cisco ccna r&s introduction to networks

cisco ccna r&s introduction to networks.Retreat time IA frame ------------------------------------------------------------------------------------- a > 1 the frame's - recipient recipient D continuous winter null, send time; , !DIFS retreat' time |_| DIFsi retreat time try B wish I ----------------------I!-the frame's, . ;duration send time --------------1 DIFS] retreat time C frame| ----------------------------------------------A the frame's|<-continuous send timeFigure 1-34 Workstation framing process within a WLANCompared to a wired LAN, a key feature of a WLAN is that the sender needs an acknowledgement from the receiver after sending the frame, in order to let the sender know that the frame has been delivered to the receiver.1. 802.11 Architecture and Basic ConceptsUnlike wired networks, where a wired workstation requires a physical connection to send data, the wireless medium is open and any workstation can send data. The IEEE 802.11 standard defines the concept of Basic Service Set (BSS). A Basic Service Set (BSS) is a number of devices that share some common parameters and can communicate with each other over a wireless connection. A basic BSS is called an Independent BSS (IBSS) and consists of two or more wireless workstations that communicate directly with each other. IBSS is sometimes referred to as an ad-hoc wireless network.An example of an IBSS is shown in Figure 1-35. .... There is another type of BSS called infrastructureBSS.O The core of an infrastructure BSS is the unmarshaled wire access point (or simply the access point [AP]). Each workstation is associated with an AP, and each frame is delivered to the AP before being forwarded by the AP to the destination workstation. The AP advertises the Service Set Identifier (SSID), and each workstation is assigned a SSID based on38 Chapter 1 Network Protocols and Network Device BasicsSSID to identify the specific wireless network.To communicate with other workstations that are not part of the same BSS (for example, servers within the unit's data center network), the AP can be given access to the unit's (wired) network via an uplink. A wired network that is accessed via an uplink is called a distribution system (DS).The AP is the boundary device between the BSS and the DS.