2. data transmission Flashcards
how is data transmitted
by breaking it down into smaller chunks called packets
what is a packet
A packet is a small unit of data that can be transmitted from a sending device to a receiving device via a network communication protocol.
what is the sturcture of a packet, and what does each layer contain
packet header:
senders and receivers ip address, packet number
payload:
data/ part of the message
trailer:
bits to show the end of the packet
what is packet switching and explain its process
a way of transmitting data, process:
- Data is broken down into packets
- Each packet could take a different route
- A router controls the route a packet takes
- Packets may arrive out of order
-Once the last packet has arrived, packets
are reordered
what are the 2 transmission methods
serial and parallel transmission
descirbe serial transmission
a single wire is used to connect the sending device to the receiving device. Bits are transmitted one at a time.
more reliable over long distances, slow so not suitable for transmission of large files over short distances
describe parallel transmission
multiple wires are used to connect the sending device and the receiving device. Several bits are sent simultaneously down the wires
faster, however bits can arrive out of order so might need rearranging before complete transmission, expensive method to implement over longer distances
what are the types of data transmission
Simplex data transmission
Half-duplex data transmission
Full-duplex data transmission
describe simplex data transmission
only one device can transmit data; as such, data moves in one direction only eg only from senders device to receiving, for example using a usb cable to send info to a printer
describe half duplex transmission
here both the sending device and the receiving device can transmit data, but not at the same time. This means that data can move in both directions, but only in one direction at a time. eg walkie talkies
describe full duplex transmission
where both the receiving device and the sending device can send and receive data at the same time, i.e. data is transmitted in both directions simultaneously eg. iphone call
what dos usb stand for
universal serial bus
what is a USB
a hardware device that enables you to connect your peripheral devices to your computer so that those devices can exchange data with the computer.
USB uses what type of transmission
serial, through one mire one bit at a time
advantages of using USB
-universal, used in almost all common devices
-can transfer power as well as data, even at the same time
disadvantages of using USB
-there are multiple different connectors (updates, changes the size and pattern of the usb)
why were error detection methods established
to ensure that transmission errors are detected as early as possible as many errors can happen during data transmission due to interference, e.g. data loss, data gain and data change
what does parity check use
using a parity bit at the end or start of the binary number and sent along with the data
how does parity check work
there are two established checks
even parity check: total number of 1’s in a byte is even
odd parity check: total number of 1’s in a byte is odd
The sending and receiving computers must both agree on which parity to use – even or odd, if the type of parity check isnt the same for the sender and receiver, an error has been made
what is a disadvantage of parity check
they cannot tell us exactly which bit has been corrupted or changed during transmission
what is a checksum
another type of error detection method. In this method, data is sent in blocks together with a calculated value known as the checksum. receiver calculates the checksum if equal to senders checksum= no error different= error during transmission
what are the rules for checksum
1- if number of bytes in a block is less or equal to 255 than that is the checksum number
2- if bigger than:
-divide sum of bytes in block by 256
-convert this value int integer and round down
-multiple integer value by 256
-subtract,sum of bytes- calculated value
describe echo check
method of error detection where the receiving computer sends back an exact copy of the data to the sending computer. The sending computer then compares the data it originally sent to the data it has received back. the sending computer performs the error checking and not the receiving computer,
state one disadvantage of echo check
is difficult to tell whether the data was corrupted in transit to the destination or on its way back. Another disadvantage is speed, because the complete data has to be sent twice.
what is a check digit
A check digit is an extra digit added to a number calculated from the existing digits in the number and used to check the integrity of the data entered.
what are some uses for check digit
ISBN, barcodes, product codes etc
how do you calculate if an ISBN has been transmitted correctly using check digit
1- remove last digit of number
2- create a pattern of 1 and 3 under each value remaining eg:
1 6 2 0
1 3 1 3
3- multiply each value by the pattern beneath eg:
(1x1)=1
(6x3)=18
(2x1)=2
(0X3)=0
4-add all the answers together and round the total down eg:
(1+18+2+0)= 21=20
5.subtract un rounded answer by rounded eg:
21-20= 1
6. compare value obtained by check digit
what is an automatic repeat request (arq)
A set of rules used for error control during transmission. A receiving computer may request the sending computer to resend the packet if errors are detected.
Describe the ARQ
1- when data is received to receivers end the computer sends a short message called an acknowledgment, indicating weather there was any errors, (positive acknowledgment= no errors, negative acknowledgment= errors)
- if there was a negative acknowledgment, the receiving computer will request the sending computer to resend the data
- process is repeated until receiving computer receives complete package or until the time out has run out (defined fix time)
what is encryption
a type of security measure, in which a message is made unreadable to anyone without the decryption key/ algorithm
what is un encrypted text called
plain text
what is encrypted text called
cipher text
what are the two types of encryption
symmetric and asymmetric
describe symmetric encryption
A simple method of encryption where the same key is used to encypt and decrypt the data.
less safe, because of malicious user intercepts key it can decrypt message very easily
describe asymmetric encryption
A more complex method of encryption where two different keys are used to encypt and decrypt the data, a public key (used by everyone visiting a website) and a private key (receivers key used to decrypt).
more reliable compared to symmetric encryption
