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WAIS (Wide Area Information Servers) .. to .. Worm
WAIS (Wide Area Information Servers):
This is a system designed for retrieving information from networks, based on the Z39.50 protocol. With WAIS, you enter a set of words that describe what you're looking for, and WAIS digs through whatever libraries you specify, looking for documents that match your request. Unlike Archie and Veronica, WAIS looks at the contents of documents rather than just at the titles. This requires much more work by the server, but makes it much easier to find what you want because you're not dependent on someone's coming up with properly descriptive titles.
WAIS (pronounced "weighs") returns a list of files that satisfy the search criteria. WAIS allows the use of one or more keywords, which can be combined using simple relationships (AND, OR, or NOT).Weak Entity: (Database)
An entity that cannot exist ina database unless an instance of another entity is present and related to it.Web Services:
The term Web services describes a standardized way of integrating Web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet protocol backbone. XML is used to tag the data, SOAP is used to transfer the data, WSDL is used for describing the services available and UDDI is used for listing what services are available. Used primarily as a means for businesses to communicate with each other and with clients, Web services allow organizations to communicate data without intimate knowledge of each other's IT systems behind the firewall.
Unlike traditional client/server models, such as a Web server/Web page system, Web services do not provide the user with a GUI. Web services instead share business logic, data and processes through a programmatic interface across a network. The applications interface, not the users. Developers can then add the Web service to a GUI (such as a Web page or an executable program) to offer specific functionality to users.
Web services allow different applications from different sources to communicate with each other without time-consuming custom coding, and because all communication is in XML, Web services are not tied to any one operating system or programming language. For example, Java can talk with Perl, Windows applications can talk with UNIX applications.
Web services do not require the use of browsers or HTML.
Web services are sometimes called application services.Web Site Content:
Web sites are made up of four basic types of content; static, active, dynamic, and interactive.
A static Web page is one that does not change interactively with the web server. In other words the content does not change over small intervals of time (i.e., as short as each download of the same page). Instead a static page usually remains static (content does not change) for a very long period of time. Static pages are made up of content that usually changes very slowly or not at all, for example basic mathematical concepts that have been placed on a web site would not normally change with time. Thus, the web page remains static, the information is solid and well understood. An example of a static Web page is description of Data Warehousing.
A dynamic Web page is distinguished from a static one in that there is no one unchanging document that you and others will obtain when a browser downloads a page from a particular URL. Examples of a dynamic Web page would be one that provides a weather map or shock prices in real time, or small amount of delay. In other words the page displays the most current weather radar image, temperature, winds, and weather observations for a given location. Or with the stock market example you get the current price of a stock on the New York (DJIA), NASDAC (NASD), or the SP500. Basically a dynamic site has information changing over short periods of time. An example of a dynamic site is CBS MarketWatch.com
An interactive Web page is one that allows the user of the Web browser to send information back to the server, which then acts upon or saves it to a text file or database system. The most common example of interactivity is found in Web pages with forms. Forms are used for everything on a Web site from site and/or internet searches, ordering items, to inserting information into backend databases. Interactivity is usually accomplished via CGI (Common Gateway Interface) protocol that communicates with scripts or programs back on the Server. An example of a site that is interactive is the Xerox Office Printing Service Web site.Wavelength Division Multiplexing:
In telecommunications wavelength division multiplexing (WDM) is multiplexing several optical carrier signals on a single optical fibre by using different wavelengths (colours) of laser light to carry different signals.
Throughout the last decade, optical fiber has gained more and more popularity as a transmission medium. The unprecedented capacity of the fiber makes it an ideal medium for transport of digital video or other high-bandwidth signals. An increasing number of TV stations use fiber instead of coaxial cable even for in-house applications. A fiber cable typically consists of a number of individual fibers. Four, 12, 24, 48 or more fibers in a cable are common. Today the majority of installed fiber is so-called single-mode fiber, even for in-house distances. Multimode fibers are mostly used for short-haul data applications.
It should be noted that this term applies to an optical carrier (which is typically described by its wavelength), whereas frequency division multiplexing typically applies to a radio carrier (which is more often described by frequency). However, since wavelength and frequency are inversely proportional, and since radio and light are both forms of electromagnetic radiation, the distinction is somewhat arbitrary since one can be converted to the other.
