new ccna nuggets

new ccna nuggets.7.2 Basic Topics 83conflict, the data sent from both senders will be difficult to understand and will need to be resent. This wastes time and resources & to overcome this problem, wireless networks use multiple steps to access the network. WLAN uses CarrierSenseMultipleAccess/CollisionAvoidance ( CSMA/CA, CarrierSenseMultipleAccessCollisionAvoidance) mechanism which is similar to how 802.3LAN works. CarrierSense means that a station has to determine if another station is sending data. This is done by means of Clear Channel Assessment (CCA), which is how you listen. However, you may run into the problem of two devices not listening to each other, which is called the hidden node (hiddennodeproslem) problem. This problem can be overcome by using Virtual Carrier Sense (VCS). The transport medium is not available until the physical and virtual carriers are idle.Each station must also observe the IFS, which is the interval that a station must wait before sending. IFS not only ensures that the medium is idle, but also that the interval between sending frames is not too short to avoid misinterpretation. The types of IFS intervals are as follows.Short Interframe Space (SIFS, ShortInterframeSpace): has a high priority and is used for sending ACKs, etc.Point-coordination Interframe Space (PIFS, Point-coordinationInterframeSpace): used when the AP is going to control the network.Distributed-coordinationInterframe Space (DIFS): used for data frames and is a framenormal interval between them. The IEEE defines a specific use for each of the above items. SIFSO is used when frames must be sent quickly For example, when a data frame is sent and must be acknowledged (ACK), the ACK mustmust be sent before another station can send other data. Data frames are sent using DIFSODIFS has a longer time value than SIFS, and because SIFS has a higher priority, it takes precedence over DIFS.Figure 7.1 shows the transmission process of a frame. In the figure, site A wants to send a frame. When the transmitting process starts, the physical and virtual carriers need to be idle. This means that the client must listen. To listen, the client chooses a random number and starts a countdown process called a back. any timer. The rate at which the countdown is generated is called slottime, and it differs from 802.11a,b and g°.Select a random timer ( 29),28,27, 26... /.a