Data Transmission Flashcards
Data packets?
a small part of a data that is transmitted over a network ; after transmission all data are reassembled to form the original data.
a packet header?
- IP address of the sender
- IP address of the receiver
- sequence number of packet (allowing correct reassembly)
- Size of the packet in bytes
the payload?
contains the actual data in the packets
a trailer
- method of identifying the end of the packet
- some form of error checking to ensure packet arrives error-free
Cyclic redundancy checks (CRCs)?
a method of error checking in which all the 1-bits in the data packet payload are added and the total is stored in the packet trailer, the same calculation is repeated at the receiving station.
packet switching?
a method of transmission in which a message is broken into many data packets, which can then be sent along pathways independently of each other
benefits of packet switching?
- There is no need to tie up a single communication line
- it is relatively easy to expand package usage
- a high data transmission rate is possible
Drawbacks of packet switching?
- packets can be lost
- more prone to errors with real-time-streaming
- a delay at the destination whilst the packets are being re-ordered
Hopping?
Sometimes, the packets get lost because they keep bouncing around from the router and never reach the destination. Hopping is used to overcome this problem. A hop number is added to the header of each packets, and this number is reduced by 1 every time it leaves a router. When it gets to 0, the packet is deleted and is resent.
Simplex data transmission?
Occurs when data can be sent in ONE DIRECTION ONLY.
e.g. A computer to a printer
Half-duplex data transmission?
Occurs when the data is sent in BOTH DIRECTIONS but NOT AT THE SAME TIME.
e.g. walkie-talkie
Full-duplex data transmission?
Occurs when the data can be sent in BOTH DIRECTIONS AT THE SAME TIME
e.g. Broadband internet connection
Serial Data transmission?
Occurs when data is sent ONE BIT AT A TME over SINGLE WIRE
(Can be simplex, half or full duplex)
Parallel data transmission?
Occurs when SEVERAL BITS OF DATA are sent down SEVERAL WIRES
(can be simplex, half or full duplex)
What’s the problem with parallel data transmission over a longer distance?
Data can become skewed; data arrives unsynchronised
Compare between Serial and Parallel data transmissions.
- Serial has less risk of external interference than with parallel, due to fewer wires.
- Parallel has a faster rate of transmission than serial, due to more wires.
- Serial is more reliable over longer distances; parallel works well over shorter distances.
Definition for Universal Serial Bus (USB)?
a type of serial data transmission which has become the industry standard for connecting computers to devices via a USB port.
What are the four wires for USB?
Red + black for power
White + green for data transmission
Describe the process when a device is plugged into a computer using one of the USB port.
- The computer automatically detects that a device is present.
- The device is automatically recognized, and the appropriate software is loaded up so the computer and the device can communicate effectively.
- if a new device is detected, the computer will look for the device driver that matches the device, if not, the user is prompted to download the software.
Benefits + Drawbacks of USB
Benefits:
1. Devices plugged in are automatically detected by the computer.
2. Can support different data transmission rates.
3. No need for an external power source since cable supplies +5V
Drawbacks:
1. Has a limited length of 5m
2. Power limitations for high-powered devices.
3. Limited data transmission speed compared to newer technologies.
Causations for errors in data transmission
- Electrical Interference
- Problems during packet switching
- skewing of data (only in parallel)
What are the three different ways in which data can be checked for errors?
- Parity checks
- Checksum
- Echo check
Parity check?
Could make use of either EVEN or ODD parity checks
e.g, the data is 101010; you use an odd parity check, the result would be 0
Checksum?
It works by calculating a value (the checksum) based on the data being sent, usually by adding up the values of all the data bits. This checksum is then sent along with the data. Upon receiving the data, the receiver performs the same calculation. If the calculated checksum matches the received checksum, the data is considered correct; if not, an error is detected.
Echo check?
In an echo check, the system sends a message or data to the receiver, and the receiver sends the same message back (echoes it) to the sender. The sender compares the original message with the received echo. If they match, the data is assumed to have been transmitted correctly. If there is any difference, it indicates that an error occurred during transmission.
Check digits?
An additional digit is appended to a number to check if the entered number is error-free, it is a type of data entry check.
e.g. ISBN13
Automatic Repeat Requests (ARQs)?
it makes use of acknowledgment and timeout to automatically request re-sending of data if the time interval before positive acknowledgment is too long.
what is an eavesdropper?
another way of saying hacker
Plaintext and cipher text
plaintext is the original text, cipher text is when data has gone through encryption algorithm
Symmetric encryption?
a type of encryption in which the same encryption key is used for both to encrypt and decrypt the message.
Asymmetric encryption?
a type of encryption that uses public key and private keys to ensure data is secure.
quantum computer?
a computer that can perform very fast calculations
