The 3Com
Introduction
to Networking
3
Introduction to Networking:
Get Connected
The Advantages of Networking Your
Business
1. What Is a Network?
2. LANs and WANs
Local Area Network (LAN)
Wide Area Network (WAN)
The Internet
Summary
3. The Components of a LAN/WAN
Hardware
Software
Summary
4. How LANs Work
What are “standards”?
5. Networking Technologies Explained
Ethernet
Fast Ethernet
The Advantages of 10/100 Network
Solutions
Gigabit Ethernet
ATM
Shared vs. Switched Networking:
Which Is Right for You?
Ring Technologies
How LANs Handle the Demands of
Today’s Emerging Applications
6. Planning Your Network
Summary
7. How to Grow Your Network
Scenario 1: A Small Business Network
Scenario 2: Relieving Congestion
Scenario 3: Accommodating Growth and
Migrating to Higher Performance
Scenario 4: Integrating mobile workers
Scenario 5: Integrating the remote office
Glossary
Table of Contents
5
Networking is a powerful strategy for
getting the most out of your information
resources. When you network your PC and
peripherals together, you enhance
communication between employees and
with the world outside the business—from
customers to suppliers. A network makes
users more productive and saves valuable
time as they share files, programs, and
peripherals via the network. It also helps
avoid duplication of costly peripherals
such as printers, backup data storage
devices, and CD-ROM drives.
3Com created this guide to give you a
clear understanding of networking basics
and to help you build a network that
meets your organization’s changing needs.
Today, with information technology
evolving at a mind-boggling pace, a little
networking know-how can ensure that you
get the highest return for your investment
and provide you with a strong foundation
for seizing new business opportunities as
they come your way.
The Advantages of Networking
Your Business
A network allows pcs to share and
exchange information (files and programs)
and hardware (printers, servers, image
scanners, and more). Over short
distances, for instance, between the floors
of a single building or among several
adjacent buildings, you create a local area
network (LAN). Between geographically
dispersed sites, you create a wide area
network (WAN).
LANs and WANs are private networks.
They interconnect people inside your
organization. Outside the realm of these
private networks is a vast public network
called the Internet. The Internet links pcs
at universities, research centres,
government agencies, and companies
across the globe. Gaining access to the
Internet allows you to draw on an
enormous store of information, exchange
e-mail and files with other Internet users
anywhere in the world, and use an
expanding range of electronic business
services.
INTRODUCTION
Introduction to Networking: Get Connected
Ultimately, making the best use of LANs,
WANs, and the Internet is about making
better use of your business resources,
enhancing productivity and efficiency,
reducing costs, and gaining a competitive
advantage. But with technology changing
so rapidly, you need to make your entire
networking investment count. That’s why it
pays to connect with 3Com, a global
leader in networking. 3Com offers the
industry’s most complete range of
solutions, covering everything from the
home office to the largest multinational
enterprise. 3Com will help you make the
right choices for your business and supply
practical, powerful solutions for all your
networking needs.
6
INTRODUCTION
7
A network is a series of connected PCs and
other computing devices, such as printers,
fax machines, and modems. Networking
lets individuals in an organization
communicate and share resources,
allowing them access to data stored in
individual PCs or at remote offices, and
linking them to external suppliers. Using
routers, you can enable networks at
distant sites to talk to each other and get
people at those sites working more
efficiently and productively together.
Using modems, you can dial into the
network from virtually anywhere over
ordinary phone lines. Networks can be
designed to suit organizations of all sizes,
from single sites with as few as two PCs to
the largest international corporations
linking thousands of workstations.
The first principle of good network design
is to plan ahead. Because demands on the
network are certain to rise, the network
must meet present needs and
accommodate future growth, both in the
number of users and devices it
interconnects and the amount of data it
can handle.
There are two basic types of small
business networks: peer-to-peer and
client/server. A peer-to-peer network is
generally the easiest to install and can
accommodate up to about five PCs.
Small office network (peer-to-peer)
WHAT IS A NETWORK?
What Is a Network?
All users share 10 Mbps Ethernet bandwidth
Teleworker/Dial-up usere.g. Sales Representative
†Notebook PC with modem PC card
TelephoneLine
Printer
Printer
*3Com’s OfficeConnect product family and Remote Access.† 3Com’s Etherlink III LAN modem PC card
*
In a peer-to-peer network, the PCs are
connected to a central point, usually a
device called a hub. All PCs on the
network can communicate with each
other.
If you have approximately six or more PCs
to connect and you are interested in
sharing larger items such as databases,
then you should consider a client/server
network. In a client/server network, all
shared applications and files are stored on
one central computer known as the server.
Network users can store their own files on
their own pcs, then use the server to
access shared files and peripherals, such
as printers, fax machines, and modems.
Small office network (client - server)
8
WHAT IS A NETWORK?
3Com OfficeConnect Hub
PC
PC
PC
Server
Printer
9
A LAN, or local area network, links PCs and
printers together, usually within a single
building or site. In contrast, a WAN, or
wide area network, links a number of LANs
connected across a wide geographical
area.
Local Area Network (LAN)
LANs are the most basic form of
networking and involve linking a series of
PCs to each other or to a more powerful
PC, which acts as the network server. (See
diagram on page 8.) All PCs on the LAN
can then share specialized applications
stored on the network server and share a
printer, fax, or other peripherals. Each PC
on the LAN is known as a workstation or
node on the network.
LANs enable individuals to communicate
quickly and easily with colleagues. Here
are some tasks you can accomplish with a
LAN:
• Share documents.
• Streamline workflow by revising and
annotating documents without having
to attend time-consuming meetings or
leave the work area.
• Save and archive work on a server
instead of using valuable PC hard
drive memory on individual PCs.
• Access applications on the server
with ease.
LANs also make it easy for organizations
to share expensive resources such as
printers, CD-ROM drives, hard drives, and
applications such as word processing or
database software.
LANs AND WANs
LANs and WANs
Wide Area Network (WAN)
WANs offer the same business advantages
as LANs but over a wider, multisite area. A
WAN will use either a public switched
telephone network (PSTN) with a modem
or a high-speed, digital ISDN (Integrated
Services Digital Network) line. ISDN lines
are frequently used to move large files
such as graphics or video images.
By incorporating WAN functionality into a
basic LAN, such as a modem or Remote
Access Server, businesses can start to
take advantage of external technology
applications such as:
• Send and receive messages via
email (electronic mail).
• Access the Internet.
• Increase employee productivity
and flexibility by offering benefits
such as working from home
(telecommunicating or teleworking).
If the WAN link is used frequently, you may
also consider a leased line, which is a
dedicated service that is always on, 24
hours a day, 365 days a year. A leased line
can provide analog or digital service
(digital lines are subject to fewer errors
and generally offer higher performance
than analog lines). For a leased line, you
pay a fixed amount and no variable usage
charges, while modem and ISDN services
involve usage charges.
Whichever service you choose, connecting
distant sites into a single WAN allows all
users to take full advantage of centralized
data and applications—while helping
extend a uniform high standard of
customer service across your organization.
10
LANs AND WANs
11
LANs AND WANs
The Internet
The Internet is an enormous public WAN—
and a conduit between network users and
a worldwide store of data, images, and
sound. Growing at an annual pace of
about 200% each year, the Internet is
playing an increasingly important role for
businesses.
The primary functions of the Internet to
date have been e-mail and information
exchange between special interest groups
and research. As networks become more
powerful and more businesses and homes
become connected, the Internet will serve
as a contact point between businesses
and their potential customers and
suppliers. Even now, the Internet can
support emerging voice and video
applications, such as distance learning
and telemedicine, bringing educational
opportunities and healthcare into any
home or business with an Internet link.
As a public network, the Internet lacks the
security protection that is built into most
private LANs and WANs. As such, making
sensitive business information available
over the Internet’s World Wide Web
requires special care.
Summary
• Sharing technology resources reduces
costs and increases productivity.
• Network planning should reflect the
needs of the business, rather than
the requirements of the technology.
• LANs link PCs usually at a single site.
• WANs connect remote offices to
central resources.
• The Internet is a WAN that presents
numerous new opportunities.
13
THE COMPONENTS OF A LAN/WAN
The Components of a LAN/WAN
The basic components and technologies
involved in a LAN or WAN architecture can
include the following:
Hardware
• Cables
• Servers
• Network interface cards (NICs)
• Hubs
• Switches
• Routers (WAN)
• Remote access servers (WAN)
• Modems (WAN)
Software
• Network operating system
• Network management software
Structured Wiring Solutions As your network grows, every employee
in your facility will require a LAN
connection. Because of this need,
coupled with the frequent movement of
employees from one location to another,
a structured wiring solution makes the
most sense for new networks. Structured
wiring enables a PC network to reach
each user’s desk, similar to phone and
power connections.
