The debate between TDM circuit-switch and IP softswitch is over. Even the largest circuit switch vendors have come around to saying that IP is the way to go. However, what remains an interesting point for debate is how to get to the next-generation telecom network. Should operators deploy softswitches at all levels of the network and start providing IP telephony services at once? Or, should they go in for a phased transition from a TDM infrastructure, starting by implementing softswitches at the core of the network and then expanding to the rest of the network?

Technology Comparison

n Core Switch: There is no excuse for operators not to deploy softswitches at the core level of the telecom network. One, there is no point building parallel infrastructure for voice and data. IP is best in the wide area paradigm, with its ability to route traffic dynamically without reserving dedicated bandwidth for individual calls or applications.

The incumbent carriers have implemented ATM equipment on the core side of the network to carry the voice traffic while data traffic were segregated and sent over a routed IP backbone which was basically there for that specific purpose. So it basically meant having parallel networks for voice and data. This by today’s technological capabilities is unnecessary and only adds up to expenditure. The new operators who are building new infrastructures need not emulate the incumbents. Softswitches, when used for voice traffic at the point of aggregation which is at the middle of the core layer and the access layer of the network, removes the need of an ATM layer for transport. The same routed network being used for backhauling IP data traffic can now be used for IP voice traffic as well. This scenario is all the more realistic now that MPLS has drastically improved the quality of service in IP backbones. Now, an MPLS network can see to it that transport of a voice IP packet can be prioritized over other kinds of IP packets. Of course, there is the worry about having to interconnect with the incumbent’s network. And the incumbent is largely TDM.

The incumbents chose to go for a separate network for Internet-based services a few years ago. IP had then not matured and the Internet was purely an unreliable medium. But IP equipment is now more reliable while IP-based services have today become the only way for operators to reverse the dwindling ARPU trend.

n Access Switch: Telephones would remain TDM-based at the subscriber end for a long time, till IP phones become far cheaper than today. So, mostly one would need circuit switches to terminate the last mile voice traffic. Primarily, Class 5 switches are deployed at the access level of the network. Class 5 switches are the switches that terminates the calls and provides various kinds of value-added services to the subscribers, apart from plain telephone calls. Soft switches are yet to match the Class 5 service features. There is talk of Class 5 softswitches, but these are still in the development stage. Until there is matching service capabilities, the access switches will remain TDM-based.