187 Questions
What is the purpose of the MAC (Medium Access Control) sublayer?
To coordinate transmission of active nodes
Which of the following is the main task of Multiple Access Protocols?
Minimizing collisions to utilize bandwidth
What is the definition of throughput?
The amount of data moved successfully in a given time period
What is the problem with multiple nodes transmitting at the same time on a shared link?
The link bandwidth is wasted during collision
What is the purpose of Random Access (or contention) Protocols?
To minimize collisions and utilize bandwidth
What is the role of the Link Layer Control (LLC) in the data link layer?
Responsible for error and flow control
What is the purpose of Medium Access Control (MAC) Protocols?
To minimize collisions and utilize bandwidth
Which method for controlled access provides in order access to a shared medium so that every station has a chance to transfer?
Reservation
Which access method in polling uses a primary station and secondary stations for data exchanges?
Centralized polling
Which access method in polling does not have a primary and secondary station?
Distributed polling
Which access method in polling can be done in order or based on a predetermined order?
Distributed polling
Which network protocol uses a token to control access to the medium?
Token Passing
Which multiple-access method divides the transmission medium into separate frequency bands?
FDMA
Which multiple-access method shares the bandwidth capacity in time between multiple stations?
TDMA
Which multiple-access method carries all transmissions simultaneously on one channel?
CDMA
Which multiple-access method assigns a transmission channel between a sender and a receiver for a certain amount of time?
TDMA
Which of the following statements is true about the ALOHA protocol?
ALOHA is a multiple access protocol
What is the purpose of random retransmission time in the ALOHA scheme?
To reduce the likelihood of additional collisions between stations
In the Pure ALOHA protocol, what is the time out equal to?
The maximum round-trip propagation delay
Which of the following is true about Slotted ALOHA?
Time is divided into slots equal to a frame transmission time
What is the maximum throughput in Pure ALOHA?
18%
Which of the following is a disadvantage of ALOHA protocols?
Low channel utilization
What is the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
To reduce the possibility of collision
Which protocol reduces the possibility of collisions like non-persistent and reduces channel idle time like 1-persistent?
p-persistent CSMA
What should a station do in the 1-persistent CSMA protocol if the medium is busy?
Continuously listen until medium becomes idle
What is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
n/p
Which CSMA protocol requires a station to wait a random amount of time (backoff) if the medium is busy?
Non-persistent CSMA
What is the main advantage of using CSMA/CD over other CSMA protocols?
Ability to detect collisions
What happens if a collision occurs during transmission in CSMA/CD?
All of the above
Which protocol is widely used for bus topology LANs?
CSMA/CD
Which of the following is true about the ALOHA protocol?
ALOHA protocol was developed in the early 1970s to connect computers situated on different Hawaiian islands.
Which multiple-access method divides the transmission medium into separate frequency bands?
FDMA
Which multiple-access method carries all transmissions simultaneously on one channel?
CSMA/CA
What is the purpose of the MAC (Medium Access Control) sublayer?
To control access to the medium and handle data link layer protocols.
What is the maximum throughput in Pure ALOHA?
18%
What is the purpose of random retransmission time in the ALOHA scheme?
To spread out the retransmission and reduce the likelihood of additional collisions between stations.
What is the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
To detect the presence of other transmissions.
Which of the following is the purpose of the MAC (Medium Access Control) sublayer?
To minimize collisions and utilize the bandwidth
What is the main advantage of using CSMA/CD over other CSMA protocols?
It reduces the possibility of collisions like non-persistent and reduces channel idle time like 1-persistent
What is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
n=2
Which multiple-access method divides the transmission medium into separate frequency bands?
FDMA (Frequency Division Multiple Access)
What is the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
To determine when a station can use the link (medium)
Which of the following is a disadvantage of ALOHA protocols?
High collision probability
Which access method in polling can be done in order or based on a predetermined order?
Round Robin
According to the text, which CSMA protocol reduces the possibility of collisions like non-persistent and reduces channel idle time like 1-persistent?
p-persistent CSMA
According to the text, what is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
n x p
According to the text, what is the purpose of CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
To detect and handle collisions
According to the text, what should a station do in the 1-persistent CSMA protocol if the medium is busy?
Continuously listen until medium becomes idle
According to the text, what is the purpose of the jam signal in CSMA/CD?
