Networks - Circuit/Packet Switching

Question 1

What is packet switching?

Answer 1

A method of communication.

Data is communicated using packets across a network, via the most efficient route (which can vary for each packet).

Question 2

Packet switching advantages

Answer 2

Multiple routes can be used between devices. If one path breaks, another can be used.

Multiple methods to ensure data arrives intact. For example, checksums/cyclic redundancy checks

Packets can be transferred over very large networks to allow communication globally.

Question 3

Packet switching disadvantages

Answer 3

Time is spent deconstructing and reconstructing the data packets.

Must wait for all packets to arrive before data can be received.

Question 4

What is circuit switching?

Answer 4

A direct link is created between two devices. This direct link is maintained for the duration of the entire conversation between devices.

Question 5

What does circuit switching require?

Answer 5

The two devices to transfer and receive data at the same rate.

Question 6

Circuit Switching Advantages

Answer 6

Data arrives in a logical order which
results in a quicker reconstruction of the
data.

Enables two users to hold a call without
delay in speech.

Question 7

Circuit Switching Disadvantages

Answer 7

Bandwidth is wasted during periods of time in which no data is being sent.

Devices must transfer and receive data at the same rate.

Using switches means electrical interference may be produced which can corrupt or destroy data.

Ties up sections of the network which cannot be used by others data until transmission has been completed

Question 8

What is the difference between circuit switching and packet switching?

Answer 8

Packet switching involves breaking the message into smaller parts (packets), as opposed to sending a whole message in one go.

Question 9

What is the TCP/IP Stack

Answer 9

A stack of networking protocols. It sets out the rules for handling packets at each stage in their journey.

Question 10

With the TCP protocol, once all of the packets have ______ an acknowledgement message is sent to the ______ ______ as confirmation.

Answer 10

With the TCP protocol, once all of the packets have ARRIVED an acknowledgement message is sent to the ORIGINAL COMPUTER as confirmation.

Question 11

What happens with the TCP protocol if a packet is missing or corrupted?

Answer 11

The receiver sends a request for that particular packet to be resent.

Question 12

What three components do packets consist of?

Answer 12

Trailer (end of packet flag, checksum)
Payload (data)
Header

Question 13

What is an ideal payload size for packets?

Answer 13

500-1500 bytes.

Question 14

Why are packets kept small?

Answer 14

To ensure individual packets don’t take excessive time to transfer, preventing other packets from moving.

Question 15

What does the header contain?

Answer 15

Senders IP
- For replies to be sent appropriately

Recipients IP
- For appropriate direction across the network

Packet number + Overall number of packets
- To assist in reassembling the data

Time To Live (TTL) or hop limit

Question 16

What does the trailer contain?

Answer 16

Error checking components that verify the data received in the payload hasn’t been corrupted on transfer.

Question 17

What techniques does the trailer use for the receiving host to check the data?

Answer 17

Checksums or Cyclical Redundancy Checks (CRCs)

• The same checksum is recalculated at the destination end
• If it doesn’t match, data is corrupted, new data requested.

Question 18

What is the internet (in terms of packet switching)?

Answer 18

One vast packet switched network consisting of billions of nodes and connections.