RADIUS/Diameter translation is used to convert RADIUS authentication/authorization requests to Diameter and vice-versa. The IMS AAA Server converts RADIUS accounting messages to Diameter to support the Charging Data Function (CDF) function in 3GPP networks.
WLAN devices can be RADIUS or Diameter based. The IMS AAA Server determines what kind of device it is serving and adapts to the correct AAA protocol.
Figure 18 illustrates the IMS AAA Server protocol translation function. To summarize, the IMS AAA Server may perform four possible translations as follows:
- Authentication and authorization requests from a Diameter-based WLAN device may be translated to RADIUS.
- Authentication/Authorization requests from a RADIUS-based WLAN device may be translated to Diameter. (Note that in the RADIUS protocol, these requests are combined in a single request.)
- Accounting requests from a RADIUS-based WLAN device are always converted to Diameter since the CDF is Diameter-based.
- Authentication requests from a Diameter PDG may be translated to RADIUS.
In addition, the IMS AAA Server also translates Dynamic Authorization messages when necessary. RADIUS CoA/DM messages to Diameter RAR/ASR messages and vice-versa. This is illustrated in Figure 19.