Designing HP AdvanceStack Networkswhp-hou4.cold.extweb.hp.com/pub/networking/software/59670820.pdfWhenever cable is installed, plan for future expansion. Keep in mind that cable itself

H

Designing HP AdvanceStack Networks

Network Design Guide

August 1997

Features in this Version of the Design Guide

This version of the Network Design Guide now covers these new HP

products:

■ HP AdvanceStack 100T Hub-12TX

■ HP AdvanceStack Hub-12TXM

■ HP AdvanceStack Switch Port Modules (10/100TX and 100FX) for the

above hubs

2

Contents

1 Choosing the Cable Infrastructure

General Comparison of Network Cable Types . . . . . . . . . . . . . . . . . 1-2

Cabling Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

New Installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Existing Installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

A Word about Building Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

Physical Descriptions of Cable Types . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Twisted-Pair Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Fiber-Optic Cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Stacking Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

Thin Coaxial Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-9

Thick Coaxial Cabling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10

AUI Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11

Cable Connections Summary Table . . . . . . . . . . . . . . . . . . . . . . . . . 1-12

Special Situations with Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14

Extra Cable Length Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-14

Noise Immunity Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-18

Outdoor Cabling Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-18

Handling Adds, Moves, or Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 1-19

Adding a New Employee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-19

Moving an Employee from one Office to Another . . . . . . . . . . . . . 1-19

Changing an Employees Configuration . . . . . . . . . . . . . . . . . . . . . . 1-20

Disconnecting an Employee from the Network . . . . . . . . . . . . . . . 1-20

2 Designing the Shared 10 Mbps Workgroup

Designing the Standalone Workgroup . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Designing the Interconnected Workgroup . . . . . . . . . . . . . . . . . . . . 2-4

Connecting Hubs in Multiple Locations . . . . . . . . . . . . . . . . . . . . . . . 2-6

Cascading Twisted-Pair Hubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-7

Stacking Switching Hubs with Stacking Cable . . . . . . . . . . . . . . . . . 2-8

Stacks in Two Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Stacks in Three or More Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Single Hubs in Multiple Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

Ethernet/802.3 Topology Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

3

3 Designing the Switched Workgroup

Selecting An Appropriate Switch for Your Network . . . . . . . . . . . 3-3

Applying a Segment Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

Applying a Desktop Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

Backbone Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

When Not To Apply a Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

Differences Between a Switching Hub and a Switch . . . . . . . . . . . 3-8

Understanding Switching Technology . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

Shared Bus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

Shared Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

Why You Only Need a Switch Instead of a Router . . . . . . . . . . . . 3-11

Automatic Broadcast Control to Reduce Broadcast in

Your Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11

Automatic Multicast Control to Reduce Multicast Traffic on Your

Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

4 Watching & Optimizing the Network

Determining Network Congestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

Network Congestion Questionnaire . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

Causes of Network Congestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

Management Information for Network Design . . . . . . . . . . . . . . . . 4-4

Measurement of LAN Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

Ethernet/Fast Ethernet Thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

Using the Traffic Monitor to Watch the Network . . . . . . . . . . . . . . 4-6

Example: Whos Monopolizing the Server? . . . . . . . . . . . . . . . . . . . . 4-7

Example: What is Causing the Broadcast Storm? . . . . . . . . . . . . . . . 4-9

Using the Network Performance Advisor to Optimize and

Grow the Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10

How Network Performance Advisor Works . . . . . . . . . . . . . . . . . . 4-11

Tips on Gathering Data for A Successful Analysis of the Network 4-12

Example: Little Or No Problem on the Network . . . . . . . . . . . . . . 4-12

Example: Splitting a Segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

Example: Adding a Desktop Switch . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

4

5 Managing Individual Devices through SNMP

or the Console

Expansion Slot in an HP 100VG Hub . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

Terminal Consoles for Initial Configuration of the Device . . . . . 5-4

Connecting a Terminal to a Device for Initial Configuration . . . 5-5

Using Telnet to Connect to a Device . . . . . . . . . . . . . . . . . . . . . . . . . 5-8

Configuring HyperTerminal to Connect to a HP Device . . . . . . . . . 5-8

Stack Manager Consoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

Using a Distributed Management Chain to Configure

A Stack of Hubs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

HP AdvanceStack Assistant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11

Connecting HP AdvanceStack Assistant to Your Network . . . . . . 5-11

Using RMON and EASE Management for Advanced Device

Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13

6 Improving Network Performance

Typical Networking Problems and Their Solutions . . . . . . . . . . . . 6-2

Thin Coax Headaches: Convert to Twisted-Pair Cabling . . . . . . . . . 6-2

Slow Access to Server: Add More Servers . . . . . . . . . . . . . . . . . . . . . 6-3

Slow Access to Multiple Printers and Servers: Add A Switch . . . . 6-4

Switching Hubs Segmented: Add A Switch Module to Connect

Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

To Add VLANs or To Not Add VLANs . . . . . . . . . . . . . . . . . . . . . . . . 6-7

Creating Redundant Paths: Adding Backup Links . . . . . . . . . . . . . . 6-7

Providing Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

Hub Backup Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

Spanning Tree in Switches and Bridges . . . . . . . . . . . . . . . . . . . . . . 6-10

Upgrading to High Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13

Upgrading to Fast Ethernet (100Base-T) . . . . . . . . . . . . . . . . . . . . . 6-14

Upgrading to 100VG-AnyLAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

Upgrading to FDDI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-18

Upgrading to ATM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20

Upgrading to Gigabit Ethernet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-20

5

7 Adding Internet Access and Security

Connecting to the Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

Creating an Intranet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

Creating an Extranet (External Intranet) . . . . . . . . . . . . . . . . . . . . 7-4

Adding Security to Your Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

Hub Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

Switch Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

Router Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

8 Glossary

A Twisted-Pair Wiring Diagrams

4-Pair Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

25-Pair Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-4

Index

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1
Choosing the Cable Infrastructure

When you are building a network, you need to know about the different cable

types for the cable infrastructure. You have several networking cables that

you can select such as fiber or twisted-pair. This chapter describes the

available cables for you cabling infrastructure that will work in your work-

group network. It presents:

■ general comparison of network table types

■ cabling recommendations

■ physical descriptions of cable types

■ special situations with cable

■ handling adds, moves, or changes

1-1

Choosing the Cable InfrastructureGeneral Comparison of Network Cable Types

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General Comparison of Network Cable Types

The following table provides a quick comparison of several important char-

acteristics of the five cable types.

Network Cable Types

Twisted-pair cable

Fiber-optic cable

Stacking cable

Thin coaxial cable

Cable description Copper, 4 or 25 twisted pairs

Glass, 2 fibers Proprietary Copper, 2 conductors, 5-mm diameter

Connector type RJ-45 or 50-pin telco ST or SC Proprietary BNC

Maximum segment length 10Base-T, Cat 3, 4, 5:100 m, 100Base-TX, Cat 5: 100 m,100VG, Cat 3, 4: 100 m,100VG, Cat 5: 200 m

100Base-FX: 412 m, half-duplex

2000 m, full duplex

10Base-F: 1000 m

100Base-FX: 2000 m100VG fiber: 2000 m

Depends on product, usually around 30 cm

10Base2: 185 m

Maximum connections per cable

2 2 Switching Hubs: 8Hub-12TXM, 12TX: 5

30

Maximum connections per

segment

2 2 Switching Hubs: 8

Hub-12TXM, 12TX: 5

30

10-Mbps operation Yes* Yes Yes Yes

100-Mbps operation Yes* Yes Yes No

Noise immunity Good Excellent Good Good

Security Moderate Excellent Good Moderate

Reliability Good Good Good Moderate**

Ease of installation Excellent Good Excellent Good

Ease of troubleshooting Excellent Excellent Excellent Good

Ease of administration Excellent Excellent Excellent Poor

Cost per connection Very low High Included with hub:

none

Lower

Best application Workgroup cabling Long backbone, between wiring

closets, between buildings

Workgroup cabling Backbone in

wiring closet

* 10Base-T (10 Mbps) and 100VG-AnyLAN (100 Mbps) signals should not be transmitted within the same 25-pair bundled cable.