To notify other stations of collision
According to the text, what is the purpose of Random Access (or contention) Protocols?
To reduce the possibility of collisions
According to the text, what is the main advantage of using CSMA/CD over other CSMA protocols?
Reduced channel idle time
Which multiple-access method assigns a transmission channel between a sender and a receiver for a certain amount of time?
TDMA
What is the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
To detect collisions on the network
Which multiple-access method shares the bandwidth capacity in time between multiple stations?
TDMA
Which access method in polling uses a primary station and secondary stations for data exchanges?
Polling
What is the maximum throughput in Pure ALOHA?
0.36
Which multiple-access method carries all transmissions simultaneously on one channel?
CDMA
Which protocol reduces the possibility of collisions like non-persistent and reduces channel idle time like 1-persistent?
CSMA/CA
What is the purpose of Medium Access Control (MAC) Protocols?
To control access to the transmission medium
What is the problem with multiple nodes transmitting at the same time on a shared link?
Collision
Which multiple-access method allows multiple stations to transmit at the same time, resulting in collisions and wasted bandwidth?
Random access
Which of the following terms refers to the amount of time it takes for a signal to travel from the sender to the receiver?
Propagation delay
Which multiple-access method divides the transmission medium into separate frequency bands?
FDMA
What is the main task of Multiple Access Control (MAC) protocols?
To minimize collisions
Which protocol reduces the possibility of collisions by waiting for the medium to be idle before transmitting, and reduces channel idle time by transmitting immediately after the medium becomes idle?
p-persistent CSMA
What is the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
To sense the presence of other stations
Which access method in polling can be done in order or based on a predetermined order?
Round-robin polling
Which of the following is true about the ALOHA protocol?
ALOHA protocol requires stations to use a random retransmission time.
Which multiple-access method carries all transmissions simultaneously on one channel?
ALOHA
What is the maximum throughput in Pure ALOHA?
18%
What is the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
To listen to the medium before transmitting to avoid collisions.
What is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
2
What is the purpose of Random Access (or contention) Protocols?
To allow stations to transmit at any time without coordination.
What is the problem with multiple nodes transmitting at the same time on a shared link?
Low channel utilization
Which of the following is true about FDMA (Frequency Division Multiple Access)?
Each station transmits continuously on the assigned frequency band
Which of the following is true about TDMA (Time Division Multiple Access)?
The entire bandwidth capacity is shared in time between multiple stations
Which of the following is true about CDMA (Code Division Multiple Access)?
One channel carries all transmissions simultaneously
Which access method in polling uses a known polling order list based on some protocol?
Distributed polling
What is the purpose of the listen state in a token-passing network?
To check the destination address of arriving bits
Which of the following is a restriction of CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
Packet transmission time should be longer than the maximum propagation delay
What is the purpose of controlled access or scheduling in medium access control protocols?
To provide fair access to the shared medium
What is the purpose of the reservation interval in the reservation access method?
To make reservations in minislots
What is the purpose of the poll frame in centralized polling?
To ask if a secondary station has data to send
Which of the following is true about CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
CSMA/CD reduces the possibility of collisions by continuously listening to the medium until it becomes idle before transmitting.
What is the purpose of the jam signal in CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
To ensure that the collision signal will stay until detected by the furthest station.
What is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
n x p < 1
What is the purpose of carrier sense in the CSMA (Carrier Sense Multiple Access) protocol?
To ensure that the medium is idle before transmitting.
What is the main advantage of using CSMA/CD (Carrier Sense Multiple Access with Collision Detection) over other CSMA protocols?
CSMA/CD reduces the possibility of collisions like non-persistent CSMA.
What is the purpose of controlled access or scheduling in medium access control protocols?
To allocate the medium to different stations based on a predetermined order.
What is the main task of Multiple Access Protocols?
To allow multiple stations to share a common communication channel.
Which CSMA protocol requires a station to wait a random amount of time (backoff) if the medium is busy?
Non-persistent CSMA
What is the purpose of the CSMA/CD protocol?
To detect and handle collisions in the network
What is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
n x p < 1
What is the purpose of random retransmission time in the ALOHA scheme?
To reduce collisions in the network
Which multiple-access method divides the transmission medium into separate frequency bands?
Frequency Division Multiple Access (FDMA)
Which access method in polling can be done in order or based on a predetermined order?
