COMPUTER NETWORKING

·         Connecting to a computer with other computers or other devices to enables them to communicate together with each other.
-it can be :  -  devices equipment
                    - transmission media to send/control data/signals
                    - communication devices to transmit/send data from source to destination

·         In the world of computer, NETWORKING is the practice of linking two or more computing devices together for the purpose of SHARING DATA.

NETWORK COMPONENTS

v  Terminals
-Refers to data sources and destination .
examples-workstation,personal computer,terminals,automatic teller machine

v  Transmission Media
-Used to transmit data in a networked environment and transmit pulse through a medium. There are 2 types of it, bounded and unbounded.

v   Network electronic devices

- Control data transmission from sources to destinations. It also act as interface between different transmission media or communication protocol. For examples: Bridges, concentrators, routers, Front End Processors, Private Branch, Switches Exchange (PBX), Hubs, Multiplexers, and Gateways.

v   Software:

-At the nodes, it involves techniques and protocols. Functions of the software are measure the data transmits to the destination.

v  Network architecture standards:

-Architecture is blueprint of standards for a network consisting of items such as choice of media, media interfaces, encoding methods, transmission protocols, routing protocols and so on. It is needed to ensure interoperability between various devices and equipment made by different vendors.

LAN - Local Area Network (LAN) is a small-scale private network inside the building. LANs are often used for connecting personal computers and workstations in a corporate office or factories to use shared resources (e:g printers) and exchange information.

MAN - Metropolitan Area Network (MAN) basically a LAN version of the larger size and usually use the same technology to the LAN. MAN could include corporate offices are located adjacent or also a town and can be used for private purposes (private) or public. MAN is able to support data and voice, even may be associated with cable television network.

WAN - Wide Area Network (WAN) its scope covers a wide geographical area, often covering a country or even continent. WAN consists of a collection of machines that aim to run the programs (applications) user.

VIRTUAL PRIVATE NETWORK (VPN )

  

PAN - Personal Area Network

BLUETOOTH

      Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances (using short-wavelength radio transmissions in the ISM band from 2400–2480 MHz) from fixed and mobile devices, creating personal area network (PANs) with high levels of security. It can connect several devices, overcoming problems of synchronization. The devices can switch roles, by agreement, and the slave can become the master. At any given time, data can be transferred between the master and one other device.

INFRA-RED

      This is a very familiar method of transferring data if you are at all aware of your remote control ! The television remote control makes use of an infra-red link. Personal organisers often make use of an infra-red link to synchronise calendars and 'to-do' lists.

Amplitude Modulation.

ü  Method of broadcasting electrical signals that cannot travel very far on their own. In this method, the signal is imposed or 'imprinted' on a carrier wave whose amplitude increases or diminishes with the amplitude of the signal. AM transmission operates in the 535 to 1705 kilohertz frequency band used for shortwave broadcasting and some citizen band (CB) aviation services. See also frequency modulation.

Freqeuncy modulation.

ü  Method of broadcasting electrical signals that cannot travel very far on their own. In this method, the signal is imposed or 'imprinted' on a carrier wave whose frequency increases or diminishes with the frequency of the signal. FM transmission operates in 88 to 108 megahertz frequency band, and is less susceptible to electromagnetic interference than amplitude modulation (AM).

week 4- DATA COMMUNICATION

TYPES OF SIGNAL

-variety style : TEXT, PICTURE. etc

ANALOG SIGNAL :

Analog signals are signals with continuous values. Analog signals are used in many systems, although the use of analog signals has declined with the advent of cheap digital signals.

Analog systems are less tolerant to noise, make good use of bandwidth, and are easy to manipulate mathematically. However, analog signals require hardware receivers and transmitters that are designed to perfectly fit the particular transmission. If you are working on a new system, and you decide to change your analog signal, you need to completely change your transmitters and receivers.

DIGITAL SIGNAL :

Digital signals are signals that are represented by binary numbers, "1" or "0". The 1 and 0 values can correspond to different discrete voltage values, and any signal that doesnt quite fit into the scheme just gets rounded off.

Digital signals are sampled, quantized & encoded version of continuous time signals which they represent. In addition, some techniques also make the signal undergo encryption to make the system more tolerent to the channel.

DATA FLOW

Simplex, half-duplex and full-duplex connections

There are 3 different transmission modes characterised according to the direction of the exchanges:

A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer...).

A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.

A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission.

DATA TRANSMISSION MODES

Serial connection

In a serial connection, the data are sent one bit at a time over the transmission channel. However, since most processors process data in parallel, the transmitter needs to transform incoming parallel data into serial data and the receiver needs to do the opposite.

These operations are performed by a communications controller (normally a UART (Universal Asynchronous Receiver Transmitter) chip). The communications controller works in the following manner:

The parallel-serial transformation is performed using a shift register. The shift register, working together with a clock, will shift the register (containing all of the data presented in parallel) by one position to the left, and then transmit the most significant bit (the leftmost one) and so on:

The serial-parallel transformation is done in almost the same way using a shift register. The shift register shifts the register by one position to the left each time a bit is received, and then transmits the entire register in parallel when it is full.

MODES OF TRANSMITTING DATA

Synchronous Transmission:

 Large volumes of information can be transmitted at a single time with synchronous transmission. This type of transmission involves the simultaneous flow of several bytes of data. Because a large block of data being sent synchronously cannot be interrupted, a synchronized clock is necessary to carefully schedule the transmission of information. This special communications equipment is expensive; but this cost can be made up in part by faster, less expensive transmission of information.

Asynchronous Transmission: 

Conversely, asynchronous transmission involves the sending and receiving of one byte of data at a time. This type of transmission is most often used by microcomputers and other systems characterized by slow speeds.