Cabletron Systems bridges, switches User Manual

Cabletron Systems

Networking Guide

Workgroup Solutions

Notice

Cabletron Systems reserves the right to make changes in speciﬁcations and other information contained in this document without prior notice. The reader should in all cases consult Cabletron Systems to determine whether any such changes have been made.

The hardware, ﬁrmware, or software described in this manual is subject to change without notice.

IN NO EVENT SHALL CABLETRON SYSTEMS BE LIABLE FOR ANY INCIDENTAL, INDIRECT, SPECIAL, OR CONSEQUENTIAL DAMAGES WHATSOEVER (INCLUDING BUT NOT LIMITED TO LOST PROFITS) ARISING OUT OF OR RELATED TO THIS MANUAL OR THE INFORMATION CONTAINED IN IT, EVEN IF CABLETRON SYSTEMS HAS BEEN ADVISED OF, KNOWN, OR SHOULD HAVE KNOWN, THE POSSIBILITY OF SUCH DAMAGES.

Printed in the United States of America.

Order Number: 9032094 January 1997

Cabletron Systems, Inc. P.O. Box 5005 Rochester, NH 03866-5005

Cabletron Systems , SPECTRUM , BRIM , FNB , LANVIEW , Multi Media Access Center , are

registered trademarks, and Bridge/Router Interface Module , BRIM-A6 , BRIM-A6DP , BRIM-E6 ,

BRIM-E100 , BRIM-F6 , BRIM-W6 , EPIM , EPIM-A , EPIM-C , EPIM-F1 , EPIM-F2 , EPIM-F3 , EPIM-T , EPIM-X , APIM , APIM-11 , APIM-21 , APIM-22 , APIM-29 , APIM-67 , FPIM , FPIM-00 , FPIM-01 , FPIM-02 , FPIM-04 , FPIM-05 , FPIM-07 , TPIM , TPIM-F2 , TPIM-F3 , TPIM-T1 , TPIM-T2 , TPIM-T4 , WPIM , WPIM-T1 , WPIM-DDS , WPIM-E1 , WPIM-SY , MicroMMAC , MMAC , MMAC-Plus , SEH , SEHI , STH , STHI , FN10 , FN100 , MR9T , MR9T-C , MR9T-E , ESX-1320 , ESX-1380 , NBR-220 , NBR-420 , NBR-620 , SEH100TX , SEHI100-TX , SPECTRUM Element Manager , SPECTRUM for Open Systems ,

are trademarks of Cabletron Systems, Inc.

All other product names mentioned in this manual may be trademarks or registered trademarks of their respective companies.



Notice

Chapter 1 Introduction

Using This Guide.........................................................................................................................1-1

Document Organization ............................................................................................................. 1-2

Document Conventions..............................................................................................................1-3

Warnings and Notiﬁcations ................................................................................................1-3

Formats ..................................................................................................................................1-3

Additional Assistance .................................................................................................................1-3

Related Documentation .............................................................................................................. 1-4

Chapter 2 Review of Networking

Ethernet.........................................................................................................................................2-2

Fast Ethernet................................................................................................................................. 2-3

Token Ring....................................................................................................................................2-5

Chapter 3 The Workgroup Approach

Standalones................................................................................................................................... 3-1

Standalones, the Original Networking Devices............................................................... 3-2

Management of Standalones...............................................................................................3-3

Limitations of Standalones.................................................................................................. 3-3

Stackables...................................................................................................................................... 3-4

How Stacks Work .................................................................................................................3-5

Intelligence in the Stack.......................................................................................................3-6

Internetworking for Stacks.................................................................................................. 3-6

Limitations of Stacks............................................................................................................3-7

Chapter 4 PIMs and BRIMs

Port Interface Modules................................................................................................................4-1

Types of PIMs........................................................................................................................ 4-2

Bridge/Router Interface Modules............................................................................................. 4-8

Types of BRIMs.....................................................................................................................4-8

iii

Contents

Chapter 5 Network Design

The Role of the Workgroup ........................................................................................................5-2

Workgroup Establishment Criteria....................................................................................5-3

Selecting Workgroup Technologies....................................................................................5-9

Creating a Manageable Plan.....................................................................................................5-10

Logical Layout.....................................................................................................................5-10

Fault Aversion .....................................................................................................................5-12

Network Maps and Record Keeping ...............................................................................5-14

Network Expandability.............................................................................................................5-15

The Workgroup as the Network..............................................................................................5-16

The Workgroup in the Larger Network..................................................................................5-16

What Is a Backbone?...........................................................................................................5-17

