Cabletron Systems MMAC-5FNB, MMAC-FNB Networking Manual
Cabletron Systems
Networking Guide
MMAC-FNB™ 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.
Copyright
Printed in the United States of America.
Order Number: 9031706-01 March 1996
Cabletron Systems, Inc.
P.O. Box 5005
Rochester, NH 03866-5005
Cabletron Systems , SPECTRUM , BRIM , DNI , FNB , INA , Integrated Network Architecture ,
LANVIEW , LANVIEW Secure , Multi Media Access Center , MiniMMAC , MicroMMAC , and
TRMM are registered trademarks, and Bridge/Router Interface Modules , CRXMIM , CXRMIM ,
Desktop Network Interface , Distributed LAN Monitoring , Distributed Network Server , DLM ,
EMM-E6 , EMME , EPIM , EPIM-A , EPIM-C , EPIM-F1 , EPIM-F2 , EPIM-F3 , EPIM-T , EPIM-X ,
ESXMIM , ESXMIM-F2 , ETWMIM , FDCMIM-04 , FDCMIM-08 , FDCMIM-24 , FDCMIM-28 ,
FDCMIM-44 , FDCMIM-48 , FDMMIM , FDMMIM-04 , FDMMIM-24, FDMMIM-44, Flexible
Network Bus , FOMIM , FORMIM , HubSTACK , IRBM , IRM , IRM-2 , IRM-3 , Media Interface
Module , MIM , MMAC , MMAC-3 , MMAC-3FNB , MMAC-5 , MMAC-5FNB , MMAC-8 , MMAC8FNB , MMAC-M8FNB , MMAC-Plus , MRX , MRXI , MRXI-24 , Multichannel , NB20E , NB25E , NB30 ,
NB35 , NBR-220/420/620 , RMIM , SecureFast Packet Switching , SFPS , SPECTRUM Element
Manager , SPECTRUM for Open Systems , SPIM-A , SPIM-C , SPIM-F1 , SPIM-F2 , SPIM-T , SPIM-T1 ,
TPMIM , TPMIM-22 , TPMIM-T1 , TPRMIM , TPRMIM-36 , TPT-T , TRBMIM , TRMM-2 , TRMMIM ,
and
1996 by Cabletron Systems, Inc. All rights reserved.
other Cabletron product names are trademarks of Cabletron Systems, Inc.
All other product names mentioned in this document may be trademarks or registered trademarks of
their respective companies.
i
ii
Chapter 1 Introduction
Using This Guide.........................................................................................................................1-1
Organization of Document.........................................................................................................1-1
Conventions of This Document.................................................................................................1-3
Warnings and Notifications ................................................................................................1-3
Formats and Measures.........................................................................................................1-3
Additional Assistance .................................................................................................................1-4
Associated Documentation ........................................................................................................1-4
Contents
Chapter 2 Overview of Networking
Discussion of Networking..........................................................................................................2-1
Why Network?...................................................................................................................... 2-1
What Is a Network?.....................................................................................................................2-3
The Classification of Networks..................................................................................................2-3
Network Topology ...............................................................................................................2-4
Network Technologies.........................................................................................................2-6
Media......................................................................................................................................2-7
Interoperability and Standards Bodies...................................................................................2-13
Interoperability, the Ideal of Networking.......................................................................2-13
Standards and Compliance...............................................................................................2-13
The OSI Model, Basis of Standards.................................................................................. 2-14
Application of the OSI Model........................................................................................... 2-18
Chapter 3 Technology Basics
Ethernet.........................................................................................................................................3-1
Abstract..................................................................................................................................3-1
Theory .................................................................................................................................... 3-2
Operation...............................................................................................................................3-2
Segmentation.........................................................................................................................3-4
Strengths and Weaknesses ..................................................................................................3-6
Special Design Considerations ........................................................................................... 3-8
Token Ring....................................................................................................................................3-9
Abstract..................................................................................................................................3-9
Theory .................................................................................................................................... 3-9
Operation...............................................................................................................................3-9
Segmentation....................................................................................................................... 3-11
Strengths and Weaknesses ................................................................................................3-13
Special Design Considerations ......................................................................................... 3-15
iii
Fiber Distributed Data Interface..............................................................................................3-15
Abstract ................................................................................................................................3-15
Theory ..................................................................................................................................3-15
Operation.............................................................................................................................3-16
Strengths and Weaknesses.................................................................................................3-17
Special Design Considerations .........................................................................................3-18
Chapter 4 Network Design
Workgroup Creation....................................................................................................................4-2
What Is a Workgroup? .........................................................................................................4-2
Workgroup Establishment Criteria....................................................................................4-2
Selecting Workgroup Organization....................................................................................4-7
Selecting Workgroup Technologies..................................................................................4-12
Backbone Planning ....................................................................................................................4-13
What Is a Backbone?...........................................................................................................4-13
Methods of Configuring Backbones ................................................................................4-14
Choosing Backbone Technologies....................................................................................4-17
Creating a Manageable Plan.....................................................................................................4-18
Logical Layout.....................................................................................................................4-19
