Network Communication

Question 1

What is circuit switching?

Answer 1

Circuit switching is a method of sending data across a network using a physical path between the sender and receiver using wires of fibre optic cables to transmit the message. the path remains open throughout the communication and is only released for use by others once the message is complete.

Question 2

Name three problems for using circuit switching

Answer 2

• It is difficult to scale up to deal with millions of devices
• Every connection has to be capable of supporting the maximum bandwidth that may be required
• It is inefficient, as 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

Question 3

Explain how packet switching works

Answer 3

The TCP breaks down the message into data packets. Each packet is given a packet number, return address and destination address. The IP sends the data packets individually through the network by the quickest route available. When all the packets arrive at their destination, they need to be reassembles in the correct order. Once all the packets have arrived safely a message will be sent to the original computer as confirmation. If a packet is missing or corrupt, the message will instead be sent asking for that particular packet to be resent.

Question 4

What three pieces of information are contained in the packet header?

Answer 4

• Return Address (to say where the packet originated from)
• Destination Address (To tell the packet where it has to go)
• Sequence Number (So individual data packets can be reassembled in the correct order once they have safely arrived at their destination)

Question 5

How does a router determine the best route which to send the data packets?

Answer 5

The router uses a table in it’s memory to look up details of every other router to which it is connected. It uses a set of rules called the Internet Protocol to find the fastest route to send the data packet.

Question 6

What are four benefits of packet switched networks?

Answer 6

• They are robust as if a router fails or goes offline, there usually many paths for packets to travel
• The connection is only required for a brief amount of time unlike circuit switching where it is held until the message is transmitted
• If a packet is lost or corrupt only that packet needs to be resent unlike circuit switching where the whole message has to be resent
• Each packet carried it’s own error correction codes, so if a few bits are corrupted, they can often be corrected

Question 7

What are the two disadvantages of packet switched networks?

Answer 7

• Latency can occur if a data packet is missing or corrupt as there is no guarantee that they will arrive within a certain time period
• The packets arrive in a random order, so they have to be re-assembled