Methods of Conﬁguring Backbones ................................................................................5-17

Choosing Backbone Technologies....................................................................................5-21

Chapter 6 Ethernet

Ethernet Workgroup Devices.....................................................................................................6-2

Shared Devices......................................................................................................................6-2

Switched Devices..................................................................................................................6-4

Ethernet Workgroup Design ......................................................................................................6-5

The Home Ofﬁce...................................................................................................................6-5

The Small Ofﬁce..................................................................................................................6-11

The Remote Ofﬁce ..............................................................................................................6-16

The High-End Department ...............................................................................................6-19

Permutations .......................................................................................................................6-24

Chapter 7 Fast Ethernet

Fast Ethernet Workgroup Devices.............................................................................................7-1

Shared Devices......................................................................................................................7-1

Switched Devices..................................................................................................................7-2

Fast Ethernet Workgroup Design..............................................................................................7-3

Small Ofﬁces..........................................................................................................................7-3

High-End Department .........................................................................................................7-6

Fast Ethernet as a Backbone................................................................................................7-9

Chapter 8 Token Ring

Token Ring Workgroup Devices................................................................................................8-1

Shared Devices......................................................................................................................8-1

Token Ring Workgroup Design .................................................................................................8-3

Small Ofﬁce............................................................................................................................8-3

Appendix A Charts and Tables

Workgroup Design Tables.........................................................................................................A-1

Ethernet.................................................................................................................................A-1

Fast Ethernet.........................................................................................................................A-3

Token Ring............................................................................................................................A-4

PIMs and BRIMs..................................................................................................................A-5

Networking Standards and Limitations..................................................................................A-8

Ethernet.................................................................................................................................A-8

Fast Ethernet.........................................................................................................................A-9

Token Ring..........................................................................................................................A-10

FDDI ....................................................................................................................................A-12

Contents

Introduction

Using This Guide

The Cabletron Systems Networking Guide - Workgroup Solutions is intended to provide much of the information necessary to allow Network Managers to design and evaluate workgroup networks using the Cabletron Systems family of standalone and stackable networking products. This guide also provides the methods for associating these workgroups into larger networks or incorporating them into existing facility networks.

Chapter 1

This document was written with the assumption that the reader has some familiarity with four networking technologies; Ethernet, Fast Ethernet, Token Ring, and FDDI. If you are unfamiliar with these technologies, Cabletron Systems produces instructional and reference materials that may be of assistance in learning these networking technologies. The available instructional materials are referred to in Related Documentation , later in this chapter. For those already familiar with the Ethernet, Fast Ethernet, and Token Ring technologies, a brief refresher in the main design-speciﬁc aspects of these technologies is provided in later chapters.

NOTE

This document assumes that the reader has read the

Systems Networking Guide - MMAC-FNB Solutions

document is available on the Cabletron Systems Hardware Manuals CD-ROM. If you are unable to locate a copy of that document, you may also order a printed version of any document listed above from Cabletron Systems.

Cabletron

. The

1-1

Introduction

Document Organization

The following summarizes the organization of this manual:

Chapter 1, Introduction , provides basic information about this document, including the organization and format of the document.

Chapter 2, Review of Networking , describes the important design restrictions and characteristics of three basic networking technologies.

Chapter 3, The Workgroup Approach , explains the history and product philosophy behind standalone and stackable workgroup networking devices.

Chapter 4, PIMs and BRIMs , details the operation and use of Cabletron Systems’ various speciality interface modules.

Chapter 5, Network Design , covers the information and decisions involved in the identiﬁcation of networking needs and formation of solutions which meet those needs.

Chapter 6, Ethernet , explains and illustrates the network design process involved in creating Ethernet workgroups.

Chapter 7, Fast Ethernet , provides information and examples that show the design issues that must be dealt with when conﬁguring a Fast Ethernet network.

Chapter 8, Token Ring , supplies design and conﬁguration information for Token Ring workgroup solutions.

Appendix A, Charts and Tables , provides a centralized source for the design tables found throughout this document, and useful information relating to the networking technologies that are discussed.

1-2 Document Organization

Document Conventions

Warnings and Notiﬁcations

Introduction

NOTE

Note symbol. Calls the reader’s attention to any item of

information that may be of special importance.

Formats

References to chapters or sections within this document are printed in boldface type.

References to other Cabletron Systems publications or documents are printed in

italic type.

Additional Assistance

The design of a network is a complex and highly specialized process. Due to the different nature of each and every cabling installation and the special problems and concerns raised by any facility, there may be aspects of network design that are not covered in this guide.

