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Network choice - Alternative strategy
As the industry rushes headlong into a seemingly unstoppable love affair with VoIP, is there still a role for Time Division Multiplexing (TDM) technology in an organisation’s network? Grant Notman thinks the answer is ‘yes’
Today’s voice communication market is changing. All-IP networks are coming, the architecture has been defined, investments made and everybody agrees that Voice over IP (VoIP) is the ‘killer app’ of the future that will bring the holy grail of near-to-free calls for everyone. Right? Wrong! In the race to IP networks, upgrade decisions are being made that are both costly and time consuming, with too many organisations needlessly upgrading telecoms equipment before legacy systems have run their profitable course.
Traditional voice communications outside the office has always been available in two flavours; switched or fixed. Switched or Public Switched Telephone Network (PSTN) is the normal dial-up service that we are all familiar with, where users call a different number each time they make a call outside the building in which they work. Fixed or Leased Line is where it has been established that a user calls the same number so often that it is cheaper to put in a permanent connection between two locations – this is normally when a user has to dial 9, for example, for an outside line and a short number for internal calls.
As the industry moves into the next generation of network, many organisations are adopting IP as the network of choice but mistakenly assume that there is now only one type of voice traffic that can run over it – switched (VoIP). This is not so. Simply because the base technology has changed from Time Division Multiplexing (TDM) to IP, it does not mean that the other rules of how to build a network have also changed. Indeed, fixed links still exist using TDM over IP – a migratory technology that allows customers to use legacy equipment in an all-IP environment. TDMoIP is seen as the ideal solution for campus or metropolitan area networks, or other sizeable institutions or enterprises. The base technology change is then shown simply as a reduction in cost to the customer of telephone network charges.
The situation today is that VoIP is being, or will be, implemented for companies that need a new telephone switch and are going to be predominantly making switched calls. Meanwhile TDMoIP is actually the better technology for companies who are making switched calls but have locations where they regularly dial, thus make savings by retaining a fixed infrastructure. The added benefit is that these companies will not need to change their telephone switch to retain these savings in an all-IP world.
Evolution not revolution
That is not to say that IP isn't an important new technology in the telecommunications industry – the capacity of these networks is increasing at a prodigious rate, fuelled by the popularity of the Internet and decreasing costs associated with the technology. IP traffic has already exceeded that of global TDM, and in many cases the cost of IP data has dropped below the tariffs associated with traditional TDM services. For this reason, significant effort is being put into VoIP technologies. Despite the hype, this effort has been more protracted and less successful than initially expected. Put simply, the technology that VoIP will replace and hopes to compliment is extremely complex. Revolutionary implementation of hundreds of legacy features and thousands of variations cannot be expected to be developed in a short time frame.
There is, however, an alternative method of exploiting IP networks for telephony service that is evolutionary rather than revolutionary. This method uses IP networks as a replacement for legacy TDM networks, seamlessly interfacing with existing equipment such as the PABX – the private telephone exchange located in your business acting as the interface between your internal phones and the telephone network – and inherently providing all the hundreds of telephony features and the PSTN quality to which customers have become accustomed. This alternative is circuit extension over IP using TDMoIP.
There are two primary incentives for taking the TDMoIP route – one economic, one technological. The obvious economic benefit of IP networks, as with all packet data, is that multiple streams can share a single circuit, while a TDM timeslot engages a dedicated line for the duration of a call. If we make the assumption that two callers are speaking “politely” then there will be a 50 per cent bandwidth saving. Even with overheads, the savings will be substantial.
The added mechanism for change is to do with the way traffic is metered. Presently, data and voice are measured separately – with data traffic offered at a substantial discount. While voice pricing is still mostly determined by incumbent carriers with high overhead costs, IP traffic costs are much more competitive, as the provider incurs lower costs and is more focused on increasing market share.
Then there's convergence – technological simplification and synergy will result from consolidation of the various sources into an integrated environment. For example, a single residential telephony, data and entertainment programming service would in principle decrease end user prices, resulting in a single unified billing package, and eventually enable advanced services, such as video-on demand.
Combining TDMoIP and VoIP
VoIP will work for customers who have switched and fixed voice communications needs, however they will need to buy new telephone switches for their office and it is unlikely that they will benefit from the maximum saving possible. Moreover, customers may find that they need to acquire a new PABX before legacy products have been written down in the company's books. This is a major barrier to entry into the IP market for many organisations.
TDMoIP is not suitable for switched applications. It can, however, be used by organisations who have an existing PABX and have been offered a lower cost IP connection to their remote sites. These companies can retain their existing PABX, making a low investment in TDMoIP technology and save even more than the company would have made on new IP inter-office links.
Moreover, TDMoIP is simpler than VoIP to implement and is able to take advantage of all the existing legacy system telephone features. The technology is also relevant because it doesn't require a compromise to be made on voice quality and latency. The simplicity of TDMoIP translates into lower cost of ownership with initial expenditure savings and operational cost benefits. These savings are significant for the enterprise consumer who is typically not interested in replacing legacy TDM equipment and associated training and maintenance expenses.
Time and money
In the rush to IP, networks decisions will be made that will ultimately cost organisations both time and money. Replacement of legacy equipment isn't necessarily the answer – evolution, not revolution may well be the appropriate way forward. From a service provider point of view, TDMoIP and VoIP complement each other too. By extending TDM over the IP network from the customer site to the carrier point-of-presence the carrier can deploy larger, scalable VoIP gateways and provide the user with a simple TDMoIP Network Termination Unit at the customer premises. These TDMoIP circuits could then be used to provide a number of services in addition to VoIP - making the deployment a winner for all concerned. •
Grant Notman is General Manager of RAD UK, and can be contacted via tel: +44 118 982 0900; e-mail: grant@raddata.co.uk
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