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look up ccna certification.By studying the above, now that you have an idea of how data is encoded and how it is modulated, the situation becomes much simpler. Another important aspect to understand one not only for the exam, but for the actual wireless section one is that the further you are from the AP, the lower the data rate you can achieve. This is true regardless of the technology used. Although higher data rates can be achieved using different standards. you still need to deal with this issue.All Cisco wireless products are capable of performing a feature known as Dynamic Rate Shifting ( DRS, DymanticRateShifting). In an 802.11 network, devices operating in the 2.4GHz range can shift from UMbit/s to 5.5MbiVs or even to 2Mbit/s and lMbit/s, depending on the environment.0 This rate shift can be performed even without disconnecting. Again, this is done on a transmission-by-transmission basis, so if you are transferring a transmission from llMbit/s to5.5Mbit/s, and then move closer to the AP, the next transmission rate will be back to HMbit/so.This process can also occur in 802.11g and 802.11a. In all deployments, DRS supports multiple clients operating at multiple rates.4. Sending data using CSMA/CAWireless networks must deal with the potential for conflicts to occur. This is because in a wireless topology, the AP acts as the equivalent of a hub. Multiple client devices are able to send data at the same time. When this happens, conflicts arise just like in a wired network where there is a hub. The problem for a wireless network is that it is not clear when a conflict will occur. If you are in a wired network, you can receive congestion signals by listening to the line. In order to listen for congestion signals, wireless devices need to have two antennas. These devices use one antenna to send data, while listening for congestion signals with the other antenna. Although this approach seems feasible, especially because MIMO technology allows the use of multiple antennas, transmitting from one antenna1.3 Pro Forma Task 15 will drown out the signal received at the other antenna, thus resulting in the inability to listen for congestion signals.To avoid the occurrence of conflicts on a wireless network, you can use the Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA,Carrier SenseMultipleAccessCollisionAvoidance) technique. You may be familiar with the Carrier Sense Multiple Access/Collision Detection ( CSMA/CD, CarrierSenseMultipleAccessCollisionDetect) technique used in wired networks. Although they are very similar, conflict avoidance means that when a device wants to send data, it must first listen. If the channel is free, the device sends a signal to inform the other devices that it is about to send data and asks the other devices not to send data. It then listens again for a while before sending the data. Another complementary approach to this method is the use of Request To Send ( RTS, RequestToSend) and Clear To Send (CTS, ClearToSend) packets. With the RTS/CTS method, the sending device uses an RTS packet and the destination receiver uses a CTS packet. This informs other devices not to send data for a period of time.1.3 Preparation tasks.1.3.1 Review the exam points to focus on the points marked with the "Exam Points" icon at the edge of the page, which are the focus of this chapter. Table 1-4 lists these exam points.