ch08.htm

this describes managing multivendor networks

and Sun is in order.</P>
<P><B>Digital Equipment&#160;&#160;</B>Digital Equipment's networking architecture
is based on the IEEE 802 family of standards. In terms of networking software, Digital
offers a range of utilities and services under the umbrella of DECnet. DECnet protocols
and services allow remote file operations, print sharing, remote logon, program-to-program
communications, and other functions. Because DECnet is tightly integrated with Digital's
operating systems (VMS and ULTRIX), DECnet is part of the user and file-naming conventions
and structures used by the operating systems. Another Digital LAN protocol that has
gained wide popularity is the <I>Local Area Transport (LAT)</I>. LAT is a protocol
used by <I>terminal servers</I> (devices that attach terminals directly to the LAN)
to route terminal traffic to and from one or more hosts on that LAN. LAT is not a
formal part of the DECnet service suite and has gained some usage and acceptance
in non-DEC networks and hosts.</P>
<P>All things considered, Digital Equipment has one of the most well-integrated network
archi-tectures--it was one of the first companies to integrate networking into their
standard computing environment.</P>
<P><B>Hewlett-Packard&#160;&#160;</B>HP's primary LAN architecture relies on the
IEEE 802.3 standard. It, however, does have some peripheral products that also use
Ethernet. HP's networking software is called NS and is similar to both TCP/IP and
DECnet in its architecture and implementation. Because HP added networking to its
core products much later in life than Digital, networking routines and utilities
have been implemented as extensions to its existing products.</P>
<P>HP's most significant contribution to LAN computing has been its use and endorsement
of the client/server computing architecture, which is discussed later in this chapter.</P>
<P><B>IBM&#160;&#160;</B>IBM's LAN strategy is primarily focused on its token-ring
network, compatible with the IEEE 802.5 specification. For networking services, IBM
has implemented those defined in its SNA. Specifically, in a mainframe environment,
token-ring networks can be used to tie workstations to controllers, and controllers
to communications processors (front ends). Token-ring networks provide high-speed
communication links for these traditionally distributed and hierarchical SNA connections.</P>
<P>Token-ring LANs can also connect AS/400 computers. With these implementations,
IBM offers a set of services to enable file sharing between systems (the Distributed
Data Manager) or the logging on to one system from another (Display Station Passthrough).</P>
<P>Again, because the token ring is part of the bigger SNA picture, standard SNA
transports such as LU 6.2 can run across a token ring LAN just like they run across
SDLC links.</P>
<P>In addition to its token ring implementations, IBM also offers a number of products
to provide connectivity to both Ethernet and IEEE 802.3 networks. These connectivity
products typically use IBM's implementation of TCP/IP for network services to non-IBM
computers.</P>
<P>IBM has further reinforced its commitment to establishing connections between
SNA and the LAN by purchasing Novell's NetWare for SAA (System Application Architecture)
gateway business. NetWare for SAA is a leading LAN-to-SNA gateway, and connects NetWare
LANs to IBM SNA applications. However, the deal now places IBM in the position of
having two competing products. IBM's Communications Manager/2 accomplishes the same
functions as the former Novell product. Both of these products in turn compete with
Microsoft's PC LAN-to-SNA integration product, SNA Server.</P>
<P><B>Sun Microsystems&#160;&#160;</B>Sun Microsystems provides Ethernet connections
with most of its equipment. Its networking services are layered on top of TCP/IP
and are focused on Sun's Network File System (NFS) product, which provides transparent
file access between systems participating on the same network. In fact, Sun's approach
to networking is an interesting hybrid between Digital's distributed processing techniques
and the shared file server technology now commonly used in PC LANs. To a certain
extent, Sun enjoys the best of both worlds.</P>
<P>Such functions as program-to-program communications, print services, and remote
logon are handled through services integrated into the operating system. These services
are based on the TCP/IP model.</P>
<P>For file services, however, Sun has introduced the concept of NFS servers to its
LANs. In this approach, one or more systems contains the physical disk and the logical
files used by other systems throughout the systems. As in PC networks, a user wanting
to access a file on a server must issue special network requests (such as a mount
command) to make the files available.</P>
<P>This use of NFS servers is quite different from Digital's approach of giving each
system its own local disk to share. If nothing else, Sun's networking approach puts
a new spin on traditional TCP/IP implementations.</P>
<P>And finally, note that standard implementations of TCP/IP are available for all
of these vendors systems, although in some cases TCP/IP must be obtained through
third-party sources. Unlike the manufacturer's proprietary networking services, TCP/IP
has no particular ties to any one manufacturer or operating system. See Chapter 9,
&quot;PC LAN Network Operating Systems,&quot; for TCP/IP details.
<H3><A NAME="Heading4"></A><FONT COLOR="#000077">PC LAN Implementations</FONT></H3>
<P>Because most of the companies that developed LAN software for PCs have no vested
interest in any particular LAN, their products can typically be configured for any
type of network. This brings tremendous flexibility to the desk of the haggard network
administrator who desperately wants only one network for the corporate equipment
connections.</P>
<P>While achieving this distance from the manufacturers offers benefits (in the form
of LAN independence), it also contributes complications because the network vendor
and the operating system are not closely related. Again, this situation sharply contrasts
with the implementation of networking services in the larger computers. In that environment,
networking functions can often be incorporated into the operating system itself,
offering a seamless, or nearly seamless, interface between the two.</P>
<P>In the land of the PCs, however, Microsoft dominates the market with its Windows
