Changes between Version 17 and Version 18 of 802.11/wlan_exp/app_notes/dcf_with_multiple_flows

Timestamp:

Apr 17, 2014, 8:33:45 AM (10 years ago)

Author:

chunter

Comment:

--

802.11/wlan_exp/app_notes/dcf_with_multiple_flows

@@ -84 +84 @@
 The above figure has two interesting features that we would like to point out:
 
-1. Even though this experiment has no channel dynamics
+1. Even though this experiment has no channel dynamics, the 802.11 DCF itself is fundamentally dynamic -- between each transmission of each node is a random backoff interval. Furthermore the interval over which the backoff time is randomly drawn is itself dependent on how successful the node is performing at any given time. The effect is that the three nodes running the DCF are constantly giving and taking their relative share of the wireless medium. You can see this in the throughput traces. As one flow dips, another flow increases to take up the gap from their absence. The sum throughput of all four flows together is less dynamic than any one of them. This is the result of this natural ebb and flow of channel access provided by the DCF.
+1. Notice that Flows 1 and 2 have nearly the same throughput timeline. In fact, it is a little difficult to even see Flow 1's timeline because Flow 2 is plotted directly in front of it. The AP is sourcing Flow 1 and Flow 2 in a round-robing fashion -- it simply alternates between each. What this throughput timeline tells us is that both flows are exposed to the same effective network dynamics: both Flows 1 and 2 show the AP's view of the network.
+
+The 802.11 DCF treats makes no real distinction between an AP or a STA even though an AP might need to source many more traffic flows than STAs. In the next section, we make a slight modification to the 802.11 DCF to give the AP some help with its extra burden.
 
 === A Simple Modification to the DCF ===
+
+How can we improve the performance of Flows 1 and 2 from the AP relative to Flows 2 and 3 from each of the stations? There are many ways to do this, but one approach can be modifying the DCF at the AP such that, on average, it has a higher likelihood of winning the backoff game over the other two stations.
+
+==== Backoff Primer ====
+
+The 802.11 DCF employs a binary exponential backoff (BEB)
 
 == Experiment 2: Symmetric with Hidden Stations ==