Even as the telecom world appears committed to fulfilling the all-IP vision in both fixed and wireless networks, the reality in wireline networks is that old-school, big-iron TDM switches remain firmly entrenched, and in some cases continue to be the dominant technology in carrier networks. The first Class 5 TDM products hit the telecom market 30 years ago. The questions now are, what exactly will it take for network operators to finally pull the plug on TDM, and will they manage to do this before TDM turns 40?

There are many factors that could ultimately trigger this migration – including a decision by vendors to simply stop supporting TDM switches. With every passing vendor earnings call, it is becoming clearer that TDM fixed-switching revenues are rapidly drying up and that vendors are curtailing hardware and software development.

At some stage, vendors will have to cease manufacturing these products. If a vendor stated that it would discontinue a product on a future date, such as year-end 2010, then the string could play out: Although new TDM gear would not be sold from this date, existing switches would continue to be supported for approximately five to seven years. This means that by 2017, operators who continued on the TDM path would have switches that would be at "end-of-life" and without software and hardware support. While vendors could outsource support to third parties to provide additional options for telcos, realistically this is not a cost-effective long-term approach, and only delays the inevitable.

Heavy Reading research in this area has shown a clear disconnect between equipment makers' plans for IP transformation and network operators' realities. In a study conducted late last year, we found that a number of network operators have yet to craft a timeline for network transformation, and plan instead to use TDM switching indefinitely; while others propose a very gradual process, making a ten-year extension of TDM's life more than a distinct possibility.

For telecom equipment vendors, the ongoing reluctance of incumbent telcos to wean themselves completely off Class 5 TDM has the potential to be crushingly costly – not only because of the ongoing cost to support aging products, but also because of the need to convert legacy footprint into new sales of next-generation equipment. If telcos are reluctant to cut the cord to the Class 5 TDM past, vendors may have to make the hard decision to force their customers off their big-iron switches.

— Jim Hodges, Senior Analyst, Heavy Reading