Hardware Reference
In-Depth Information
No encryption required (Security Mode 1, Level 1)
The attribute is accessible on a plain-text, non-encrypted connection.
Unauthenticated encryption required (Security Mode 1, Level 2)
The connection must be encrypted to access this attribute, but the encryption
keys do not need to be authenticated (although they can be).
Authenticated encryption required (Security Mode 1, Level 3)
The connection must be encrypted with an authenticated key to access this
attribute.
Authorization
Determines whether user permission (also known as authorization , as discussed in
“Security Modes and Procedures” on page 46 ) is required to access this attribute.
An attribute can choose only between requiring or not requiring authorization:
No authorization required
Access to this attribute does not require authorization.
Authorization required
Access to this attribute requires authorization.
All permissions are independent from each other and can be freely combined by the
server, which stores them in a per-attribute basis.
Value
The attribute value holds the actual data content of the attribute. There are no restric‐
tions on the type of data it can contain (you can imagine it as a non-typed buffer that
can be cast to whatever the actual type is, based on the attribute type), although its
maximum length is limited to 512 bytes by the specification.
As discussed in “Attribute and Data Hierarchy” on page 56 , depending on the attribute
type, the value can hold additional information about attributes themselves or actual,
useful, user-defined application data. This is the part of an attribute that a client can
freely access (with the proper permissions permitting) to both read and write. All other
entities make up the structure of the attribute and cannot be modified or accessed di‐
rectly by the client (although the client uses the handle and UUID indirectly in most of
the exchanges with the server).
You can think of the whole set of attributes contained in a GATT server as a table (such
as Table 4-1 ), with each row representing a single attribute and each column represent‐
ing the different parts that actually constitute an attribute.
Search WWH ::




Custom Search