Data Communication and Networking Technology

INTRODUCTION TO DATA COMMUNICATION

DEFINITION OF DATA COMMUNICATION

“DataCommunication is the exchange of Information from one entity to the other using a Transmission Medium”.

DEFINITION OF DATA COMMUNICATION (Cont’d)

As you can clearly notice, the definition of Data Communication although Simple leaves many questions unanswered:

Y Exchange??????

Y Information?????

Y Entities???????

Y Transmission????

Y Medium????

We will try to answer all these Questions in this Course

History of Data Communication

Data communications history represents a blend of histories, including:

Y  The history of the telecommunications industry

Y  The history of data communications, and

Y  The history of the Internet

•Telegraph 1837 Samuel Morse

Modern telecommunication industry began in 1837 with the invention of the telegraph by Samuel Morse

This led to building a telecommunications infrastructure of poles and wires as well as to the development of communication hardware and protocols

•Telephone 1876 Alexander Graham Bell

Invention of telephone by Alexander Graham Bell in 1876 and the development of wireless communication technology by Guglielmo

Marconi in the 1890s set the stage for   today‟s   communicat

•By 1950’s

By 1950s, telephone and telegraph companies had developed a network of communication facilities throughout the industrialized world

•1970’S

Although development of databases, languages, operating systems, and hardware was strong from 1950s to 1970s, large-scale data communication systems did not emerge until the 1970s.

This was stimulated by 3 major developments:

Y    Large-scale integration of circuits reduced cost and size of terminals and communication equipment 

Y    New software systems that facilitated the development of data communication networks

Y Competition among providers of transmission facilities reduced the cost of data circuits

TODAY’SEVERGHANGING & BUSY WORLD

o   Today‟sfastworld demands better, secure and most of all FAST ways of communication

o   Gone are the days when you had to wait a couple of weeks to get a letter from USA

o   Why wait ONE week when you can get the information you require in just a split of a second, using what we know by the name of “DATA COMMUNICATION”.

HOW TO ACHIEVE THIS?

o   How to achieve this ACCURACY, SECURITY and SPEED for the transfer of this information?

o What HARDWARE and the SOFTWARE is needed? o And, what should be the MEANS of sending this info?

ARE SOME OF TOPIC WE WILL BE EXPLORING DURING THE COURSE OF OUR STUDY

DATA COMMUNICATION

o When we communicate , we share information o Information can be LOCAL or REMOTE

o Between Individuals LOCAL communication occurs face to face o REMOTE communication occurs over a long distance

o   When we refer to COMPUTER SYSTEMS, Data is represented in the form of Binary Units (Bits) in the form of ZerosOne‟s(0‟s)(1‟and

o  Also the entities can most of the times be considered to be COMPUTERS

Data Communication Definition (Modified)

Therefore, our earlier definition can easily be modified to:

“DatCommunication is the exchange of data (in the form of 0’sand 1’s) between two devices (computers) via some form of the transmission medium.”

LOCAL and REMOTE Data Communication

•LOCAL

Data communication is considered to be local if the communicating devices are present in the same building or a similarly restricted geographical area

•REMOTE

Data Communication is considered remote, if the devices are farther apart.

VAGUE DEFINITIONS

We will clarify

Data Communication System

For Data Communication to occur, the communicating devices must be a part of a communication system made up of some specific kind of hardware and software

This type of a system is known as a

“DATA COMMUNICATION SYSTEM”

Effectiveness of Data Comm. System

Effectiveness depends upon three fundamental characteristics:

Y Delivery

Y Accuracy

Y  Timeliness (Better NEVER than LATE)

./ Example of the POSTAL MAIL

Components of Data Comm. Systems

Components of Data Com Systems

Any system is made up of more than one component. Similarly, a data communication system is made up of 5 components as shown in the fig:

Y Message

Y Sender

Y Receiver

Y Medium

Y Protocol

•MESSAGE

Y  Information or Data to be communicated

Y  Can be text, numbers, video or any combination of these

Y  In short anything that can be represented using binary bits

Data Communication Messages

./ Files (meaningful collections of records)

./ Data/information requests (database queries, Web page requests, etc.)

