Introduction to data communication and networking

Data communication:is the exchange of data b/w two devices via some form of transmission medium such as wire cable.

Effectiveness of a data communications system depends on three fundamental characteristics delivery, accurancy and timeliness.

Delivery:System must deliver data to the correct destination.

Accurancy:data delivered should be accurate. Data that have been altered in transmission and left uncorrected are unusable.

Timeliness:System must deliver data in a timely manner.

Components

5 components Message Sender Receiver Medium- physical path.can be twisted pair

wire, coaxial cable, radio waves. Protocol-set of rules that governs data

communication.

Data representation

Information comes in different forms − Text,numbers,images,audio and video.

Text

Text is represented as a bit pattern a sequence of bits(0's and 1's).Different sets of bit patterns have been designed to represent text symbols.Each set is called a code.

ASCII

ANSI developed a code called the American Standard Code for Information Interchange(ASCII).

This code uses 7 bits for each symbol. This means 27 different symbols can be defined

by this code.

Extended ASCII

Augmented with an extra 0 at the left.

This code uses 8 bits for each symbol. Unicode

neither of the foregoing codes represents symbols belongings to languages other than English.

Uses 16 bits and can represent 65,536 symbols.

ISO

International organization for standardization has designed a code using 32 bit patterns.

This is definitely enough to represent any symbol in the world today.

Directions of data flow

Communication b/w 2 devices can be simplex, half-duplex or full duplex.

Simplex:

communication is unidirectional. Eg:Keyboards

Half-Duplex: Each station can both transmit and receive, but

not at the same time. Eg:Wakie-talkies and CB(citizen band) radios.

Full Duplex: Both stations can transmit and receive

simultaneously. Eg:telephone network

Networks

A network is a set of devices(often referred to as nodes) connected by communication links.

Node(computer,printer or any other device) Distributed processing: Task is divided among multiple computers.

Network criteria:

Must be able to meet a certain criteria.

*Performance

*Reliability

*Security

Performance:

Measured in many ways

-transmit time(time taken to transmit message from one device to another), response time.

-including no of users, type of transmission medium, capabilities of the connected hardware and efficiency of the software.

Reliability:

Frequency of failure• The time it takes a link to recover from a failure.

Security:

Protecting data from unauthorized access.

Data Transmission

Point to Point:Provides a dedicated link b/w two devices.

Multipoint also called multidrop:connection is one in which more than two specific devices share a single link.

Bus topology:

Multipoint.

Nodes are connected to the bus cable through droplines and the main cable.

Categories of networks

Three primary categories:

LAN

MAN

WAN

Local Area Network:

A LAN connects network devices over a relatively short distance.

A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings.

Metropolitan-Area Network:

Extend over an entire city.

May be wholly owned and operated by a private company or it may be a service provided by a public company such as telephone company.

Eg:Switched Multi-megabit data services(SMDS)

Wide area network:

Span an unimited number of miles.

When two or more networks are connected they become internetwork or internet.

The InternetCame into being in 1969.

ARPANET- a small network of connected computers.

Idea:

Each host will be connected to a specialized computer called an interface message processor(IMP). The IMPs in turn would be connected to one another.

Communication takes place with each IMPs.

Thereafter split TCP in two protocols:

Transmission control protocol(TCP)

And internetworking protocol(IP)

TCP responsible for higher-level functions such as segmentation, reassembly and error detection.

IP would handle datagram routing.

The internet today

Most end users use the services of internet service providers(ISPs).

Internet today is run by private companies.

International service providers:

Top of the hierarchy.

Connect nations together.

National service provider:

Backbone networks created and maintained by specialized companies.

To provide connectivity b/w end users these backbone networks are connected by complex switching stations called Network Access Point.

Regional service provider:

Smaller ISP that are connected to one or more NSPs.

Local Internet service provider:

Provide direct service provider to the end users.

Local ISP's are connected to regional ISP or directly to NSP.

Most end users are connected to local ISP.

Local ISP can be a company,or non profit organization such as college or university.

Protocols

Set of rules that governs data communications.

Protocol defines what is communicated, how it is communicated and when it is communicated.

Key elements:

Syntax- format of the data, meaning the order in which they are presented.

Eg:a simple protocol might expect the first 8 bits of the data to be the address of the sender. The second 8 bits be the address of the receiver and the rest of the stream message itself.

Semantics:refers to the meaning of each section of bits.

Example:does an address identify the route to be taken or the final destination of the message.

Timing:

Refers to 2 charcteristics

When data should be sent and how fast they can be sent.

Eg:if a sender produces a data at 100 Mbps but the receiver can process data at only 1 Mbps the transmission will overload the receiver and data will be largerly lost.

Standards organization

Standards are developed through the cooperation of standards creation committees,forums and government regulatory agencies.

ISO:is a multinational body whose membership is drawn mainly from the standards creation committees of various governments throughout the world.