Circuit-Switched Networks

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End-to-end permanent connection

Dedicated path for communication

No need for a destination address since a path is already established

Once communication is complete, connection is ended and links are

released.

Advantages of Circuit Switching

Guaranteed bandwidth (Quality of Service)

Predictable bitrate and delay

Good for delay-sensitive applications

Reliable communication

Rare packet loss

Packets are delivered in order

Simple data routing

Forwarding based on time slot or frequency (multiplexing)

No need to inspect a packet header for address

Low per-packet overhead

Forwarding based on time slot or frequency

No IP (and TCP/UDP) header on each packet

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