150 Questions
Pure ALOHA allows stations to transmit frames at completely random times.
True
Slotted ALOHA divides time into slots equal to a frame transmission time.
True
In Pure ALOHA, the maximum throughput occurs at G = 1/2, which is 18%.
True
Slotted ALOHA has a higher maximum throughput than Pure ALOHA.
True
In Pure ALOHA, the vulnerable time is equal to 2 times the frame transmission time.
True
Carrier Sense Multiple Access (CSMA) eliminates the possibility of collision.
False
In Pure ALOHA, the channel utilization is the percentage of transmitted frames that arrive successfully.
True
True or false: The MAC layer is responsible for error and flow control.
False
True or false: The MAC layer is responsible for framing and MAC address.
True
True or false: The main task of Multiple Access Protocols is to maximize collisions.
False
True or false: Throughput is the amount of time it takes for the head of the signal to travel from the sender to the receiver.
False
True or false: Random Access Protocols assign control over one station to another.
False
True or false: Random Access Protocols are also known as contention protocols.
True
True or false: No station is superior to another station in Random Access Protocols.
True
True or false: Collision can only happen when more than one station begin transmitting within a short time (the propagation time period)
True
True or false: The longer the propagation delay, the worse the performance of the protocol
True
True or false: Non-persistent CSMA is a protocol where a station with frames to be sent will immediately transmit if the medium is idle
True
True or false: 1-persistent CSMA is a protocol where a station continuously listens to the medium until it becomes idle, then transmits immediately with probability 1
True
True or false: P-persistent CSMA is a protocol where time is divided into slots and a station will transmit with probability (p) or wait one time unit (slot) with probability (1 - p)
True
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs
True
True or false: CSMA/CD protocol uses one of the CSMA persistence algorithms for transmission and if a collision is detected, the station will abort transmission, transmit a jam signal, and backoff for a random amount of time
True
True or false: CSMA/CD is a fair protocol that provides in-order access to the shared medium and eliminates collisions completely.
False
True or false: Reservation access method in controlled access allows stations to take turns transmitting a single frame at a full rate.
True
True or false: In centralized polling, one device is assigned as the primary station and all data exchanges are done through the primary.
True
True or false: Distributed polling does not have a primary and secondary station distinction.
True
True or false: Token-passing network uses a special frame called free token to control access to the medium.
True
True or false: FDMA assigns a frequency to a transmission channel and each station transmits continuously on the assigned band.
True
True or false: TDMA assigns the 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 and each station codes its data signal by a specific code before transmission.
True
True or false: In CSMA/CD, the packet transmission time should be at least as long as the time needed to detect a collision.
True
True or false: The MAC layer is responsible for error and flow control.
False
True or false: Random Access Protocols assign control over one station to another.
False
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs.
True
True or false: TDMA assigns the fixed sending frequency to a transmission channel between a sender and a receiver for a certain amount of time.
True
True or false: FDMA assigns a frequency to a transmission channel and each station transmits continuously on the assigned band.
True
True or false: CDMA carries all transmissions simultaneously on one channel and each station codes its data signal by a specific code before transmission.
True
True or false: Slotted ALOHA divides time into slots equal to a frame transmission time.
True
True or false: ALOHA is a random access scheme 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: Pure ALOHA has a higher maximum throughput than Slotted ALOHA?
False
True or false: Carrier Sense Multiple Access (CSMA) eliminates the possibility of collision?
False
True or false: The maximum throughput occurs at G = 1 which is 37% in Slotted ALOHA?
True
True or false: The channel utilization is the percentage of transmitted frames that arrive successfully in Pure ALOHA?
False
True or false: Collision can only happen when more than one station begin transmitting within a short time (the propagation time period)
True
True or false: CSMA/CD protocol uses one of the CSMA persistence algorithms for transmission and if a collision is detected, the station will abort transmission, transmit a jam signal, and backoff for a random amount of time
True
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs
True
True or false: Non-persistent CSMA is a protocol where a station with frames to be sent will immediately transmit if the medium is idle
False
True or false: 1-persistent CSMA is a protocol where a station continuously listens to the medium until it becomes idle, then transmits immediately with probability 1
True
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: In Pure ALOHA, the maximum throughput occurs at G = 1/2, which is 18%
False
True or false: In reservation access method, each cycle begins with a reservation interval that consists of N minislots, one minislot for each of the N stations.
