Data transmission (paper 1) Flashcards
define a data packet
a small part of data that is transmitted over a network
define a packer header
the part of the data packet that contains the IP addresses and inclueds the packet number
define packet trailer
the part of a data packet that indicates the end of the data packet and cyclic reduncancy check error check
what is a cyclic redundancy check (CRC)
an error check method in which all the 1-bits in the data packet payload are added and the total is stored in the packet trailer
what is the payload
the actual data being carried in a data packet
what is a node
Stages in a network that can receive and transmit data packets
what is packet switching
a method of transmission in which a message is broken into many data packets which can be sent along pathways independently
what is a router
a device that enables data packets to be moved between different networks
what is real time streaming
the transmission of data over a network for live events where the data is sent as soon as it is received or generated
what is hopping / hop number
a number in a packet header used to stop data packets that never reaches their destinataion from ‘clogging up’ the data paths
define simplex data
data that can be sent in one direction only
define half-duplex data
data that can be sent in both directions but not at the same time
define full-duplex data
data that can be sent in both directions at the same time
what is serial data transmission
sending data down one channel/wire one bit at a time at very high speeds
what is parallel data transmission
sending data down several channels/wires serveral bits at a time over short distances
what is skewed data
data that arrives at the destination with the bits no longer synchronised
what does a USB stand for
universal serial bus
what is a USB
a type of serial data transmission which has become the industry standard for connecting computers to devices via a USB port
what is an IP address
a unique string of characters that identifies each computer using the Internet Protocol to communicate over a network
what are the benefits of packet switching
- no need to tie up a single connection line
- can easily overcome failed lines by re-reouting packets
descirbe the process of packet switching
- data is broken donw into packets
- each packet is given a sequence number and sent
- each packet may take a different route depending on the quickest route in the moment
- routers control the route the packet takes
- packets may arrive out of order
- the sequence numbers put them back into order
what are the benefits of serial data transmission
- lower interference
- more reliable over longer distances
- smaller, simpler and cheaper connections to produce
what are the negatives of serial data transmission
- lower transmission speeds
what are the benefits of parallel data transmission
- very fast data transfer
- can send data in both directions at the same time
what are the negatives of parallel data transmission
- interference issues between wires
- data corruption can occur over longer distances
- suffer from skewing: data bits travelling parallel to each other can move at different speeds causing them to arrive out of sync
what types of parity may a computer use
- even
- odd
how does a parity check work
- Checks a byte of data
- Check is performed when data is received
- A parity bit is added (to the parity byte)
- Counts number of 1’s to see if 1’s are even or odd
- Can be even or odd
- If parity is incorrect, error is detected
when is a parity block check used
when sending multiple bytes in one transmission block: each byte has its own paratiy bit and there is a final parity bit for each collumn
what is a checksum
an additional method of checking for errors following the transmission of data - it is sent with the data and is recalculated once received
explain a check digit
- A digit that is calculated from the data, uses modulo to calculate digit
- It is added to the data
- Digit is recalculated when data is entered
- Digits are compared to check for error
explain automatic repeat request
- computers automatically send back a positive acknowledgement if a data packet is deemed correct
- or it will ask for data to be resent if error is detected
- if no acknowledgement is sent within a certain time
- a timeout is registered and the sending computer resend the data
- this process continues until data is completely correct or the ARQ limit is reached
explain a checksum
- A value is calculated from the data
- It is transmitted with the data
- Value is recalculated after transmission
- Values are compared after transmission to check for error
- if they are not identicle then an error message will be sent
why are codes/encryption used
to prevent interception of messages
what is plaintext
the original message to be encrypted
what is ciphertext
the encrypted message
what is symmetric encryption
a type of encryption in which the same encryption key is used both to encrypt and decrypt a message
what is asymmetric encryption
a type of encryption that uses public keys and private keys to ensure data is secure
what are the two types of encryption
- symmetric
- asymmetric
what is acknowledgement
a message sent to the receiver indicating that data has been received
what is an eavsdropper
another name for a hacker who intercepts data being transmitted one a wored or wireless connection
what is an encryption algorithm
a complex piece of software that takes plaintext and generates an encrypted string known as ciphertext
what is a public key
a type of encryption key that is known to all users
what is a private key
a type of encyrption key which is known only to the single coputer/user
what is a quantum computer
a computer which can preform very fast calculations, based on probability rather than simple 1 or 0 values
describe the structure of a data packet
- packet header = destination IP address, packet number, senders address
- payload = data
- packet trailer = error checks
why are error checks important
because data can be lost, gained or changed during electrical interfereance which makes the data incorrect
how can errors occur
By bits of data being lost in transmission
what are the error checks that you have studied
- parity check (odd and even)
- checksum
- echo check
- automatic repeat request
what is an echo check
- it is performed by asking the recipient computer to send back an exact copy of data it received back to the originator
- the data is compared
- if both copies match then the data is deemed to have arrived without error
give examples of how check digits / check sums are used day to day
- book numbers
- bar codes in stores
