How to understand the Bandwidth Quality Test for VOIP
From PhonePower Knowledge Base
The speed test that Phone Power uses tests the connection you would make as if a phone call was connecting through the phone power servers. This test will show a basic idea of what your current download and upload speeds are as well as the maximum pause, jitter, and any packet loss that your internet connection is experiencing.
Please run any speed test at least 3 times in a row with no files being downloaded or uploaded, or any voip phone conversations. This will enable you to see a basic outline of the connection stability. The test will run three times.
Click Here to test your speed with VoIP
Quality of Service (QOS): What is quality of service? If these graphs represent typical download rates over time from two different broadband Internet providers, both providing an average of 3 Mbps, which service provider should get the higher quality of service rating?
The first provider (A) should win hands down and that is the basis for the VoIP Quality of Service measurement. Being able to provide a consistent download capacity is what quality of service is all about. The VoIP Quality of Service measurement is a very simple calculation:
————————————— = Quality of Service
which is just the minimum speed observed during a large download divided by the maximum speed observed, resulting in a percentage number from 0 (worst) to 100 (best). The higher the percentage, the better the quality of service. Variation in the download rate is undesirable and is penalized (resulting is a lower percentage number).
In the example graphs above, the QOS for provider A is 100% (5/5), whereas the QOS for provider B is 20% (1/5).
Please note that the VoIP QOS percentage is independent of line speed. The above graphs could be Kbps instead of Mbps and the providers would still obtain the same QOS numbers. This is by design. The VoIP QOS metric measures line quality, not line speed.
T1 Line: For example, on a virtually unused T1 line (1.544 Mbps), the test repeatedly reported a download speed of 1.46 Mbps and an upload speed of 1.44 Mbps, and as you expect, a QOS in the upper 90's.
DSL: On a DSL connection, you can expect to see a consistently high QOS number (when you are the only person using the DSL connection). If you don't, contact your DSL provider to file a problem report.
Cable Modem: On a high quality cable modem network, you can expect a QOS in the 90's or 80's. However, because you have the potential for sharing your connection with everyone in your neighborhood, some low quality networks will see lower numbers, sometimes even below 10!
Voice over IP (VoIP), Multimedia: For today's popular multimedia, IP telephony and similar bandwidth-hungry applications, consistent download capacity and a high QOS are imperative. Fluctuating bandwidth frequently results in jitter and broken connections. More information.
Round Trip Time (RTT)
The round trip time reports the time it takes for data to travel to the target destination for the speed test and back. The RTT provides a clue to the length of the journey between you and the testing server. The length of the journey will affect the performance of the test. Ideally the lower the RTT the better, less than 70ms. However, for certain tests such as trans-pacific or trans-atlantic, the results may be higher.
Jitter & Max Pause
Jitter is a key measure of VoIP quality. Jitter refers to is the variation in time between packets sent and packets arriving caused by network difficulties such as route changes, congestion, packet loss, traffic regulators etc. VoIP works by sending voice data as a stream of packets from source to destination. These packets can take a varying amount of time to reach the destination and invariably do not arrive in the order in which they were sent.
For a VoIP telephone call to work well the packets sent from the source must arrive within a certain time window (or ‘buffer’) in order for the receiving end to reassemble the packets in the correct order and reproduce the spoken words. When there is excessive jitter the time delay is too long (high latency) and packets arrive outside the time window and get lost from the call (discarded). As a result, the recomposed sound no longer reflects exactly what was sent, and depending of the extent of the delay may not be understandable by the recipient. The test measures the level of jitter on a connection and reports the associated level of VoIP sound quality.
The max pause reports the maximum amount of time spent waiting for data to arrive. A high max pause value is a sign of a bad connection. In a good test, this value will be less than 15ms to 30ms.
Packet loss plays a key role in the quality of VoIP connections, as high packet loss causes some of the voice data not to arrive to the recipient. Packet loss occurs when voice packets are discarded by the jitter buffer, or dropped by network routers/switches due to high congestion. The test measures the percentage of packet loss and reports the associated level of sound quality.
Mean Opinion Score (MOS)
The MOS, or Mean Opinion Score, is a numeric measure used for VoIP, indicating the sound quality at the receiving end of a communication circuit. Although the score is subjective it provides a widely-used method to rate the quality of voice communication in a simple way that meaningful to end users. The score is normally between 1 and 5 with 5 being the best.
The test will test the line quality and measures the highest MOS that a connection can achieve - this is independent of the CODEC selected for the VoIP test. The MOS value is reported in the test summary tab once a connection test completes, a VoIP simulation that drops below 3.5 is considered poor quality, a measure of 4.2-4.5 is considered good quality.
Taken in whole numbers, the numbers are quite easy to grade.
Here are a few tests to compare to:
- Note: Delay is measured in milliseconds - 1000 milliseconds is equal to 1 second.
This test is a 'good' test.
This test shows the high jitter.
What makes this test a poor test is the high maximum pause, high round trip times and high jitter that the test saw while the test was running. To resolve issues with tests that look like this one, please contact your internet service provider to improve the test results.