2.1 - Data Transmission Flashcards
What are data packets? [1]
data sent over long distances is broken up into data packets
How much are the data packets? [1]
64Kib
What is a typical packet split into? [3]
Header, Payload, Trailer
What’s in the header? [4]
- IP address of the source device (sender)
- IP address of the destination device (receiver)
- Sequence number of the packet
- Size of the packet in bytes
Why does the header need a sequence number? [1]
So that the packets can be reassembled correctly once they reach the destination
What’s in the payload? [1]
The actual data in the packets
What’s in the trailer? [2]
Method of identifying the end of the packet
Some form of error checking (CRC)
What is CRC long form? [1]
Cyclic redundancy checks
How does CRC work? [4]
Sender adds up all the 1-bits in the payload and stores it as a hex value in the trailer
Receiver counts up all the 1-bits once received
Computer then checks if there’s the same number of 1-bits in sender and receiver
If they match then no error if they don’t match then error occurred and the packet needs to be resent
What does a router do? [1]
It receives a data packet and based on the information in the header it decides where to send it next
What is packet switching? [1]
A method of data transmission in which a message is broken up into a number of packets
What are drawbacks of packet switching? [3]
Packets can be lost and need to be resent
This method is more prone to errors with realtime streaming
There’s a delay at the destination whilst the packets are being reordered
What are nodes? [1]
They contain a router and are at each stage in the transmission
What are benefits of packet switching? [3]
No need for a single communication line
possible to overcome failed, busy or faulty lines by simply rerouting packets
Relatively easy to expand package usage
What is circuit switching? [1]
When data is transferred by making connections and travelling along a dedicated path
What are the 3 phases of circuit switching? [3]
Connection establishment between sender and receiver
Data transfer
Connection released
Why don’t the packets need packet numbers in circuit switching? [1]
Because there’s a dedicated path
What are the benefits of circuit switching? [3]
Dedicated pathway
No delay in data transmission
Predictable performance
What are the drawbacks of circuit switching? [4]
Inefficient resource utilisation (locks network resources along the path)
Prone to failures because if any part of the circuit fails the whole connection is lost
There’s a delay in the establishment of connection
It’s expensive
What is simplex data transmission? [1]
When data is sent in one direction only
What is half-duplex data transmission? [1]
When data is sent in both directions but not at the same time
What is full-duplex data transmission? [1]
When data is sent in both direction at the same time
What is serial data transmission? [1]
When data is sent one bit at a time over a single wire/channel
What is parallel data transmission? [1]
When several bits of data are sent down several channels/wires
What does it mean if data becomes skewed? [1]
The data arrives unsynchronised and bits arrive out of order
What does USB stand for? [1]
Universal Serial Bus
What is a USB?
A form of serial data transmission and is the most common type of input and output port
What are the four cables inside of USB? [4]
Red, White, Green, Black
What is the red cable for? [1]
It’s a power cable
What is the white cable for? [1]
For sending data
What is the green cable for? [1]
For receiving data
What is the black cable for? [1]
For earthing
What type of data transmission does USB allow? [2]
Both half-duplex and full-duplex
How are the types of USB ports differentiated? [1]
They have different numbers of pins
