ISG prepaid billing support allows ISG to check the available credit for a subscriber to determine whether to activate the service for the subscriber and how long the session can last. The subscriber's credit is administered by a prepaid billing server as a series of quotas representing either a duration of use (in seconds) or an allowable data volume (in bytes). A quota is an allotment, or fragment, of available credit. Allocating quotas in fragments rather than providing all the credit at once enables ISG to support the use of credit for multiple simultaneous prepaid sessions.

ISG uses the RADIUS protocol to facilitate interaction between ISG and external authentication, authorization, and accounting (AAA) servers and prepaid billing servers. A single device can serve as the AAA server and the billing server.

To obtain the first quota for a session, ISG submits an authorization request to the AAA server. The AAA server contacts the prepaid billing server, which forwards the quota values to ISG. ISG then monitors the session to track the quota usage. When the quota runs out or a specified limit is reached, ISG performs reauthorization. During reauthorization, the prepaid billing server may provide ISG with an additional quota if there is available credit. If no further quota is provided, ISG will log the user off from the service or perform some other specified action.

When a service is deactivated, the cumulative usage is provided to the prepaid billing server in an Accounting-Stop message.

The Cisco IOS prepaid volume monitor polling timer determines when ISG will initiate a prepaid reauthorization. The polling timer value is (15 seconds < polling-monitor-time < 300 seconds). This value is calculated dynamically based on the quota volume (QV) value, actual rate and the configured volume threshold. The prepaid volume monitor polling timer is not directly configurable.

To avoid revenue leak during the first authorization (when usage rate is unknown), the QV value should be a minimum of (15 x access-rate). In cases in which the usage rate is known, the QV value should be at least (15 x usage-rate).

In cases in which the input access-rate is much higher than the QV value, it is recommended that the correct QV value be calculated using the following formula: access-rate x 15 > QV < access-rate x 300. For example, an ADSL2 or VDSL user access-rate can be up to 20 Mbps. That is approximately 2.5 megabytes of data in one second. Calculate the QV value by using the following formula: 2.5 MB x 15 seconds > QV < 2.5 MB x 300 seconds. This calculation results in a QV value between 37.5 and 750 MB. We recommend avoiding the boundaries, so for this example you might pick a value of QV = 100MB

By default, ISG sends reauthorization requests to the billing server when a subscriber's quota is exhausted. ISG prepaid thresholds allow ISG to send reauthorization requests before a quota is used up. When a prepaid threshold is configured, ISG sends a reauthorization request to the billing server when the amount of remaining quota is equal to the value of the threshold. Prepaid thresholds can be configured for both time and volume.

For example, if the prepaid threshold is configured for 10 seconds, and the prepaid billing server sends ISG a quota of 30 seconds, ISG will send a reauthorization request to the prepaid billing server when the subscriber has used up 20 seconds of the quota and has 10 seconds remaining.

The ISG prepaid idle timeout can be used to suspend a prepaid service session if no traffic is received for a specified period of time. ISG keeps the session up during the suspension but releases all quota previously received for the prepaid session. Subsequent traffic on the session will cause ISG to send a reauthorization request and download a new quota for the session.

Prepaid tariff switching allows changes in tariffs during the lifetime of a session. Typically, a service provider uses prepaid tariff switching to offer different tariffs to an end user during an active connection; for example, changing a user to a less expensive tariff during off-peak hours.

Note	ISG is not involved in computing the billing rate changes that occur at tariff switch points. Billing rate change computations are performed by the prepaid billing server.

ISG supports prepaid tariff switching by using two quotas that correspond to the time before and the time after the switch point. In the authorization response to ISG, the prepaid billing server specifies the tariff switch point and the quotas for the periods before and after the tariff switch.

ISG uses the pre-tariff switch quota until the tariff switch occurs. If the pre-tariff switch quota is exhausted (or the threshold is reached) prior to the tariff switch, reathorization occurs as usual. Upon tariff switch, ISG starts using the post-tariff switch quota for prepaid session monitoring. Reauthorization occurs only when either of these quotas is exhausted, not when a tariff change occurs.

This dual-quota approach to accounting for prepaid tariff switching staggers reauthorization requests according to the usage of the subscriber and prevents the billing server from being overwhelmed with reauthorization requests at the time of a tariff switch.

1.    enable

2.    configure terminal

3.    radius-server attribute 44 include-in-access-req [vrf vrf-name]

4.    radius-server attribute 55 include-in-acct-req

5.    end

6.    show subscriber session [detailed] [identifier identifier | uid session-id| username name]

subscriber feature prepaid default
 threshold time 0 seconds
 threshold volume 0 bytes
 method-list authorization default
 method-list accounting default
 password cisco

1.    enable

2.    configure terminal

3.    subscriber feature prepaid {name-of-config | default}

4.    interim-interval number-of-minutes

5.    method-list {accounting | authorization} name-of-method-list

6.    password password

7.    threshold {time seconds | volume {kilobytes Kbytes | megabytes Mbytes | bytes bytes}}

8.    end

9.    show subscriber session [detailed] [identifier identifier | uid session-id| username name]

Perform one of the following tasks to enable prepaid billing in a service policy map or a remote service profile:

• Enabling ISG Prepaid Billing in a Service Policy Map
• Enabling ISG Prepaid Billing in Service Profile on the AAA Server

Service providers often want to offer subscribers an opportunity to recharge their accounts when they have run out of credit for their prepaid services. The tasks in this section enable you to redirect a subscriber's Layer 4 traffic to a specified server when the subscriber has run out of credit.

Before you configure ISG Layer 4 Redirect for exhaustion of credit, you should understand the following concept:

Perform the following tasks to redirect a subscriber's Layer 4 traffic upon exhaustion of credit:

• Credit-Exhausted Event
• Configuring L4 Redirection in a Service Policy Map
• Applying a Service Policy Map to Subscriber Traffic upon Exhaustion of Credit
• What to Do Next

By default, ISG drops subscriber packets when a subscriber's quota has been depleted. This task enables you override the default and forward subscriber traffic when the quota-depleted event occurs.

Before you perform this task you should understand the concept described in the "Quota-Depleted Event" below.

• Quota-Depleted Event
• What to Do Next

1.    Use the show subscriber session command to make sure the service in which prepaid billing support is configured has been activated.

2.    If the service requires service authentication, make sure the authentication succeeded.

3.    Make sure the AAA method list referred to in the prepaid billing configuration is valid and has been configured with the aaa accounting network command.

4.    Use the test aaa command to make sure the AAA server is reachable from ISG.

5.    Use the debug subscriber policy prepaid command to display debug messages about prepaid operation.