Hardware Reference
In-Depth Information
Procedures
A procedure is a sequence of actions (usually Link Layer control sequences or packet
exchanges) that allows a device to attain a certain goal. A procedure is typically
associated with a mode on the other peer, so they are often tightly coupled together.
Security
GAP builds on top of the Security Manager and the Security Manager Protocol by
defining security modes and procedures that specify how peers set the level of se‐
curity required by a particular data exchange and later how that security level is
enforced. GAP further defines additional security features not associated with par‐
ticular modes or procedures, and implementations are free to use those to increase
the level of data protection required by each application.
Additional GAP Data Formats
In addition to all of the above, GAP is also used as a placeholder for certain addi‐
tional data format definitions that are related to the modes and procedures defined
by the GAP sepcification.
The corresponding sections in this chapter will examine these elements in detail.
Roles
GAP specifies four roles that a device can adopt to join a BLE network:
Broadcaster
Optimized for transmit-only applications that distribute data regularly, the
broad‐
caster
role periodically sends out advertising packets with data. Theoretically, the
broadcaster role could be used with transmitter-only radios, but in practice, this
role is usually assigned to a device capable of both transmitting and receiving. A
public thermometer that broadcasts temperature readings to any interested devices
would be a good example of a broadcaster. Broadcasters send data in advertising
packets rather than connection data packets, and the data is accessible to any device
that is listening. The broadcaster role uses the Link Layer advertiser role.
Observer
Optimized for receive-only applications that want to collect data from broadcasting
devices, the
observer
role listens for data embedded in advertising packets from
broadcasting peers. For example, a device with a display is a typical application of
this role, such as a table computer that displays temperature data from a broadcast-
only temperature sensor. The observer role uses the Link Layer scanner role.
Central
The central role corresponds to the Link Layer master. A device capable of estab‐
lishing multiple connections to peers, the
central
role is always the initiator of con‐
nections and essentially allows devices onto the network. The BLE protocol is
