Cisco Cisco IOS Software Release 12.2(16)B

The SSG Prepaid feature allows SSG to check a subscriber’s available credit to determine whether to 
connect the subscriber to a service and, how long any connection can last. The subscriber's credit is 
administered by the 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 of available credit.

To obtain the first quota for a connection, SSG submits an authorization request to the AAA server. The 
AAA server contacts the prepaid billing server, which forwards the quota values to SSG. SSG then 
monitors the connection to track the quota usage. When the quota runs out, SSG performs 
reauthorization. During reauthorization, the billing server may provide SSG with an additional quota if 
there is available credit. If no further quota is provided, SSG logs the user off. The following sections 
provide more detail about how the SSG prepaid feature and associated enhancements work.

SSG differentiates prepaid services from postpaid services by the presence of the Service Authorization 
vendor-specific attribute (VSA) in the service profile. The presence of this attribute in the service profile 
means that SSG must perform authorization before providing access to the service. 

 lists the elements of the Service Authorization VSA.

Once a service has been identified as prepaid, SSG generates an Access-Request packet called a Service 
Authorization Request. The contents of this new type of Access-Request packet are listed in 

26

9

251
Service-Info

Service Authorization The value “Z” indicates that 

authorization is required.

1

User-Name

Mobile Station (MS) 
subscriber name

—

2

PAP Password

Global service profile 
password

—

4

NAS IP Address

SSG IP address

—

6

Service-Type

Framed-user

—

26

Vendor-Specific

Name of service

Subattribute ID 251; code N.