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...workstation. The document stored on the file and print server is loaded into your workstation's memory so that you can edit or use it locally. In other words, file and print servers are used for file and data storage. If you wish to print the document, the file and print server manages the transfer of that file to the network printer.
- Database servers In most cases, a database server is a server that runs an SQLbased database management system (DBMS). Client computers send the SQL requests to the database server. The server accesses the stored database to process the request, and then returns the results to the client computer. When referring to a database server, the term "server" may refer to the computer itself or the DBMS software that manages the database (such as Microsoft SQL Server).
- Application servers Where file and print servers will download a file to the requesting client PC, an application server does not-only the results of a request are sent to the client PC. For example, you might search the employee database for all employees who were born in November. Instead of the entire database being downloaded to your PC so that you can search it, the search is performed on the application server itself, and only the result of your query is sent from the server to your computer. This subtle but powerful difference makes application servers (such as Lotus Domino) ideal for maintaining vast quantities of data and efficiently providing that data to clients.
- Mail servers E-mail is an important part of modem communication, so mail servers (such as Microsoft Exchange Server) handle the flow of e-mail and messaging between network.-users. In most cases, mail servers are similar to application servers because the e-mail typically remains on that server. When you check your email, you only see the e-mail intended for your screen name. Storing e-mail in a central fashion such as this allows for better security and e-mail management (i.e., old e-mails can be purged after so many days in a system-wide fashion). A variation of this is the mailing list server (a.k.a., list server), which is needed for creating, managing, and serving mailing lists. Stand-alone list servers (such as Majordomo) generally offer more features arid better performance than their integrated counterparts. Uses for mailing lists and list servers include the distribution of e-zines, newsletters, product updates, technical support documents, classroom schedules, and product brochures, along with discussion forums for clubs and groups, electronic memos, and so on.
- Fax and communication servers Networks rarely exist in a vacuum, and there are generally several ways to access the network from outside. Two popular means of external network access are faxes and dial-up. A fax server (such as FaxMaker) manages fax traffic into and out of the network using one or more fax/modem cards. This allows network users to send faxes outside of the network (and vice tea). Communication servers handle data file and e-mail transfers between your own networks and other networks, mainframe computers, or remote users who dial in to the servers over modems and telephone lines. For example, a network user may access the Internet through a communication server.
- Audio/video servers Audio and video servers deliver multimedia capabilities to Web sites by giving users the ability to listen to sound or music and watch movie dips through Web browser plug-ins. While the use of traditional formats like .WAV, .MIDI, .MOV, or .AVI on Web sites doesn't really demand a specialized server, the recent emergence of streaming audio and video content has made the audio/video server a necessity in many cases (with tools such as RealServer Plus). New streaming technologies mark an important transition for multimedia on the Web, and will undoubtedly become one of the Internet's most exciting technologies as it evolves.
- Chat servers It is common practice for two or more users to exchange real-time messages. This is called a chat, and chat servers (using tools like MeetingPoint) provide the management for real-time discussion capabilities for a large number of users. Potential chat uses include teleconferences, private meeting areas, help support forums, and employee recreational get-togethers. The three major types of communications servers are Internet Relay Chat (IRC), conferencing, and community servers. The most advanced chat servers have recently started augmenting the text-based medium of conversation with dynamic voice (and even video) support. It is common for IRC-based chat to use dedicated IRC servers (with software like IRCPlus).
- FTP servers From downloading the newest software to transferring corporate documents, a significant percentage of Internet traffic consists of file transfers. File Transfer Protocol (FTP) servers make it possible to move one or more files between computers with security and data integrity controls appropriate for the Internet (using tools like ZBServer Pro). FTP is a typical client/server arrangement. The FTP server does the main work of file security, file organization, and transfer control. The client (sometimes part of a browser and sometimes a specialized program such as FTP Voyager) receives the files and places them onto the local hard disk.
