PC Support and LANs in the corporate computing environment.
Brief: This article is specifically designed to aid the IS Manager in understanding the issues involving the PC Support network and PC-based LAN software. It will focus on what makes a good PC network, and the differing features of PC Support and PC-based LAN software packages. Finally, it will identify the key technical features which help to explain the developing trend in networking facilities for the corporate computing environment.
The AS/400-based product called PC Support is a terminal emulation and networking facility for personal computers (PCs). PC-based local area network (LAN) software packages, such as Novell NetWare, Microsoft LAN Manager and IBM LAN Server, are also networking facilities. Both services are capable of using the high-speed IBM Token Ring interface. Both services are "host-based" or "server-based" facilities (data and software are "served" to workstation PCs from a central computer). Finally, both services are proven solutions to the problems of sharing data and resources between PCs.
Yet, in a given situation, there must clearly be some advantages in the use of one particular type of support over the other. Each organization's individual needs largely determine whether AS/400 PC Support or a PC-based network is the stronger solution.
Competing Claims in a Confusing Market
Listening to claims of the various
software vendors doesn't help Information Systems (IS) managers to understand the influx of PC-based LANs in a corporate computing environment traditionally serviced by PC Support. IBM, for example, markets both PC Support and its own OS/2-based IBM LAN Server packages. Microsoft and Novell both claim that they provide interfaces to work with PC Support, giving IS the best of both possible worlds. Does this suggest some basic advantage to using PC Support? Or, conversely, are marketers implying that PC-based products deliver something that is missing from PC Support?
These competing claims create confusion among IS managers who are simply trying to provide service and maximize resources at minimum cost. But-in a technology which is rapidly changing-it's difficult to find concrete reasons to justify whether a shift from traditional IS-managed PC Support to newer PC- based networking facilities is advisable. And this is the crux of the dilemma facing AS/400 professionals: PC Support seems like a fine networking facility, so why do some people recommend PC-based LANs instead? What are the differences, and what do they really mean to the installation?
What is PC Support and What is a PC-based LAN?
In order to fully explore the differences and their meanings, it's important to understand the underlying functionality of both facilities.
PC Support is an AS/400 application and a group of PC software products which interconnect the AS/400 and PCs through software emulation techniques and PC device redirection.
By comparison, PC-based LAN software packages, such as Novell NetWare, IBM LAN Server and Microsoft LAN Manager, are PC software environments or-in Novell's case-operating systems, which interconnect PCs and other computers using peer-to-peer techniques.
The dominant focus of PC Support is to make the central resources of the AS/400 available to the connected PCs. By comparison, the dominant focus of PC-based LAN products is to centralize the computing resources of all PCs and to make them generally available to all connected devices.
On the surface, the different focal points might seem unimportant-after all, they both work to centralize resources and distribute computing function. As a result, the initial tendency to favor one strategy over another can often be attributed to one's background. For instance, the day-to-day focus on the AS/400 could naturally cause IS personnel to adopt the PC Support approach. But to the everyday PC user, the AS/400 is merely one of many resources which needs to be shared.
PC data, highly functional PC peripherals and the power of packaged PC software all represent resources which-though not perhaps "mission critical"-are tools which might be better utilized in a shared fashion. The well-researched IS decision is based not on the approach the decision maker alone is most comfortable with, but on the networking facility which, upon closer examination, most directly answers the collective need of the company.
What is a Good Networking Facility for Personal Computers?
As indicated by the common goal of shared resources, PC Support and PC-based LAN software contain a great deal of overlapping of functionality. In order to judge the effectiveness of these networking facilities-and to distinguish their differences-there must be some criteria for measurement. From a purely technical perspective, most professionals agree that a good networking facility has the following:
1. The ability to share data and resources, such as programs, printers, modems, peripherals, etc.
2. High performance. Performance is measured by the speed with which a resource is made available to a networked PC.
3. The flexibility to adjust to the changing office environment. This may include physical changes in the environment, or software upgrades which require reinstalling or changing configurations.
