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Embedded Systems November 2000 Vol13_12

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Knowing the format of the data (an image, is it an audio stream, or data to be printed?), what devices exist on the network, and what Jini should be done with the data are all essential parts of true Jini has received a tremendous interoperability. amount of press coverage. It's a mid- dleware layer tl1at resides on top of a Java Virtual Machine and uses Java's Remote Method Invocation (RMI) to make use of a remote device's ser- vices. Jini technology has a lookup ser- vice with which devices and se• ·vices • Discovery • Simple Discovery • Auto IP/DHCP • Auto DNS/DNS •XML • Control • Management • Monitoring • Stream Management • Streaming register. When a device plugs in , it goes through an add-in protocol, called discovery and join-in . The device first locates the lookup service (d iscov- ery) and then uploads a J ava obj ect that implements all of its services' interfaces Uoin). Nterwards, devices that want to make use of that service will be given the obj ect to use as an API. As an example, a digital camera demanding imaging appl ications, and it is questionable whether any kind of QoS guarantees can made with power- line carrier systems. Advanced powerline systems use the ame spread spectrum or frequen- cy shift keying techniques that are used in RF systems. The big hurdle with powerline communications is that while they have to deal with the same microvolt signals as their RF brethren, they aJso have to deal with hundreds of AC volts, thousand-volt spikes, and power transformers within a home. Clearly not an environment for the faint of heart. All of the curren tly announced pow- erline systems are proprietary and con- sequently very little technicaJ informa- tion on their operation is available pub- licly. (There are quite a few more than those listed in Table 1.) To make mat- ters worse, many of tl1ese companies have proprietary layers tl1at extend far above the data link layer in tl1e proto- col stack. This is a major dt·awback for any protocol wishing to become a force in home Internet appliance network- ing and the chances of any success are slim until one of these companies opens up the kimono a little bit or HomePlug gets them all to agree. Service and discovery- focused standards As mentioned previously, moving data bits from one place to another is only half the battle. Knowing the format of the data (an image, an audio stream, or data to be printed?), what devices exist on tl1e network, and what should be done with the data are all essential parts of true interoperability. Table 2 lists the upper level proto- cols that are vying for dominance in the home (and elsewhere). One thing is apparent in examining any of these protocols: if information is to be shared witl1 devices on tl1e Internet, ultimately the Internet Protocol comes into play. Many of tl1ese proto- cols rely on IP being part of the pro- tocol stack. That does not mean that all devices will speak IP, but if tl1ey don't, there must be some sort of proxy or gateway device t11at will allow communications with devices that do use IP. In addition, many of these pro- tocols and APis are complementary, rather than competitive. In many cases however, the complementary schemes overlap somewhat. It is cur- rently a very muddled situation and only time will tell who the winners and losers will be. 76 NOVEMBER 2000 Embedded Systems Programming that wants to find a color printer would first query the lookup service. If a color printer has registered with the lookup service, the printer's methods for accessing the printing capabili ty will be downloaded to the digital camera. The digital camera will then communicate directly with the printer using RMI and the down- loaded methods or RMI stubs. See Figure 8. Jini devices must have access to a Java Virtual Machine to participate. The device may either have tl1e JVM built into it or use a proxy device that does. Jini uses multicast packets for discovering the lookup service provider. Thi is not likely a problem in the home environment, but it may be an issue in an office or larger space where routers and firewalls come in to play. JetSend JetSend is a technology introduced by Hewlett-Packard tl1at is focused on tl1e session, format, and context layers of the interoperability protocol stack. The protocol stack is shown in Figure 9. The most enticing feature of JetSend is its definition of what it terms e-material. E-material provides

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