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as the purpose of the a se control point command is to effect a change to an ase either by
changing its state or updating a parameter values the initiator will be expecting these
notifications however not all ases need to be transitioned or updated in each ase control
point operation this means that different ases on an acceptor associated with the same
chapter setting up unicast audio streams
initiator could be in different states if in doubt the initiator should read their ase
characteristics this should not be the case if a cap audio streaming procedu re has been
used as that requires all acceptors to be transitioned to the same state before proceeding with
the next command however even here some ases may not be in the enabled or streaming
state if they were configured as spare ases for future us e which well cover in section
a simplified sequence chart for this process is shown in figure the same process applies
to both sink ases and source ases
figure simplified sequence diagram for ase control point operations
the clever or complicated depending on your point of view part of this process is that the
parameters in the ase control point command and sink ase and source ase characteristics
are different for each state as you move through the stream establishment process providing
the information that the initiator needs for its next operation the different parameters in the
first few operations allow the initiator to understand all of the ases capabilities and gather
the information it needs to set up the cig and its constituent cises
all of the initiators op erations have the same basic format which was shown in table but
the state specific ase parameters change with each asestate the individual sets of
parameters a re defined in tables to of ascs for the ase characteristic notifications
and sections for the ase control point commands
the initiator can configure multiple ases with its ase control point operation command
but each configured ase notifies its state independently for example if the initiator were
to enable four ases for a headset separate sink ases for left and right stereo and two source
ases for a microphone on each side it would receive one notification of the updated ase
control point characteristic and four independent notifications from the two pairs of sink and
source ases
each step through the ascs state machine is defined as a specific procedure in bap in the
next section well go through these to see how the proces s works
section configuring an ase and a cig
configuring an ase and a cig
an initiator that wants to make a connection whether in response to a user action an external
event or a request from an acceptor needs to start by determining the capabilities of all of
the acceptors involved in t he use case assuming that its the first time the devices have
connected and nothing is cached there are various options for the initiator to determine the
acceptors capabilities depending on whether the initiator only requires the basic capabilities
mandated by bap whether there are mandated features from another top level profile which
means it needs to follow cap as well or whether it wishes to use optional or proprietary
features these options are shown in table in subsequent connections there may be
cached information about the acceptors capabilities that allow the initiator to skip these steps
initiator action result
discover sink pac acceptor c an receive unicast audio with bap mandatory
settings
discover sink audio
locations acceptor can receive unicast audio with bap mandatory
settings
discover sink ase acceptor can receive unicast audio with bap mandatory
settings
discover source pac acceptor can transmit unicast audio with bap
mandatory settings
discover source audio
locations acceptor can transmit unicast audio with bap
mandatory settings
discover source ase acceptor can transmit unicast audio with bap
mandatory settings
discover profile or service acceptor supports additional mandatory requirements
read sink pac discover the acceptors capabilities for reception
read source pac discover the acceptors capabilities for transmission
table options for an initiator to determine an acceptors capabilities
lets assume that were dealing with either tmap or hap and want to connect to a left and
right pair of acceptors having discovered that hap or tmap is supp orted on at least one
of the acceptors by discovering their service uuid the initiator knows the mandatory codec
configurations and qos settings that are supported so it can jump straight into cap and run
the cap connection procedure for nonbonded devices cap to make a connection
the initiator would determine if the first earbud is a member of a coordinated set and as it
is in our example would then run the cap procedure preamble cap bond ing with
both devices in that set having done that it can start the main business of establishing a
connection using the cap unicast audio start procedure cap this tells the
initiator to step through the underlying bap procedures
chapter setting up unicast audio streams
first the initiator needs to discove r all of the sink and source ases on each acceptor and
confirm that each acceptor has at least one ase supporting the correct direction for each
audio stream it wants to set up it should also check the pac characteristics to make sure
the acceptor is cap able of supporting the settings it wants to use these procedures are
described in bap in the audio role discovery procedure bap the audio capability
discovery procedure bap and the aseid discovery procedure bap
audio role discovery and aseid discovery are both mandatory as you cant proceed unless
you know there is a suitable ase to connect to audio contexts discovery bap is
optional but is necessary if the initiator wants to use optional settings
bap has been designed to provide a fall back level of interoperability that will allow every
initiator to be able to set up an audio stream with any acceptor with a reasonable quality of
audio to ensure that they will always be able to connect if an initiator is just using mandatory
settings for bap or a profile which it has already discovered that the acceptor supports it
may have enough information to skip this stage similarly if the request for connection came
from the acceptor either directly or through an announce ment that may have already
provided this information
the next step is to configure the codec for each ase before doing that the initiator should
check that each ase can support the intended use case by checking the acceptors
supportedaudiocontexts and availableaudiocontexts characteristics using the
supportedaudiocontexts procedure bap and the availa bleaudio context s
procedure bap these were described in section
the bap codec configuration procedure
assuming that the requisite sink andor source ase requirements are met the initiator will
start to set up the isochronous stream s by configuring each ase on each acceptor it does
this by employing the bap codec configuration procedure bap whe re it writes to the
ase control point characteristic with the configcodec opcode of x in order to move