Switching to VoIP

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QoS Past and Present

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perceived by your system users will be lower than it ought to be. It also illustrates

that you must arm your IP network against congestion.

How you can use the MOS scale

MOS can aid you in rating the perceived quality of your legacy system. Not all sys-

tem builders will have the time or inclination to do this. But, if you support more

than a few-dozen users or if call quality can vary depending on the call path, you

should determine the MOS rating of all call paths on your current system. Ask a

group of users to place calls across each call path and then record their MOS opin-

ions of each call.

Do this before you replace your legacy links with VoIP. This way, you can use the

scores as a guide when selecting standards and equipment for your new VoIP sys-

tem. You can also tell whether you’ve succeeded in replicating the call quality you

had before you started to replace legacy equipment.

After the implementation, particularly in large corporate or carrier-class networks,

establish an SLA (service-level agreement) between you and your users that provides

an MOS expectation for every call path that meets or exceeds that of your legacy

system.

Noise

In traditional telephone networks, like the PSTN, the MOS scale was used to give

engineers feedback that could be used ...