data communications and network, fourth edition

Data Communications and Network, Fourth Edition

Chapter 1: Introduction to Network and Communications


Learning Objectives• Define data communications• Describe the difference between data

communications and telecommunications• Define network models, local area

networks, wide area networks, metropolitan area networks, wireless networks, and personal area networks

• Understand the internet• Look at the network protocols and

standardsChapter 1: Introduction to

Network and Communications

Introduction

• Communications began from primitive methods

• More efficient communications were needed with the advance of the industrial age

• The telegraph began the age of electronic communications

• Voice, video, and data transmitted in modern communications systems


Simplified Communications Model (1)

Simplified Communications Model (2)

• Source– generates data to be transmitted

• Transmitter– converts data into transmittable signals

• Transmission System– carries data

• Receiver– converts received signal into data

• Destination– takes incoming data from the receiver

Key Communication Tasks (1)

• Transmission System Utilization– multiplexing, congestion control

• Interfacing with the transmission system• Signal Generation

– Form– Intensity

• Synchronization– the receiver must be able to determine

when a signal element begins

What is Data Communications?

• Sharing information• Transmission of data over a network• Subset of telecommunications• Networks

– Telephone system– May connect computers and related devices– PC prices have dropped – Data communications network

• Computers and related devices• Devices and lines used to connect the devices


Data Communications characteristics

• Delivery : data must be deliver to the correct destination.

• Accuracy: must be deliver accurately.• Timeliness: must be deliver on acceptable time• Jitter : is the variation in the packet arrival time

– Has negative effect when transmitting audio or vidiopackets


Data Communications Components

• Message• Sender• Receiver• Transmission medium• Protocol


Data Representation

• Text – (ASCII), set of 1’s and 0’s, Unicode• Number converted directly to binary numbers• Image treated as pixls and converted to patterns

of zero and ones• Audio refer to sound it differ by its continuity• Video same idea as Audio, but it can be

continues or sequences of images– (Audio and Video are covered in chapter 4)


Data flow

• Simplex: unidirectional, one device is send and the other is receiving only. (ex Keyboard, normal monitors)

• Half-Duplex: each station can both transmit and receive, but not at the same time (ex Walkie-talkies, citizens band radios

• Full-Duplex: both station send and receive at same time here the capacity of the line must be divided. (ex telephone line)


Data flow


Networks– Network a group of nodes connected by

communication link – can be computer, printer, server– Distributed processing where tasks are divided

between different nodes– Network is required to meet some criteria

• Performance - such transit time, response time – other networks metrics throughput and delay- net work require more throughput and less delay

• Reliability – accuracy , frequency of failure • Security - data protection from unauthorized access,

damage, or lose


Networks attributes

– Network is two or more devices connected through links.– Link is a communication pathway that transfer data from one

device two anther.• Point-to-Point connection – provide dedicated links between devices• Multipoint connection – where more than two specific devices share a singl

link – spatially shared , or timeshared


Networks Physical Structures– Physical Topology – how the network is laid

physically– There are four basic topologies– Mesh – every device (node) has dedicated link to each other

nodes– The number of link in a mesh calculated as n(n-1)/2 where n is

the number of devices on the mesh• Ex 3 nodes mesh will have 3(3-1)/2 = 3 links, four node will be 4(4-1)/2 = 6 links (duplex)


Networks Physical Structures– Mesh advantages

• Dedicated link guaranteed data load• Robust if one link fail does not effect other links • Privacy and security since the data from node A travel to node B in

dedicated link.• Identified error faster since point-to-point connection limits the error to single

link

– Mesh disadvantages • Large amount of cables• Number of I/O port require – each node would require as many as the

number of nodes in mesh


Networks Physical Structures– Star topology each node has dedicated link (point-to-point

connection) to controller advice called a HUB– Nodes transmit to the controller and the controller forward the

data to the intended node.– Star topology is cheaper and easy to manage since each device

require one connection and one I/O port – One link failure affect only single device – The main disadvantage is dependency in one controller (single

point of failure)


Networks Physical Structures– Bus topology each node has a link (drop line) to the backbone

through tap– As signal travel in the link it weaker and create limitation in the

usage of bus topology.– Compare to mesh and start bus require less cable and easy to

install.– Disadvantage

• Default reconnection and fault isolation• Any failure or brake in the bus cable stops all transmission


Networks Physical Structures– Ring topology each node has two dedicated links to

the nearest two nodes– Each connection include repeater when device

receive a signal for other devices the repeater recreate the bits and pass to the next device

– It is easy to configure to add device require to change to connection only.

– Disadvantage • Any failure of one device will all transmission this can avoided by

creating dual ring


Networks Physical Structures– Hybird topology


Networks Models– Computer network created by different entities

• Need for central entities to setup standards• OSI models and internet models

– OSI (Open system interconnection) models seven-layer– Internet Model define five-layer

– Network categories• Mainly two type of network LAN or WAN• The size of the network and the way it is

connected


Local Area Network (LAN)– Usually privately owned

• Link devices in single a office, building, • Can be simple as 2 pc and printer in one office

or can extend through out the organization.• Currently LAN limited to two km• It designed to allow sharing resources• In general LAN use only one type of

transmission media• LAN speed start between 4 to 16 megabits per

second today speed 100 or 1000 Mbps– OSI (Open system interconnection) models

seven-layer– Internet Model define five-layer


Wide Area Network (WAN)– Wide Area Network

• Provide long-distance data transmission• Can be complex as the internet backbone or

simple as dial-up line connect home pc to the internet

• Network switches are used connect local net work (LAN) to the internet or other lans

• Example the early switched WAN X.25, asynchronous transfer mode (ATM)


Other network– Metropolitan area network (MAN)

• Cover city• Ex telephone company with DSL

services, TV cable networks– Interconnection of networks:

Internetwork• Combination of more than one type of

network , LAN, WAN, or MAN• These type of network called

heterogeneous network


The Internet

• Internet evolved from the ARPANET– developed by the Advanced Research

Projects Agency (ARPA) of the U.S. DoD.– first operational packet switching network– applied to tactical radio communication

(packet radio, PRNET) & satellite communications (SATNET)

– need for internetworking between ARPANET, PRNET and SATNET

– led to standardized TCP/IP protocols

Internet Elements

Internet Architecture

Example Configuration

Chapter 1: Introduction to Communications 29Chapter 1: Introduction to

Network and Communications

More network examples

• Networks– Types of networks

• Wide area network (WAN)• Local area network (LAN)• Metropolitan area network (MAN)• Internet• Wireless networks• Personal Area Network (PAN)


data communications and network, fourth edition

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