**Different states of devices in Bluetooth:

**

Connection Modes:

A Bluetooth device in the connection state can be in any of the four following modes:Active, Hold, Sniff and Park mode.

Active Mode:

• In the active mode, the Bluetooth unit actively participates on the channel. The master schedules the transmission based on traffic demands to and from the different slaves. In addition, it supports regular transmissions to keep slaves synchronized to the channel.
• Active slaves listen in the master-to-slave slots for packets. If an active slave is not addressed, it may sleep until the next new master transmission.

Sniff Mode:

• Devices synchronized to a piconet can enter power-saving modes in which device activity is lowered.
• In the Sniff mode, a slave device listens to the piconet at reduced rate, thus reducing its duty cycle. The Sniff interval is programmable and depends on the application. It has the highest duty cycle (least power efficient) of all 3 power saving modes (sniff, hold & park).

Hold Mode:

• Devices synchronized to a piconet can enter power-saving modes in which device activity is lowered. The master unit can put slave units into Hold mode, where only an internal timer is running. Slave units can also demand to be put into Hold mode.
• Data transfer restarts instantly when units transition out of Hold mode. It has an intermediate duty cycle (medium power efficient) of the 3 power saving modes (sniff, hold & park).

Park Mode:

• In the Park mode, a device is still synchronized to the piconet but does not participate in the traffic.
• Parked devices have given up their MAC address and occasional listen to the traffic of the master to re-synchronize and check on broadcast messages. It has the lowest duty cycle (power efficiency) of all 3 power saving modes (sniff, hold & park).

Scatternet:

• If multiple piconets cover the same area, a unit can participate in two or more overlaying piconets by applying time multiplexing.
• To participate on the proper channel, it should use the associated master device address and proper clock offset to obtain the correct phase.
• A Bluetooth unit can act as a slave in several piconets, but only as a master in a single piconet.
• A group of piconets in which connections consists between different piconets is called a scatternet.