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Intermittently Connected Devices (ICD)

In Matter 1.4 and later, devices that are not continuously reachable are defined as Intermittently Connected Devices (ICDs). An ICD spends most of its time asleep and wakes only at controlled intervals or when triggered by specific events. When sleeping, the device is intentionally unreachable on the Matter fabric.

ICD functionality builds on the low‑power mechanisms covered earlier in Reducing power consumption in Matter (Thread SED/SSED roles, polling, and timeouts) and adds a Matter‑level model that defines when the device must be available and how it communicates during short, energy‑efficient windows.

This topic explains the ICD model, its modes, parameters, and how Nordic devices support efficient ICD configurations.

ICD operating modes

An ICD alternates between two operating modes: Idle mode and Active mode. These modes define how often the device communicates and how long it keeps its radio awake.

Idle mode

In Idle mode, the device prioritizes energy savings. It follows a Slow Polling Interval, checking for messages only occasionally. The device may sleep for minutes or hours, depending on its configuration. Long Idle intervals dramatically reduce radio use but limit how quickly the device can respond.

Active mode

In Active mode, the device becomes temporarily responsive. It uses a Fast Polling Interval and processes exchanges promptly. This mode is entered when the device initiates communication, when a new exchange begins, or after a timeout transition from Idle mode.

Transitions between modes

Several parameters regulate transitions. For example, an ICD can only stay in Idle mode for a maximum period defined by Idle Mode Duration, after which it must enter Active mode. Conversely, Active Mode Duration enforces a minimum time in Active mode, and Active Mode Threshold extends Active mode after the last exchange to accommodate delayed traffic.

These mechanisms ensure the device strikes a balance between responsiveness and battery life.

ICD parameters

The behavior of an ICD is controlled by five primary parameters. Understanding these is essential for creating devices with predictable responsiveness and optimized energy consumption.

Slow Polling Interval: This interval defines how often the ICD checks for messages during Idle mode. Longer values significantly reduce power use but introduce latency. Sensors that only report periodically often use very long Slow Poll values.
Fast Polling Interval: Used during Active mode, this determines how frequently the device listens for messages. It ensures a responsive user experience but increases radio‑on time.
Idle Mode Duration: This parameter limits the maximum time a device may remain in Idle mode. When the timer expires, the device transitions to Active mode to allow clients to interact with it.
Active Mode Duration: After entering Active mode, the device must remain active for at least this period. This prevents the device from returning to sleep prematurely during ongoing exchanges.
Active Mode Threshold: This value adds additional guaranteed Active time after the most recent network activity. It helps handle retransmissions and ensures stable communication, especially in networks with variable latency. It is also one of the largest contributors to energy consumption in deeply sleeping devices.

ICD configurations: SIT and LIT

Matter defines two ICD profiles: Short Idle Time (SIT) and Long Idle Time (LIT). The choice between them greatly affects device performance and battery life.

Short Idle Time (SIT)

SIT devices have a Slow Polling Interval of 15 seconds or less. This configuration is ideal for actuators such as door locks or window coverings, where user experience requires relatively low latency.

Because SIT devices stay reachable more often, they consume more energy, but they deliver consistent responsiveness.

Long Idle Time (LIT)

LIT devices use Slow Polling Intervals longer than 15 seconds, often lasting several minutes or even hours. This configuration suits devices that primarily report data, such as smoke/CO alarms or environmental sensors.

Because LIT devices sleep for long stretches, they rely on additional ICD features for reachability, such as the Check-In Protocol (CIP) and User Active Trigger (UAT).

LIT devices achieve extremely low power consumption but only respond to clients after they wake for scheduled communication or reporting events.

Additional ICD features: CIP and UAT

Check-In Protocol (CIP)

The Check-In Protocol is required for LIT devices. A Check-In is a short sessionless message sent by the ICD to indicate that it is temporarily reachable. Clients that have pending commands must act during this window.

CIP uses rotating keys and message counters to provide security without establishing a full secure session.

User Active Trigger (UAT)

The UAT mechanism allows the user to press a physical button (or trigger another local action) to immediately place the ICD into Active mode. This is essential for configuration flows or local interactions with a device that otherwise sleeps deeply.

ICD behavior over thread: SED and SSED

ICDs rely on the Thread low‑power roles introduced in Reducing power consumption in Matter. The roles define how the device wakes, polls, and maintains connectivity.

ICD with SED (Sleepy End Device)

SEDs wake periodically to poll their parent for any pending messages.
For ICD behavior, it is crucial that Thread polling aligns with the ICD’s Slow and Fast Polling Intervals.

Thread timeouts such as MLE (Mesh Link Establishment) Child Timeout and Child Supervision timeouts must be set to values greater than or equal to the Slow Polling Interval to avoid forcing extra wakeups.

ICD with SSED (Synchronized Sleepy End Device)

SSEDs use Coordinated Sampled Listening (CSL) to wake at precise intervals synchronized with their parent router. This can be more efficient than polling, but CSL requires accurate clocking and well‑tuned timing values.

If synchronization is lost, the SSED may need to send Data Requests, increasing consumption.

ICD configuration in nRF Connect SDK

Let’s take a look at how to configure ICD behavior in the nRF Connect SDK using Kconfig options.

These options enable ICD functionality and set the core timing parameters for Idle and Active modes.

ICD management	`CONFIG_CHIP_ICD`	Enables the Matter ICD Management cluster, allowing the device to operate as an intermittently connected node.
Slow polling interval	`CONFIG_CHIP_ICD_SLOW_POLL_INTERVAL=<ms>`	Specifies how often the ICD polls during Idle mode.
Fast polling interval	`CONFIG_CHIP_ICD_FAST_POLL_INTERVAL=<ms>`	Specifies how often the ICD polls during Active mode.
Idle mode duration	`CONFIG_CHIP_ICD_IDLE_MODE_DURATION=<ms>`	Maximum time the ICD may spend in Idle mode before transitioning to Active mode.
Active mode duration	`CONFIG_CHIP_ICD_ACTIVE_MODE_DURATION=<ms>`	Minimum required time in Active mode when the device becomes active.
Active mode threshold	`CONFIG_CHIP_ICD_ACTIVE_MODE_THRESHOLD=<ms>`	Extends Active mode after the last message exchange to support delayed traffic.

LIT-specific features

Check-In Protocol (CIP)	`CONFIG_CHIP_ICD_CIP=y`	Required for LIT devices to periodically inform clients of availability.
User Active Trigger (UAT)	`CONFIG_CHIP_ICD_USER_ACTIVE_TRIGGER=y`	Allows a user action to force a transition into Active mode.

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