Fault Aversion .....................................................................................................................4-21
Network Maps and Record Keeping ...............................................................................4-22
Network Expandability.............................................................................................................4-24
Network Migration....................................................................................................................4-24
Designing with the MMAC......................................................................................................4-25
Modular Chassis .................................................................................................................4-25
Reliability and Recovery....................................................................................................4-26
Technology Flexibility........................................................................................................4-27
Power Redundancy ............................................................................................................4-29
Chapter 5 Ethernet
Description....................................................................................................................................5-1
CSMA/CD.............................................................................................................................5-1
Media......................................................................................................................................5-4
Connectivity/Transceivers..................................................................................................5-4
Rules and Regulations .........................................................................................................5-5
Repeating ...............................................................................................................................5-6
Repeaters/Hubs....................................................................................................................5-6
Simple Ethernet Configuration................................................................................................5-10
Design Philosophy..............................................................................................................5-10
Design Example ..................................................................................................................5-10
Segmentation..............................................................................................................................5-15
Bridges..................................................................................................................................5-16
Multichannel Ethernet .......................................................................................................5-21
Segmented Ethernet Configuration.........................................................................................5-23
Design Philosophy..............................................................................................................5-23
Design Example ..................................................................................................................5-24
iv
Segmentation - Special Cases...................................................................................................5-30
Port Assignment .................................................................................................................5-30
Port Assignment Configuration............................................................................................... 5-31
Design Philosophy .............................................................................................................5-31
Design Example..................................................................................................................5-32
Ethernet Switching ....................................................................................................................5-34
Switching Configurations......................................................................................................... 5-35
Permutations.......................................................................................................................5-37
Chapter 6 Token Ring
Description ...................................................................................................................................6-1
Fault Isolation .......................................................................................................................6-4
Fault Recovery ......................................................................................................................6-6
Media......................................................................................................................................6-9
Connectivity/Transceivers................................................................................................6-10
Token Ring Network Rules...............................................................................................6-12
Single Ring Configuration........................................................................................................6-13
Design Philosophy .............................................................................................................6-13
Design Example..................................................................................................................6-13
Extending the Ring (Ring-In/Ring-Out)......................................................................... 6-20
Brief Review of MAUs.......................................................................................................6-21
Segmentation..............................................................................................................................6-22
Multi-Ring Configuration.........................................................................................................6-24
Design Philosophy .............................................................................................................6-24
Design Example..................................................................................................................6-24
Multichannel Token Ring..................................................................................................6-33
Multichannel Token Ring Configuration ...............................................................................6-34
Design Philosophy .............................................................................................................6-34
Design Example..................................................................................................................6-35
Chapter 7 FDDI
Description ...................................................................................................................................7-1
Media......................................................................................................................................7-2
Rings and Devices ................................................................................................................7-3
Concentrators........................................................................................................................7-5
Bridges ...................................................................................................................................7-7
FDDI Backbone Configuration ..................................................................................................7-7
Design Philosophy ...............................................................................................................7-7
Design Example....................................................................................................................7-7
FDDI Workgroup Configuration...............................................................................................7-8
Design Philosophy ...............................................................................................................7-8
