BLE advertising and scanning in IOT Protocols - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is BLE advertising in simple terms?

BLE advertising is like a device shouting out its name and some info so nearby devices can hear and decide if they want to connect.

beginner

What does BLE scanning do?

BLE scanning is when a device listens quietly to find nearby devices that are advertising, so it can learn about them or connect.

intermediate

Name two types of BLE advertising.

1. Connectable advertising: invites devices to connect.
2. Non-connectable advertising: just shares info without allowing connections.

intermediate

Why is advertising interval important in BLE?

It controls how often a device sends out its advertisement. Short intervals mean faster discovery but use more battery; longer intervals save battery but slow discovery.

intermediate

What is the difference between active and passive scanning in BLE?

Active scanning sends a request to get more info from advertisers, while passive scanning just listens without sending anything.

What does BLE advertising primarily do?

A Encrypts data for security

B Connects directly to Wi-Fi

C Broadcasts device info to nearby devices

D Saves battery by sleeping

BLE advertising broadcasts device info so other devices can discover it.

Which BLE advertising type allows other devices to connect?

A Connectable advertising

B Active advertising

C Passive advertising

D Non-connectable advertising

Connectable advertising invites other devices to connect.

What is the main difference between active and passive scanning?

A Active scanning listens only, passive sends requests

B Passive scanning listens only, active sends requests

C Both send requests

D Neither listens

Passive scanning listens quietly; active scanning sends requests to get more info.

Why might a device use a longer advertising interval?

A To save battery life

B To connect to more devices

C To increase discovery speed

D To improve signal strength

Longer advertising intervals reduce how often the device broadcasts, saving battery.

What role does scanning play in BLE communication?

A It sends data to other devices

B It powers the device

C It encrypts the connection

D It listens for advertising devices

Scanning listens for devices that are advertising to discover them.

Explain how BLE advertising and scanning work together in device discovery.

Think of one device shouting and another listening.

Describe the impact of advertising interval on battery life and device discovery speed.

Compare it to how often you shout to get attention.

Practice

1. What is the main purpose of BLE advertising in Bluetooth Low Energy communication?

easy

A. To broadcast small packets of data repeatedly to nearby devices

B. To establish a full connection between devices

C. To encrypt data between devices

D. To scan for other devices' signals

Solution

1. Step 1: Understand BLE advertising role

   BLE advertising sends small data packets repeatedly to announce presence.

2. Step 2: Differentiate from scanning and connection

   Advertising is broadcasting, not scanning or connecting.

3. Final Answer:

   To broadcast small packets of data repeatedly to nearby devices -> Option A

4. Quick Check:

   Advertising = broadcast small data [OK]

Hint: Advertising means sending out info repeatedly [OK]

Common Mistakes:

• Confusing advertising with scanning
• Thinking advertising establishes connections
• Assuming advertising encrypts data

2. Which of the following is the correct command to start BLE scanning using the Linux tool bluetoothctl?

easy

A. ble scan start

B. start scan

C. scan start

D. scan on

Solution

1. Step 1: Recall bluetoothctl scan command

   The correct command to start scanning is exactly scan on.

2. Step 2: Check other options for syntax

   Other options are incorrect commands or invalid syntax in bluetoothctl.

3. Final Answer:

   scan on -> Option D

4. Quick Check:

   bluetoothctl scan on = start scanning [OK]

Hint: Use exact command 'scan on' in bluetoothctl [OK]

Common Mistakes:

• Using 'start scan' instead of 'scan on'
• Typing commands not supported by bluetoothctl
• Confusing scan commands with advertising commands

3. Given this Python snippet using a BLE library to scan devices:

devices = scanner.scan(5.0)
for dev in devices:
    print(dev.addr)

What will this code output?

medium

A. Empty list because scan time is too short

B. List of device addresses found during 5 seconds scan

C. Error because scan() needs no arguments

D. List of device names found during 5 seconds scan

Solution

1. Step 1: Understand scan() usage with timeout

   The scan method scans for devices for given seconds and returns device objects.

2. Step 2: Identify printed attribute

   Printing dev.addr outputs device MAC addresses found.

3. Final Answer:

   List of device addresses found during 5 seconds scan -> Option B

4. Quick Check:

   scan(5.0) returns devices; dev.addr prints addresses [OK]

Hint: scan(timeout) returns devices; print dev.addr for addresses [OK]

Common Mistakes:

• Thinking scan() takes no arguments
• Confusing device address with device name
• Assuming scan always returns empty list

4. You wrote this code to scan BLE devices but get no output:

scanner = Scanner()
devices = scanner.scan()
for dev in devices:
    print(dev.addr)

What is the likely problem?

medium

A. print(dev.addr) is incorrect attribute

B. Scanner() class does not exist

C. Missing scan timeout argument causes no devices found

D. scan() method should be called with 'start' keyword

Solution

1. Step 1: Check scan() method requirements

   scan() requires a timeout argument to specify scan duration.

2. Step 2: Understand effect of missing timeout

   Without timeout, scan may return immediately with no devices.

3. Final Answer:

   Missing scan timeout argument causes no devices found -> Option C

4. Quick Check:

   scan() needs timeout to find devices [OK]

Hint: Always provide scan timeout to get results [OK]

Common Mistakes:

• Omitting scan timeout argument
• Assuming dev.addr is invalid
• Thinking scan() uses 'start' keyword

5. You want to filter BLE scan results to only show devices advertising a specific service UUID. Which approach correctly applies this filter in Python?

hard

A. Use a list comprehension: [dev for dev in devices if '1234' in dev.getScanData()]

B. Check if '1234' in dev.addr for each device

C. Filter devices by comparing dev.name to '1234'

D. Use devices.filter('1234') method directly

Solution

1. Step 1: Understand filtering by service UUID

   Service UUIDs appear in scan data, not in address or name.

2. Step 2: Use list comprehension with getScanData()

   getScanData() returns advertised data; check if UUID '1234' is present.

3. Final Answer:

   Use a list comprehension: [dev for dev in devices if '1234' in dev.getScanData()] -> Option A

4. Quick Check:

   Filter by UUID in scan data using list comprehension [OK]

Hint: Filter devices by checking UUID in scan data list [OK]

Common Mistakes:

• Checking UUID in device address
• Filtering by device name instead of UUID
• Using non-existent filter() method on devices