802.11 RTS/CTS and hidden node problem

Guys,
A little confused here.
The hidden node problem is if two nodes within a cell can hear the AP but not each other. OK.
But, when we talk about 802.11b and 802.11g backwards compatibility causing reduced throughtput in terms of bandwidth, it seems that this is always blamed on 802.11g stations having to use RTS/CTS.
But,
Even in an 802.11g only cell, dont stations still have to use RTS/CTS mechanisms for the hidden node problem?
I'm confused.com!
Thx
Ken

When 802.11b clients are associated to an 802.11g access point, the access point will turn on a protection mechanism called Request to Send/Clear to Send (RTS/CTS). Originally a mechanism for addressing the "hidden node problem" , RTS/CTS adds a degree of determinism to the otherwise multiple access network. When RTS/CTS is invoked, clients must first request access to the medium from the access point with an RTS message. Until the access point replies to the client with a CTS message, the client will refrain from accessing the medium and transmitting its data packets. When received by clients other than the one that sent the original RTS, the CTS command is interpreted as a "do not send" command, causing them to refrain from accessing the medium. One can see that this mechanism will preclude 802.11b clients from transmitting simultaneously with an 802.11g client, thereby avoiding collisions that decrease throughput due to retries. One can see that this additional RTS/CTS process adds a significant amount of protocol overhead that also results in a decrease in network throughput.
In addition to RTS/CTS, the 802.11g standard adds one other significant requirement to allow for 802.11b compatibility. In the event that a collision occurs due to simultaneous transmissions (the likelihood of which is greatly reduced due to RTS/CTS), client devices "back off" the network for a random period of time before attempting to access the medium again. The client arrives at this random period of time by selecting from a number of slots, each of which has a fixed duration. For 802.11b, there are 31 slots, each of which are 20 microseconds long. For 802.11a, there are 15 slots, each of which are nine microseconds long. 802.11a generally provides shorter backoff times than does 802.11b, which provides for better performance than 802.11a, particularly as the number of clients in a cell increases. When operating in mixed mode (operating with 802.11b clients associated) the 802.11g network will adopt 802.11b backoff times. When operating without 802.11b clients associated, the 802.11g network will adopt the higher-performance 802.11a backoff times.

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import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Enumeration;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTree;
import javax.swing.event.TreeExpansionEvent;
import javax.swing.event.TreeExpansionListener;
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import javax.swing.tree.DefaultTreeModel;
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import com.talgentra.tallyman.util.properties.VersionProperties;
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import javax.swing.tree.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.util.*;
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               int[] indexArray = new int[someIndices.size()];
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                    ColorNode colorNode = (ColorNode)theChildren.elementAt(i);
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          frame.setContentPane(new TreeTest());
          SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    frame.setSize(200, 200);
                    frame.show();

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nts
www.ni.com/ask

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Hi everybody,
Iam reading through the frame handshake in WiFi. Also went through some of the good articles in this forum.
I understand that to avoid collision, RST/CTS handshake is used in the wireless Air medium.
I have attached the RTS-CTS handshake and I would like to know if these frames are unicast or broadcast.
Since they are sent from a specific source say Wifi Client to a specifc destination say Wifi AP, i assume the RTS and CTS signals to be unicast but i dont understand then how the other wifi stations/clients will listen/get the duration (NAV)
Also regarding the backoff time interval, I would like to know how this time is decided by the waiting clients? Say client A and Client B are waiting for the medium to be free. Both get the NAV duration as client C is using the medium. Now after the NAV time is complete, the clients A and B will wait for a backoff time.
>how much is this random time?
>Can both set the same backoff time say 1? >Will the clients with min backoff time will get to check the medium first.
>What is the max time each client will get to use the medium? What if Cient C using the medium has lots of data to send. Will clients A and B have to wait till Client C finishes? OR is there a max time duration.
Pl advise.

Whenever a wireless client wants to send a data packet to the access point, it actually transmits a four-packet sequence called the RTS-CTS-DATA-ACK packet sequence. Each of the four 802.11 frames carries a NAV field that indicates the number of microseconds that the channel is reserved for by a wireless client. During the RTS/CTS handshake between the wireless client and access point, the wireless client sends a small RTS frame that includes a NAV interval large enough to complete the entire sequence. This includes the CTS frame, the data frame, and the subsequent acknowledgment frame from the access point.
When the wireless client transmits its RTS packet with the NAV set, the transmitted value is used to set the NAV timers on all other wireless clients associated to the access point. The access point replies to the RTS packet from the client with a CTS packet that contains a new NAV value updated to account for the time already elapsed during the packet sequence. After the CTS packet is sent, every wireless client that can receive from the access point has updated their NAV timer and defers all transmissions until their NAV timer reaches 0. This keeps the channel free for the wireless client to complete the process of transmitting a packet to the access point.

802.11 RTS/CTS and hidden node problem

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