True
True or false: In centralized polling, one device is assigned as the primary station and all data exchanges are done through the primary.
True
True or false: Token-passing network uses a special frame called free token to control access to the medium.
True
True or false: FDMA assigns a frequency to a transmission channel and each station transmits continuously on the assigned band.
True
True or false: CSMA/CD is a fair protocol that provides in-order access to the shared medium and eliminates collisions completely.
False
True or false: TDMA assigns the 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 and each station codes its data signal by a specific code before transmission.
True
True or false: In CSMA/CD, the packet transmission time should be at least as long as the time needed to detect a collision.
True
True or false: Random Access Protocols assign control over one station to another.
False
True or false: The purpose of the MAC layer is to minimize collisions and utilize the bandwidth efficiently.
True
True or false: Random Access Protocols do not assign control over one station to another.
True
True or false: TDMA assigns a fixed sending frequency to a transmission channel for a certain amount of time.
True
True or false: CDMA carries all transmissions simultaneously on one channel and each station codes its data signal by a specific code before transmission.
True
True or false: CSMA/CD is widely used for bus topology LANs.
True
True or false: Pure ALOHA allows stations to transmit frames at completely random times.
True
True or false: In CSMA/CD, the packet transmission time should be at least as long as the time needed to detect a collision.
True
True or false: ALOHA is a random access scheme developed at the University of Hawaii in the early 1970s to connect computers situated on different Hawaiian islands?
True
True or false: Pure ALOHA has a higher maximum throughput than Slotted ALOHA?
False
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs?
True
True or false: The maximum throughput occurs at G = 1/2, which is 18% in Slotted ALOHA?
False
True or false: In Pure ALOHA, frames are transmitted at completely random times?
True
True or false: In CSMA/CD, the packet transmission time should be at least as long as the time needed to detect a collision?
True
True or false: CDMA carries all transmissions simultaneously on one channel and each station codes its data signal by a specific code before transmission?
True
True or false: Collision can only happen when more than one station begins transmitting within a short time (the propagation time period)
True
True or false: The longer the propagation delay, the worse the performance of the protocol because of the above case.
True
True or false: Non-persistent CSMA is a protocol where a station with frames to be sent should sense the medium: 1. If the medium is idle, transmit; otherwise, go to 2 2. If the medium is busy, (backoff) wait a random amount of time and repeat 1
True
True or false: If two or more stations become ready at the same time in 1-persistent CSMA, a collision is guaranteed
True
True or false: P-persistent CSMA is a protocol where time is divided into slots and a station will transmit with probability (p) or wait one time unit (slot) with probability (1-p)
True
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs (IEEE 802.3, Ethernet)
True
True or false: CSMA/CD protocol uses one of the CSMA persistence algorithms for transmission and if a collision is detected, the station will abort transmission, transmit a jam signal, and backoff for a random amount of time
True
True or false: CSMA/CD is a fair protocol that provides in-order access to the shared medium and eliminates collisions completely.
False
True or false: Token-passing network uses a special frame called free token to control access to the medium.
True
True or false: FDMA assigns a frequency to a transmission channel and each station transmits continuously on the assigned band.
True
True or false: TDMA assigns the 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 and each station codes its data signal by a specific code before transmission.
True
True or false: In Pure ALOHA, the vulnerable time is equal to 2 times the frame transmission time.
True
True or false: In reservation access method, each cycle begins with a reservation interval that consists of N minislots, one minislot for each of the N stations.
True
True or false: Non-persistent CSMA is a protocol where a station with frames to be sent will immediately transmit if the medium is idle.
True
True or false: Random Access Protocols are also known as contention protocols.
True
True or false: MAC protocols are responsible for error and flow control at the data link layer?
False
True or false: The main task of MAC protocols is to maximize collisions?
False
True or false: FDMA assigns a frequency to a transmission channel and each station transmits continuously on the assigned band?
True
True or false: CSMA/CD is widely used for bus topology LANs?
True
True or false: Random Access Protocols assign control over one station to another?
False
True or false: CDMA carries all transmissions simultaneously on one channel and each station codes its data signal by a specific code before transmission?
True
True or false: Slotted ALOHA has a higher maximum throughput than Pure ALOHA?