Design Example....................................................................................................................7-8
v
Chapter 8 Expansion - Ethernet
Simple Ethernet............................................................................................................................8-1
Adding Stations ....................................................................................................................8-1
Adding Segmentation..........................................................................................................8-3
Incorporating Token Ring....................................................................................................8-5
Incorporating FDDI..............................................................................................................8-6
Segmented Ethernet.....................................................................................................................8-8
Adding Users to One Segment ...........................................................................................8-8
Adding Users to Several Segments....................................................................................8-9
Incorporating Port Assignment..........................................................................................8-9
Incorporating Token Ring....................................................................................................8-9
Incorporating FDDI............................................................................................................8-10
Port Assignment and Virtual LANs........................................................................................8-11
Adding Users to Any Segment.........................................................................................8-11
Incorporating Token Ring..................................................................................................8-11
Incorporating FDDI............................................................................................................8-11
Chapter 9 Expansion - Token Ring
Single Ring....................................................................................................................................9-1
Adding Stations ....................................................................................................................9-1
Adding New Rings...............................................................................................................9-2
Incorporating New Technologies .......................................................................................9-2
Multi-Ring.....................................................................................................................................9-3
Adding Stations to Any Ring..............................................................................................9-3
Incorporating New Technologies .......................................................................................9-4
Port Assignment...........................................................................................................................9-4
Adding Stations to Any Ring..............................................................................................9-4
Incorporating New Technologies .......................................................................................9-5
Chapter 10 Expansion - FDDI
FDDI Workgroups .....................................................................................................................10-1
Adding Single Attached Stations .....................................................................................10-1
Adding Dual Attached Concentrators.............................................................................10-2
Connecting Multiple Rings ...............................................................................................10-3
Chapter 11 Product Descriptions
Chassis.........................................................................................................................................11-2
Ethernet ....................................................................................................................................... 11-5
Token Ring ................................................................................................................................11-16
FDDI...........................................................................................................................................11-25
Miscellaneous/Multiprotocol................................................................................................ 11-31
vi
Appendix A Charts & Tables
Network Design Flowcharts .....................................................................................................A-2
Ethernet Network Design Flowchart................................................................................A-2
ESXMIM Network Design Flowchart...............................................................................A-3
Single Token Ring Network Design Flowchart...............................................................A-4
Segmented Token Ring Network Design Flowchart ......................................................A-5
Multichannel Token Ring Network Design Flowchart ..................................................A-6
FDDI Backbone Network Design Flowchart...................................................................A-7
FDDI Workgroup Network Design...................................................................................A-8
MMAC Design Tables ................................................................................................................A-9
Ethernet Design Tables .......................................................................................................A-9
Token Ring Design Tables ................................................................................................A-13
FDDI Design Tables...........................................................................................................A-16
Networking Standards and Limitations................................................................................A-17
Ethernet...............................................................................................................................A-17
Token Ring..........................................................................................................................A-18
FDDI ....................................................................................................................................A-20
vii
viii
Introduction
Using This Guide
The purpose of this Networking Guide is to provide the customers and strategic
partners of Cabletron Systems with information which allows them to configure
and expand their own networks. As it is impossible to foresee every possible
situation that may arise when a new network must be created or an existing one
expanded, this guide deals with several of the most common networking
situations.
Chapter 1
If you are unfamiliar with the basics of the Ethernet, Token Ring, and Fiber
Distributed Data Interface (FDDI) networking technologies, read the chapters in
order. Pay particular attention to Chapters 3 through 7. These chapters should
provide you with the basic information necessary to generate a relatively
straightforward network design.
If you have experience with the design or operation of Cabletron networking
products, you may wish to refer mainly to the chapters dealing with the
expansion of existing networks, Chapters 8 through 10.
Organization of Document
In the interests of making this document accessible to as many customers of
differing levels of experience as possible, this Networking Guide begins with a
discussion of the various reasons for networking and a short overview of Local
Area Networks (LANs). Following this brief overview, a series of short,
introductory level training documents is provided. These documents provide
general information on Ethernet, Token Ring and Fiber Distributed Data Interface
networking, including examples of needs analysis and initial network designs
utilizing Cabletron equipment. A short treatment of other networking
technologies follows these individual subsections.
