17 Questions
What is the formula for calculating the throughput of Pure ALOHA?
S = G × e^(-2G)
When does the maximum throughput occur in Pure ALOHA?
When G = 0.5
How does the vulnerable time in Pure ALOHA compare to Slotted ALOHA?
Pure ALOHA vulnerable time is twice the vulnerable time in Slotted ALOHA
What is the formula for calculating the throughput of Slotted ALOHA?
S = G × e^(-G)
When does the maximum throughput occur in Slotted ALOHA?
When G = 1
What is the maximum throughput achieved with a value of G = 1?
0.368
In the context of Aloha protocols, which one has an efficiency of 0.2?
Slotted Aloha
Which Aloha protocol has a success rate of 0.1?
Slotted Aloha
What is the efficiency of Pure Aloha protocol?
1.0
In the context of Aloha protocols, which one has a throughput of 0.3?
Pure Aloha
Which protocol should you use to avoid definite collisions according to the text?
Carrier Sense Multiple Access (CSMA)
What is the vulnerable time in Pure ALOHA protocol if the frame transmission time is $T_{fr}$ seconds?
$2T_{fr}$ seconds
What is the maximum throughput achievable in Pure ALOHA when $G = 0.5$?
0.184
In Pure ALOHA, what does the sender do if it does not receive an acknowledgment after transmitting a frame?
Assume that the frame or ACK has been destroyed and resend it after a random amount of time
What does the station do if it fails to receive an ACK after repeated transmissions in Pure ALOHA protocol?
Gives up
How does the throughput formula for Pure ALOHA differ from that of Slotted ALOHA?
The throughput formula for Pure ALOHA includes exponential decay, while Slotted ALOHA does not.
If two stations are widely separated, how does the maximum propagation delay relate to the vulnerable time in Pure ALOHA protocol?
The maximum propagation delay is twice the vulnerable time
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.
Test your understanding of calculating the throughput in Pure and Slotted ALOHA protocols. Questions may involve determining the maximum throughput, average transmission time, and the number of frames generated by the system. Prepare to apply the formulas S = G × e^(-2G) and Smax = 0.184 when G = 0.5.
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