** Thin coax cable itself is reliable, but connectors allow easy cable disruption by untrained network users.

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Choosing the Cable InfrastructureCabling Recommendations

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Cabling Recommendations

The best cable for your situation depends if you are installing cable for a new

installation or adding cable to an existing installation. Always consider future

expansion and building codes when installing cable.

New Installations

For most new installations, we recommend using 100 meter lengths of

Category 5 twisted-pair cabling in the workgroup, with fiber-optic cabling for

long backbone connections. The Stacking Cable is appropriate for short

backbone connections within wiring closets. Both twisted-pair and fiber-

optic cabling let you upgrade from a 10-Mbps network to a 100-Mbps

network. (If you are upgrading to 100Base-TX, the twisted-pair cable must

be Category 5 or better.)

Since twisted-pair networks use the same cabling as your telephone system,

you will find that your telephone maintenance people can install and admin-

ister the network in the same way that they handle the telephone system.

Administrative changes (adds, moves, and drops) are the same as with

telephones, and troubleshooting the point-to-point cables of a twisted-pair

network is far simpler than troubleshooting a bus-structured coaxial cable

system. Noise immunity for twisted-pair cabling is of the same order as for

coaxial cabling: both are suitable for general office environments. For envi-

ronments with heavy electrical noise, we recommend fiber-optic cabling.

Twisted-pair cabling offers better reliability in the workgroup than coaxial

cabling, largely because of the human factor: an individual user who unplugs

his twisted-pair cable while investigating a network problem can affect only

his own connection; with coaxial cabling, he can bring down the whole

segment.

For long backbones we recommend fiber-optic cabling because it allows long

cable runs and offers excellent security and noise immunity. It is the only

cable type we recommend for cable runs outdoors between buildings. For

short backbones in a wiring closet, such as the connections between stack-

able network components in racks, use Stacking Cable (included with each

Switching Hub) which is inexpensive, effective, and reliable.

Existing Installations

For existing installations, it generally makes sense to use whatever cable

types are installed, as long as they provide the bandwidth and capacity that

you need for your operations. As your needs expand, however, we recom-

mend that you consider moving in the direction outlined in the preceding

paragraphs. Available networking equipment allows you to mix cable types

easily, so that it is quite feasible to operate, say, an older coaxial cable system

in conjunction with a new section of twisted-pair cabling.

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In 1997, most network administrators will be installing Category 5 cable to

replace Category 3 cable. Make sure the Category 5 cable is marked as

Category 5 verified. Unverified Category 5 cable may not work to Category

5 specifications. In the future, Category 6 cable will probably replace Cate-

gory 5. The Category 6 specification is not finished as of this printing, so look

for Category 6 well into the next decade.

Expansion

Whenever cable is installed, plan for future expansion. Keep in mind that

cable itself is inexpensive, relative to the cost of installing it. When you pull

new cable into the walls, floors, and ceilings of your buildings, it is much less

expensive to pull additional cables now than to come back a few months or

a year later and pull new cable again.

Planning the future capacity of your cable system can be something of a

guessing game, depending on how fast your organization grows, how it

adopts new information technologies, and how networking technologies

may change. The basic rule of thumb is a simple one: make your best

estimate, double it, and round up to the next even cable. For example, if you

were planning for the installation of 10Base-T twisted-pair wiring for your

employees a couple of years ago, you might have allowed one telephone

connection (1 twisted pair) and one computer connection (2 twisted pairs)

for a typical employee. If you were installing standard 4-pair cabling and

applying the rule of thumb, you would have doubled it (6 pairs), rounded up

to the next even cable (8 pairs), and installed two 4-pair cables for each

employee.

That would have given you plenty of capacity to change to a digital phone

(1 more pair) and to handle vastly more data by changing to 100VG-AnyLAN

or 100Base-T networking (2 more pairs), and still left you a couple of pairs

for patching around the occasional faulty wire.

A Word about Building Codes

Building and electrical codes can affect the way you install your network

cabling, particularly in the areas of grounding and cable jacket material. The

codes generally require that cables with an insulation that does not give off

toxic fumes when burning, such as FEP (fluoro-ethylene polymer), be used

in air ducts, air plenums, and other environmental air spaces. In addition,

some fiber-optic cables contain metallic strength members (that are not used

as conductors); consult your codes for guidance on how to handle such

cables, especially between buildings.

To avoid electrical interference, run networking cable and electrical cable

away from each other and away from electrical motors if possible.

Note that specific codes may impose different requirements from the general

ones that we have just mentioned. Be sure that you check the building and

electrical codes that apply in your area.

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At this point, you are ready to read Designing the Shared Workgroup to build
your network. Or you can read about the physical description of cables next.

Physical Descriptions of Cable Types

There are many types of cables to choose from:

■ twisted-pair cable

■ fiber-optic cable

■ stacking cable

■ thin coaxial cable

■ thick coaxial cable

■ AUI cable

Twisted-Pair Cable

Twisted-pair cabling includes a variety of twisted-pair cable types with a

nominal impedance of 100 ohms. It comes in cables of 4 pairs or bundles of

25 or more pairs, and can be either unshielded (UTP) or shielded (STP). It is

suitable for use in both 10-Mbps networks (Type 10Base-T) and 100-Mbps

networks (100Base-TX or 100VG-AnyLAN). 10Base-T, 100Base-TX, and

100VG-AnyLAN networking devices all use unshielded twisted-pair cable.

The standard for Ethernet-style twisted-pair cabling (IEEE 802.3 Type

10Base-T, 100Base-T, and 100VG-AnyLAN) specifies that cables be run in

point-to-point cable segments. These segments connect to network devices

at each end of the cable, with no device connections anywhere else along

the cable. All cable sections must use twisted pairs; no untwisted wire is

permitted anywhere.

Workgroup: twisted-pair

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The following table describes the categories of unshielded twisted-pair cable

types that you can use:

Unshielded Twisted-Pair Cable Types

Twisted-Pair Cable in 10 Mbps Networks

Category 5 is the popular choice for new networks but most companies still

have Category 3 cable because it is standard telephone wire and works well

with 10 Mbps networks. Standard connectors for twisted-pair network cable

are the same RJ-45 (8-pin) and 50-pin telco connectors used in telephone

systems. In addition, standard telephone cross-connect blocks can be used

for cable administration; adds, changes, and drops can be made in the same

way as for the telephone system. Many buildings of recent construction have

been pre-wired with enough telephone cabling that the extra capacity can be

used for networks. Sometimes, both telephone and network signals can be

freely intermixed in the same cables and bundles. All these factors make it

easy for your telephone system people to install, maintain, and administer

your twisted-pair network cabling.

For 10Base-T networks, in addition to the maximum cable lengths specified

by the 10Base-T standard, Hewlett-Packard provides for extended cable

lengths as described under special situations.

Twisted-Pair Cable in 100 Mbps Networks

The cabling standard for 100Base-TX and 100VG-AnyLAN are slightly

different.

For 100Base-TX networks, you need to use Category 5 cable or better. The

segment length from hub to end node is 100 meters for twisted-pair.

The standard for 100-Mbps 100VG-AnyLAN cabling is the same as for 10Base-

T cabling, except that all 4 wire pairs are required for communication over

UTP (Categories 3, 4, and 5) cables: the cables most commonly used. The

long cable options available for 10-Mbps operation are not available for 100-

Mbps operation, although, because of the tighter cable specifications of

category 4 and 5 cables, they can support longer distances: for example,

category 5 supports lengths of up to 150 meters.

