26.4 DATABASE QUERY USING SS7

---

26.4 DATABASE QUERY USING SS7

One of the most attractive features of SS7 is its ability to provide value-added services to subscribers such as toll-free numbers (800 numbers) and calling card facilities. For instance, a subscriber can call the toll-free number of an organization and obtain product information without paying for the call. In such services, information has to be obtained from databases. For instance, the toll-free number is generally not assigned to any particular subscriber line. It is in fact a virtual telephone number. When a subscriber dials an 800 number such as 800-123-4567, the switch gets the actual telephone number from a database. Alternatively, the database may indicate to which network the call has to be routed. Depending on the calling number, time of the day, day of the week, and so on, the actual telephone number can be different. The procedure to query a database is described with reference to Figure 26.3.

Figure 26.3: Querying a database using SS7.

1. Subscriber of switch A calls an 800 number.

2. Switch A formulates an 800 message that contains the calling number and the called number and forwards it to the STP over link AX.

3. STP selects a suitable database for responding to the query (M) and forwards the 800 message to the database over the link MX.

4. SCP M processes the query and selects the real telephone number or network or both and forwards the result to the STP over the link MX.

5. STP receives the message and routes it to switch A.

6. Switch A then identifies the number to be called and generates the IAM message as in the previous example for call setup, and then the call setup is carried out.

Value-added services such as toll-free numbers and prepaid calling cards can be provided using the SS7 network.

Note 

When a subscriber dials a toll-free number, the actual telephone number corresponding to that toll-free number is obtained from a database. Hence, the toll-free number is only a virtual telephone number.

---