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Advertising types

There are many different ways that a peripheral can advertise.

Definition

Connectable vs. non-connectable: Determines whether the central can connect to the peripheral or not.
Scannable vs. non-scannable: Determines if the peripheral accepts scan requests from a scanner.
Directed vs. undirected: Determines whether advertisement packets are targeted to a specific scanner or not.

The type of advertisement being used is set in the advertisement packet. We will take a look at how to set the advertising type in the exercise section of this lesson.

There are four main advertisement types to cover in legacy advertisements, as well as a fifth one that is used in scan responses but will not be covered here.

Scannable and connectable (ADV_IND): This is the most common type of advertising. If a peripheral uses this type of advertising, it means that it is both scannable and connectable. This means that the peripheral is advertising its presence and allows the central to send a scan request and will respond with a scan response (hence scannable) which is followed by establishing a connection (hence connectable).

Directed connectable (ADV_DIRECT_IND): This type of advertisement is used for directed advertisement where the advertiser does not accept scan requests. It is directed, connectable but non-scannable. This can be used in cases where the advertiser already knows the scanner and just wants to reconnect quickly. A good example for this scenario is a Bluetooth mouse that has lost the connection with the PC and just wants to reconnect again. In this case, there is no need to accept scan requests and it is faster to send a directed advertisement packet to shorten the connection process.

Non-connectable and scannable (ADV_SCAN_IND): An advertiser using this type of advertisement will only accept scan requests, but will not allow establishing a connection with it (hence non connectable).

Non-connectable and non-scannable (ADV_NONCONN_IND): This type of advertisement does not accept scan requests nor does it accept establishing connections. A typical use-case for this type of advertisement is a beacon, where the device does not need to switch the radio to receiver mode since they do not allow receiving any data, which in turn reduces battery consumption.

As you can see, the advertising types are connectable or non-connectable, scannable or non-scannable, directed or undirected. The following table gives an overview of the four types of legacy advertising and their properties.

ConnectableScannableDirected
ADV_INDxx
ADV_DIRECT_INDxx
ADV_SCAN_INDx
ADV_NONCONN_IND
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