RADIUS attribute from rfc4372
The Chargeable-User-Identity attribute, or CUI, (Type value 89) is a
unique, temporary handle used as means to, for example, correlate
authentication, accounting, and bill post-processing for a particular
chargeable subscriber. The CUI format and use follows guidelines
defined by .
In the scope of this document, the CUI attribute MAY be present in
the Access-Request. The CUI MAY also be present in the Access-
Accept. The CUI MUST be present in the Access-Accept if it was
present in the Access-Request. If the use of the Chargeable-User-
Identity attribute is supported, then the MAG and/or the LMA commits
to include the Chargeable-User-Identity attribute in all subsequent
RADIUS Accounting packets they send for the given user.