4. The malleability to connect a variety of differing machines and operating systems. Offices are no longer bastions of single-vendor operating systems. UNIX, OS/2, Macintosh System 7 and other operating systems are rapidly making their way into the business arena.
5. Ease of use for those PCs connected. A network which is cumbersome to use will rarely be maximized.
6. The protection of resources, through security procedures.
7. The capability to centrally administer the network, its software components and its user population.
The chart in 1 uses these factors to illustrate how PC Support and "generic" LAN software compare as networking solutions. The chart indicates that PC Support offers many of the same networking functions as PC-based LAN packages.
The chart in Figure 1 uses these factors to illustrate how PC Support and "generic" LAN software compare as networking solutions. The chart indicates that PC Support offers many of the same networking functions as PC-based LAN packages.
A closer look at the functions provided by both techniques is even more intriguing. PC Support appears to offer a highly attractive combination of networking capability and host support.
2 and 3 compare PC Support and LAN software from two different perspectives. 2 concentrates on the strengths and benefits of PC Support, some of which are available with PC LANs. Conversely, 3 emphasizes functions which are primary objectives of PC LAN software.
Figures 2 and 3 compare PC Support and LAN software from two different perspectives. Figure 2 concentrates on the strengths and benefits of PC Support, some of which are available with PC LANs. Conversely, Figure 3 emphasizes functions which are primary objectives of PC LAN software.
An examination of these two charts shows that PC Support and PC-based LANs have a great deal of functionality in common. On the one hand, PC Support appears to be an excellent choice for attaching the AS/400 and utilizing its central computing role within the organization. On the other hand, performance using PC Support is low, and its capabilities with other non-IBM operating systems is nonexistent. The decision maker must weigh the pros and cons against the company's particular focus to ensure maximum benefit.
Maximizing Resources: Who Gets What
Since both PC Support and PC-based LAN software offer functions designed to capitalize upon a specific computing resource, determining which resource management wants to maximize-AS/400 or PC-will ultimately determine the appropriateness of the solution.
If the AS/400 is perceived to be under-utilized, PC Support represents a cost- effective means of providing network functions to PC users, allowing data and peripheral sharing. If there is a need to maximize the investment in PC software and devices, LAN software will provide a cost-effective solution for sharing data and peripherals.
But determining the effectiveness of these competing solutions must also be cost-justified. Either approach has a cost-perhaps now, perhaps in the future. There may be compelling reasons why management prefers to spend now or later, on AS/400 resources or PC resources. These reasons must become part of the cost-effectiveness evaluation.
The cost of setting up a PC-based network on existing PCs usually averages out to be about $1,500 per device. The cost of adding memory to the AS/400 or auxiliary DASD can be considerably more. Identifying the bottom line, in costs, usually starts out by favoring an under-utilized AS/400. As the network becomes more sophisticated, the PC-based LAN may provide overwhelming cost effectiveness.
Why PC LANs?
If PC Support offers more or equivalent function than the PC-based LANs, why are so many AS/400 organizations installing PC LANs? Is it because LANs are getting more press, or is there some basic technical advantage to using them?
The answer has to do with the level of computing sophistication which the PC user community has achieved. While PC Support provides many (though not all) of the functions of LAN software, it has several serious drawbacks for users whose primary focus is PC-based applications.
First of all, PC Support does not provide the same performance levels as a PC- based LAN. Secondly, PC Support does not provide the same measure of transparency to PC applications as does a PC-based LAN. Finally, the most important drawback is that PC Support cannot provide the same functional equivalency to many PC applications which are available to these same programs through a PC-based LAN. One possible solution is to use a combination of PC Support and a PC-based LAN. Again, each organization needs to evaluate the benefits and the costs.
