Why Calling-Station-Id [31] attribute is "async"??

[hetene_kaz]

AS5350, IOS tried 12.4(4T) and 12.4(3b).

Cisco configured as dial-up server. When subscriber connects to some SPE via usual modem using radius authentication, his callback number may not be determined. Then I see in radius debug, that:

RADIUS: Calling-Station-Id [31] 7 "async"

When I used ios 12.3(3a) in that case i saw a blank field instead of "async".

When callback number is determined i see, i.e.:

RADIUS: Calling-Station-Id [31] 12 "3272779467"

What does "async" mean? Why exactly this? How to cut this async off?

[#2]

The word async is an NAS format type. It is like an inteface identifier.

[hetene_kaz]

Okay. Let it so. But in IOS 12.3(3a) there was a blank field. No "async" words.

Have you got any link to a document where it is said that "async" is a normal value of 31th attribute of RADIUS protocol?