For the purpose of charging National STD Calls, the country is divided into a no. of    Long Distance Charging Areas (LDCA). Each LDCA comprises of several Short
    Distance Charging Areas (SDCA). For each LDCA, there is one Stn designated
   as Long Distance Charging Centre (LDCC). For each SDCA also, there is one
   Stn designated as Short Distance Charging Centre (SDCC).

   Calls between two stations in two different non-adjacent LDCAs are charged
   depending on the radial distance between the corresponding LDCCs.

   Calls between two stations in two different SDCAs located in same LDCA or
   adjacent LDCAs are charged depending on the radial distance between the
   corresponding SDCCs.