True
True or false: ALOHA is a random access scheme developed at the University of Hawaii in the early 1970s to connect computers situated on different Hawaiian islands?
True
True or false: Pure ALOHA allows stations to transmit frames 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 occurs at G = 1/2, which is 18%.
False
True or false: CDMA carries all transmissions simultaneously on one channel and each station codes its data signal by a specific code before transmission.
True
True or false: CSMA/CD is a fair protocol that provides in-order access to the shared medium and eliminates collisions completely.
False
True or false: In Pure ALOHA, the maximum throughput occurs at G = 1/2, which is 18%.
True
True or false: Collision can only happen when more than one station begins transmitting within a short time (the propagation time period)
True
True or false: The longer the propagation delay, the worse the performance of the protocol because of the above case.
True
True or false: Non-persistent CSMA is a protocol where a station with frames to be sent will immediately transmit if the medium is idle.
True
True or false: 1-persistent CSMA is a protocol where a station continuously listens to the medium until it becomes idle, then transmits immediately with probability 1
True
True or false: P-persistent CSMA is a protocol where time is divided into slots, and each station listens to the medium and transmits with probability p or waits with probability (1-p)
True
True or false: CSMA/CD is widely used for bus topology LANs.
True
True or false: CSMA/CD is a fair protocol that provides in-order access to the shared medium and eliminates collisions completely.
False
True or false: Reservation access method in controlled access provides each station with a fixed time slot to transmit its data frame?
False
True or false: In centralized polling, all data exchanges are done through the primary station?
True
True or false: Token passing network has stations in two states: listen state and transmit state?
True
True or false: FDMA assigns a frequency to a transmission channel and each station transmits continuously on the assigned band?
True
True or false: TDMA assigns the 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 and each station codes its data signal by a specific code before transmission?
True
True or false: Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations?
True
True or false: In CSMA/CD, the packet transmission time should be at least as long as the time needed to detect a collision?
True
True or false: Random Access Protocols are also known as contention protocols?
True
True or false: The MAC layer is responsible for error and flow control?
False
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs?
True
True or false: Random Access Protocols assign control over one station to another?
False
True or false: Pure ALOHA allows stations to transmit frames at completely random times?
True
True or false: FDMA assigns a frequency to a transmission channel and each station transmits continuously on the assigned band?
True
True or false: In Pure ALOHA, the maximum throughput occurs at G = 1/2, which is 18%?
False
True or false: P-persistent CSMA is a protocol where time is divided into slots, and each station listens to the medium and transmits with probability p or waits with probability (1-p)?
True
True or false: ALOHA is a random access scheme 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, the vulnerable time is equal to 2 times the frame transmission time.
True
True or false: Slotted ALOHA divides time into slots equal to a frame transmission time.
True
True or false: The channel utilization is the percentage of transmitted frames that arrive successfully in Pure ALOHA?
True
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs
True
True or false: Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations?
True
True or false: The MAC layer is responsible for error and flow control.
True
True or false: Collision can only happen when more than one station begins transmitting within a short time (the propagation time period)
True
True or false: Non-persistent CSMA is a protocol where a station with frames to be sent will immediately transmit if the medium is idle.
False
True or false: P-persistent CSMA is a protocol where time is divided into slots and a station will transmit with probability (p) or wait one time unit (slot) with probability (1 - p)
True
True or false: CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is widely used for bus topology LANs
True
True or false: CSMA/CD protocol uses one of the CSMA persistence algorithms for transmission and if a collision is detected, the station will abort transmission, transmit a jam signal, and backoff for a random amount of time
True
True or false: In CSMA/CD, the packet transmission time should be at least as long as the time needed to detect a collision
True
True or false: CSMA/CD is a fair protocol that provides in-order access to the shared medium and eliminates collisions completely
False
True or false: CSMA/CD eliminates collision completely?
False
True or false: Reservation access method in controlled access allows stations to take turns transmitting a single frame at a full rate?
True
True or false: Token-passing network uses a special frame called free token to control access to the medium?
True
True or false: CDMA carries all transmissions simultaneously on one channel and each station codes its data signal by a specific code before transmission?
True
True or false: Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations?
True
True or false: Non-persistent CSMA is a protocol where a station with frames to be sent will immediately transmit if the medium is idle?
True
True or false: In TDMA, the entire bandwidth capacity is a single channel with its capacity shared in time between M stations?
