- The physical layer is responsible for movement of individual bits from one hop (node) to the next.
---- ( Features / Responsibilities ) ----
Physical characteristics of interfaces and medium:
- Define the characteristics of the interface between device and transmission medium.
- Define type of transmission medium.
Representation of bits:
- Data consist of a stream of bits (sequence 0 or 1)
- Bit must be encoded into signal (electrical or optical)
- Number of bit sent each second is called transmission rate
Synchronization of bit:
- Sender and receiver clock must be synchronized used same bit rate.
- Point to point : dedicated link
- Multipoint: link is shared among several device
- Define how device are connected in network Bus, ring, mesh, star, hybrid
Define the direction of transmission between two device Simples, half duplex and full duplex
Computer speakers or multimedia speakers , are speakers external to a computer , that disable the lower fidelity built-in speaker. They often have a low-power internal amplifier. The standard audio connection is a 3.5 mm (approximately 1/8 inch) stereo phone connector often color-coded lime green (following the pc 99 standard) for computer sound cards. A few use an RCA connector for input. There are also USB speakers which are powered from the 5 volts at 500 miliamps provided by the USB port , allowing about 2.5 watts of computer power.
Computer speakers range widely in quality and in price. The computer speakers typically packaged with computer systems are small plastic , and have mediocre sound quality. Some computer speakers have equalization features such as bass and treble controls.
The internal amplifiers require an external power source , usually an AC adapter. More sophisticated computer speakers can have a subwoofer unit , to enhance bass speaker , and the small satellite speakers.
LAN (Local Area Network)
- Refer as privately owned or privet data networks.
- It is used to links device in single office, building or campus.
- Limited to few kilometers.
- Topology: Bus, Ring, Star
MAN (Metropolitan Area Network)
- Bigger version of LAN and uses similar technology.
- Owned and operated by privet company.
- Design to extend over an entire city.
- It may be connecting number of LANs into large networks.
- It is link using fiber optics connection.
WAN (Wide Area Network)
- Provides long transmission of data, voice, image and video information over large geographic area that may comprise a country, a continent or even the whole world.
- It is connected across distance of more than 30 miles.
- John Bardeen, willian shockley, and Walter Brattain invented a new electronic switching device called transistor at Bell Laboratories in 1947.
- Transistor proved to be better device than vacuum tube because,
- They are easy to handle than tubes because they are made of germanium semiconductor material rather than glass.
- They were highly reliable as compared to tubes because they had no parts like a filament.
- They could switch faster than tube.
- They consumed almost one tenth power consumed by a tube.
- They were much smaller than tube.
- They were less expensive.
- They dissipated less heat as compared to vacuum tube.
- Second generation computer emerged around 1955 transistor instead of Vacuum tube.
- Magnetic cores for storage was generated in this period, it was a tiny ring made up of ferrit and can be magnetized in either clockwise or anticlockwise direction to represent 0 and 1.
- Memory capacity was about 100 KB.
- Higher level programming language like FORTRAN, COBOL, Algol SNOBOL & operating System were developed during this generation.
- International Business machine (IBM) 700 series computer emerged during second generation using batch oriented operating system.
- Commercial application rapidly developed during this period.
- More than 80% installed computer used in business and industry.
- Payroll, inventory control, marketing, production planning and general ledger system were developed.
- New professions in computing such as System Analyst and Programmer emerged during second generation.
- Smart card is an equipment that comprise of an embedded integrated circuit chip also known as ICC. This ICC can either be a self-asserting micocontroller or matching intelligence with inbuilt memory or just a memory chip lone. A smart card gets connected to the reader only when its directly physically contacted or with the aid of a remote contactless radio-frequency interlace
- There are basically two types of smart cards.
1. Contact Smart Card
A contact smart card ought to be introduced within a smart card reader with a direct physical union to a conductive contact tray noticed on the surface of the smart card, in general the surface is gold plated. Over this substantial contact points processing of commands, data, and card status takes place.
2. Contactless Smart Card
A Contactless smart card as the name suggests it only needs close immediacy with the card reader. The card reader as well as the card has antennae, and both devices communicate with the help of RF (radio frequency) above this contactless link. Some contactless cards also generates power for the inbuilt chip from this electromagnetic field produced. The range of the signals are generally one-half to maximum 3 inches for non-battery powered smart cards, this is perfect for applications like- payment that necessitates an extremely fast card interlace and entry in a building.
Smart Card Applications
Some of the most common smart card applications are
- Credit cards
- Satellite TV
- Computer security systems
- Electronic cash
- Wireless communication
- Government identification
- Loyalty systems (like regular consumer points)