There are different ways to transport more data on a single fiber. One can use time division multiplexing (TDM), where many signals of the same type are multiplexed together electrically before they are put on a single wavelength. An alternate solution is to transmit each optical signal on a different wavelength, known as wavelength division multiplexing (WDM). This is analogous to transmitting different radio channels on different frequencies through air. Recalling the school experiments with white light and prisms is also useful in understanding WDM. The visible white light can be split (demultiplexed) into its components by a prism in the same way as the invisible WDM wavelengths on the fiber can be demultiplexed at the receiving end by an optical filter.
It is quite common to talk about different colors of light instead of wavelengths when describing WDM systems. A number of different wavelengths will, in this case, be denoted as a set of colors. A WDM channel is a signal running on a unique wavelength. Each WDM channel is completely independent of the other channels, both with regards to bit rates, as well as protocols, so running a mixture of SDI, HD-SDI, SDH/SONET, Gigabit Ethernet and Fast Ethernet on the same fiber is easy to do with WDM.
Multichannel WDM exists in two flavors; one is called dense WDM (DWDM) and the other is called coarse WDM (CWDM). When it comes to transporting lots of digital video over a single fiber, DWDM as a technology is very effective. On the other hand, if you have a short fiber span and need a few channels more, CWDM, with its lower cost per channel, can be a good alternative to laying new fiber cable.
WDM in practice
In practice, WDM systems are built by combining signals from multiple different single-wavelength end devices onto a single fibre.
The device that joins the signals together is known as a multiplexer, and the one that splits them apart is a demultiplexer. With the right type of fibre you can have a device that does both at once, and can function as an optical add-drop multiplexer.
The first WDM systems combined two signals and appeared around 1985. Modern systems can handle up to 160 signals and can expand a basic 10 Gbit/s fibre system to a theoretical total capacity of over 1.6 Tbit/s over a single fiber pair.
WDM systems are popular with telecommunications companies because they allow them to expand the capacity of their fibre networks without digging up roads again more than necessary which is extremely costly. By using WDM and optical amplifiers, they can accommodate several generations of technology developement in their optical infrastructure without having to overhaul the backbone network. All they have to do is to upgrade the multiplexers and demultiplexers at each end.
This is often done by using optical-to-electrical-to-optical translation at the very edge of the transport network, thus permitting interoperation with existing equipment with optical interfaces.
Dense and coarse WDM
Early WDM systems were expensive and complicated to run. However, recent standardization and better understanding of the dynamics of WDM systems has made WDM much cheaper to deploy. The market has segmented into two parts, "dense" and "coarse" WDM.
Dense WDM (DWDM) is generally held to be WDM with more than 8 active wavelengths per fibre, with systems with fewer active wavelengths being classed as coarse WDM (CWDM).
As of 2003, CWDM devices have dropped in price to the point where they are similar in price to end-user equipment such as Ethernet switches.
The introduction of the ITU-T G.694.1 frequency raster in 2002 has made it easier to integrate WDM with older but more standard SONET systems. It specifies a 200 GHz frequency raster, with 100 GHz channel spacing as a refinement. Today's DWDM systems use 50 GHz channel spacing.
DWDM systems are significantly more expensive than CWDM because the laser transmitters need to be significantly more stable than those needed for CWDM. In addition, DWDM tends to be used at a higher level in the communications hierarchy, and is therefore associated with higher modulation rates, thus creating a smaller market for DWDM devices with very high performance levels, and corresponding high prices.
Optical receivers, on the other hand, tend to be wideband devices, with the wavelength selectivity at the receive end provided as part of the optical demultiplexer.What is a Network?:
Network is such a common term, yet it can mean so many different things. In a social sense, networking relates to the gathering of various persons of similar interest for purposes of communicating those interests. Computer users, on the other hand, tend to think of the network as the components involved in connecting various computers that allow users to share information or resources such as printers or CD-ROM drives. Once that connection exists, other sharing occurs, such as electronic mail or file transfers. Regardless of how you use the network, any connection of two or more computers qualifies as a network.
