计算机网络译文

┊┊┊┊┊┊┊┊┊┊┊┊┊装┊┊┊┊┊订┊┊┊┊┊线┊┊┊┊┊┊┊┊┊┊┊┊┊The Future of The Computer and The Internet Since Tim Berners-Lee developed the World Wide Web, Web sites and the Web itself have gone through several phases. Berners-Lee intended for the Web to be free and open to everyone. That was pretty much the case in Phase 1, as people used the Web primarily to search for information and in Phase 2 when it became a publication tool. But now that we are in Phase 3, companies are using the Web for business, and holding on to the “free and open” concept is becoming more difficult.The dot-com bubble proved that some Internet companies were just a flash in the pan. But is that really so different from business in general? The survivors are those no doubt have a truly valuable product or service, and use the Internet as a tool. So life goes on, and Web development goes on for companies with a firm foundation.When the Web went online in 1991, HTML was the language used. We’ve since graduated to XML, and it looks like the World Wide Web Consortium (W3C) is guiding us to us e additional languages in the next generation’ s Semantic Web. W3C languages XML, XML Schema, XML Signatures and Resource Description Framework (RDF) provide the groundwork of the Semantic Web, and they are based more on easy communication between computer s than today’ s languages, which are really designed for communication among people.Once we get the Semantic Web implemented, we’ll enter Phase 4 of Web development, in which Web-based programs will use standard interfaces and protocols to interact with a network of databases and with each other. This will make the Web even more valuable than it is today, as people begin using all its capabilities. Today’s information agents on some sites give you a tiny taste of what the future holds.W3C is now focusing on the standards that will be necessary to make the Semantic Web work. These standards will provide a framework to enable further innovation and the creation of new products and markets, including Web infrastructure solutions and application software. The standards are really the “glue” that holds the whole thing together, allowing information to be shared among different programs.The areas that the W3C standards development teams are working on reads like the hot buttons in today’s technology developmen t areas: device-independent computing, digital rights, e-commerce, math markup language, mobile access, digital signatures and more.One issue that overarches all categories deals with royalties on standards. Some W3C member companies want standards users to pay royalties-IBM is in this group. Other┊┊┊┊┊┊┊┊┊┊┊┊┊装┊┊┊┊┊订┊┊┊┊┊线┊┊┊┊┊┊┊┊┊┊┊┊┊member companies feel that all W3C standards should be royalty free-HP is the leader in this group. HP’s position is that companies should profit from building or licensing value-added features on its products, not from royalties on fundamental standards that users need for interoperability. Standards are vastly important to the future of the Web, but the question is: Will they be universally used if they are not available without charge? Guess we’ll have to wai t and see what happens next.If a vendor claimed to offer a storage-area network (SAN) with the performance of Fibre Channel (FC) but without the cost and complexity, jaded FC administrators might be a hard sell. After all, FC network devices have been notoriously incompatible, expensive and complex to administer.But IP SANs promise to change all that by implementing the Internet Small Computer Systems Interface (iSCSI) protocol, which enables SANs to operate over industry-standard TCP/IP and Ethernet.The concept of storage networking over IP isn’t new: Network-attached storage appliances have long delivered file services over IP using Network File System or other file-sharing protocols. But creating storage networks that allow highly efficient block-level transfers between application servers and shared storage pools has been the domain of FC networks，switched, high-speed serial interconnect requiring specialized cabling, host bus adapters (HBA), switches and management software.IP SAN architecture, an extension of existing SCSI and TCP/IP Ethernet standards, could reduce costs by creating a unified corporate IP network that’s easier to design, integrate and manage than a traditional FC SAN. ISCSI networks are also compatible with IP-based security mechanisms such as Kerberos, public-key encryption and IPsec.Setting up an IP SAN isn’t simply a matter of plugging in iSCSI storage, however. While an IP SAN can run on standard Gigabit Ethernet switches, the overhead involved in processing of TCP and iSCSI protocols can quickly overwhelm the CPU in servers with significant storage network traffic. IT managers may need to replace standard Ethernet adapters with special HBAs called TCP off-load engines (TOE).It might not be compatible, either. Standards committees are hammering out iSCSI draft standards (the final version is expected this summer), but vendors are rushing products to market. There are no standards for TOE, different vendor interpretations of the iSCSI standard could lead to interoperability problems, and no certification exists. And vendors have little credibility in the user community after the interoperability debacle with early FC devices.┊┊┊┊┊┊┊┊┊┊┊┊┊装┊┊┊┊┊订┊┊┊┊┊线┊┊┊┊┊┊┊┊┊┊┊┊┊Once the standard is stable, analysts predict, IP SANs will slowly replace FC, but users with an investment in FC are unlikely to change over soon.