CHAPTER 26

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1. When you buy a prepaid telephone calling card, the card contains a number and a telephone number you need to call. The procedure for verification is as follows:

   • You dial the telephone number given on the calling card.

   • You hear a message to dial the calling card number.

   • You dial the calling card number.

   • The server checks the database and finds out the value of the calling card, how much has already been spent, and how much is still left.

   • You will hear this information, and then you can dial the telephone number of your choice.

   • You can converse with the person.

   • The total cost of the call will be deducted from the remaining amount, and the new amount will be stored in the database.

   The entire signaling is done through the SS7 network.

2. In a GSM network, a separate data communication network is used to carry the signaling information. This network is based on SS7. Even for communication between mobile phone and the base station, there will be a separate time slot that carries the signaling information. The voice slots are only to carry the voice data.

3. You can obtain the information on SS7 over ATM from http://www.cisco.com.

4. SS7 protocol stack is available from http://www.openss7.org.

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