Most networks connect using some form of physical wire usually referred to as cabling. Network staff also commonly refer to these physical cables as bounded media. Larger, more complex networks use unbounded media. This media type consists of radio frequencies, microwave transmissions, and infrared technologies. This type of media is typically used to transmit over great distances or in places where cables are hard to place.
The major components of a good network include various pieces:
Wide Area Networks (WAN):
-- Computers and/or networks connected to each other using long distance communication methods, such as telephone lines, fiber optics, and satellites. Basically it is a network that spans many geographically separated locations. As stated above WAN links between each local network are provided by a telecommunications service, such as leased line, SMDS (Switched Multimegabit Data Service), or other long-distance carriers. Compare with Local Area Network.
A WAN is a network whose elements may be separated by distances great enough to require telephone communications. The WAN supports communications between such elements. For most WANs, the long distance bandwidth is relatively slow: on the order of kilobits per second (kbps) as opposed to megabits per second (Mbps) for local area networks (LANs). For example, an Ethernet LAN has a 10 Mbps to 100 Mbps bandwidth; a WAN using part or all of a T1 carrier has a bandwidth determined by the number of 64 kbps channels the WAN is using up to 24 such channels for a maximum T1 bandwidth of 1.544 Mbps (including control bits).
There is no specified upper limit to the radius of a WAN, but in practice, machines distributed over areas larger than a state almost certainly belong to different networks that are connected to each other. Such a setup is known as an internetwork. Thus, although they are simply called WANs, these are more accurately wide-area internetworks (WAIs). One of the oldest, best known, and most widely used examples of a WAI is the Department of Defense's ARPAnet, from which we have inherited many of the important concepts and protocols used in networking.
Centralized versus Distributed WANs
WANs can be centralized or distributed. A centralized WAN generally consists of a mainframe (or minicomputer) host connected over telephone or dedicated lines to terminal at remote sites. The terminals are usually dumb. Centralized WANs generally use polling to control access to the network.
A distributed WAN may include intelligent nodes, which are nodes that have processing capabilities independent of their connection to a host mainframe. The ARPAnet was one of the first distributed WANs.
WANs do not always involve mainframes. In fact, WANs consisting solely of PC-based networks (such as Novell NetWare LANs) are fairly common.
WAN Connection Approaches
Three types of approaches are used to connect WANs:
Windows NT is a 32-bit operating system with preemptive multitasking and memory protection, as well as support for symmetrical multiprocessing and networking, all with a graphical user front-end. The ability of Windows NT to fully access 32-bit processor allows it to work with larger numbers, memory addresses, and instructions. Overall throughout, which is the combination of processor performance, data transfer, and memory access, improves.
Multitasking means that the operating system can do several things at once. Preemptive means that the user or another task can interrupt a task if necessary, rather than wait for it to completely finish. As processing speeds get faster, hardware-related activities such as accessing a disk can seem incredibly slow. When a non-preemptive operating system access the disk, the processor waits while the mechanical disk is accessed, thus wasting processing cycles. In Windows NT, multiple tasks can occur simultaneously, so if one task gets hung up when accessing a slow device such as a disk, the processor can turn its attention to other tasks. Basically, there are no wasted processing cycles.
Memory protection ensures that multiple programs run in their own memory area and don't corrupt the memory used by other applications. If one application crashes, the other applications and the operating system remain alive so users can close their work and exit properly.
Symmetrical multiprocessing lets Windows NT take advantage of multiple processors. While multiprocessor systems have existed for a while, these systems typically assigned dedicated tasks to each processor, such as network input/output. This asymmetrical multiprocessing -- having one processor dedicated to one task -- meant that each processor sat idle when finished with its specific job. Symmetrical multiprocessing, on the other hand, allocates tasks to any processor; if one processor finishes before another, the operating system can assign it other tasks. Symmetrical multiprocessing is harder to implement, but provides superior performance.
Networking features in Windows NT let you share files on your system with other network users and connect with shared directories on other systems. Computers running Windows for Workgroups can participate in the network. In addition, Windows NT comes with software and drivers to support connections to other types of operating systems, such as UNIX and IBM mainframes.