Older LANs used a bus architecture, with
all networked PCs connected in a string
on a single length of coaxial cable. In the
past, the largest percentage of costs
associated with operating a LAN arose
from adding new users or relocating users
when they changed jobs or locations—
because the bus configuration did not
accommodate changes very easily.
Structured wiring uses a star configu-
ration, with a dedicated piece of
inexpensive cable extending from each
user’s computer to a central hub or, in
demanding networks, a switch. Moving or
adding an employee to the network is
easy and less costly. The wiring is already
installed at the employee’s new work
area, and the employee’s network
connection can be moved to the
appropriate network segment simply by
plugging the cable end into the
appropriate hub or switch.
Hardware
Cables
Cables carry data in packets from one
networked device to another. There are
several cable types, each with its own
distinct advantages.
Twisted Pair (TP)
This comes in shielded (STP) and
unshielded (UTP) forms and consists of
twisted pairs of copper wires. The
unshielded form has become the most
popular due to its low cost, flexibility, and
ease of installation. The only downside is
possible vulnerability to electrical
interference and line noise. Twisted pair
cables come in different categories
(Category 3, 4, and 5); the greater the
number, the greater the speed the cable is
able to support.
Thin and Thick Coaxial (or Coax)
This type of cable is similar to standard TV
cable line. Because coax cable is harder to
work with, new installations almost always
use twisted pair or fiber optic cable.
Fiber Optic
Fiber optic cable supports 10, 100, or
1000 Mbps packet transmission. Data is
transmitted as light pulses through fiber
optic cable. Although more expensive and
difficult to install than UTP, this cable is a
popular choice for central network
backbones, because it provides total
protection against electrical interference
and accommodates extremely long
transmission distances. Best of all, as
fiber optic technology advances, this cable
is becoming more affordable.
14
THE COMPONENTS OF A LAN/WAN
ETHERNETCABLING
TOKEN RING CABLING
FDDI
ATM
See page 46 for information on cable distance specifications*Can be used to run Gigabit Ethernet traffic.
*
*
Twisted Pair
Fiber Optic
Coaxial
Coaxial/Thinnet
Fiber Optic
Twisted Pair
Twisted Pair
Fiber Optic
Fiber Optic
Coaxial
Servers
In a client/server network, a server is a PC
with a large hard disk drive where
applications and files can be saved and
accessed by other PCs on the network.
The server also controls access to
peripherals such as printers and is host to
the Network Operating System (See
page 21).
Network Interface Cards
Network interface cards (NICs) are
installed in desktop PCs and notebooks
and are used to listen and talk to other
devices on the LAN. A range of NICs is
available for different PC types and for
different performance needs.
Once considered merely a way to get data
into and out of networked PCs, today’s
NICs play an active role in enhancing
performance, setting traffic priorities for
critical traffic, and monitoring traffic
patterns. They also support functions such
as remote power-up from a central
workstation or remote reconfiguration,
which save significant time and effort in
growing networks.
15
THE COMPONENTS OF A LAN/WAN
10BASE-T 100BASE-TX 100BASE-T4 100BASE-FX 1000BASE-FX(Ethernet) (Fast Ethernet) (Fast Ethernet) (Fast Ethernet) (Gigabit Ethernet)
Number of pairs required 2 2 4 N/A N/A
Cable category Category 3/4/5 Category 5 Category 3/4/5 Fiber Fiber
Which Cable Should You Choose?
The following table shows which cable is
needed for various LAN technologies,
10 Mbps Ethernet, 100 Mbps Fast Ethernet
and 1000 Mbps Gigabit Ethernet. Generally,
all new installations use Category 5 UTP for
workgroup and desktop connections.
Hubs
In a structured wiring configuration, all
networked PCs communicate via a hub (or
switch). All PCs connected to the hub
communicate as a single LAN segment.
This makes it easy to provide network
connections to a large number of people,
even when they move frequently. At their
most basic, hubs interconnect PCs users in
a single network segment. They come in a
variety of shapes and sizes, connecting a
few users in a small business or hundreds
of users in a large campus. They also vary
in functionality—from simple wiring
concentrators to large devices that act as
the heart of the network, support network
management, and integrate a range of
standards (Ethernet, Fast Ethernet, Gigabit
Ethernet, FDDI, and more). There are even
some hubs that play a role in network
security.
The entry-level (basic) hub is a simple,
stand-alone device that provides a cost-
effective starting point for many organi-
zations.
3Com’s OfficeConnect 8-port hub is ideal for
small businesses wanting to create a LAN.
This would also be referred to as an
entry-level or basic hub.
16
THE COMPONENTS OF A LAN/WAN
Power adaptorsocket
Coaxial port for connection to network backbone
Twisted pair ports for workstation connection to the network
Hub 8/TPC3C16701
ALERT
!PWR 1
1% 2% 3% 6% 12% 25% 50% 80%
Network UtilizationPort Status
2 3 4 5 6 7 8 COAXgreen = link OK off = link fail yellow = partition
COLL
Network utilization LEDs indicate how much your network is being usedPort status LEDs
Alert LED
Front view
Rear view
Stackable hubs let you start small and
grow your network at your own pace.
Stackable hubs are connected by flexible
expansion cables and, once stacked
together, function as one hub. Because of
their low price per port, stackable hubs
have become popular.
SuperStack II Dual Speed Hub 500 (24 port)
SuperStack II hubs from 3Com enable you to
create an entire network system from stackable
solutions, leveraging the simplicity and price
performance of a stackable architecture.
Chassis hubs consist of a chassis
(cabinet) with expansion slots for plug-in
hub modules and a hub backplane, which
interconnects the hub modules. This type
of hub is typically deployed in larger
organizations where the concentration of
users is higher.
3Com offers a comprehensive range of
CoreBuilder chassis solutions, with high-density
hub modules, for scaling network capacity to
meet your growing needs.
17
THE COMPONENTS OF A LAN/WAN
SuperStack II Dual Speed Hub/PS Hub Cascade Converter
PS Hub 40/50
PS Hub 40/50
Dual Speed Hub 500
Dual Speed Hub 500
18
THE COMPONENTS OF A LAN/WAN
How Do Hubs Work?
In a hub, all users share the same
bandwidth. A packet received on one of
the hub’s ports is broadcast to all other
ports, which examine the packet to
determine if it is intended for them. With a
small number of users, this system works
well. As you add more users, competition
for bandwidth can start to slow down
traffic on the LAN.
Traditional hubs support only a single
network segment, forcing all attached
users to share the same bandwidth. Port
switching or segmentable hubs, like the
SuperStack II PS Hub family, alleviate this
problem, allowing you to assign users to
any of the hub’s four internal segments,
each with 10 Mbps of bandwidth. This
provides flexible allocation of bandwidth
among users and enables you to balance
the network load.
Dual-speed hubs have a powerful
advantage for building today’s shared
network segments. They accommodate
existing 10 Mbps Ethernet links and
newer 100 Mbps Fast Ethernet links,
automatically sensing the speed of the
connection and requiring no manual re-
configuration. This makes it easy to
upgrade your connections from Ethernet
to Fast Ethernet when you need to handle
new, bandwidth-hungry applications and
boost performance in crowded network
segments.
Hubs also provide a central point for
cabling, making reconfiguration, fault
finding, and centralized management
more convenient.
Switches
A switch provides dedicated bandwidth to
every device—server, PC, or hub—
connected to one of its ports. This
improves performance and shortens
network response times by reducing the
number of users per segment. Like dual-
speed hubs, newer switches are often
designed to support dual-speed
connections at both 10 Mbps or
100 Mbps, depending on the maximum
speed of the connected device. When they
are equipped with auto sensing, they can
adjust automatically to the optimum
speed without manual reconfiguration,
providing a simple means of upgrading a
network at a gradual pace.
How Do Switches Work?
Unlike hubs, which broadcast all packets
received on any port to all other ports,
switches send packets only to the
intended device. They do this by first
learning the MAC (Media Access Control)
address for each attached device—much
like a letter carrier knows where to deliver
a package based on the mailing address.
This results in reduced traffic and higher
total throughput—critical factors in light
of the rising bandwidth demands of
today’s sophisticated business
applications.
Switching is gaining popularity as a
simple, low-cost technique for increasing
available bandwidth on a network. And
today’s switches are adding support for
features such as traffic prioritization (a key
factor when you wish to send voice or
video over the network), network
management, and multicast control.
19
THE COMPONENTS OF A LAN/WAN
Routers
Routers can perform multiple functions:
1 Connect LANs to wide area networks
(WANs)
2 Connect Multiple LANs together
Routers are protocol dependant (i.e.
