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As we examine the mobile evolution and the introduction of new and improved systems, at first glance we tend to focus on the radio and network characteristics. Everyone wants to know how high the bit rates will be and what kinds of
functionalities the handsets will have. Many other things have to come into place, however, in order to make the mobile Internet as flexible as possible. Remember that telecommuniations networks were traditionally built to carry voice and just a few vertical applications. Compared to the fixed Internet, these networks are secure and extremely reliable but also extremely rigid. Third parties have not found it easy to add functionalities and applications that are limited to SMS, voice mail, and other features that are tightly integrated into the existing networks. One system had a set of applications that was incompatible with those of other systems. Thus, a Code-Division Multiple Access (CDMA) user could not access an SMS center for a Global System for Mobile communications (GSM) network, and a fixed-line user had an answering machine that was different from the voice mail of his mobile telephone. Figure 9.1 illustrates this architecture of services that are dedicated to the individual networks.
When developers added data functionality (mostly circuit switched) to 2G networks, these limitations became more and more visible—especially with the rapid growth of the openly designed Internet. The Internet facilitated an enormous growth of applications and content, and it was extremely easy for anyone (user, content/applications developer, and so on) to connect to the Internet. With the advent of wireless packet data networks, the telecommunications
Figure 9.1 Old architecture of dedicated applications.
industry realized that the fixed-Internet developer community had to be mobilized in order for the mobile Internet to take off. A key issue that needed to be resolved was how to introduce an open and flexible application architecture to mobile networks without jeopardizing security and reliability. Another important aspect was to make applications for one network available to others as well. Someone might develop a banking application for Wideband Code Division Multiple Access (WCDMA) users, and it should then also be possible for CDMA2000 users to access it, as well.
The solution is a horizontally layered architecture that we touched upon in Chapter 4, ‘‘3G Wireless Systems.” The three main planes are transport, control, and applications (services), as shown in Figure 9.2. We now want to dive deeper into the application layer and see how it consists of many components (more than just WAP gateways and application servers).
We will describe the three planes in detail:
Application plane. Not only are the applications located here, but a number of nodes that facilitate the new services also reside in this location. These applications include positioning servers, WAP gateways, and so on, as we will describe in the Service Network section of this chapter. As a result, mobile networks and clients or servers on the fixed Internet can all access these applications (provided that the owner of the service network allows
Figure 9.2 A new, layered applications architecture.
this access). The applications can be anything from browser-based WAP applications to any generic, IP-based application.
Control plane. This layer handles setting up calls, tracking mobiles, and managing billing information. Practically all of the intelligence of the mobile networks resides here.
Transport plane. Once the control plane decides to set up a call, the actual transportation of the bits takes place in the transport layer. This process includes all sorts of routing, coding, and switching. Some functionalities that previously took place on the middle of the mobile network, such as voice transcoding, can now instead be moved to the edge of the networks. This feature makes things more efficient and easier to control for the operator.
This new architecture provides the opportunity to divide the networks into logical entities based on functionality rather than on system technology (GSM, CDMA, and so on). All three layers are based upon open interfaces, which open the possibility for third parties to enter the game. If there were no open interfaces, the applications would have to terminate the telecommunications protocols and communicate with them directly. This process is not only inefficient and difficult, but it also directly limits the application to a particular network. The nodes of the application layer that offer these APIs now perform this dirty work, and the application developer gains access to high-level, network-independent functions. In the Service Network section of this chapter, we describe the service enablers that facilitate this process.
Note that these layers are logically separated, which means that they can be physically located at different places (not a requirement, however). Therefore, it would be possible for a company to start a business as a service provider, operating an application layer (called a service network) and not have to have any wireless infrastructure. This service provider offers services and applications, rather than the traditional mobile subscriptions that primarily offer network access. The service provider could then optionally choose to sell subscriptions that include network access as well and then buy this capacity from a traditional mobile system operator. In other words, the existing operators will have to decide what their role in the value chain should be. Should the operator not only offer the bit pipe (transporting traffic) but also be an Internet Service Provider (ISP) and offer services on top? Some operators will try to be one-stop providers, offering everything the user needs (including terminals, applications, and Internet and mobile system access). Other operators will take pride in owning global wireless networks and will focus on offering mobile system access. Today we can already see how some network operators divide their company internally in order to have one part working with the applications offerings and another part working on the actual mobile network. Later some