A service data point is the node

Node (computer science)

A node is a record consisting of one or more fields that are links to other nodes, and a data field. The link and data fields are often implemented by pointers or references although it is also quite common for the data to be embedded directly in the node. Nodes are used to build linked, often...

 in the IN

Intelligent network

The Intelligent Network , is the standard network architecture specified in the . It is intended for fixed as well as mobile telecom networks...

 GSM which is responsible for providing subscriber information. A GSM network

GSM services

GSM services are a standard collection of applications and features available to mobile phone subscribers all over the world. The GSM standards are defined by the 3GPP collaboration and implemented in hardware and software by equipment manufacturers and mobile phone operators...

 element that needs information about subscriber will interrogate the SDP about such information.

The operator

Operator (programming)

Programming languages typically support a set of operators: operations which differ from the language's functions in calling syntax and/or argument passing mode. Common examples that differ by syntax are mathematical arithmetic operations, e.g...

has to define all the rate plans in SDP. The SDP is being interrogated on a periodical interval to evaluate the validity of the current call by the subscriber. The validity is being measured according to several criteria:

• The subscriber balance cover the charge of the service being requested by him/her.
• The subscriber is eligible to use the service according to his rate plan.