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<META NAME="Author" Content="Steph Mineart">
<TITLE>Managing Multivendor Networks -- Ch 8 -- Services</TITLE>
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<FONT COLOR="#000077">Managing Multivendor Networks</FONT></H1>
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<H1><FONT COLOR="#000077">- 8 -<BR>
Services</FONT></H1>
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<UL>
<LI><A HREF="#Heading1">The Scope of Services</A>
<LI><A HREF="#Heading2">LAN Services</A>
<UL>
<LI><A HREF="#Heading3">Minicomputer/Mainframe LAN Implementations</A>
<LI><A HREF="#Heading4">PC LAN Implementations</A>
<LI><A HREF="#Heading5">PC LAN Players</A>
<LI><A HREF="#Heading6">Server Alternatives</A>
<LI><A HREF="#Heading7">PC/Minicomputer/Mainframe LAN Integration</A>
<LI><A HREF="#Heading8">The Client/Server Model</A>
<LI><A HREF="#Heading9">X Window Interface</A>
</UL>
<LI><A HREF="#Heading10">WAN Services</A>
<UL>
<LI><A HREF="#Heading11">Document Content and Interchange Architectures</A>
<LI><A HREF="#Heading12">X.400</A>
<LI><A HREF="#Heading13">X.500</A>
<LI><A HREF="#Heading14">Emulation</A>
<LI><A HREF="#Heading15">Middleware</A>
<LI><A HREF="#Heading16">SNA-LAN Internetworking</A>
</UL>
</UL>
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<H2><A NAME="Heading1"></A><FONT COLOR="#000077">The Scope of Services</FONT></H2>
<P>Services are a very elusive aspect of networking. Because they cannot be seen
or held in the palm of your hand, it is difficult to envision connecting them together.
Yet services are the make-or-break component of a network implementation. If the
underlying services cannot support the demands of the applications and the users,
then the network will collapse.</P>
<P>And while networks depend greatly on services, the reverse is not true. In most
cases, services are independent from the type of network on which they run. For example,
multivendor office automation services have similar applicability and functions in
both LANs and WANs. The same is true of manufacturer-specific services, such as IBM's
Systems Network Architecture (SNA) and Digital's DECnet.</P>
<P>Sometimes, however, services are married to networks for a reason. For example,
PC (MS-DOS) virtual disk services could technically be implemented on a midrange
host over a WAN or LAN, but the need for transmission speed dictates a close marriage
to the LAN environment.</P>
<P>In fact, the very nature of a LAN poses certain requirements for services. After
all, if a LAN presented no benefits, no one would consent to attach to it. For minicomputers
and mainframes, the purpose of a LAN is to share terminals, printers, and disk space.
For PCs, however, the prime requirement is to share files and applications, and to
promote communication. Furthermore, not only do PC LANs and minicomputer/mainframe
LANs have separate service needs, but when both types of systems need to be integrated
as a whole, yet another set of services is necessary. In this arena, then, the choices
become broader, the players grow in number, and the mind begins to boggle.</P>
<P>Rising to meet this need for better integration among all types of computers is
the concept of <I>client/server computing</I>. This concept provides a distributed
environment for all application programs, while still giving the user a consistent
and understandable appearance.</P>
<P>The LAN environment contrasts sharply with that of a WAN. For one thing, transmission
speed in a LAN is virtually free (in other words, there are no ongoing costs for
daily operation of the network). In a WAN, however, you get what you pay for when
it comes to speed. Sure, you can get breathtaking speed with T1 links, satellite
links, and even microwave links, but these technologies don't come cheap.</P>
<P>At the other extreme of cost/performance is low-speed networking. Where high speed
WANs engendered concern about optimum use, slower networks tend to be used for lower
volume and less critical information. In this category fall the traditional phone-dial
and packet switching networks. They are excellent, cost-effective solutions for occasional
terminal access, intermittent and non-critical file transfers, or electronic mail.</P>
<P>In particular, electronic mail services have enjoyed explosive growth in WANs
of all varieties. Electronic mail products have become much more sophisticated and
have begun to offer real value to companies implementing them. And with this increase
in use has come an increase in the need to expand the communications sphere of the
product. Often, electronic mail starts in one department on one type of computer
but grows into a corporatewide network encompassing many different departments and
many different types of computers.