Categories of unshielded twisted-pair cable Required for Cable Lengths for

Category Bandwidth Designation 10Base-T 100Base-TX 100VG-AnyLAN

10Base-T 100Base-TX 100VG-AnyLAN

Category 3 15 MHz Voice Grade 2 pairs not available: use 100Base-T4

4 pairs 100 m not available: use 100Base-T4

100 m

Category 4 20 MHz None 2 pairs not available 4 pairs 100 m not available 100 m

Category 5 100 MHz Data grade 2 pairs 2 pair 4 pairs 100 m 100 m 200 m

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Because twisted-pair cabling is familiar and easy to administer, it makes an
excellent choice for workgroup networking. Its ability to operate at either

10 Mbps or 100 Mbps allows it to adapt readily to changing organizational

situations over long periods of time.

Fiber-Optic Cabling

Fiber-optic network cabling is made up of two strands of optical fiber

running parallel to each other in a plastic, zip-cord jacket or multiple fibers

in a single jacket. The fibers are made of glass. Three types of connectors

are attached to fiber-optic cable:

Long Backbone: fiber-optic cable with SC connectors

Fiber-Optic Cable With ST connectors

Connector Type Technology

SC connector 100Base-FX

ST connector 10Base-FL, 100VG

FDDI connector FDDI

Fiber-optic cable. The maximumdistance depends on the device connected to this port.

See the table below.

Category 5 cable.Maximum: 100 metersHub to hub: crossover cableSwitch to switch: crossoverSwitch to end node: straight-through

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Fiber-optic cabling can be used under several network standards:

■ IEEE 802.3 Type 10Base-FL

■ FDDI (Fiber Distributed Data Interface)

■ IEEE 802.12 (100VG-AnyLAN)

■ IEEE 802.3u (100Base-T)

You can meet the specifications for all these standards by using 62.5/125-µm, dual-window cabling; dual-window cabling is designed for operation at both

850-nm and 1333-nm wavelengths. Check with your cable supplier for

complete specifications and conformance information on the cables you use.

The cable segment lengths vary.

Fiber-Optic Cable Lengths

Though fiber-optic cabling can be relatively expensive, its other characteris-

tics make it suitable for a number of applications. Because it is an optical

rather than an electrical medium, it is immune to electrical noise and

lightning strikes, and can not cause ground loops. It can be somewhat

difficult to attach connectors to fiber-optic cable cleanly; this makes it

generally unsuitable for office environments with their frequent changes.

Because of this characteristic, however, it is very difficult to tap fiber-optic

cable undetected, making this a very secure cable type.

With its capacity for long cable runs, one primary use of fiber-optic network

cable is for long backbones. There are strong secondary uses in areas with

high electrical noise-such as a factory floor in a heavy industrial setting-or

where physical network security is important.

Stacking Cable

Stacking cable is a thick cable that connects one hub to another and is usually

about 30 cm long. Stacking cable carries network management as well as

data between segments. You will find stacking cable included with each

Switching Hub.

Fiber-Optic Cable Maximum Segment Length

Ethernet, Type 10Base-FL 1000 m from repeater to end node

2000 m switch to switch

100Base-FX 412 m, half-duplex multimode fiber: switch to switch

2000 m, full duplex multimode fiber switch to switch

100VG-AnyLAN 2000 m

FDDI 2000 m node to node

10Base-F 2 km

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Note that each networking company makes their own stacking cable for a
product line so stacking cables are not interchangable from stack to stack.

However, the benefits of stacking cables outweigh this disadvantage. The

benefits of stacking cable are:

■ high speed: 1 gigabit speed between hubs

■ high bandwidth: carries both network management traffic and data

between hubs

■ cable included: cable is included with the hub so you dont need to find

or purchase this cable

■ reliability: stacking cable is less apt to have termination problems like

thin coaxial cable

Thin Coaxial Cable

Thin coaxial cabling (thin coax) has a diameter of approximately 5 mm and

an impedance of 50 ohms. It comes with a jacket material of either polyvinyl

chloride (PVC) or fluoroethylene polymer (FEP), a Teflon-like substance.

(The FEP cable is for use in air ducts, air plenums, and other environmental

air spaces; check your building and electrical codes to see where you should

use this cable.) Thin coaxial cabling requires a 50-ohm terminator (termi-

nating resistor) at each end to maintain the correct cable impedance.

Thin Coaxial Cable

The governing standard for thin coaxial network cabling (IEEE 802.3, Type

10Base2) permits a maximum cable segment length of 185 meters. The cable

segment can be built up from shorter sections, allowing connection of

network devices along the length of the cable through BNC T connectors;

the cable sections must be at least 0.5 meters (20 inches) long. The standard

limits the number of connections to a thin coaxial cable segment to 30.

Thin coaxial cabling should not be grounded at any point, unless grounding

is required by your local electrical code; in that case, ground the cable

segment at one point only.

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Generally, thin coaxial cable is not recommended for the workgroup. The

cable itself works fine electrically; its problem is the ease with which it can

be disconnected. When thin coax is in an unprotected area (as it must be

where it connects to a node), network users can and do get to it. It is not

uncommon for a user to disconnect the cable in the course of attempting to

isolate a network problem at his node. In doing so, if the user separates the

cable (rather than just disconnecting the T from the computer), the entire

coaxial cable segment becomes unterminated, which disables all network

communications on the cable. This condition may also cause network soft-

ware to crash. (A terminator left off the end of the cable, or a stray section

of 75-ohm video cable mixed in with the 50-ohm network cable, will cause

the same problem.) For this reason it is best to use thin coaxial cable only

in secure areas like wiring closets.

In addition, the bus structure of thin coaxial cable is harder to troubleshoot

than the star structure of twisted-pair cable. A twisted-pair cable segment

has a very simple topology, as it involves only a single node, the hub, and the

cable between them; it is not difficult to isolate a problem on such a simple

cable segment. A thin coaxial cable segment, on the other hand, has a much

more complex topology, since the cable is shared by many nodes. A network

problem could be caused by any of the nodes, any of the cable sections that

make up the cable, or either of the two terminators; such a problem typically

takes much more time to troubleshoot.

Currently, the preferred cable is using Stacking Cable, or twisted-pair cable

from hub to hub using the MDI port.

Thick Coaxial Cabling

Thick coaxial cabling (thick coax) has a diameter of 10 mm and an

impedance of 50 ohms. It comes with a jacket material of either polyvinyl

chloride (PVC) or fluoroethylene polymer (FEP), a Teflon-like substance.

(The FEP cable is for use in air ducts, air plenums, and other environmental

air spaces; check your building and electrical codes to see where you should

use this cable.) Thick coaxial cabling requires a 50-ohm terminator (termi-

nating resistor) at each end to maintain the correct cable impedance.

The governing standard for thick coaxial network cabling (IEEE 802.3, Type

10Base5), permits a maximum cable segment length of 500 meters. To

minimize impedance discontinuities and the resultant signal reflections, the

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standard recommends that the entire thick coaxial segment be a single length
of unbroken cable. If that is not possible, the alternatives are, in decreasing

order of preference: cable sections from the same manufacturer and lot

number, using sections of any length; or cable sections from different manu-

facturers and/or lot numbers, with lengths of 23.4 meters, 70.2 meters, or 117

meters (the odd half-wavelengths of the network signals, to minimize reflec-

tions). Connection to cable is made with a transceiver, using a vampire tap

that pierces the cable without cutting it into sections, or by cutting the cable

to install N-series connectors and a T; the transceiver connects to the AUI

port of a network device via an AUI cable. Transceivers should be attached

only at the black bands marked every 2.5 meters along the cable (to minimize

the constructive interference of reflections caused by the impedance discon-

tinuity at the points of attachment). The standard limits the number of

connections to a thick coaxial segment to 100.

Each thick coaxial cable segment should be grounded at one (and only one)

point. Check with your building and electrical codes for further details on

grounding requirements.

