Chapter 2 Communication and internet technologies

Data transmission can be either a short distance (computer to printer) or over a long distance (telephone to network).

There are 3 factors needed to be considered when transmitting data:

  1.  The direction of the data (either in one direction or the other, or even in both)
  2. The method of transmissions (how many bits are sent at the same time)
  3. The method of synchronizing between 2 devices

Transmissions:

Simplex Data Transmissions:  One direction transmission, example: keyboard to your computer or computer to a printer.

Half Duplex Data Transmissions: Both directions but never at the same time, example: CB radio or walkie  talkie. (unidirectional)

Full-Duplex Data Transmissions: Data sent over simultaneously in both directions at the same time, example: social network,messenger,and multiplayer games. (Bidirectional)

Serial transmission – 1 bit at a time in a single stream.  A favored method of transmission for long distance transmission as only one wire is used.  Data cannot become unsynchronised using a single cable
Parallel transmission – several bits of data send over multiple wires.  1 wire per bit is used.  Great for short distance communication, if used over long distance, data can become skewed.

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Task 2.1:

a) Serial transmission is good for long distances. Data is unidirectional,with half duplex. Serial transmission is safer, better way of communication. Popular, and commonly used in government/military for security

     b)  Parallel data transmission required many wires (1 wire per bit) and is expensive. Data can become skewed over long distances. Bidirectional. Parallel, full duplex could be used within a LAN, server would talk to computer, computer would talk to the server. Household appliances use this method of transmission also

c)  Works well over long distances using a single cable. Data can be sent one bit at a time, but only in one direction . This method of communication would be used in a radio broadcasting.

Asynchronous Data Transmission, refers to data being transmitted in an agreed bit pattern. Data bits (1s and 0s) are grouped together and sent with Control Bits

Synchronous Data Transmission is a continuous stream of data.  It has timed signals and an internal clock. This ensure that the sender and receiver are synchronized with each other.

The Universal Serial Bus (USB) is an asynchronous serial data transmission method. The USB consists of

  1. four wire shielded cable
  2. two of the wires are used for power and the earth
  3. two of the wires are used in the data transmission

When a device is plugged into a computer using one of the USB ports:

  1.  The computer immediately gets to know (there is a change of voltage level)
  2. The device is recognized, and there is a Device Driver that makes it easier to communicate with the USB and help recognize it.
  3. If  new device is detected, the computer will loom for the device driver which matches the other plugged in device. If that doesn’t match, then the user has to have or download the right software’s.

 

 

There is always a risk when data has been in sync or changed in some way.

My nmae is Mnaav. This text is quite hard to understand, but for the computer, it thinks its in sync.

Parity Checking is one way to check whether or not the data has changed or not. A byte of data is allocated a Parity Bit.  Systems which use even parity  have an equal number of 1 bits, and systems which use an odd parity have an odd number of 1 bits.

Remember, a byte has 8 digits (mainly 0s and 1s)

For example:

01101100 is an even parity, since it consists of even number of 1s in the byte.

01110101 is an odd parity since it consists of odd number of 1s in the byte.

Before data is transferred, an agreement is made between sender and receiver regarding which one of the 2 types of parity are used. This is an example of a Protocol. 

Senders Byte: 01011100

Receivers Byte: 01001100

In this case, the senders byte had 4 1 bits in, which is an even parity, but the receiver got only 3 1 bits, which means he got an odd parity. There had been an error in the transmission of data.  The error is spotted by the computer, since it checks the number of parity used.

If there is data transmission in even parity, and the numbers are swapped, the computer wont recognize the error since the even parity is correct, but not the order.

There are other ways to check data as well:

ARQ – Automatic repeat request.

  • An acknowledgment sent  by receiver indicating data packet has arrived.  If receiver doesn’t notify sender, there is a timeout.  Sender will then send the data packet again

Echo check

  • data sent from sender to receiver and back again to check if the data send is the same as what is received.  Not a reliable way to check for errors as there is no error checking or trace route being carried out.

Checksum: Checksum is another method of data checking. Checksum checks if the data is corrupt, and identifies the sequence of the numbers in transmission. Blocks of data are transferred, and each block contains 1 byte (thats what IGCSE requires). Maximum size is 255. If numbers are under 255, the checksum will allow it to pass through.  a—–b if 1010111.

Steps to do Checksum:

  1. Divide the sum (x) of the bytes 256
  2. Round down to the nearest whole number (y)
  3. z = y *256
  4. calculate the difference (x-z)
  5. You got your value.

Example:

  1. 266/256
  2. 1.03 = y = 1
  3. z = 256
  4. x = 266
  5. z = 256
  6.  answer is 10

There is also another type of data transmission correction. Its called Check Digit. Check digit is associated with bar codes, ISBN numbers, Vehicle Identification Numbers, etc.

How to calculate Check Digit:

A video our teacher made for check digit:

Steps: Check digit.PNG

Internet Technologies

Internet Technologies: The internet a world wide system where the system of computer networks and computers. You can communicate, share files and lots of things over the internet.

Internet Service Provider: The internet service provider is basically the router you pay for, so you can use WiFi at home, school and other places. This also includes cellular data like 4G and everything.

Internet Protocol (IP) Address : Each device is given an IP address,  a unique address. It is a 32 bit number. When you have a home computer, you are given an IP as soon as you connect to the internet.

MAC Address: Media Access Control, it is basically the same as IP address but it remains unchanged.

Web Client is basically any device you are using right now, it can be either a phone

Web browser is something like Google Chrome or Mozilla Firefox, a place where you can browse through the internet.

A network architecture in which each computer or process on the network is either a client or a server.

Internet server (web server) is a special computer, on which websites are stored. Web Server is constantly switched on and connected to the Internet so that each Internet user around the world can access website at all times. This computer is built up with selected high quality components, which can endure incessant work and high load.

Clients are PCs or workstations on which users run applications.

HTML

HTML is the “mother tongue” of your browser.

HTML (Hyper Text Mark-up Language) is the authoring language, used to create web pages and other information that can be displayed in a web browser. 

The websites are developed in HTML and stored on Web Servers. When User types the URL of website, browser locates and fetches the website from server on clients computer and displays contents.

HTTP =  (Hyper Text Transfer Protocol), the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page.

HTTPS = is the safer version of the website, it has a padlock symbol on the top and you can make sure that the website is not a scam.

Web servers : Web serves are programs that use HTTP (Hypertext Transfer Protocol) to serve the files that form Web pages to users, in response to their requests, which are forwarded by their computers’ HTTP clients.

Protocols

A protocol is a set of rules that define how devices communicate. Here are the factors the protocol affect when you are using the internet.

  • how the communication will start
  • the transmission speed
  • the significance of the bits being transmitted
  • how the bits will be delivered (one at a time or in groups of 16 for example)
  • error checking procedures used
  • The Internet Protocol is known as TCP/IP.

 

 

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