2 Data Transmission Flashcards
Data sent over long distance is usually broken into ______ _______
data packets
What are the 3 parts of a dat packet
headler
payload
trailer
What is in the header? (4)
IP address of the sender
IP address of the receiver
Sequence number of the packets
Size of the packet (in bytes)
What does the payload contain? (1)
The actual data in the packets (64KiB)
What does the Trailer contain? (2)
Methods of identifying the end of a packet
Some forms of error checking to ensure packet arrives error free
Define packet switching
method of transmission in which a message is broken up into a number of packets
Describe how packet switching occurs (4)
Each packet sent independently from start point to end point
At the destination, packets reassembled into their correct order
At each stage of transmission, there are nodes that contain a router
Each router determines the route the packet needs to take
Benefits of packet swtiching(3)
no need to tie up a single communication line
possible to overcome failed, busy, faulty lines by rerouting packets
high data transmission rate is possible
Drawbacks of packet switching(3)
packets can be lost and need to be resent
method is prone to errors with real time streaming
delay at destination while the packets are restructured
Why might pathways become clogged (2)
packets keep bouncing around from router to router
Lost packets mount up, clogging the system
What is simplex transmission mode
data can be sent in only one direction only
What is half-duplex transmission mode
When data is sent in both directions but not at the same time
What is full-duplex transmission mode
Both directions at the same time
What are the two types of data transmission (2)
Serial data transmission
Parallel data transmission
What is serial data transmission (2)
ONE BIT AT A TIME over a SINGLE WIRE/CHANNEL
What is parallel data transmission? (2)
SEVERAL BITS OF DATA over SEVERAL WIRES/CHANNELS
Advantage of serial data transmission (4)
reliable over long distances
Data arrives in order as bits transmitted through single wire
less risk of external interference than parallel
less expensive than parallel data transmission (fewer wires)
Disadvantage of serial data transmission (2)
relatively slower than parallel data transmission
not suitable for transmitting data over short distances
Advantage of parallel data transmission (2)
faster than serial data transmission
works well over short distances
Disadvantage of parallel data transmission (2)
expensive than serial (requires more hardware)
bits can arrive out of synchornisation (skewed)
What does USB stand for
Universal Serial Bus
What happens when a device is plugged into a USB? (3)
computer automatically detects that device is present (small change in voltage in the USB cable)
device is automatically recognised, appropriate device driver loaded so that computer and device can communicate
if a new device detected, computer looks for device driver that matches device
Benefits of USB systems (4)
industry standard
Devices automatically detected and device drivers automatically loaded
backwards compatible (older versions still supported)
connections can only be one way, prevents incorrect connection being made
Drawbacks of USB systems (2)
Very old USB versions not supported
maximum cable length is roughly 5 metres
What are the 4 ways of data can be checked for errors (4)
Parity checks
checksum
echo check
Automatic repeat request (ARQ)
Why might errors occur during data transmission
Interference
skewing of data
probelsm during packet switching
Describe what a parity check is (2)
A method used to check if data has been transmitted properly
makes use of even parity and odd parity
What is a parity bit
a bit added to a byte of data to ensure that the byte follows the correct even or odd parity protocol
What is a parity block
A horizontal and vertical parity check on a block of data being transmitted
What is the limitation of parity check? (1)
Cannot tell which bit has been corrupted or changed
Describe the checksum process (5)
when a block of data is about be transmitted, checksum value calculated
checksum transmitted with block of data
at the receiving end, checksum is recalculated using the blocks of data
recalculated checksum is compared with the initial checksum value
If they are the same, no errors have taken place during transmission
Describe the process of echo check (3)
a copy of data is sent back to the sender
the returned data is compared with original data by the sender’s computer
if there are no diffrerences, then data sent without errors
Describe the process of Automatic repeat request (ARQ) (3)
uses positive and negative acknowledgements and timeout
receiving device receives an error detection code as part of the data transmission (used to detect where data has any errors)
If no error detected, positive acknowledgment sent to sender
What happens if an error is detected in a computer system that uses ARQ (1)
negative acknowledgement sent to sender and requests data to be resent
What happens if no acknowledgement of any sort has been received by the sending device after a certain amount of time (ARQ) (1)
resends data until positive acknowledgement is sent to sender
What is the original data being sent also known as in encryption?
plaintext
Define encryption
the process of making data meaningless using encryption keys; without the correct decruption key the data cannot be decoded [unscrambled]
What is symmetric encryption
both parties given identical secret key to encrypt or decrypt information
What is the main problem with symmetric encryption
if hacker gains access to the key, they can decrypt the information
What is asymmetric encryption
type of encryption that uses both public and private key to ensure data is secure
define public key
a key known to everyone
define private key
a key known to the receiver
Describe the process of asymmetric encryption (3)
Sender encrypts data using public key
Encrypted data is sent to the receiver
Receiver decrypts the encrypted data using a MATCHING private key
Advantage of asymmetric encryption
much more reliable compared to symmetric key
What is check digit
extra digit added to a number that is calculated from the existing digits in the number.
Examples of when check digit is used (2)
ISBN
barcodes
(used to check for errors during data entry)