Because of its thickness and consequent stiffness, thick coax is cumbersome

to install and administer. In the situations where it is generally used it does

not offer significant advantages over other cable types, so we do not recom-

mend it for new cable installations. It is, however, already in place as

backbone cabling at many sites, and we see no reason to replace it where it

is working well. Since it interoperates readily with other cable types, it is

easy to expand an existing thick coaxial cabling system using new cabling

of other, more suitable, types.

AUI Cables

AUI cables contain individual, untwisted copper wires and come in both

thick and thin varieties. Thick AUI cables can be up to 50 meters long, and

thin AUI cables can be up to 15 meters long. We recommend that you use

thin AUI cable wherever the AUI cable distance is short, as the thick AUI

cable is inflexible and difficult to handle.

AUI cables do not constitute a separate cable type under the standards; they

are simply a means of connecting a network device to its network cable (via

transceiver) under certain circumstances. But the standards do take them

into account in determining the limits of network topologies.

The table below summarizes the relative strengths and weaknesses of the

different cable types in backbone applications.

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Comparison of Cable Types for Backbone Applications

Cable Connections Summary Table

The following table summarizes how to stack HPs networking products

together. Note that this table includes three concepts: stacking, cascading,

and using a backbone.

■ Stacking is using a wide cable called stacking cable such as the cable

used with the Switching Hubs and the HP AdvanceStack 100Base-T Hub-

12TX, 12TXM Hubs. This cable carries both management and data and

allows the stack of hubs to act as one repeater instead of several.

■ Cascading is connecting twisted-pair cable from one hub to the other.

The twisted-pair is straight through if you connect from the MDI/MDI-X

port to a port on the next hub. The twisted-pair cable is crossed over if

no MDI/MDI-X port is available. When you cascade hubs together, each

hub is a repeater.

■ For the ThinLAN Hub plus and other hubs with a BNC connector, thin

coax cable can be used to create a thin coaxial backbone.

Fiber-optic Twisted-pair Thin coaxial

Growth potential S A A

Topological flexibility S S A

Upgrade potential: FDDI S* n/a n/a

Upgrade potential: 100Base-T S* S n/a

Upgrade potential: 100VG-AnyLAN S* S n/a

Cable lengths S A A

Security S A A

Noise Immunity S A A

Ease of Troubleshooting S S A

Cost A S S

S = superior solutionA = acceptable solutionn/a = solution not available* = when using multi-mode cable

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The following products are not stackable: Switch 2000, Switch 208/224, and

Switch 800T.

Hub or Switch Type of Cable for Stacking/Cascading for Network Data and/or In-Band Management

Number of Hubs or Switches Allowed in a Stack

Port for Stacking/Cascading

Distance Limits from Hub to Hub or Switch to Switch

Hub-8E, Hub-8U, Hub-16U unshielded, twisted-pair cable, Category 3 or better

4 hubs using twisted-pair cable

MDI/MDI-X Port

100 meters

Switching Hub-12R, 24R, 24T Stacking Cable 12.5 in or Long Stacking Cable 28 in

8 hubs using provided stacking cable

In and Out ports Same as Stacking Cable length. Up to two Long Stacking Cables per stack

Hub-12, 24, 48 Category 3 twisted-pair cable 16 hubs with twisted-pair cable through the Distributed Management Chain ports

In and Out ports 185 meters for twisted-pair cable

100VG Hub-7M, Hub-14, 7E EITHER:

unshielded, twisted-pair cable, Category 3 or better or fiber-optic cable

3 hubs using twisted-pair cable

Uplink twisted-pair: 100 meters,

fiber: 2 km

ThinLAN Hub Plus, and others with BNC ports

thin coax 30 hubs using thin coax cable

BNC port Varies. Total distance cannot exceed 185 meters of thin coax cable

Fiber-Optic Hub Plus thin coax or fiber-optic cable thin coax connection: 30 hubs/

fiber connection: 4 levels of hubs

BNC port or fiber optic port

thin coax: 185 meters,

fiber: 1000 meters

100Base-T Hub-8TXE unshielded twisted-pair cable, Category 5 or better

2 hubs MDI port 23 meters

100VG Switch 200 twisted-pair cable, Category 3 or better

3 switches (each switch has SNMP built-in)

Uplink 100 meters

100Base-T Hub-12TX, 12TXM Stacking Cable 8.5 in 5 hubs using

provided stacking

cable

In and Out ports Same as Stacking Cable

length

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Choosing the Cable InfrastructureSpecial Situations with Cable

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Special Situations with Cable

Special situations are:

■ Extra cable length required

■ Noise immunity required

■ Outdoor cabling required

Extra Cable Length Required

The nominal maximum length of a twisted-pair cable is 100 meters.

(Nominal indicates that the actual, maximum length may vary from manu-

facturer to manufacturer. Check with your cable supplier to find the actual

maximum length for the cable you use.) If you need a longer run than 100

meters, there are two solutions, one using twisted-pair cable and one using

fiber-optic cable. You can get cable lengths up to 225 meters with twisted-

pair cable, and up to 1000 meters with fiber-optic cable.

Twisted-Pair Solution: Long Cable Option

The extent of an Ethernet/IEEE 802.3 LAN (collision domain) is limited by

the Ethernet topology. There are a couple of ways you can get around these

limitations.

The twisted-pair solution uses an HP twisted-pair transceiver at each end of

the cable, installed in the hubs transceiver slot or connecting to an available

AUI port on a hub or other network device. For the HP AdvanceStack hubs,

the transceiver can be either:

■ an HP J2607A Twisted-Pair Transceiver Module that slides into the AUI/

Xcvr slot, or

■ an HP 28685B EtherTwist Transceiver (an external transceiver) that you

can attach to an HP J2609A AUI Port Module.

The AUI Port Module installs in the AUI/Xcvr slot on the HP AdvanceStack

hub and provides a standard AUI connector, allowing you to attach any

standard external transceiver or transceiver cable. You might encounter this

situation if you are expanding an existing HP EtherTwist network with new

AdvanceStack hubs; the external transceivers you are accustomed to using

with your EtherTwist hubs will work with the AUI Port Module installed in

an AdvanceStack hub.

These twisted-pair transceivers have a long cable option that increases the

sensitivity of their receiver circuits, thus allowing the receivers to pick up

fainter signals that have traveled through a greater length of cable. This

option is set with a switch on the external transceiver, and with a jumper on

the internal transceiver. Due to the transceivers increased sensitivity when

the long cable option is enabled, it is more susceptible to crosstalk. There-

fore, you must use only 4-pair cable (not 25-pair cable) with only one set of

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signals running in it, to eliminate any potentially disturbing adjacent pairs.
The specific cable requirements are described in detail in the product

documentation that is provided with each of these transceivers.

The long cable option must be enabled on the transceivers at both ends of

the cable. In such a configuration, the maximum lengths are 150 meters using

Category 3 cable and 225 meters using Category 5 cable. The extra cable

length adds approximately 1.5 bit times of delay, and is unlikely to invalidate

an otherwise valid topology.

The illustration below shows the cable connections.

Fiber-Optic Solution

For longer cable runs between a hub and a computer or a printer, there is a

fiber-optic solution. The fiber-optic solution uses a fiber-optic cable with a

fiber-optic transceiver attached to the device at each end. Depending on the

product, different transceivers are available:

■ AUI Port that accepts an external transceiver: HP 28683A Fiber-Optic

Transceiver

■ HP AdvanceStack 10BT Switching Hub-12R, 24R, 24T and HP 10Base-T

Hub-12, 24, 48, Hub-8U, Hub-16U accept an internal transceiver:

HP J2606A Fiber-Optic Transceiver Module (Note that the Hub-12 and

Hub-48 are no longer available from HP but are listed here in case you

want to add a transceiver to these hubs.)

