A topology is the representation of the network's
layout. There are a few basic types including: star, ring, star
wired and linear bus. Of these, the most commonly deployed topology
today is the star wired.
Star:
In a star topology, there is a central device to
which all nodes are connected. The central device polls each connected
node and allows that node to communicate its information for the
destination node to the central computer which stores that data
until it communicates to the destination node and can pass the
data on. The most common type of star topology is the mainframe
and terminal type systems. These have been deployed all over the
world for many years, and there are still many of them in service
today.
Ring:
A ring configuration has all nodes connected to each
other in a series; in to an out, and the two end points also connecting
each other. Unfortunately, this design makes for a very difficult
cabling plant, so it was never really implemented on a large scale.
There were a few proprietary systems marketed this way. The better
design called for a star wired ring.
Star wired ring:
A star wired ring affords the same function of the
ring communication, while allowing a much better designed and
implemented cable plant for the network. The basic function of
a ring is that every node, whether PC or server, gets an equal
time to communicate on the network. The design of the ring also
provides some self-healing properties in the case of the IBM Token
Ring system. Token Ring is the most widely deployed star wired
ring topology.
Linear bus:
Many folks who have been around the networking industry
will be familiar with this topology if they have worked with coax
based Ethernet. The linear bus has two finite end points, meaning
the ends don't connect together (as in the ring topology). Because
of its design, in order to connect each node into the network,
you have to daisy chain the cable from each node to the next.
The actual connection is only broken at the NIC, and each cable
end is connected to a "T" connector, which then connects
to the NIC. Although this topology was the most prominently deployed,
over the years network support personnel discovered that its most
major headache was when someone disconnected the cables at the
T connector, instead of disconnecting the T from the NIC.
Star wired:
Since the mid to late 1980's, the star wired topology
has been the most popular deployed technology. Since the star
wired topology is configured in a spoke or star of spokes configuration,
Ethernet and token ring networks can use the same cable plant.
IBM first used the star wired configuration for its token ring
network technology during the mid 1980's. In late 1989, 10BaseT
(twisted pair Ethernet) was standardized. This now allowed network
designers the capability of forming structured cabling systems,
and then deciding which network technology to run over it. Today,
almost every network technology that comes out runs over a star
wired topology configuration.
10Base2
10Base5
10BaseT
10BaseFL
100BaseTX
1000BaseT
Token Ring
FDDI
ATM
ARCnet
LocalTalk
IBM 3270 (mainframe)
IBM 5250 (AS/400)
Gateway Comm G-Net
ProNET10
ProNET80
AT&T StarLAN
Corvus Omninet
Novell S-Net
IBM PC Network
Glossary:
10Base2 10Mbs Ethernet running on RG-58 coax at a max distance
of 185M per segment
10Base5 10Mbs Ethernet running on thicknet coax at a max distance
of 500M per segment
10BaseFL 10Mbs Ethernet running on fiber optic 62.5um cabling
at a max distance of 2KM per segment
10BaseT 10Mbs Ethernet running on UTP/STP at a max distance of
100M per segment
100BaseTX 100Mbs Ethernet running on UTP at a max distance of
100M per segment
100BaseF 100Mbs Ethernet running on fiber optic 62.5um cabling
at a max distance of 2KM per segment
Ethernet Baseband network specification as defined by the IEEE
802.3 series standards
FDDI Fiber Distributed Data Interface
NIC Network Interface Card
STP Shielded Twisted Pair
Token Ring Token passing LAN technology developed by IBM
UTP Unshielded Twisted Pair
In the next article I'll discuss network protocols.
Copyright © 1997 Jeffrey L. Carrell. All Rights Reserved.
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