All Simple Network Tester tests run between pairs of Windows PCs. Simple Network Tester is a Windows service containing network test code and a small web server. You open a web page on one PC called the "control"
PC. This "control" PC is responsible for communicating with a second Simple Net Tester agent running on a PC elsewhere.
|
|
 |
The response time or latency is computed by sending a packet from the
control PC to a reflector PC. The reflector PC will copy the incoming packet
and return it back to the control PC which will divide the transit time by 2 for the final answer. The beauty of this approach is that the control PC and the reflector PC do not need to have synchronized system clocks. However, this technique presumes that
the network speed is symmetric and this is often not true. Most broadband network service providers
provide faster download speed than upload speed.
Note that the reflector PC might take some time to return the packet. Windows is a multi-tasking
operating system. Some other task can interrupt the process of sending out the reflected packet. If this happens then Simple Network Tester will notice and deduct this time
from the transit time.
|
 |
|
The available bandwidth is the bytes per second that a PC can copy a file over the network and close its network connection. The
available bandwidth is a function of the speed of the two computers and the bandwidth that is currently available (in the face of
competition from other programs) on the network.
|
 |
Streaming media applications such as voice or video send packets of audio or video data over UDP
at evenly spaced time intervals. These packets
are accumulated into a jitter buffer at the receiving end. The jitter buffer provides these benefits:
- The sound or video is played at a constant rate even if the packets do not come in evenly. This variation in
arrival time is termed jitter.
- Out of order packets are sorted and duplicates are dropped. A route
could change in the middle of a stream. A router might re-order queued packets. Some networks may accidentally (or on purpose) duplicate packets.
The
jitter buffer inserts late packet in the right place in the playback queue and will ignore duplicated packets.
The jitter buffer only plays out media once it is full. This introduces a
delay. For voice calls, the delay
most commonly chosen for an upper delay limit is 200 milliseconds, but in practice a much shorter duration is
better. For non-real-time media (watching a video stream) a much larger buffer can be used.
Sequential packet drops are bad. For voice calls, 1 or 2 packet drops don't noticeably affect the
perceived quality of a conversation. Longer sequences of dropped packets will ruin a call. For this reason,
version 3 of Simple Network Tester reports on the number and size of sequential packet drops.
The Mean Opinion Score (MOS) is a number between 1 and 5
that expresses the quality of a voice call. These range from 5 to 1:
- 5 - Perfect. Like face-to-face conversation or radio
reception.
- 4 - Fair. Imperfections can be perceived, but sound still
clear. This is (supposedly) the range for cell phones.
- 3 - Annoying.
- 2 - Very annoying. Nearly impossible to communicate.
- 1 - Impossible to communicate
Usually the MOS is estimated from network test results (rather than using
groups of people who subjectively rate what they hear.) Using a
combination of the latency, jitter, and sequential packet drop test results,
you can compute an estimate of MOS between locations. Simple Network
Tester comes with instructions to do this.
|
Simple Network Tester comes as an easy to run "setup.exe" installer program.
We suggest that you install Simple Network Tester on a lightly loaded PC
connected to the same subnet as the PC or server you want to test. Suggestions for locations include:
- Branch
office locations
- Campus buildings, or even floors on buildings.
- Wireless locations (put it on your notebook computer!)
- Data centers containing email, web, and application servers.
- Call centers with VoIP gateways, IP PBX, unified communication services.
- Streaming music or video servers.
One license key covers multiple computers within one enterprise. There is no need to count licenses or to
obtain a unique license for each agent PC.
|
|
© 2003 - 2010 SimpleNet Software
