Zigbee IEEE 802.15.4
The improvement of wireless protocols is a major factor driving the development of newer Internet of Things (IoT) devices and systems. The Zigbee suite of communication protocols is used to create personal area networks with small, low-power digital radios, such as home automation, medical device data collection, and other low-power low-bandwidth needs. The Zigbee physical layer performs modulation on outgoing signals and demodulation on incoming signals. It transmits information and receives information from a source, and uses different frequency bands based on region as shown below.
Zigbee uses the Media Access Control (MAC) layer to access networks using Carrier-Sense Multiple Access with Collision Avoidance (CSMA/CA), to transmit beacon frames for synchronization and to support reliable transmission. It does not use all of the MAC functions used in other protocols, but uses the physical layer and MAC for CSMA/CA functions as previously mentioned, and as a method for defining the type of network topology in use This provides the ability to discover and join networks and expand on topologies defined by 802.15.4 at the MAC layer which allows mesh networking.
Devices in a Zigbee network have two addresses, a MAC address and a Network Address (NwkAddr). The MAC address comes from the underlying 802.15.4 protocol and the NwkAddr is part of the Zigbee layer itself. As in Ethernet networks, Zigbee networks use the MAC address to map to network addresses. Zigbee networks also use an Extended PAN ID (EPID) which is used in conjunction with the MAC address to filter out packets that are not part of the network.
When examining network broadcasting functions, specifically Unicast, a Network ACK is returned to the original node once a messages reaches its destination. At the MAC level, a MAC ACK is sent between each hop as the message propagates. Additionally, encryption can be applied at the MAC level as well as at the network and application support layers.
Silicon Labs IOT. (n.d.). The Wireless Protocols Tying Together the Internet of Things. Retrieved August 3, 2017, from https://www.silabs.com/documents/public/user-guides/ug103-02-fundamentals-zigbee.pdf.