The Windows NT Server product is an enhanced version of Windows NT Workstation that provides sophisticated file server features for large network environments. It includes additional features for data protection, such as automatic duplication of data to secondary disks.
Microsoft Windows NT is designed to take advantage -- and to allow software vendors to design applications that take advantage -- of powerful new desktop systems, including those designed around Intel, DEC, PowerPC, and other processors. Windows NT expands on the features of Windows 3.1 and Windows 95, and offers many features that make it unique among operating systems. Windows NT has a wide target audience:
The last point is especially important. Windows NT is not restricted to Intel systems as are DOS and Windows. It runs on the following processors:
IBM is working to make Windows NT available on its super server systems, which include features such as fault tolerance, redundant arrays of inexpensive disks (RAID) systems, error-correcting memory, and hardware error logs. The PS/2 Server 195 and Server 295 super server will run adapted version of Windows NT. Another platform for Windows NT is the Intergraph Corporation's Intergraph Ultra SPARC system. The Ultra SPARC is a high-end version of the SPARC chip developed jointly by Sun and Microsystems, Inc. and Intergraph. The SPARC-based Windows NT systems are designed for high-end workstations and multiprocessing servers.Wireless:
Currently there are three wireless-networking standards competing for your airtime. Wi-Fi (802.11b) is the corporate darling and has a suitably wide range for use in big office spaces. 802.11a offers bigger bandwidth and fewer interference problems but a shorter range. Bluetooth is meant for short-range, temporary networking in conference rooms, schools, or homes. In addition to the detailed rundowns below, check out our side-by-side comparison of these different technologies with traditional, wired Ethernet.
Wi-Fi reigns supreme: Wi-Fi is currently the most popular and least expensive wireless LAN specification. It operates in the 2.4GHz radio spectrum and can transmit data at speeds up to 11Mbps within a 100-foot range. Its balance of economy, bandwidth, and particularly range have made it the dominant standard for business, and many employees have taken the technology home with them for work and family computing. The Wireless Ethernet Compatibility Alliance (WECA) has done its part by certifying hundreds of products to make sure they work together. But Wi-Fi has a couple of drawbacks. It shares airspace with cell phones, Bluetooth, security radios, and other devices, so it's vulnerable to interference. And because of data-transfer overhead and the inevitable wall or other transmission obstacle, its real throughput is closer to 5Mbps, or about half of its spec.
802.11a: new kid on the block: A recent arrival, 802.11a has a couple of advantages over Wi-Fi. It runs at a less-populated frequency (5.15GHz to 5.35GHz) and, thus, is less prone to interference. Its bandwidth is much higher, at a theoretical peak of 54Mbps. Even though actual throughput is closer to 22Mbps, it still offers a lot more elbowroom than Wi-Fi does for transferring high-quality digital audio and video or other large files across the network, as well as for sharing a broadband connection. And some manufacturers offer proprietary modes that can push throughput a little higher. Its main problem is its shorter range: 50 feet compared to Wi-Fi's 100, forcing you to buy more access points to ensure full coverage. 802.11a equipment is also currently more expensive than its Wi-Fi counterparts, although the price gap is narrowing steadily. In November (2002), WECA will start certifying 802.11a products, which will carry the organization's new Wi-Fi Certified capabilities label.
Because Wi-Fi and 802.11a use different radio technologies and portions of the spectrum, they are incompatible with one another. However, twin-standard equipment is currently available, which makes switching back and forth surprisingly simple. Still, if you want to make a choice between the two and stick to it, consider these factors: If you already use one or the other standard at your business, you should probably use the same one at home to make telecommuting easier. If compatibility and price are not issues, 802.11a's better performance could be worth the extra expense. But if you need to cover a lot of ground cheaply, Wi-Fi's the more efficient choice.
