As Per RFC 2865
This Attribute indicates the type of the physical port of the NAS which is authenticating the user. It can be used instead of or in addition to the NAS-Port (5) attribute. It is only used in Access-Request packets. Either NAS-Port (5) or NAS-Port-Type or both SHOULD be present in an Access-Request packet, if the NAS differentiates among its ports.
A summary of the NAS-Port-Type Attribute format is shown below. The fields are transmitted from left to right.
Type (IETF Number) = 61 for NAS-Port-Type.
Length = 6
Value = The Value field is four octets. "Virtual" refers to a connection to the NAS via some transport protocol, instead of through a physical port. For example, if a user telnetted into a NAS to authenticate himself as an Outbound-User, the Access-Request might include NAS-Port-Type = Virtual as a hint to the RADIUS server that the user was not on a physical port.
ISDN Async V.120
ISDN Async V.110
HDLC Clear Channel
SDSL - Symmetric DSL
ADSL-CAP - Asymmetric DSL, Carrierless Amplitude Phase Modulation
ADSL-DMT - Asymmetric DSL, Discrete Multi-Tone
IDSL - ISDN Digital Subscriber Line
xDSL - Digital Subscriber Line of unknown type
Wireless - Other
Wireless - IEEE 802.11
PIAFS is a form of wireless ISDN commonly used in Japan, and stands for PHS (Personal Handyphone System) Internet Access Forum Standard (PIAFS).