L23. What are different approaches for Medium Access Control? Flashcards
What is Medium Access Control?
Medium Access Control (MAC) is a sublayer of the Link Layer that manages the protocols for accessing the physical transmission medium.
What is the role of MAC?
To ensure efficient, fair, and collision-free communication between devices in a network.
What are the four approaches to MAC?
- Random access protocols - provide immediate, unscheduled access to the communication medium, which can lead to potential collisions.
- Controlled access protocols - offer scheduled, collision-free access by managing transmissions through methods like polling or token passing.
- Channelization protocols - prevent collisions by dividing transmission resources such as frequency, time, or codes
- Hybrid approaches - combine features from various methods to optimize performance
Name examples of random access protocols
Pure Aloha, Slotted Aloha, CSMA/CD, CSMA/CA
Name examples of controlled access methods
Reservation, Polling, and Token Passing
Name examples of channelization protocols
FDMA, TDMA, CDMA
Name examples of hybrid approaches
OFDMA (a combination of FDMA and TDMA), CSMA/CA with RTS/CTS
What MAC protocol is typically used in Ethernet networks?
CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
What MAC protocol is typically used in Wi-Fi networks?
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) with optional RTS/CTS (Request to Send/Clear to Send) handshakes
What MAC protocol is typically used in Bluetooth networks?
Bluetooth networks utilize a frequency-hopping spread spectrum technique for MAC, where devices hop between different frequencies in a synchronized manner to avoid interference.
Why are different MAC approaches needed?
Different MAC approaches cater to various network environments and requirements. Random access protocols like Aloha and CSMA handle dynamic, low-traffic networks but suffer from collisions. Controlled access protocols like polling and token passing offer collision-free communication at the cost of increased latency. Channelization protocols like FDMA, TDMA, and CDMA provide structured, efficient access for high-capacity networks. Hybrid approaches like OFDMA and enhanced CSMA/CA combine the strengths of multiple techniques to optimize performance in modern networks. Each approach balances trade-offs in efficiency, complexity, and suitability for specific applications and network conditions.
What is ALOHA, what are the different versions, and how do they differ?
ALOHA is a random access protocol, originally developed in the 1970s for radio networks. It can however be used in any situation where multiple devices share a common communication channel
Pure ALOHA is the original version of the protocol. Devices transmit whenever they have data to send. If a collision occurs, they wait a random time before retransmitting. Simple but inefficient due to high collision rates.
Slotted ALOHA is an improved version of the pure ALOHA protocol. In this version, the channel is divided into small, fixed-length time slots and users are only allowed to transmit data at the beginning of each time slot, reducing the chances of collisions between devices and increasing the overall efficiency of the network.
What is CSMA/CD and how does it work?
CSMA/CD (Carrier Sense Multiple Access/Collision Detection) is a random access protocol used in Ethernet. Devices listen to the medium before transmitting. If a collision is detected during transmission, they stop, wait a random time, and retransmit. It reduces collisions but can’t eliminate them.
What is CSMA/CA and how does it work?
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) is a random access protocol used in Wi-Fi networks. Devices listen before transmitting and use mechanisms like RTS/CTS (Request to Send/Clear to Send) to avoid collisions. This is more effective than CSMA/CD in wireless environments where collision detection is difficult.
What is Polling and how does it work?
Polling is a controlled access method. A central controller (master) polls each device (slave) to check if it has data to transmit. Only the polled device can send data, eliminating collisions. It is efficient in low-traffic scenarios but introduces delay due to the polling process.
