Diameter SWx Interface
The SWx interface is a diameter protocol based interface between AAA server and HSS. The AAA means Authentication, Authorization and accounting. The standard protocol is defined in 3GPP Spec. This interface is uses when UE does a non 3GPP access. We have discussed in s6a interface that MME is the node in EPC which does the authentication with the HSS over s6a interface. But why we need another interface for authentication e.g SWx. This is because , LTE provides a way to connect UE from network other then MME. This may be non 3GPP network. One example is WiFi calling. Where a home wifi antenna works as a LTE tower. Following diagram shows the SWx interface and other interfaces in EPC.
Procedures/messages over SWx interface:
This section describes the protocol messages over SWx interface. The base protocol is diameter. On base protocol application uses 3GPP application id 16777265.
Multimedia Authentication Request (MAR)/Answer(MAA) :
AAA server sends this command to the HSS for accessing security information. The command code value is 303. In message there is a diameter AVP called User Name . This AVP may have subscriber IMSI for identifying a subscriber on HSS. If the subscriber is found and allowed to use non 3GPP access, HSS returns the security information in answer command else and error is returned and subscriber is not allowed to use services.
Push Profile Request (PPP)/Answer(PPA):
The push profile request command have command code 505. HSS sends this command to the AAA server if any subscription data has been changed on the HSS for a subscriber. The data may be related to call or other. E.g if for a mobile user the validity has been expired , then HSS will push the subscriber data , where subscriber will not be allowed to make calls. AAA server successfully updated the data then answer message have success else have error code.
Server Assignment request (SAR)/ Answer (SAA):
The command code for server assignment request is 301. AAA server initiates the request towards the HSS. This can be register , user profile download and use de-registration request. If all fine on HSS , there is success in answer else error code.
Registration termination request (RTR)/Answer(RTA) :
Command code is 304. Multimedia server sends this message to multimedia client over Swx interface for de-registration of a client.