Examining the Performance Differences
There are serious differences in performance between PC Support and LAN software which cannot be overstated. These performance differences exist in the ready availability of shared devices, data and software.
Benchmarks loading identical software from a LAN shared directory versus a PC Support shared folder demonstrated an eightfold increase in speed advantage for LAN-based software. (This benchmark was performed at Sutter Home Winery on January 10, 1991, on a 4-megabit Token Ring network. The program loaded was Norton Commander. The LAN Operating System was IBM OS/2 Version 1.2 running IBM LAN Server software. The PC Support Server was an IBM AS/400 B-35 running OS/400 PC Support Version 1.2 on the same 4-megabit Token Ring network.)
The difference in performance levels is so pronounced that, for PC users, it can spell the difference between readily maximizing the use of the network or relegating it to the ranks of the "occasionally used."
Remapping Versus Emulation
Why is there such a performance difference between PC-based LAN software and AS/400 PC Support? The answer relates to the means by which the function is provided. PC Support functions through a com-bination of resource re-
mapping and software emulation. PC-based LAN software, by comparison, addresses the resource needs of the PC with only resource re-mapping and dedicates its power to providing direct access to the requested resources. In order to comprehend how this impacts performance, one needs only to trace the complicated pathway by which PC Support works.
The PC Support Scenario
A shared folder on the AS/400 is, for the PC using it, an emulated disk or diskette drive. This emulation is provided by device drivers which are implanted by PC Support into the configuration file of the PC. When it is powered up, a part of the PC's memory is reserved for the emulation device driver.
The process of enabling a PC Support shared folder is a step-by-step routine which eventually fools the PC into believing that it has the resource of the shared folder available to it as another disk drive.
First, a program called an Adapter Handler must be executed. This Adapter Handler activates the hardware interface between the PC and the AS/400. A second program, called the Router, must then be executed. The Router is the communications program which acts as mediator between the AS/400 and the PC. It talks to the Adapter Handler and to subsequently loaded PC programs. The third program which must be loaded is STARTFLR, which bonds the facility for sharing AS/400 folders with the PC. The final program which must be executed is called FSPC, which stands for Folder Sharing to Personal Computer. This program instructs the AS/400 to share an assigned folder as a specific emulated disk drive on the PC.
Every request for data from the shared folder passes through these layers of PC application programs and device drivers, carefully wending its way toward the AS/400 to retrieve the data or resource.
At the same time, the AS/400's time is not devoted to waiting for requests from the attached PCs. Instead, its task is to service all the resources and requests of its attached users. Running within its main storage is an Advanced Program-to-Program Communication (APPC) application to service the attached PC. This APPC application is maintained by a whole set of device descriptions created specifically for the attached PC. These device descriptions are managed by an APPC Controller device which interacts with the attached PC's Router program through the communication adapter.
Because the AS/400 has many other tasks which preoccupy it (providing responses to display terminal users, managing DASD, etc.), the availability of the information which is requested from the shared folder is impacted by the overall priorities of the loaded mini-computer. Secondly, because there are so many layers between the requesting PC and the actual information, processing time is increased as each layer is traversed.
The point of describing this arduous journey of data through PC Support is to document the layers of effort which are expended by the equipment and the software in order to provide network function. The fact that the cost of this network function is a slower response time should not come as a surprise.
The LAN Software Scenario
By comparison, the role of LAN software is simply to remap resources on the personal computer and to make available all required server re-sources for the attached PCs.
A single device driver is implanted within the configuration file of the PC by the LAN software installation process. Thereafter, calls to these resources by the PC are directly intercepted by the device driver and forwarded to the server.
Instead of relying upon emulated device descriptions, as in the AS/400 PC Support scenario, the LAN Server simply retrieves the data from its disk and passes this information back to the PC's memory. If there is a requirement for security, the server gates the accessibility to the resource. If there is a requirement for file, record or field locking, the server maintains a status roster to prevent sharing conflicts.
