Voice over Internet Protocol (VOIP) phone systems are becoming more and more prevalent. They depend on sending the phone voice traffic over your internet connection, rather than a dedicated wireline. They offer some clearcut advantages over old fashioned wire connections: lower cost, better audio quality, more feature rich service are usual.
But many people have found out that not all high speed internet connections are equal. The principal available internet connections at this time fall into 4 groups:
VOIP phones use approximately 80Kb/sec in each direction, when a call is active. They use almost no bandwidth when they are idle. So the first consideration for any VOIP installation is the total bandwidth available. In a typical small office, where no more than 5 phones are ever in use at one time, the bandwidth required would be 400Kb/sec up and 400Kb/sec down.
But that cannot be your only worry; you may also have computers that use the same internet connection for web browsing and email traffic. Computer traffic bandwidth varies widely, from next to nothing to view a web page to very high for downloading software, music, or videos. And sending an email with a large attached photo can draw down available bandwidth to almost zero.
When that happens, phone traffic will appear very choppy, with bursts of silence amongst the words.
So, no matter what type of internet connection you have, you will need to limit the bandwidth that computers can draw. This means that some sort of rate limiting switch should be connected between your internet connection and the computers in the office. (VOIP phones do not have to be so limited, since they draw no more than 80Kb/sec no matter what.)
For a VOIP installation, the preferred connection would be fiber, with a typical bandwidth of 10-20 Mb/sec in the up and down direction. Limit the computers to 2 Mb each and they will scarcely notice.
The second best type of connection is usually cable, where bandwidths of 10Mb/sec down and 2 Mb/sec up are common. The computers on the line should be limited to 2Mb down and 500kb up. Again, they will scarcely notice the reduction.
DSL connections can get very dicey. DSL providers often use DSL modems that include (by default) a system called SIP-ALG (application level gateway). The implementation of SIP-ALG has been very poorly done, and can often cause problems with VOIP phones. Typical problems range from no connectivity at all to intermittent call drops, and a variety of other systems. There is a list of modems with this problem at http://www.voip-info.org/wiki/view/Routers+SIP+ALG. If you have one of these modems and are seeing any problems with your VOIP service, call your DSL provider and request that they deactivate SIP-ALG.
DSL connections also suffer from bandwidth problems, because they are normally asymmetric (sold as ADSL). These connections may have up to 2 Mb/sec download speeds, but only 500Kb/sec or even 256 Kb/sec on the upload. If you were paying attention earlier in this article, you can see that a 256K connection will only support 3 concurrent calls IF NO TRAFFIC IS BEING USED BY COMPUTERS ON THE LINE.
The bottom line: If you are thinking of installing VOIP and have an ADSL connection, check everything out thoroughly before making any commitment.
Finally, there is dialup. Dialup connections offer no more than 40Kb/sec in either direction. In a word, they are not suitable for VOIP calls.
The moral of this story is this: If you are having trouble with your existing VOIP system, look first at your internet connection. It is a more likely culprit than your phone system or your VOIP provider. If you are just considering a move to VOIP, get all the facts about your internet connection before even calling a VOIP provider.
William Neely is Marketing Director for Business-Phones.US, a supplier of VOIP systems for small and medium sized businesses. For more information, visit his web site at http://business-phones.us/. You may also reach him by email at support@business-phones.us or by telephone 1-866-553-3833. Your questions about VOIP installations are welcome.
Business-Phones.US is a division of Xantek, Inc. located in Las Vegas, Nevada, USA.