Arunachalam’s Weblog

Application Servers

Sometimes referred to as a type of middleware, application servers occupy a large chunk of computing territory between database servers and the end user, and they often connect the two.

Middleware is a software that connects two otherwise separate applications For example, there are a number of middleware products that link a database system to a Web server This allows users to request data from the database using forms displayed on a Web browser and it enables the Web server to return dynamic Web pages based on the user’s requests and profile.

The term middleware is used to describe separate products that serve as the glue between two applications. It is, therefore, distinct from import and export features that may be built into one of the applications. Middleware is sometimes called plumbing because it connects two sides of an application and passes data between them. Common middleware categories include:

* TP monitors
* DCE environments
* RPC systems
* Object Request Brokers (ORBs)
* Database access systems
* Message Passing

Audio/Video Servers

Audio/Video servers bring multimedia capabilities to Web sites by enabling them to broadcast streaming multimedia content. Streaming is a technique for transferring data such that it can be processed as a steady and continuous stream. Streaming technologies are becoming increasingly important with the growth of the Internet because most users do not have fast enough access to download large multimedia files quickly. With streaming, the client browser or plug-in can starts displaying the data before the entire file has been transmitted.

For streaming to work, the client side receiving the data must be able to collect the data and send it as a steady stream to the application that is processing the data and converting it to sound or pictures. This means that if the streaming client receives the data more quickly than required, it needs to save the excess data in a buffer If the data doesn’t come quickly enough, however, the presentation of the data will not be smooth.

There are a number of competing streaming technologies emerging. For audio data on the Internet, the de facto standard is Progressive Network’s RealAudio.

Chat Servers

Chat servers enable a large number of users to exchange information in an environment similar to Internet newsgroups that offer real-time discussion capabilities. Real time means occurring immediately. The term is used to describe a number of different computer features. For example, real-time operating systems are systems that respond to input > immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Most general-purpose operating systems are not real-time because they can take a few seconds, or even minutes, to react.

Real time can also refer to events simulated by a computer at the same speed that they would occur in real life. In graphics animation, for example, a real-time program would display objects moving across the screen at the same speed that they would actually move.

Fax Servers

A fax server is an ideal solution for organizations looking to reduce incoming and outgoing telephone resources but that need to fax actual documents.

FTP Servers

One of the oldest of the Internet services, File Transfer Protocol makes it possible to move one or more files securely between computers while providing file security and organization as well as transfer control.

Groupware Servers

A GroupWare server is software designed to enable users to collaborate, regardless of location, via the Internet or a corporate Intranet and to work together in a virtual atmosphere.

IRC Servers

An option for those seeking real-time capabilities, Internet Relay Chat consists of various separate networks (or “nets”) of servers that allow users to connect to each other via an IRC network.

List Servers

List servers offer a way to better manage mailing lists, whether they are interactive discussions open to the public or one-way lists that deliver announcements, newsletters, or advertising.

Mail Servers

Almost as ubiquitous and crucial as Web servers, mail servers move and store mail over corporate networks via LANs and WANs and across the Internet.

News Servers

News servers act as a distribution and delivery source for the thousands of public news groups currently accessible over the USENET news network. USENET is a worldwide bulletin board system that can be accessed through the Internet or through many online services The USENET contains more than 14,000 forums called newsgroups that cover every imaginable interest group. It is used daily by millions of people around the world.

Proxy Servers

Proxy servers sit between a client program typically a Web browser and an external server (typically another server on the Web) to filter requests, improve performance, and share connections.

Telnet Servers

A Telnet server enables users to log on to a host computer and perform tasks as if they’re working on the remote computer itself.

Web Servers

At its core, a Web server serves static content to a Web browser by loading a file from a disk and serving it across the network to a user’s Web browser. The browser and server talking to each other using HTTP mediate this entire exchange.

Grid computing (or the use of a computational grid) is applying the resources of many computers in a network to a single problem at the same time – usually to a scientific or technical problem that requires a great number of computer processing cycles or access to large amounts of data. A well-known example of grid computing in the public domain is the ongoing SETI (Search for Extraterrestrial Intelligence) @Home project in which thousands of people are sharing the unused processor cycles of their PCs in the vast search for signs of “rational” signals from outer space. According to John Patrick, IBM’s vice-president for Internet strategies, “the next big thing will be grid computing.”Grid computing requires the use of software that can divide and farm out pieces of a program to as many as several thousand computers. Grid computing can be thought of as distributed and large-scale cluster computing and as a form of network-distributed parallel processing. It can be confined to the network of computer workstations within a corporation or it can be a public collaboration (in which case it is also sometimes known as a form of peer-to-peer computing).

A number of corporations, professional groups, university consortiums, and other groups have developed or are developing frameworks and software for managing grid computing projects. The European Community (EU) is sponsoring a project for a grid for high-energy physics, earth observation, and biology applications. In the United States, the National Technology Grid is prototyping a computational grid for infrastructure and an access grid for people. Sun Microsystems offers Grid Engine software. Described as a distributed resource management (DRM) tool, Grid Engine allows engineers at companies like Sony and Synopsys to pool the computer cycles on up to 80 workstations at a time. (At this scale, grid computing can be seen as a more extreme case of load balancing.)

Grid computing appears to be a promising trend for three reasons: (1) its ability to make more cost-effective use of a given amount of computer resources, (2) as a way to solve problems that can’t be approached without an enormous amount of computing power, and (3) because it suggests that the resources of many computers can be cooperatively and perhaps synergistically harnessed and managed as a collaboration toward a common objective. In some grid computing systems, the computers may collaborate rather than being directed by one managing computer. One likely area for the use of grid computing will be pervasive computing applications – those in which computers pervade our environment without our necessary awareness.

DISTRIBUTED DENIAL OF SERVICE (DDOS)

Short for denial-of-service attack, a type of attack on a network that is designed to bring the network to its knees by flooding it with useless traffic. Many DoS attacks, such as the Ping of Death and Teardrop attacks, exploit limitations in the TCP/IP protocols. For all known DoS attacks, there are software fixes that system administrators can install to limit the damage caused by the attacks. But, like viruses, new DoS attacks are constantly being dreamed up by hackers.

What is a Distributed Denial of Service (DDoS) attack?

Have you ever tried to make a telephone call but couldn’t because all the telephone circuits were busy? This may happen on a major holiday and often happens on Mother’s Day. In fact, in the United States, telephone companies used to air commercials on television and radio that suggested you avoid peak calling times by making your calls early or late in the day.

The reason you couldn’t get through is because the telephone system is designed to handle a limited number of calls at a time. That limit was determined by weighing the cost of having all calls get through all the time with the amount of traffic the system receives. If the total number of calls is always high, it makes economic sense for the telephone company to provide more capacity to match that demand. However, if the number of calls is low compared to the holiday peaks, then the telephone company will build networks that accommodate only the lower off-peak number of callers and advise their customers to avoid peak calling times. It’s a basic matter of supply and demand.

Imagine that an intruder wanted to attack the telephone system and make the system unusable by telephone customers. How would they do this? One way would be to make call after call in an attempt to make all circuits busy. This type of attack is called a denial of service, or DoS, attack. In essence, the intruder has caused the telephone system to deny service to its customers. It is not likely that one caller working alone can tie up all telephone circuits. To do that would require making as many calls as possible from as many telephones as possible.