9.1 Interim Accounting Updates

RADIUS now includes support for interim accounting updates. Prior to the issuing of the RADIUS Extensions RFC in June 2000, accounting updates were done primarily at the beginning and end of a transaction, when the server received Accounting-Start and Accounting-Stop packets from the user. However, now the server can include the Acct-Interim-Interval attribute in the message. The value of this attribute is the time (in seconds) between accounting update messages. An administrator can also choose to configure a minimum value locally on the RADIUS client, but this value always overrides any Acct-Interim-Interval value found in an Access-Accept packet.

This attribute can include all the attributes found in the standard Accounting Stop message except the Acct-Term-Cause attribute. The data sent within the Acct-Interim-Interval packet is always cumulative; that is to say, the data in each interim update contains data from the start of the session through the current state of the session at the time the packet is sent. Because this data is cumulative, it's up to the RADIUS client gear to ensure that only one interim update packet exists on the wire at once. Some RADIUS client machines may choose to add a delay of some amount of seconds to make sure that the previous condition is satisfied.