Round Robin
Which of the following is a disadvantage of ALOHA protocols?
High collision probability
Which of the following is true about the ALOHA protocol?
Frames are transmitted at completely random times
What is the maximum throughput in Pure ALOHA?
18%
What is the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
To listen to the medium to see if another transmission is in progress
What is the main advantage of using CSMA/CD (Carrier Sense Multiple Access with Collision Detection) over other CSMA protocols?
It can detect and handle collisions
What is the purpose of Random Access (or contention) Protocols?
To allow multiple stations to access a shared medium
Which access method in polling can be done in order or based on a predetermined order?
Round-robin polling
Which of the following is a disadvantage of ALOHA protocols?
Many collisions can occur when multiple nodes want to transmit
According to the text, what is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
1/n
What is the purpose of the jam signal in CSMA/CD?
To notify other stations of a collision
What is the problem with multiple nodes transmitting at the same time on a shared link?
Collisions occur
Which of the following is true about CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
It uses random delays to reduce collisions
Which multiple-access method allows multiple stations to transmit at the same time, resulting in collisions and wasted bandwidth?
ALOHA
Which of the following is true about the ALOHA protocol?
It allows multiple stations to transmit at the same time
What is the purpose of carrier sense in the CSMA (Carrier Sense Multiple Access) protocol?
To reduce collisions
Which multiple-access method divides the transmission medium into separate time slots for each station to transmit?
TDMA
What is the purpose of the jam sequence in the CSMA/CD protocol?
To indicate a collision has occurred
Which access method in polling uses a known polling order list based on some protocol?
Token Passing
Which multiple-access method assigns a transmission channel between a sender and a receiver for a certain amount of time?
TDMA
What is the purpose of carrier sense in the CSMA protocol?
To synchronize the transmission between stations
What is the purpose of the poll frame in centralized polling?
To check if a station has data to send
What is the purpose of the MAC (Medium Access Control) sublayer?
To manage access to the medium
Which multiple-access method carries all transmissions simultaneously on one channel?
CDMA
What happens if a collision occurs during transmission in the CSMA/CD protocol?
The transmission is aborted and a jam sequence is sent
Which of the following is true about the purpose of the MAC (Medium Access Control) sublayer?
It coordinates the access of multiple sending/receiving nodes to the shared link.
What is the main advantage of using TDMA (Time Division Multiple Access) over other multiple-access methods?
It allows multiple stations to share the bandwidth capacity in time.
Which of the following is true about the purpose of carrier sense in the Carrier Sense Multiple Access (CSMA) protocol?
It reduces the possibility of collisions by waiting for the medium to be idle before transmitting.
What is the maximum throughput in Pure ALOHA?
$ rac{1}{2e}$
Which of the following is a disadvantage of ALOHA protocols?
They do not provide in-order access to a shared medium for every station.
Which protocol reduces the possibility of collisions by waiting for the medium to be idle before transmitting, and reduces channel idle time by transmitting immediately after the medium becomes idle?
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)
What is the purpose of Random Access (or contention) Protocols?
To minimize collisions and maximize bandwidth utilization
According to the text, what is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
n < 1/p
What is the purpose of the jam sequence in the CSMA/CD protocol?
To notify other stations of a collision
Which of the following is a disadvantage of ALOHA protocols?
High collision probability
What should a station do in the 1-persistent CSMA protocol if the medium is busy?
Listen continuously until the medium becomes idle
What is the maximum throughput in Pure ALOHA?
0.1
What is the purpose of carrier sense in the CSMA (Carrier Sense Multiple Access) protocol?
To detect collisions
What is the main advantage of using TDMA (Time Division Multiple Access) over other multiple-access methods?
Higher throughput
What is the purpose of the jam sequence in the CSMA/CD protocol?
To detect collisions during transmission
According to the text, what is the purpose of Random Access (or contention) Protocols?
To ensure fair access to the transmission medium
Which of the following is a disadvantage of ALOHA protocols?
High probability of collisions
What is the main task of Multiple Access Control (MAC) protocols?
To ensure fair access to the transmission medium
Which multiple-access method carries all transmissions simultaneously on one channel?
FDMA
What happens if a collision occurs during transmission in CSMA/CD?
The transmitting station stops transmission and waits for a random time before retransmitting
Which multiple-access method divides the transmission medium into separate frequency bands?
