Changes between Version 86 and Version 87 of 802.11/wlan_exp/app_notes/dcf_with_multiple_flows

Timestamp:

Jun 19, 2015, 11:23:44 AM (9 years ago)

Author:

murphpo

Comment:

--

802.11/wlan_exp/app_notes/dcf_with_multiple_flows

@@ -99 +99 @@
 The DCF backoff procedure divides each waiting period into discrete slots. Nodes wait an integral number of slots before transmitting. The slot duration is 9 µsec.
 
-When physical carrier sensing works correctly, we expect that collisions will occur when two nodes select the same backoff slot count and initiate their transmissions in the same slot. When physical carrier sensing is disabled, nodes will still collide when they choose the same slot count. But other nodes, with larger backoff slot values, will fail to sense the collision and will initiate their own transmission in a future slot that may overlap the ongling colliding transmissions.
+When physical carrier sensing works correctly, we expect that collisions will occur when two nodes select the same backoff slot count and initiate their transmissions in the same slot. When physical carrier sensing is disabled, nodes will still collide when they choose the same slot count. But other nodes, with larger backoff slot values, will fail to sense the collision and will initiate their own transmission in a future slot that may overlap the ongoing colliding transmissions.
 
 We can test these expectations by analyzing the timestamps of PHY Tx events in the node logs by extracting the Tx timestamps and Tx durations overlapping Tx events. When overlapping Tx events are located, the timestamps of the Tx events are compared to compute the difference in Tx start times. We expect this difference to be small (specifically, within a single 9 µs slot) when carrier sensing allows nodes to defer to ongoing collisions.