Datasets:
kkboy1
/
LeAudio

Dataset card Data Studio Files
xet
 Community
1
text
stringlengths
1
112
to look like a conventi onal remote control it could be in the form of a smartwatch another
wearable device or even buttons on a battery case moreover there can be multiple clients
operating on the server at the same time you could accept a phone call on your earbud bu t
terminate it with your watch
as well see the control profiles can move us around the media and call states on an initiator
reflecting the users desire to start or accept a phone call or play or pause a piece of music
what they dont do is start o r stop any audio streams associated with those decisions the
link between control commands and the configuration and establishment of the audio
streams which transport the audio data is entirely down to the implementation it is up to
applications on th e initiator to tie them together as it wishes
in both tbs and mcs the service specification includes individual tbs and mcs instances
which can be instantiated for each application on the device for example if you r phone
supports skype whatsapp and zoom as well as cellular calls it can include a separate instance
of tbs for each one of those applications if its a media playback device it can include an
instance of mcs for spotify bbc sounds and netflix
however if youre controlling either te lephony or music from a pair of earbuds with a very
limited user interface youre unlikely to want to or even be able to discriminate between the
different applications to cope with this the tbs and mcs specifications each contain a
generic version o f the service called the generic telephone bearer service gtbs and
generic media control service gmcs respectively these behave in exactly the same way
as tbs and mcs but provide a single interface to the server device it is up to the
implementation to map incoming commands from a client to the appropriate application
chapter telephony and media control
figure representation of control services and their generic counterparts
figure is a simplistic representation of how this works every content control server must
include a single instance of the generic service either gtbs or gmcs and may have
individual instances of tbs and mcs if it wants to expose control directly to an application
you can have as many instances of each service as you have telephony and media applications
with that mapping is down to the implementation
the respective profiles ccp and mcp define client and server roles which are illustrated
in figure
figure relationship of generic and specific control services
implementations can use the combination of these services to
treat each application as a unique media player or telephony service
treat the device as a single telephony or media player where commands act on the
whole device or
a combination where a subset of commands may be directed to specific
applications being mapped according to their specifi c content control ids
ccids
in all cases the mapping is down to the product implementation
section control topologies
both tbs and mcs include a wide range of features which well cover below a lot of the
time bluetooth le audio is concerned with earbuds as that is by far the largest market by
volume the limited user interface ui of an earbud may make readers wonder why so many
of these features are included and also why so few of them are mandated that ignores the
history of bluetooth audio where until recently the major audio application was in carkits
where a very rich control and information interface is provided both tbs and mcs were
designed to replicate many of the features currently available in carkits so that bluetooth le
audio can be used to build the next generation of these products as well as extending them
to add new features particularly for the control of media players
control topologies
at the heart of both of the pairs of control specifications is the concept of st ate defined in
the service specification the state is held on the device where the audio originates the
media player for mcs or the telephon y device acting as a gateway to the call bearer for tbs
but always the initiator client devices can implem ent the corresponding profile which writes
to a control point on the server causing its state to transition once that transition has been
made which may also happen locally by the user pressing a button or touching a screen the
server notifies its ne w state its exactly the same principle we came across in the ascs state
machine there is one device which has the state and multiple clients which can read and
manipulate it in the case of both mcp and ccp the client can be the device receiving th e
audio stream or a device including the commander role such as a remote control or a
smartwatch however in this case the client in the commander would be operating on the
initiator not the acceptor as shown in figure
figure topologies for content control
chapter telephony and media control
in addition to the control point and state characteristics each service contains a wide selection
of characteristics which can be read or notified to determine further information about the
application and external service supplying it
tbs and ccp
at the heart of the telephony control specifications is a generic call state machine illustrated
in figure
figure the tbs state machine asterisks denote remote operations
the heart of the state machine is the active state which signifies the presence of a call in
most cases this state would be attained when a unicast audio stream had been established
between the initiator and acceptor normally consisting of a bidirecti onal stream however
the state machine is equally valid if the call is being taken using a wired headset or if the phone
is being used as a speakerphone with no active audio streams this emphasises the distinction
between the control plane which in t his case is the tbs ccp relationship and the audio
data plane which is the bap ascs relationship it is up to the application to tie them
together as it wishes although they are an integral part of gaf they are not restricted to
bluetooth le aud io and could be used with other applications
section tbs and ccp
the transitions around the state machine can be prompted by external events such as
an incoming call
a ccp client writing to the tbs call s tate characteristic
a local user action suc h as answering a call on the phone or
an operation by the remote caller
the remote operations in figure remote alert start remote answer remote hold and
remo te retrieve are marked by an asterisk at the end of each command these transitions
can only be made by the remote caller the states are exposed by the call state characteristic
which is notified to clients whenever the state of the call changes
the call state characteristic
the call state characteristic is an array of all of the current calls on the device as soon as any
call enters a non idle state it is assigned a unique single octet sequential index number by
tbs called the callindex with a value between and which is notified in the call state