If you have doubts about your network design, or if you require installation personnel to perform the actual installation of hardware and cabling, Cabletron Systems maintains a staff of network design personnel and highly-trained cabling and hardware installation technicians. The services of the Networking Services group are available to customers at any time. If you are interested in obtaining design assistance or a network installation plan from the Networking Services group, contact your Cabletron Systems Sales Representative.

In addition to the availability of Networking Services, the Cabletron Systems Technical Support department is available to answer customer questions regarding existing Cabletron Systems networks or planned expansion issues. Contact Cabletron Systems at (603) 332-9400 to reach the Technical Support department with any speciﬁc product-related questions you may have.

Document Conventions 1-3

Introduction

Review of Networking

This chapter discusses the deﬁning characteristics of three major Local Area Network (LAN) technologies.

Before discussing the selection of networking hardware for workgroup design, an understanding of the major standardized networking technologies available for these designs is necessary. This chapter provides a brief review of the three major networking technologies that are to be treated in this document: Ethernet, Fast Ethernet, and Token Ring.

This section is intended to be a review of the most important aspects of these technologies, and is not expected to stand alone. For more detailed information, Cabletron Systems publishes a series of other documents that treat these technologies in greater detail. For introductory information, the Cabletron Systems Networking Guide - MMAC-FNB Solutions manual provides extensive training information in the basics of these technologies. Further technical detail is available in the Cabletron Systems Technology Overview Guides. A list of associated publications, including these titles, is supplied in the Related Documentation section of Chapter 1.

2-1

Review of Networking

Ethernet

Ethernet is a local area networking technology that was initially developed in the 1970s by the Xerox Corporation. It is based on the principles of workstations being responsible for their own transmissions and operation. It is sometimes referred to as 802.3 networking, in reference to the number of the IEEE standards body which subsumes all Ethernet operations.

Ethernet networks provide an operating bandwidth of 10 megabits per second (Mbps). Bandwidth is a networking term which describes the operating speed of a technology. In the case of Ethernet, a perfectly operating, theoretical Ethernet network, can move 10,000,000 bits of data each second between two stations on the network.

Ethernet is a Carrier Sense Multiple Access/Collision Detection (CSMA/CD) LAN technology. Stations on an Ethernet LAN can access the network at any time. Before sending data, Ethernet stations “listen” to the network to see if it is already in use. If so, the station wishing to transmit waits and examines the network again later. If the network is not in use, the station transmits. A collision occurs when two stations listen for network trafﬁc, “hear” none, then transmit simultaneously. In this case, both transmissions are damaged and the stations, sensing this collision, must retransmit at some later time. Backoff algorithms determine when the colliding stations retransmit.

Ethernet is a broadcast network. In other words, all stations see all frames (collections of data), regardless of if they are an intended destination. Each station must examine received frames to determine if it is the destination. If so, the frame is passed to a higher protocol layer for appropriate processing.

Ethernet transmits data frames over a physical medium of coaxial, ﬁber optic, or twisted pair cable. The coaxial and ﬁber optic cable typically represents the backbone of an Ethernet LAN, while twisted pair is used as a low cost connection from the backbone to the desktop.

Ethernet LANs have the following media restrictions in order to adhere to IEEE

802.3 standards:

• Bus Length: The maximum bus length for an Ethernet LAN for all media types are as follows:

- 500 m for 10BASE5 coaxial cable

- 185 m for 10BASE2 coaxial cable

- 2,000 m for multi mode ﬁber optic (10BASE-F) cable

(5,000 m for single mode)

- 100 m for twisted pair (10BASE-T) cable.

NOTE

These media lengths are not precise values. Actual maximum cable lengths are strongly dependent on the physical cable characteristics.

2-2 Ethernet

Review of Networking

• AUI Length: The maximum Attachment Unit Interface (AUI) cable length is

50 m for connections from a transceiver to an Ethernet device. The 50 m distance is the allowable maximum for standard AUI, while a maximum length of 16.5 m has been set for ofﬁce AUI.

• Number of Stations per Network: IEEE standards specify that the maximum

allowable number of stations per un-bridged network is 1,024, regardless of media type. The 10BASE5 networks are allowed 100 taps per segment, while 10BASE2 networks are allowed 30 taps per segment with a maximum of 64 devices per tap each. (Fiber optic and twisted pair cable are point-to-point media which do not allow taps or branches).

