Tuesday 24 September 2013

TRANSMISIION MEDIA

Factors Affecting Data Transmission
1. Bandwidth. It refers to the data carrying capacity of a channel or medium. Higher bandwidth communication channels support higher data rates.





Bandwidth
Bandwidth in computer networking refers to the data rate supported by a network connection or interface. One most commonly expresses bandwidth in terms of bits per second (bps). The term comes from the field of electrical engineering, where bandwidth represents the total distance or range between the highest and lowest signals on the communication channel (band).
Bandwidth represents the capacity of the connection. The greater the capacity, the more likely that greater performance will follow, though overall performance also depends on other factors, such as latency.
Also Known As: throughput
Examples:
A V.90 modem supports a maximum theoretical bandwidth of 56 Kbps. Fast Ethernet supports a theoretical maximum bandwidth of 100 Mbps.

Bandwidth is typically measured in bits per second (bps). Commonly used larger units are kilobits per second (Kbps), megabits per second (Mbps) and gigabits per second (Gbps).
It is important to distinguish between bits per second (bps) and bytes per second (Bps). One byte is equal to 8 bits. Most data measurements in computing are made in bytes and units of that, such as megabytes or gigabytes. Since network speeds are measured in bits, not bytes, a 10 Megabyte file will take 8 seconds to download on a 10 Mbps connection, not 1 second.
Internet speed measurement can be complicated by the fact that although you may have a high-speed link to your Internet Service Provider (ISP), you will then have to contend (share) the bandwidth with other users of the same ISP.

2. Radiation. It refers to the leakage of signal from the medium due to undesirable electrical characteristics of the medium.

3. Noise Absorption. It refers to the susceptibility of the media to external electrical noise that can cause distortion of data signal.

4. Attenuation. It refers to loss of energy as signal propagates outwards. The amount of energy lost depends on frequency. Radiations and physical characteristics of media contribute to attenuation.

Wireless Transmission Media:

Many users opt for wireless transmission media because it is more convenient than installing
cables. In addition to convenience, businesses use wireless transmission media in locations where it
is impossible to install cables. Types of wireless transmission media used in
communications include infrared, broadcast radio, cellular radio, microwaves, and communications
satellites.



Infrared
As discussed earlier in the chapter, infrared (IR) is a wireless transmission medium that sends
signals using infrared light waves. Mobile computers and devices, such as a mouse, printer,
and smart phone, often have an IrDA port that enables the transfer of data from one device to
another using infrared light waves.



Broadcast Radio
Broadcast radio is a wireless transmission medium that distributes radio signals through
the air over long distances such as between cities, regions, and countries and short distances
such as within an office or home. For radio transmissions, you need a transmitter
to send the broadcast radio signal and a receiver to accept it. To receive the broadcast radio signal, the receiver has an antenna that is located In the range of the signal. Some networks use a
transceiver, which both sends and receives signals from wireless devices. Broadcast radio is slower
and more susceptible to noise than physical transmission media but it provides flexibility and
portability.Bluetooth, UWB, Wi-Fi, and WiMAX communications technologies discussed earlier in this chapter use broadcast radio signals. Bluetooth and UWB are alternatives to infrared communications, with the latter designed for high bandwidth transmissions. Hot spots use
Wi-Fi, WiMAX, and Bluetooth networks.




Example of transmission media :

TRANSMISSION MEDIA

  DEFINITION OF TRANSMISSION MEDIA



Transmission media refers to any form of media that is primarily used for the transfer of signals. The media may be a wire, coaxial cable, fiber optics, air or even a vacuum through which the signal is transferred from one point to another.


Describes the type of physical system used to carry a communication signal from one system to another. Examples of transmission media includetwisted-pair cable, coaxial
cable, and fiber optic cable.




Types of Transmission Media


Transmission media is broadly classified into two groups.
1. Wired or Guided Media or Bound Transmission Media
2. Wireless or Unguided Media or Unbound Transmission Media
Wired or Guided Media or Bound Transmission Media:
Bound transmission media are the cables that are tangible or have physical existence and are limited by the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable and fiber optical cable. Each of them has its own characteristics like transmission speed, effect of noise, physical appearance, cost etc.
Wireless or Unguided Media or Unbound Transmission Media:
Unbound transmission media are the ways of transmitting data without using any cables. These media are not bounded by physical geography. This type of transmission is called Wireless communication. Nowadays wireless communication is becoming popular. Wireless LANs are being installed in office and college campuses. This transmission uses Microwave, Radio wave, Infra red are some of popular unbound transmission media.
                      



Tuesday 17 September 2013

network

computer network

(n.) A network is a group of two or more computer systems linked together. There are many types of computer networks, including:




  • local-area networks (LANs) : The computers are geographically close together (that is, in the same building).
  • wide-area networks (WANs) : The computers are farther apart and are connected by telephone lines or radio waves.
  • campus-area networks (CANs): The computers are within a limited geographic area, such as a campus or military base.
  • metropolitan-area networks MANs): A data network designed for a town or city.
  • home-area networks (HANs): A network contained within a user's home that connects a person's digital devices.

  • In addition to these types, the following characteristics are also used to categorize different types of networks:




  • topology : The geometric arrangement of a computer system. Common topologies include a bus, star, and ring. See the Network topology diagrams in the Quick Reference section of Webopedia.
  • protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate. One of the most popular protocols for LANs is called Ethernet. Another popular LAN protocol for PCs is the IBM token-ring network .
  • architecture : Networks can be broadly classified as using either apeer-to-peer or client/server architecture.

  • Computers on a network are sometimes called nodes. Computers anddevices that allocate resources for a network are called servers.
    (v.) To connect two or more computers together with the ability to communicate with each other.