TCP/IP, IPX, Appletalk) and work at layer 3
of the 7 Layer OSI model (page 26), unlike
bridges and switches that work at layer 2.
The performance of a router in terms of
the amount of data it can pass per second
is normally proporiante to it’s cost. As a
router is protocol dependant it can make
decisions on the best path to forward data
based on line cost, speed etc. In addition
Routers are very effective at controlling
broadcast traffic ensuring the data is only
sent to the ports that need it.
Layer 3 Switches
Are so called because they work at the 3rd
layer of the 7 layer model, like routers
they are protocol dependent, however
they work much faster and have a lower
price. Layer 3 Switches are normally
designed to connect multiple LANs
together and do not normally support any
WAN connections
Remote Access Servers
If you need to provide network access to
remote users dialing in from home or from
the road, you can install a remote access
server. This device allows multiple users to
dial in using a single phone number and
connect with central network resources as
though they were in the home office. Also,
remote access servers can provide security
to protect against unauthorized users.
Routers move data by finding the best path
from the sender to the receiver. Here, LAN 1
transmits through LAN 3 to LAN 5; however,
data can also pass through LAN 4 if the
connection between LAN 1 and LAN 3 fails.
20
THE COMPONENTS OF A LAN/WAN
LAN 3
† Centralized Chassis Router
LAN 4
LAN 1
LAN 2
* 3Com’s SuperStack II NETBuilder Router† 3Com’s NETBuilder II Router
* Boundary Router
* Boundary Router
* Boundary Router
* Boundary Router
LAN 5
Modems
Modems allow PC users to exchange
information and connect to the Internet
over ordinary phone lines. The name
comes from their modulate/demodulate
function. Modems modulate digital signals
from pcs into analog signals that pass
over the public telephone network, and
then demodulate those signals back into
digital form when they arrive on the
receiving end.
Unlike routers, which provide shared
access to the outside world, modems
support only one connection at a time.
They incur usage charges just like a
phone—including long distance, when
applicable. Modems can be shared if
installed in a central network server.
External and internal formats are available
for desktop PCs while PC Card format
modems are the usual choice for notebook
PCs. Today’s fastest modems are rated at
56 Kbps.
Software
Network Operating Systems
The network operating system (NOS) is
software on each network PC that controls
and coordinates access to network
resources. The NOS is responsible for
routing messages through the network,
resolving contention between devices on
the network, and working with the PC’s
operating system, for example, Windows
95™, Windows NT™, UNIX™, Macintosh™, or
OS/2™.
The NOS software enables applications
and files residing on one workstation to be
shared, transferred, or altered from
another workstation. The major portion of
the NOS software will reside on the
network server, although smaller portions
are located on all workstations on the
network.
The Brains of Your Network
Network operating systems recognize all
devices on the network and prioritize
access to shared peripherals when a
number of workstations are trying to use
them at once. The NOS acts as a traffic
controller and provides directory services,
security checking, and network
management. Popular NOS software
includes Windows NT Server™, Novell
NetWare™, and Banyan VINES™.
21
THE COMPONENTS OF A LAN/WAN
Network Management Software
Network management software plays a
vital and increasingly important part in the
monitoring, control, and security of the
network. It also provides a proactive
solution so you can avoid potential
network bottlenecks and downtime,
thereby lowering your network’s total cost
of ownership. Research suggests that the
largest single cost of running a network is
not hardware or even WAN line charges,
but rather management and maintenance
(from configuration duties to downtime);
hence, a strong network management
software package is essential for most
medium and larger networks.
From a management workstation—or over
the World Wide Web—network managers
can monitor traffic patterns, spot trends
that can lead to overcrowding on a
segment, trace and solve problems, and
reconfigure the network for the best
possible performance. As networks grow
larger and more complex, monitoring tools
such as RMON and RMON2 help network
managers stay in control. These
monitoring tools report traffic details from
the edge of the network and highlight
potential trouble in time for the network
manager to take preventive action.
Network management software also
secures data being exchanged over the
network. From the management station,
network administrators can set
passwords, determine which users gain
access to which resources, and log
attempted intrusions by unauthorized
users.
The ideal network management software
is sophisticated to track events
throughout your network, yet easy to
use—with graphical representation of
network elements and performance
trends. The software you choose should
also scale easily to support significant
growth in traffic and in the user
population.
22
THE COMPONENTS OF A LAN/WAN
The Benefits of RMON/RMON2
Remote Monitoring (RMON) enables the
network management software to filter the
information reported to the management
workstation. This prevents the
management workstation from becoming
clogged with routine traffic reporting and
reserves reports for when problems are
about to occur. An RMON probe can
respond proactively to network trouble
without user intervention. In addition, the
network manager can define the type of
information the RMON probe should filter
and analyze. Most 3Com network
solutions provide standard RMON support.
SNMP: Making Network
Management Simple
The Simple Network Management Protocol
(SNMP) provides a series of protocols for
the transfer of management information
between network devices. Although it was
initially designed for networks running the
TCP/IP protocol suite, SNMP has become
so successful that it is now used with all
types of networks. SNMP benefits
everyone because it is nonproprietary,
easy and inexpensive to use, and requires
a minimum of memory and processing
power. Look for network management
software that is SNMP compatible.
23
THE COMPONENTS OF A LAN/WAN
SmartAgent
SmartAgent
SmartAgent SmartAgent
TM®
• Transcend Network Control Services, Transcend Enterprise Manager, and
Transcend WorkGroup Manager deliver precise device
management control and troubleshooting
• Powerful Transcend Traffix Manager interprets RMON2 protocol and
application statistics to provide complete views
of enterprise network traffic
• InfoVista software provides a powerful service
level management tool
• Open platforms support for Unix and Windows
- HP OpenView
- IBM NetView
- Sun Solstice Domain Manager
• High-speed, dedicated RMON/RMON2 Enterprise
Monitors connected to local and remote
network segments
• Economical SmartAgent intelligent management
agents embedded in 3Com network systems
• Innovative dRMON Edge Monitor software that
leverages SmartAgent software in 3Com NICs
3Com’s Transcend Network
Management Architecture
encompasses a full range
of network management
applications and data
collection methods,
and supports open
platforms
Summary
• Different cable types support different
speeds and networking technologies.
• A network interface card (NIC) enables
a PC to communicate on the network.
• Servers are pcs that hold
applications and files for sharing by
network users.
• Hubs/switches act as a central point
for distribution and management of
data on a network.
• Switches increase bandwidth for users
and workgroups on the network and
filter data between ports.
• Routers determine the best path for
moving data from sender to receiver,
and can find alternate paths if one
link fails. They also provide a
connectivity for remote sites access
and the Internet.
• Remote access servers allow multiple
users to dial into a network
simultaneously using a single phone
number to connect as though they
were together in the same office.
• Modems allow PC users to
exchange information and connect to
the Internet over ordinary phone lines.
• Based within the network server,
network operating systems (NOS)
control access to the network and
allow files and programs to be shared.
• Network management software plays
a vital role in the management,
monitoring, and control of the network,
with RMON easing the management
burden by only reporting when
problems occur.
• SNMP (Simple Network Management
Protocol) is a nonproprietary standard
that helps minimize the processing
power and memory required by a
network management station.
24
THE COMPONENTS OF A LAN/WAN
25
HOW LANs WORK
When two PCs want to communicate, they
must follow the same rules. These rules
are contained in software residing either
in the PCs memory or on the NIC inside
the PC.
These rules determine how networked PCs
can signal the information to be sent and
received and the order it occurs. The
software is responsible for packaging the
data into appropriately sized packets.
These consist of information and include
headers, which indicate the size of the
packet, where it started, and where it is
going.
Along the way, devices on the network
examine the header to determine where
the packets are going and where they
should be transferred. Different devices
use different levels of detail to make these
forwarding decisions. For example, hubs
do not examine headers; they broadcast
all frames received. In contrast, routers
carefully examine the header to determine
the packets precise destination.
These decisions occur at various levels of
the Open Systems Interconnection (OSI)
reference model (see page 26), developed
by the International Standards
Organization (ISO). The OSI model is
similar to the various levels found in a
mailing address—from the country, to the
state or district, to the street, to the mail
stop, to the recipient’s name. Devices
along the way use various levels of detail
to ensure the information gets to the
proper destination.
Another important set of rules is
Transmission Control Protocol/Internet
Protocol (TCP/IP). This is an open
standard that is now the most commonly
used protocol in the world.
How LANs Work
Open Systems Interconnection (OSI)
reference model
CCoommmmuunniiccaattiioonn::
Provide accurate
data delivery
between
end-stations
CCoonnnneeccttiioonn::
controls physical
delivery of data
over the network
What Are Standards?