NOTE

• Maximum Signal Path: The maximum allowable signal path is 4 repeaters, 5

There are other limitations involved in the IEEE 802.3 standard and the various cable speciﬁcations, which are more detailed and complex. These limitations are covered in detail in the Cabletron Systems Cabling Guide and the Cabletron Systems Ethernet Technology Overview.

Fast Ethernet

Fast Ethernet is a networking technology that grew out of the popular Ethernet technology described above. Fast Ethernet uses the same CSMA/CD media access method and basic network operation. The main differences between Ethernet and Fast Ethernet are the available bandwidth and media limitations.

Fast Ethernet increases the available bandwidth of a single network to 100 Mbps, ten times faster than normal Ethernet. This increase in transmission speed, however, comes at a cost to the ﬂexibility of the network. By increasing the speed of transmission by a factor of 10, the required characteristics of Ethernet links were likewise reduced.

If it becomes necessary to extend the network beyond the IEEE limit of 1,024 devices, a bridge can be used to connect another full speciﬁcation Ethernet network.

segments (with at least 2 segments being unpopulated Inter-Repeater Links), and 7 bridges for all media types.

Fast Ethernet networks only support UTP and multimode ﬁber optics as standard transmission media. The two standards for these media are 100BASE-TX for Category 5 UTP, and 100BASE-FX for multimode ﬁber optics.

The IEEE 802.3u standard deﬁnes two different types of Fast Ethernet repeaters: Classes I and II. All Cabletron Systems Fast Ethernet products discussed in this document are Class I repeaters. A Fast Ethernet network designed with Class I repeaters allows a signal path from one station, through a Fast Ethernet link, to a Class I repeater, through another Fast Ethernet link, to a receiving station. No other Class I repeaters may be placed in this signal path.

Fast Ethernet 2-3

Review of Networking

This signal path, two end stations and the repeaters between them, is called the network radius. Unlike standard Ethernet networks, Fast Ethernet networks have a maximum network radius that may restrict the lengths of station cabling to less than the maximum allowable distances for single links. Typically, network radius calculations are only important when mixing 100BASE-TX and 100BASE-FX networks. The maximum network radius limits are provided later in this section.

As the imposition of a maximum network radius on mixed 100BASE-TX and 100BASE-FX networks severely limits the design options of Fast Ethernet networks, Fast Ethernet devices may incorporate buffered uplinks. A buffered uplink is a Fast Ethernet port on a repeater which allows the repeater to ignore the collision domain of the uplink. This allows the buffered uplink to be a maximum-length segment even in mixed media environments.

NOTE

connection only for purposes of determining cable length.

Fast Ethernet LANs must meet the following media and network restrictions in order to adhere to IEEE standards:

• Cabling Quality: All 100BASE-TX links require UTP cabling meeting or exceeding the Telecommunications Industry Association (TIA) Category 5 speciﬁcation. The link must be compliant from end to end, including all connectors and patch panels.

• Link Length: No single link in the Fast Ethernet network may exceed the limitations given below, including jumper cables and patch cables:

- 100 m for 100BASE-TX networks

- 400 m for 100BASE-FX networks

• Network Radius: Network radius is the distance traveled from the station with the longest media link to the Fast Ethernet repeater and out to the station with the second-longest media link. In order to meet IEEE standards, Fast Ethernet networks constructed with Class I repeaters must not exceed the following maximum network radii:

- 200 m for homogenous 100BASE-TX networks

- 260 m for mixed 100BASE-TX and 100BASE-FX networks

- 272 m for homogenous 100BASE-FX networks

A buffered uplink is considered a bridged or switched

NOTE

maximums will lead to poor network performance.

2-4 Fast Ethernet

These media lengths are ﬁxed values. Deviation from these

Review of Networking

Fast Ethernet networks designed using Class II repeaters may not exceed the following maximum network radii:

- 200 m for homogenous 100BASE-TX networks

- 320 m for homogenous 100BASE-FX networks

• Buffered Uplinks: If a buffered uplink is used to make a connection, the

allowable length of the buffered uplink itself does not change, but the maximum network radius calculations will change. Assuming that the buffered uplink is the longest link in the repeater radius, the maximum allowable network radius will change to the values given below:

- 500 m for mixed 100BASE-TX and buffered 100BASE-FX uplink

- 800 m for homogenous 100BASE-FX networks

• Number of Stations per Network: IEEE standards specify that the maximum

allowable number of stations per single-segment network is 1,024, regardless of media type.

