At its simplest, the convergence argument states that running one network is cheaper than running two. There's one set of routers, one set of cables and only one set of technologies and standards for your staff to understand. You only need to buy and manage one wide area network.
However, an IP phone network has other benefits. All your intra-company calls across it come at no extra cost. IP phones have all sorts of enhanced features, like follow-me roaming, presence applications and instant messenger compatibility.
Most interestingly for many businesses, though, is that IP phone systems make it easy to provision and move users. On a normal system, to move a number from one desk to another requires the services of an engineer.
With an IP phone, a user can just log in to a phone wherever in the office he or she feels like sitting down and the number will instantly be assigned to that desk.
For many companies, this portfolio of benefits is persuasive. But integrating the telephone and data networks is a step too far.
The argument simply boils down to cost. They will already have made a considerable investment into their existing phone and data networks and can't justify ripping one out to replace it all with something else.
Tim Bishop, director of marketing strategy at Siemens Communications, says: "The larger corporate organisations recognise that they have got quite a substantial infrastructure and to provide a reliable level of service they would have to spend a considerable amount of money. When they do the sums it is cheaper to do a low capacity high availability network for voice than to upgrade the whole thing at once."
Jason Angelus, product manager at Cisco, says: "Customers who want to go with a cost effective switching network, if they have already paid for all the cabling, sometimes it makes sense to do it that way."
Voice doesn't necessarily require a lot of bandwidth, it just requires that bandwidth to be guaranteed. And in some cases, the cheapest way to do that is to run it over a separate network.
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