Unit 2 Data Transmission & Encryption Flashcards
What is the trailer in a data packet?
The trailer has data that indicates the end of the packet and a
checksum for the destination to check it transmitted correctly
What is the payload in a data packet?
The payload is the contents that need to be sent
What is the header in a data packet?
The header contains the destination IP address, originating IP
address and the packet number so that the
correct order is restored once it arrives
What is packet switching?
As each packet may take a different route through
the network, they may arrive out of order
The destination computer or server will need to reorder the
packets into the correct order
The packet number is used to do this
What is serial transmission?
Bits are sent one signal at a time over a single wire
One bit is sent at a time
Once the bit has been received, the next bit is sent
What is parallel transmission?
In parallel transmission a number of wires are used
so that many bits may be sent at the same time
What is wrong with parallel transmission?
- Crosstalk may occur when a signal on one line
creates a disturbance in another line ( The longer a line, the more likely it is for a crosstalk to occur. - Skew
Each wire in a parallel cable has slightly
different properties. Signals therefore arrive at slightly different times
The receiver must wait until all
lines are received until the next
set of bits may be sent
Transmission needs to be
over very short distances
to reduce the problem
What are some advantages of serial transmission?
Serial cables only require one wire for the data itself
This means that far fewer wires are needed in the cable,
making it cheaper to make and smaller
This also allows for longer cables without the risks of greater
crosstalk and skew
What are the features of the USB
Universal serial bus (USB) is a serial cable that is
commonly used to connect external
devices to computers, laptops,
tablets and smartphones
The USB cable may be plugged in or
removed whilst the device is turned on
To connect older cables, such as serial mice
or keyboards and parallel printers, the
computer first needed to be turned off
What are some upsides of the USB?
USB 1 connections operate between
1.5 and 12 Mbps
Parallel cables operate at a much
slower 110 kbps
The later standard of USB 3 operates
up to 20 Gbps
Older parallel and serial cables
normally required small screws to
connect the cables
All sorts of devices could be connected
by simply installing the necessary drivers
What are some drawbacks of the USB?
USB connections should only be
5 meters in length before a
USB hub is used
The data transfer speeds are
not fast enough to use in
internal devices such as CPU
and hard drive
The transfer of data with DDR4 RAM is
up to 200 Gbps
This is around 10 times faster than USB 3
What is simplex transmission?
In simplex transmission, data travels in one
direction only
What is Half-duplex transmission?
Data is able to travel in both directions along a single
connection, but it cannot travel at the same time
What is Full duplex transmission?
In full duplex transmission, traffic is able to move in
both directions simultaneously using two cables
What are transmission errors?
When data is transmitted, errors may
be introduced due to:
Electrical interference
Power surges
Synchronisation issues
Wear and tear on the cable or connectors
These errors may cause:
Data to be lost
Data to be gained
Data to be changed
What is error checking?
Computers need methods to check for data
transmission errors caused by interference
These methods include the use of:
Parity bits
Check digits
Check sums
Echo checks and
Automatic Repeat reQuests (ARQ)
What are parity bits?
Every byte transmitted has one of its bits allocated as a parity bit
If odd parity is used then there must be an odd number of 1’s in the byte, including the parity bit
If even parity is used then there must be an even number of 1’s in the byte, including the parity bit
What are check digits?
A check digit is an additional digit at the end of a set
of other numbers designed to check for mistakes in
input or transmission
Printed books have a unique barcode with an ISBN
(International Standard Book Number)
Other products contain bar codes using formats such as UPC
(Universal Product Code)
Both codes make use of check digits to make sure
they have been scanned or entered correctly
What are checksums?
The file is run through an algorithm that produces a checksum
which it also sends
When the file arrives, the receiving computer generates the
checksum and compares it with the checksum that was sent
If the checksums don’t match, the file may have been
corrupted or altered in transmission
What is an echo check?
An echo check acts in the same way as an echo
from a wall
The data is transmitted to the receiver
The same data is then echoed back to the transmitter
The transmitter compares the data with the original. If it isn’t
the same, the data is transmitted again
What is an Automatic Repeat query(ARQ) and how is it used?
Automatic repeat requests
(ARQs) work as follows:
The sender first sends a block of data
The receiving computer then sends
back an acknowledgement
When the sender receives the
acknowledgement it sends the next
block of data
If the acknowledgement is not
received after a period of time, a
timeout occurs and the data is resent
This process continues until the
acknowledgement is received
Why is encryption needed in data transmission?
Large amounts of personal data are now stored and
transmitted on computers
Data is also stored on computers and servers on the Internet
which may be hacked
If a hacker gains access to the data, they won’t be able to
understand it if it is encrypted
What is encryption?
The purpose of encryption is to encode a file or data
into something that cannot be read or understood
What is symmetric encryption?
In symmetric encryption, a key is first shared
between the sender and receiver
This key encrypts the data before it is transmitted
The receiver uses the key to decrypt the data
