NDT-DEV email list created

Revision: 659
Author:   

Date:     Thu Sep 29 08:03:57 2011
Log:      Fixed the description of the Cwnd limiting mechanism in the  
middlebox test.
http://code.google.com/p/ndt/source/detail?r=659

Modified:
 /wiki/NDTTestMethodology.wiki

=======================================
--- /wiki/NDTTestMethodology.wiki       Wed Sep 21 12:27:31 2011
+++ /wiki/NDTTestMethodology.wiki       Thu Sep 29 08:03:57 2011
@@ -45,13 +45,13 @@
  # The server sets the MSS on this port to 1456
  # The client creates a connection to the server's port
  # The server sets the congestion window of the connection to be `2 * (The  
current MSS)`
+    By setting this congestion window setting the code limits TCP to  
sending only 2 packets per RTT. This mechanism is a part of the duplex  
mismatch detection. The idea for this came from Matt Mathis, and the NPAD  
duplex mismatch detection. If the server sends a maximum of 2 packets then  
it will never trigger a mismatch condition. Later when the Server-To-Client  
test is run a duplex mismatch will cause the Middlebox test to be faster  
than the Server-To-Client test.
  # The server performs a 5 second throughput test over the connection
  # The server can temporarily stop sending packets when the following  
formula is fulfilled:
     {{{
     BUFFER_SIZE * 16 < ((Next Sequence Number To Be Sent) - (Oldest  
Unacknowledged Sequence Number) - 1)
     }}}
-    The both `"Next Sequence Number To Be Sent"` and `"Oldest  
Unacknowledged Sequence Number"` values are obtained from the connection  
with the help of the [http://www.web100.org/ web100] library.<br/>
-    The above mechanism is a part of the duplex mismatch detection. The  
idea for this came from Matt Mathis, and the NPAD duplex mismatch  
detection. If the server sends a maximum of 2 packets then it will never  
trigger a mismatch condition. Later when the Server-To-Client test is run a  
duplex mismatch will cause the Middlebox test to be faster than the  
Server-To-Client test.
+    The both `"Next Sequence Number To Be Sent"` and `"Oldest  
Unacknowledged Sequence Number"` values are obtained from the connection  
with the help of the [http://www.web100.org/ web100] library. This code is  
trying to keep the server from filling up the TCP transmit queue.
  # After the throughput test, the server sends the following results to  
the client:
     || CurMSS || The current maximum segment size (MSS), in octets.||
     || !WinScaleSent || The value of the transmitted window scale option  
if one was sent; otherwise, a value of -1. ||
@@ -65,8 +65,6 @@

 The middlebox test's use of sequence numbers assumes that TCP Reno is  
being used.

-The formula used to find out when to temporarily stop sending packets is  
probably wrong, because it allows for more packets in flight (16?).
-
 === Simple Firewall Test ===

 The simple firewall test tries to find out any firewalls between the NDT  
client and the NDT server that will prevent connections to an ephemeral  
port numbers. The test is performed in both directions (i.e. the NDT client  
is trying to connect to the NDT server and the NDT server is trying to  
connect to the NDT client).