Tune the network

The unicast dwell interval is the time the PAN spends on a single unicast channel before hopping. Shorter dwell times increase frequency diversity and can reduce the impact of narrowband interference, but they also increase hopping overhead and can raise per-packet latency when retransmissions are needed. Longer dwell times improve MAC efficiency on a channel and can increase throughput for bursty traffic, but they reduce hopping diversity and may approach or exceed regulatory dwell-time limits if set too high. This value directly affects end-to-end latency because nodes can only exchange unicast frames while they are on the same channel within the same dwell window as determined by the hopping function. Choose a dwell that balances link robustness and latency targets. Changing this parameter on a running PAN forces nodes to adjust their hopping schedule and can temporarily increase loss while neighbors resynchronize.

The broadcast dwell interval is the time allotted to broadcast operation on a single channel before the broadcast schedule hops. Broadcast windows carry multicast traffic and the Wi-SUN asynchronous management frames used for discovery and configuration. Shorter broadcast dwell times reduce channel occupancy for shared control traffic and can lower collision probability in dense deployments, but they may limit the number of frames that can be sent per window and can lengthen discovery if multiple fragments are required. Longer broadcast dwell times increase the chance that advertisements and multicast frames are received on the first try, but they consume more airtime on a single channel and can increase contention with neighboring PANs. This value should be coordinated with the Broadcast Interval because together they define the broadcast duty cycle and the capacity available for control traffic.

The Broadcast Interval is the period between the start of successive broadcast windows in the frequency-hopping schedule. Longer intervals reduce energy consumption for nodes that only need to wake for broadcast reception, but they increase the latency of multicast delivery and can lengthen the time to complete discovery and configuration exchanges. Shorter intervals improve control-plane responsiveness and reduce join time, but they increase airtime devoted to control traffic and can raise collision probability in crowded spectrum. The combination of Broadcast Interval and Broadcast Dwell Interval determines how often and how long the network is collectively listening for broadcasts, which directly impacts discovery reliability and multicast throughput. Set this interval according to the deployment’s join-time targets and control-traffic load, and verify that sleepy devices can still meet their power budget.

The LFN broadcast interval applies to Low Power Field Nodes introduced in Wi-SUN FAN 1.1 and defines how often LFN-oriented broadcast windows occur. LFNs use this interval to schedule wakeups for network beacons, configuration updates, and downlink notifications while spending most of their time in deep sleep. Longer LFN intervals maximize battery life for LFNs but increase downlink latency and the time to deliver control updates to those nodes. Shorter LFN intervals improve responsiveness and reduce the risk that an LFN misses critical updates, at the cost of higher energy consumption and more shared airtime.

The LFN broadcast sync period defines how often, in units of LFN Broadcast Intervals, the Border Router emits synchronization information intended to correct LFN clock drift. A larger sync period reduces broadcast overhead and further conserves LFN energy, but it increases the risk that accumulated clock drift causes an LFN to miss its scheduled window and then require re-synchronization or rejoin procedures. A smaller sync period improves timing accuracy and reduces missed windows at the cost of additional control traffic and energy for LFNs. Select a value that matches the clock accuracy and sleep behavior of LFNs and the environmental temperature range that can influence oscillator drift.

The async fragment duration limits how long the network may devote to transmitting a single asynchronous frame fragment or a contiguous burst of asynchronous fragments within a broadcast window. Asynchronous frames include discovery and configuration messages such as PAN Advertisements, PAN Configuration frames, and their solicitations as defined by the Wi-SUN FAN specification. A longer fragment duration increases the likelihood that multi-fragment control messages complete within fewer broadcast windows, improving join speed in lossy conditions, but it can starve other control or multicast traffic during that window. A shorter fragment duration reduces per-window contention and keeps broadcast windows fair, but it may spread large control exchanges over more intervals and lengthen discovery.