Electromagnetic compatibility and Radio spectrum Matters (ERM);Short Range Devices;Smart Metering Wireless Access Protocol;Part 2: Data Link Layer (MAC Sub-layer)

The present document, together with its associated PHY Technical Specification [1], provide radio communications connectivity for continuously powered or battery operated Smart Metering devices which, when coupled with suitable transport protocols, support advanced metering and other energy related applications. The MAC/PHY combination is also suitable for a wide range of sensor and Machine-to-Machine applications characterised by low device duty cycle and operation in shared spectrum.
This wide range of applications requires efficient connectivity protocol support for intermittent bi-directional data exchanges between devices in both low density (e.g. rural) and high density (e.g. urban) environments covering operations as simple as discovery and connection between one pair of devices (e.g. for walk-by meter reading) up to networks of many devices sharing a Network Point of Attachment to an external wide area network.
Spectrum sharing imposes additional requirements on the lower layer communications protocols governed by regulations limiting power and duty cycle among other characteristics. Such regulations taken into account by the present document include those governing the operation of Short Range Devices. Simple and low density deployments may be supported by distributed or cluster-based control algorithms, e.g. as found in [3] and [4], operating on a single channel. Frequency agility to select or change operating channel to minimise interference is advantageous for these applications but not essential for their operation.
Dense deployments and more complex applications may be constrained by spectrum sharing rules designed to limit the interference to other devices or services from the data traffic generated. In these cases the optimum control algorithms spread the population of devices uniformly over the available spectrum (channels) to minimise the number of devices on any given channel thereby minimising interference from their generated traffic. Device behaviour defined in [2] automatically distributes devices over the available channels by using device-centric pseudo-random channel hopping but also supports single channel operation via a degenerate hopping algorithm always returning the same channel number.
Both approaches to systems design may be deployed using the same PHY protocol and in the same frequency range and it is therefore necessary to include facilities to discriminate between information belonging to each MAC approach. Nothing prevents an implementation choosing to use only one of the alternate approaches or supporting both and the present document provides the necessary data structure encoding to identify each unit of information in its correct context.