MODEM

Modem is short for MOdulator DEModulator. It’s an electronic device used to access the Internet that modulates carrier waves to encode information to be transmitted and also demodulates incoming carrier waves to decode the information they carry.

What is a modem?

A modem is a very important piece of network hardware that allows a computer to send and receive data through a telephone line or cable connection. In simple words, it’s the device that connects a computer to the Internet using telecommunication network.

The Importance of a Modem

Back in the old days, when landline phones were the primary tool to communicate over long distances, modems came in pretty handy to gain Internet connectivity using telephone lines. In fact, without modems, it would have been impossible for most users to connect to the Internet. While computer technology is purely digital, i.e., it relies on numbers to transmit and receive information, telephone technology, even to this day, is partly analog, meaning that it uses continuously varying electrical signals to transmit information.

Since your modem sends information through a telephone line by modulating digital signals, it also needs to have another kind of translator that helps it demodulate the analog signals it receives via the telephone line.

That’s why a modem is named as such, because it both modulates and demodulates signals.

ETHERNET

Ethernet is the technology that is most commonly used in wired local area networks (LANs). A LAN is a network of computers and other electronic devices that covers a small area such as a room, office, or building. It is used in contrast to a wide area network (WAN), which spans much larger geographical areas. Ethernet is a network protocol that controls how data is transmitted over a LAN. Technically it is referred to as the IEEE 802.3 protocol. The protocol has evolved and improved over time to transfer data at the speed of a gigabit per second. 

How Ethernet works

The Institute of Electrical and Electronics Engineers Inc. (IEEE) specifies in the family of standards called IEEE 802.3 that the Ethernet protocol touches both Layer 1 -- the physical layer -- and Layer 2 -- the data link layer -- on the OSI network protocol model. Ethernet defines two units of transmission: packet and frame. The frame includes not just the payload of data being transmitted, but also:

• the physical media access control (MAC) addresses of both the sender and receiver;
• VLAN tagging and quality of service information;
• Error correction information to detect transmission problems.

Advantages of using wired Ethernet network

• It is very reliable.
• Ethernet network makes use of firewalls for the security of the data.
• Data is transmitted and received at very high speed.
• It is very easy to use the wired network.

Disadvantages of using wired Ethernet network

• The wired Ethernet network is used only for short distances.
• The mobility is limited.
• Its maintenance is difficult.
• Ethernet cables, hubs, switches, routers increase the cost of installation.

Types of Ethernet network

The maximum data rate of the original Ethernet technology is 10 megabits per second (Mbps), but a second generation fast ethernet carries 100 Mbps, and the latest version called gigabit ethernet works at 1000 Mbps. Ethernet network can be classified into 3 types:

Fast Ethernet

This type of Ethernet can transfer data at a rate of 100 Mbps.  Fast Ethernet makes use of twisted pair cable or fiber optic cable for communication.
There are three types of fast Ethernet, which are as follows:
• 100BASE-TX
• 100BASE-FX
• 100BASE-T4

Gigabit Ethernet

This type of Ethernet network can transfer data at a rate of 1000 Mbps. Gigabit Ethernet also makes use of twisted pair cable or fiber optic cable. 48 bits used for addressing in Gigabit Ethernet. Nowadays gigabit Ethernet is very popular. The latest Gigabit Ethernet is a 10 Gigabit Ethernet, which can transfer data at a rate of 10 Gbps. Gigabit Ethernet was developed so that it can meet the needs of the user like faster communication network, faster transfer of data etc.

Collision and Broadcast Domain

Collision Domain

A collision domain is a network segment connected by a shared medium or through repeaters where simultaneous data transmissions collide with one another. The collision domain applies particularly in wireless networks, but also affected early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network segment at the same time. Members of a collision domain may be involved in collisions with one another. Devices outside the collision domain do not have collisions with those inside.

The following example illustrates collision domains.

As you can see, we have 6 collision domains.

Here, each port on a hub is in the same collision domain. Each port on a bridge, a switch or router is in a separate collision domain.

