NDT-DEV email list created

Revision: 577
Author:   

Date:     Thu Sep  1 07:23:36 2011
Log:      Added Bottleneck Link Detection heuristic description.
http://code.google.com/p/ndt/source/detail?r=577

Modified:
 /wiki/NDTTestMethodology.wiki

=======================================
--- /wiki/NDTTestMethodology.wiki       Thu Sep  1 06:26:58 2011
+++ /wiki/NDTTestMethodology.wiki       Thu Sep  1 07:23:36 2011
@@ -124,6 +124,37 @@

 === 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:
+ * 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.
+
+The speed calculation is done using the following formula:
+{{{
+bits/time
+}}}
+
+where:
+ * *bits* - the number of bits in the current packet
+ * *time* - the time in 10^-6 seconds from the last packet arrival
+
+It means that the calculated speed is in mbits/second. The results are  
then quantized into the following beans:
+
+ * 0 < bits/time <= 0.01 - *RTT*
+ * 0.01 < bits/time <= 0.064 - *Dial-up Modem*
+ * 0.064 < bits/time <= 1.5 - *Cable/DSL modem*
+ * 1.5 < bits/time <= 10 - *10 Mbps Ethernet or WiFi 11b subnet*
+ * 10 < bits/time <= 40 - *45 Mbps T3/DS3 or WiFi 11 a/g subnet*
+ * 40 < bits/time <= 100 - *100 Mbps Fast Ethernet subnet*
+ * 100 < bits/time <= 622 - *a 622 Mbps OC-12 subnet*
+ * 622 < bits/time <= 1000 - *1.0 Gbps Gigabit Ethernet subnet*
+ * 1000 < bits/time <= 2400 - *2.4 Gbps OC-48 subnet*
+ * 2400 < bits/time <= 10000 - *10 Gbps 10 Gigabit Ethernet/OC-192 subnet*
+ * bits cannot be determined - *Retransmissions*
+ * otherwise - ?
+
 === Duplex Mismatch Detection ===

 The NDT contains two heuristics for the duplex mismatch detection.