14.2 - Circuit Switching and Packet Switching

Question 1

Describe Packet Switching

Answer 1

• A large message is divided into a group of smaller chunks called packets
• Packet has header and payload
• Header contains a source IP, destination IP and sequence number
• Each packet is dispatched individually, and may travel along different routes
• Packets may arrive out of order, and are reasembled into origional message at destination
• If packets are missing, re-transmission request is sent

Question 2

Pros of packet switching

Answer 2

• Accuracy, allows accurate deliver of message
• Completness, missing packets can easily be detected and re-transmission request can be sent
• Resilience, if network changes, router can detect this and send packets another way

Question 3

Cons of packet switching

Answer 3

• Unsuitable for real time transmission
• Time taken to reasemble packets at destination
• Requires complex protocl
• Time delay to correct errors, and re-request missing packets

Question 4

Describe circuit switching

Answer 4

• A dedicated cricuit is established at the start of the communication
• Between the sender and receiver
• All data is transmitted along the same route
• This lasts for the duration of the call/transmission
• Data is transfered using the entire bandwidth

Question 5

Pros of circuit switching

Answer 5

• Reduced latency
• Little delay in sending and receiving packets, as error checking is not required
• Allows 2 way real time transmission
• Full bandwidth available

Question 6

Cons of packet switching

Answer 6

• Bandwidth not available to others
• Need extra time to set up circuit before communication
• Failure of single route means failure of entire transmission
• Less secure
• Alternative route not available without restarting whole conversation

Question 7

Purpose of packet header

Answer 7

• To store data
• Ensures packet reaches correct data
• Stores IP address, IP destination, and packet number

Question 8

Function of router in packet switching

Answer 8

• Examines packet header
• Reads destination IP
• Has acces to routting table, which has the status of routes
• Decides the next hop
• Sends packet to next hop