FDMA
Which of the following is true about the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol?
It reduces the possibility of collisions by waiting for the medium to be idle before transmitting.
What is the purpose of the jam signal in CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
To indicate that a collision has occurred and all stations should stop transmitting.
What is the main advantage of using CSMA/CD (Carrier Sense Multiple Access with Collision Detection) over other CSMA protocols?
It reduces channel idle time by transmitting immediately after the medium becomes idle.
What is the purpose of Random Access (or contention) Protocols?
To minimize collisions and efficiently utilize the bandwidth in a shared link.
What is the maximum number of stations (n) for which stability is ensured in p-persistent CSMA?
n
What is the purpose of the reservation interval in the reservation access method?
To reserve a transmission channel for a station to transmit during a specific time interval.
What is the problem with multiple nodes transmitting at the same time on a shared link?
The link bandwidth is wasted during collision.
Which of the following is true about CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
CSMA/CD requires a station to wait a random amount of time (backoff) if the medium is busy.
What is the purpose of the jam signal in CSMA/CD?
To indicate that a collision has occurred and all stations should stop transmitting.
Which multiple-access method divides the transmission medium into separate frequency bands?
FDMA (Frequency Division Multiple Access)
Which multiple-access method shares the bandwidth capacity in time between multiple stations?
TDMA (Time Division Multiple Access)
Which multiple-access method allows multiple stations to transmit at the same time, resulting in collisions and wasted bandwidth?
CSMA/CD
What is the main advantage of using TDMA (Time Division Multiple Access) over other multiple-access methods?
TDMA assigns a fixed sending frequency to a transmission channel.
Which method for controlled access provides in order access to a shared medium so that every station has a chance to transfer?
Reservation
According to the text, what is the purpose of CSMA/CD (Carrier Sense Multiple Access with Collision Detection)?
To provide in order access to a shared medium.
Which of the following is a disadvantage of ALOHA protocols?
ALOHA protocols have a high probability of collisions.
True or false: The MAC Layer is responsible for error and flow control.
False
True or false: The main task of Multiple Access Protocols is to maximize collisions.
False
True or false: Random Access Protocols assign control over one station to another.
False
True or false: Throughput is the amount of time it takes for the signal to travel from the sender to the receiver.
False
True or false: Random Access Protocols do not assign control to any station.
True
True or false: CSMA/CD reduces collisions and idle time on the channel.
True
True or false: The MAC sublayer is responsible for determining when a station can use the link.
True
True or false: The ALOHA protocol was developed at the University of Hawaii in the early 1970s to connect computers situated on different Hawaiian islands.
True
True or false: In Pure ALOHA, frames are transmitted at completely random times.
True
True or false: Slotted ALOHA divides time into slots equal to a frame transmission time.
True
True or false: The maximum throughput in Pure ALOHA occurs at G = 1/2 which is 18%.
True
True or false: Carrier Sense Multiple Access (CSMA) protocol requires a station to wait for the medium to be clear before transmitting.
True
True or false: The maximum number of stations (n) for which stability is ensured in p-persistent CSMA is determined by the formula: n ≤ (1/G) - 1.
True
True or false: The purpose of carrier sense in the CSMA protocol is to reduce the possibility of collision.
True
True or false: Collision can only happen when more than one station begin transmitting within a short time period?
True
True or false: The longer the propagation delay, the better the performance of the protocol?
False
True or false: Non-persistent CSMA is a protocol where a station transmits immediately if the medium is idle and waits a random amount of time if the medium is busy?
True
True or false: 1-persistent CSMA reduces the probability of collisions compared to non-persistent CSMA?
False
True or false: P-persistent CSMA reduces the possibility of collisions like non-persistent and reduces channel idle time like 1-persistent?
True
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs?
True
True or false: If a collision has occurred, the channel is unstable until colliding packets have been fully transmitted in CSMA/CD?
False
True or false: FDMA assigns a frequency to a transmission channel permanently.
True
True or false: TDMA assigns a fixed sending frequency to a transmission channel between a sender and a receiver for a certain amount of time.
True
True or false: CDMA carries all transmissions simultaneously on one channel.
True
True or false: Reservation access method organizes transmissions into variable length cycles.
True
True or false: Polling can be done in order (Round-Robin) or based on a predetermined order.
True
True or false: Token-Passing network has two states for station interface: listen state and transmit state.
