BLE Connection Establishment Workbench

Step from BLE advertising into scheduled connection events while tuning interval, latency, timeout, and channel conditions.

Interactive BLE connection animation showing peripheral advertising, central scanning and initiating, CONNECT_IND, data channel connection events, connection interval, peripheral latency, supervision timeout, and channel map tradeoffs.

Animation Bluetooth LE Connection Link Layer

BLE Connection Establishment Workbench

Step through the moment a peripheral stops only advertising and becomes part of a scheduled BLE link. Tune the interval, latency, timeout, and channel conditions to see what changes for latency, power, and reliability.

Phase Advertising

Active Channel 37

Interval 30 ms

Link Health 94/100

1. Advertise

The peripheral sends connectable advertising on primary channels 37, 38, and 39 so a central can discover it.

2. Initiate

The central listens, then sends a connection request on an advertising channel after receiving a suitable advertisement.

3. Schedule

Both devices move to data channels and meet at regular anchor points set by the connection interval.

4. Maintain

Peripheral latency can save energy, but the supervision timeout must still be long enough to avoid false disconnects.

Advertising to Connected Trace

A connectable advertisement creates the opportunity; CONNECT_IND turns it into a timed data-channel connection.

Passive scan Timeout margin OK

1. Packet ADV_IND Connectable advertising

2. Channel Ch 37 Primary advertising

3. Timing 30 ms Connection interval

Peripheral Advertiser

ADV_IND

Central Scanner

Advertising on channel 37 before the data link exists.

Ch 37 Ch 38 Ch 39 Data

Current Packet ADV_IND from peripheral

Timing Role Discovery window

Data Channel Not connected

Timeout Margin Safe

Peripheral Advertising Connectable ADV_IND uses primary advertising channels.

Central Scanning Passive scan only listens; active scan can request more data.

Optional Scan Response SCAN_REQ and SCAN_RSP happen before the connection request.

Central Initiating CONNECT_IND carries access address and timing parameters.

Both Connection Event Central starts each event at the anchor point.

Link Maintain Latency saves energy only when the timeout margin remains valid.

Scenario

Choose a design goal, then adjust the parameters to see whether the link still makes sense.

Device pattern Phone setup flow Interactive wearable Periodic sensor Battery asset tag

Scan behavior Passive scan then connect Active scan before connect

Channel conditions Clean 2.4 GHz room Busy Wi-Fi overlap Crowded industrial floor

Connection Parameters

The workbench keeps the slider range visible for teaching. The notes below give the full baseline limits.

Connection interval

30 ms

Peripheral latency

4 events

Supervision timeout

4.0 s

Balanced sensor link

The timeout is comfortably above 2 x (1 + latency) x interval, so skipped events should not look like a lost link.

Event Trace

BLE Connection Quick Reference

Roles

Peripheral Advertises

The peripheral offers a connectable advertisement; the central decides whether and when to initiate.

Discovery

37, 38, 39 First

Legacy connectable advertising starts on the three primary advertising channels before a data link exists.

Request

CONNECT_IND Starts It

The central sends the connection request on an advertising channel and supplies the first connection parameters.

Schedule

Anchor Points

Once connected, events repeat at the connection interval; the central transmits first at the anchor point.

Channels

37 Data Channels

Connected traffic uses data channel indices 0 through 36 with channel selection and channel map filtering.

Latency

Skip Only When Idle

Peripheral latency allows skipped connection events when there is no data, but it does not remove supervision rules.

Timeout

Must Exceed Margin

For this baseline model, timeout must be greater than 2 x (1 + latency) x interval to avoid false loss.

Tradeoff

Fast Costs Power

Short intervals reduce response delay; longer intervals and latency reduce radio wakeups for quiet sensors.

Learning Support

What Changed?

Advertising is opportunistic broadcast. A connection is scheduled: both radios know when to wake and which access address identifies the link.

Why The Central Leads

The central initiates and starts connection events. That role gives it control over timing across multiple peripherals.

Common Misread

Active scanning is not required to connect. It only adds a scan request and response before the central initiates.

Technical Accuracy Notes

Timing Model

Baseline BLE connection intervals are shown in 1.25 ms units. The slider is limited to 1.0 s for visibility, while the full baseline upper bound is 4.0 s.

Timeout Rule

The supervision check uses the baseline subrate factor of 1: timeout must be greater than 2 x (1 + peripheral latency) x interval.

Channel Selection

The data channel strip is a teaching view of channel map filtering and hop progression. Modern controllers may use CSA #2; the page does not claim to reproduce a full controller algorithm.