 at the same time, thus allowing the possibility that information could flow beyond the coverage area of a single piconet. A device in a scatternet would be a slave in several piconets, but master in only one of them. Figure 13.4 shows various ways that Bluetooth devices interconnect to form communicating systems. Figure 13.5 shows the Bluetooth protocol stack. Single Slave Multi-Slave Multi-Masters (Point-to-point) (Point-to-multipoint) (Scatternet) Master Slave Master/Slave Figure 13.4 Various piconet formations: (A) single-slave operation, (B) multislave operation, and (C) scatternet operation. [From Figure 4, page 25, IEEE 802.15 (Ref. 6).] Applications/Profiles OTHER RFCOMM L2CAP Audio Control Link Manager Baseband Physical Radio Figure 13.5 Bluetooth protocol stack. L2CAP stands for logical link control adaptation protocol. SDP is a service discovery layer. TCS is the telephony control and signaling layer. METROPOLITAN AREA NETWORKS 13.6 IEEE 802.16 STANDARD This is a broad-scoped standard for systems that operate between 10 and 66 GHz for a fixed point-to-multipoint service. The air interface involves both PHY and MAC sublayers. There is a base station (BS) connected to the PSTN. The BS serves a number of subscriber stations (SS). BS and SSs are stationary. Figure 13.6 is the IEEE 802.16 reference model. The system provides for broadband channels, 20, 25, or 28 MHz for both downlink and uplink, full-duplex or half-duplex, multiple access TDM/TDMA. The IEEE 802.16 system can tradeoff capacity with robustness in real-time. On the downlink, the SS (subscriber station) is associated with a specific burst. On the uplink, the SS is allotted a variable length time slot for their transmissions. When using time-division duplex (TDD), the downlink and uplink share the same RF channel. However, for economic design the downlink and uplink do not transmit simultaneously. A typical TDD frame is illustrated in Figure 13.7. Figure 13.8 shows the IEEE 802.16 TDD downlink subframe. When using the fre- quency division duplex