xed-size access code, which is used, among other things, to distinguish one Bluetooth WPAN from another; a fixed-size packet header, which is used for managing transmission of the packet in a Bluetooth WPAN; and a variable-size payload, which carries upper layer data. Due to the small size of these packets, large upper-layer packets need to be segmented prior to transmission over the air. 13.5.1.6 Bluetooth WPAN Connectivity Topologies The Bluetooth WPAN Piconet. A piconet is a WPAN formed by a Bluetooth device serving as a master in the piconet and one or more Bluetooth devices serving as slaves. A frequency-hopping channel based on the address of the master defines each piconet. All devices participating in communications in a given piconet are synchronized to the microseconds microseconds microseconds 1/1600 second The payload can be fragmented to fit into one, three, or five 625 microsecond slots. 68 72 bits 54 bits 0 2745 bits Access Code Header Payload The 18 bit heater is encoded with a rate 1/3 FEC resulting in a 54 bit header. Preamble Trailer AM ADOR The 64-bit Sync Word is derived from a 18 bits 24-bit address (LAP) Figure 13.3 Format for an over-the-air payload bearing Bluetooth WPAN packet. (From Figure 3, page 24, IEEE 802.15.1 Reprinted with permission, Ref. 6.) 13.5 IEEE 802.15 STANDARD frequency-hopping channel for the piconet, using the clock of the master of the piconet. Slaves communicate only with their master in a point-to-point fashion under control of the master. The master's transmissions may be either point-to-point or point-to-multipoint. Usage scenarios may dictate that certain devices act always as masters or slaves. However, this standard does not distinguish between devices with permanent master and slave designations. A slave device during one communications session could be a master in another and vice versa. The Bluetooth WPAN Scatternet. A scatternet is a collection of operational Bluetooth piconets overlapping in time and space. A Blue device may participate in several piconets