A standard is a set of guidelines that
enables you to deploy network devices
with an assurance that they will work
together. It can describe the signaling
method used in a network, or the way
packets gain access to and move through
network pathways. Some important
standards in networking include:
• IEEE 802.3—the standard for Ethernet
• IEEE 802.5—the standard for Token Ring
• IEEE 802.1p—the standard for network
policy control, covering such activities
as traffic prioritization (which packets
get through the network first) and
multicast control (how packets go from
one station to multiple stations at once)
26
HOW LANs WORK
Application
Presentation
Session
Transport
Network
Datalink
Physical
Routers, Layer 3Switches
Bridges, Switches
Cabling, Repeaters,Hubs, Modems
27
NETWORKING TECHNOLOGIES
Networking Technologies
Ethernet
Ethernet is the most popular topology for
LANs. Based on the IEEE 802.3 standard,
Ethernet moves data at 10 Mbps. In an
Ethernet network, devices listen to the
network channel. If no other device is
using the channel, an Ethernet device
sends its data. Then, each workstation on
the same LAN segment examines the data
to see if it is intended for that workstation.
This arrangement works well if there are
only a few users involved or only a few
messages are moving within a segment.
As you add more users, the network will
not run as efficiently. Your best solution is
to offer more segments serving smaller
groups of users. Recently, there has been
a strong trend toward giving dedicated
10 Mbps links to each desktop, driven by
the availability of low-cost Ethernet
switches. Ethernet packets are variable
in length.
Fast Ethernet
Fast Ethernet uses the same basic
technology as Ethernet—CSMA/CD
(carrier sense multiple access with
collision detection). Both are based on the
IEEE 802.3 standard; as a result, they can
use the same cabling (in most cases),
network devices, and applications. Fast
Ethernet allows data transmission at
100 Mbps, 10 times the speed of Ethernet.
As applications become more complex and
more users gain network access, this
increased speed or wider channel for data
can help avoid bottlenecks which cause
slow responses.
The Advantages of 10/100 Mbps Network
Solutions
Recently, a new solution has emerged to
deliver both the broad compatibility of
10 Mbps Ethernet and the speed of
100 Mbps Fast Ethernet in one package.
Dual-speed 10/100 Mbps Ethernet/Fast
Ethernet technology allows devices such
as NICs, hubs, and switches to operate at
either speed, depending on the device to
which they are attached. Connect a PC
with a 10/100 Mbps Ethernet/Fast
Ethernet NIC to a 10 Mbps port on a hub
and it operates at 10 Mbps. Connect it to a
10/100 Mbps port on a hub such as the
3Com SuperStack II Dual Speed Hub 500
and it automatically senses the new speed
and operates at 100 Mbps. This makes it
easy to migrate to faster performance at
your own pace. It’s also easier to equip
network clients and servers to handle new
generations of bandwidth-hungry
applications and network services.
Gigabit Ethernet
Gigabit Ethernet is compatible with the
Ethernet and Fast Ethernet network
infrastructure, but it operates at
1000 Mbps—10 times the speed of Fast
Ethernet. Gigabit Ethernet is a powerful
solution for alleviating bottlenecks at the
core of the network, where network
segments are aggregated and servers are
located. Bottlenecks are caused by
emerging high-bandwidth applications
and the increasingly unpredictable traffic
flows of intranets and multimedia
applications. Gigabit Ethernet provides a
seamless migration path for Ethernet and
Fast Ethernet workgroups with minimal
disruption required to achieve higher
performance.
ATM
ATM (Asynchronous Transfer Mode) is a
switching technique that uses fixed-length
cells to move data. Operating at high
speeds, ATM integrates voice, video, and
data traffic on one channel, and works in
both LANs and WANs. Because it operates
differently from the Ethernet varieties and
requires a special infrastructure, it is
largely used in network backbones—the
place where network segments come
together and are interconnected.
28
NETWORKING TECHNOLOGIES
29
NETWORKING TECHNOLOGIES
Ring Technologies
Token Ring and FDDI are token-passing
technologies. They operate in a
continuous loop—a series of bits called a
token flows in one direction around the
ring past every workstation on the
network. The workstation can add a frame
of data to the token if it has something to
send; otherwise, it passes the token to the
next workstation. Token Ring operates at
either 4 Mbps or 16 Mbps and is predomi-
nantly found in the IBM environment.
FDDI (Fiber Distributed Data Interface) is
also a ring technology but is designed for
fiber optic cabling and is reserved for
network backbones. This protocol is
similar to Token Ring—a token is passed
around a loop from workstation to
workstation. Unlike Token Ring, FDDI
usually consists of two counterrotating
rings, normally of fiber optic cable, for
protection against downtime caused by
faults in one of the rings. It operates at
100 Mbps. FDDI can operate over long
distances with a maximum ring circum-
ference of 100 km and as far as 2 km
between workstations.
Both ring technologies are giving way to
varieties of Ethernet and ATM in newer
network installations.
30
NETWORKING TECHNOLOGIES
How LANs Handle the Demands of
Today’s Emerging Applications
Today’s complex applications, such as
multimedia and voice over the network,
require new levels of network performance
and intelligence with sophisticated traffic
controls to ensure quality and prevent
delays.
For example mission-critical traffic, such
as airline reservations or medical
information, real-time traffic (voice and
video), require top priority as they move
through network pathways to avoid delays
or inconsistent results on the receiving
end. To handle these demands many
Switches such as 3Com Switches, now
support standards-based traffic prioriti-
zation, using the IEEE 802.1p standard.
And to define control even further - right
down to the desktop - many NICs now
operate as an intelligent part of the
network. For example 3Com EtherLink III
NICs with DynamicAccess software provide
this control at the desktop, requesting the
appropriate priority level for traffic, based
on the application that generated the
data.
Shared vs. Switched Networking:
Which Is Right for You?
In a shared segment, all users compete for
the same bandwidth. This is the type of
network connectivity hubs provide. Data is
sent by one PC and travels to all other PCs
on the same segment. The packet is
examined by each PC, which determines
whether it is intended for them. As the
network grows, this can lead to
congestion and poor network response.
Switching, by contrast, provides dedicated
bandwidth directly to individual users,
decreasing competition for the link and
eliminating typical bottlenecks. For
example, if 30 users are competing for the
same 10 Mbps link, you can install a
10/100 Mbps switch to provide dedicated
bandwidth channels to individual Ethernet
and Fast Ethernet hubs, switches, servers,
and even demanding clients requiring
their own 100 Mbps links. Using the auto-
sensing feature of the 10/100 Mbps
switch, any connected device will
automatically operate at the highest
available speed—either 10 Mbps or
100 Mbps.
Looking to the future, Networking
for larger organizations.
To alleviate congestion in networks where
routers may have caused serious
bottlenecks, larger organizations are
turning to Layer 3 switching. Combining
the traffic controls of routing and the
unimpeded wire speeds of switching,
Layer 3 switching offers the best of
both worlds.
For environments where routers are used
for security, segmenting traffic, or
multiprotocol translation, organizations
are also able to leverage Fast IP
technology— which allows certain traffic
to bypass routers, moving from client to
server along fully switched paths,
delivering faster responses to the client.
What’s more, new applications are
emerging that send one stream of data to
multiple PCs (multi-casting). This can
easily overwhelm network links when all
PCs are receiving a transmission intended
for only a few. Based on the IEEE 802.1p
standard. Multi-cast Control, a feature
found in 3Com switches and NICs, allows
network managers to direct the stream of
multicast data to only those PCs that
need it, eg a company President can
address all employees at their desktop
rather than having to physically convene
at a cental point.
31
NETWORKING TECHNOLOGIES
32
You may not need to deploy all of these
complex applications now, but with the
rapid pace of evolution in network
technology, it’s important to choose
equipment that will meet your future
needs. No matter what the requirements
of your network’s future, 3Com will
provide the standards-based support you
need to integrate emerging technologies.
33
PLANNING YOUR NETWORK
It’s impossible to predict the future, but
it’s certain that demands on your network
will keep expanding. There are two factors
that fuel this inevitable pressure to grow—
the ever-increasing sophistication of
software applications and increasing
reliance on your network by everyone in
your organization.
The critical consideration in any network
plan is to ensure that the equipment you
invest in today will continue serving you
as your network evolves. Specifically, the
solutions you choose must be:
Scalable
You should be able to begin with an
investment that suits your immediate
needs, then leverage that investment as
you expand capacity, performance, and
functionality at your own pace. It is
important that you plan ahead and map
out a migration path using your initial
network technology as the foundation.
