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x network congestion
x a client ended the call
x no service
x no answer
x unspecified
xa xff reserved for future use
table termination code characteristic reasoncode values
other tbs characteristics
as mentioned above tbs contains a large number of other characteristics for the call contr ol
server role these characteristics provide more detailed information about the phone call
they can be read by more complex clients such as carkits which can use them to replicate
the user experience of the phone by mirroring the level of informatio n which is available from
the original telephony application
table provides a list of the additional characteristics which have not been covered above
all of the m are mandatory for a gtbs or tbs instance to support with the exception of the
bearer signal strength characteristic and its dependent bearer signal strength reporting
interval characteristic they are all described in the telephone bearer service speci fication
section mcs and mcp
characteristic name description
bearer provider name telephony service eg vodafone t mobile
bearer uniform caller identifier uci eg skype wtsap from assigned numbers
bearer technology as displayed on the phone eg g g wi fi
bearer signal strength optional signal strength from no signal to
bearer signal strength reporting
interval how often the signal strength is reported
bearer uri schemes supported list a list of supported uri schemes
bearer list current calls a list of all current calls and their state
content control id ccid a ccid value which remains static until a service
change
incoming call target bearer uri the incoming uri of the call eg your phon es
number
table other characteristics specified in tbs
there are corresponding procedures to rea d all of the tbs characteristics in the call control
profile although support for most of the character istics in tbs are mandatory the only call
control procedure which is mandatory is the read call state procedure this reflects the fact
that for devices with a constrained user interface such as hearing aids and earbuds most
control actions are likely to take place on the phone
mcs and mcp
once youve understood telephony control the media control specifications will look very
familiar the media control profile defines two roles the media control client and the
media control server the latter resides on an initiator where the media control service
defines a state machine for media playback which is shown in figure along with a
plethora of characteristics to notify what its doing
chapter telephony and media control
figure mcs state machine for media control
for media the player normally resides in the inactive state moving to the paused state when
a track is selected from which it can be transitioned to playing from playing it can return
to paused by stopping it or be moved to the seeking state by issuing a fast forward or fast
rewind command there is no stop state or command in the state machine for digital
media there is no real distinction between the stop and pause command that difference
harks back to analogue devices wher e stop turned off the motor of a record or cassette deck
whereas pause left the motor running and lifted the stylus or playback head off the playback
medium when everything is in digital memory the operations are the same
groups and tracks
the three ma in states paused playing and seeking are only valid when there is a current
track selected which brings us to the concept of tracks and groups which is a key part of
mcs figure illustrates the concept showing a hierarchy of groups which contain
tracks it is entirely up to an implementation to define how these are structured but a group
is probably best visualised as a traditional album where the tracks are individual songs
groups can be nested to become parts of larger groups so a parent group c onsisting of the
entire works of beethoven might contain subgroups of orchestral music chamber music
piano vocal works etc which could each contain further collections of subgroups all that
mcs requires is that there is a defined structure to creat e a playing order from the start of the
first group to the end of the last group
section mcs and mcp
figure mcs arrangement of groups and tracks
groups contain tracks which may also contain segments most of the mcp controls operate
on tracks which are what most people would regard as conventional tracks on a record or
cd specifically the operations of the state machine focus on the current track the key
elements of a track are shown in figure which are the track duration offsets from
either end of the track and the playing position
figure key elements of a track
chapter telephony and media control
object types and search
mcp and mcs include a lot of functionality to support complex user interfaces such as the
screen of a cars av system most of this is based on the existing bluetooth le object
transfer service ots which allows extended information to be associated with groups and
tracks this includes extended names icons and urls which can be used to fetch more
complex objects such as album covers ots is also used for returning search results mcs
allows some very comprehensive se arch functions you can search using combinations of
track name artist name album name group name earliest year latest year and genre
for more information on these look at the msc specification theyre unlikely to be used in
products in the sho rt term so ill skip the detail and concentrate on the key aspects of media
control
playing tracks
with the structure of groups and tracks explained we can look at how media control works
once a track is selected which is gener ally a user action on the media player the player will
notify all of its connected clients using the track changed characteristic this characteristic
has no value ie its empty but is a statement that the media player now has a current track
so a client can start to control it a client can read the track title characteristic and the
track duration characteristic it can also read the track position which is returned with a
msec resolution from the start of the track the maximum track duration allowed is just
over months
a client can now write to the media control point characteristic with the values shown in
table
opcode name