P2P Devices

In a world where every device that has power will also probably have an IP address and some sort of network connectivity, it is a logical expectation that these devices will participate in some sort of peer-to-peer interactions. The concept of Universal Resource Identifiers (URIs), described in Chapter 11, "Web Services Explained," will greatly facilitate these interactions, because URIs can point to any resource on the network, including a networked microwave oven! Devices will participate by either requesting or providing services (or both), combining concepts from the Web services and P2P architectures. This world is almost upon us, and although this was the original vision of Jini, several technical and social hurdles got in the way. A combination of P2P and Web services concepts seems to be the right thing at the right time for enabling this vision.

However, devices bring a host of issues of their own. The term device itself encompasses a wide range of computing platforms with widely varying capabilities. You might easily and naturally think of laptops and desktops as devices. PDA devices and cell phones are next in line in this evolution of computing devices. You can even start thinking of traditionally noncomputing devices as peers in P2P networks. As an example, you can easily see how a home entertainment center will communicate with other devices on a home network to schedule some shows according to the owner's calendar, record them, upload or download media files, and so on.

In the device world, however, both hardware capabilities, such as processing power, storage and bandwidth, and software capabilities, such as operating systems and languages, can make for some very diverse environments. On the positive side, the computing power and capacity of devices has been growing in conjunction with the decreasing footprint of embedded Java and other computing platforms. These two lines have already crossed to the point where relatively complex standards-based implementations are possible on some everyday devices. On the other hand, the sheer number of different platform and operating system combinations, along with different capabilities will make interoperability harder.

For example, implementing P2P capabilities on a handheld running Windows CE is a very different proposition from implementing similar (or any) capabilities on a smart phone. This does not even take into account issues of presentation on the client, where work such as the Composite Capability/Preference Profile (CC/PP) from the W3C will be of great value (http://www.w3.org/Mobile/CCPP/). This area of interoperability among a large number of platforms is where Web services and P2P are coming into close alignment. Already the concepts of interoperability, capability, profiles, and introspection are being debated in the Web services community. Initiatives like the Web Services Inspection Language (WSIL) and Web Services Interoperability (WS-I) have made significant progress toward eventually solving these issues. A foundation for true interoperability, however, will require some form of semantic representation, possibly through ontologies and a formal framework such as the Resource Definition Framework (RDF). RDF is one of the enabling technologies of the Semantic Web effort, and is already used in CC/PP to represent profiles. The next sections will cover these topics in more detail.