family of operating systems. The bulk of network services have been designed around
the Microsoft operating system structure. Windows 3.1 and previous releases are not
true operating sys-tems; rather, they are operating environments that run on top
of MS-DOS. Windows 95 and Windows NT, however, are true operating systems that incorporate
the functionality of MS-DOS within the overall operating system.</P>
<P>In order to understand how LAN services came to the PC environment, you need to
look at the original MS-DOS architecture. As shown in Figure 8.1, the MS-DOS operating
system uses two sets of low-level services for interface with the physical hardware.
One set of services is provided through a ROM-based BIOS (Basic Input/Output System)
program, and the other set is provided through a set of MS-DOS BIOS routines.</P>
<P><A HREF="javascript:if(confirm('http://docs.rinet.ru:8080/MuNet/ch08/08fig01.gif  \n\nThis file was not retrieved by Teleport Pro, because it was redirected to an invalid location.  You should report this problem to the site\'s webmaster.  \n\nDo you want to open it from the server?'))window.location='http://docs.rinet.ru:8080/MuNet/ch08/08fig01.gif'" tppabs="http://docs.rinet.ru:8080/MuNet/ch08/08fig01.gif"><B>FIG. 8.1</B></A> <I>Basic Input/Output System</I></P>
<P>The two sets of BIOS services are not independent of one another. Specifically,
the MS-DOS BIOS services provide generalized services that are requested by application
programs (such as read a record in a file or send print to a printer), while the
ROM BIOS provides extremely low-level services such as read a specific sector on
a disk or write this information to a machine-level I/O port.</P>
<P>In practice, many MS-DOS BIOS services actually end up calling the lower-level
ROM BIOS service. For example, when an application requests MS-DOS to read a record
from a file, the MS-DOS BIOS service translates the request to a specific sector
on the physical disk drive and then requests the ROM BIOS to read that sector. Similar
relationships are in place for printer and communications services.</P>
<P>This channeling of basic input/output services through a common point gives networking
software the opportunity to impose itself between the operating system and the hardware,
without forcing any changes in the application program. This insertion can be done
in several ways: by adding a device driver to the standard MS-DOS environments to
redirect services on to the network; by replacing the MS-DOS BIOS routines with network-oriented
routines compatible with the MS-DOS services; or by combinations of the two techniques.</P>
<P>When network services are put in place of or added to the MS-DOS BIOS services,
requests for disk information and printed output can then be routed from one machine
to another through the physical network (see Figure 8.2). Obviously, practical use
of this technique also involves specifying which machines are servers for which services.
But, when properly configured, a request to print a file on computer A can be routed
to print on computer B. Furthermore, the disk resources of computer C can also be
made available on computers A and B.</P>
<P><A HREF="javascript:if(confirm('http://docs.rinet.ru:8080/MuNet/ch08/08fig02.gif  \n\nThis file was not retrieved by Teleport Pro, because it was redirected to an invalid location.  You should report this problem to the site\'s webmaster.  \n\nDo you want to open it from the server?'))window.location='http://docs.rinet.ru:8080/MuNet/ch08/08fig02.gif'" tppabs="http://docs.rinet.ru:8080/MuNet/ch08/08fig02.gif"><B>FIG. 8.2</B></A> <I>Network Redirection</I></P>
<P>As mentioned earlier, disk sharing is a common function of most PC LANs. A network
disk to be shared is normally mounted on the local workstation and accessed as if
it were a normal, local drive. For example, a workstation might have two floppy drives,
a local hard disk, and two network drives. The operating system and the application
programs should not be able to distinguish the mounted network drives from local
drives. This makes for relatively smooth integration.</P>
<P>Integration notwithstanding, the speed of performing network disk access is an
issue. The issue is not the raw access speed of the physical disk drive (although
it certainly is a factor), but how quickly and efficiently an access can be serviced
over the network.</P>
<P>A PC can serve as both a workstation and as a network file server. However, PCs
were originally designed as single-task machines, so only one operation could occur
at a time. When the CPU is busy (doing a spreadsheet recalculation, for example),
a network request would have to wait to be serviced. Newer PC operating systems are
now based on multithreaded, multitask-ing architectures, and are able to accommodate
several tasks at once (given powerful enough hardware). Still, larger LANs require
a system to solely function as a file server. These file servers do not need to run
the PC operating system. Thus, special operating systems were developed for network
file servers to maximize performance and minimize the potential for disk errors.
<H3><A NAME="Heading5"></A><FONT COLOR="#000077">PC LAN Players</FONT></H3>
<P>Both Microsoft and IBM offer networking solutions to go along with their PC operating
systems. Other networking products are available from Novell, Banyan Systems, and
other companies, which provide high-performance networks that are compatible with
an operating system over which they have no control.</P>
<P>Thus far, Novell has gained the greatest degree of acceptance and use in the corporate
market. In a traditional Novell environment, one or more high performance computers
are dedicated as the file servers. In terms of network-level communications, Novell
has implemented its own protocols, named the <I>Internetwork Packet Exchange (IPX)</I>
and the <I>Sequenced Packet Exchange (SPX)</I>, that run on top of IPX. Novell's
software offering is referred to as <I>NetWare</I>. Several different implementations
are available to accommodate different networking scenarios. Because the file server
is central to the network, it must offer high performance.</P>
<P>The greatest changes in the PC networking arena are driven by the need to integrate
PC information with minicomputer/mainframe information. As more and more devices
reside on the same physical LAN, it becomes more difficult to overlook their inability
to communicate with one another. Some of the most widely-used PC LAN operating systems
include:

