An ACL link carries data packets, whereas an
SCO link supports real-time audio traffic.
??? Audio is really not a layer of the protocol stack, but it is shown here
because it is uniquely treated in Bluetooth communication. Audio
data is typically routed directly to and from the baseband layer over
an SCO link. Of course, if a data channel is used (e.g., in VoIP
applications), audio data will be transmitted over an ACL link.
??? The Link Manager Protocol (LMP) is responsible for link setup and
link configuration between Bluetooth devices, managing and negotiating
the baseband packet sizes. The LMP manages the security
aspects, such as authentication and encryption, by generating,
exchanging, and checking link and encryption keys.
??? The HCI provides a command interface to the radio, baseband
controller, and link manager. It is a single standard interface for
accessing the Bluetooth baseband capabilities, the hardware status,
and control registers.
??? The Logical Link Control and Adaptation Protocol (L2CAP) shields
the upper-layer protocols from the details of the lower-layer protocols.
It multiplexes between the various logical connections made
by the upper layers.
??? The SDP provides a means for applications to query services and
characteristics of services. Unlike in an LAN connection, in which
one connects to a network and then finds devices, in a Bluetooth
environment one finds the devices before one finds the service.
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