NDT Usage Statistics - Description

This page provides a summary view of how often the NDT server is used and what problems it has found. The purpose is to allow NDT administrators and users to monitor the health of the NDT server.

The page contains:

• A Current Test Results summary table. This table shows several important results from the latest user test.
• A graph showing the Bottleneck Link distribution. This graph shows the usage distribution broken down by the slowest link in the end-to-end path.
• A Historical Summary table. This table shows a summary of several NDT variables.
• A description of the tables and graphs.

Current Test Results

This table provides insite into how the last NDT client performed. It provides the administrator with some of the basic troubleshooting information that was displayed in the users desktop browser. The table contains the following fields:

Date/Time - The date and time of the latest test.

Total - The total number of tests recorded in the web100srv.log file.

Bottleneck Link - The slowest link in the end-to-end path as determined by the NDT Link detection algorithm>

Theoritical Limit - The maximum throughput that a connection could achieve over the end-to-end path. This value is calculated using web100 values for Round-Trip-Time, Packet size, and Packet loss. A properly functioning TCP implementation will never exceed this value. This value does not take the physical network interface speeds into account. This value is meaningful when packet loss rates are large, RTT's are big, or packet sizes are small.

C2S Speed - The Client-to-Server throughput measured by the NDT.

S2C Speed - The Server-to-Client throughput measured by the NDT.

Packet Loss - The packet loss calculated by the NDT using the Web100 variables.

Average RTT - The average Round Trip Time (RTT) calculated by the NDT. This is the time it takes a data packet to go from the NDT server to the desktop client and an Ack packet to return to the NDT server.

Minimum RTT - The minimum Round Trip Time measured by the NDT server. The NDT server uses a 10 msec resolution clock so values are rounded down to the closest 10 msec value.

Retrans/sec - The number of Packets Retransmitted per second over the 10 second throughput test.

Timeouts/sec - Them number of times per second the TCP needed to retransmit a packet based on the Timeout timer expiring.

% Out of Order - The percentage of packets that were received out-of-order. This value is calculated based on the percentage of duplicate Ack packets that were received that didn't result in a packet being retransmitted.

Send Buffer - The size, in Bytes, of the NDT server's transmit buffer.

BW*Delay - The Bandwidth * Delay product for the Send buffer. This value is the maximum throughput that could be obtained over the end-to-end path based on the NDT servers transmit buffer and the RTT of this path. This value is meaningful if the connection is reported to be sender limited.

Receive Buffer - The size, in Bytes, of the Desktop Clients advertised receive buffer.

BW*Delay - The Bandwidth * Delay product for the receive buffer. This value is the maximum throughput that could be obtained over the end-to-end path based on the Desktop Clients receive buffer and the RTT of this path. This value is meaningful if the connection is reported to be receiver limited.

Congestion Window - The size, in Bytes, of the NDT servers congestion window (CWND) variable.

BW*Delay - The Bandwidth * Delay product for the NDT servers maximum congestion window (CWND) value. This value is the maximum throughput that could be obtained over the end-to-end path based on the NDT servers CWND value and the RTT of this path. This value is meaningful if the connection is reported to be Congestion Window limited.

Bottleneck Link Graph

The NDT contains a link detection algorithm that determines the slowest physical link in the end-to-end path. The end-to-end network path is composed of numerous physical links, each with its own transmission rate. The NDT link detection algorithm attempts to determine the slowest link in the end-to-end path. This information is used to determine if problems exist or if the network is performing properly. This graph shows the distribution of bottleneck link types reported by this detection algorithm. The X axis shows the different link types the NDT is capable of detecting, the Y axis shows the percentage of connections that were determined to be a specific link type, and the numbers listed over each bar show the total number of connections of that type.

Historical Summary Statistics

This table shows some historical summary statistics. They are generated based on data stored in the web100srv.log log file. The NDT is designed to log numerous Web100 variable data to aid the NDT administartor in debugging problems. This table shows some of the historical data collected in this log

Log Starts - The date and time of the first entry in the log file.

Current - The date/time and throughput values of the latest entry. Note: this is the same as that in the Current Statistics table.

Maximum - The date/time and throughput values of the connection that achieved the highest throughput since the Start Date.

Minimum - The date/time and throughput values of the connection that achieved the lowest throughput since the Start Date.

Duplex Mismatch - A boolean flag that indicates if the current connection was reported to have a duplex mismatch condition.

Errors - A boolean flag that indicates if the current connection was reported to have an excessive error rate indicating a faulty NIC or patch cable.

Total Mismatch - The total number of duplex mismatch conditions detected since the Start Date.

Total Errors - The total number of excessive error condition detected since the Start Date.

For more details contact Richard Carlson email:rcarlson501@comcast.net