NDT-DEV email list created

Revision: 596
Author:   

Date:     Fri Sep  2 07:23:36 2011
Log:      Feedback based modifications to the detection algorithms.
http://code.google.com/p/ndt/source/detail?r=596

Modified:
 /wiki/NDTTestMethodology.wiki

=======================================
--- /wiki/NDTTestMethodology.wiki       Fri Sep  2 06:32:38 2011
+++ /wiki/NDTTestMethodology.wiki       Fri Sep  2 07:23:36 2011
@@ -193,7 +193,6 @@

 The condition "The link type detected by the  
[NDTTestMethodology#Link_Type_Detection_Heuristics Link Type Detection  
Heuristics] is not a wireless link" is always fulfilled, because the Duplex  
Mismatch Detection heuristic is run before the Link Type Detection  
heuristic.

-
 === Link Type Detection Heuristics ===

 The following link type detection heuristics are run only when there is no  
duplex mismatch condition detected and the  
[NDTTestMethodology#Web100_measured_speed web100 measured speed] is the  
same or smaller than the [NDTTestMethodology#Speed_estimate speed estimate]  
(which is a correct situation).
@@ -210,7 +209,7 @@

 ==== IEEE 802.11 (!WiFi) ====

-The link is treated as a wireless one when the  
[NDTTestMethodology#DSL/Cable_modem DSL/Cable modem] heuristic gives  
negative results, the receiver is a bottleneck and the  
[NDTTestMethodology#Web100_measured_speed web100 measured speed] is less  
than 5 Mbps but the [NDTTestMethodology#Speed_estimate speed estimate] is  
greater than 50 Mibps.
+The link is treated as a wireless one when the  
[NDTTestMethodology#DSL/Cable_modem DSL/Cable modem] is not detected, the  
receiver is a bottleneck and the [NDTTestMethodology#Web100_measured_speed  
web100 measured speed] is less than 5 Mbps but the  
[NDTTestMethodology#Speed_estimate speed estimate] is greater than 50 Mibps.

 This means that all of the following conditions should be met:
  * The heuristic for DSL/Cable modem link *gives negative results*
@@ -222,7 +221,7 @@

 ==== Ethernet link (Fast Ethernet) ====

-The link is treated as an Ethernet link (Fast Ethernet) when the  
heuristics for !WiFi and DSL/Cable modem links give negative results, the  
[NDTTestMethodology#Web100_measured_speed web100 measured speed] is between  
3 and 9.5 Mbps and the connection is very stable.
+The link is treated as an Ethernet link (Fast Ethernet) when the !WiFi and  
DSL/Cable modem are not detected, the  
[NDTTestMethodology#Web100_measured_speed web100 measured speed] is between  
3 and 9.5 Mbps and the connection is very stable.

 This means that all of the following conditions should be met:
  * The heuristics for !WiFi and DSL/Cable modem links *give negative  
results*
@@ -240,20 +239,30 @@

 A bad cable (faulty hardware link) is detected when all of the following  
conditions are met:
  * The [NDTTestMethodology#Packet_loss packet loss] multiplied by 100 and  
divided by the [NDTTestMethodology#Total_test_time_in_seconds total test  
time in seconds] *is greater than 15*
- * The  
[NDTTestMethodology#'Congestion_Limited'_state_time_share 'Congestion  
Limited' state time share] divided by the  
[NDTTestMethodology#Total_test_time_in_seconds Total test time in seconds]  
*is greater than 0.6* (*WARNING: this condition cannot be met*)
+ * The  
[NDTTestMethodology#'Congestion_Limited'_state_time_share 'Congestion  
Limited' state time share] divided by the  
[NDTTestMethodology#Total_test_time_in_seconds total test time in seconds]  
*is greater than 0.6*
  * The [NDTTestMethodology#Packet_loss packet loss] *is less than 1%*
  * The maximum slow start threshold, excluding the initial value, *is  
greater than 0*

+==== Known limitations ====
+
+The condition "The  
[NDTTestMethodology#'Congestion_Limited'_state_time_share 'Congestion  
Limited' state time share] divided by the  
[NDTTestMethodology#Total_test_time_in_seconds total test time in seconds]  
is greater than 0.6" cannot be met, because the state time share is less  
than 1 and the total test time in seconds is around 10, so this result will  
be always less than 0.1.
+
+The both conditions "The [NDTTestMethodology#Packet_loss packet loss]  
multiplied by 100 and divided by the  
[NDTTestMethodology#Total_test_time_in_seconds total test time in seconds]  
is greater than 15" and "The [NDTTestMethodology#Packet_loss packet loss]  
is less than 1%" cannot be met at the same time, because if the packet loss  
is less than 0.01, then the packet loss multiplied by 100 and divided by  
the total test time in seconds is less than 1.
+
 === Full/Half Link Duplex Setting ===

-A half duplex is detected when all of the following conditions are met:
+A half duplex is detected when the connection is receiver limited 95% of  
the time, but is flapping between 'receiver limited' and 'sender limited'  
states.
+
+This means that all of the following conditions should met:
  * The [NDTTestMethodology#'Receiver_Limited'_state_time_share 'Receiver  
Limited' state time share] *is greater than 95%*
  * The number of transitions into the 'Receiver Limited' state *is greater  
than 30 per second*
  * The number of transitions into the 'Sender Limited' state *is greater  
than 30 per second*

 === Normal Congestion Detection ===

-A normal congestion is detected when all of the following conditions are  
met:
+A normal congestion is detected when the connection is congestion limited  
a non-trivial percent of the time, the duplex mismatch is not detected and  
the receive window isn't the limiting factor.
+
+This means that all of the following conditions should be met:
  * The  
[NDTTestMethodology#'Congestion_Limited'_state_time_share 'Congestion  
Limited' state time share] *is greater than 2%*
  * The duplex mismatch condition heuristic *gives negative results*
  * The maximum window advertisement received *is greater than* the maximum  
congestion window used during Slow Start