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Communication between SBR Carrier Server and the Elements in LTE Network

The network devices that are used to setup an LTE network are called network elements. Each network element performs a specific function. The network elements communicate with each other over reference points, which can also be referred to the interface. Figure 124 illustrates the usage of SBR Carrier in a LTE network environment.

Figure 124: SBR Carrier in a LTE Network Environment

SBR Carrier in a LTE Network Environment

Communication with Non-3GPP Network

The SWa reference point connects the non-3GPP access network with the SBR Carrier server or proxy server (that is, 3GPP AAA server or proxy server) and transports access authentication, authorization and charging-related information in a secure manner. The SWa reference point determines whether the non-3GPP access network is trusted or not during the authentication and authorization procedures executed between the non-3GPP access network and the 3GPP AAA server.

Some specific characteristics of the SWa reference point are:

  • It may not include the information about the user's service request and the access network in the authentication and authorization request.
  • It does not download the information that describes the user's subscription profile to the non-3GPP access network.

Communication with HSS

SBR Carrier uses Diameter to communicate with an HSS through the SWx reference point to obtain authentication, subscription and PDN connection-related data. HSS contains subscriber information and authentication credentials such as user identity keys and subscription information (for example, International Mobile Subscriber Identity (IMSI), mobile station ISDN (MSISDN), and user profile information), including service subscription states and QoS parameters specific to the user.

The SWx reference point is used to perform non-3GPP access location management procedure for the following purposes:

  • To register the current SBR Carrier server address in the HSS for a 3GPP user. SBR Carrier initiates the registration procedure after authenticating a new subscriber (either during attach or handover). As part of the response, HSS returns the subscriber's user profile data (QoS profile, user capabilities, and so on.) to SBR Carrier.
  • To de-register the currently registered SBR Carrier server address in the HSS for the 3GPP user and purge any related non-3GPP user status data in the HSS. SBR Carrier de-registers its address and purges user status data when the user is not within the non-3GPP access coverage area, another evolved packet core (EPC) network entity (for example, charging system) has initiated a disconnection, or a re-authentication failure occurs.
  • To purge the user equipment from SBR Carrier. HSS initiates the purging process when the user's subscription has been cancelled or for other operator-determined reasons.

Communication with Proxy Servers

The SWd reference point connects the proxy servers, possibly through intermediate networks, to the SBR Carrier server. Some specific characteristics of this reference point are:

  • Carries data for authentication and authorization signaling between the proxy server and the SBR Carrier server.
  • Carries keying data for the purpose of radio interface integrity protection and encryption.
  • Purges a user from the access network for immediate service termination.

Communication with ePDG

The SWm reference point connects the Evolved Packet Data Gateway (ePDG) with the SBR Carrier server or proxy server (that is, 3GPP AAA server or proxy server) and transports access authentication, authorization, and subscription profile data from the SBR Carrier server or proxy server to the ePDG. The subscription profile information is fetched from the HSS by the SBR Carrier server. The SWm reference point is also used to transport session termination indications and requests initiated from both the SBR Carrier server and ePDG. Figure 125 illustrates the EAP authentication message flow between the ePDG and HSS.

Figure 125: EAP Authentication - Message Flow

EAP Authentication
- Message Flow

The SWm reference point supports both pseudonym authentication and fast re-authentication. SBR Carrier makes access restriction decisions based on the values in the following AVPs that are transmitted from the HSS as part of the Non-3GPP-User-Data AVP, which is a Grouped AVP:

  • Non-3GPP-IP-Access
  • Non-3GPP-IP-Access-APN
  • Service-Selection
  • Visited-Network-Identifier
  • VPLMN-Dynamic-Address-Allowed

Note: SBR Carrier supports all the mandatory SWm AVPs specified in 3GPP TS 29.273.

Communication with PDG or PGW

The S6b reference point connects the packet data gateway (PDG) (that is, Packet Data Network Gateway (PGW)) with the SBR Carrier server or proxy server (that is, 3GPP AAA server or proxy server). The S6b reference point is used to authenticate and authorize the user equipment and update the PDG address to the SBR Carrier server or proxy server and HSS. The S6b reference point is also used to download subscriber information to the PDG. Figure 126 and Figure 127 respectively illustrate the EAP authentication message flow and authorization message flow between the PDG and HSS.

Note:

  • SBR Carrier supports only the Diameter EAP-AKA authentication method for the S6b reference point.
  • SBR Carrier supports all the mandatory S6b AVPs specified in 3GPP TS 29.273.

Figure 126: EAP Authentication Message Flow Between PDG and HSS

EAP
Authentication Message Flow Between PDG and HSS

Figure 127: Authorization Message Flow Between PDG and HSS

Authorization
Message Flow Between PDG and HSS

Modified: 2017-03-07