- News servers News servers function as a distribution and delivery source for over 20,000 public newsgroups currently accessible over the USENET news network (the largest news and discussion group-based network on the Internet). News servers use tools (like INN News Server) that employ the Network News Transport Protocol (NNTP) to interface with other USENET news servers and distribute news to anyone using a standard NNTP newsreader (such as Agent or Outlook Express). News servers also make it possible to serve your own news and discussion groups publicly over the Internet-or privately over your own local network.
- Gateway servers A gateway is a translator that allows differing networks to communicate. For example, one common use for gateways is to act as translators between personal computers and minicomputer or mainframe systems. In a LAN environment, one computer is usually designated as the gateway computer. Special application programs in the desktop computers access the mainframe by communicating with the mainframe environment through the gateway computer, and users can access resources on the mainframe just as if those resources were on their own desktop computers.
- Firewalls and proxy servers Simply stated, a firewall is a feature designed to prevent unauthorized access to or from a private network (i.e., a corporation's LAN), and is generally considered to be a first line of defense in protecting private information. Firewalls can be implemented in both hardware and software (and often involve a combination of both). When properly implemented, firewalls prevent unauthorized Internet users from accessing private networks that are connected to the Internet-especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the required security criteria. There are numerous firewall techniques including packet filters, application gateways, circuit level gateways, and proxy servers. The proxy server is perhaps the most popular form of firewall. In actual practice, a proxy server sits between a client program (i.e., a Web browser) and some external server (usually another server on the Web f . The proxy server effectively hides the true network address, then monitors and intercepts any requests being sent to the external server, or that come in from the Internet connection. This allows the proxy server to filter messages, improve performance, and share connections.
- Web servers Web servers allow you to provide content over the Internet using the Hypertext Markup Language (HTML). A Web server (with software like Microsoft PWS) accepts requests from browsers like Netscape and Internet Explorer, and then returns the appropriate HTML document(s) to the requesting computer. A number of server technologies can be used to increase the power of the server beyond its ability to simply deliver standard HTML pages-these include CGI scripts, SSL security, and Active Server Pages (ASPs).
- Telnet/WAIS servers Telnet servers give users the ability to log on to a host computer and perform tasks as if they're actually working on the remote computer itself. Users can access the host system through the telnet server from anywhere in the world using a telnet client application. Before the arrival of the Web, Wide Area Information Server (WAIS) servers were critical for allowing users to perform searches for keywords in files. While telnet and WAIS are really not that popular today, network developers looking to broaden their selection of Internet services may consider supporting telnet or WAIS services.
One major issue that separates servers from peer computers is the use of software. No matter how powerful a server may be, it requires an operating system (i.e., Windows NT/2000 or Novell NetWare) that can take advantage of the servers resources. Servers also require their specific server applications in order to provide their services to the network. For example, a Web server may use Windows NT and Microsoft PWS. It's not important for you to fully understand software issues at this point. Chapter 2 covers network protocols and operating systems in more detail.
Client/Server Advantages There is little doubt that server-based networks are more complicated to install and configure, but there are some compelling advantages over peer-to-peer networks:
- Sharing Servers allow for better resource organization and sharing. A server is intended to provide access to many files and printers while maintaining performance and security for the user. A server's data and resources can be centrally administered and controlled. This centralized approach makes it easier to find files and support resources than would otherwise be possible on individual computers.
- Security In a server-based environment, one administrator can manage network security by setting network policies and applying them to every user.
- Backups Backup routines are also simplified because only servers need to be backed up (client/workstation PCs do not). Server backups can be scheduled to occur automatically (according to a predetermined schedule) even if the servers are located on different parts of the physical network.
- Fault tolerance Because data is mainly held on servers, fault-tolerant data storage (i.e., RAID) can be added to the servers to prevent data loss due to drive failures or system crashes. This creates a more reliable server subject to less downtime.
- Users A server-based network can support thousands of users. Such a large network would be impossible to manage as a peer-to-peer network, but current monitoring and network-management utilities make it possible to operate a server-based network for large numbers of users.