./ Responses to requests and commands or error messages

./ Status messages (about the network‟sfunctional status)

./ Control messages transmitted between network devices to control network traffic

./ Correspondence among network users

MESSAGE TYPES

•SENDER

Y  Device that sends the data message

Y  Can be a Computer , Workstation, Video camera etc

Y As already discussed, the data from the sender might not be in the appropriate format for the transmission medium and will need to be processed

•RECEIVER

Y  Device that receives the message

Y  Can be a computer, workstation, Television etc

Y   At times, the data received from the transmission medium may not be in a proper form to be supplied to the receiver and it must be processed 

•MEDIUM

Y    Physical path that a message uses to travel from the Sender to the Receiver

Y    Can be a Copper Cable (Telephone), Coaxial Cable (Cable TV), Fiber Optic Cable, LASERS or Radio Waves (Wireless Medium)

Y We will see that Data needs to be transferred in the form of ELECTROMAGNETIC signals and The Transmission Medium should be capable of carrying these EM Signals

Y Transmission Media

Transmission Media

Medium	Speed	Cost
Twisted Wire	300bps-10Mbps	Low
Microwave	256Kbps-100Mbps	Low
Coaxial Cable	56Kbps-200Mbps	Low
Fiber Optic Cable	500Kbps-10Gbps	High

•PROTOCOL

Y  Set of Rules Governing Communication

Y  Represents an Agreement between communication devices

Y    Without Protocol, two devices may be connected but they will not be able to communicate

./ EXAMPLE: Consider the communication between two individuals. They can only communicate provided they both speak the same language.

A little more complex Comm. System

Y  User of a PC wishes to send a message „m‟

Y User activates electronic mail package e.g. hotmail Y Enters the message via input device (keyboard)

Y Character string is buffered in main memory as a sequence of bits „g‟ Y PC is connected to some trans system such as a Telephone Network via

an I/O Transmitter like Modem

Y  Transmitter converts incoming stream „g‟into a signal „s‟

•RECEIVER SIDE

Y    The transmitted signal „s‟issubject to a number of impairments depending upon the medium

Y  Therefore, received signal „r‟may differ from   „s‟.

Y  Receiver attempts to estimate original „s‟based on its knowledge of

the medium and received signal   „r‟

Y  Receiver produces a bit stream g‟(t)

Y  Briefly buffered in the memory

Y    Data is presented to the user via an output device like printer, screen etc.

Y    The data viewed by user m‟will usually be an exact copy of the data sentm‟ „

EXAMPLE-Telephone System

o  Input to the Telephone is a messagem‟in„   theofsound wavesform

o   The sound waves are converted by telephone into electric signals of the same frequency

o These signals are transmitted w/o any modification over the telephone line o Hence g(t) and s(t) are identical

o  S(t) will suffer some distortion so that r(t) will not be the same as s(t)

o   R(t) is converted back to sound waves with no attempt of correction or improvement of signal quality

o Thus m‟   isan exactnotreplica of m

An Actual Digital Data Communication System Key Data

Communication Terminology

•Session: communication dialog between network users or applications Different Types of this session for Info Exchange

•Network: interconnected group of computers and communication devices We will look into it in a little bit

•Node: a network-attached device Node can be any device in the network

LECTURE #2

KEY DATA COMMUNICATION TERMINOLOGY

•Link: connects adjacent nodes

Wires, Cables, Any thing that physically connects two nodes

•Path: end-to-end route within a network

•Circuit: the conduit over which data travels

•Packetizing: dividing messages into fixed-length packets prior to transmission over a network’s communication media

•Routing: determining a message’spath from sending to receiving nodes

./ The transmission medium may itself be a network, so route needs to be specified

Network

“ANETWORK is a set of devices (Nodes) connected   by   Communicatio

•Node: Can be a Computer, Printer or any other device capable of sending or receiving

Y    The links connecting Nodes are called COMMUNICATION CHANNELS Networks- Why we need them?

Networks- Why we need them?

