10.1 Architecture Description

The packet network for cdma2000 is an adjunct to the IS-41 based cdma2000 CS network. The IP network is composed of PCF, PDSN, mobile IP home agent, and AAA servers. The packet network for cdma2000 offers mobility as an option. It provides two types of access: simple IP and mobile IP. Simple IP provides nomadic access, meaning the user cannot carry its IP sessions from one point of network attachment to another. Mobile IP provides complete IP mobility based on a set of IETF specifications, including RFC2002. It is possible for a cdma2000 MS to have simultaneous mobile IP and simple IP services for different IP sessions. The network architecture for both simple IP and mobile IP is illustrated in Figure 10-1.

Figure 10-1. Simple IP and mobile IP network architecture.

10.1.1 AAA Home, Visited, and Broker Server

The authentication, authorization, and accounting (AAA) services can be provided by either the RADIUS (remote authentication dial-in user service) or Diameter protocol. The cdma2000 network first selected the RADIUS protocol and therefore RADIUS is widely used. The TIA/EIA/IS-835 specification mentions that the Diameter protocol will be supported also. In this chapter, AAA services are explained using RADIUS.

The AAA servers provide roaming. The AAA server that resides in the home IP network is called the AAA home server. The server that resides in the visited access provider network is called the AAA visited server. The AAA home server contains the subscriber profile for a user, whereas the AAA visited server contains only temporary information regarding the sessions in use by a given user. The profile may contain information such as QoS subscription and is transferred to the PDSN. The PDSN may utilize this information for authorizing access to certain services or allocating resources based on QoS requests . The AAA broker server is an intermediate server that has security relationships with the visited and the home AAA server. It is used to transfer AAA messages securely between the visited access provider network and the home IP network. A network may or may not involve any AAA broker server.

10.1.2 Packet Data Serving Node

The PDSN acts as an anchor network element (NE) inside the visited network and performs multiple functions in this role. For the mobile IP service, it provides foreign agent (FA) functionality as specified in RFC 2002. The FA is a router and provides routing services to an MS in a visited network. For both mobile and simple IP, the PDSN provides the data link layer connection to the MS by using point-to-point protocol (PPP). It is connected to the PCF using A10/A11 interface (R-P interface). It provides an association between the cellular link layer address and the IP address of a MS. The link layer address is composed of MS identifier (e.g., IMSI) and MS connection identifier (a parameter to distinguish multiple sessions per MS). The PDSN also acts as a RADIUS client and communicates user authentication information to the visited AAA server. It also collects accounting data from the PCF, correlates the data, generates accounting information, and relays it to the visited AAA server.

10.1.3 Packet Control Function

The PCF maintains a state of reachability between the RN and the MS. When packets arrive for an MS that is not reachable , the PCF buffers the packets and requests the RN to page the MS. It also collects and sends accounting information to the PDSN. The PCF interworks with the BSC and the PDSN to perform handover. In the Inter-Operability Standards (IOS) specifications, 3GPP2 A.S00001, PCF is connected to BSC by using an open A8/A9 interface. Usually in commercial products PCF is implemented as part of the BSC with a proprietary interface.

10.1.4 Radio Network

The RN is used for all the NEs used in the CS network, such as MSC/VLR, HLR, and BS. These NEs and the corresponding interfaces are enhanced to support the IP services. The MSC implements IS-41 MSC and is connected to the BSC using the A1 (control plane) and A2 (user plane) interface protocols. It performs the telephony switching functions and the mobility functions of the system. The HLR/VLR contains the subscriber information, which is needed in servicing a roaming MS. The cdma2000 BSC has radio resource management (RRM), mobility management (MM), and interconnections to the MSC. It provides bypass of voice codecs for the data packets.

10.1.5 Home Agent

The Mobile IP HA is a router on an MS's home link, which has the serving FA/PDSN registered for an MS. The serving PDSN for an MS is registered using the notion of care-of address (CoA), which is an IP address of the serving PDSN. While the MS is away from home network, the HA intercepts packets on the home link destined to the MS's home address, encapsulates them in another IP header, and tunnels them toward the PDSN.