The Quality of VoIP Calls: Learn More about VoIP Phone Service

By: Alon Cohen – EVP/CTO at Phone.com

We got some interesting comments on our VoIP quality claims described in our post about “Why Consumers Like Our Home Phone Service?” where we claimed that VoIP quality is (ok… could be) even better than a land line!

People also commented about the fact that having a reliable network at the backend of the service provider has no relevance to VoIP call quality, stating that VoIP relies on the public internet anyway which has no real quality of service (QOS) guarantees.

First, we want to thank those who responded and pushed us to elaborate on those complex aspects just a bit more.

The QOS issue is not a simple one. The quality of VoIP is composed of many elements and the combination of which also changes from provider to provider. The usual culprits are network topology, end-point codecs, audio capabilities of end-points, end-point data latency and jitter handling; end-point network characteristics, central office redundancy, reliability and connection bandwidth and central office peek hour performance.
I will try to shed some light on few and how they affect the quality of VoIP and I apologize for using some technical terms.

VoIP Network Topology:

End-to end VoIP
• Two end-points communicate directly end-to-end. Here the quality of service depends primarily on the quality of the two Internet service providers at the end and the quality of router used at the subscriber home. Most routers today support QOS settings for VoIP or in simple words capable of providing higher priority for voice traffic. Even in this topology when a VoIP user calls a land line user the VoIP provider needs to send it’s subscriber’s data to the Land Line carrier so the call can terminate on a land line, this means that even here VoIP traffic is routed via the VoIP service provider network.

VoIP via the Central Office
• The end-points always communicate via the central office (never directly). This topology although considered more conservative allow for better call control and usually supports more in-call features.

In both topologies the quality, redundancy, and bandwidth of the connection between the VoIP service Provider’s central office and the internet backbone is critical. Given good connectivity the later topology usually guarantees better performance in terms of latency. In the first case traffic can be averted by the end point service providers via back channels or “side roads”, where in the second the traffic is directed to a very big pipe connecting the central office to the internet and then back from that pipe to the second user, which means that it is more likely that the data will to travel over major highways.

Most major Internet providers that are not involved in some vengeance against specific VoIP service provider will provide higher priority to real time VoIP traffic to keep their customers satisfied.

Better connectivity of your VoIP service provider networks to the Internet Backbone is hence crucial for providing good VoIP call quality specifically in both topologies where the data actually go through the central office. Good redundant connectivity of your VoIP Service provider is also critical to ensure overall reliability and availability of the service.

End Points
Today we can find three distinct types of VoIP endpoints on the market.

Direct VoIP Phones.
• Directly connected VoIP phones provide the highest quality calls you ever experienced, the reason is that they are not confined to the base low audio quality dictated by the analog phone system (300Hz-3400Hz). In fact they negotiate a Codec (Audio Compression Decompression Algorithm) that can even be a High Definition Audio Codec and use that to send your voice over the network in CD or (say FM radio) quality. The codec selection can be affected by the network quality, the service provider’s settings and preferences, the type of phone on the other side, and so on.

Analog Phones Connected to via an ATA (Analog Telephone Adapter)
• The ATA or home VoIP gateway is similar to a VoIP Phone but it has no headset, instead it uses standard Analog Phone as its “headset” (or handset). For an ATA there is no real need to negotiate a very good Codec as it is, after all, fed with limited sound quality of the standard analog phone (even if it is in fact a digital wireless phone, it is still working within the confines of the standard for analog phones). The fact that we use a short line between our Analog phone and the ATA ensures that we don’t loose more quality or pick up interferences over a long land line distance usually connecting standard analog phone to the nearest land line neighborhood box.

Soft Phones End Points
• We have discussed Softphone Quality Aspects in the past, so I will leave this one out for now.

To summaries, when I call my colleague using my VoIP Polycom phone connected to my WiFi network and to the Internet via Cablevision, and my colleague using Comcast Cable Internet also uses VoIP Polycom phone, we feel as if we are sitting in the same room. There is no land line system that can emulate that. Needless to say we both use the Phone.com infrastructure along the way, in fact we insist on eating what we cook on a daily basis.

As for the ATA (which I also use) given a decent service provider, your VoIP traffic is a small drop in the sea and seldom we encounter the problems that VoIP had when we first started the VoIP industry back in 1995. It’s a new world now.

If you live in a rural area and try to use a satellite dish as your internet connection for VoIP, I suggest you re-consider and use a Land Line. If you live far from your nearest telephone company and your DSL connection is intermittent, I suggest you use a Land Line, but if you have decent high-speed internet connectivity and good VoIP service provider, VoIP is the way to go.