PC-based LAN products use a number of techniques such as "elevator finding" and "directory caching"-which greatly enhance the speed of access. Finally, because the server is not preoccupied-as the AS/400 is with OS/400 applications-the availability of the server is considerably higher than that of a fully utilized AS/400. Programs don't get swapped out of main storage to make room for other resource calls, as they do with OS/400.
Examining Software Transparency
The second issue-that of PC software transparency-concerns the operating system functions of the PC, the application software which is running on it and the devices which the application software requires in order to function.
When a PC application is loaded into the memory of the computer, it relies upon the set of computer instructions which identify its re-sources. These instructions include device interfaces to disk drives, monitors and printer ports. The application uses these instructions to send and receive information to and from the device.
Because PC Support is acting as a mediator between the PC and emulated devices-such as networked folders and printers-the potential for problems is significantly increased. The simplest example might be a case in which a new printer is added to the PC Support network.
If the printer is to function properly on the PC Support network with all the advanced features which made the printer desirable, the PC application must, of course, be capable of talking to it. This is usually accomplished by the purchase of a software printer driver for the PC application.
But, in a PC Support network, a second printer driver must also be obtained from IBM. This second printer driver interacts with the Work Station Function (WSF) of PC Support, through the IBM proprietary window of emulation, so that the functionality of the printer may be made transparent through the layers of PC Support. (Remember, all PC-attached printers are perceived by the AS/400 as native devices, and the number of potential AS/400 printers is significantly small.)
But what happens if IBM doesn't make this printer driver available? If any special functions of the new printer are not readily available through standard PC Support device drivers, the capabilities of the new printer will be crippled. Instead, PC Support must be configured to accept all data coming to this printer as straight ASCII data.
Now, according to IBM, this ends the issue of printer data stream transparency. The argument goes "whatever you sent to this printer must have finally arrived, because the AS/400 didn't do any translation!" But, in reality, the transparency issues for printer data streams and other device emulations only get more complicated. This is because-in the process of communicating-the AS/400 must decide how and when it will control the data, signals, and the timing of those signals sent to the printer.
The result of this networking scheme, using the virtual print facility, is fraught with problems. This is not because Virtual Print does not work. Rather, it's the limitation which is inherent with emulation technologies: the devices attached are pretending to be something they are not.
Why is this a problem? Follow this route through-from the time the PC application begins printing until the time it actually arrives as a piece of paper!
A PC application sends plotter data out to the device identified to it as the parallel port of the PC.
In actuality, however, the PC has been instructed to intercept this activity and route it through the Virtual Print facility.
From the Virtual Print program, the data is redirected through the Router program and then through the Adapter Handler program, which communicates with the AS/400. The data passes through the APPC session on the AS/400 and is then directed to an outqueue. This outqueue is attached to an AS/400 printer device description, which is defined as an AS/400 printer connected on another PC running the WSF.
The data travels through to the PC, back down through the Adapter Handler and Router until it finally arrives at the WSF program. WSF redirects the output to the parallel port of the PC and out to the plotter. This actual plotter must pretend that it's a native AS/400 IPDS printer in order for the WSF program to make use of all its functions. Otherwise, the AS/400 must pass data through to this printer as straight ASCII data.
The potential for difficulties is obvious. Additional problems may occur if the AS/400 is heavily burdened with other tasks. The printer can actually time out in the middle of a print stream. The result is that printer control codes are interrupted, the printer is automatically reset, and the actual output looks nothing like the plotter data which was originally sent to the device.
In comparison, PC-based LAN software is designed for remapping of resources and for security. Devices aren't emulated, but exist as resources with their own native identities.
There are three means by which printers are addressed in PC-based LAN software. A printer can reside on one of the parallel ports of the server; it can reside upon a dedicated PC which acts as a print server on the network; or its identity can be "published" on the network for use by other PCs. (Recently announced devices by some printer manufacturers also allow printers to be directly attached to the network without being attached to a PC at all.) There is no emulation of foreign devices, no translation of codes through WSF, and no need for secondary printer device drivers. The printer receives the print stream as fast as the hardware of the network can feed it, and subsequent timing problems are greatly reduced.