■ HP AdvanceStack 100Base-T Hubs: HP J3248A AdvanceStack

100Base-T FX Switch Uplink

■ HP AdvanceStack 100VG Hubs, Switches: HP J3028A 100VG UTP

Transceiver

■ HP AdvanceStack Switch 2000: HP 100Base-T Transceiver Module that

accepts the HP 100Base-FX Transceiver

■ HP AdvanceStack Switch 800T: HP 100Base-FX Transceiver Module

For connections between distant LANs, you can use up to 2000 meters of

fiber-optic cable in a single segment. See the illustration below.

Long twisted-pair cable (up to 150 meters with Category 3 cable, up to 225 meters with Category 5 cable)

Fiber-optic hub

LAN card in PC

Twisted-pair transceiver (long cable option enabled)

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Extended cable segment lengths using fiber-optic cable

If the cable is connected between devices that form LAN boundaries

(bridges, switches, and routers), the cable is a valid topology under the delay

rules of the IEEE 802.3 standard. In fact, you could even attach a small

workgroup to the fiber-optic cable, as long as the fiber-optic cable connects

on the other end to a device that forms a LAN boundary (a router, bridge, or

switch). Be sure to check the validity of your final topology, using the

Ethernet topology rules.

The second way to extend a maximum topology is to add a bridge, switch,

or router. Any of these devices will provide a boundary for the LAN (collision

domain); once you cross the boundary you are in a new LAN. You can build

a completely new topology, up to the maximum IEEE 802.3 limits, in the new

LAN.

Expanding into a new collision domain is a particularly good way to extend

a network that has reached the maximum number of cable segments and

repeaters. Be aware, however, that the IEEE 802.1 Spanning Tree Protocol

recommends a limit of 7 bridges or switches between any 2 nodes in a bridged

local area network; it is a good idea to follow this practice even if you dont

currently have plans for using spanning tree bridging.

Switch

Switch

Fiber-optic cable up to 2000 meters

Fiber-optic cable up to 2000 metersHub

Router

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Expanding network by adding new collision domains
Stack of Hubs

Fiber-optic hub

NodeNew collision domain boundary allows expansion.

Maximized topology limits network growth.

Bridge

Switch

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Hub Connected to a PC With Fiber-Optic Cable

If you want more than one fiber-optic port per hub, look at the HP Fiber-

Optic Hub for 10Base-T networks.

Noise Immunity Required

Since fiber-optic cable uses optical, not electrical, signals, fiber-optic cable

is immune to electrical noise. If you need to make network connections

through an area of high electrical noise, fiber-optic cable will provide the

noise immunity you need. Connections are as described above for fiber-optic

cabling under Extra Cable Length Required and as shown in the above

illustration.

Outdoor Cabling Required

For cabling that must run outdoors between buildings, the only cable we

recommend is fiber-optic cable. Since fiber-optic cable is an optical rather

than an electrical medium, it is immune to disturbance by lightning strikes.

Outdoor fiber-optic cable should be buried to prevent physical abuse caused

by foot traffic, vandalism, gnawing animals, and lawnmowers. Connections

are as described above for fiber-optic cabling under Extra Cable Length

Required and as shown in the above illustration.

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Choosing the Cable InfrastructureHandling Adds, Moves, or Changes

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Handling Adds, Moves, or Changes

One of the top tasks for you as a network administrator is adds, moves,

changes, or disconnects. Adding new employees or moving employees from

one building to the other usually involves a hardware change in the wiring

closet or a software change.

Adding a New Employee

When a new employee starts work, you need to do the following steps:

1. If your network is using IP, assign an IP address to the new employees

PC.

2. Enter the LAN adapters MAC address in a database for troubleshooting

in the future. The MAC address needs to be kept because troubleshooting

software identifies the PC by MAC address.

3. Connect the PC's LAN adapter cable to the LAN drop or drop in the

employee's office or cube. This drop is numbered. Write down the

number.

4. In the wiring closet, find the drop number on the patch panel or punch

down block. Connect the desired cable from the patch panel or punch

down block to the hub.

If you have not done so already, have each empty cube pre-wired for future

employees.

Moving an Employee from one Office to Another

For all of HPs hubs (except the HP Switching Hubs), a move is handled by

the following steps:

1. Identifying the number of the old drop and the new drop.

2. Find the numbers on the patch panel or punch down block and move the

cable from one patch panel connection to another.

3. If the employee will be using a different printer and server, then you need

to move the cable from one hub to another.

For the HP Switching Hubs, a move can be handled in software instead of

the wiring closet. In the ASCII console or HP AdvanceStack Assistant, specify

the new segment (1-4) that a user will be on. With the Switch 2000, you can

also use VLANs.

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Choosing the Cable InfrastructureHandling Adds, Moves, or Changes

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Changing an Employees Configuration

Usually a change of configuration such as a change in user rights or privileges

involves a software change at the server level. If you already have the

network segmented into groups-based on rights then you simply move the

user to the desired segment using the terminal console or HP AdvanceStack

Assistant.

Disconnecting an Employee from the Network

A list of IP addresses with the cubicle number along with the employee

number will allow you to quickly identify which port each employee uses.

Before or after an employee leaves your company, you need to disconnect

that employees workstation from the network in either software or hard-

ware. In network management software, you can disable the port using the

port disable command. The hardware method depends on your wiring:

■ If the wiring closet uses cross-connect blocks, you can easily ensure the

security of the network by removing the employees twisted-pair cable

out of the cross-connect block.

■ If the cables are 50-pin telco, then use the port disable command by

using the terminal console or HP AdvanceStack Assistant.

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Designing the Shared 10 Mbps Workgroup

When you design a shared workgroup, you will design one of the following

architectures:

■ standalone workgroups that can be set up using only a single 10Base-T

hub or stack of 10Base-T hubs supporting a a single Ethernet segment

■ interconnected workgroups that have grown to include several hubs

supporting more than one segment; the hubs may be located in one place

or spread out in several locations

■ Ethernet topology rules for a basic understanding of the IEEE 802.3

rules.

All of the designs described in this chapter are limited to a single Ethernet/

IEEE 802.3 segment (local area network (LAN)), also described as a collision

domain. If you are not familiar with the concept of collision domains, you

can find a description of the term in the glossary.

If you have a shared workgroup that is overloaded, consider a switched

workgroup as described in the next chapter.

Designing the Standalone Workgroup

The basic unit of network design is the workgroup. For a small organization,

especially one that is just starting to use a network, the small-scale

networking solution is simple: computers and printers connected to a single

twisted-pair hub. (In the past, networks were connected to single thin coaxial

cable but that method is no longer preferred because of thin coaxial cable

tends to be unreliable.)

Building a network with a single twisted-pair hub is simple: just connect

twisted-pair cable between the nodes (computers, printer, server) and the

hub, and your network is ready to operate. Hubs come in a variety of sizes

to match the requirements of different workgroups.

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Designing the Shared 10 Mbps WorkgroupDesigning the Standalone Workgroup

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Single Hub in a Workgroup

For 10-Mbps networks, the HP AdvanceStack Hub-8E, Hub-8U, and Hub-16U

are units, suitable for small workgroups that dont expect much growth and

will not necessarily need network management. The HP AdvanceStack 10BT

Switching Hub-12R and Hub-24R offer greater flexibility in configuration and

opportunity for growth. All of these AdvanceStack 10Base-T hubs (except

the Hub-8E) allow you to add security and management features when your

network grows to need them.

Selecting a Hub by Port Density

Note that the cost per port is lower with the larger hubs, so if you are

connecting, for example, 20 computers and printers, it costs less to buy a

single 24-port hub than to buy two 12-port hubs. When deciding what size

hub to buy, you will probably want to consider both your existing computers

and any computers you expect to add to the network in the near future.

