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kkboy1
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LeAudio

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identity of the broadcast source and the big so that it knows which device or more correctly
device identity this information refers to the advertising set id the sid which is
contained in the primary advertisements and is defined when the extended advertising is set
up vol part e section generally stays static for the life of a device and isnt allowed
to change between power cycles although it is only a single octet it can help to iden tify the
device the broadcastid is in the auxadvind of the extended adv ertising and is
static for the lifetime of a big which may be shorter than the sid along with the
advertising addresses this is enough information for a broadcast sink to scan for the
broadcast source
the next group of parameters tells the broadcast sink what it should do this would normally
be triggered by the user selecting a broadcast source on the user interface of their commander
pasync tells it to synchronise to the periodic advertising train which lets it obtain the base
chapter setting up and using broadcast audio streams
and biginfo setting the pasync to either x or x tells the broadcast sink to go and
do that the painterval is the interval between successive auxadvind packets and if
known can help the scanner numsubgroups provides the number of subgroups in the
base followed by the most important parameter which is the bissync
bissync is the instruction from the commander to the acceptor to tell it which specific
broadcast stream or streams to connect to its a four octet wide bitmap of all of the bises
with values set to x for any stream which the acceptor should connect to theres a slight
subtlety here which is why its arrayed rather than a single octet which is that it is effectively
masked for each subg roup so each bissynci is only valid for that subgroup all other
values are set to b the reason for that is that an acceptor is never expected to receive
bises from different subgroups at the same time as the whole point of a subgroup is to
arrange associated streams together if two subgroups carried different languages say
japanese and german the expectation is that you would only choose one
figure illustration of mapping from bis num ber to bisindex
figure illustrates how bisindex values in subgroups relate to the ordering in a big where
bises are arranged in numeric order in this case tho se dont align with the bisindex values
hence the mapping of bisindex in writing a bissync value only one subgroup can be
selected so if subgroup were selected from figure the only allowable values for
bissync would be that one or both of bits and are set to b
a broadcast assistant can set the value of bissync to xffffffff meaning no
preference in which case the broadcast sink is free to make its own decision regarding which
bises to use
finally the metadata fields provide the level metadata for each subgroup typically the
audio contexts and the audio locations allowing the acceptor to decide whether they are
appropriate for what it wants to do ie do they match its current avai lable audio context
type settings the data sent in the add source operation which is written into each broadcast
section commanders
receive state can be modified at any time by the modify source operation which will update
the current information despite the specific c onnection information which is conveyed in
these two operations it is entirely up to the acceptor whether it follows the request to
synchronise with the pa and the bises which are written to it thats up to the
implementation
if the acceptor decides to act on the instruction from the commander it will use the
instructions to synchronise to the periodic advertising train either by using past or scanning
with the broadcast source information its been given retrieving the base and biginfo from
the aca d and basic audio announcement in the pa these give it all of the information it
needs to synchronise to the big after which it will use the bissync value to select which
specific bis or bises it receives
past the periodic advertising sync transfer procedure core vol part b section
is the most efficient method as the broadcast assistant provides the scan delegator with the
syncinfo data allowing it to synchroni se directly to the pa this process is known as scan
offloading
disconnection can be performed autonomously by the acceptor or a commander can use
the modify source operation to set the appropriate bissync bit to b it may also tell the
acceptor to stop synchronising to the pa but retain the rest of the source information
alternatively it can delete the source record by performing the remove source operation on
that sourceid
set source and broadcast ids
its worth a quick precis of the different ids involved in these operations as they can be
confusing
figure set and broadcast ids
chapter setting up and using broadcast audio streams
refer ring to figure the set and broadcast ids are properties of the broadcast source
both are randomly generated numbers the advertising setid is included in the primary
advertise ments and identifies a specific set of extended and periodic advertising trains the
sid is normally static for the lifetime of the device but must remain unchanged within every
power cycle sid can be useful when an acceptor or commander wants to recon nect regularly
to a known source whether thats a personal device or a fixed infrastructure broadcast
transmitter
the broadcastid is specific to a big and is carried in the broadcast audio announcement
service uuid it remain s static for the lifetime of the big
the sourceid is an acceptor generated number which is used to identify a specific set of
broadcast device and big information it is local to an acceptor and used as a reference for
a broadcast assistant in the case of a coordinated set of acceptors such as a left and right
earbud the sourceids are not related and may be different even if both are receiving the
same bis as each acceptor independently creates their own source id values
the broadcas t receive state characteristic
on the acceptor the broadcast receive state characteristic is used to inform any broadcast
assistant of its current status regarding broadcast audio streams its structure is s hown in
table
field size
octets description
sourceid assigned by the acceptor
source address type from the add modify source operation or an
autonomous action
sourceaddress from the add modify source operation or an
autonomous action
sourceadvsid from the add modify source operation or an
autonomous action
broadcastid from the broadcast audio announcement service
uuid
pasync state current synchronisation status to the pa
x not synchronised to the pa