Packet Switching

Question 1

What is circuit switching

Answer 1

It is something two telephones or computers use to connect across the national network

Question 2

What does circuit switching enable you to do

Answer 2

It enables you to send digital massages across a network by setting up a physical path between the sender and receiver

Question 3

What are the disadvantages of circuit switching

Answer 3

Very inefficient - once the connection is made the line is tied up and no one else can use them

• Difficult to scale up the network to deal with millions of devices
• High bandwidth

Question 4

What is packet switching

Answer 4

It is an alternative method of sending data across a network

Question 5

What is the difference between packet switching and circuit switching

Answer 5

Unlike circuit switching where the whole message is sent in one go, witch packet switching the message is broken down into smaller parts

Question 6

How does packet switching work

Answer 6

1. The packets are given a ‘packet number’ to identify the order they are in
2. The packets will travel across the network in different directions taking the shortest route
3. When the individual packets arrive at their destination they will be reassembled back together in the correct order
4. Once all the packets have safely arrived a message will be sent to the original computer as confirmation

Question 7

What happens if a packet is missing or corrupted

Answer 7

the computer will be sent asking for that particular packet to be resent

Question 8

What 3 pieces of information does each packet contain

Answer 8

• 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

Question 9

What happens when a router receives a data packet

Answer 9

it uses a table in its memory to look up details of every other router to which it is connected. Then using IP it works out the fastest route through which send the data packets

Question 10

What are the benefits of a packet switched network

Answer 10

• They are robust - If one router fails there is another path available
• They make efficient use of connections compared to circuit switching
• The message is very resilient - If a circuit switch network goes down then the whole message does but with packet switching only the packets get lost
• Each packet carries its own error connections codes, so if a few get corrupted they can be easily fixed

Question 11

What are the disadvantages of a packet switched network

Answer 11

• The packets travel along random paths so there is no guarantee that they will arrive in a certain time period
• The packets arrive in a random order so they have to be reassembled, so if a few bits are corrupted they have to be resent in order to complete the message