Hardware Reference
In-Depth Information
Figure 1-4. Connected topology
A connection is therefore nothing more than the periodical exchange of data at certain
specific points in time (connection events) between the two peers involved in it. It is
important to note that, although the central is the device that manages the connection
establishment, data can be sent independently by either device during each connection
event, and the roles do not impose restrictions in data throughput or priority.
Beginning with version 4.1 of the specification, any restrictions on role combinations
have been removed, and the following are all possible:
• A device can act as a central and a peripheral at the same time.
• A central can be connected to multiple peripherals.
• A peripheral can be connected to multiple centrals.
Previous versions of the specification limited the peripheral to a single central connec‐
tion (although not conversely) and limited the role combinations.
The biggest advantage of connections (when compared to broadcasting) is the ability
to organize the data with much finer-grained control over each field or property through
the use of additional protocol layers and, more specifically, the Generic Attribute Profile
(GATT). Data is organized around units called
services
and
characteristics
(discussed
in more detail in
Chapter 4
).
The key thing to keep in mind is that you can have multiple services and characteristics,
organized in a meaningful structure. Services can contain multiple characteristics, each
with their own access rights and descriptive metadata. Additional advantages include
higher throughput, the ability to establish a secure encrypted link, and negotiation of
connection parameters to fit the data model.
