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Questions and Answers
What is the formula for calculating the throughput of Pure ALOHA?
What is the formula for calculating the throughput of Pure ALOHA?
- S = G ^ 2 × e^(-2G)
- S = G ^ 3 × e^(-G)
- S = G × e^(-G)
- S = G × e^(-2G) (correct)
When does the maximum throughput occur in Pure ALOHA?
When does the maximum throughput occur in Pure ALOHA?
- When G = 1
- When G = 0.25
- When G = 0.5 (correct)
- When G = 2
How does the vulnerable time in Pure ALOHA compare to Slotted ALOHA?
How does the vulnerable time in Pure ALOHA compare to Slotted ALOHA?
- Pure ALOHA has no vulnerable time
- Pure ALOHA and Slotted ALOHA have the same vulnerable time
- Pure ALOHA vulnerable time is half the vulnerable time in Slotted ALOHA
- Pure ALOHA vulnerable time is twice the vulnerable time in Slotted ALOHA (correct)
What is the formula for calculating the throughput of Slotted ALOHA?
What is the formula for calculating the throughput of Slotted ALOHA?
When does the maximum throughput occur in Slotted ALOHA?
When does the maximum throughput occur in Slotted ALOHA?
What is the maximum throughput achieved with a value of G = 1?
What is the maximum throughput achieved with a value of G = 1?
In the context of Aloha protocols, which one has an efficiency of 0.2?
In the context of Aloha protocols, which one has an efficiency of 0.2?
Which Aloha protocol has a success rate of 0.1?
Which Aloha protocol has a success rate of 0.1?
What is the efficiency of Pure Aloha protocol?
What is the efficiency of Pure Aloha protocol?
In the context of Aloha protocols, which one has a throughput of 0.3?
In the context of Aloha protocols, which one has a throughput of 0.3?
Which protocol should you use to avoid definite collisions according to the text?
Which protocol should you use to avoid definite collisions according to the text?
What is the vulnerable time in Pure ALOHA protocol if the frame transmission time is $T_{fr}$ seconds?
What is the vulnerable time in Pure ALOHA protocol if the frame transmission time is $T_{fr}$ seconds?
What is the maximum throughput achievable in Pure ALOHA when $G = 0.5$?
What is the maximum throughput achievable in Pure ALOHA when $G = 0.5$?
In Pure ALOHA, what does the sender do if it does not receive an acknowledgment after transmitting a frame?
In Pure ALOHA, what does the sender do if it does not receive an acknowledgment after transmitting a frame?
What does the station do if it fails to receive an ACK after repeated transmissions in Pure ALOHA protocol?
What does the station do if it fails to receive an ACK after repeated transmissions in Pure ALOHA protocol?
How does the throughput formula for Pure ALOHA differ from that of Slotted ALOHA?
How does the throughput formula for Pure ALOHA differ from that of Slotted ALOHA?
If two stations are widely separated, how does the maximum propagation delay relate to the vulnerable time in Pure ALOHA protocol?
If two stations are widely separated, how does the maximum propagation delay relate to the vulnerable time in Pure ALOHA protocol?
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Study Notes
ALOHA Protocols
- In pure ALOHA, the average transmission time for a frame is Tfr, and the average number of frames generated by the system during one frame transmission time is G.
- The maximum throughput (Smax) of pure ALOHA is 0.184, occurring at G=0.5, which corresponds to a total arrival rate of one frame per vulnerable period.
- The throughput (S) for pure ALOHA is S = G × e^(-2G), with a maximum throughput Smax = 0.184 when G=0.5.
Slotted ALOHA
- Slotted ALOHA was invented to improve the efficiency of pure ALOHA.
- The throughput for slotted ALOHA is S = G × e^(-G), with a maximum throughput Smax = 0.368 when G=1.
- The vulnerable time for slotted ALOHA is Tfr.
Carrier Sense Multiple Access (CSMA)
- CSMA avoids transmissions that are definite to cause collisions by sensing the medium for the presence of another transmission before starting its own transmission.
- The vulnerable time for CSMA is the maximum propagation time.
- The longer the propagation delay, the worse the performance of the protocol.
Types of CSMA Protocols
- Non-Persistent CSMA, 1-Persistent CSMA, and other protocols determine what a station should do when the medium is idle or busy.
- A station that has data can transmit at any time, but after transmitting a frame, it waits for an acknowledgment for an amount of time equal to the maximum round-trip propagation delay.
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