Introduction

to Data

Communication

Transmission Basics

In data networking, the term transmission has some meanings. It can refer to the progress of data signals over a medium from one point to another. Long ago, people transmitted information across distances via smoke or fire signals.One important characteristic of data transmission is the type of signaling involved. On a data network, information can be transmitted via one of two signaling methods:

i. Analog

ii. DigitalBoth types of signals are generated by

electrical current, the pressure of which is measured in volts. The strength of an electrical signal is directly proportional to its voltage.

The essential difference between analog and digital signals is the way voltage creates and sustains the signal.

Analog Signaling

In analog signals, voltage varies continuously. In digital signals, voltage turns off and on repeatedly, pulsing from zero voltage to a specific positive voltage. An analog signal’s voltage appears as a continuous wave when graphed over time.

To understand this concept, think of two tin cans connected by a wire. When you speak into one of the tin cans, you produce analog sound waves that vibrate over the wire until they reach the tin can at the other end. These sound waves are merely approximations of your voice, and they are significantly affected by the quality of the wire.

Analog Signaling

Digital Signaling

Unlike analog signals where there is a smooth curve, digital signals jump directly to the next value.When digital signals can exist in only one of two values, they go directly to the next value, typically changing between 0 and 1. The jump from one value to another is known as a transition.

Data Modulation

analog signals to transmit data is when you use a modem to connect two systems.

The modem may transmit signals in analog over the phone lines, but the signals must be converted into digital signals by the modem at the receiving computer.

The word modem reflects this device’s function as a modulator/demodulator—that is, it modulates digital signals into analog signals at the transmitting end, then demodulates analog

signals into digital signals at the receiving end.

Transmission Direction

Data transmission, whether analog or digital, may also be characterized by the direction in which the signals travel over the media.

1. Simplex- In cases where signals may travel in only one direction, the transmission is considered simplex.

2. Half Duplex - In half-duplex transmission signals may travel in both directions over a medium but in only one direction at a time. Half-duplex systems contain only one channel for communication, and that channel must be shared for multiple nodes to exchange information.

3. Full-DuplexWhen signals are free to travel in both directions over a mediumsimultaneously, the transmission is considered full-duplex.Full-duplex may also be called bidirectional transmission orsometimes, simply duplex.

Compression

Types of Networks

There are three types of networks -1. LAN (Local Area Network)

A LAN is a network that cover a relatively small geographical area, such as a home, Lab, office building or school.The devices can be connected with either wired or wireless communication media.

2. MAN (Metropolitan Area Network)A MAN is a network designed for a metropolitan area, typically a

city or country. MANs fall between LANs & WANs on the size typically consists of multiple LANs.

3. WAN (Wide Area Network) A WAN is a network that cover a large geographical area, The

INTERNET is the world’s largest WAN. WAN may be publicly accessible, like the internet, or may be privately owned.

Networks topology

Topology refers to the way in which the network of computers is connected. Each topology is suited to specific tasks and has its own advantages and disadvantages.

The choice of topology is dependent upon type and number of equipment being used planned applications and rate of data transfers required response times cost

Bus Star Ring Mesh

Hub

In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions.

A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

switch

Definition: A network switch is a small hardware device that joins multiple computers together within one LAN. Technically, network switches operate at layer two (Data Link Layer) of the OSI model.

Network switches appear nearly identical to network hubs, but a switch generally contains more "intelligence" (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of that packet, and forwarding it appropriately. generally it gives better performance than a hub

Router

A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP’s network. Routers are located at gateways, the places where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.

Gateway

A gateway is a device that connect two dissimilar networks, such as two networks using different networking communication protocols.

The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes.

BridgeBridge

On the other hand Bridge is a device that On the other hand Bridge is a device that connects two networks based on similar connects two networks based on similar topologytopology

Cable

A cable is one or more wires or optical fibers bound together, typically in a common protective jacket or sheath. The individual wires or fibers inside the jacket may be covered or insulated. Combination cables may contain both electrical wires and optical fibers. Electrical wire is usually copper because of its excellent conductivity, but aluminium is sometimes used because it is lighter or costs less.

Types of cable

1. Coaxial cable

2. Multicore cable (consist of more than one wire and is covered by cable jacket)

3. Optical fiber cable

4. Ribbon cable

(from time to time this name is used for wire)

NOTE : Assignment to explain these term