Token Ring

NOTE

• Maximum Signal Path: The maximum allowable signal path for a Fast

Token Ring network operation is based on the principle that the operation of the entire network determines when a station may transmit and when it will receive. Stations monitor one another, and one station acts as an overall ring monitor, keeping track of important statistics. Token Ring stations are connected to one another in a predetermined order, and network frames pass from one station to the next, following that order. A specialized network frame, called a token, is passed around the ring at regular intervals. The transmission of the token helps establish some of the operational statistics for the network, and receiving it allows a station to transmit.

The Token Ring technology is designed to operate at either of two speeds: 4 Mbps or 16 Mbps. This speed selection is made when the network is installed, and the speed must apply equally to all stations (you may not split a ring into groups of 16 Mbps and 4 Mbps stations).

If it becomes necessary to extend the network beyond the IEEE limit of 1,024 devices, a bridge or switch can be used to connect another full speciﬁcation Fast Ethernet network.

Ethernet network is one Class I repeater, two segments for all media types. The use of bridges, switches, or routers can allow the creation of larger networks.

Token Ring 2-5

Review of Networking

The transmission and reception of the token determines the amount of time that any station will have to transmit data during its turn, offering a measure of predictability not available in Ethernet or Fast Ethernet. This predictability also allows Token Ring networks to incorporate special error-detection and correction functions which can locate and correct network problems without human intervention.

The predictability of the Token Ring technology also leads to a number of limitations on the number of stations that can be connected to a network and the maximum cable lengths that a signal may be passed across. Since the stations are conﬁgured to expect reception of the token at certain increments of time, exceeding the maximum number of stations or the maximum length of cabling between stations can delay the token’s progress, causing the Token Ring network to suffer errors and poor performance.

In order to stretch the capabilities of a Token Ring network, various technologies are available which extend the distance a signal can travel before suffering degradation or loss of signal timing due to cable lengths or high station count.

One method of increasing the resilience of a Token Ring network is the incorporation of what is called “active circuitry.” Token Ring station ports with this active circuitry regenerate, strengthen, and re-time any Token Ring signal received by or transmitted from that interface.

NOTE

products incorporate active circuitry on all ports.

Token Ring devices can also extend the distance that a ring can cover through the use of Ring-In/Ring-Out, or RI/RO cables. RI/RO cables are designed only to make connections between Token Ring concentrator devices, and extend the area that a ring can support by allowing long-distance links to other Token Ring devices.

RI/RO connections are not bridge or switch interfaces. They do

All Cabletron Systems stackable and standalone Token Ring

NOTE

not create a new Token Ring network.

2-6 Token Ring

Review of Networking

Token Ring networks can use a variety of physical cabling, including Unshielded Twisted Pair (UTP), Shielded Twisted Pair (STP), or ﬁber optic cabling. The characteristics of the various cables can directly impact the operational limitations of a Token Ring network which uses a particular media.

• Lobe Cable Lengths for 4 Mbps Token Rings: The operation of a 4 Mbps Token

Ring network imposes some relatively generous limitations on the maximum length of any station cable (also called a lobe cable) connected to an active port in the network as shown in the following list:

- IBM Types 1, 2 STP: 300 m

- IBM Types 6, 9 STP: 200 m

- Category 5 UTP: 250 m

- Categories 3, 4 UTP: 200 m

- Multimode Fiber Optics: 2000 m

- Single Mode Fiber Optics: 2000 m

• Lobe Cable Lengths for 16 Mbps Token Rings: 16 Mbps Token Ring networks

also impose limitations on the maximum length of any media connected to an active port as shown in the following list:

- IBM Types 1, 2 STP: 150 m

- IBM Types 6, 9 STP: 100 m

- Category 5 UTP: 120 m

- Categories 3, 4 UTP: 100 m

- Multimode Fiber Optics: 2000 m

- Single Mode Fiber Optics: 2000 m

• RI/RO Cable Lengths for 4 Mbps Token Rings: 4 Mbps Token Ring networks

also require that Ring-In/Ring-Out (RI/RO) connections be no longer than a certain amount. This amount is dependent upon the media being used for the RI/RO connection as shown in the following list:

- IBM Types 1, 2 STP: 770 m

- Category 5 UTP: 250 m

- Categories 3, 4 UTP: 200 m

- Multimode Fiber Optics: 2000 m

- Single Mode Fiber Optics: 2000 m

• RI/RO Cable Lengths for 16 Mbps Token Rings: 16 Mbps Token Ring networks

also require that Ring-In/Ring-Out (RI/RO) connections not exceed the lengths given below:

