Conceptual Questions: [10 points per question] 1- What is the main difference be
ID: 3741590 • Letter: C
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Conceptual Questions: [10 points per question] 1- What is the main difference between the collision-avoidance and collision-detection CSMA methods? 2- Can we use a standard reservation based method, in a system with dynamic number of users? Why? 3- What is the difference between half duplex and full duplex transmission method? 4 Explain token passing method using sequential ordering. True/False Statements [No justification is required] [5 points per question] 5- In slotted Aloha system, a user sends a packet AS SOON AS it is generated (T/F) 6- In a token passing method, a user who takes turn and has no information to send, holds the token until collecting some information to send (T/F). Token passing method is an appropriate access method for Ad-hoc sensor networks without a central controller (T/F). In reservation based method with n users, there are exactly n transmit intervals between two consecutive reservation intervals (T/F). 7- 8- Problems 9- Consider a wireless communication system with timing advance of 30us. What is the maximum acceptable 10-In a wireless system with Aloha access method, the transmission interval is T = 20ms and the probability distance of a user from the base station? Why? [10 pts of a user to generate a packet in time [t, t + T] is P.-2%. Calculate the following quantities in a system with n 5 users 140 points a) Probability of success for user #1 [5 pts] b) Probability of success for a user: pluser#1 success)+-p(user#5 success) [5 pts] c) What is the optimal pe that maximizes the success probability? [5 pts] d) What is the exact success probability in this case? 15 pts] Repeat parts (a) to (d) for slotted Aloha system (20 points). 11- Consider a system with CSMA-CD, where we use slotted Aloha (with optimal transmission probability) in the contention period. If a contention time slot is 10 pas and a transmission time slot is 1ms, what is the channel utilization rate? [20 points] 12- Consider a system with CSMA-CD, where we use slotted Aloha (with optimal transmission probability) in the contention period. The users are distributed in a circle around the base station with radius of 5 km. Contention time slot is set to the minimum acceptable value based on timing advance. The transmission time slot is set to 1ms. What is the channel utilization rate? [20 points 13- Consider a TDMA system with two users. If the total bitrate is 30kbps and the input traffic for user 1 and user 2 is respectively 12 kbps and 24kbps, calculate the total throughput of the system as well as the fairness metric (in terms of Jain index and the entropy) for the following systems. [30 points] a) Using 1 timeslot for user#1 and 1 timeslot for user#2 in a 2TS TDMA system User#1 User#2 User#1 User#2 b) Using 1 timeslot for user#1 and 2 consecutive timeslots for user#2 in a 3TS TDMA system User#1 Userez userg2 User#1 Usem user82-Explanation / Answer
Conceptual Questions:
1. CSMA is Carrier Sense Multiple access protocol.It is a protocol that controls the flow of data in the transmission media so that the data packets are not lost during transmission. The CSMA protocol comes in two forms:
CSMA CA and CSMA CD
CSMA/CDstands for Carrier Sense Multiple Access/Collision Detection Protocol. This protocol detects the collision between the data packets during transmission.When the collision is detected the protocol stops the transmission so that no more data packets are wasted.The data packet destroyed in the collision is resent to the reciever before stopping the transmission.
CSMA/CA stands for Carrier Sense Multiple Acces/Collision avoidance protocol. This protocol first senses the path where the data packet has to be sent,if the path is clear only then the protocol will trasmit the data packet.This way the collision is mostly avoided.In this protocol the lost data is not recovered or resent.
Another difference between CSMA/CD and CSMA /CA is that CSMA/CD is used in wired installations because in wired installations the collision is detected whereas CSMA/CA is used in wireless installations since it is n ot possible to detect a collision in wireless installation.
3. The main difference between half duplex and full duplex is that in half duplex the transmission between the sender and the receiver is two way but only one side can transmit at one time whereas in full duplex the transmission is also two way but both the sides can transmit simultaneously.
Half Duplex mode:
In this mode there is a two communication between the sender and the reciever but only one side can transmit at one time i.e when the one side is sending the data packet the other side has to wait for the path to get free and once the path is free then the other side will send the packet.
Full Duplex:
In this mode both the sender and the receiver transmit the data packet at the same time. No side has to wait for the path to get free, both the sides can trasmit simultenously.
4.Token passing method using sequential ordering is called token ring. In this an empty frame of size three bytes called a "token" moves around the work station in a ring toplogy. The data is transmitted sequentially from one station to another.
The transmission process is as follows:
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