6. Match the description with the associated random access protocol. 7. A link-l

Question

6. Match the description with the associated random access protocol.

7. A link-layer address is called a
a. LAN address.
b. physical address.
c. MAC address.
d. All of the above.

8. Both ARP query and response packets have the same format.
True or False

9. Both ARP query and response packets are sent within a broadcast frame.
True or False

1. Fully decentralized a. CSMA/CD 2. Nodes are synchronized b. ALOHA 3. Listen before transmitting c. CSMA 4. Stops transmitting if interference is detected d. Slotted ALOHA

Explanation / Answer

6.

(a) Fully decentralized ------------------> ALOHA

In pure ALOHA, the stations transmit frames whenever they have data to send. When two or more stations transmit simultaneously, there is a collision and the frames are destroyed. In the ideal case, whenever any station transmits a frame, it expects the acknowledgement from the receiver. If the acknowledgement is not received within the specified time, the station assumes that the frame (or acknowledgement) has been destroyed. If the frame is destroyed because of the collision the station waits for a random amount of time and sends it again. This waiting time must be random otherwise same frames will collide again and again. Therefore pure ALOHA dictates that when time-out period passes, each station must wait for a random amount of time before resending its frame. This randomness will help avoid more collisions. Since this synchronization regarding sending is independently handled by each machine, the system is fully decentralized.

(b) Nodes are synchronized -------> Slotted ALOHA

(c) Listen before Transmitting ---------> CSMA

Message is sent only if the channel is sensed idle.

(d) Stops transmitting if interference is detected -----------> CSMA/CD

Station checks whether another station is transmitting. If not, it sends the first bit of information. If no collision is detected, it continues to send the other bits of information while continuously checking whether a collision has been detected. If a collision is detected, it calculates a random amount of time to wait and start the process again. If the maximal amount of attempts is reached, then no transmission is possible and it is aborted.

7. A link-layer address is variously called a LAN address, a physical address, or a MAC address. Thus, option (d) is the correct answer.

8. True.  

Both the ARP request and ARP reply packets use the same format.

9. False.

All ARP request packets are transmitted with the Ethernet broadcast address so that all hosts in the network will receive the request. For the response, the sending node knows the adapter address to which the response should be sent, so there is no need to send a broadcast frame and thus the ARP response is sent to a specific destination address.

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