Current Wireless Systems Industry and Evolution of 3G Systems

Service Aspects

In Chapter 1, we discussed how 3GPP- and 3GPP2-defined systems are evolving toward a common IP-based core network to support multimedia services. We use the term "multimedia," since it is the original language used by the standards bodies. However, multimedia support is not the only goal of IP-based services capabilities. Rather, the goal is the integration of data and other media onto a single uniform session-handling system. This approach will allow for novel service experiences and the integration of media-based interaction with humans and machines with data-based interaction with humans and machines, resulting in an innovative ways to present services to a user equipped with mobile devices radically different from today's mobile phones

The architecture of all-IP-based systems, or IP Multimedia Subsystems (IMSs), shown in Figure 9.1, is based on the Home Subscriber Server (HSS). An enhancement of the Home Location Register, HSSs support subscriber data related to IMSs based on Session Initiation Protocol (SIP—[RFC2543]) servers that control media sessions establishment and gateways used to interwork with other systems such as the PSTN and legacy mobile systems. The HSS will include functionality previously associated with the HLR, including wireless network access control and subscriber profile management, as well as multimedia services subscription data and IP-based registration information. The registration information sets up a mapping between user public identities and the services that the user has currently activated (for instance, presence or multimedia conferencing services nicknames), the user private identity (such as the IMSI), and the current IP address used to reach the user. User registration to services depends on explicit authentication, subscription, and possibly credit checking. The interface to the HSS in 3GPP is based on MAP (for wireless access network access control) and DIAMETER, while in 3GPP2 it is only DIAMETER based.

Figure 9.1: Simplified IMS architecture.

Figure 9.2 outlines the registration process for a subscriber accessing IMS services in 3GPP-compliant networks (Release 5). The subscriber equipped with a proper terminal first attaches to a UMTS network. Then a Packet Data Protocol (PDP) context is set up for an IMS-enabled APN (associated to an IPv6 network hosting IMS servers). Then it uses the services of a Proxy CSCF (Call Session Control Function, a SIP proxy server defined for 3GPP IMS architecture) to register with the HSS in the home network. In the process, the home network assigns the subscriber to a Serving CSCF (a SIP server defined in the 3GPP IMS architecture to offer service control and session control to subscribers). The S-CSCF is located in the home network, and it can therefore deliver the same look and feel of services independent of the current user location and serving network.

Figure 9.2: The 3GPP IMS subscriber registration.

The IMS uses packet-based services. At this time, packet-based services do not include efficient support of multicast, which is currently supported via replication of the multicast information over unicast bearers at the gateway nodes (the GGSN). A set of specifications is being readied for 3GPP Release 6, so that the radio interface will become multicast and broadcast services capable, and a new set of services will be made available.

This creates significant new revenue potential, since the availability of IP-based broadcast services will certainly make it possible to generate revenues from advertising in ways unknown to current networks. This will create a demand for multicast and broadcast content distribution networks, which will need to track user mobility. This in turn will drive a new kind of MVPN, namely multicast MVPNs, where traffic is sent only once to any IP network access point and the access point has at least one member of the multicast group. This can also be accomplished simply by extending current multicast routing protocols, or by using multicast tunnels between the multicast distribution gateway and the access points.

IMS will be IPv6-based, and it will potentially aid the large-scale introduction of the IPv6 protocol in carriers' networks. As a result, the IP VPN technology, which needed to support IMS VPNs—such as those associated with MVNOs or large organizations—will need to be IPv6-aware. In our view the use of MVPN will still persist in IPv6 networks, despite the disappearance of its need in real private address space. In fact, tight access control is a prerequisite for commercial data service delivery, which makes it necessary to use MVPN technologies to govern access to services at the network layer.

Finally, the ability to deliver media flows comes in 3GPP, recently 3GPP2 started some activity on this too, with the ability to bind a UMTS network bearer to the related media session via a COPS-PR-based [RFC3084] policy control mechanism that uses the delivery of media authorization tokens to the session endpoints. These tokens are then used during the bearer allocation request to validate the association of the bearer to the media stream and to install the associated packet filters, thus allowing service providers to charge simply based on media session duration or content and not for the bearer service. This feature is supported by the so called Go interface between the GGSN and the Packet control function of the CSCF

IP-Based Mobility

IP mobility support is an increasingly popular method for keeping a mobile station connected to the Internet while changing the point of attachment to the Internet. However, sometimes a mobile station isn't required to be permanently reachable at the IP layer, so this kind of mobility support may not be part of the evolution of mobile systems.

The IETF Seamoby (for Seamless Mobility) Working Group has drafted a different proposal addressing this issue. The MS would not be involved in explicitly registering with the HA; rather, the network tracks it so that the MS is always reachable at a tracking server, which then could page the MS when some entity need to communicate with it. We believe this may not prove to be a successful approach, since most access networks come with this capability at the link layer. More interestingly, when multiple IP level handoff candidates exit at a given location, the problem exists on how to detect the best handoff candidate. This problem is somewhat philosophical, but it has both business and technical implications, such as roaming to another provider network, choosing a low-cost option, and using an access point that allows for service continuity with unchanged QoS. The Seamoby WG is also considering a proposal on how to address this problem. This proposal from the Seamoby Working Group faces an enormous set of unresolved problems that would limit its practical deployment, if the standards were approved.

There is an urgent need to make some methods available for mobile user authentication in an IP-based network by just using IP to exchange authentication information, with the access point acting as a network access server. In the IETF, the Protocol for Carrying Authentication for Network Access (PANA) Working Group has been formed to address this issue. Many proposals are on the table—some that reuse DHCP authentication [RFC3118] and others that extend EAP [RFC2284] to be IP based, in accordance with some recent trends in 802.11. The PANA WG promises to develop a universal authentication protocol that may be used in any network to allow for universal and seamless roaming. However, it may well be that the industry—especially driven by proliferation of WLAN applications—will converge on another de facto standard if the PANA WG is not quick enough to find a solution.

Billing for Wireless Data Services

Originally, billing for wireless data services in the cellular environment was based on the innovative concept of volume-based billing. This model was expected to be more attractive to the consumer than the traditional time-based usage metering, which kept a connection on continually and used it only when necessary to transmit and receive data. Service providers saw the added benefit of encouraging limited use of radio resources while offering high-margin data delivery services. However, this model has proven unsuccessful for the general consumer market, other than for transactional applications such as those offered via i-mode in Japan.

Nevertheless, beyond its use in i-mode, volume-based charging in general is not considered to be an attractive option for consumers and corporations alike. In fact, unless volume fees become sufficiently low, there is no acceptance of paying hefty amounts of money to transfer documents or multimedia over the wireless link. On many occasions, the cost of this may surpass the productivity gain or time value of having ubiquitous access to information, making this business model not viable, since users would rather wait to access information until they are at some location allowing them to use an alternate network access technology that suits their needs and finances better.

As a result, one expected trend is for wireless carriers using the flat-fee approach already adopted by the WLAN access providers. This will attract the masses to the wireless network data services experience and let them become familiar with and pay for an ever-growing host of applications, offering unique value needed to compensate for the commoditization of voice-based services. Competition will not be solely in the access fees, but also in the ability to deliver content and services that are valuable to customers. Sophisticated application level billing will be an integral service, as well as the collection of billing information from partner ASPs, and the correlation of network access level Charging Detail Records (CDRs) with application level CDRs.

Finally, credit management via prepaid or credit card accounts may be extended with the integration of financial or banking services offered by the wireless carrier, who may tap into the financial services market, perhaps with the aid of some existing online merchant services or specialized online banking partners, and offer micro-payment service for a multitude of everyday purposes.