Bluetooth takes small bites, chews slowly: Named for a tenth-century Danish king, Bluetooth is a somewhat different standard from Wi-Fi or 802.11a, offering much more flexibility but on a smaller, "personal area network" scale. Its actual throughput is a poky 300Kbps, and its range is just a couple dozen feet. But unlike Wi-Fi and 802.11a, which require adapters, routers, gateways, access points, and synchronized setup schemes to connect devices, any devices with a Bluetooth radio and antennae can speak to each other with little or no preparation. It's also poised to replace infrared ports as the instant-transfer mode of choice, with better range and no line-of-sight requirement. Meeting attendees can immediately transfer files between their Bluetooth-equipped notebooks across a conference table, or they can send a file to a Bluetooth-equipped printer without downloading drivers. Bluetooth-equipped kiosks in airports and coffee houses let you log on to the Internet through your laptop or PDA. Bluetooth will soon be standard equipment on many cell phones and handheld computers. There's even talk of putting Bluetooth into home appliances. But for all the theoretical benefits of Bluetooth, the reality is that it's currently a mess of incompatible hardware and software. And because Bluetooth and Wi-Fi occupy the same frequency range, they can eat into each other's bandwidth and reduce throughput by 10 percent or more.
What lies ahead? This alphabet soup of standards will get even more complicated over the next few years, as upcoming standards come to market. For instance, 802.11g promises to increase Wi-Fi bandwidth to 22Mbps, while 802.11i will plug some of the security holes in the WEP protocol. A new Bluetooth specification will operate at a higher frequency, yielding twice its present bandwidth.
In the next section, we'll look at how to set up a wireless LAN, what equipment you'll need, and how much it will cost.
Because physical structures can eat up wireless signals, the layout of your home or office-- the placement of walls, hallways, and doors--counts for everything. If you ignore the floor plan, you may end up with a network that fails to reach every nook and cranny.
Break out the blueprints: First, size up your location. We know Wi-Fi works best for large spaces and 802.11a for high-throughput applications, while Bluetooth simply requires devices to be in close proximity. Our sample office floor plan shows how you could use just one Wi-Fi access point, centrally located, to cover a 20,000-square-foot workspace. It could also cover a typical one- or two-story home and the outdoor property around it. A single 802.11a access point could cover a modest house or apartment. Remember, wireless networks range vertically as well as horizontally; depending on the building's construction, you may be able to cover as much as a floor above and below the access point or router. Still, various physical and technical obstacles may require you to place networking devices strategically or add extras to compensate for problems.
Every wall and ceiling is a potential barrier to radio signals of any kind. Plaster walls are the easiest to go through, although older construction (which includes wood, lathe, metal screens, and plaster) can eat up signals. Steel or stone is the worst wall material; the signal barely trickles through. Glass acts like a reflector, bouncing back the signal. The only solution is to place the access points to avoid walls and dead ends. Sometimes the best technique is trial and error--testing a device in a variety of locations for the best receptivity.
Choosing the right gear: In most environments, you'll need three different types of equipment. Every device you want to network will need a radio for exchanging communications wirelessly. If you have an older notebook, you can easily add a wireless PC Card adapter (such as the Orinoco or a USB radio), while newer notebooks such as the Dell Inspiron 8200 and the HP Pavilion zt1195 offer these features as standard equipment. (There are currently no integrated 802.11a radios available for notebooks.) Smaller CompactFlash cards such as the D-Link DCF-650W work well for handheld computers, but they're expensive and have limited range. For desktops, think USB or PCI adapters. The WECA logo assures Wi-Fi compatibility, but the organization's process for testing 802.11a devices is just getting started.
Once all your devices are wireless ready, they need a basic access-point (AP) radio to communicate. An AP can act as the wireless network's hub, letting multiple computers share a broadband connection, or it can be hooked up to a wired network to add wireless devices. If your network needs to span larger spaces, you can always add extra access points and place them in an overlapping pattern to minimize dead spots. You can connect the extra access points to your wired network or use them as bridges to relay the signal to other APs.
