Unit 2 Flashcards
what are data packets
a packet is a small unit of data that being transmitted
what is the structure of a data packet
header
payload
trailer
what does the header contain
senders IP address
Recievers IP address
Packet number
what does the payload contain
data/part of the message
what does the trailer contain
bits to show end of packet
what is packet switching
data packets are sent through different routes so that data transfer is efficient
what are the advantages of packet switching
packets can take different routes to get to their destination
this ensures message is delivered despite the unavailability of a route
describe the process of packet switching
data is broken down into packets
each packet takes a different route
a router controls the route a packet takes
the packets are reassembled at the destination
what is simplex data transmission
when data is sent in one direction only
computer to a printer
what is half duplex data transmission
when data is sent in both directions but not at the same time
walkie talkies
full duplex transmission
when data is sent in both directions at the same time
broadband internet connection
serial data transmission
one bit at a time over a single wire/channel
connecting a computer through a USB connection
advantage of serial data transmission
works well over long distances since data is fully synchronised in the correct order
disadvantage of serial data transmission
transmitted at a slower rate than parallel data transmission
parallel data transmission
when several bits of data is sent down several channels/wires at the same time
used in the internal circuits of a computer
advantage of parallel data transmission
works well over short distances
faster than serial transmission
disadvantages of parallel transmission
data can become skewed(mixed)
the longer the wire, the worse it becomes
what is the USB
Universal Serial Bus
form of serial data transmission
allows both half duplex and full duplex transmission
standard method for transmission of data
benefits of USB
become industry standard
is backward compatible
automatically detected when plugged in
no need for external power source
easy to add more USB ports
drawbacks of USB
only supports cable length of 5 metres
early forms of USB may not be supported by computers
data transfer rate is slow
how can errors occur during data transmission
interference
problems due to packet switching
skewing of data
what is parity checking
it can be called even or odd
one of the bits is reserved for a parity bit and the number of 1’s is counted. the even or odd parity check will make the total number of 1s even or odd
what is the problem with parity checks
sometimes more than 1 byte it corrupted but the parity is maintained
this is why other methods are needed to ensure errors are never missed
what are parity blocks
a block of data is sent and the number of 1bits are totalled horizontally and vertically.
this identifies that an error has occurred and where the error is
what is checksum
used to check if data has been changed or corrupted following data transmission
data is sent in blocks and an additional value, the checksum, is sent
what is the process of checksum
the checksum is calculated from a block a data
the calculation is done using an agreed algorithm
checksum is transmitted with the block of data
the reciever recalculates from the block of data
if the checksums are the same, no error occured otherwise a request is made to resend the data
what is echo check
when data is sent to one device, it is sent back to the reciever
the sender then compares the sets of data to check if errors occur
what is the problem with echo check
it isnt known whether the error has been made while sending the data or recieving it meaning it isnt reliable
what is check digit
the final digit included in a code
calculated from all other digits in the code
example- ISBN
what is check digit used for
used to identify errors that occur in data entry caused by mistyping or misscanning
What are ARQ’s
Automatic Repeat Requests
used to check data following data transmission
How do ARQ’s work
the reciever sends back a positive or negative acknowledgements to the sender and the data is the resent depending
also uses timeouts where if no data is recieved by the sender, the data is automatically resent
what is plaintext
the data being sent is known as plaintext
what is cyphertext
the data once it has gone through an encryption algorithm
what is symmetric encryption
the same key is used to encrypt and decrypt the encoded message
disadvantage of symmetric encryption
the encryption key can always be intercepted which brings about the question of security
what is asymmetric encryption
uses 2 keys called the private and public key
the private key is known only to the computer user
the public key is known to everybody
process of asymmetric encyption
a matching pair of keys is generated
the public key is then sent to user 2 from user 1
user 2 encrypts their own message with the key and sends the encrypted data back to user 1
the private key is used by user 1 to decrypt the data
