3.3: Data Packets & Switching
Eduqas / WJEC
What is a data packet?
When sending data across a network, files are broken down into smaller parts called data packets.
Whole files are too large to transfer as one unit so data packets allow data to be transferred across a network quickly.
Each packet of data is redirected by routers across networks until it arrives at its destination. Data packets may split up and use alternative routes to reach the destination address.
When all the packets have arrived at the destination address the data is reassembled back into the original file.
Contents of a Data Packet
Data packets contain six distinct pieces of data which are used to redirect the packets towards the destination address.
Packet Switching vs. Circuit Switching
The key difference is that a circuit-switched network sends data along the same route. A packet-switched network sends data packets along different routes.
With a packet-switched network the data is split into packets.
The data packets are transmitted over a network and may take different routes to its destination.
When all the packets have arrived the data is reassembled.
The Internet is an example of a packet-switching network.
Advantages of Packet Switching:
Transmission is more secure as it is harder for a hacker to intercept complete data because it can take different routes.
If a network device fails the data packets can take an alternative route.
Data packets can be sent efficiently and individually across less busy routes.
Disadvantages of Packet Switching:
Reassembling the data takes longer because packets may arrive out of order.
It is less reliable than circuit switching as some data packets may not reach the destination (this is called packet loss).
When data is transmitted over a circuit-switched network all of the data takes the same route to the destination address in one continuous stream.
The data is quickly reassembled at the destination because it is already in the correct order.
The old telephone system is an example of a circuit-switched network.
Advantages of Circuit Switching:
Reassembling the data is quick because the packets arrive in the order that they were sent.
It is more reliable than packet-switching because data is sent in one continuous stream.
The transmission is fast and should encounter fewer errors - once the connection has been securely established.
Disadvantages of Circuit Switching:
Less secure as hackers could intercept the data and more easily access the data as it all takes the same route.
Establishing a connection takes time to set up.
If any device fails on the route then the whole connection breaks and data transfer will be incomplete.
3.3 - Data Packets & Switching:
1. Draw the data packet diagram and label all 6 pieces of information. 
2a. Describe how packet switching works. 
2b. Describe the advantages of packet switching. 
2c. Describe the disadvantages of packet switching. 
3a. Describe how circuit switching works. 
3b. Describe the advantages of circuit switching. 
3c. Describe the disadvantages of circuit switching.