For the PC application, the advantages are obvious. When the application calls for the use of a resource, the resource is provided transparently, without pretense and without a convoluted emulation process.
Functional Equivalency Examined
Although PC Support provides data and resource sharing, it cannot provide the software functional equivalency of PC-based LAN products. This is because networked PC application software-Lotus 1-2-3, WordPerfect or dBase IV- doesn't have the capability of perceiving PC Support as a true network. What does this mean?
AS/400 users have grown accustomed to the security and functionality of their applications. These features of the AS/400 are deeply embedded in the operating system itself. Running an application on the AS/400 presupposes that the operator at the terminal is working in an environment in which security has been defined, and that the operator's data is protected.
By comparison, the PC user running an application from a shared folder has no such protection. While shared folders have some limited security functions, they are rudimentary. A person loading a PC-based spreadsheet from a shared folder may be automatically protected should another user choose to access that same file, but that second user can override this protection at the time at which he accesses the folder.
More significantly, PC-based databases aren't provided with a record or field locking protection through PC Support. And since most PC databases require some minimal record locking capability-through "network awareness hooks"- loading a database from a shared folder can result in operational difficulties or, even worse, a corrupted database. The bottom line is that PC Support has some major limitations in its capabilities to act as a true server through shared folders.
By comparison, PC-based LAN software products provide published hooks and handles through which all record access passes by the database application. These hooks enable the record locking and multi-user features which are required in this environment-things which AS/400 application users have come to expect as natural. This network awareness prevents catastrophes associated with unprotected data-base access.
An Evolution Toward PC-based LANs
IS departments are witnessing the rapidly accelerating networking needs of the corporate PC user. This acceleration is fueled by inexpensive, high-quality packaged software designed to run on the desktops of the office workplace.
The evolutionary needs of these users have previously been well served by the AS/400 and its networking capabilities through PC Support. This facility has allowed resource and data sharing at a marginal expense while adding great value to the overall information system. But as these users increase their sophistication, and as the packages which run on these desktops increase their capabilities, PC Support is unable to adequately compete with true PC-based networking software as a network server. What was once designed as a facility to bond PCs to the central mini-computer-through device emulation and resource remapping-is now being asked to serve as the major conduit for inter-PC traffic. What was once called "casual connectivity" has now blossomed into a requirement for a six-lane highway. PC Support was not designed for this traffic load.
PC-based LAN software, on the other hand, was designed as a true inter-PC resource highway. It uses a server-based technology which-at first glance- offers many of the same facilities which PC Support has provided. But beneath this patina of similarity is a dedicated technology designed for the specific needs of the evolving PC community.
As a networking facility, PC-based LAN software outperforms PC Support while overcoming many of its transparency and functional limitations. But a PC-based LAN should not be seen as a competitor of the AS/400, nor of PC Support itself. When implemented in an AS/400 environment, it should be used as "one more facility" made available to all users.
This value-added perspective works well with the evolutionary goals which IS has set for itself: as users require more service, IS will be there to provide it. Novell, Microsoft and IBM itself all benchmark the success of their PC- based LAN packages by their abilities to work with PC Support and the AS/400. It's by finally examining the networking capabilities of PC Support and recognizing their limitations that IS can take the first step toward meeting the evolutionary goals for the IS PC users. The second step, of course, is providing a PC-based LAN which can best meet the long-term needs of the organization.
