Cisco Cisco Access Registrar 3.5 - Manual (Page 55)

C H A P T E R
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Cisco Access Registrar 3.5 Concepts and Reference Guide
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6
Prepaid Billing Solution
This chapter describes the generic call flow between the three components required to support a prepaid
billing solution using the RADIUS protocol: the AAA client, the Cisco Access Registrar 3.5 server, and
a prepaid billing server.
Overview
When a subscriber uses a prepaid billing service, each call requires a set of data about the subscriber.
However, the AAA network has no previous knowledge of the of the subscriber’s usage behavior. To
support the prepaid billing solution, Cisco AR 3.5 uses an iterative authorization paradigm over multiple
sessions.
Each time an authorization request is made, the billing server apportions a fraction of the subscriber’s
balance into a quota. When a subscriber uses multiple sessions, each session must obtain its own quota.
When a previously allocated quota is depleted, a session must be reauthorized to obtain a new quota.
Note The granularity and the magnitude of the quota is in the design and implementation of the prepaid billing
server and is beyond the scope of this document. In general, a smaller the quota generates more network
traffic, but allows more sessions per subscriber. When the quota is equal to a subscriber’s total account
balance, there is minimal network traffic, but only one session can be supported.
When a subscriber’s current quota is depleted, the AAA client initiates a reauthorization request sending
Access-Request packets. After the Cisco AR 3.5 server receives the request, it forwards the request to
the billing server. The billing server then returns the next quota to use. The new quota might not be the
same as the previous, and the billing server might adjust the quota dynamically.
Cisco Access Registrar 3.5 uses vendor-specific attributes (VSA) to extend the standard RADIUS
protocol to carry information not usually present in the standard RADIUS packet. Cisco AR 3.5 uses a
set of VSAs allocated to the Cisco VSA pool [26,9].
Cisco Access Registrar 3.5 required several different types of measurements to support a prepaid billing
solution. These measurements require the use of metering variables to perform usage accounting.
Table 6-1 lists the different measurements and what the AAA client, Cisco AR 3.5 server, and billing
server do with them.