PCO Operation on Wireless Network
PCO Operation on Wireless Network is made thru CDMA or GSM network.
Both the networks have capability to deliver basic two types of services:
Tele-services: Tele-services include standard telephony and mobile generated or base generated traffic.
Data-services: Data-services include computer to computer communication and packet switched traffic.
Fixed Cellular Terminal, GSM Coin Phone, Fixed Cellular Phones etc are based on these technologies to provide the wireless communication.
These products communicate with the network by converting the Analog signal to Digital signal while transmitting and Digital Signal to Analog signal while receiving.
For a call connection the mobile phone communicates with the BSS (Base Station Subsystem) which manages the radio interface between the mobile phone and NSS (Network Switching Subsystem) through the MSCs (Mobile Switching Center).
The BSS consists of many BSCs which connect to a single MSC, and each BSC typically controls upto several hundred BTS.
The NSS manages the switching function of the system and allows the MSCs to communicate with other network such as PSTN and ISDN.
PCO Operation on Land Line
In Land Line PCO the Telephone line is connected to Mechanical Exchanges in past but now Electronic Exchanges are used e.g. Alcatel E-10 B and Siemens.
For metering the call, the equipment must have some signal when call matures, this is made available by way of Polarity Reversal & 16KHz pulse.
Polarity Reversal: After dialing the number, ring goes to the called party, when called party picks up the phone, the polarity of the voltage on the caller’s telephone line reverses.
The billing equipment on receipt of this signal initiates the metering and performs billing as per data programmed in default.
16 KHz Metering: To ensure accurate metering, DOT gives 16 KHz metering pulses to PCOs from telephone exchanges. These pulses are given on telephone line every time the subscriber meter in the exchange is incremented.
Call Cost calculations
There is a mathematical relation between the number of units, total call duration and pulse rate.
Total call duration is seconds
No. of Units = -----------------------------------------------
Suppose a 600 sec. call is made to Bombay and the pulse rate of Bombay is 15 sec. for this call:
Units = 600 / 15 = 40
Note that if on division the result is not a whole number, then the number will be rounded up to its nearest higher integer number. For example if time duration is 77 seconds and the pulse rate is 15 seconds, then:
Units = (77/15)
Also note that the first unit is counted as soon as the called party picks up the phone. The second unit will be counted after time equal to the pulse rate. For example if the pulse rate is 30 seconds, units are as per the table given below:
Time duration Units
... and so on.
0 to 30 seconds
31 to 60 seconds
61 to 90 seconds