02 - Packet Switching and Routers

 1. Packet switching is…

  a method of grouping data transmitted over a digital network into packets

  a method of transferring data from primary to secondary storage

  the use of telephone cables to send data

  an international postal service

 2. What does each packet contain?

  a header and a payload

  a front and back end

  a banner and a body

  an engine and a carriage

 3. Some packets may also have a trailer to detect transmission errors.



 4. The header includes:
1. The postal address of the sender
2. The IP address of the sender
3. The IP address of the recipient
4. The protocol 
5. The algorithm for the fastest route
6. The packet number 

  1, 2, 4, 5 and 6

  2, 3, 4 and 6

  2, 4 and 6

  1, 3, 5 and 6

 5. Older telephone networks use circuit switching. What does this mean?

  They used valve technology

  Calls had to be manually connected by a human operator

  Calls used direct reserved lines between telephones

  The network could transmit sound but not data

 6. Why is packet switching more efficient than circuit switching?

  Because bandwidth is wasted when no data is sent on a reserved line

  Because the signals travel faster using packet switching

  Because packet switching is more reliable

  Because routes are shortened using packet switching

 7. Packets can be sent along completely different routes and reassembled by the recipient.



 8. What devices forward packets from one network to another?





 9. When would a gateway be needed?

  If the networks use different protocols

  If there is an error in the packet

  If the networks are in different countries

  If the router is overloaded

 10. Every device that can be connected to a network has a unique MAC address. MAC stands for…

  Media Access Control

  Main Access Computer

  Memory Assisted Communication

  Mobile Area Connection

 11. Packet switching is the method by which the internet works, it features …………………………..between devices over a shared network.

  delivery of packets of data

  delivery of binary sequences in the form of ASCII code

  delivery of physical cabled connections with hard coded bits

  None of the above

 12. To get from one device to another the _________ will have to travel through network adapters, switches, routers and other network nodes.

  internet sequences

  data packets

  ASCII codes


 13. If you play computer games online you might have heard the term latency (or lag), this is ….
People with low latency tend to do better at games as their machines are more responsive!

  the size x 256 of the data packet sent each time you click 'send'

  None of the above

  the time taken to send data from one device to another.

  the length of each data packet sent across the network

 14. To see the time it takes to send a message using packet switching you can use the ping command on the command prompt.



 15. Packet switching defines just one set route for data to be sent by so any disruption in the network cannot be circumnavigated by re-routing



 16. The following are the steps involved in packet switching. Fill in the blanks
Packet Switching Steps
Data split into chunks (packets)
Each packet has a from address, to address and payload (data chunk)
If data requires multiple chunks then the order of each packet is noted
Packets sent onto the network, moving from router to router taking different paths
Each packet's journey time can therefore differ.
Message sent from recipient to sender indicating that the message has been received
If no confirmation message, sender transmits data again

  Once packets arrive they are left in the same order as they arrived

  Once packets arrive they are re-ordered

  Once packets arrive they are assigned an index and sent back

  Once packets arrive they are delivered in alphabetical order

 17. For the following packets (Green, Blue, Red), assuming each step from router to router takes an equal time. Answer the question below.
What order will the packets arrive at their destination? How do we make sure that the packets are read in the correct order?

  Red, Green, Blue

  Blue, Blue, Green (Red will not arrive)

  Blue, Green, Red

  Green, Red, Blue

 18. What happens if a packet gets permanently lost on the way to a host?

  It will be deleted instantly and a message sent to the host

  It will be sent back to the ISP which holds all lost messages until called for

  It will be lost forever

  The packet will be resent until a confirmation message is returned from the recipient

 19. What happens if a router on the network fails? How will the packets get to their destination?

  The packets will be destroyed on arrival for security reasons

  The packets will be stopped and sent to the ISP for safe keeping (taking up to two weeks to arrive)

  The packets will be re-routed around the failed node

  The packets will be stopped and deleted

 20. With packet switching, every request that gets sent over the internet is sent with the sender's IP address attached



 21. Circuit switching was the alternative to packet switching where there was one dedicated line. The advantages of packet switching include:

  makes efficient use of the network

  there are no tied up lines and packets can easily get round broken bits of network

  As customers increase, the network only has to expand slowly compared to circuit switching

  All of the above

 22. Disadvantages of packet switching include:

  It isn't always very good for very small packages (e.g if 600 bytes long) then two packets of 512 bytes are needed plus the address info

  For time critical information the time lag in re-ordering etc. can be an issue

  It takes time to put back the data package in order and this time changes each time.

  All of the above are valid disadvantages

 23. Read the following excerpt which discusses the future of packet switching and big questions. Define the term 'packet'
There are many questions that big companies are asking regarding the future of packet switching and the internet. It’s a bit like the old First and Second class post. You pay extra for first  class delivery so that your letter will get to its destination faster.

It is possible that people would pay more for their broadband connections if they could guarantee that their data would be sent and retrieved faster than someone else's data.
It is worth noting that this technology is possible, but it means the internet could be divided up into 'motorways' or 'slow country lanes', causing another form of 'digital divide'. This is a sensitive matter and will require great wisdom. 

  All of the above are valid definitions of a data packet

  An analogy of the packet concept is the postal letter: the header is like the envelope, and the payload is the entire content inside the envelope

  A packet is also called a datagram, a segment, a block, a cell or a frame, depending on the protocol used for the transmission of data.

  A packet is a formatted unit of data sent by a packet switched network

 24. Packets can be defined as 'data' that is sent over a network in manageable amounts



 25. Data packets are usually less than 128 KB and contain details of the destination computer.