Radius Attribute: Called-Station-Id
As per RFC 2865:
This Attribute allows the NAS to send in the Access-Request packet the
phone number that the user called, using Dialed Number Identification
(DNIS) or similar technology. Note that this may be different from the
phone number the call comes in on. It is only used in Access-Request packets.
A summary of the Called-Station-Id Attribute format is shown below.
The fields are transmitted from left to right.

Type = 30 for Called-Station-Id.
Length = (>= 3)
String = The String field is one or more octets, containing the phone
number that the user's call came in on. The actual format of the information
is site or application specific. UTF-8 encoded 10646 [7] characters are
recommended, but a robust implementation SHOULD support the field as undistinguished
octets. The codification of the range of allowed usage of this field is
outside the scope of this specification.