It is often impractical for devices to be directly connected for two major reasons:

o   The devices are very far apart. They are expensive to connect just two devices with one in Lahore and other in Islamabad

o   Large set of devices would need impractical number of connections e .g. Telephone Lines in the world and all the computers owned by a single organization

Solution to the Problem=Networks

o   Solution is to connect all devices to a central system known as a NETWORK in which all terminals or computers share the links.

o  Two Main Classifications of the Networks

Y LANS

Y WANS

DISTRIBUTED PROCESSING

o   Instead of a single large machine being responsible for all aspects of a process , each separate computer handles a subset of the task

./ Example –Project Given as a part of the Course

./  Example –Office Work

Advantages of Distributed Processing

•Security

A system designer can limit the kind of interaction that a given user can have with the entire system.

./  For example : Bank‟sATM

•Distributed Data bases

No one system need to provide storage capacity for the entire database

./ For example WWW gives user access to pages stored anywhere on Internet

•Faster Problem Solving

Multiple computers working on a problem can solve a problem faster than a computer working alone

•Security through Redundancy

Multiple computers running the same program provide security through redundancy

If one computer hardware breaks down then others cover up.

•Collaborative Processing

Both multiple computers and multiple users can interact for a task

Network Criteria

•Performance

Can be measured in many ways including Transit and Response Time

o  Depends on a no. of Factors:

Y  Number of USERS

Y  Type of Transmission Medium

Y Hardware

Y Software

Y Network Criteria

Y Number of USERS

./ Large Number of concurrent users slow network

./  Design of a network

./ Peak Load Periods

./ Network Criteria

Y  Type of Transmission Medium

./ Medium defines speed at which data can travel

./ Fiber Optic Cable

./  100Mbps and 10 Mbps

./ Hardware

./ Software

Y Hardware

./ Effect speed and the capacity of transmission

./ Fast computer with large storage capacity

./ Software

./ Network Criteria

Y Software

./	Software   processes  data  at   sender  ,   receiver  and
	intermediate nodes
./	All communication steps need software:
./ Moving message from node to node
./Transforming,
./ Processing at the sender and receiver
./	Error Free Delivery

Well designed software can speed up the process

•Reliability

o  Depends on a no. of Factors:

Y Frequency of Failure

Y  Recovery Time of a Network after Failure

Y Catastrophe

Y  Fire , Earthquake or Theft

•Security

o   Unauthorized Access

Y  Sensitive data

Y  Protection at multiple levels:

Y Lower level: Passwords and user ID codes Y Upper Level: Encryption

o Viruses

Network Applications

•Marketing and Sales

o  Marketing

Y Collect, exchange and analyze data relating to the customers needs Y Product development cycles

o  Sales

Y  Tele shopping,

Y  On line reservation systems

•Financial Services

o  Online Banking

o  Foreign Exchange Transfers

o  Rates

•Manufacturing

o  Computer Aided Design

o  Computer Assisted Manufacturing

o  Network Applications

•Electronic Messaging

•Teleconferencing

o Conferences to occur w/o participants at the same place o Chat

o  Voice Conferencing

o  Video Conferencing

•Cable Television

LECTURE #3

Communication Tasks

There are some key tasks that must be performed in a data communication system Elements can be added, deleted, or merged together

Transmission System utilization	Interfacing
Signal Generation	Synchronization
Exchange Management	Error Detection and Correction
Flow Control	Addressing
Routing	Recovery
Security	Network Management

•Transmission System Utilization

Need to make efficient use of Transmission facilities that are shared among a no. of communicating devices

For Example:

./ Techniques like Multiplexing to allow multiple users to share total capacity of a Transmission Medium

./ Congestion Control: TX. System should not be overwhelmed by traffic

•Interfacing

A device must have an Interface with the Transmission System/Transmission Medium

•Signal Generation

Electromagnetic Signals travel over Transmission Medium. Once an interface is established, Signal generation is required

Y Properties of Signals

./ Capable of being propagated over TX. Medium

./ Interpretable as data at the Receiver

•Synchronization

The transmission and the reception should be properly synchronized. Synchronization means that the receiver must be able to determine, when to

expect a new transmission and when to send acknowledgements. In other words transmitter and receiver should have an agreement on the nature as well as timing of the signals

•Exchange Management

If the data needs to be exchanged in both directions over a period of time, both parties must cooperate as follows

Y Whether both devices must transmit simultaneously or take turns Y Amount of Data to be sent at one time

Y  Format f the Data

Y  What to do when an Error Arises

•Error Detection and Correction

In all comm. Systems, there is a potential risk for errors and impairments.