 Broadcast Domain 

A broadcast domain is a domain in which a broadcast is forwarded. A broadcast domain contains all devices that can reach each other at the data link layer (OSI layer 2) by using broadcast. All ports on a hub or a switch are by default in the same broadcast domain. All ports on a router are in the different broadcast domains and routers don’t forward broadcasts from one broadcast domain to another.

The following example clarifies the concept.

In the picture above we have three broadcast domains, since all ports on a hub or a switch are in the same broadcast domain, and all ports on a router are in a different broadcast domain.         

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Generations of programming language

Programming languages have been developed over the year in a phased manner. Each phase of developed has made the programming language more user-friendly, easier to use and more powerful. Each phase of improved made in the development of the programming languages can be referred to as a generation. The programming language in terms of their performance reliability and robustness can be grouped into five different generations,
Generations of programming language

1. First generation languages (1GL)

1. Second generation languages (2GL)

1. Third generation languages (3GL)

1. Fourth generation languages (4GL)

1. Fifth generation languages (5GL)

1. First Generation Language (Machine language)

• They are translation free and can be directly executed by the computers.

• The programs written in these languages are executed very speedily and efficiently by the CPU of the computer system.

• The programs written in these languages utilize the memory in an efficient manner because it is possible to keep track of each bit of data.
  
  
  The first generation programming language is also called low-level programming language because they were used to program the computer system at a very low level of abstraction. i.e. at the machine level. All the commands and data values are given in ones and zeros, corresponding to the "on" and "off" electrical states in a computer. In machine language, all instructions, memory locations, numbers, and characters are represented in strings of zeros and ones. Although machine-language programs are typically displayed with the binary numbers translated into octal (base-8) or hexadecimal (base-16), these programs are not easy for humans to read, write, or debug. machine language also referred to as the native language of the computer system is the first generation programming language. In the machine language, a programmer only deals with a binary number.

2. Second Generation language (Assembly Language)

• It is easy to develop understand and modify the program developed in these languages are compared to those developed in the first generation programming language.

• The programs written in these languages are less prone to errors and therefore can be maintained with a great case.
  The second generation programming language also belongs to the category of low-level- programming language. The second generation language comprises assembly languages that use the concept of mnemonics for the writing program. In the assembly language, symbolic names are used to represent the opcode and the operand part of the instruction. Assembly languages are symbolic programming languages that use symbolic notation to represent machine-language instructions. Symbolic programming languages are strongly connected to machine language and the internal architecture of the computer system on which they are used. They are called low-level languages because they are so closely related to the machines. Nearly all computer systems have an assembly language available for use. Examples of these codes include A for add, CMP for compare, MP for multiply, and STO for storing information into memory.

3. Third Generation languages (High-Level Languages)

• It is easy to develop, learn and understand the program.

• As the program written in these languages are less prone to errors they are easy to maintain.

• The program written in these languages can be developed in very less time as compared to the first and second generation language.
  
  
  The third generation programming languages were designed to overcome the various limitations of the first and second generation programming languages. The languages of the third and later generation are considered as a high-level language because they enable the programmer to concentrate only on the logic of the programs without considering the internal architecture of the computer system.
  
  
  Examples: FORTRAN, ALGOL, COBOL, C++, C
  

4. Fourth generation language (Very High-level Languages)

• These programming languages allow the efficient use of data by implementing the various database.

• They require less time, cost and effort to develop different types of software applications.

• The program developed in these languages are highly portable as compared to the programs developed in the languages of other generation.
  
  
  The languages of this generation were considered as very high-level programming languages required a lot of time and effort that affected the productivity of a programmer. The fourth generation programming languages were designed and developed to reduce the time, cost and effort needed to develop different types of software applications.
  Advantages of fourth generation languages
  Examples: SOL, CSS, coldfusion
  

5. Fifth generation language (Artificial Intelligence Language)

• These languages can be used to query the database in a fast and efficient manner.

• In this generation of language, the user can communicate with the computer system in a simple and an easy manner.

