The 3Com Introduction to Networkingcna.mamk.fi/Public/Drivers/3Com/Network...

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.


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


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


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


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


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


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


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


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


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 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


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


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


29


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


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


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.


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


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

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


Floor 1

PCs

SuperStack II

Dual Speed Hub 500


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


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


Floor 1

Floor 2

PCs

SuperStack II

Dual Speed Hub 500

SuperStack II

Dual Speed Hub 500


Ethernet 10 Mbps

Ethernet 10 Mbps


Server with

Fast Etherlink XL NICs

Server Farm

PCs

PCs


Fast Ethernet

100 Mbps


Fast Ethernet

100 Mbps


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


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


Ethernet 10 Mbps

Ethernet 10 Mbps

Fast Ethernet

100 Mbps

Server with


Server Farm

PCsFast Ethernet 100 Mbps


Internet



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


Total Control

Access Conentrator

NETBuilder II

PCs

SuperStack II NETBuilder Router

SuperStack II NETBuilder Router


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


Ethernet 10 Mbps

Ethernet 10 Mbps

Fast Ethernet

100 Mbps

Server with


Server Farm

PCsFast Ethernet 100 Mbps




43

GLOSSARY OF NETWORKING TERMS

10BASE2 (Thin Coaxial)

The IEEE 802.3 specification for Ethernet

over thin coaxial cable.

10BASE5 (Thick Coaxial)


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)


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


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


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


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.

47


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.

48


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


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


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


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.


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


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


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


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


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


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


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


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.)

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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


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.

Printed in the U.K. Stock Number 100291-004 6/00

3Com Corporation P.O. Box 581455400 Bayfront PlazaSanta Clara, CA 95052-8145Phone: 1 800 NET 3Com

or 1 408 326 5000Fax: 408 326 5001World Wide Web:

www.3com.com

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