- IBM Types 1, 2 STP: 346 m

- Category 5 UTP: 120 m

- Categories 3, 4 UTP: 100 m

- Multimode Fiber Optics: 2000 m

- Single Mode Fiber Optics: 2000 m

Token Ring 2-7

Review of Networking

• Number of Stations Per 4 Mbps Token Ring: In the same fashion as the limits imposed on cable lengths due to the operating speed of the network and type of cabling used, there are limitations on the number of stations that may be connected to a single ring using active circuitry. If these numbers are exceeded, a bridge, switch, or other segmentation device must be used to break the ring into two or more smaller rings as detailed in the list below:

- IBM Types 1, 2 STP: 250 stations

- IBM Types 6, 9 STP: 250 stations

- Category 5 UTP: 150 stations

- Categories 3, 4 UTP: 150 stations

- Multimode Fiber Optics: 250 stations

- Single Mode Fiber Optics: 250 stations

• Number of Stations Per 16 Mbps Token Ring: The limitation on the number of stations in the Token Ring also applies to 16 Mbps networks. In one case, the number of stations supported by these faster Token Ring networks is signiﬁcantly lower than the number supported by the 4 Mbps rings.

- IBM Types 1, 2 STP: 250 stations

- IBM Types 6, 9 STP: 136 stations

- Category 5 UTP: 150 stations

- Categories 3, 4 UTP: 150 stations

- Multimode Fiber Optics: 250 stations

- Single Mode Fiber Optics: 250 stations

The Token Ring limitations that are described above are summarized for your ease of reference in Table 2-1. This table is also repeated in Appendix A, Charts and Tables.

Table 2-1. Token Ring Maximums

Max Lobe Cable

Length

Media

Cable

Type

Max # of Stations

4 Mbps 16 Mbps 4 Mbps 16 Mbps

STP IBM Types 1, 2 250 250 300 m 150 m

IBM Types 6, 9

250 136 200 m 100 m

UTP Category 5 150 150 250 m 120 m

Categories 3, 4 150 150 200 m 100 m

Fiber Optics Multimode 250 250 2000 m 2000 m

Single Mode 250 250 2000 m 2000 m

a. IBM Type 6 cable is recommended for use as jumper cabling only and should not be used for facility cabling installations.

2-8 Token Ring

Review of Networking

There are other limitations involved in the IEEE 802.5 standard and the various cable speciﬁcations that are more detailed and complex. These limitations are covered in detail in the Cabletron Systems Cabling Guide and the Cabletron Systems Token Ring Technology Overview.

Token Ring 2-9

Review of Networking

2-10 Token Ring

Chapter 3

The W orkgroup Approach

This chapter describes the basic operation and design of stackable and standalone devices and the methods used to meet common networking needs with these devices.

Standalone and stackable networking devices are specialized and important parts of any end-to-end network design strategy. Understanding the design philosophy and product evolution of these products can greatly aid a Network Designer in determining where, and to what extent to implement standalone and stackable devices in a new or existing network.

Standalones

A standalone device is one which, as the name implies, “stands alone” in the network. A standalone device does not rely on any other network device to operate, nor does it provide for the operation of other devices itself. This is a distinct difference from networking devices such as modular networking chassis, which require combinations of discrete modules be plugged into them for their own operation.

3-1

The Workgroup Approach

Standalones, the Original Networking Devices

Standalone devices are the second oldest devices in Local Area Networking, having been developed shortly after transceivers. The basic and most straightforward standalone device is the repeater or concentrator, a device that allows a network signal received on one interface, or port, to be strengthened, regenerated, and sent out another port. Figure 3-1 illustrates the operation of a repeater, receiving a weak signal and transmitting a cleaner, stronger signal.

incoming signal outgoing signal

repeater

Figure 3-1. Repeater Operation

2094n01

These simple, inexpensive devices were designed to expand the limitations and capabilities of early networks, allowing them to grow beyond the limitations imposed by the cabling they were based upon. As time went on, and networks grew in size, the standalone devices began to offer greater control and expandability. The design of multiport repeaters allowed one signal to be sent out several interfaces simultaneously, and the standalone bridge offered the ability to localize network trafﬁc for security and improved performance.

The other most common standalone device in early networks was the standalone bridge. The standalone bridge was commonly a two-port device which performed segmentation functions between two networks. The multiport bridge was eventually followed up by the multiport switch, which made switched connections between several network interfaces.

The use of these standalone devices allowed simple networks to expand beyond the limits of the cabling and the physical constraints of the technologies being used. The standalone networking devices were relatively simple, however, and did not always support the numbers of users that facilities contained.

