Information Technology Reference
In-Depth Information
Figure 6: Data flow between a host and its Bluetooth device.
RFComm is a transport protocol that provides emulation of serial ports
over the L2CAP layer.
The Service Discovery Protocol (SDP) layer provides a method for
applications to discover which services are available and what are their
characteristics. There can be different kinds of service, such as fax, printing
and access to wired networks. However, SDP only provides a way to discover
what services are available in a certain area, but does not allow access to them.
To use the services offered by a particular server, there must be opened a
connection to it. A network of Bluetooth devices is highly dynamic (some
servers may leave the coverage range and others may enter at any time). For
this reason, there is a notification mechanism that indicates when a new server
is available, allowing the client to request the list of services it offers. When
a server leaves the client range there is no notification, but the client can
update the server list via SDP, thus cancelling those which may no longer be
available. The service discovery can take place in two ways:
The client is looking for a service with given attributes and wants to know
if the server is able to provide a service that meets those requirements.
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