True
True or false: Distributed polling does not have a primary and secondary station distinction?
True
True or false: Slotted ALOHA has a higher maximum throughput than Pure ALOHA?
True
Study Notes
Multiple Access Control (MAC) Layer
- A broadcast link in LAN consists of multiple sending and receiving nodes connected to a single shared link.
- Data link layer is divided into two sublayers: Link Layer Control (LLC) and MAC Control, responsible for error and flow control, framing, MAC address, and Multiple Access Control.
Multiple Access Problem
- When two or more nodes transmit at the same time, their frames will collide and the link bandwidth is wasted during collision.
- Solution: A protocol is needed to coordinate the transmission of active nodes, known as Multiple Access Control (MAC) Protocols.
Characteristics of Multiple Access Protocols
- Minimize collisions to utilize bandwidth:
- Determine when a station can use the link (medium).
- Determine what a station should do when the link is busy.
- Determine what a station should do when it is involved in a collision.
Types of Multiple Access Protocols
- Random Access (or contention) Protocols:
- No station is superior to another station and none is assigned control over another.
- A station with a frame to be transmitted can use the link directly based on a procedure defined by the protocol.
ALOHA Random Access Scheme
- Developed at the University of Hawaii in the early 1970s to connect computers on different Hawaiian islands.
- Computers transmit on the same radio channel whenever they have a packet to transmit.
- Packet transmission will collide, but these can be treated as transmission errors, and recovery can take place by retransmission.
Pure ALOHA
- All frames from any station are of fixed length (L bits).
- Stations transmit at equal transmission time (all stations produce frames with equal frame lengths).
- A station that has data can transmit at any time.
- After transmitting a frame, the sender waits for an acknowledgment for an amount of time (time out) equal to the maximum round-trip propagation delay.
Slotted ALOHA
- Time is divided into slots equal to a frame transmission time (Tfr).
- A station can transmit at the beginning of a slot only.
- If a station misses the beginning of a slot, it has to wait until the beginning of the next time slot.
- A central clock or station informs all stations about the start of each slot.
Advantage and Disadvantage of ALOHA Protocols
- Advantage:
- A node that has frames to be transmitted can transmit continuously at the full rate of channel (R bps) if it is the only node with frames.
- Simple to be implemented.
- No master station is needed to control the medium.
- Disadvantage:
- If (M) nodes want to transmit, many collisions can occur and the rate allocated for each node will not be on average R/M bps, causing low channel utilization.
Carrier Sense Multiple Access (CSMA)
- A user wishing to transmit first listens to the medium to see if another transmission is in progress (carrier sense).
- Based on the fact that in LAN propagation time is very small.
- A station with frames to be sent should sense the medium for the presence of another transmission (carrier) before it starts its own transmission.
Types of CSMA Protocols
-
- Non-Persistent CSMA
-
- 1-Persistent CSMA
-
- p-Persistent CSMA### Types of CSMA Protocols
-
Non-Persistent CSMA
- A station with frames to send senses the medium
- If medium is idle, transmit; otherwise, wait a random amount of time and repeat
- Performance: random delays reduce probability of collisions, but bandwidth is wasted if waiting time is large
-
1-Persistent CSMA
- Station wishing to transmit listens to the medium
- If medium is idle, transmit immediately; if medium is busy, continuously listen until medium becomes idle
- Performance: 1-persistent stations are selfish, guaranteeing collision if two or more stations become ready at the same time
-
P-Persistent CSMA
- Time is divided into slots, typically equal to maximum propagation delay
- Station wishing to transmit listens to the medium
- If medium is idle, transmit with probability (p) or wait one time unit (slot) with probability (1 – p)
- Performance: reduces possibility of collisions like non-persistent, reduces channel idle time like 1-persistent
CSMA/CD (Collision Detection)
-
Inefficiency of CSMA
- If a collision has occurred, the channel is unstable until colliding packets have been fully transmitted
-
CSMA/CD Overcomes Inefficiency
- While transmitting, the sender is listening to the medium for collisions
- Sender stops transmission if collision has occurred, reducing channel waste
- Widely used for bus topology LANs (IEEE 802.3, Ethernet)
-
CSMA/CD Protocol
- Use one of the CSMA persistence algorithms (non-persistent, 1-persistent, p-persistent) for transmission
- If a collision is detected, abort transmission, transmit a jam signal, and backoff (wait) for a random amount of time
- Then, transmit the frame again
-
Restrictions of CSMA/CD
- Packet transmission time should be at least as long as the time needed to detect a collision
