Repenting At Leisure

In the initial years, most cellular operators plan to set up only one mobile switching centre (MSC, the equivalent of an exchange in a fixed network) per circle. And, in a few cases they plan to have small switches like the C-DoT rural automatic exchanges in cities or towns which generate enough call traffic to justify such investments.

However, given the scale of investments, it needs almost Rs one crore to install a small switch in each city or town no cellular operator plans to adopt such an architecture at least in the first few years of operation. Therefore, it is safe to assume a single MSC-network in a circle.

 

Take the case of a beleagured DoT subscriber at Chandrapur, Maharashtra. Assume he makes a call to a local Chandrapur cellular number. The path of the call would be: first, it gets switched at the Chandrapur or nearest DoT trunk automatic exchange (TAX). Then it gets routed on to a long-distance circuit or line (Route A, in the graphic) which is leased by the cellular operator from DoT. The call then gets handed over to the Pune TAX, 600 km away after which it goes on to the cellular operators MSC. The MSC searches where the cellphone user is located and routes the call to him. This operation is what DoT believes is the villain of the piece and rapid advances in wireless technologies have made it virtually impossible to find out where the call will finally end.

Once the fixed-to-cellular call reaches the Pune MSC, the software of the switch searches for her location in a computer called the home location register (HLR). The HLR updates on a real-time basis the actual location of every cellphone user; that is, it knows under which cellsite or base station she is.

Now, assume two scenarios. One, the Chandrapur cellphone user is in his office. In this case, the call is routed back to Chandrapur from Pune over the cellular operators own lines or those leased (Route B in the graphic) from DoT and the gadget next to him rings. The problem arises in the second scenario when the cellphone user goes on a business trip to Kolhapur in the same state. In this case, when the Chandrapur DoT subscriber dials his (Chandrapur) cellular number, the call once again travels to the Pune MSC.

Here, the switch queries the HLR for the called cellphones actual location. On finding that he is within the footprint of a base station in Kolhapur, the MSC directs the call on to the town (over Route C in the graphic). This potential bypass has irked DoT and resulted in a knee-jerk reaction of the new tariffs. Such a call would have technically been carried over DoTs network and would have resulted in long-distance revenues, says the DoT official.