Tx. Signals are distorted to some extent before reaching their destination. Error Detection & Correction needs to be employed in Data Processing Systems where a change in say the contents of a file cannot be tolerated

•Flow Control

To make sure that source does not overwhelm destination by sending data faster than it can be handled and processed

•Addressing & Routing

If TX facility is shared by two or more devices, source must specify the identity or the address of the destination system and if Tx. System is itself a system, a proper route must be allocated that the data will take in order to reach the desired destination

•Recovery

If a data transmission is interrupted due to a fault somewhere in the system, recovery techniques are needed. The objective is either to resume activity at the point of interruption and to restore the state of the system to what it was prior to the interruption

•Security

Security is very important issue in a Data Communication System. The sender needs to be assured that

Y  Only the Intended receiver receives the data

Y  Data is delivered unaltered

Introduction to Protocol

In computer Networks, communication occurs between two entities in different systems.

o  Entity is anything sending and receiving information

o  SYSTEM is a physical object containing more than one entities

Now, two entities in different systems cannot just send data and expect to be understood. For communication to occur, these entities must agree on a PROTOCOL

PROTOCOLS

As discussed earlier, “Protocol is a set of rules governing communication”

o   Two computers cannot just send bit streams to each other and expect to be understood

o  Entities must agree on a PROTOCOL

./ Same Example French and German

Protocol defines:

Y  What is Communicated?

Y  How it is Communicated?

Y  When it is Communicated?

KEY elements of a PROTOCOL

•Syntax:

Y  Represents the Structure or the format of the Data

Y    Meaning the order in which data is presented

For Example

./  First eight bits to be Sender address

./ Next eight to be Receiver‟sAddress

./  The Rest to be Data

•Semantics:

Y  Refer to the Meaning of each section of bits

Y  How is a particular pattern to be interpreted?

Y  What action should be taken based on interpretation?

For Example

./ Does an address identify the route to be taken or the final destination of the message?

•Timing

Refers to 2 characteristics:

Y  When data should be sent?

Y    How fast it should be sent?

For Example

./ If sender produces data at 100 Mbps

./ But Receiver can only process data at 1 Mbps

./ The TX. will overload receiver and data will be lost

Protocol Architecture

Instead of having a single Module for performing communication, there is a structured set of modules that implement communications function”

This structure is called Protocol Architecture Let‟splain itexbyan example of File transfer system.

 Simplified File Transfer Architecture

In the above example File transfer could use three modules

Y File transfer application

Y Communication service module

Y Network access module

•File transfer application

File Transfer contains all of the logic is unique to the file transfer application such as: Y Transmitting passwords

Y  File Commands

./ Checking File System on other machine if it is ready

./ Check File System Compatibility Y File records

•Communication service module

Instead of allowing File Transfer Module to deal with actual transfer of data and commands, we can have a separate module for this transfer. This module must make sure that the receiver system is ready to receive and look into the reliable exchange of data

•Network access module

Nature of the exchange between systems is independent of the network that connects them. That allows us to have a 3rd module that handles the details of the Network interface and interacts with the network. If Network to be used changes, only Network access Module has to change

Characteristics of a Protocol

Y  Direct or indirect

Y Monolithic or structured

Y Symmetric or asymmetric

Y Standard or nonstandard

•Direct

Y  Systems share a point to point link or

Y  Data can pass without intervening active agent

Y Simple Protocol

•Indirect

Y Switched networks or

Y  Interne works or internets

Y  Data transfer depend on other entities

Y Complex Protocol

•Monolithic or Structured

Y  Communications is a complex task

Y  To complex for single unit

Y  Structured design breaks down problem into smaller units

Y Layered structure

•Symmetric or Asymmetric

Symmetric

Y  Communication between peer entities

Asymmetric

Y Client/server

Standard or Nonstandard

Y  Nonstandard protocols built for specific computers and tasks

LECTURE #4

Standards

“Astandard provides a model for development that makes it possible for a product to work regardless of the individual manufacturer|”

Y    A great deal of coordination and cooperation is required by the devices to communicate

Y    A device prepared by a specific manufacturer may not be compatible with the devices prepared by other manufacturers

Y    Unavailability of standards creates problems and puts a halt to product growth

./ An example of non-standardized products is AUTOMOBILES

Why Standards are Essential?

