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Link Manager is used for managing the security, link set-up and
control. It talks to the other link manager to exchange information and
control messages through the link controller using some predefined
link-level commands. Its support for upper layer protocols is bit hazy but
possibly a upper layer interface can be used to execute algorithms for
mode managment (park, hold, sniff, active), security managment, QoS
managment etc. These algorithms may themselves have some input from the
user itself. For example, if the user requests a low power operation
(lower range operation in a home or a room), then link manager can
negotiate with the other link manager about the power control and both can
go into some sort of low power mode according to some pre-set algorithm.
Also if the security is not a big issue, a user can decide about the level
of security by choosing some reduced security option and therefore inform
link manager to go soft on security.
Information Exchange and Request
A bluetooth link manager can request from other link manager the clock
offset (master requesting the slave to tell it the current clock offset
stored by it which slave itself got from master during some packet
exchange), slot offset (slot offset is the time in microseconds between
the start of the master's transmission slot in the piconet where the PDU
is transmitted and the start of the master's transmission slot where the
BD_ADDR device in the PDU is master. It is useful in master-slave switch
and inter-piconet communications ), timing accuracy (clock drift and
jitter), link manager version and information about supported features
like support for authentication, SCO packets etc.
Mode management and SCO connections
The link manager also handles master-slave switch procedure and mode
switching procedures (forcing or requesting a device to change mode to
either hold, sniff or park mode). In parking mode, it has to take care of
how to broadcast a message to the parked devices, how to handle beacon
parameters and how to unpark a parked device gracefully.
Apart from above features a link manager can handle power control
(lower or increase the power) and can establish SCO links by reserving
slots and negotiating SCO parameters. If a device wants to establish
connections using layers above the Link Manager, then it can open
connections between the two devices too.
Next, Higher layer adaptation...
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