Each hub has RJ-45 ports or modular ports for connecting end nodes and a

specialized uplink port(s) for connecting to other 100 Mbps hubs. A single

twisted-pair hub forms a physical star configuration with its nodes, as shown

above. Note that the HP JetDirect network interfaces for printers and plot-

ters allow you to place your printers and plotters wherever you want them

on a 10-Mbps network (just like computers); they dont have to be attached

directly to servers or other computers. (In fact, they will probably print faster

if they are attached through JetDirect interfaces.)

PCs (each PC has a LAN adapter)

All cables are: straight-through unshielded twisted-pair Category 3 or better, maximum 100 meters

Printer Servers

Hub-8E, Hub-8U, Hub-16U

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Designing the Shared 10 Mbps WorkgroupDesigning the Standalone Workgroup

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Choosing the Location of the Hub

While the hub can be left out in the open, most work areas are not well suited

to cables running all over the place, and the cables dont stand up well to

people walking on them and fork lifts rolling over them. In an open office

that uses cubicles, where you can run the cables along the base of partitions,

an open hub with direct wiring can be reasonably practical. The biggest

drawback is that the cables are out in the open, leaving your network

connections unsecured and subject to possible disconnections, changes, or

damage.

It is generally better to get the hub into a more secure area. A telephone

wiring closet is ideal for this purpose. Cables can be laid from there to the

work area in floors, walls, or ceilings; in a similar way to your telephone

cables. The cables can come out in wall plates, as shown below; the connec-

tion from the wall plate to the computer or printer can be made with a short

length of 4-pair twisted-pair cable.

Cables Running From Hub in a Wiring Closet

Placing the hub in the wiring closet also gives you the opportunity to combine

telephone wiring and network wiring. You can use a cross-connect block to

route telephone and LAN wiring through 4-pair cables to individual desks.

Check restrictions of chosen technology before combining in the same

sheath. Or you can run several nodes worth of wiring in a 25-pair bundle,

and break it out into 4-pair cabling in the work area using a harmonica; this

works well in open office (cubicle) situations. Such an arrangement is

illustrated below. The Twisted-Pair Wiring Diagrams section provides wiring

information for typical 25-pair bundles.

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Designing the Shared 10 Mbps WorkgroupDesigning the Interconnected Workgroup

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Telephone and Network Cabling in the Same Bundle

Designing the Interconnected Workgroup

As your workgroup grows, into a larger workgroup or into several small

workgroups, you will eventually outgrow your hub. Rather than replace your

existing hub, just add another hub to your network and connect the hubs

together with network cabling. You can use any combination of HP

AdvanceStack hubs to get the capacity you want, and the hubs can be located

in a central location or they can be placed in several locations to be near the

individual workgroups. This section describes the connections between the

hubs.

Connecting Hubs at a Single Location

For connecting hubs in one place, such as a stack of hubs in a wiring

closet, Stacking Cable or twisted-pair cable is the preferred solution.

Stacking cable and twisted-pair cable can be a suitable alternative for two

or eight hubs if you expect minimal growth and you dont expect to place

hubs in more than one location.

Twisted-Pair Cable and the MDI Port

If you use twisted-pair cable to connect hubs together, you can use straight-

through cable if you have a port labeled MDI or Cascade. The following

illustration shows two hubs cascaded together.

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Cascading Hubs Using the MDI (Cascade) Port

If there is no port labeled MDI or Cascade, and no wide cable ports for

Stacking Cable marked In and Out, you must use a crossover cable to

make sure that the Transmit lines of one port connect to the Receive lines of

the other port, and vice versa. For example, the Hub-8U, Hub-16U, and Hub-

8TXE have an MDI port that allows you to connect hubs together using a

straight-through twisted-pair cable. The Switching Hubs do not have an

MDI port, but have ports for Stacking Cable marked In and Out.

In fact, the twisted-pair cascading method is limited to a maximum of five

hubs; beyond that it exceeds the IEEE 802.3 standard. In contrast, the

Stacking Cable can connect up to eight 10 Mbps Switching Hubs.

If you want to cascade more than 4 hubs together, use the BNC port and thin

coaxial cable to stack up to 32 hubs.

Standard twisted-pair cableMaximum length: 100 metersCascade up to 4 hubs

MDI port

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Stacking Cable

The Switching Hubs use a fat cable to make hub to hub connections. By using

this cable, all of the hubs stacked together count as 1 repeater hop.

The reason for using Stacking Cable rather than thin cable or cascading

between hubs, is that the IEEE 802.3 standard limits the number of repeaters

(hubs) and cable segments in the path between any two nodes in a collision

domain (that is, within the scope of the uncomplicated networks we are

discussing here). In general, it is best to minimize the number of hubs and

cables segments in the path. This will optimize the performance of a given

network topology, and also allow the greatest possibility for growth in the

network.

The complexity of the path in a stack will become a significant factor when

you need to connect stacks in multiple locations. This is considered

cascading. Because the network will operate erratically (at best) if it doesnt

adhere to the IEEE 802.3 standard, and it may not work at all. A counter to

check in network management software during this type of erratic behavior

would be late collisions.

Connecting Hubs in Multiple Locations

For connecting hubs in multiple campus or high-rise locations, a fiber-

optic backbone is the preferred solution. Twisted-pair and thin coaxial

backbones can be used, but they dont offer the growth potential and other

advantages that optical fiber offers.

As far as the topology rules are concerned, there is little difference between

fiber-optic, twisted-pair, and thin coaxial backbone; all are allowed by the

IEEE 802.3 standard. The superior characteristics of fiber-optic cabling

cause us to recommend it over the other two types. The cost and distance is

a main consideration of what cable to install.

Stacking Cable

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The following illustration shows schematically the typical connections

between stacks of Switching Hubs using the three different cable types.

Cascading a Fiber Hub to Stacks of Switching Hubs

Cascading Twisted-Pair Hubs

In the topology drawings above we have shown the hubs at the center of the

backbones as though they were in their own separate locations. We show

them in this manner because it is the clearest way to present the topological

information. But you should be aware that in most cases the central hub is

not actually located in a separate wiring closet; it is typically located with

one of the stacks of hubs as shown below:

Fiber-optic hub

Stacking cable

Fiber-optic cable1000 meters 1000 meters

Fiber-optic transceiver

Switching Hubs

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Stacking Switching Hubs with Stacking Cable

The central hub usually connects to that stack through Stacking Cable that

connects the other hubs in the stack, as indicated below.

In addition to these general considerations for making backbone connec-

tions between stacks of hubs in different locations, there are additional

considerations that apply to a few particular situations. These are detailed

in the next few paragraphs.

Stacking Cable

Stacking Cable Twisted-pair cable

MDI/MDI-X Ports

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Stacks in Two Locations

If there are only two locations for stacks of hubs, you can make a fiber-optic

backbone connection of up to 1000 meters without using a fiber-optic

transceiver. Use a fiber-optic transceiver to connect a twisted-pair hub in

each stack to the fiber-optic backbone cable as shown below. (This type of

connection is limited to two stacks of hubs. To connect a third stack would

require a fiber-optic hub.)

Stacks in Three or More Locations

A thin coaxial backbone is effectively limited to a single cable segment with

a maximum length of 185 meters. It is possible to attach two thin coaxial

segments to a central twisted-pair hub (using a built-in BNC connector and

a thin coaxial transceiver), or to use a thin coaxial hub; but such arrange-

ments frequently exceed the maximum allowed topology. See Ethernet

Topology Rules for more details.

Single Hubs in Multiple Locations

If you have multiple locations with single hubs rather than stacks, there are

additional possible backbone configurations (there are no cables for the

stacks). See Ethernet Topology Rules for details.

1000 meters fiber-optic cable

Switching Hubs Stacks

Stacking Cable

Fiber-optic Transceiver

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Designing the Shared 10 Mbps WorkgroupEthernet/802.3 Topology Rules

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Ethernet/802.3 Topology Rules

Rule 1: All cable segments must be linear, with no branches or loops.

Rule 2: At any time, only one path between any two nodes in the network is permitted.