3-2 Standalones

Management of Standalones

As standalone devices became more complex, the need to control them became greater. The need to have some form of troubleshooting and control process in place for an eight-port repeater is minimal. In a repeated network where more than 200 users are connected to a single repeater, management capabilities are no longer luxuries, they are a necessity. The advent of standalone bridges, which required software conﬁguration and monitoring, marked the introduction of management capabilities to the standalone devices.

While the most basic standalone devices were unable to support any management and control operations, networking hardware vendors such as Cabletron Systems began to incorporate management functions into their devices, making intelligent networking devices. The growth of networks and the control offered by these intelligent devices paved the way for the modular networking chassis, or hub. Standalones could handle the growing size of networks, but not always the growing complexity. The modular chassis allowed facility networks to support far greater numbers of users from a single location than was possible with standalone devices.

The Workgroup Approach

Limitations of Standalones

In time, the networking market broke into facilities that were small enough to use standalone networking devices and facilities that required the control and ﬂexibility of the modular hub. As this trend continued, a gap widened between the low-cost, low-ﬂexibility standalone devices and the more expensive, more ﬂexible modular chassis. Facilities that had opted to use standalone devices were painting themselves into a corner. The standalone devices had no option for adding more users other than expanding the network. There were no options available for adding new networking technologies to the standalone devices, and any upgrade to the capabilities of the network would involve a costly, all-or-nothing replacement of all equipment.

At the same time, the limitations that nobody thought they would reach became very real threats to the continued growth of networks reliant on standalones. That old repeater rule, which Network Managers had been able to get around with clever tricks of physical layout, was looming on the horizon, and user counts continued to climb.

Standalones 3-3

The Workgroup Approach

Stackables

To cope with the limited ﬂexibility and expandability of standalones, the stackable hub, or stackable, was developed. The stackable design allowed a series of devices to act as a single device. With a stackable hub system, ﬁve separate devices could act as a single device. From the point of view of network design, this was a master stroke. A single stack, which operated as one big device, could support as many users as four or ﬁve standalone repeaters. To the network, the separate devices appeared to be a single device, as shown in Figure 3-2.

physical organization logical organization

2094n02

Figure 3-2. Physical and Logical Views of Stackables

The stackable has a smaller network footprint than an equivalent number of standalone devices. In effect, the stack fools the network into thinking that the users connected to the stack are in a single repeater or concentrator.

By placing stackables together in a collection called a stack, the available options for user connections at individual workgroup locations grew dramatically. Also, the ability to simply add stackables to the stack in order to accommodate new users gave some measure of an upgrade path to users of stackable devices.

NOTE

Stackables, being less expensive than modular hubs and more ﬂexible and expandable than standalones, helped to ﬁll in the chasm between the high-end and low-end network strategies.

Stackable hubs of diff erent technologies cannot be mixed. Each stack must use a single networking technology. For example, you cannot combine Ethernet and Fast Ethernet stackables in a single stack.

3-4 Stackables

How Stacks Work

Stackable hubs communicate with one another through proprietary interconnection cables. The cables used in Cabletron Systems’ stackable hub solution are called HubSTACK Interconnect Cables. In Ethernet stackable environments, these cables are short, multistrand cables with special, D-shaped connectors that attach to ports on the backs of the stackable hubs, as shown in Figure 3-3. In Token Ring stackable solutions, the interconnect cables are short twisted pair segments that connect each stackable unit directly to the base unit.

REAR VIEW SEHI Managing 4 SEH Non-Intelligent Hubs

SEH

100TX

-22

100BASE-TX HUB WITH LANVIEW®

SEH

100TX

-22

100BASE-TX HUB WITH LANVIEW®

OUT

SEH100TX INTERCONNECT

OUT

SEH100TX INTERCONNECT

The Workgroup Approach

SEH

SEHI

100TX

-22

100BASE-TX HUB WITH LANVIEW®

100TX

-22

100BASE-TX HUB WITH LANVIEW®

100TX

-22

100BASE-TX HUB

The HubSTACK cables handle the communications between stackable devices, including network trafﬁc and management communications. The use of these custom, short cables allows the stack to act as a single repeater or concentrator. In essence, the cables and connectors used to chain the stackable hubs together mimic the operation of the backplane of a modular hub.

OUT

SEH100TX INTERCONNECT

OUT

SEH100TX INTERCONNECT

WITH

LANVIEW®

OUT

SEHI100TX INTERCONNECT

Figure 3-3. HubSTACK Interconnect Cables

HubSTACK Interconnect Cable

2094n03

Stackables 3-5

The Workgroup Approach

HubSTACK Interconnect Cables are connected in a particular sequence, from the OUT port of the ﬁrst device in the stack to the IN port of the next. This arrangement is repeated from device to device as more stackable hubs are incorporated in the stack, as shown in Figure 3-3.