For example you can begin with a
stackable 10/100 Mbps Ethernet/Fast
Ethernet hub such as the 3Com
SuperStack II Dual Speed Hub 500, and
then as you connect more users and add
servers, you can install a SuperStack II
Switch 1100. This will and provide a
dedicated 10 Mbps or 100 Mbps links to
the original hub, the servers, and even
power users who need their own high-
speed connections.
Then you can expand the capacity of the
same stack with more hubs or switches,
routers, remote access servers, and a
redundant power system—all manageable
either built-in or optional. 3Com’s
OfficeConnect family of solutions offers
similar expandability in capacity and
function for smaller businesses (less
than 25 nodes).
Another strategy for scalability in large
networks is to install a chassis hub or
switch such as the 3Com CoreBuilder
range. This enables you to add modules or
cards to a single chassis to increase
capacity, add new functions, or increase
redundancy at your own pace.
Flexible
Because network needs change so quickly,
your configuration should be designed to
adapt without major overhauls. The
solutions you choose should be able to
support a range of cable types, such as
Twisted Pair, Coaxial, or fiber. Installing
10/100 Mbps Ethernet/Fast Ethernet
solutions such as the 3Com SuperStack II
Dual Speed Hub 500 ensure that you will
be ready to meet increasing demands on
workgroup links when needed. For diverse
networks, you will also need solutions
that can accommodate multiple
technologies, from Ethernet and Fast
Ethernet to Gigabit Ethernet.
Planning Your Network
34
Resilient
Resilient links provide protection against
downtime by allowing multiple
attachments between a piece of network
equipment and the network. If one of
these redundant connections fails, the
traffic it carries instantly moves to the
backup link. For example, you can attach a
server to two hubs with resilient link
features in a stack. If one hub is turned off
or fails, the server’s backup attachment is
activated automatically—without
interrupting users.
Reliable
As your business or organization begins to
depend more on your network, downtime
becomes increasingly costly. Look for
solutions that provide superior reliability,
backed by strong warranties and service
policies. You should consider critical factors
such as fault tolerance and redundancy.
For example 3Com products have features
such as dual power supplies in its chassis
and stackable families of solutions, dual
switching engines, and support for
resilient links (if one fails, the backup
goes to work automatically to prevent
downtime). 3Com also supports uninter-
rupted networking with Transcend network
management software, a comprehensive
collection of tools that allows you to
prevent problems before they start.
Manageable
As the network grows, so does the
importance of being able to monitor and
control traffic flows, predict problems, and
troubleshoot faults. Support for RMON in
network switches, hubs, and NICs
provides an effective way to gather data
about traffic performance and spot trends
that could lead to trouble. You should
choose solutions that support SNMP, a
widely accepted standard for managing
diverse devices throughout your network.
With Web-based management capability,
you can manage devices from any PC with
a web browser for remote configuration
and problem solving.
In addition, a powerful set of graphical
management tools, such as 3Com’s
Transcend network management software,
gives you end-to-end network visibility.
This allows you to see where, when, and
why bottlenecks occur, identify trends
before they evolve into network delays,
move users easily and transparently
between segments, and reconfigure
devices throughout the network—all from
a central management workstation.
Transcend software even allows
management of larger networks via any
Web-based browser, so managers are
never out of touch with their networks.
PLANNING YOUR NETWORK
Secure
Every network needs some form of
security; the simple password protections
provided by your operating system are
rarely enough protection. Look for
networking solutions that provide
additional layers of protection at the hub,
switch, router, and remote access server
levels, allowing you to block access to
certain devices, create various clearance
levels for access to sensitive data, and
block your internal network from invasions
over the Internet or public phone network.
You should keep in mind that good
security is not merely a device or group of
devices. Good security is a detailed set of
policies that govern PC sharing and the
use of portable media such as floppies,
removal of data from the network, and
more.
Summary The golden rules for building a successful
network include the following:
• Identify the future needs of your
network—evolving work practices,
adding remote offices and mobile
staff, increasing your use of
multimedia applications.
• Plan for change—choose products
that are scalable and flexible.
• Look for a supplier who can offer
reliable products based on open
industry standards and backed by
strong warranties.
• Create a comprehensive security plan
and choose products that provide
multiple layers of protection for
sensitive network resources.
35
PLANNING YOUR NETWORK
37
HOW TO GROW YOUR NETWORK
Scenario 1: A Small Business Network
A small business has four users with their
own PCs and one printer connected to one
of the PCs. To simplify file sharing and avoid
having to purchase additional printers, the
company installs 3Com EtherLink XL
10/100 Mbps NICs in the PCs and adds a
3Com OfficeConnect Dual Speed Hub 8 with
eight 10/100 Mbps ports.
This peer-to-peer, shared configuration
supports both 10 Mbps connections and
100 Mbps connections for high-demand
users and connects to a network server at
100 Mbps. The hub provides a shared
connection to the printer and with 8 ports
has room to accommodate more users
when necessary.
Then, as the business grows, the business
can purchase additional OfficeConnect
products that will allow it to integrate
remote access and WAN functions into its
network stack.
How to Grow Your Network
OfficeConnect Dual Speed Hub 8
Printer
Ethernet 10 Mbps
Ethernet 10 Mbps
Ethe
rnet
10
Mbp
s
Fast Ethernet 100 Mbps
Fast Ethernet 100 Mbps
Fast
Eth
erne
t 100
Mbp
s
PCs
Server
Scenario 2: Relieving Congestion in Small-
to Medium-Sized Businesses
In this company, all users previously
shared a single Ethernet segment, which
led to slow network response early in the
morning and late in the day when usage
was heaviest. To alleviate the problem and
maximize its investment in existing
equipment, the company installs a
3Com SuperStack II Switch 1100, which
segments the network by providing
dedicated 10/100 Mbps paths to the
hubs. The company can also choose
3Com’s SuperStack II PS Hub family with
port switching capability that enables the
network manager to connect and segment
users to one of the 4x 10 Mbps segments.
Thus reducing the number of users
sharing a 10 Mbps segment. For example
instead of 40 users sharing a single
segment, the company has 10 users on
each of four 10 Mbps segments.
38
HOW TO GROW YOUR NETWORK
Floor 1
PCs
SuperStack II
Dual Speed Hub 500
Fast Ethernet 100 Mbps
Ethernet 10 Mbps
Ethernet 10 Mbps
SuperStack II
PS Hub 40 & 50
Server
100 Mbps
100 Mbps
PCs
Ethernet 10 Mbps
SuperStack II Switch 3300
SuperStack II Switch 1100
Scenario 3: Accommodating Growth and
Migrating to Higher Performance
As the company’s needs evolve, it can
leverage its existing investment while
migrating to higher performance. New
workgroups on Shared 100 Mbps for the
marketing department and executive staff.
In addition, servers are equipped with
EtherLink XL NICs, consolidated into a
server farm and given dedicated 100 Mbps
links through the SuperStack II
Switch 3300.
Now, communication between the
workgroups and the servers occurs at
100 Mbps. The company also adds
Transcend network management software
to monitor traffic and assist future planning.
Then, for small groups of power users who
need fast response times with dedicated
100 Mbps bandwidth are provided by the
SuperStack II Switch 3300.
39
HOW TO GROW YOUR NETWORK
Floor 1
Floor 2
PCs
SuperStack II
Dual Speed Hub 500
SuperStack II
Dual Speed Hub 500
Fast Ethernet 100 Mbps
Ethernet 10 Mbps
Ethernet 10 Mbps
SuperStack II Switch 3300
Server with
Fast Etherlink XL NICs
Server Farm
PCs
PCs
Fast Ethernet 100 Mbps
Fast Ethernet
100 Mbps
Fast Ethernet 100 Mbps
Fast Ethernet
100 Mbps
SuperStack II Switch 1100
Scenario 4: Integrating Mobile Workers
Next, the company wanted to provide dial-
in access for employees working from
home or on the road. A 3Com SuperStack II
Remote Access System 1500 is added to
handle the incoming traffic, with the
added benefit of allowing dial-out access
to the Internet for users at the central site.
Remote users can dial in using their 3Com
Megahertz PC Card modems in their
notebook PCs, or with 3ComImpact IQ
ISDN modems for digital connections at
128K. The remote access server allows
users to call in using ISDN (in this
scenario), Frame Relay, X.25, leased line,
or public telephone lines and access an
Ethernet or Token Ring based LAN
network. This enables remote users to
work as though they were at their desks at
the central site.