1-1
Introduction
Following the discussions of the major networking technologies supported, this
guide shows how networks, based on the examples from the training sections, can
be expanded.
The remainder of this guide contains brief descriptions of Cabletron Systems
modular chassis products, charts and tables which supply much of the
information that the network design process requires, and an extensive glossary
of the terms used within this guide and in other Cabletron Systems publications.
The following summarizes the organization of this manual:
Chapter 1, Introduction, discusses the use and contents of this guide.
Chapter 2, Overview of Networking, explains the fundamentals of Local
Area Networks (LANs), including the reasons to utilize a network, and
discussions of factors such as standards-compliance and interoperability.
Chapter 3, Technology Basics, provides some introductory training into the
LAN technologies which are treated in this Networking Guide.
Chapter 4, Network Design, discusses the procedures and steps involved in
planning out a network, including the selection of a LAN technology and its
organization.
Chapter 5, Ethernet, offers training in greater depth for the Ethernet LAN
technology. This training includes the creation of example network
configurations based on the concepts introduced.
Chapter 6, Token Ring, provides training and configuration instruction for
the Token Ring LAN technology, including example configurations.
Chapter 7, FDDI, is a training chapter which details the operation of the Fiber
Distributed Data Interface (FDDI) technology and the creation of FDDI
networks using Cabletron products.
Chapter 8, Expansion - Ethernet, shows how an existing Ethernet network
can be expanded to include new users or capabilities.
Chapter 9, Expansion - Token Ring, provides instructions and guidelines for
expanding existing Cabletron Token Ring network configurations.
Chapter 10, Expansion - FDDI, describes the means by which FDDI
configurations which use Cabletron products may be expanded to include
new users or stations.
Chapter 11, Product Descriptions, provides short descriptions of many
Cabletron products referred to in this Networking Guide.
Following Chapter 11, Appendix A, Charts & Tables, provides
quickly-accessible tables and flowcharts for network design.
Following Appendix A, the Cabletron Systems Glossary of Terms may be
found.
1-2 Organization of Document
Conventions of This Document
Warnings and Notifications
Introduction
NOTE
CAUTION
TIP
Note symbol. Used to provide additional information
concerning subsequent steps or actions that enhance the
operator’s knowledge of the step or action.
Caution symbol. Used to caution against an action that could
result in damage to equipment or poor equipment performance.
!
Tip symbol. Used to convey helpful hints concerning
procedures or actions which would assist the operator in
performing the task in a more timely manner in the future.
Warning symbol. Used to warn against an action that could
result in personal injury or death and equipment damage.
Formats and Measures
Figures throughout the document are identified by chapter and illustration
number. Many figures contain small numbers at the lower right-hand corner of
the illustration. These are Cabletron Systems document control numbers and are
not essential to understanding of the document.
When measurements are given in the text, they will be presented in both metric
and U.S. Customary units. The metric unit will precede the U.S. Customary unit,
and the latter will be contained in parentheses.
References to chapters or sections within this document will be printed in
boldface type.
References to other publications or documents will be printed in italic type.
Conventions of This Document 1-3
Introduction
Additional Assistance
This publication describes many possible network configurations and designs.
Due to the nearly limitless possibilities involved in network design, there are
some aspects of the design process which are not addressed in this guide. If you
have any doubts about your configuration or expansion plans, Cabletron Systems
maintains a staff of network design personnel and a sizable team of
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) 335-9400 to reach the Technical Support
department with any specific product-related questions you may have.
Associated Documentation
The following publications may be of assistance to you in the design process.
Several of these documents treat concepts raised in this Networking Guide in
greater detail than they are presented here.
• The Cabletron Systems Product Catalog
1-4 Additional Assistance
Chapter 2
Overview of Networking
This chapter introduces and discusses several basic concepts and definitions essential to the
understanding of local area networking.
Discussion of Networking
Why Network?
In this day and age, all companies and agencies have two resources in common,
information and ability. No matter what a company may produce, market, offer or
observe, the final result is one that comes from a combination of ability and
information. Every company with more than one employee is in the business of
sharing information abilities. Information and ability may take many forms: stock
reports and market prediction; manufacturing processes and skilled quality
assurance; accounting information and efficiency examination.
