Packet Switching Flashcards
Give an example of a use of circuit switching
Telephone System in UK
What does circuit switching enable?
Enables you to send digital messages across a network by setting up a physical path between the sender and receiver
How are circuit switching connections set up?
Using wires or fibre optic cable and is set up prior to transmission of the message
Why is circuit switching very inefficient?
Once the connection is made, the line is tied up and no one else can use them, even if no data is passing between them
Give another big disadvantage with circuit switching
Difficult to scale up the network to deal with millions of devices
What does every connection have to be capable of in circuit switching?
Supporting the maximum bandwidth required
What is packet switching an alternative method of?
Sending data across a network
What is the difference between packet switching and circuit switching?
Unlike circuit switching where the whole message is sent in one go, with packet switching the message is broken down into smaller parts (data packets) and these parts are sent individually through the network
What is each packet give in packet switching?
A ‘packet number’ to identify the order they are in
How do packets travel across a network?
By taking the shortest route possible
What happens once the individual packets arrive at their destination in packet switching?
They are reassembled back together in the correct order
What happens if a packet is missing or corrupted?
The message will instead be sent asking for that particular packet to be resent
What are the 2 protocols used in packet switching?
Ethernet
TCP/IP
What does each packet contain?
A header which contains 3 important pieces of information
What are the 3 pieces of information that the header of a packet contains?
A source or return address to say where the packet originated from
A destination address to tell the packet where it has to go
A sequence number so that the individual data packets can be reassembled in the correct order once they have all safely arrived at their destination
What is preamble?
Is data that is attached to the front of a data packet to prime the receiving hardware that a data packet is about to arrive
What check is done when a packet is received?
An Error Check
What calculation does an error check involve?
‘Check sum number’
What is the Internet?
One vast packet switched network consisting of billions of nodes and connections
What are 4 advantages with packed switching?
They are robust
They make efficient use of connections
The message is very resilient
Each packet carries its own error correction codes
What are 2 disadvantages with packet switching?
The packets travel along random paths, so there is no guarantee that they will arrive within a certain time period (delay called ‘Latency’)
The packets arrive in random order, so they have to be re-assembled