40
HOW TO GROW YOUR NETWORK
SuperStack II Remote
Access System 1500
Notebook PC with 3Com/
Megahertz Modem PC Card
PC with 3Com Impact
ISDN Modem
ISDN
56k
Floor 1
Floor 2
PCs
SuperStack II
Dual Speed Hub 500
SuperStack II
Dual Speed Hub 500
Fast Ethernet 100 Mbps
Ethernet 10 Mbps
Ethernet 10 Mbps
Fast Ethernet
100 Mbps
Server with
Fast Etherlink XL NICs
Server Farm
PCsFast Ethernet 100 Mbps
Fast Ethernet 100 Mbps
Internet
SuperStack II Switch 3300
SuperStack II Switch 1100
Scenario 5: Integrating the Remote Office
Now the company is opening a pair of
branch offices. At the central site, a
NETBuilder II router serves as the central
connecting point for the WAN. The remote
sites are connected to the central site via
the SuperStack II NETBuilder routers. This
configuration enables the company to
deploy a firewall service in its
NETBuilder II router to protect the internal
network against remote hackers and
unauthorized use. As new branch offices
are added, they
can be integrated into the WAN using a
similar set of SuperStack II building
blocks.
As the connections to remote sites place
higher demands on the network backbone
at the central office, the company could
migrate to Gigabit Ethernet or ATM in the
backbone.
41
HOW TO GROW YOUR NETWORK
Total Control
Access Conentrator
NETBuilder II
PCs
SuperStack II NETBuilder Router
SuperStack II NETBuilder Router
SuperStack II Switch 1100
ISDN/Dial-up
SuperStack II Dual Speed Hub 500
PCs
Floor 1
Floor 2
PCs
SuperStack II
Dual Speed Hub 500
SuperStack II
Dual Speed Hub 500
Fast Ethernet 100 Mbps
Ethernet 10 Mbps
Ethernet 10 Mbps
Fast Ethernet
100 Mbps
Server with
Fast Etherlink XL NICs
Server Farm
PCsFast Ethernet 100 Mbps
Fast Ethernet 100 Mbps
SuperStack II Switch 3300
SuperStack II Switch 1100
43
GLOSSARY OF NETWORKING TERMS
10BASE2 (Thin Coaxial)
The IEEE 802.3 specification for Ethernet
over thin coaxial cable.
10BASE5 (Thick Coaxial)
The IEEE 802.3 specification for Ethernet
over thick coaxial cable.
10BASE-FL (10 Mbps over Fiber Optic)
A part of the IEEE 10BASE-F specification
covering Ethernet over fiber. It is interop-
erable with Fiber Optic Inter Repeater Link
(FOIRL).
100BASE-FX (100 Mbps over Fiber Optic)
100 Mbps Ethernet implementation over
fiber.
10BASE-T (10 Mbps over Twisted Pair)
The IEEE 802.3 specification for Ethernet
over unshielded twisted pair (UTP).
100BASE-T (Fast Ethernet)
A 100 Mbps technology based on the
Ethernet/CD network access method
running over twisted pair cabling.
AAdapter Card
Refer to NIC.
Administrator
A network user who can access commands
that set up, configure, and manage the
network.
Analog
Continuous signals formed from physical
variables such as voltage, current, or
resistance.
Application
A program used for a particular kind of
work, such as word processing or
database management.
Architecture (Network)
A structured, modular network design,
such as assigning different layers or levels
to different data communication tasks.
Glossary of Networking Terms
Auto-sensing 10/100 Mbps
A feature that allows switches and hubs to
sense automatically and adapt to the
speed of the cable (also referred to as
auto-negotiation). Smart auto sensing
also detects the link quality and automat-
ically adjusts to maximize transfer speeds.
Asynchronous Transfer Mode (ATM)
The CCITT standard for cell relay wherein
information for multiple types of services
(voice, video, data) is conveyed in small,
fixed sized cells. ATM is a connection-
oriented technology used in both LAN and
WAN environments.
AUI
A [NUMBER]-pin, plug-type cable interface
for backbone connections.
BBackbone
The backbone is the core of the network.
See also Collapsed Backbone.
Backplane
The common data bus performing high-
speed data transfer in a router or hub.
Bandwidth
The range of frequencies assigned to a
communications channel. Bandwidth often
refers to the data-carrying capacity of a
channel.
BNC
A cable interface for coaxial backbone
connections.
Bps
Acronym for bits per second, which
defines the bit rate or number of bits
passing a point each second.
Bridge
A combination of hardware and software
that connects two LANs and allows
communication between the stations on
each. Bridges operate at the Data Link
layer (Layer 2) of the OSI reference model.
44
GLOSSARY OF NETWORKING TERMS
Bridge/Router
A device that can operate as a pure
bridge, a pure router, or both concurrently.
Broadband
The use of coaxial cable to provide data
transfer using analog (radio frequency)
signals. Digital signals must be passed
through a modem and transmitted over
one of the frequency bands of the cable.
Cable TV is an example of broadband
transmission.
Broadcast
A message sent to all network
destinations.
Broadcast Domain
The set of all devices that will receive
broadcast frames originating from any
device within the set. Broadcast Domains
are normally bounded by routers..
Broadcast Storm
Multiple simultaneous broadcasts that
typically absorb available network
bandwidth and can cause network
timeouts.
Bus Topology
1. A physical topology in which all servers
and stations are connected to the same
cable.
2. A logical topology in which packets are
distributed to all stations at the same
time.
See also logical topology, network
topology, physical topology, ring topology,
and star topology.
Byte
An 8-bit sequence treated as a unit.
45
GLOSSARY OF NETWORKING TERMS
CCabling Distance Specifications
Ethernet:
10BASE -T (Twisted Pair)
330ft/100m maximum segment length.
Hub can have RJ-45 or Telco RJ-21
connectors. 100
100BASE TX (Twisted Pair)
330ft/100m maximum segment length
RJ-45. 100
100BASE-FX Fiber Optic
100BASE-FX (fiber link) supports
1320ft/400m switch to switch over
62.5/125 micron cable. SC Connector
10BASE -5 (Coaxial, needs transceiver to
link hub)
1650ft/500m maximum segment length.
100 transceivers per segment. 7.75ft/2.5m
transceiver spacing. Absolute maximum of
9900ft/3000m DTE to DTE path length.
N-Type Connector 50
10BASE -2 (Coaxial/Thinnet)
613.5ft/185m maximum segment length.
Maximum 30 transceivers per segment.
1.55ft/0.5m minimum transceiver spacing.
Absolute maximum of 4620ft/1400m DTE
to DTE path. BNC Connector 50
10BASE -FL Fiber Optic
10BASE-FL (fiber link) supports 6600ft/
2000m over 62.5/125 micron cable.
Maximum of 13200ft/4000m DTE to DTE path.
Gigabit Ethernet:
1000BASE-SX 850nm
2m to 260m @62.5/125um MMF
(IEEE P802.3z/D4)
2m to 550m @50/125um MMF
(IEEE P802.3z/D4)
1000BASE-LX 1300nm
2m to 440m @62.5/125um MMF
(IEEE P802.3z/D4)
2m to 550m @50/125um MMF
(IEEE P802.3z/D4)
Token Ring:
Active Token Ring
(B) category 3 UTP at 4 Mbps (600ft/200m)
or 16 Mbps (330ft/100m) 100
(B) Category 4 or 5 UTP on 4Mbps(1320ft/
400m) or 16 Mbps (600ft/200m) 100
(A) Type 1 STP on 4 Mbps (2000ft/ 600m)
or 16 Mbps (1000ft/300m) 150
Token Ring Expansion
Maximum Main Ring Lengths.
(B) Category 3 UTP on 4 Mbps (600
ft/200m) or 16 Mbps (300ft/100m) 100
(B) Category 4 or 5 UTP on 4 Mbps
(1320ft/400m) or 16 Mbps
(600ft/200m) 100
(A) Type 1 STP on 4 Mbps (2000ft/600m)
or 16 Mbps (1000ft/300m) 150 50/125
micron fiber on 4 Mbps (6600ft/2000m) or
16 Mbps (6600ft/2000m) 62.5/125 micron
fiber on 4Mbps (6600ft/2000m) or
16 Mbps (6600ft/2000m) 100/140 micron
fiber on 4 Mbps (3300ft/1000m) or
16 Mbps (3300ft/1000m)46
GLOSSARY OF NETWORKING TERMS
FDDI
Fiber Optic Supports
6600ft/2000m over 62.5/125 micron cable
Media interface connector (MIC)
ATM
Fiber Optic OC-3c 155 Mbps
6600ft/2000m over 50/125 micron cable
or 62.5/125 micron cable. SC Connector
DS-3 45 Mbps
450ft/38.7m maximum over Coaxial to
point of presence over 62.5/125 micron
cable. BNC Connector 50
Carrier Sense Multiple Access with
Collision Detection (CSMA/CD)
A communication medium access
technique allowing many separate
transceivers to share a single channel. All
units monitor the channel (carrier sense)
and do not transmit while receiving a
signal. Whenever the channel is idle, any
unit can transmit (multiple access). If two
or more units begin transmitting at the
same time, their signals collide and they
realize that a problem occurred (collision
detection). They stop transmitting and
then wait for a separate randomly
determined short time before trying to
retransmit the data. See also Token
Passing.
