Decimal and Hexadecimal
COMMUNICATION AND INTERNET TECHNOLOGY
Data Transmission:
Direction of Data
Simplex data transmission = One direction, Sender to Reciever
E.x: Computer to Printer
Half-Duplex data transmission = Both directions, one at a time
E.x: Walkie-Talkies
Full-Duplex data transmission = Both directions, at the same time
E.x: A phone conversation
Method of Transmission
Serial data transmission = Over a single wire, data is sent one bit at a time continuously. Works well over long distances but data transmission is slower.
Parallel data transmission = Over several wires, data is sent in several bits, normally 1 byte is total at a time. Data transmission is faster but data can get unsynchronized/skewed over long distances.
Method of Synchronization
Asynchronous data transmission = Agreed bit pattern. Groups of bits are sent along with control bits, a start bit at the beginning, and a stop bit at the end. This prevents data from getting mixed up.
Synchronous data transmission = Continuously sending data that is accompanied by timing signals from an internal clock. The bits are reassembled depending on the signals. This is faster than asynchronous, but the timing needs to be very accurate.
Universal Serial Bus (USB)
•Asynchronous, serial data transmission.
•Made of a four-wire shielded cable. Two used for power and the earth. Other two used for data transmission.
Pros:
•Device is automatically detected.
•Different transmission rates are supported.
•Connects only one way, preventing incorrect connections.
Cons:
•Max cable length is only 5 metres.
•Transmission rate is less than 500 mb/sec.
Error-Checking methods:
Error-Checking methods:
1. Parity checking = Data is sent with a parity bit. The parity bit’s value depends on if even or odd parity is being used. First digit is parity bit. After transmission, if the number of 1s doesn’t align with the chosen parity, there’s an error.
Disadvantage: If two bits switch places, parity will stay the same, and the error won’t be detected.
E.x: 0 1 1 0 1 1 0 0 if even parity (four 1s)
1 1 1 0 1 1 0 0 if odd parity (five 1s)
2. Automatic Repeat Request (ARQ) = After sending, an acknowledgement needs to be sent by the reciever to the sender, to confirm that data is fine. If it’s not sent before a timeout, the request for an acknowledgement is sent again.
3. Checksum = Blocks of data are sent with a checksum at the end of each. Checksum is calculated using the rest of the data. If checksum is different after transmission, there’s an error.
4. Echo check = After transmission, data is sent back to the sender to check if it’s the same as before transmission. This is unreliable because you wouldn’t know if the error happened from sender to receiver or on the way back.
Internet Service Provider (ISP) = Companies that provide a user with access to the internet for a monthly fee.
Hypertext Transfer Protocol (http) = A set of rules for transferring files over the internet. When SSL, which is a form of security, is used on a website, http changes to https. This is slower but safer for private data.
Web browser = Allows user to display web pages. Translates HTML. Features: Home page, Storage of favorite webpages, History, Go back and forth to opened websites.
Internet Protocol (IP) address = 32-bit number. Given when a device connects to the internet. It’s unique to that specific internet session. Can be used to find device’s home address/location.
Media Access Control (MAC) address = 48-bit number. Can be used to identify the device and it’s manufacturer.
M=manufacturer,
D=device.
Format = (MM:MM:MM:MM:DD:DD:DD)
•Universally Administered MAC Address (UAA) = Common. Set by manufacturer. Rarely changed.
•Locally Administered MAC Address (LAA) = Changed to adhere to a format, bypass a filter on a router or firewall, or get past network restrictions.