The programming languages of this generation mainly focus on constraint programming. The major fields in which the fifth generation programming language are employed are Artificial Intelligence and Artificial Neural Networks

Examples: mercury, prolog, OPS5

CATHODE RAY TUBE (CRT)

The primary output device in a graphical system is the video monitor. The main element of a video monitor is the Cathode Ray Tube(CRT))The cathode-ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen and is used to display images. It modulates, accelerates, and deflects electron beam(s) onto the screen to create the images. The images may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets, or other phenomena.

The operation of CRT is very simple −


• The electron gun emits a beam of electrons cathode rays.
• The electron beam passes through focusing and deflection systems that direct it towards specified positions on the phosphor-coated screen.
• When the beam hits the screen, the phosphor emits a small spot of light at each position contacted by the electron beam.
• It redraws the picture by directing the electron beam back over the same screen points quickly.

  It consists of a glass envelope made from a neck and cone. All air has been extracted so that it contains a vacuum. At the narrow end are pins which make connection with an internal ELECTRON GUN. Voltages are applied to this gun to produce a beam of electrons. This electron beam is projected towards the inside face of the screen.
The face is coated with a PHOSPHOR which PHOSPHORESCES (glows) when hit by the beam. This produces a spot of light on the centre of the face of the CRT. By varying the beam current, spot BRIGHTNESS can be controlled. Controlling the diameter of the beam controls FOCUS. Phosphors come in a range of colours.
On its way from the gun to the screen the beam passes between  2 sets of plates. They are called the X and Y plates (as in graphs). By applying voltages to these plates the beam can be deflected. This causes the spot to move from the centre of the screen to another position on the screen. The X plates plates deflect the spot horizontally, the Y plates vertically. Thus the spot can be deflected to any position on the screen. External deflection coils are often used instead of the internal deflection plates.

Features, Hardware & Challanges for a Multimedia System

Desirable Features & Hardware for a Multimedia System

·         Very High Processing Power - needed to deal with large data processing and real time delivery of media. Special hardware commonplace.

·         Multimedia Capable File System - needed to deliver real-time media -- e.g. Video/Audio Streaming. Special Hardware/Software needed e.g RAID technology.

·         Data Representations/File Formats that support multimedia - Data representations/file formats should be easy to handle yet allow for compression/decompression in real-time.

·         Efficient and High I/O - input and output to the file subsystem needs to be efficient and fast. Needs to allow for real-time recording as well as playback of data. e.g. Direct to Disk recording systems.

·         Special Operating System - to allow access to file system and process data efficiently and quickly. Needs to support direct transfers to disk, real-time scheduling, fast interrupt processing, I/O streaming etc.

·         Storage and Memory - large storage units (of the order of 50 -100 Gb or more) and large memory (50 -100 Mb or more). Large Caches also required and frequently of Level 2 and 3 hierarchy for efficient management.

·         Network Support - Client-server systems common as distributed systems common.

·         Software Tools - user friendly tools needed to handle media, design and develop applications, deliver media. 

Challenges for Multimedia Systems

Supporting multimedia applications over a computer network renders the application distributed. This will involve many special computing techniques -- discussed later.

Multimedia systems may have to render a variety of media at the same instant -- a distinction from normal applications. There is a temporal relationship between many forms of media (e.g. Video and Audio. There 2 are forms of problems here

1. Sequencing within the media -- playing frames in correct order/time frame in video
2. Synchronisation -- inter-media scheduling (e.g. Video and Audio). Lip synchronisation is clearly important for humans to watch playback of video and audio and even animation and audio. Ever tried watching an out of (lip) sync film for a long time?

The key issues multimedia systems need to deal with here are:

• How to represent and store temporal information.
• How to strictly maintain the temporal relationships on play back/retrieval
• What process are involved in the above.

Data has to represented digitally so many initial source of data needs to be digitize -- translated from analog source to digital representation. The will involve scanning (graphics, still images), sampling (audio/video) although digital cameras now exist for direct scene to digital capture of images and video.

The data is large several Mb easily for audio and video -- therefore storage, transfer (bandwidth) and processing overheads are high. Data compression techniques are very common.