Category 3 Cabling
Twisted pair cabling; the minimum
standard for connecting Ethernet devices.
Category 5 Cabling
Twisted pair cabling; the minimum
standard for connecting 100BASE-TX and
100BASE-FX Fast Ethernet devices
(100BASE-T4 may use Category 3 cabling).
CoreBuilder Chassis
3Com’s multiservices platform for high-
density switching and wiring concen-
tration, routing, remote access, redundant
power, and other network functions.
Central Processing Unit (CPU)
The circuit board or chip that controls all
activity within a PC system to retrieve
information, act on it, and then send it
somewhere else.
Circuit
A path for communication between points;
a communication link.
Class A
In FDDI networks, a dual-attached station
(DAS) that attaches to both rings for
added fault tolerance. A DAS can also be
dual-homed—or connected to two
separate FDDI concentrators for protection
against downtime. See FDDI.
Class B
In FDDI networks, a single-attached
station (SAS) that connects to only one of
the two FDDI rings.
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GLOSSARY OF NETWORKING TERMS
Client
A station on a network that requests
services from a server.
Client/Server Application
A software architecture in which the user
interface processing resides on a network
workstation (the client) and the majority of
the data manipulation resides on a
separate machine (server).
Client/Server Architecture
A LAN architecture in which network
resources are centralized and controlled at
one or more servers. Individual stations
(clients) must request services through
the server(s).
Coaxial Cable
A cable consisting of a small conducting
wire enclosed in a large insulated
conductor, shielded on the outside by a
wire braid. It is also known as coax.
Collision
The condition in which two packets are
being transmitted over a medium at the
same time. Their interface causes packet
corruption resulting in the packet not
being usable by the intended recipient.
Concentrator
A device that serves as a wiring hub in a
star-topology network. It sometimes refers
to a device containing multiple modules of
network equipment.
Configuration
1. The total combination of hardware
components (for example, CPU, keyboard,
and display device) that make up a PC
system.
2. The software settings that allow
different hardware components of a PC
system to communicate with each other.
Connection
In data communications technology, a
logical link established between
application processes that allows them to
exchange information.
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GLOSSARY OF NETWORKING TERMS
DData
1. A general term for information.
2. A collection of interrelated, unique data
items or records, in one or more PC files.
Data Communications
The transmission and reception of data
between locations. Data communications
require a combination of hardware
(terminals, modems, multiplexers, and
other hardware) and software.
Destination Address
The location where a packet is sent.
Dial-up
The use of a telephone to establish a
connection.
Digital
Data characters coded in discrete,
separate pulses or signal levels.
Driver
A small software program for operating a
specific peripheral device such as a NIC or
printer.
Duplex
Transmission that permits two-way
communication. Synonymous with full
duplex. See also half duplex and simplex.
EEnd User
In a network, the person or program that
is the ultimate source or destination of
data.
Enterprise Network
A large internetwork typical of a large
business enterprise.
Ethernet
A local area network (LAN) specification
that uses baseband signaling at 10 Mbps
and uses the CSMA/CD Media Access
Control (MAC) technique. The original
Ethernet LAN is slightly different from the
IEEE 802.3 standard. See Carrier Sense
Multiple Access with Collision Detection
(CSMA/CD) and Media Access Control
(MAC).
49
GLOSSARY OF NETWORKING TERMS
FFault Tolerance
Generally the ability to prevent a problem
on a device affecting other devices on the
same port.
FDDI
Fiber Distributed Data Interface—The
ANSI standard for high-speed
transmission over fiber optic cable.
FDDI-II
A new FDDI standard based on a circuit-
switching architecture rather than a timed
token passing scheme. Intended for
isochronous voice, video, and multimedia
applications in addition to asynchronous
data traffic.
Fiber Optic Cable
Thin, transparent fibers of glass or plastic
that transmit data through pulses of light
from a laser or light-emitting diode (LED).
File Transfer Protocol (FTP)
A TCP/IP application used to send
complete files within TCP/IP services.
Full-Duplex Transmission
Transmission that provides greater
distance on fiber (up to 2 km) for campus
networks and doubles available network
bandwidth.
Frequency
The number of times a periodic analog
signal occurs within one second. The
number is expressed in Hertz (Hz).
GGigabit Ethernet
A networking technology that allows
transmission of data at 1000 Mbps.
50
GLOSSARY OF NETWORKING TERMS
HHalf-Duplex Transmission
Transmission between two end points in
either direction, but not in both directions
simultaneously. See also full duplex and
simplex.
Hardware
1. Collectively, electronic circuit
components and associated fittings and
attachments.
2. In PC systems, the machinery
associated with computation.
Header
Coded information that precedes a data
message and gives information about it,
such as its destination address and
length.
Hertz (Hz)
Transmission speed in cycles per second.
Host Computer
The main computer or large computer
(mainframe) in a network.
Hub
A multiple device that forms the central
point of connectivity in a physical star
topology. Also known as a concentrator.
IInput/Output
1. The method, medium, or device (for
example, keyboard, monitor, floppy disk,
hard disk, NIC, or printer) used to transfer
data to a computing system or from the
computing system to the outside world.
2. The interface between humans and a
computer, or between PCs.
Interface
1. A physical device that connects two
systems or two devices.
2. A standard, such as RS-232-C, that
specifies how two systems can connect to
each other.
Internet
The Internet is an enormous public WAN—
and a conduit between network users and
a worldwide store of data, images, and
sounds.
Internet Protocol (IP)
The standard used in the context of the
TCP/IP protocol suite for sending a basic
unit of data, the IP datagram, through an
internetwork. IP is the Network-layer
protocol of the TCP/IP protocol suite.
51
GLOSSARY OF NETWORKING TERMS
Internetwork
Two or more networks that can pass data
and share resources as if they were a
single network.
ISDN
Integrated Services Digital Network—Pay
as you go telephone line for remote
connectivity of multiple networks (WANs)
for fast data transfer. (See page 10.)
KKilobit (Kb)
One thousand bits. Bit is the contraction
of binary digit. A bit is the electrical
equivalent of a value 0 or 1 that
represents the basic unit of computer
information.
Kilobyte (KB)
One thousand bytes. A byte is 8 bits long
and represents one character.
LLAN Segmentation
The process of dividing LAN bandwidth
into multiple independent LANs to
improve performance.
Light Emitting Diode (LED)
A fiber optic light source.
Link
A physical or logical circuit between two
points in a network.
Local Area Network (LAN)
A data communications network within a
limited physical area (up to about 6 miles
or 10 kilometers). The three basic
components of a LAN are the NICs that
plug into each PC to connect it to the
network, cabling and server hardware, and
software for network control.
52
GLOSSARY OF NETWORKING TERMS
MMedia Access Control (MAC)
A method for controlling access to a
transmission medium. An example is the
Ethernet CSMA/CD access method.
Megabit per Second (Mbps)
The speed of transmission is measured in
Megabits (one million binary digits (ones
and zeroes). The term bit is the
contraction of binary digit. It is the
electrical equivalent of a value 0 or 1 and
represents the basic units of PC
information.
Megabyte (MB)
One million bytes. A byte is eight bits long
and represents one character.
Modem
Contraction for modulate/demodulate.
A modem coverts the serial digital (binary)
data from a transmitting terminal into a
form suitable for retransmission over an
analog telephone channel. A second
modem reconverts this signal to binary
data for acceptance by the receiving
terminal.
NNetwork Interface Card (NIC)
A circuit board inside each workstation or
server on the network. It allows a device
to listen and talk to other stations on the
network.
Network Management
Administrative services performed in
managing a network, such as network
topology and software configuration,
downloading of software, monitoring
network performance, maintaining
network operations, and diagnosing and
troubleshooting problems.
Network Management Platform
Powerful network management software
programs, such as 3Com’s Transcend
network management, which provide a set
of network management utilities and
application program interfaces that enable
software developers to write network
management applications for specific
devices. (See page 23).
53
GLOSSARY OF NETWORKING TERMS
Network Operating System (NOS)
A set of operating system protocols that
control the resources of a network.
Network Topology
The pattern of connection between points
in a network.
Node
A communication device attached to a
network, such as an intelligent
workstation, file server, or host computer.
Noise
Undesirable signals on a communication
channel that can interfere with or distort
data signals.
OOfficeConnect
3Com’s OfficeConnect family of networking
products provides all the networking
capabilities a small office needs to begin
sharing its PC and information resources
effectively.
