Because Z-Wave is a very low bandwidth protocol that is intended to have a sparse network topology, the protocol stack attempts to communicate in as few bytes per message as possible. The stack consists of five layers, as shown in the following figure:
Z-Wave Protocol Stack and OSI model comparison. Z-Wave uses a five-layer stack with the bottom two layers (PHY and MAC) defined by the ITU-T G.9959 Specification.
The layers can be described as follows:
- PHY layer: Defined by the ITU-T G.9959 Specification. This layer manages the signal modulation, channel assignment, and preamble binding at the transmitter and preamble synchronization at the receiver.
- MAC layer: This layer manages the HomeID and NodeID fields, as defined in the previous section. The MAC layer also uses a collision avoidance algorithm and backoff strategy to alleviate congestion and contention on the channel.
- Transfer layer: Manages the communication of Z-Wave frames. This layer is also responsible for the retransmission of frames as needed. Additional tasks include acknowledgment of transmissions and checksum binding.
- Routing layer: This provides routing services. Additionally, the network layer will perform a topology scan and update of the routing tables.
- Application layer: Provides the user interface to applications and data.