- SNIFF, HOLD and PARK modes of operation: These are the three power saving modes of operation for Bluetooth devices which are connected to a piconet. These modes are used when no data is to be transmitted.
i. SNIFF mode:
- The slave device listens to the piconet in this mode, but at a reduced rate. Thus reducing its duty cycle.
- The SNIFF interval is programmable and depends on application.
ii. HOLD mode:
- The master unit can put a slave unit into HOLD mode or a slave unit can demand to be put into HOLD mode.
- Data transfer restarts instantly when units transition out of HOLD mode.
- The HOLD is used when connecting several piconets or managing a low-power device such as temperature sensor.
iii. PARK mode:
- The device is still synchronized to the piconet but does not participate in traffic.
- PARKED devices have given up their MAC address and occasionally listen to the traffic of the master to resynchronize and check on broadcast messages. In the increasing order of power efficiency, the SNIFF mode has higher duty cycle, followed by HOLD mode with a lower duty cycle, and PARK mode with lowest duty cycle.
NETWORK connection Establishment:
Before any connection in a piconet is created, all devices are in STANDBY mode.
In this mode, an unconnected unit periodically listens for messages every 1.28
i. STANDBY mode:
seconds. It listens the messages on a set of 32 hop frequencies defined for that unit.
The device is said to be wake-up when it listens to messages. When it does not listen
to messages, it is said to be in sleep.
ii. PAGE mode:
- The connection procedure is initiated by any one of the device, which then
becomes master. A connection is made by PAGE message if the address is
- The master sends a train of 16 identical page messages on 16 different hop
frequencies defined for device to be paged (slave).
- If no response is received, the master transmits a train on remaining 16 hop
frequencies in wake-up sequence i.e. when the slave listens on messages in
- Maximum delay before master reaches is twice the wake-up period(2.56
seconds) while average delay is half the wake-up period(0.64 sec).
iii. INQUIRY mode:
- A connection is made by the master by an INQUIRY message followed by a
subsequent PAGE message if the address is unknown.
- The INQUIRY message is typically used for finding devices like public
printers, fax machines, and similar devices with unknown address.
- The INQUIRY message is similar to PAGE message, but may require one
additional train period to collect all responses.
Fig4. Device States in Bluetooth