The correct answer is: D. Medium Access layer
The ZigBee stack is a set of protocols that define how devices communicate with each other on a ZigBee network. The stack is divided into four layers:
- Physical layer: This layer is responsible for the physical transmission of data between devices. It defines the modulation scheme, frequency, and power level used to transmit data.
- Medium Access layer: This layer is responsible for managing access to the shared wireless medium. It uses a contention-based protocol called CSMA/CA to ensure that all devices have a fair chance to transmit data.
- Network layer: This layer is responsible for routing data between devices on a ZigBee network. It uses a mesh topology to route data through multiple devices to reach its destination.
- Application layer: This layer is responsible for the application-specific data that is exchanged between devices. It defines the application protocols that are used by devices to communicate with each other.
The Medium Access layer is the most important layer in the ZigBee stack. It is responsible for ensuring that all devices on a ZigBee network can communicate with each other without interfering with each other. The Medium Access layer uses a contention-based protocol called CSMA/CA to ensure that all devices have a fair chance to transmit data.
CSMA/CA stands for Carrier Sense Multiple Access with Collision Avoidance. It is a protocol that is used to manage access to a shared wireless medium. In CSMA/CA, devices listen to the medium before transmitting data. If the medium is busy, the device waits until it is idle before transmitting. If two devices transmit data at the same time, a collision occurs and both devices must retransmit their data.
CSMA/CA is a very efficient protocol for managing access to a shared wireless medium. It ensures that all devices have a fair chance to transmit data and that collisions are minimized.