Operating System (OS)
The fundamental software instructions
controlling a local PC.
Optical Fiber Cable
A thin cable with glass or plastic core used
in fiber optic communications. The fiber
transmits light instead of electrical
signals.
54
GLOSSARY OF NETWORKING TERMS
PPacket
A block of data handled by the network
that includes a header and data field.
PBX
An automated telephone switching system
serving one company, located on the
company’s premises, and connecting to
the public telephone network.
Peer-to-Peer Architecture
A network architecture in which stations
can share information and each other’s
resources without relying on a centralized
server.
Physical Topology
The actual physical pattern in which
devices are interconnected.
Port
A place where a physical connection is
made between a computing device and
cabling to a peripheral, a network, and
others.
Port Density
The number of ports, physical and logical,
per network device.
Port switching Hub or segmentable Hub.
A hub allowing the creation of virtual
workgroups through remote configuration
and relocation of users to multiple LAN
segments regardless of their physical
location (for example, 3Com’s
SuperStack II PS Hub family).
Protocol
1. A strictly defined procedure and
message format allowing two or more
systems to communicate over a
transmission medium.
2. A formalized set of rules that PCs use to
communicate. Because of the complexity
of communications between systems and
the need for different communications
requirements, protocols have been divided
into modular layers, where each layer
performs a specific function for the layer
above.
55
GLOSSARY OF NETWORKING TERMS
RRemote Access
A user’s ability to connect to a distant
network through a modem.
Remote Monitoring
(See RMON/RMON2.) - See page 23
Repeater
Functioning at the physical layer of the
OSI Reference Model, they extend and
regenerate digital signals traveling from
one cable segment to another.
Resilient Link Support
Allows you to define main and standby
links. If the main link fails, the standby link
is selected automatically.
Ring Topology
1. A physical topology with network
devices arranged in a closed circle.
2. A logical topology where packets travel
sequentially through all devices around
the ring. See also bus topology, network
topology, and star topology.
RJ-11
A twisted pair cable connector that
resembles a common modular phone jack.
RJ-45
A slightly larger variant of the RJ-11
twisted pair cable connector with six
wires.
RMON/RMON2
A specialized SNMP MIB for use with
remote control monitoring devices.
(See page 23).
Route
To direct a packet of data (or a message)
along a path of intermediate nodes.
Router
A device that connects multiple networks
together and forwards packets between
them. A router operates at Layer 3 of the
OSI Reference Model. It is also called a
network relay.
56
GLOSSARY OF NETWORKING TERMS
SSegment
1. A portion of a LAN separated from the
rest of the LAN by a bridge.
2. An uninterrupted length of Ethernet
cable within a network.
3. The SuperStack II PS Hub family
provides four LAN segments within one
hub. (See page 38).
Segmentable Hub
A hub allowing the creation of virtual
workgroups through remote configuration
and relocation of users to multiple LAN
segments regardless of their physical
location (for example, 3Com’s SuperStack
II PS hub family.
Server
Shared resource for the storage of data.
Session
The connection time during which data is
transmitted between two users, two
devices, or a user and a computing device
on a network.
Shared Ethernet
Conventional CSMA/CD Ethernet configu-
ration to which all stations are attached by
a hub and share 10 Mbps or 100 Mbps of
bandwidth. Only one session can transmit
at a time.
Shielded Twisted Pair (STP)
A twisted-pair cable with foil shielding
around each pair.
Shielding
Insulation using a grounded, metallic
covering to protect a cable or wire against
interference.
Simple Network Management Protocol
(SNMP)
A network management protocol for
TCP/IP-based networks.
Smart Auto Sensing
An enhancement to the standard auto-
sensing feature. Each port not only senses
the speed of the attached connection
automatically, but it also senses the
quality of the cable and automatically sets
the speed to maximize the real
throughput.
Source Address
The address (unique node identifier) of
the location from which a packet is sent.
57
GLOSSARY OF NETWORKING TERMS
Star Topology
A network configuration in which all
stations are individually connected to and
all messages pass through a central node.
See also bus topology, network topology,
physical topology, ring topology, and star
topology.
Structured Wiring System
A plan for building cabling that is based
on modular subsystems and which
specifies consistent wiring practices and
materials.
SuperStack II
3Com’s architecture for stackable connec-
tivity systems. It allows you to combine
diverse technologies and network services
in one system with a common network
management package and a choice of
redundant or uninterruptible power
systems.
Switch
1. A multiport device that provides high-
speed packet switching between ports.
2. In packet switching networks. The
device that directs packets, usually
located at one of the nodes on the
network’s backbone. It is also known as
data PABX.
TTelecommunications
The transmission of data, voice, or video
using telephone, radio, or other communi-
cation channels.
Thick Ethernet Cable
A 0.4-inch diameter cable or RG-8 with
four shields cable. It requires an external
transceiver cable or N-series to BNC series
adapter. It is often called thick Ethernet
cable. (See also thin Ethernet cable.)
Thin Ethernet Cable
A cable standard for Ethernet (IEEE 802.3)
networks using RG-58 A/U or RG-58 C/U
cable and BNC connectors. The coaxial
cable is 0.2 inches in diameter, so it is
more flexible than thick Ethernet. Thin
Ethernet operates at the same frequency
as thick Ethernet but over shorter
distances, and it provides less insulation
from interference than thick Ethernet.
Throughput
The total of correctly transmitted
information processed or communicated
during a specified time period, expressed
in bits per second or packets per second.
58
GLOSSARY OF NETWORKING TERMS
Token
A bit pattern that travels in a
predetermined direction along the
transmission line of a ring or bus network.
It can indicate that the line is currently
transmitting information or that it is clear
for transmission for the next station that
wants to transmit on the network.
Token Passing
A communication medium access
technique on a ring or bus network that
circulates a token from node to node.
When a station wants to transmit, it grabs
the token and attaches an information
packet to it. Only one message can be
transmitted on one channel at a time, and
only the station with control of the token
can transmit.
Token Ring
A baseband industry standard (designed
to the IEEE 802.5 standard and the OSI
Reference Model) that comprises a token
passing access method and a ring
topology.
Topology
The physical or logical layout of stations in
a network. See also bus topology, physical
topology, star topology, and ring topology.
Transcend Networking
3Com’s architecture for building
enterprisewide networks. Transcend
Networking incorporates the data center,
the campus backbone, workgroup, and
remote and personal office into a centrally
managed framework. Transcend
Networking addresses the three key
network evolution issues facing today’s
network managers: Scaling performance,
managing growth, and extending the reach
of their networks.
Transmission Control Protocol/Internet
Protocol (TCP/IP)
A widely used set of communication
protocols developed to conform to the
Department of Defense ARPANET
standard.
Transparent
Invisible to or unnoticed by the user.
Examples include the topology of a
network and location of a resource on a
remote station.
Twisted Pair
Refers to wiring commonly found in
telephone systems, consisting of two
insulated wires loosely twisted around
each other to help cancel out induced
noise. (See also 10BASE-T.)
59
GLOSSARY OF NETWORKING TERMS
UUnstructured Wiring System
A network wiring system that has grown in
an unplanned or inconsistent way.
User
A person who uses but does not
administer network resources.
UTP
Unshielded twisted pair—The most
popular wiring used for desktop and
workgroup connections.
VVirtual LAN (VLAN)
A virtual local area network (VLAN)
consists of a related group of users who
may communicate directly with each
another and receive broadcasts from each
another, yet may be geographically
dispersed. On a network infrastructure
built around port switches and hubs, all
workstations can communicate directly
with each another and receive broadcasts
from each another. In this network, VLANs
are used to control traffic patterns, to
provide security, and to control broadcast
behavior.
WWide Area Network (WAN)
A network covering an area larger than a
city or a metropolitan area.
Workgroup Switching
The ability to handle asymmetric traffic
patterns via high-speed interface and
intelligent switching.
Workstation
1. A single user PC, in many cases
specialized for high performance.
2. Any personal computer or terminal.
60
GLOSSARY OF NETWORKING TERMS
To learn more about 3Com products and services, visit our World Wide Web site at http://www.3com.com.
Copyright © 1999 3Com Corporation or its subsidiaries. All rights reserved. 3Com, 3ComImpact, DynamicAccess, EtherLink, Megahertz,
NETBuilder, NETBuilder II, OfficeConnect, Parallel Tasking, Sportster, SuperStack, and Transcend are registered trademarks of 3Com Corporation
or its subsidiaries. CoreBuilder and Total Control are trademarks of 3Com Corporation or its subsidiaries. Other brands and product names may
be trademarks or registered trademarks of their respective owners. All specifications are subject to change without notice.
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