(Among other things, this keeps packets from colliding with themselves.)

Note that it is permissible, however, to have multiple paths as long as no

more than one path is active at any one time. This allows for redundant

connections in which a backup path can be activated and continue the flow

of information when a primary path fails. These types of connections can be

made using the backup links available with HP AdvanceStack hubs, and

using the Spanning Tree Protocol available with certain bridge and switching

products.

Point to Point

Coaxial No Loops

No Branches

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Rule 3: Within any single local area network (Ethernet collision domain) you should have no more than 1024 nodes.

This rule is not explicitly stated in the standards; rather, it is a result of the

back-off algorithm that determines how long nodes should wait before

retransmitting after a collision. Because the back-off algorithm doesnt work

perfectly, it is better to keep the collision domain to less than 500 nodes.

Rule 4: Between any 2 nodes in a network there should be no more than 7 bridges or switches.

This is a recommendation imposed by the Spanning Tree Protocol in IEEE

802.1, and is a useful limit for non-spanning-tree networks as well, because

of the transmission delays introduced by store-and-forward devices such

as bridges and switches.

Rule 5: Cable segment limits are as shown below:

In addition to the maximum cable lengths specified in the table, Hewlett-

Packard offers two ways of extending those maximum lengths in special

situations. You can extend the length of a twisted-pair segment by using

4-pair cable with an HP J2607A Twisted-Pair Transceiver Module or an

HP28685B EtherTwist Transceiver at each end. Both of these transceivers

have a Long Cable option. When enabled, you can use a maximum length of

150 meters with Category 4 cable, or 225 meters with Category 5 cable. For

fiber-optic cable, the maximum length of a cable segment connecting two

HP bridges, switches, or routers can be increased to 2000 meters. This

amounts to an application of the topology guidelines given in the next rule;

from the maximum topology standpoint, you can think of it as a collision

domain containing two full-length fiber-optic segments with the fiber-optic

repeater left out.

Twisted-pair cable

Thin coaxial cable

Thick coaxial cable

Fiber-optic cable

Maximum segment length Cat 3, 4, and 5: 100 m

185 m 500 m 1000 m

Minimum section length none 0.5 m 2.5 m none

Connection interval none none 2.5 m (at markings)

none

Terminators not applicable at each end at each end not applicable

Maximum connections per segment

2 30 100 2

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Rule 6: For a single collision domain, the rules that determine allowable cable topologies are given below.

These rules are based on round-trip collision delay times and interpacket gap

shrinkage.

The IEEE 802.3 standard specifies that 3-repeater and 4-repeater LANs

meeting the criteria in the above table for the worst-case path between any

two nodes are valid. (Note that a hub is a repeater.) In addition, Hewlett-

Packard has derived criteria for 5-repeater LANs that meet the calculated

maximum topology requirements; these criteria are also listed below.

Constraints on Prequalified Maximum Topologies

For example, the original maximum topology specified by IEEE 802.3 looked

like the following figure. It was specified at a time when coaxial cable was

the dominant cable type. (It is, of course, still valid.)

Source Max. # of repeaters

Max. # of segments

Limitations

IEEE 802.3 3 4 Fiber-optic segments may be up to 1000 meters each, up to a maximum total of 2000 meters in the topology.

IEEE 802.3 4 5 No more than 3 segments may be coaxial segments.

HP 5 6 Fiber-optic segments may be up to 500 meters each.

No segments may be thick coaxial segments.

No more than 2 segments may be thin coaxial segments.

No more than 2 segments may be fiber-optic segments.

Total length of all AUI cables in the path may not exceed 50 meters.

If the total length of thin coaxial segments exceeds 20 meters, fiber-optic segments are limited to 750 meters each; otherwise, fiber-optic segments may be 1000 meters each.

In all cases, these topologies take into account the delays for the maximum possible number of transceivers that may be attached to repeaters and nodes.

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Original IEEE 802.3 Standard Topology Using Coaxial Cables

Now that twisted-pair cabling has become more common, the following

topology, with two levels of twisted-pair hubs cascaded from a coaxial

backbone, is perhaps more representative of a 4-repeater/5-segment LAN.

Application of IEEE-Standard Limits to Twisted-Pair LAN

The next three figures show applications of HPs specialized rules for

5-repeater topologies. The topology shown below is similar to the next figure,

except that the coaxial backbone has been replaced with a fiber-optic

backbone (a fiber-optic hub and two fiber-optic cable segments).

Terminator

Fiber-optic cable segment

Coaxial cable segment

Fiber-optic repeater

Hub

Twisted-pair cable

Thin coaxial cable

Twisted-pair cable

Twisted-pair cable Twisted-pair cable

Hub

Hub

Hub

NodeNode

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HPs Extended 5-Repeater LAN with No Coaxial Segments

The topology in the illustration below is appropriate for a fiber-optic back-

bone connecting wiring closets that contain racks of twisted-pair hubs. The

racked hubs are connected by short segments of thin coax. Because the total

length of thin coax is less than 20 meters, the fiber-optic cables in the

backbone can be the full 1000-meter length.

HPs Extended 5-Repeater LAN With Short Coaxial Segments

Note that intermediate hubs in the stack do not figure in the repeater count,

because the signal does not pass through them on the way to the node; the

coaxial cable lets the signal bypass intermediate hubs.

Hub

Twisted-pair cable

Fiber-optic hub

Twisted-pair cable

Twisted-pair cable Twisted-pair cable

Hub

Hub

Hub

NodeNode

Fiber-optic cable

Stack of hubs

Fiber-optic hub

Thin coaxial cable(less than 10 meters each)

Node

Node

Fiber-optic cable(up to 100 meters)

Stack of hubs

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The topology below is similar to the one above, except that long segments

of thin coax allow the twisted-pair hubs to be distributed over a wide area.

Because the total length of thin coax in the path is greater than 20 meters,

the fiber-optic cable segments are limited to a maximum length of 750 meters

each.

HPs Extended 5-Repeater LAN with Long Coaxial Segments

In the illustrations above we have been showing individual worst-case paths.

This tends to make it look as though networks are linear arrangements that

occupy single collision domains. In fact, they tend not to be linear or single

domains at all. The following two figures try to redress these imbalances by

showing a more complex local area network and a larger network composed

of a number of local area networks (collision domains).

Fiber-optic cable(less than 750 meters)

Fiber-optic hub

Thin coaxial cable(more than 10 meters each)

Node

Node

Distributed hubs

Distributed hubs

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More Complex LAN

Larger Network Composed of Several LANs

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3

Designing the Switched Workgroup

This chapter covers the following topics:

■ Selecting an appropriate switch for your network

■ Applying a segment switch

■ Applying a desktop switch

■ Applying a backbone switch

■ When not to apply a switch

■ Differences between a Switching Hub and a Switch

■ Understanding switch technology

■ Why you only need a switch instead of a router

3-1

Designing the Switched Workgroup

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Before selecting a switch for your network, verify that a switch is what your

network needs. The following table shows the definition and purpose of a

hub, switching hub, switch, and router:

Device Description Purpose

Hub A hub is a multiport repeater that repeats any incoming packet to all other ports on the hub. By cascading hubs together, you can or small workgroups with low-intensity applications such as word processing, spreadsheets, and email. Everyone shares the same bandwidth.

A hub is for a small network anticipating little growth.

Switching Hub

A repeater which contains four distinct network segments (as if there were four hubs in one device). Through software, any of the ports on the hub can be moved to any of the four segments at any time. This allows for a maximum capacity of 40 Mbps in a single hub or stack of hubs.

A Switching Hub is for a medium-sized network anticipating growth and uses bandwidth-hungry applications. A Switching Hub is less expensive than a switch.

Switch* A very fast, low-latency, mulitport bridge that is used to segment local area networks. Switches also increase cross-segment communication paths and multiple parallel conversations and provide communication across technologies. To determine the bandwidth of a switch, multiple the number of ports by the speed (e.g., 8 ports x 10 Mbps is 80 Mbps bandwidth).

