g different de- long as it is addressed, or for an agreed time-out period. grees of power consumption during operation: sniff, hold, and park. Even in the normal active mode, some power Hold mode saving can be achieved, as described below. The master can put a slave in the hold mode when data transfer between them is being suspended for a given Active mode period of time. The slave is then free to enter a low- During normal operation, a slave can transmit in a par- power state, or do something else, like participate in ticular time slot only if it is specifically addressed by the another piconet. It still maintains its membership in the master in the proceeding slot. As soon as it sees that its original piconet, however. At the end of the agreed time address is not contained in the header of the master's interval, the slave resynchronizes with the traffic on the message, it can "go to sleep," or enter a low-power state piconet and waits for instructions from the master. MASTER SLAVE 1 SLAVE 2 NUMBER Figure 5.2-18 Bluetooth timing. CHAPTER 5.2 Short-range wireless applications and technologies Park mode The header contains six fields with link control in- Park has the greatest potential for power conservation, formation. First, it has a three-bit active member address but as opposed to hold and sniff, it is not a directly ad- which identifies to which of the up to seven slaves dressable member of the piconet. While it is outside of a master's message is destined. An all zero address sig- direct calling, a slave in park mode can continue to be nifies a broadcast message to all slaves in the piconet. The synchronized with the piconet and can rejoin it later, next field has four bits that define the type of packet either on its own initiative or that of the master, in being sent. It specifies, for example, whether one, three, a manner that is faster than if it had to join the piconet or five slots are occupied, and the level of error correction from scratch. In addition to saving power, park mode can applied. The rem