NDT-DEV email list created

Revision: 592
Author:   

Date:     Fri Sep  2 05:30:03 2011
Log:      Feedback based modifications in the Bottleneck Link Detection  
section.
http://code.google.com/p/ndt/source/detail?r=592

Modified:
 /wiki/NDTTestMethodology.wiki

=======================================
--- /wiki/NDTTestMethodology.wiki       Fri Sep  2 05:03:19 2011
+++ /wiki/NDTTestMethodology.wiki       Fri Sep  2 05:30:03 2011
@@ -128,12 +128,12 @@

 === Bottleneck Link Detection ===

-The NDT can find the answer to the question "What is the slowest link in  
the end-2-end path?" by doing the following:
+The NDT tries to find the answer to the question "What is the slowest link  
in the end-2-end path?" by doing the following:
  * monitoring packet arrival times using libpcap routine
- * using TCP dynamics to create packet pairs
- * quantizing results into link type bins (no fractional or bonded links)
-
-The NDT uses packet dispersion techniques; e.g., it measures the  
inter-packet arrival times for all data and ACK packets sent or received.  
It also knows the packet size, so it can calculate the speed for each pair  
of packets sent or received. The results are then quantized, meaning that  
the NDT doesn’t recognize fractional link speed (Ethernet, T3, or FastE).  
It also wouldn’t detect bonded Etherchannel interfaces.
+ * using TCP dynamics to create packet pairs (i.e. compare two subsequent  
packets on the same connection)
+ * quantizing results into link type bins
+
+The NDT uses packet dispersion techniques; e.g., it measures the  
inter-packet arrival times for all data and ACK packets sent or received.  
It also knows the packet size, so it can calculate the speed for each pair  
of packets sent or received and quantize the results into the link type  
bins.

 The speed calculation is done using the following formula:
 {{{
@@ -159,6 +159,10 @@
  * bits cannot be determined - *Retransmissions*
  * otherwise - ?

+==== Known limitations ====
+
+The results are quantized, meaning that the NDT doesn’t recognize  
fractional link speed (Ethernet, T3, or FastE). It also wouldn’t detect  
bonded Etherchannel interfaces.
+
 === Duplex Mismatch Detection ===

 The NDT contains two heuristics for the duplex mismatch detection.