[...]... corrupted frames; higher layers normally handle this behavior 1.3.3 Layer 3 Network Layer Moving up from the data link layer, which sends frames over a network, we reach the network layer The network layer deals with data packets, rather than frames, and introduces several important concepts, such as the network address and routing Packets are sent across the network, and in the case of the Internet, all... between networks, by creating network protocols that support internetwork communication or "internetting." The various protocols that make up the Internet must support a variety of networking gateways Hardware and software independence, by creating network protocols that would be interoperable with any CPU architecture, operating system, and networking card Reliability and robustness, by creating network. .. access a network (for example, allowing two desktop machines to access a local area network) Gateways connect one network to another—for example, a local area network to the Internet While routers and gateways are similar, a router does not have to bridge multiple networks In some cases, routers are also gateways While it is useful to understand such networking terminology as it is widely used in networking... of networking hardware is used, it will almost certainly support IP networking IP acts as a bridge between networks of different types, forming a worldwide network of computers and smaller subnetworks (see Figure 1-3) Indeed, many organizations use the IP and related protocols within their local area networks, as it can be applied equally well internally as externally Figure 1-3 Support for IP networking... operating system and device driver developers, who work with low-level assembly language and operating system calls Instead, programmers use standard Internet services, and let the operating system and device drivers handle such complexities This is one of the perks of being a network programmer Figure 1-6 Data encapsulation between OSI layers 15 1.8 Security Issues: Firewalls and Proxy Servers Network security... details of Layer n-1, Layer n-2, and so on Lower-level layers, for example, can be substituted and replaced without having to modify or redesign higher-level layers, or recompile application software For example, a network layer protocol can work with an Ethernet network and a token ring network, even though at the physical and data link layers, two different protocols and hardware devices are being... information There are a wide variety of network mediums, ranging from dial-up modems to local area networks At the physical and data link layers, various hardware types and network protocols can be used, making networks inter operable We as Java programmers do not need to concern ourselves with such issues, however, and in fact are unable to access such low-level network devices TCP/IP communication uses... model, dealing only with the network, transport, and application layers It is these layers, more than any others, that Java programmers must be familiar with As one moves higher and higher up the OSI levels, hardware issues are put aside and more and more levels of abstraction are introduced First there is the network layer, which deals with the dispatch of packets over a network and the issue of addresses... features such as class inheritance and visibility modifiers (the public, private, and protected keywords of Java) make object-oriented languages much easier and safer to work with than older procedural languages 21 Procedural languages can be used to develop networking software, and indeed C remains a popular choice today for Unix networking software However, network programming in any language is not... widely used in networking texts and protocol specifications, programmers do not generally need to be concerned with the implementation details of a network and its underlying architecture However, it is important for programmers to be aware of the various elements making up the network 1.2 How Do Networks Communicate? Networks consist of connections between computers and devices These connections are . Java(TM) Network Programming and Distributed Computing is an accessible introduction to the changing face of networking theory, Java(TM) technology, and. networking. Because it was created with extensive networking features, the Java programming language is uniquely suited for network programming and distributed