NOTE

If it becomes necessary to disconnect a HubSTACK Interconnect Cable from a device in the stack, disconnect the cable at the OUT port of the previous device in the stack to ensure proper termination of the Interconnect Cable chain.

Intelligence in the Stack

Once stackables became accepted in networks, users demanded management for them. The response from manufacturers was to make intelligent stackable devices. The design of intelligence and management capabilities for the stackable devices followed a path similar to the incorporation of management into modular chassis. Rather than requiring that all the stackables in a stack be intelligent in order for management functions to be performed, stackable intelligence is contained in only one device and is extended to the non-intelligent devices in the stack. Thus, only one intelligent device is needed to manage a full stack, keeping the costs of management down.

The basis of the intelligent stack is that the ﬁrst device in each stack is the only one that requires this management intelligence. This intelligent stackable, or base, provides management services for the rest of the devices in its stack over the same connection that is used for stackable to stackable communications. The management trafﬁc moves across the artiﬁcial backplane that is set up through the interconnect cables.

Internetworking for Stacks

As stackable devices and stacks are easy to design and conﬁgure, and often have a lower cost than modular networking chassis for these small-scale, simplistic network implementations, they are often found in large enterprise networks acting as fringe devices. These devices operate at the frontier areas of the network, where users connect to small shared network segments.

The use of stackable devices in these frontier workgroup environments often necessitates the use of a differing network technology, such as Fiber Distributed Data Interface (FDDI) or Asynchronous Transfer Mode (ATM) to make high-bandwidth connections to the enterprise network backbone or a central campus switch. The basic design of stackable hubs does not allow for the incorporation of different network technologies as does a modular networking chassis such as the Cabletron Systems Multi-Media Access Center, or MMAC.

3-6 Stackables

The Workgroup Approach

Initially, Network Designers wishing to make connections from stacks to backbone technologies would be forced to add an additional standalone device to the network at the workgroup area. The addition of a standalone switch, bridge, or router that supported the technology of the stack and the technology of the backbone would allow for the interconnection, or internetworking, of the stack and the backbone.

To assist Network Designers in creating a ﬂexible and elegant solution to the problem of internetworking for stacks, and to reduce the number of separate devices that had to be shepherded at any facility, Cabletron Systems introduced Bridge/Router Interface Module (BRIM) technology to the stackable and standalone product line.

The BRIM is a specialized module that can be added to any BRIM-capable Cabletron Systems device. The BRIM provides two interfaces: one to the internal network segment of the device that it is placed in, and one to an external network. Several BRIMs are available to support a wide variety of networking technologies. The available BRIMs and their conﬁguration options are detailed in Chapter 4, PIMs and BRIMs.

By incorporating the BRIM technology into a number of standalone and stackable devices, Cabletron Systems makes it easy to use stackable hubs and standalone switches as frontier devices for an enterprise network, or as a small workgroup solution at any location. The availability of Wide Area Network (WAN) technology BRIMs also makes the BRIM-capable stackable devices ideal choices for branch ofﬁce scenarios.

Limitations of Stacks

While stackables are very well suited to a number of network implementations, they have their limitations. As stackables were developed to ﬁll the gap between standalone devices and modular chassis, some networking capabilities are better handled by modular hubs.

Modular chassis allow for the mixing of multiple technologies in a single location much more readily than stackables. If a network implementation requires 43 Ethernet users, 11 Token Ring users, and four FDDI stations, a single modular chassis will support these requirements, while a series of stackable and standalone devices would have to be purchased, installed, and maintained to accommodate the same need.

Stackables 3-7

The Workgroup Approach

In addition, stackable and standalone devices are typically available for only the most common of networking media: UTP and STP. In situations where several users connect to the network with UTP, a few make their connections with ﬁber optics, and there is a handful of existing coaxial cable segments, a solution using stackables would have to provide a series of external transceivers at each location. While not extremely expensive, these external transceivers can become maintenance and design hurdles when troubleshooting or expanding the network. Modules for modular chassis, with support for a wider variety of networking media, are more able to accommodate different existing and future needs.

The design of a modular chassis also allows for the segmentation and interconnection of networks within a single chassis, the incorporation of power redundancy and added fault-tolerance, and a longer path of growth and expansion, both to add new users and incorporate new technologies.

3-8 Stackables

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