How to chose small business VoIP

In part one of a new series, Richard Chirgwin looks at important considerations for SMEs contemplating the move to VoIP-based business telephony.

Given that the telephone is still the lifeblood of the small business, the move to VoIP should be planned carefully – the system you choose, the VoIP provider you choose, and the broadband the VoIP is running on. This week, we start by looking at what considerations should be taken into account in the choice of broadband.

The first thing you need to know as a business owner is that a “cheap and cheerful” consumer DSL service won't meet your needs if you want it to support your office phones as well.

For a start, you'll need bandwidth for the voice calls. While you can use advanced voice codecs to compress the voice, it's still worth using uncompressed voice as a rule-of-thumb: each voice call should have 64 Kbps of bandwidth available to it.

So if you're planning to run ten VoIP services over the business broadband, the voice alone will need 640 Kbps – more than the most common consumer broadband service sold in Australia at the moment, which is 512 Kbps.

So if you're currently on (for example) a 1.5 Mbps connection just to handle the office traffic, you'll need an upgrade to add business voice to the mix. Your choices are to take an ADSL2+ service from a serious provider (one way to tell if they can cope with business services is in the matter of QoS, discussed below), or to look for a symmetrical (SHDSL) service with at least 2 Mbps or better bandwidth.

A good reason to consider a symmetrical service is that even though its top speed (6 Mbps) is lower than ADSL2+, SHDSL offers the same speed upstream as downstream.

If you don't have much upload traffic – if you're more likely to receive huge e-mail attachments rather than send them, for example – then an ADSL2+ service (which offers around 1 Mbps uploads) may be sufficient. If you need both uploads and downloads, then look at SHDSL.

But you also need to be able to quarantine the voice bandwidth from other traffic. For example, you absolutely don't want to lose voice calls because someone's chosen to send you a 200 Mbyte e-mail attachment.

So your next question – one which will set consumer DSL apart from business services – is to ask whether your provider supports QoS (Quality of Service) over your connection. QoS gives priority to important traffic between yourself and the ISP, meaning the voice calls don't suffer when your link is congested.

Some businesses avoid the QoS question entirely by setting up their VoIP system on a second DSL link, to split the voice and data entirely.

Although it sounds like an extravagance, doubling the DSL spend is worth considering, even for relatively small businesses. A service that's only handling voice traffic won't need huge download capacity, and it may still help you eliminate some of the PSTN links.

A Contentious Question

“Contention” in broadband refers to how providers share their bandwidth between their customers. Because there are many spots in an ISP's network in which customer traffic shares the same infrastructure, it's an over-simplification to give a single number for contention, but for the purposes of this article, we'll do just that.

If an ISP has (for example) 10 Mbps of capacity, and shares it bewteen 100 users subscribing at 1 Mbps, then we would consider that provider to be operating at a 10:1 contention ratio.

In the world of consumer DSL, contention may be as low as 50:1 or as high as 200:1 – there's no way of knowing just by looking at the network from the outside.

However, there are some companies that specialise in business services, and which publish the contention ratios of their various services. A contention ratio of 1:1 is obviously the best – but it's also the most expensive. However, if you can afford a DSL service offering around 20:1 contention, then that's probably sufficient for the SME's VoIP requirements.

Keep in mind, however, that not all providers believe contention is as important now as it has been in the past. They argue that in the era of dark fibre, they're able to buy almost unlimited capacity from a Telstra exchange back to their own infrastructure – and the users never experience congestion. That may be true, but right now, it's only true for a limited number of providers.

Calculating Downloads

As I mentioned earlier, advanced codecs will compress voice calls a very long way. But if you haven't yet chosen your VoIP equipment and VoIP service, then you haven't settled on a codec yet – so let's instead work out download requirements based on a “worst case” of 64 Kbps.

At 64 Kbps, a conversation is consuming 8 Kbytes per second – or, since conversations run in two directions, 16 Kbytes per second. That, of course, is ignoring tricks such as silence suppression, which reduce bandwidth consumption.

In a worst case, then, you could use a phone line constantly for eight hours a day, 20 days a month, and still only generate 4.6 Gbytes in each direction.

Unless you're running a call centre, you’re not going to generate anywhere near so much traffic as this. For an ordinary office with ten phones, an allowance of 10 Gbytes for telephony should be more than sufficient.

Who Owns the Infrastructure?

Most people never think about whether they're buying their DSL service from an infrastructure owner or a reseller: it doesn't matter in the consumer space.

For a business implementing VoIP, the question is worth considering. Some broadband providers (especially those offering advanced services like ADSL2+) have built their own networks; others resell Internet access on other providers' equipment.

The main reason for favouring an infrastructure owner is the question “what if it goes wrong?”

Providers who own their DSLAMs (DSL Access Multiplexers) installed in Telstra exchanges minimise the number of fingers in the pie: if something goes wrong, it will almost certainly be in the hands of the DSL provider or Telstra. So your call for help will be closer to the source of the problem than if you've bought your broadband service from a retailer buying services from an aggregator buying services from an infrastructure owner. If you're too far down the retail chain, your provider may have no better idea than you do if something goes wrong.

There are exceptions, of course: major resellers with a close relationship to their upstream provider. It depends on whether you have the skills to take into account wholesale-retail relationships in the telecommunications industry.

An exception to this general rule about infrastructure applies to the company Nextep. Nextep owns DSL infrastructure, but it does not operate its own retail sales network, instead using a community of business-focussed resellerst as its 'feet on the street'.

In researching your broadband provider, you should also consider the question of “reach”: does the provider own infrastructure where I have my offices?

If your offices are inside the “footprint” of a single provider, you'll only ever have to deal with one organisation.

But some companies, even SMEs, don't get that luxury. A few providers – Telstra, Optus, iiNet, TPG, AAPT, Primus and Internode – have extensive rollouts, but even in cities, most providers have only partial coverage.

It's well worth working out which exchange areas your offices are in, and looking for those exchanges on the coverage lists of various DSL providers to see who can serve you without calling on someone else's equipment. A list of links to selected providers' coverage lists is at the end of this article.

Loss of Service

No matter what broadband service you choose, you'll quickly learn that nobody guarantees DSL availability to “five nines” levels. You may never experience a serious outage – scheduled outages are targeted for the wee small hours, for example – but the chances are that at some point, the DSL service will disappear.

So the question of backup service is very important.

The first thing to remember is that if you're using a DSL service, there will be at least one PSTN line coming into your office. Most of the time, it will probably be serving the fax machine – but it will be there.

So in choosing a VoIP system that serves your business, make sure it has at least one PSTN line card, and keep one PSTN number active in your business. That way, if you lose broadband connectivity for any reason other than loss of the PSTN line, you will still be able to make some calls.

If you're in a 3G coverage area, you might also consider buying a pre-paid 3G data card. These aren't expensive to buy (typically less than $200), and you can buy service if and when it's needed. It may never be needed – but if your business is dependent on the broadband connection, a backup service is worth having, never more so than if you're suddenly without telephones.

  DSL Provider Coverage Lists

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