If you want to create a network combining both wired and wireless connections, a wireless gateway, which adds an Ethernet router, would be a good choice. At less than $200, Wi-Fi devices can be an inexpensive, one-stop distribution center for your wireless LAN. Some good choices include:
Wireless Application Protocol (WAP):
A standard for providing cellular phones, pagers, and other handheld devices with secure access to e-mail and text-based Web pages. Introduced in 1997 by Phone.com (formerly Unwired Planet), Ericsson, Motorola, and Nokia, WAP provides a complete environment for wireless applications that includes a wireless counterpart of TCP/IP and a framework for telephony integration such as call control and phone book access.Wireless Bridges:
A wireless bridge is a radio connection between two network segments. Wireless bridges generally have a range of a few hundred yards, depending on the terrain. Most bridge products operate in the 2.4- and 5.7-GHz unlicensed bands, but some operate in the unlicensed 24-GHz spectrum, which provides for greater throughput.Workstation:
A computer on a network, usually reserved for end users. A workstation is a client machine. In general, a workstation is a consumer of network services, although it is not uncommon for a workstation to serve as a special-purpose server, such as a server for a printer or backup tape drive.
Workstations can be viewed as interchangeable units, which need not be particularly powerful unless they are being used for a resource-intensive purpose. In contrast, a file server should be a high-speed, powerful machine that can deal with dozens of requests at once.
Each workstation needs a network interface card (NIC) that is compatible with the workstation's hardware and with the NIC used by the network's server. External and PCMCIA (Personal Computer Memory Card International Association) NICs are available so that even a machine with minimal capabilities (such as a palmtop) can be used as a workstation. Laptops have some important advantages as workstations -- most notably, portability -- and are becoming more common in networks.Workstation Session Socket (WSS):
A socket in a workstation to which all session-related packets are sent.World Web Web (WWW):
The World Wide Web has grown from a ditributed document lending service for a group of high energy physicists to the world's largest libary -- at least in geogrophical extent. WWW - known simply as the Web -- is the name for a network of links to hypertext documents. Documents are known as Web pages, and the starting point in a document are for a corporation is known as the home page.
Information about the documents and access to them are controlled and provided by Web Servers. At the user's end, a Web client takes the user's requests and passes them on to the server. Such a client is generally a browser application -- that is, a hypertext reader application. Browsers and server communicate using a transfer protocol -- generally HTTP (Hypertext Transfer Protocol). Netscape Navigator, various flavors of Mosaic, IE (Internet Explorer), and Cello are all examples fo Web Browsers.
Web pages are identified by their URLs (Uniform Resource Locators), which are a form of Web address and document description. For example, the following URL for the Xerox home page:
This URL has two components. The first part (http) indicates the protocol being used for the documents to be retrieved. In this case, the http refers to the hypertext transfer protocol, which is used to transport hypertext files across the Internet. Other protocols that are generaly handled by browsers include FTP (File Transfer Protocol) and Gopher.
The second part specifies the domain name for the machine on which the home page is found. In this case it's a machine named xerox.com, which is accessed through the Web server (www).
The World Wide Web is a collection of computers on the Internet running HTTP servers. The WWW allows for text and graphics to have hyperlinks connecting users to other servers. By using a Web browser, such as Netscpe or Internet Explorer, a user can cross-link from one server to another at the click of a button or link.World Wide Web Worm (WWWW):
A search program for the World Wide Web (WWW). WWWW was developed by Oliver McBryan at the University of Colorado, and it works by sending out a Web robot to search documents. The robot begins by searching documents on a list, then searching all documents accessible through the original documents, etc.
WWWW is one of the most popular search engines, and was chosen the Best Navigational Tool at the Best of the Web '94 contest. The home page for WWWW is: http://www.cs.colorado.edu/home/mcbryan/WWWW.html.
Other search engine products include Lycos, NIKOS, WebCrawler, and Yahoo.Worm:
A program that is designed to infiltrate an operating system and keep replicating ifself. Eventually, there are so many copies of the worm floating around that the computer cannot do any work, and a system crash results.WSDL: (Web Services Description Language)
Released by Microsoft, IBM, and Ariba (the three initiators of UDDI), WSDL is an XML language used to describe network services or endpoints. WDSL 1.0 includes bindings of service descriptions for the SOAP protocol and also for simple HTTP GET and POST requests. WSDL supersedes IBM's NASSL and Microsoft's SCL efforts, and it's a key part of the UDDI initiative.
Networking "W" Definition and Conceptsrobert.email@example.com
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