new ccna book 2020 pdf

new ccna book 2020 pdf.40 Chapter 4 Wireless LAN Technologies and TopologiesEach computer has only one wireless channel. Because there is only this one wireless channel, signals cannot be sent and received simultaneously,so throughput is low and devices can only work in half-duplex mode.In these networks, the user does not have much control, so when it comes to problems such as authentication, the user is in trouble. In addition, there is a need to declare who initiates the session and who decides the order of communication, and these are the only two issues that will be addressed here as an example.2. Network Infrastracture mode In a wireless network, the AP acts as a connection point for the client. APs are actually a combination of hubs and bridges. The reasons for this are.Since there is only one wireless channel and thus cannot transmit and receive at the same time. Here the AP is only equivalent to a hub and operates in half-duplex mode.The AP has intelligence similar to that of a bridge. This is how the AP is able to discover frames and decide to forward them based on their MAC address.The difference between APs and bridges is that wireless frames are more complex. A standard Ethernet frame has a source MAC address and a destination MAC address. Wireless frames can have 3 or 4 MAC addresses. Two of these are the source MAC address and the destination MAC address, and one is the MAC address of the AP bound to the workgroup. The fourth MAC address can represent the NEXT_HOP address when using a workgroup bridge ( WGB,WorkgroupBridge).An AP is actually a type of wireless site. This terminology can lead to confusion between APs and clients in a network, and to distinguish them, clients are called stations (SIAs), and APs are called infrastructuredevices. Of course, wireless clients need to be associated with APs. In the wireless space, the AP's coverage area is called the Basic Service Area (BSA), or sometimes the Wireless Cell. o The two terms mean the same thing. When only one AP exists, the coverage area is called BSA, as shown in Figure 4.3. Usually there is an Ethernet connection between the AP and an 802.3 LAN, depending on the function of that AP.Note: Some APs have a repeater mode feature, where an Ethernet connection is not required.Figure 4.3 Basic Service Area