True
True or false: Channelization is a multiple-access method that shares the available bandwidth of a link in time, frequency, or through code.
True
True or false: FDMA and TDMA are examples of frequency-division multiple access methods.
True
True or false: CDMA uses specific codes to recover data for desired stations.
True
Study Notes
Multiple Access Control (MAC) Layer
- The data link layer is divided into two sublayers: Link Layer Control (LLC) and Medium Access Control (MAC)
- The MAC sublayer is responsible for error and flow control, framing, and MAC addressing
- Multiple Access Control (MAC) protocols coordinate the access of multiple sending/receiving nodes to a shared link
Problem of Multiple Access
- When two or more nodes transmit at the same time, their frames will collide, wasting link bandwidth
- Solution: MAC protocols minimize collisions to utilize bandwidth by determining when a station can use the link, what a station should do when the link is busy, and what a station should do when involved in a collision
Throughput and Propagation Delay
- Throughput: the amount of data moved successfully from one place to another in a given time period
- Propagation delay: the time it takes for the head of a signal to travel from the sender to the receiver
Random Access Protocols
- ALOHA: a random access scheme developed at the University of Hawaii in the early 1970s
- Pure ALOHA:
- Frames are transmitted at completely random times
- A station can transmit at any time
- If no acknowledgment is received, the sender assumes the frame was destroyed and resends it after a random amount of time
- Maximum throughput is 18% at G = 1/2
- Slotted ALOHA:
- Time is divided into slots equal to the frame transmission time
- A station can transmit only at the beginning of a slot
- Maximum throughput is 37% at G = 1
Carrier Sense Multiple Access (CSMA)
- A user wishing to transmit first listens to the medium to see if another transmission is in progress
- If the medium is idle, the station transmits; otherwise, it waits
- Vulnerable time for CSMA is the maximum propagation time
Types of CSMA Protocols
- Non-Persistent CSMA:
- A station with frames to be sent senses the medium
- If the medium is idle, the station transmits; otherwise, it waits for a random amount of time and repeats
- 1-Persistent CSMA:
- A station with frames to be sent senses the medium
- If the medium is idle, the station transmits immediately; otherwise, it continuously listens until the medium is idle
- P-Persistent CSMA:
- A station with frames to be sent senses the medium
- If the medium is idle, the station transmits with probability p; otherwise, it waits one time unit and repeats
CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
- If a collision occurs, the sender stops transmission and transmits a jam signal to notify other stations
- After sending the jam signal, the station waits for a random amount of time and then retransmits the frame
- CSMA/CD is widely used in bus topology LANs (IEEE 802.3, Ethernet)
Controlled Access or Scheduling
- Provides in-order access to the shared medium so that every station has a chance to transfer (fair protocol)
- Eliminates collisions completely
- Three methods for controlled access: Reservation, Polling, and Token Passing
Reservation Access Method
- Stations take turns transmitting a single frame at a full rate
- Transmissions are organized into variable-length cycles
- Each cycle begins with a reservation interval that consists of N minislots
- Stations make reservations in their own minislot and then transmit their data frames
Polling
- Stations take turns accessing the medium
- Two models: Centralized and Distributed Polling
- Centralized Polling:
- One device is assigned as the primary station and the others as secondary stations
- All data exchanges are done through the primary
- When the primary has a frame to send, it sends a select frame that includes the address of the intended secondary
- Distributed Polling:
- No primary and secondary stations
- Stations have a known polling order list made based on some protocol
- The station with the highest priority will have the access right first, then it passes the access right to the next station
Token-Passing Network
- Stations interface is in two states: Listen and Transmit
- Station captures a special frame called a free token and transmits its frames
- Sending station is responsible for reinserting the free token into the ring medium and removing the transmitted frame from the medium
Channelization
- FDMA (Frequency Division Multiple Access): assigns a frequency to a transmission channel permanently
- TDMA (Time Division Multiple Access): assigns a fixed sending frequency to a transmission channel between a sender and a receiver for a certain amount of time
- CDMA (Code Division Multiple Access): one channel carries all transmissions simultaneously, each station codes its data signal with a specific code before transmission, and receivers use these codes to recover the data for the desired station
Test your knowledge on different CSMA protocols and their vulnerability to collisions. Learn about the impact of propagation time and how it affects the performance of these protocols.
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