A switch is also for a medium or large-sized network but can also accommodate a large-sized network. Some switches such as the Switch 2000 and Switch 800T include these router features: automatic broadcast control and automatic multicast control.

Router A router is an internetworking device that selects the best path for data traffic as well as simply connect networks. A router has the highest latency of all of these devices because it needs to reach each frame and determine where to send each frame.

Routers are for connecting heterogeneous networks, building firewalls to protect your intranet, and implementing WAN connectivity for remote users.

* Remember that a network can have up to a maximum of seven switches between end nodes. More than seven switches violates IEEE 802.1d Spanning Tree Protocol.

3-2

Designing the Switched WorkgroupSelecting An Appropriate Switch for Your Network

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Selecting An Appropriate Switch for Your Network

When you are selecting a switch for your network, you need to select either

a desktop switch (also called workgroup switch) or a segment switch. A

desktop switch is a switch that directly connects nodes. A segment switch

is used to describe both 10 Mbps workgroup switches and 100 Mbps inter-

connect (backbone) switches that are used to interconnect hubs and desktop

switches. The following table lists the features of both types:

Features Workgroup/Desktop Switch Segment Switch

Typical use Economical desktop switch with fixed configuration for end-node connections. Designed for standalone networks or distributed workgroups in a larger network.

Modular, high-performance switch for interconnecting workgroups in mid- to large-size networks. Provides a choice in port density, technology, and media, for a fully customized solution.

Topology end user -> switch end user -> hub -> switch

or

switch to switch

Number of ports 8, 16, or 24 Switch 2000: Varies. Six bays to hold up to 24 ports of 10Base-T and 12 ports of 100 Mbps. The number of ports depends on which modules are installed: 10Base-T, 100VG, Fast Ethernet, ATM, FDDI, or 10Base-FL.

Switch 800T: 8

Switches to Choose From

Switch 208, 224 (100T)Switch 200 (100VG)

Switch 2000, Switch 208, Switch 800T

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Applying a Segment Switch

The following illustration shows the application of the Switch 2000 or 800T

to the sample network. Simultaneous communication can occur between any

of the clients and any of the servers. In this illustration only six of the switchs

ports are being used, resulting in the possibility of six simultaneous 10-Mbps

communications, for an aggregate bandwidth of 600 Mbps. It is optimal to

attach the servers to these high-speed ports.

You should monitor all segments attached to the switch for their traffic levels.

You would ideally like to know which clients talk with which servers most

of the time, so clients that talk to common servers can be grouped together

in a LAN.

Applying a Desktop Switch

With the Switch 208, 224, you can place this switch in a 100Base-T environ-

ment. If your users already have either 100Base-T LAN adapters in their PCs

or they have 10/100T LAN adapters, you just swap out the hub in place of the

Switch 208, 224. Use the extra hub for a new workgroup with low traffic. The

following illustration shows the HP AdvanceStack Switch 200.

Ethernet Hub

Ethernet Hub

Ethernet Hub

Server Server Server

Switch 2000 or 800T

10-Mbps or 100-Mbps connections to servers

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Example of a 100VG Desktop Switch

Example of a 100Base-T Workgroup Switching

High-Performance PCs

Sixteen 10Base-T Ports

HP AdvanceStack Switch 200

100VG Port

HP AdvanceStack Switch 208/224

100Base-T Port

Sixteen 10Base-T Ports

3-5

Designing the Switched WorkgroupBackbone Switching

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Backbone Switching

The following illustration shows how to use the Switch 2000 as a backbone

switch for an FDDI network.

3-6

Designing the Switched WorkgroupWhen Not To Apply a Switch

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When Not To Apply a Switch

Note that there are some situations in which the switch will not improve the

network performance. If there is heavy traffic destined for a single server, as

shown below, there is no benefit to adding a switch.

When Not to Add a Switch

There are two alternatives:

■ Add a second server, or

■ Put a 10/100 or 100 Mbps LAN adapter in the server and connect to a 100

Mbps port on the switch.

Server

Hub

Hub

Hub

Segment Switch

3-7

Designing the Switched WorkgroupDifferences Between a Switching Hub and a Switch

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Differences Between a Switching Hub and a Switch

A switching hub is a hub with up to 4 segments per stack. To increase

bandwidth for each segment, you can move ports from one segment to

another. This is called port switching. In contrast to a switch, each port on

a switch has its own segment.

The HP AdvanceStack Switching Hubs are multiport repeaters that conform

to the IEEE 802.3 repeater specification. Data signals coming into the hub

from any of its ports are automatically regenerated and transmitted to all

other network ports on the same segment in the hub stack. The hub regen-

erates the data without interpreting the contents, so it can be used in either

IEEE 802.3 or Ethernet networks and with any upper-level protocol.

Each switching hub starts out as a simple shared 10Base-T hub. When you

add the HP J3210A AdvanceStack Management Pack, you get a multisegment

architecture. Each hub can be partitioned into four fully managed LAN

segments for a total of four segments per pack. Each segment is an indepen-

dent 10 Mbps collision domain shared by fewer users and network devices.

For even more flexibility, place any port on the hub onto any segment using

drag-and-drop color-coded software (included in management pack).

Segments as small as one port are possible, allowing you to optimize work-

group performance based on user requirements. The result is a new level of

scalability and flexibility not previously available in stackable 10Base-T

hubs.

On a switch, each port can automatically talk to the other ports. With the

Switching Hubs, you need to add the HP J3212A Hub 10Base-T Switching

Module or an external switch to connect the segments together. An auto-

configuration feature in the switch module automatically assigns ports

across segments for better performance. Push a load-balancing button in

HP AdvanceStack Assistant software to fine-tune performance even more.

3-8

Designing the Switched WorkgroupUnderstanding Switching Technology

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Understanding Switching Technology

Switches use different technologies to store and forward packets. The

technologies are:

■ shared bus: HP Switch 2000

■ shared memory: HP Switch 200

Shared Bus

Shared bus switches use a high-speed backplane to interconnect switch

ports. Shared bus architectures are frequently used to build modular

switches that can scale to high port densities and interconnect multiple LAN

technologies such as 100VG-AnyLAN, FDDI, 100Base-T, and ATM. For

example, the HP AdvanceStack Switch 2000 uses a shared bus architecture

as shown below:

3-9

Designing the Switched WorkgroupUnderstanding Switching Technology

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Shared Memory

Shared memory architectures are very common for low-cost, small scale

switches and have the advantage of easily accommodating mixed LAN types

and speeds within a single switch. The following illustration shows shared

memory:

Switch memory (used for buffers, address tables, etc.) can be allocated in a

number of different ways such as:

■ Pooled memory: allocates memory as needed from a common pool of

memory shared by all ports within the switch.

■ Dedicated shared memory: allocates a fixed amount of memory from a

common pool of memory to be shared by a single pair of I/O ports.

■ Distributed memory: each port has its own dedicated, fixed size memory

and the switch also has central memory for shared operations such as

global address tables (usually a more costly solution).

For example, the HP AdvanceStack Switch 200 uses a shared memory

architecture. It has a 1.6 Mbytes memory pool.

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Designing the Switched WorkgroupWhy You Only Need a Switch Instead of a Router

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Why You Only Need a Switch Instead of a Router

HP offers two switches that incorporate features of a router. This feature is

called Layer 3 Switching. Layer 3 Switching decreases the cost and

complexity of building, growing, and maintaining networks by merging the

control of a router with the performance, simplicity and low cost of a switch.

Layer 3 Switching does the following:

■ stabilizes traffic by isolating network prob

Documents

Designing HP AdvanceStack Networkswhp-hou4.cold.extweb.hp.com/pub/networking/software/59670820.pdfWhenever cable is installed, plan for future expansion. Keep in mind that cable itself