Application Servers

One of the quiet revolutions changing the nature of computer networking is the growing use of special-purpose, or application servers. Whether they offer network users online access to facsimile capabilities, a mainframe gateway, or any of a variety of other sophisticated features, application servers add significant value to a network.

Unlike traditional network file servers, which act as intelligent , high-capacity data-storage and input/output systems, application servers perform specialized roles within a network environment. These may encompass managing printing queues, storing and routing electronic mail, or providing access to a database.

Application servers also reduce the demands placed on traditional file servers. Without having to handle special responsibilities, file servers can focus their processing resources on their primary jobs, network I/O and storing network data.

Application Server Types

[Editor's note: Even in 2003, the definition of "application server" has yet to converge around a single meaning. "Application servers" may be object-oriented middleware for distributed execution, or Web server/database combinations, or some other form of multiuser execution platform (such as Citrix MetaFrame or Microsoft Terminal Server,) as well as relatively simple single-purpose servers devoted to a particular application. This tutorial is about this last meaning of "application server."]

Like many areas in the continually evolving electronics industry, compiling a comprehensive list of application server types is probably impossible . Still, we can pinpoint at least nine distinct types of application servers: asynchronous communications servers, backup servers, database servers, e-mail servers, fax servers, image servers, optical disk servers, print servers, and directory servers.

Briefly, communications servers provide dial in and dial out access to networks; backup servers manage the archiving of a network's data-storage systems; database servers allow accessing data stored on a variety of computers; e-mail servers act as electronic post offices; and fax servers allow multiple network users to send and receive faxes online. Image-processing servers permit entering and maintaining digitally processed images, such as cancelled checks, into a database; optical disc servers grant access to the huge amounts of data stored on CD-ROMs, and print servers manage the printing process, including changing fonts and forms.

We'll describe the operation of four application servers-fax, print, management, and backup-in more detail shortly. Other application servers are described elsewhere in this book.

They Work Together

Before continuing, it's important to clarify one point: With the exception of a traditional file server, application servers generally require the services of another server to operate properly. This means a network would contain several types of application servers, all working in tandem and relying on each other.

For example, a fax server requires access to a file server and the word-processing files contained thereon, before it can transmit data. And it might require using the resources of a print server for access to a laser printer. A database server requires access to data stored on a variety of other application servers and hosts , especially those where corporate databases are located.

Similarly, a key trend in the development of e-mail servers is to allow the e-mail "post office" machine to use the naming or directory service maintained by the network operating system, which is generally found on a file server. This simplifies managing the network because the administrator must keep track of and update only one naming service, not two.

Transparent Operation

One of the major strengths of application servers is their "transparent" operation to end users. That is, other than invoking an e-mail program, fax menu, or similar start-up program, most network users aren't even aware they're using an application server.

For instance, users of fax servers don't need to know they're accessing a device dedicated to sending and receiving faxes online. When they want to send a fax, they merely respond to onscreen prompts from the server software program by typing a destination fax machine's telephone number, the name of the file they want sent, the name of the recipient, and a short cover letter.

The fax server takes care of the rest automatically. It dials the phone number, transmits the fax via an internal modem, even redials the number should it get a busy signal. It also retrieves and stores incoming faxes without user intervention.

Serving Printing Needs

Print servers were among the first of the special-purpose devices to appear on the network scene. Originally, they acted much like "traffic cops," starting and stopping print jobs or redirecting them to a specific printer, leaving functions such as font and forms management to the user.

Now, however, a print server can be configured so it lets one user print in Helvetica and a second in Times Roman without either user worrying about changing fonts. Print servers must be aware of which hard and soft fonts are available, which page description languages are installed, and the like. (Hard fonts are those provided by the printer itself; soft fonts are those downloaded from a PC application to the printer.)

Intelligent print servers know which printers are capable of certain tasks or have certain size paper trays, and direct output accordingly . Some advanced print servers can balance loads among multiple printers. Some also offer management and accounting features, enabling a network administrator to charge back users for the printers' services.

Publishing The Fax

A fax server can turn anyone with the correct destination phone numbers and the willingness to pay the associated line costs into an electronic publisher. In many ways, fax servers can replace both regular mail and electronic-mail systems. And they certainly reduce the time spent manually feeding sheets of paper into a standard fax machine.

A fax server is a hardware-software combination with connections to both the network-this can be any of the commonly used Ethernet, ARCnet, or Token Ring connectors-and the telephone system (via a standard RJ-11 modular jack). The fax server works in conjunction with a file server to let users send copies of their network-based electronic files-they can be word processing documents, spreadsheet forms, or graphics images-directly across the phone system to another fax machine.

In this application, users specify which files they want faxed, and the fax server accesses the correct file server to retrieve the needed files. It sends the fax out over the telephone system via its internal modem.

Obviously, this process eliminates several steps, including printing the original file on paper, then feeding it to a fax machine for transmission. It also holds more far-reaching ramifications , especially for organizations that need to fax out multiple copies of a single document.

With a fax server, the fax-sending process can be automated, much like a mail merge operation. This means, for example, that a company could use a fax server to "publish" dozens or even hundreds of personalized copies of a newsletter electronically , without requiring someone to manually perform the chore.

Backing Up The LAN

Several vendors have taken a similar approach to providing backup capabilities. Backup servers, as the name implies, are dedicated to providing centralized data archival (and recovery) facilities.

Legato Systems (Palo Alto, CA) has moved the backup-and-recovery process into the client-server environment with its NetWorker product. NetWorker is made up of client and server software, with the latter running on one or more backup servers. The client software, which runs on each PC on the network, determines which files to back up and routes them across the network to the right backup server. The server software manages the backup media-generally, tapes-and maintains an index of previous backups and their associated media volumes .

This system lets servers back up files on any network client. The online file backup history index also simplifies recovery operations-as users browse the index, they see historical views of the network file system at specified times. A lost file can thus be quickly identified and recovered.

On The Downside

Naturally, there's a downside to using application servers. The most obvious, of course, is the cost of the additional hardware for each special-purpose server. And compatibility issues often create problems-that is, one application server may not operate on the same network with another. Placing numerous application servers on a network also adds complexity.

Because of these kinds of issues, application servers are more apt to be found in large corporate networks, where technical personnel are readily available, than in small, departmental workgroups. Still, many network users have discovered that the value added by application servers makes them well worth the expenses they entail.

This tutorial, number 34, by Jim Carr, was originally published in the May 1991 issue of LAN Magazine/Network Magazine.