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<TITLE>Managing Multivendor Networks -- Ch 7 -- LANs and WANs</TITLE>
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<FONT COLOR="#000077">Managing Multivendor Networks</FONT></H1>
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<H1><FONT COLOR="#000077">- 7 -<BR>
LANs and WANs</FONT></H1>
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<UL>
<LI><A HREF="#Heading1">The Many Faces of Networking</A>
<LI><A HREF="#Heading2">Local Area Networks</A>
<UL>
<LI><A HREF="#Heading3">LAN Topologies</A>
<LI><A HREF="#Heading4">LAN Protocols</A>
<LI><A HREF="#Heading5">LAN Implementations</A>
</UL>
<LI><A HREF="#Heading6">LAN Implementation Standards</A>
<UL>
<LI><A HREF="#Heading7">IEEE 802.2</A>
<LI><A HREF="#Heading8">IEEE 802.3</A>
<LI><A HREF="#Heading9">IEEE 802.4</A>
<LI><A HREF="#Heading10">IEEE 802.5</A>
<LI><A HREF="#Heading11">802.3 Versus Ethernet</A>
</UL>
<LI><A HREF="#Heading12">Wide Area Networks</A>
<UL>
<LI><A HREF="#Heading13">Point-to-Point Links</A>
<LI><A HREF="#Heading14">ISDN</A>
<LI><A HREF="#Heading15">Asymmetric Digital Subscriber Line (ADSL)</A>
<LI><A HREF="#Heading16">X.25</A>
<LI><A HREF="#Heading17">LAN Switches</A>
<LI><A HREF="#Heading18">Tools of the Trade</A>
</UL>
</UL>
<P>
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<H2><A NAME="Heading1"></A><FONT COLOR="#000077">The Many Faces of Networking</FONT></H2>
<P>efore the great LAN explosion, networking, for the most part, addressed the connection
of distributed devices to a central location. Although some pioneering companies,
such as Digital Equipment, offered LAN technology in these early days, the bulk of
the market was accustomed to a centralized computing environment.</P>
<P>In this centralized approach, the primary concern was to find the most practical
and economical way to connect terminals, printers, and other data collection/reception
devices to the primary location. When connectivity was required between systems,
the link was approached typically as a special-case, point-to-point operation, rather
than part of a peer-oriented, distributed processing network. However, as requests
mounted to link computer systems over wide areas, multiple, point-to-point operations
became very cost ineffective, and the door opened to such alternative wide-area connections
as X.25 and ISDN. Wide-area technologies have continued to evolve, and now include
Frame Relay, Asynchronous Transfer Mode (ATM), and Switched Multimegabit Data Service
(SMDS).</P>
<P>All things considered, this system-to-system connectivity hardly concerned the
end user--after all, this was the job of the communications analyst. But when the
LAN wave finally reached the PC on the end user's desk, that user suddenly encountered
and became concerned about connectivity issues. At first it was just local (LAN)
connectivity and terminal emulation. Then, as networks grew and costs increased,
products such as gateways, bridges and routers snaked their way into the LAN. Today,
the end user has an unprecedented amount of power at his or her disposal. Consolidated,
enterprise-wide data is no longer in the hands of a few technical elite; off-the-shelf
desktop software now gives the end user the ability to access data anywhere in the
enterprise--whether it is on the PC, server, minicomputer, or mainframe.</P>
<P>This progression of connectivity changed the role of the LAN. Whereas the LAN
began as a local computing environment (usually an island unto itself) it grew into
an area of computing, normally linked to other computing areas. The fact that one
computing area might be a LAN, another a mainframe, and yet another a combined midrange
computer and PC LAN has become almost irrelevant.</P>
<P>From this high-level perspective, the world of distributed networks can be broken
down into two large categories: local-area links and wide-area links. A <I>local
area network (LAN)</I> typically is limited to one geographic area and allows individual
workstations to access data or applications on a server. In smaller LANs, a peer-to-peer
arrangement can be deployed to allow each station to function as both server and
client. A<I> wide area network (WAN),</I> on the other hand, typically covers a large
geographic area, and often links together multiple LANs. Within each category, however,
are a wide variety of implementations and strategies.</P>
<P>LANs often play a pivotal role in modern networks. This chapter will address the
following LAN issues:
<UL>
<LI><I>Topology.</I> LANs can be implemented in a variety of topologies (or structures),
such as star, bus, ring, hub, and so forth.<BR>
<BR>
<LI><I>Protocols.</I> LANs can run token-passing or collision sensing protocols.<BR>
<BR>
<LI><I>LAN implementations. </I>This section will examine IEEE standards and how
they compare to each other (and to Ethernet).
</UL>
<P>WANs can be used in both centralized and distributed processing environments to
tie all of the necessary devices together. This chapter will discuss the following
WAN issues:
<UL>
<LI><I>Point-to-point links.</I> In the most basic of cases, creating a WAN might
simply involve tying together two LANs or two systems. These connections are most
often implemented using standard telephone links.<BR>
<BR>
<LI><I>Integrated Services Data Network (ISDN).</I> This service is offered by the
telephone industry as a modern, high-speed, multi-point connectivity solution.<BR>
<BR>
<LI><I>X.25.</I> This chapter will examine X.25 as a wide-area, packet-switching
network. The use of such networks has become a low-cost solution for low-volume networking
on a worldwide basis.<BR>
<BR>
<LI><I>Asynchronous Transfer Mode (ATM).</I> ATM is a high-speed protocol that offers
every client on the network the capability to send data at speeds of up to 155 Mbps,
or nearly 15 times the speed of a standard Ethernet LAN. ATM is especially useful
for those applications with high bandwidth requirements, such as videoconferencing.<BR>
<BR>
<LI><I>Frame Relay.</I> Frame Relay can carry multiple types of traffic, including
voice and Systems Network Architecture (SNA). It is extremely fast, and less costly
than a dedicated line solution.<BR>
<BR>
<LI><I>Switched Multimegabit Data Service (SMDS).</I> SMDS is a connectionless service
and is simpler to implement than Frame Relay or ATM. SMDS is used to establish any-to-any
connectivity and is a highly scalable solution. Technologies such as frame relay
require permanent virtual circuits (PVCs) to be established between each and every
location; SMDS, on the other hand, takes a much simpler approach. Each workstation
on the network is given an address, and any site can communicate with any other site.
The administrator does not have to set up individual connections ahead of time.<BR>
<BR>
<LI><I>Fiber Distributed Data Interface (FDDI).</I> This token-passing technology
uses optical fiber cabling, and can transmit data at 100 Mbps. Because of its superior
speed, FDDI is especially useful for sending large files such as graphics or digital
video. It is a useful method of adding bandwidth without having to make a costly,
long-term commitment.<BR>
<BR>
<LI>FDDI switching can also have a big impact on a backbone network. Digital Equipment
has led the way in FDDI switching with its GigaSwitch product; other vendors are
also now starting to offer FDDI switching products. FDDI switching, like other types
of LAN switching architectures, can significantly increase bandwidth and extend the
lifetime of the network.<BR>
<BR>
<LI><I>Fibre Channel.</I> Fibre Channel is a high-speed architecture for connecting
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