Introduction of LTE and Triple-A Diameter
Although 3G technologies deliver significantly higher bit rates than 2G technologies, there is still a great opportunity for wireless service providers to concentrate on the demand for “wireless broadband”. There is an increasing opportunity from a growing number of consumers and business professionals who are demanding the same experience and applications that they enjoy on a fixed wire line connection over wireless — anywhere, any content, stationary or mobile.
The solution is LTE, (3GPP Long Term Evolution), the next-generation network beyond 3G. In addition to enabling fixed to mobile migrations of Internet applications such as Voice over IP (VoIP), video streaming, music downloading, mobile TV and many others, LTE networks will also provide the capacity to support in demand for connectivity from a new generation of consumer devices adapted to those new mobile applications.
DIAMETER protocol is an extension of RADIUS which is intended to provide an Authentication, Authorization and Accounting (Triple-A) framework for applications such as Network access or IP-mobility.
Unified Triple-A solution Architecture in LTE
Triple-A Diameter is the preferred solution over its counterpart RADIUS protocol and is being widely adopted in with world markets today. Because of potential advantages of diameter over RADIUS and extensive features to cater the 3GPP old releases and new LTE specifications along with other system like IMS, diameter is recommended in the LTE specification as an unified solutions.
Triple-A for 3GPP System Access
The 3GPP Triple-A server is located within the 3GPP HPLMN (Home Public Land Mobile Networks). It performs the Triple-A functions and may also act as an Triple-A proxy server. For WLAN 3GPP IP Access it provides authorization, policy enforcement and routing information to the PDG, WAG and WLAN AN. For charging, the 3GPP Triple-A Server:
o Generates and reports charging/accounting information to the CDF.
o Performs offline charging control for the WLAN AN.
o Performs RADIUS to Diameter and vice versa protocol conversion when necessary.
Triple-A for Non-3GPP System Access
The 3GPP SAE (Third Generation Partnership Project System Architecture Evolution) related specifications are almost completely defined except for some detailed specifications. Among them is the PDN GW (Packet Data Network Gateway) selection for non-3GPP IP (Internet Protocol) access.
At present, the PDN GW selection function interacts with the 3GPP Triple-A (Authentication, Authorization and Accounting) server or the 3GPP Triple-A proxy and uses subscriber information provided by the HSS (Home Subscriber Server) to the 3GPP Triple-A server.
During the initial authorization, PDN GW selection information for each of the subscribed PDNs is returned to the non-3GPP access system. The PDN GW selection information includes an IP address of a PDN GW and an APN (Access Point Name).
Charging & Billing for LTE/SAE
Mobile networks have adopted many technologies during their development including GSM, GPRS/EDGE and WCDMA/HSDPA. Moreover, long-term evolution (LTE) will make its debut before long on the global technical stage. The inception of LTE/SAE (system architecture evolution) network architecture will transform the charging architecture as follows:
Firstly, the LTE network environment requires that operators deploy a network entity to detect and acquire service traffic information, and implement charging control by interacting with the online/offline charging system.
Secondly, LTE/SAE architecture supports access for LTE and 2.5G/3G networks, and also for non 3GPP access mode radio systems such as WLAN and WiMAX. LTE/SAE architecture should enable user terminals’ network handover processes that are supported by the charging system.
The 3GPP SAE adopts packet data network gateway (PDN-GW) between the SAE core network and the PDN, which acts as a data control gateway under different access modes. As a core network central control node, the PDN-GW is similar to the GPRS network’s GGSN in that it can detect service data flows and implement traffic collection. The mechanism is connected with the online/offline charging system through the Ro/Rf interface.
The PDN-GW forms the anchor for various access modes. It controls connections, disconnections and all access mode switching. Unified service flow detection and traffic collection through PDN-GW form the optimum charging solution when LTE/SAE architecture is adopted. Online charging should prompt its corresponding system to manage charging session handover and the tariff changes that are triggered by mobile access mode switching.
Unified Triple-A Interfaces for LTE/SAE
This section details the common interfaces that are required for Triple-A diameter to cater the 3GPP and non 3GPP systems:
Wa: The Wa reference point is defined between the untrusted non-3GPP IP access and the 3GPP Triple-A Server or Proxy, this reference point is optionally used to authenticate and authorize the UE for the access to the Evolved Packet System (EPS).
Ta: The Ta reference point is defined between the trusted non-3GPP IP access and the 3GPP Triple-A Server or between the trusted non-3GPP IP access and the 3GPP Triple-A Proxy. This reference point is used to transport charging-related information and optionally information about IP Mobility Mode Selection.
Wm The Wm reference point is defined between the ePDG and the 3GPP Triple-A Server or between the trusted non-3GPP IP access and the 3GPP Triple-A Proxy. The Wm reference point is used to authenticate and authorize the UE and to transport PMIPv6 related mobility parameters in case the UE attaches to the EPC via the 2b and Wn reference points.
Wx: The Wx reference point is defined between the 3GPP Triple-A Server and the HSS. The Wx reference point is used to authorize the UE and to transport PMIPv6 related mobility parameters in the chained tunnel cases.
S6c: The S6c reference point is defined between the Serving GW and the 3GPP Triple-A Proxy. The S6c reference point is used to authorize the UE and to transport PMIPv6 related mobility parameters in the chained tunnel cases.
Wn: Reference point between ePDG and a untrusted non-3GPP IP Access Gateway.
Glossary
Triple-A Authentication, Authorization & Accounting
CDF Charging Data Field
ePDG Evolved Packet Data Gateway
3GPP 3rd Generation Partnership Project
HPLMN Home Public Land Mobile Networks
HSS Home Subscriber Server
PCRF Policy Control and Charging Function
POC Proof Of Concept
PDNGW Packet Data Network Gateway
RADIUS Remote Authentication Dial In User Service
LTE Long Term Evolution
SAE System Architecture Evolution
WLAN Wireless LAN Access Network
UE User Equipment
WAG WLAN Access Gateway
Venkat R Annadata