Devil's Advocate: VoIP not for everyone

Though clearly on the agenda, IP telephony is not the holy grail for every business looking to revamp voice and data networks, says Martin Brampton.

There is quite a bandwagon for adoption of voice over IP (VoIP) technology. There seems no doubt that everything electronic will become digital but the road from analogue to digital for telephony is likely to be a rocky one for some.

In fact, to talk of migration from analogue to digital is already to oversimplify what is happening. So-called analogue private exchanges have long had digital interfaces. All but the smallest organisations have interfaced to the public telephone network via ISDN digital connections, and private digital links have been common and frequently multiplexed with data.

Really, there are several technical issues at stake. One is the move towards IP from other kinds of digital transmission, another is the trend to take digital voice all the way to the handset and a third is the merging of voice and data networks.

There is talk of the latter two being driven by the operators taking their networks into IP. Yet this does not follow automatically, any more than the fact that networks have long been digital and ISDN has forced private exchanges to go wholly digital. In the end, it is economics and practicality that need to drive decisions, not blanket 'principles' of uniformity.

And here we run into current issues that throw up conflicts with the obvious long-term trend. Cost saving is often cited as a driver for VoIP. But questions about telephony costs are only loosely connected with technology. Nor are the operators blind to the various trade-offs involved.

Both personal and business telephone bills are increasingly dominated by calls to mobiles and to non-geographic numbers. Larger organisations have scope to reduce mobile costs by better management of the high volume of calls that occur between their own pool of telephone users, both fixed and mobile. Non-geographic calls offer very few opportunities for cost avoidance, with apparently cut-price operators frequently increasing the price of 0845 calls.

Switching from the public switched network to private data lines is often represented as cutting or even eliminating cost. This approach only works between fixed locations, where local and national calls have merged into a single steadily falling price. Data links are by no means free, even if they are charged at a flat rate.

The operators, notably BT, are well aware of the possibility of voice being carried over data links and are doing their best to juggle pricing to their own best advantage. And some organisations will choose to outsource both data and voice communications, thereby losing interest in the exact path followed by any particular communication.

It is widely known that the requirements for voice and data are often different. There is a good deal of interest in using low-cost broadband services for the transmission of non-critical data. But these services are vulnerable to contention, while telephony needs protected bandwidth. Even if this can be achieved within a contended service, the residual capacity for data will be badly compromised.

Similar issues arise within organisations. Expectations of telephone services are very high. Data networks have traditionally not attained such high standards. Although both the technology and deployment skills available are steadily improving, there is still a long way to go.

Ordinary telephones are frequently business-critical and sometimes safety-critical. Voice networks have commonly been wholly powered from central points, with substantial battery and generator backup to maintain extremely high levels of availability.

Data networks commonly rely on a distributed population of powered active devices, which are both harder to maintain than a central installation and also vulnerable to loss of power. They can also be difficult to site securely because of the heat they generate. Until power over Ethernet is better established, these issues remain hard to overcome.

Returning to the higher level justification of advanced facilities offered with VoIP phones, we must bear in mind that conventional private exchanges can offer a good many of these. While sophisticated facilities will sometimes provide a sound justification for a system, often disappointing take up by users frustrates good intentions.

So while it looks a safe bet to see VoIP as the long-term destination, immediate installations need to be justified on a detailed assessment of costs and benefits. For the time being, different situations will create different answers.