“You don’t replace existing technology with emerging technology,”says Dan Tanner, an analyst at Aberdeen Group Inc., adding that FC now supports 2G bit/sec. speeds while Ethernet still maxes out at 1G bit/sec. Initially, the best fit for iSCSI may be around the edges of the FC SAN, where its lower cost makes more sense.The firewall industry split into two camps in the early ’90s. On one side was the traditional proxy-based firewall gang; on the other were some upstarts, led by Check Point Software Technologies, looking for faster technology and greater flexibility with packet-filtering. The debates were furious, the mud-slinging intense, but the market eventually sided with Check Point. Today, packet-filtering firewalls account for more than 90% of the market.However, the proxy firewall folks haven’t rolled up their tents yet. They continue to sell product because their basic argument holds true: Proxy firewalls, with two independent TCP connections for each application, can be more secure than packet filters. With no IP-layer packets passing directly between the inside and the outside, proxies are inherently immune to most kinds of reconnaissance and spoofing attacks. Proxy-based firewalls can easily do all kinds of application-layer validity checking, antivirus scanning and content filtering, as well as granular access control, because they are truly aware of the application data flow. This is particularly important given the rise in application attacks over port 80.Packet filters excel at speed and scalability. It takes very little CPU power and not much memory for a packet-filtering firewall to run rings around a high-end, high-priced proxy firewall. While proxy-based firewalls were struggling to meet the needs of companies with their newfound Internet T1 lines, packet filters stepped up to the challenge and quickly dominated the market.The trade-off between security and performance has been acceptable to many network managers. Nevertheless, proxy firewalls continue to have a following, especially in the most conservative and security-aware organizations: government, military, financial services and health care. Proxy firewall vendors, sensitive to their performance constraints, have added packet filtering where appropriate.The sharp rise in application-layer security attacks has revived the debates. After years of considering simple access control “good enough”，many security managers are demanding granular and powerful application-layer controls found in proxy firewalls to compensate for poorly written applications.┊┊┊┊┊┊┊┊┊┊┊┊┊装┊┊┊┊┊订┊┊┊┊┊线┊┊┊┊┊┊┊┊┊┊┊┊┊So, it’s no surprise that packet-filter firewall vendors are building application-layer controls into their products. Although the products will never look like each other on the inside, they are moving to meet a common standard of security.Computers of the future may perform tasks based on what you say to them, how you gesture or even where you look. But that doesn’t mean your keyboard and mouse are going away anytime soon.Researchers working on new generations of interfaces are taking a pragmatic approach to how we’ll interact with machines, adding support for text, speech, gaze, gesture and more, depending on circumstances and what seems to make sense.Ideally, tomorrow’ s computers will be better at anticipating what users want, with out needing typed commands. This will involve “context-aware”interfaces, according to Ted Selker, head of the context-aware computing research group at MIT’s Media Lab. That might mean a Web application will be able to sense both your mouse and eye movements to determine whether you’ve visited a site before and what items most interest you——and then dynamically generate a page based on those interests.Speech-recognition software is already making inroads in telephone-based customer service applications. T oday’s systems are often limited to narrow uses, such as saying the name of a company to get a stock quote. Work on broader-based systems is under way, though.Lucent recently tested a prototype of an automated phone operator at a financial institution. C allers could say things like “I lost my checkbook”instead of wading through menu options.The test involved routing callers to one of about 40 departments. About 8% of the calls had to be switched to a human receptionist because requests weren’t specific enough. Among calls handled by the computer, the accuracy rate was 96%. Speech-recognition experts believe the technology will be increasingly used in mobile applications.Other potential uses include more sophisticated hands-free dialing as well as climate control systems.Speech recognition should also make it easier to use a small device to access data stored on a larger one. “Basically, anything that’s on your desktop will be available to you by voice,” One expert predicts.Many speech-recognition experts believe that the robust infrastructure of third-generation high-speed data transmission services will improve speech recognition in wireless applications.┊┊┊┊┊┊┊┊┊┊┊┊┊装┊┊┊┊┊订┊┊┊┊┊线┊┊┊┊┊┊┊┊┊┊┊┊┊For effective speech recognition, some processing should be done in the handset or on personal digital assistants and some across the network. That will help users overcome problems such as noise and choppy reception in some wireless connections.In some cases, it would be best for the device to do more than simply process a spoken command. For example, it might be better if a data request were sent seeking prices for a flight to Paris in October, instead of informing the computer that a caller asked,“How much is it to fly from Boston to Paris next month?”This presents an architectural challenge: How can the airline’s computer transmit something akin to a flight reservation request form to a wireless device so the speech can be understood in context and an appropriate request transmitted back?Researchers are also investigating how computers might respond to eye movements. Add an eye-tracking camera to a laptop and a system can actually see what you’re looking at on the screen，This could help make PCs and laptops easier to use.Cameras are too large and costly for commercial implementation of such a system now, but that may change within five years or so.From: Internet’s Basis And Applications Author: Liu Bing,Liu Dong┊┊┊┊┊┊┊┊┊┊┊┊┊装┊┊┊┊┊订┊┊┊┊┊线┊┊┊┊┊┊┊┊┊┊┊┊┊计算机和因特网的未来自从Tim Berners-Lee开发了万维网，网站和万维网本身已经历了几个阶段。