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conversation out to the earbud and audio from the earbud s microphone back to the phone |
cis carries the audio stream from the phone to the other earbud it is up to the application |
to determine whether it is a stereo stream thats being sent or mono in the latter case the |
same mono audio data is sent separately over cis and cis to the two earbuds |
context type s |
to make decisions about which audio streams they want to connect to devices need to know |
more about what those streams contain or what theyre for context type s have been |
introduced to describe the current use case or use cases associated with an audio stream their |
values are defined in the bluetooth assigned numbers document for generic audio context |
type s can be used by both initiators and acceptors to indi cate what type of activity or |
connection they want to participate in and are applicable to both unicast and broadcast |
with bluetooth classic audio profiles the conversation between a central and peripheral |
device is basically i want to make an audio co nnection with no more information about |
what it is as the hfp and adp profiles are essentially single purpose profiles thats not a |
problem but in bluetooth le audio where the audio stream could be used for a ringtone |
voice recognition playing mu sic providing satnav instructions or a host of other applications |
its useful to know a little more about the intended reason for requesting a stream thats |
where context type s come in |
as well see later context type s are used as optional metadata d uring the unicast stream |
configuration process an acceptor can expose which context type s it is prepared to accept |
chapter new concepts in bluetooth le audio |
at any point in time for example if a hearing aid wearer is having a private nonbluetooth |
conversation which they dont want interrup ted they can set their hearing aids to be |
unavailable for a stream associated with a ringtone context type that means that the |
hearing aids will silently reject an incoming call thats more universal than putting their phone |
on silent as by using context type s they will reject an incoming call from any phone they |
have connected or a voip call from any other connected device they could also set the |
ringtone context type while they are in a call to prevent any other call interrupting the |
current one this can be done on a per device basis meaning you could restrict incoming |
calls to one specific phone providing a powerful method for an acceptor to control wh ich |
devices can request an audio stream |
an initiator uses the context type when it is attempting to establish an audio stream |
informing the acceptor of the associated use case if that context type is set to be unavailable |
on the acceptor the configuration and stream establishment process is terminated this |
happens on the acl link befo re an isochronous stream is set up which means that these |
decisions can take place in parallel to an existing audio stream without disturbing it regardless |
of whether the request is from the device currently providing the stream or another initiator |
wanting to establish or replace an existing stream it doesnt matter whether an existing audio |
stream is unicast or broadcast which means that a hearing aid user listening to their tv using |
a broadcast audio stream can use context type s to prevent their cu rrent stream being |
disturbed by any phone call |
there are currently twelve context type s defined in the generic audio assigned numbers |
document which are exposed in a two octet bitfield of context type s as shown in table |
with each bit representing a context type this allows multiple values to be used at any one |
time |
bit context type description |
unspecified any type of audio use case which is not explici tly supported by |
another context type on a device |
conversational conversation between humans typically voice calls which can |
be of any form eg landline cellular voip ptt etc |
media audio content typically this is one way such as radio tv or |
music playback it is the same type of content as is handled by |
adp |
game audio associated with gaming which may be a mix of sound |
effects music and conversation normally with low latency |
demands |
instruct ional instructional information such as satnav directions |
announcements or user guidance which often have a higher |
priority than other use cases |
section context types |
bit context type description |
voice |
assistants manmachine communication and voice recognition other than |
what is covered by instructional it is implied that this is in the |
form of speech |
live live audio where both the bluetooth audio stream and the |
ambient sound is likely to be perceived at the same time |
implying latency constraints |
sound effects sound s such as keyb oard clicks touch feedback and other |
application specific sounds |
notifications attention seeking sounds such as announcing the arrival of a |
message |
ringtone notification of an incoming call in the form of an inband audio |
stream the ringtone context type is not applied to an out of |
band ringtone which is signalled using ccp and tbs |
alerts machine generated notifications of events these may range |
from critical battery alerts doorbells stopwatch and clock alarms |
to an alert about the completion of a cycle from a kitchen |
appliance or white goods |
emergency |
alarm a high priority alarm such as a smoke or fire alarm |
rfu not yet allocated |
table currently defined context type s |
most of these are obvious but two of the context type s are worth special attention |
ringtone and unspecified |
the ringtone context type is used to announce an incoming phone call but only where |
there is an inband ringtone which requires an audio stream to be set up if the user was |
already receiving an audio stream from a different device to the one with the incoming phone |
call this could be problematic to signal the incoming call to the user without dropping the |
current audio stream would require at least one of the earbuds to set up a separate unicast |
stream from the second initiator in practice many acceptors are unlikely to have the |
resources to support concurrent streams from different initiators at the same time the |
acceptor could drop the current audio stream to switch to the inband ringtone but if they |
then reject the call theyd need to restore the original audio stream in most cases a better |
when context types are used in text they are e nclosed in guillemets ie and |
an inband ringtone is one where the sound is carried in an audio stream from the phone so you |
can hear your customised ringtone or message in contrast an out of band ringtone is a sound |
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