Networking in the Corporate Climate
Figure 1 Comparing PC Support to LAN Software
Figure 1: Comparing PC Support to LAN Software as a Networking Facility FUNCTION IBM PC LAN SUPPORT Software RESOURCE SHARING Data Sharing Good Good Printer Sharing Good Good Modem Sharing N/A Good Other Devices N/A Good PERFORMANCE Twinax Poor N/A Token Ring Good Excellent Ethernet N/A Excellent FLEXIBILITY Ease of Installation Excellent Difficult Self-configuring Good Poor Serviceability Excellent Good EASE OF USE DOS Good Excellent OS/2 Excellent Good MALLEABILITY DOS Excellent Excellent OS/2 Excellent Excellent UNIX N/A Excellent (Novell) Macintosh N/A Excellent (Novell) Other N/A Some availability SECURITY Resource Restraint Good Excellent User Identification Good Good Ownership Poor Poor CENTRAL ADMINISTRATION Hardware Problem Solving Good Good Software Problem Solving Good Good User Monitoring Poor Good
Networking in the Corporate Climate
Figure 2 Major functions from AS/400 PC Support
Figure 2: Major Functions From AS/400 PC Support FUNCTION BENEFIT IBM PC LAN SUPPORT SOFTWARE WORKSTATION FUNCTION Allows the PC to Maximize hardware investment by YES YES emulate a 5251 providing a single device terminal, and any for both AS/400 and PC work. attached PC printer to emulate native AS/400 printers. SESSION MANAGER Allows multiple AS/400 Multi-tasks AS/400 sessions YES NO sessions to be visible for a single user. on the screen as indi- vidual windows. SHARED FOLDER Allows the AS/400 DASD Centralized data; YES NO to be used as a storage better security. medium for PC data and/or programs. VIRTUAL PRINTING ON AS/400 Allows the use of AS/400 Maximize AS/400 YES NO printers to receive the peripheral investments. printed output of a PC. PC PRINTER SHARING Allows the printer at- Maximize PC peripheral YES YES tached to one PC to be investments. shared by another PC. FILE TRANSFER FUNCTION Allows for information Reduce redundant keying of YES NO on the PC to be information into separate uploaded into a applications. database on the AS/400, or vice versa. MESSAGE FUNCTION Allows the PC to send Integrates AS/400 YES NO or receive AS/400 and PC environments. messages. SUBMIT REMOTE COMMAND Allows the PC to submit Integrates AS/400 YES NO an AS/400 command from and PC environments. the DOS command line. PC ORGANIZER Allows the functions of Integrates AS/400 YES NO the personal computer and PC environments. to be accessed from the AS/400 command line. AS/400 DATABASE Allows the use of Mission-critical YES NO AS/400 database to software available be made available to to PCs. PC.
Networking in the Corporate Climate
Figure 3 Software major functions from LAN software
Figure 3: Software Major Functions From PC-based LAN Software FUNCTION BENEFIT IBM PC LAN SUPPORT SOFTWARE SHARED PC DISKS Allows the disk space Reduced disk costs; centralized NO YES of a PC to be used as a data; centralized applications; storage medium by other better security. PCs. PC PRINTER SHARING Allows the printer at- Maximize PC YES YES tached to one PC to be peripheral investments. shared by another PC. PC APPLICATION SERVING Allows PC applications Centralized control of PC NO YES to be served from a software; data and application central device, with security. data integrity and record locking. REMOTE IPL (RIPL) WORKSTATIONS & DISKLESS PCs Eliminates local Security of corporate PC data NO YES storage on the PC. and resources; decreased hardware costs. DOS-OS/2 MULTI-TASKING SUPPORT Allows the support of Maximizes PC by permitting YES YES PC multi-tasking en- simultaneous computing. vironments and operating systems such as OS/2 and Windows. NON-DOS OS/2 ACCESS Allows computers running Integrates different OS NO YES non-DOS or OS/2 operat- within the corporate setting. ing systems to partake of network resources. (Macintosh, UNIX, etc.). MENU-DRIVEN INTERFACES Provides the user with Provides better user NO YES a fully secured, menu- productivity than driven interface for command-based interfaces. all applications available to the PC.
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