Qtcp.exe

This command-line tool measures end-to-end network service quality. Qtcp sends a sequence of test packets through a network, then reports on the queuing delay experienced by each packet. Packets that do not arrive at the destination are recorded as dropped packets. This tool can be used on either a production network or a controlled test network.

Qtcp Features

This tool:

• can report very precise delay variations, on the order of microseconds.
• invokes network Quality of Service (QoS) by default and is useful for evaluating QoS mechanisms.
• can simulate traffic flows shaped to a range of token bucket parameters for a range of user-selectable packet sizes.
• can be used on an isolated, controlled network or a production network.
• generates detailed result logs, and can collate multiple log files to produce a statistical summary across variables.

A Qtcp session is invoked on both a sending and a receiving host computer. After invocation, the tool sets up a TCP control channel between sender and receiver to properly negotiate the test. At the same time, it uses the GQoS API (part of Winsock2) to invoke QoS from local Traffic Control and from the network.

When the test is finished, the receiving host parses the log of received packets and generates three log files:

• Filename.sta reports summary statistics on the total number of packets received and specifies the sequence number of each dropped packet.
• Filename.raw contains a detailed log showing normalized send time and receive time for each packet, the latency (difference between sent and received time), packet size and sequence number.
• Filename.log normalizes the results of Filename.raw to account for clock drift between the two hosts

Details on how to use Qtcp are contained in "Using Qtcp to Measure Network Service Quality" (Qtcp.doc).

Kernel-Mode Time-Stamping Module

Qtcp works with an optional kernel-mode time-stamping module that can be run only on Microsoft® Windows® 2000. Timestmp.sys is a separate tool also included in the Windows 2000 Resource Kit, and requires separate installation with its own installer, Tsinstl.exe. As packets are transmitted and received, TimeStmp stamps them with the local time to a precision of 100 ns. If the kernel-mode time-stamping module is not installed, Qtcp uses a user-mode time stamp that is less accurate.

Files Required

• Qtcp.exe
• Timestmp.sys - optional
• Tsinstl.exe - installs Timestmp.sys

The files for Qtcp are installed by the Resource Kit setup program into the \qostools sub-directory of the Resource Kit installation directory.