How does slave latency help?

Slave latency lets the peripheral skip N consecutive events without responding, effectively multiplying the sleep time by (1+N) without changing the CI. With CI=30 ms and slave latency=9, the peripheral can sleep up to 300 ms between responses but still respond within 30 ms when data arrives.

Can CI change during a connection?

Yes. Either device can request a connection parameter update. The central can also impose changes. iOS requires CI multiples of 15 ms (minimum 15 ms). Android supports the full 7.5 ms minimum. Platform differences in accepted parameters are a common source of interoperability issues.

Wireless Protocols

BLE Connection Interval

Q: What CI should I use?

Gaming/audio: 7.5-15 ms for lowest latency. Wearable notifications: 30-100 ms for balance. Sensor reporting: 500 ms-4 s for maximum battery life. Start with the longest interval acceptable for your use case and reduce only if needed.

BLE Connection Interval (CI) is the time between the start of two consecutive connection events, configurable from 7.5 ms to 4 s in 1.25 ms steps. Shorter intervals provide higher throughput and lower latency but increase power consumption. Longer intervals maximize battery life at the expense of responsiveness. Combined with slave latency, the effective wake interval can be extended without renegotiating the CI.

Category: Wireless Protocols

Range: 7.5 ms - 4 s

Step: 1.25 ms

Understanding Connection Interval

At each connection event, the central transmits a packet and the peripheral responds within 150 μs. Multiple packets can be exchanged per event if both sides have data. After the event, both radios sleep until the next interval. The average current is dominated by the event duty cycle: shorter CI means more frequent wake-ups.

Throughput scales inversely with CI: at 7.5 ms CI with DLE (251-byte PDUs), BLE can achieve ~1.4 Mbps on 2M PHY. At 1 s CI, throughput drops to ~2 kbps. Slave latency allows the peripheral to skip events, waking only when it has data, without the central timing out the connection.

CI Power Impact

Avg current (no slave latency):
I_avg = (I_active × t_event)/CI + I_sleep

7.5 ms CI, 1 ms event, 8 mA active:
I = 8×1/7.5 + 0.002 = 1.07 mA
1 s CI: I = 8×1/1000 + 0.002 = 10 μA

CI Recommendations by Use Case

Application	CI	Latency	Battery Impact
Gaming/HID	7.5-15 ms	<15 ms	High (hours-days)
Audio (LE Audio)	7.5-10 ms	<10 ms	High
Wearable	30-100 ms	<100 ms	Medium (weeks)
Sensor	500 ms-4 s	<4 s	Low (years)

Common Questions

Frequently Asked Questions

What CI should I use?

Gaming: 7.5-15 ms. Wearable: 30-100 ms. Sensor: 500 ms-4 s. Start longest acceptable, reduce if needed.

Slave latency?

Peripheral skips N events, sleeping (1+N)×CI between responses. CI=30 ms, latency=9: sleeps up to 300 ms but can respond within 30 ms.

Can CI change mid-connection?

Yes. Either device requests update. iOS requires 15 ms multiples; Android supports 7.5 ms minimum. Platform differences cause interop issues.

Related Terms

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BLE Optimization

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