<H2><A NAME="Heading2"></A><FONT COLOR="#000077">LAN Services</FONT></H2>
<P>Despite the physical and logical connectivity provided by a LAN, a network has
no functional capabilities until network services are added to the mix. These services
facilitate shared files, shared printers, program-to-program communications, directory
services, and other more specific functions. The implementation details for network
services, however, differ from vendor to vendor and from system to system.</P>
<P>Perhaps the biggest difference is how PCs interact on LANs compared to how midrange
and larger computers interact on them. This difference results partly from the fact
that the needs of PCs on a network differ from the needs of traditional computers,
and partly from the fact that much of the LAN networking software for PCs was developed
from scratch (without respect to existing standards).</P>
<P>The requirements of a PC LAN are rapidly changing. In a larger environment, the
network is used as a collaborative tool that enables individuals in different geographical
locations to work together on individual documents. In a smaller environment, users
may have more modest needs from their networks, and may use them only for sharing
files, peripherals or applications, and for e-mail. The network interface to handle
files is at a very low (sector) level to maximize speed.</P>
<P>In minicomputer/mainframe computer LANs, however, the requirements generally focus
more on the movement of files and the optimization of terminal resources. File access
must be performed in a highly structured, secure manner, and files have specific
places of residence and ownership. When an end user wants to alter a file in this
environment, the file will probably be copied (transferred) to the user's computer
and then modified there. Terminals are the user's way of accessing applications and
information; therefore, this type of LAN maximizes the way a terminal accesses the
various systems in the LAN. As in PC LANs, though, it is common to share printing
and program-to-program communications between systems.</P>
<P>The heart of the contrast between the two operating environments lies in the operating
systems. Operating systems written for midrange and mainframe systems (for example,
VMS, MPE, OS/400, and Windows NT) are designed with networking in mind. File systems
are designed to accommodate residence on different physical hosts, physical printers
are isolated from the print generation process by print queues and spoolers, and
program compilers are developed to accommodate all of these network-oriented operations.
Thus, a program developed in this environment can immediately take advantage of the
network architecture.</P>
<P>Originally, personal computers were largely stand-alone devices. One of the first
PC operating systems was Microsoft's Disk Operating System (MS-DOS) with its IBM
derivative (PC-DOS) and other OEM versions. DOS in its various incarnations was designed
to control all resources directly. Files were on local disks, printers were locally
attached, and every program was an island incapable of communicating with other programs--and
that was that. Thus, when networking was introduced to the PC, it had to be crowbarred
in between the operating system (DOS) and the hardware. In other words, a program
operating on a networked PC had to think it was operating using its own local resources.
Faster PCs eventually led to the development of more sophisticated PC operating systems,
such as Microsoft's Windows 95 and Windows NT, which have networking features built
in.</P>
<P>The presence or absence of tight integration between network services and the
operating system makes a dramatic difference in how the network appears to the end
user. In tightly integrated systems like DECnet, the network is a widely accepted
and embraced part of the system. In loosely integrated systems, such as most implementations
of TCP/IP, the network is a separate entity, accessed through a separate set of utilities
and routines. And in between these two examples are networks that make a variety
of compromises between tight and loose integration.
<H3><A NAME="Heading3"></A><FONT COLOR="#000077">Minicomputer/Mainframe LAN Implementations</FONT></H3>
<P>Given that networks and operating systems have a significant impact on one another,
a brief recap of the networking architectures and philosophies of Digital, HP, IBM,
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