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Product Reviews
 January 2002



Telchemy Incorporated
One Focus Plaza, Suite 200
3360 Martins Farm Rd.
Suwanee, GA
Fax: 770-614-3951
Web: www.telchemy.com

Price: VQmon/EP sells for $25K for the source license, $5K for annual maintenance, and run-time royalties that start at 75 cents and reduce towards 20 cents depending on volume; VQmon/SA is similarly priced.

Occasionally, TMC Labs chooses to �spotlight� products that cannot be covered using our traditional testing methods. These types of products may be large carrier-class equipment, developmental software, or embedded tools. In these cases, we do look at every option available to us, including demos, white papers, comparative analysis, and other information so that we could understand the product as close as possible to actually testing it. After extensive research, we decided that Telchemy�s VQmon was indeed worthy of mention. However, since we did not receive any VoIP end points embedded with VQmon, we can not ascertain exactly how well the product works, but the methodology is sound and comparison analysis supports Telchemy�s claims of having quality means of testing for degradation in voice calls.

VQmon is designed to monitor the quality of every call made through a VoIP network, and operates on the received voice packet stream. There are now two versions of VQmon: End Point (EP) and Stream Analyzer (SA). The EP version is the first version to come out, and it was the one we examined more thoroughly. It is embedded in any end point, such as an IP phone or media gateway, where the end point is actually processing the voice stream and therefore has a jitter buffer and codec and recognizes the notion of ports. The SA version was just recently released. It is designed for deployment in management devices such as firewall routers, probes, and shapers. It uses a �jitter buffer simulator� in order to accurately monitor call quality for these types of products. It does this by detecting an accurate account of packet discards by the jitter buffer in the end systems, which would normally report less than actually occurred. It also allows consistent and corroborating metrics and algorithms from any point in the network.

In some ways, VQmon is similar to that of the PSQM and PAMS standards, which are means to measure the quality of VoIP calls. The main difference is that PSQM and PAMS are based on average packet loss, where it does not matter when or for how long the degradation occurs, only how often. VQmon actually measures packet bursts instead of each individual packet so that the Mean Opinion Score (MOS) can be affected severely if most of the loss takes place during one portion of the call. Furthermore, the score also depends on where in the phone call the degradation occurs. Learned from extensive research of caller behavior, people are more annoyed with degradation towards the end of a phone call than earlier. Of course, this may partly because the degradation actually caused the caller to hang up. Also, a person remembers the lack of voice quality better when it had just happened. Makes sense, doesn�t it?

One last differentiating factor between VQmon and the other measurement tools is that PSQM and PAMS requires that a pre-recorded speech file be transmitted across an IP network so that the impaired file can be compared with the original file, whereas VQmon does not require these test speech files. Therefore, VQmon has the advantage of calculating voice quality on live calls, which is especially useful to carriers and service providers. From the comparisons we studied, VQmon usually tested better than PSQM and PAMS for all of these reasons detailed above.

Besides studying the comparison data between PSQM, PAMS, and VQmon, we also analyzed a software demo for VQmon EP. This demo allowed us to select from a list of audio files and play the audio stream. When we played the file, the R-Factor, which is a transmission quality rating that is used to derive an estimated MOS, and audio output graphs showed us where there was packet loss during the call. We could zoom into the audio output graph to see more clearly about what happened when the call lost some of its quality. The different colors indicated this: green indicated normal packets, purple indicated dropped packets, blue indicated good quality packets during a burst occurrence, and red indicated the shoddy packets. We could also hear through our headphones how the packet loss effected the sound quality. After the audio file completed, a network R-Factor, User R-Factor, and overall MOS score were shown. There was also a button that displayed additional statistics. To simulate another call with impairments showing up at different times in the call, all we needed to do was press the anvil-looking button. Over all, the demo did give us a sense of how VQmon worked and how the MOS score is effected not only by packet loss (especially when coming in bursts), but also by when the packet loss occurred.

With VQmon in place, we do think that the quality of service would improve among service providers and networks using Internet telephony equipment and services and can also give a better indication of when and where a call is experiencing abnormally high packet loss. 

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