Standards are therefore essential in:

o   Creating and Maintaining an Open and competitive Market for Equipment Manufacturers

o   Guaranteeing National and International Interoperability of Data and Telecommunications Technology and Equipment

•De facto (By fact or By Convention)

Standards not approved by an organized body but have been adopted as standards through their widespread use

•De jure (By Law or By Regulation)

Standards that have been legislated by an officially recognized regulation body

Subdivision of De Facto Standards

Y PROPRIETARY (Closed Standards)

Standards that are originally invented by a Commercial Organization as a basis for the operation of its products they are wholly owned by that company. They are also called Closed Standards because they close off Communication between systems

Y  NON- PROPRIETARY (Open Standards)

They are originally developed by groups or committees that have passed them into public domains. They are also called Open Standards because they open Communication between different systems

Standard Organizations

Standards are developed mainly by 3 entities:

Y Standard Creation Committees

Y Forums

Y Regulatory Agencies

•Standard Creation Committees

They are Procedural Bodies and they are so slow moving and cannot co-op with the fast growing communication industry.

Y  ISO

./ International Standard‟sOrganization

./ Voluntary Organization

./ Created in 1947

./ Members are from Standard Creation Committees of different countries

./ Includes representatives from 82 countries

./ Open System Interconnection (OSI) Model

Y ITU-T

./ By 1970s a lot of countries were defining standards but there was no International compatibility

./  United Nations made as a part of their ITU

./ Consultative Committee for International Telegraphy and Telephony (CCITT)

./ IN 1993 , ITU-Telecomm Standards Sector

./ Important ITU-T Standards

./ V Series (V32, V33, V42, Define Data Transmission over phone lines

./ X Series(X.25, 400, 500): Define Transmission over Public Digital Network

./ ISDN: Integrated Services Digital Network

Y    The American National Standard Institute (ANSI)

./ Private-Non Profit Cooperation not affiliated with US Government

./ Members include professional societies, industrial associations, govt. and regulatory bodies

./ Submits proposal to ITU-T and is a voting member for USA in ISO

Y  The Institute of Electrical and Electronics Engineers (IEEE)

./ Largest professional engineering society in the world

./ Also oversees the development of Telecommunication and Wireless International Standards

./ Special committee for LANS out of which emerged Project 802 (802.3, 802.4, 802.5)

•Forums

Special Interest Groups with representatives from interested corporations they facilitate and fasten standardization process by working with universities, and users to test, evaluate and standardize new technologies                                             

Each Forum Concentrate on a specific technology and present their conclusions to the standard bodies

Y Frame Relay Forum

Y  ATM Forum

Y  Internet Society & IETF

•Regulatory Agencies

All communication technology is subject to regulation and laws by government agencies. The purpose is to protect Public Interest by regulating Radio, Television and Cable Communications.

Y  FCC

Before we go into the details of how data are transmitted from one device to the other, it is important to understand:

o  The relationship between communication devices.

o How the devices connect with each other in a System? o How do they do the exchange of information?

Five Concepts provide the basis

o Line Configuration o Topology

o  Transmission Mode

o Categories of networks o Internetworks

LINE CONFIGURATION

“LineConfiguration refers to the way two or more devices attach to a Link”

A link is the physical communication path that transfers data from one device to the other. Link can be thought of as a Line drawn between two points. For communication to occur, two devices must be connected to each other using a link.

                                                        Line Configuration

•Point-to-Point Line Configuration

Dedicated Link between two devices. Entire Capacity of the channel is reserved for TX B/w these two devices. Mostly point-to-point connection use wire/cable to connect with each other. But Microwave, Satellite Links can also be used

Data and Control information pas directly between entities with no intervening agent

Y Examples:

./ TV Remote Control and TV Control Systems

./ Mobile Phone (when talking) and Base Station (Antenna)

•Multipoint Line Configuration

More than two devices share the Link that is the capacity of the channel is SHARED now. With shared capacity, there can be two possibilities in a Multipoint Line Config:

Y    Spatial Sharing: If several devices can share the link simultaneously, its called Spatially shared line configuration

Y    Temporal (Time) Sharing: If users must take turns using the link , then its called Temporally shared or Time Shared Line Configuration