Flashcards
244 L10
Flashcards do conjunto (10)
- 1What is the difference between contention and collision in MAC sublayer?Contention - Devices contending to access a given medium.
Collision - two devices may attempt to simultaneously transmit. - 2What are some of the advantages of slotted ALOHA in comparison with pure ALOHA protocol?Max T time wasted instead of 2T
Higher success rate - 3In a CSMA/CD network with a data rates of 10^7 bits, the maximum distance between two stations is 5000 m, and the signal propagation speed is 2 * 10^8 m/s. What should be the minimum frame size for the collision detection to work efficiently? Explain why.Minimum frame size = B*(2L/P)
(2(5000)/2e8)*10^7 = 500bits - 4Explain the following medium access schemes: CSMA, non-persistent CSMA, p-persistent CSMA, CSMA/CDHigh Success rates
CSMA: Carrier Sense Multiple Access
Checks medium to see if busy .If not transmit.
Non-persistent CSMA
If busy, wait a random amount of time, then sense again. Reduces collisions & network efficiency.
p-Persistent CSMA
If busy, continuously sense until idle.
Transmit with a probability of p.
CSMA/CD
CSMA with collision detection. - 5What are the differences between pure ALOHA protocol and slotted ALOHA protocol?Slotted ALOHA waits until the start of a timeslot before sending whereas pure ALOHA will send immediately.
Collisions & time reduced for slotted ALOHA. - 6What are the drawbacks of ALOHA protocols in comparison with CSMA?Doesn’t reduce collisions
Poor channel utilization
CSMA has a much higher success rate - 7What are the advantages of CSMA In comparison with the ALOHA protocol?CSMA checks the medium is free before sending = no collisions
- 8Discuss the differences between persistent CSMA and non-persistent CSMANon - persistent CSMA - wait a random amount of time then “sense” for the medium again.
Persistent CSMA- If the medium is not idle, sense continuously. - 9What is CSMA/CA? List three strategies used in CSMA/CA for reducing collisionsCSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) technique in which collisions are avoided before they occur.
Interframe Space
Contention Window
Acknowledgement - 10Why cannot Wireless Lans use CSMA/CD for medium access control?May only transmit or receive therefore cannot sense for collisions
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- FlashCards sobre 244 L10, criado por samuelfoxnz em 26-10-2015.
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