Data Link Layer Problem Sheet - Faculty of Science & Technology

This problem sheet covers various topics related to the Data Link layer, including its role, constituent parts of MAC address, ARP cache, and more. It also includes questions related to protocols like Ethernet, Token Ring, and Wi-Fi. The sheet provides detailed answers to each question, making it a valuable resource for students studying computer networks.

Faculty of Science & Technology
Topic 4 – Problem sheet
Q1. Which of the following best describes the role of the Data Link layer:
(Choose 1)
(iii) It provides communication between locally networked devices
Q2. Which of the following statements about the Data Link layer are incorrect:
(Choose the one or more incorrect statements)
(i) The Data Link layer provides multiplexing of multiple upper layer conversations to the
physical media
(ii) The Data Link uses the IP address for all communications.
Q3. Define the following Data Link acronyms:
LLC: The LLC stands for the logical link control. The LLC is the Upper sub layer of the
of the data link layer in the OSI model.
MAC: The MAC stands for Media Access Control. The MAC is one of the sub layers of
the Data Link Layer.
Q4. Describe the main role of the Data Link LLC.
The main role of the data link LLC is to deal with the errors in the transmission and to provide
network layer interface.
Q5. The LLC is sometimes described as providing a multiplexed service to upper layer protocols.
Describe what this statement means and try to give an example of this in action.
The logical link control is the sub layer that is upper in the data link layer. The sub layer of the
LLC provide the mechanism of the multiplexing that provide the service to the protocols that
are in the upper layer.
Example of this action is when the LLC provide the services to the network layer.
Q6. What is the main role of the Media Access Control component of the Data Link Layer?
The MAC sub layers main role is to move the data packets from one card of interface to the
another interface card via a channel that is shared.
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Q7. Describe why routers require at least 2 network cards.
The routers required two at least network card because if the one network card fails then the
another network card will used as a back up.
[ 1 mark ]
Q8. How many binary bits constitute a MAC address?
The MAC address consists of 48bits binary digits.
[ 1 mark ]
Q9. Describe the two constituent parts of a MAC address.
The two part of the MAC address are one is the unique identifier and the second one is the
character combined address.
[ 1 mark ]
Q10. What Windows command will display the MAC address of your computers Ethernet network
interface card?
First need to open RUN . then have to open the cmd on the run then open command prompt.
Then type ipconfig into the command prompt that will show the setting of the network card, the
Mac address will be there under the physical address and IP address.
[ 1 mark ]
Q11. What Linux command will display the MAC address of your computers Ethernet network
interface card?
First open the RUN text box then type cmd on it to open the command window. At the window just
type ipconfig /all then under the etherned adaptor wireless network connection the MAC will be
located.
[ 1 mark ]
Q12. Network cards are said to be smart devices.
Justify this statement.
The network card does not need any middle ware device on the hosted device. That’s why the
network card is also called as the network smart cards
[ 1 mark ]
Q13. Describe the process that leads to the detection of corrupted frame at the Data Link layer.
[ 2 marks ]
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To detect the error on the data link layer it is needed to know what type of errors can be
generated. Three types of errors may occur like single bit error, multiple bit error and burst error.
There are many types of process by that the error are checked like the parity check method, and
cyclic redundancy check method.
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Q14. An Ethernet frame can contain each of the following:
CRC 7
Source MAC address 4
FTP header 6
IP header 2
TCP header 1
Destination MAC address 3
Protocol Type 5
Place the numbers 1 to 7 beside each part to show its order within the frame. Number 1 should
indicate the first field in the frame.
[ 2 marks for all correct ]
Q15. How many bytes constitute the Source MAC address in an Ethernet frame?
6 bytes are there in the source MAC address in an Ethernet frame. [ 1 mark ]
Q16. How many Hexadecimal digits are required to specify an Ethernet broadcast address?
6 hexadecimal digit is needed to specify an Ethernet broadcast address.
Write that address in the space below.
01:00:0C:CC:CC:CC
[ 2 marks ]
Q17. The following protocols can be categorised as either Controlled access or contention based
access. Specify the category of each protocol.
FDDI : Controlled access
Token Ring : Controlled access
WiFi : Contention based
Ethernet : Contention based
[ 2 marks ]
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Q18. Describe how each of the following work:
The CSMA/CD protocol of Etherenet : detects the collision in the Ethernet network and
after that transmits a jam signal as reuired.
The CSMA/CA protocol used in Wi-Fi : used in the wi fi stations to avoid the collisions
on the 802.11 wireless lan. Before sending the data a request is send.
Token Ring: the token ring network is connected to the star or the ring topology. Only
one host has the ability to send the data.
[ 4 marks ]
Q19. Describe when entries are added and removed from the ARP cache.
[ 2 marks ]
The new entry is added to the ERP when an ip address is successfully mapped in the MAC address.
An entry removed from the ERP after the time out period that is pre-determined.
Q20. As a Data Link frame moves through an internetwork the Ethernet frame header is modified at
each step.
Describe why this must happen at each router.
[ 2 marks ]
Q21. The number of entries in the ARP cache changes with time. Describe the events that lead to
the addition of entries to the cache and events that lead to the removal of ARP cache entries.
You discussion should also describe how a ping to a remote address (eg. www.google.com)
will affect the arp cache and why.
[ 2 marks ]
Q22. Describe how to generate an ARP request and reply from your Linux Lite machine.
[ 1 mark ]
Q23. Generate and capture an ARP request and associated reply.
From these packets determine the following:
The contents of the Target MAC address field in the ARP request.
The contents of the Target MAC address field in the ARP reply.
The contents of the Senders MAC address field in the ARP reply.
[ 1 mark ]
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Q24. If your computer determines the destination address of a network packet is to a remote
network. What does the Data Link layer software do with that packet?
[ 1 mark ]
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