<UL>
	<LI><I>Banyan VINES.</I> Banyan Systems provides many of the same functions as NetWare,
	but Banyan's VINES (VIrtual NEtwork Software) products run with existing network
	standards. Thus, unlike Novell, which implements its own transport-layer protocol,
	VINES can run with TCP/IP, SNA, and other networking protocols. VINES is similar
	to Novell's NetWare in its use of servers, but Banyan claims that it is more unstructured
	and open, and therefore easier to use.<BR>
	<BR>
	
	<LI><I>Novell NetWare.</I> For many years, Novell NetWare was the dominant file and
	print server in the PC LAN arena. NetWare runs in a designated server system and
	communicates with a variety of client systems (PC, Mac, UNIX) using either the IPX
	or TCP/IP protocol suite. Novell NetWare is the seasoned veteran of the industry,
	and has established a strong, loyal following in the corporate market. One of the
	key technological advantages of the current 4.x line of NetWare products is <I>NetWare
	Directory Services (NDS)</I>. NDS is a global directory service designed to manage
	LAN-based resources in large, enterprise-class environments. Although Novell went
	through a series of corporate twists and turns in the mid-1990s, the company has
	since refocused itself on its core NetWare technology.<BR>
	<BR>
	
	<LI><I>Windows NT. </I>For years, Microsoft stayed out of the networking business.
	However, when Microsoft acquired 3Com's networking PC LAN technology, it began to
	integrate networking services into its operating system products. The first attempt
	at this integration was Windows for Workgroups, which was a difficult product because
	of the underlying DOS component. When Microsoft designed Windows 95 and Windows NT,
	however, it seized the opportunity to integrate core networking services right into
	the operating system. Microsoft took two tracks here, pushing peer-to-peer (workgroup)
	resource sharing via Windows 95 and Windows NT Workstation, and enterprise-scale
	file, print, and application serving via Windows NT Server.
</UL>

<P>Refer to Chapter 9, &quot;PC LAN Network Operating Systems,&quot; for more information