Time Taken to complete Inquiry/Paging Procedures
Original Post: Identifying Slaves (SIG Forum) Date:
Original Post: Questions - minimum time required (eGroups Msg. 124)
The Baseband Specs can be very confusing in giving
definite minimum/maximum times used in Inquiry & paging operations between
devices, with the result that there have been a lot of speculation what these
time are. In the lack of experimental data, below is what the theory says SHOULD
be the time taken to complete a typical average successful Inquiry & Page
operation, and thus the typical times taken to setup a Bluetooth Link..
|Total (paging +inquiry)
An inquiry train must be repeated at least 256 times
(2.56s duration) , before the other train is used. Typically, in an error-free
environment, 3 train switches must take place. This means that 10.24s could
elapse unless the inquirer collects enough responses and determines to abort the
procedure. However, during a 1.28s probing window, a slave on average responses
4 time, but on different frequencies and at different times.
Minimum Inquiry Time
- A minimum time for an inquiry operation is 2 slots
(1.25ms). This is where the master transmits an inquiry message at the f(k)
frequency in the beginning, the slave scans the inquiry at the f(k) frequency at
the same time. So, the slave receives inquiry message in the first slot. The
slave responses with a FHS packet for the master's inquiry message in the next
slot. So, in total 2 slots are needed. This in highly unlikely though, as the
slave will not respond after receiving the first inquiry message but rather,
wait RAND number of slots. This RAND value varies between 0 and 1023 (Specs
Average Inquiry Time
- As stated above 10.24s could elapse unless the inquirer
collects enough responses and determines to abort the procedure. However
practice has revealed that between 3-5 seconds is sufficient. This value can
vary considerably depends on alignment of the device clocks and their respective
Maximum Inquiry Time
- 10.24 Seconds would be what the user would typically
expect for a maximum inquiry time, although the HCI specs give wait values up to
a minute (amount of time specified until the inquiry is halted). 30.72 seconds
has been suggested as a maximum time.
Assuming that you are using the mandatory paging
scheme, and using page mode R1(where each train is repeated 128 times, before
switching to the other one , Baseband p 101), then the average time for
connection should be 1.28s. The maximum time for connection is 2.56s, during
this , the A+ B train will have been repeated 128 times each, and a response
should be returned.
Note: in the specs it's not immediately
apparent that the frequency change of the page message (which changes every
1.28s) is unrelated to the train change time (also 1.28s). The frequency change
does not mark a train change event.
Minimum Page Time
- This is similar to the Minimum Inquiry Time. When the
master transmits page message at the f(k) frequency in the beginning, the salve
scans the inquiry at the f(k) frequency at the same time. So, the slave receives
the page message in the first slot. The salve responses with an ID packet for
the master's page message in the next slot. And then in the next slot the master
transmits a FHS packet to the slave. Finally in the next slot the slave answers.
So, in total 4 slots are needed for the minimum (2.5ms).
Average Page Time
- As stated above the average time for connection should be
1.28s. This is assuming that the difference between the Bluetooth clocks of the
master and the slave is between 8x1.28s and +7x1.28s, and so one of the
frequencies used by the master will be the hop frequency the slave will listen
Maximum Page Time
- As already stated , the maximum time will be 2.56s .
During this time both A+ B trains will have been repeated 128 times each, and a
response should be returned.