lar time slots and will stations are trying to transmit to a single access point, two not work in a random access environment. or more of them may be positioned such that they all are in range of the access point but not of each other. In this case, a station sensing the activity of the channel may not hear Physical layer another station that is transmitting on the same network. A refinement of the described CSMA/SA procedure is for The discussion SO far on the services and the organization a station thinking the channel is clear to send a short RTS of the WLAN did not depend on the actual type of (request to send) control frame to the AP. It will then wait wireless connection between the members of the net- to receive a CTS (clear to send) reply from the AP, which is work. Specification 802.11 and its additions specify in range of all contenders for transmission, before sending various bit rates, modulation methods, and operating its data transmission. If the originating station doesn't hear frequency channels, on two frequency bands, which we the CTS it assumes the channel was busy and SO it must try discuss in this section. (TRANSMIT IF MEDIUM FREE - DEFER IF BUSY) PREVIOUS BACKOFF TRANSMISSION TRANSMISSION MEDIUM Figure 5.2-6 CSMA/CA access method. CHAPTER 5.2 Short-range wireless applications and technologies IEEE 802.11 basic North America and most European countries is 2.400 to The original version of the 802.11 specification pre- 2.4835 GHz, and in these regions there are 79 hopping scribes three different air interfaces, each having two carrier frequencies from 2.402 to 2.480 GHz. The dwell data rates. One is infrared and the others are based on on each frequency is a system-determined parameter, frequency-hopping spread spectrum (FHSS) and direct- but the recommended dwell time is 20 msec, giving sequence spread-spectrum, each supporting raw data a hop rate of 50 hops per second. In order for FHSS rates of 1 and 2 Mbps. Below is a short description of network stations to be synchronized, they must all u