Why does telephone networks fail during emergencies?

• Mumbai has about 124 telephone exchanges, which handle 2.31 million telephone lines.
• Mumbai contributes to 10 per cent of the close to 7 million cell phone subscribers in India.

During emergencies, everyone is trying to call at the same time and there aren’t enough routes for the calls to get through from. Since nearly everyone has a cell phone, the problem is compounded. A network crash ensues when the switching capacity at Switching Centres (the telephone exchange equivalent of mobile phones) is overreached. Furthermore, some hours are marked as Busy Hour Call Attempts (BHCA), during when phone lines are at their busiest, and there is a limit to the number of calls that can be put through in one hour. Big exchanges can handle up to 5 lakh calls per hour. Unfortunately, during BHCA, every number dialled — regardless of if a connection is established or not — is counted as call. So if you hear an engaged tone, do not re-dial as this will only further reduce the chances of not only yours, but anybody else’s call getting through. Wait for three to five minutes before trying again. Service providers need to work towards increasing their switching capacities before dishing out numbers to prevent crashes such as the one that happened on Tuesday. What About landlines? Telephone traffic analysis must be conducted periodically between telephones in different parts of the city. The data should be analysed and if we find that telephone traffic between, say, Borivli and Churchgate exchanges is high, then their handling capacity should be increased. When a call is made from a mobile phone to a landline, or vice versa, it adds to the calls taken by these exchanges, further burdening them.