- Otherwise, CSMA/CD does not have an advantage over CSMA
Controlled Access or Scheduling
- Provides in order access to shared medium
- Eliminates collision completely
-
Three methods for controlled access:
-
Reservation Access Method
- Stations take turns transmitting a single frame at a full rate (R) bps
- Transmissions are organized into variable length cycles
- Each cycle begins with a reservation interval that consists of (N) minislots
-
Polling
- Stations take turns accessing the medium
- Two models: Centralized and Distributed polling
-
Token-Passing network
- Station Interface is in two states: Listen and Transmit
- Station captures a special frame called free token and transmits its frames
-
Reservation Access Method
Channelization
- Multiple-access method
- Available bandwidth of a link is shared in time, frequency, or through code, between different stations
-
Three channelization protocols:
-
FDMA (Frequency Division Multiple Access)
- Transmission medium is divided into M separate frequency bands
- Each station transmits continuously on the assigned band
-
TDMA (Time Division Multiple Access)
- The entire bandwidth capacity is a single channel with its capacity shared in time between M stations
- A node must always wait for its turn until its slot time arrives
-
CDMA (Code Division Multiple Access)
- One channel carries all transmissions simultaneously
- Each station codes its data signal by a specific code before transmission### Multiple Access Control (MAC) Layer
-
FDMA (Frequency Division Multiple Access)
- Multiple access control (MAC) layer is a sublayer of the data link layer
- It is responsible for coordinating the access of multiple sending/receiving nodes to the shared link
- MAC protocols are used to minimize collisions and utilize bandwidth
Types of Multiple Access Control Protocols
- Fixed Access:
- FDMA (Frequency Division Multiple Access)
- TDMA (Time Division Multiple Access)
- CDMA (Code Division Multiple Access)
- Random Access:
- ALOHA (developed at the University of Hawaii in the 1970s)
- CSMA (Carrier Sense Multiple Access)
- CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
FDMA (Frequency Division Multiple Access)
- Transmission medium is divided into M separate frequency bands
- Each station transmits continuously on the assigned band
- A node is limited to an average rate even when it is the only node with frames to send
TDMA (Time Division Multiple Access)
- The entire bandwidth capacity is a single channel with its capacity shared in time between M stations
- A node must always wait for its turn until its slot time arrives even when it is the only node with frames to send
CDMA (Code Division Multiple Access)
- One channel carries all transmissions simultaneously
- Each station codes its data signal by a specific code before transmission
- The stations' receivers use these codes to recover the data for the desired station
ALOHA (Random Access Protocol)
- Developed at the University of Hawaii in the 1970s
- Stations transmit on the same radio channel whenever they have a packet to transmit
- Packet transmission will collide, but these can be treated as transmission errors and recovery can take place by retransmission
- ALOHA scheme requires stations to use a random retransmission time to reduce the likelihood of additional collisions
Pure ALOHA
- All frames from any station are of fixed length (L bits)
- Stations transmit at equal transmission time (all stations produce frames with equal frame lengths)
- A station that has data can transmit at any time
- After transmitting a frame, the sender waits for an acknowledgment for an amount of time (time out) equal to the maximum round-trip propagation delay
Slotted ALOHA
- Time is divided into slots equal to a frame transmission time (Tfr)
- A station can transmit at the beginning of a slot only
- If a station misses the beginning of a slot, it has to wait until the beginning of the next time slot
CSMA (Carrier Sense Multiple Access)
- A user wishing to transmit first listens to the medium to see if another transmission is in progress (carrier sense)
- Based on the fact that in LAN propagation time is very small
- A station with frames to be sent, should sense the medium for the presence of another transmission (carrier) before it starts its own transmission
CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
- While transmitting, the sender is listening to the medium for collisions
- If a collision is detected, the sender stops transmission and transmits a jam signal to notify other stations of the collision
- After sending the jam signal, the sender waits for a random amount of time and then transmits the frame again
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
- Token Passing
Test your knowledge on CSMA protocols and collision avoidance techniques with this quiz. Learn about the vulnerable time for CSMA, the impact of propagation delay on protocol performance, and various types of CSMA protocols.
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