Information is naturally separated from ability. It is the nature of information to
accumulate beyond the point that every person has all the information required to
perform productively. This separation is a factor that has been part of the business
world for centuries. The rise of printing, a postal service, and the telephone can be
viewed as ways that businesses and agencies have created and adopted means of
providing information to those with ability.
While the separation of these factors has always existed and will always exist, the
limiting factor for businesses is not the presence of the separation, but its
magnitude. The more difficult it is to bridge the gap between information and
expertise, the less efficiently both factors are used.
A Local Area Network (LAN) allows for the rapid and direct sharing of critical
information. This sharing enables employees to act more rapidly and with more
complete access to information and resources than may have been possible with a
system of filing cabinets and interoffice mail.
2-1
Overview of Networking
The basis of the LAN is sharing. The LAN allows users to transfer information
and completed documents without the overhead and delay introduced by
hardcopy information. In addition, the LAN increases the utility of expensive
resources such as printers, disk arrays, and plotters. For example, a high-speed
printer on every desktop is an expensive and wasteful proposition, but allowing
20 users to share access to one high-speed printer reduces the overall cost of each
document printed.
As very few users create things for only their own use, the LAN allows employees
to discover means to speed the process of work or increase its efficiency. For
example, a document that was once developed, printed, carried to the Order
Entry department, signed, photocopied, sent to the Records department, updated,
and filed can now be printed in all three locations at once, freeing up each
department to perform the tasks it is intended to.
If a LAN is used on a scale that encompasses the entirety of a facility, company, or
corporation, the benefits can be enormous. The nearly instantaneous sharing of
information between several worldwide sites greatly improves the consistency of
company documents and products, provides for the rapid integration of new
policies, and supplies a system for seamless worldwide collaboration on projects.
By reducing the delay inherent in the operations of business, a LAN increases
productivity.
By providing users, management, sales, and production alike, with rapid and
monitored access to the information base on which a corporation is built, a
network empowers employees on a company-wide scale, giving them a chance to
increase their own abilities and use their talents more fully in the corporation. The
LAN is a means of bridging the chasm between information and expertise,
enabling the flow of essential information between workers, departments, offices,
and corporate partners.
The LAN is a means of bringing things together: information and ability,
customers and producers, employees and equipment. In an age where
combination leads to security and strength for corporations, streamlining the
combinations of information and ability helps erase the borders that have
traditionally slowed the business process. By reducing the overhead related in
doing business, a LAN allows your current employees to do more, improving
efficiency and effectiveness to attain greater levels of productivity.
2-2 Discussion of Networking
What Is a Network?
Simply put, a Local Area Network, or LAN, is a number of related computers and
electronic devices which share information over a transmission media. This can
be as simple as a series of electronic cash registers which send updates of
products sold during the course of the day to an inventory computer or as
complex as a network spanning an entire corporate facility or University campus,
providing high-powered communication services for hundreds of applications
and the swapping of thousands of files each day.
The Classification of Networks
While all networks are different, they all have a number of common defining
characteristics which serve to illustrate the type of network being discussed or
examined. The most important characteristics for the purposes of this guide are
topology, technology, media, and devices.
For the purposes of explanation, this chapter of the Networking Guide uses one
cohesive metaphor to describe the portions of a network, the “meeting
metaphor.” In the sections which follow, the topologies, technologies, and devices
of networks will be viewed as aspects of a business or public meeting. By viewing
the various facets of a network as parts of one common process, we can describe
the distinct concepts as parts of a larger overall system.
Overview of Networking
What Is a Network? 2-3
Overview of Networking
Network T opology
The topology of a network refers to its physical layout or “shape.” The topology
characteristic describes how components and cabling are interconnected. Using
the meeting metaphor, the topology of a network can be seen as the
organizational structure of the meeting itself; will the meeting consist of several
committees making reports to each other when necessary? Will pre-determined
representatives speak for the members of their group? Will an intermediary or
moderator determine who has the “floor,” or will the opportunity to speak pass
from participant to participant in a particular order?
Although the growing complexity and scale of networks has caused some
topologies to bleed over into others, the topologies can be useful starting points
for describing the overall layout of a network or network segment. There are a
number of widely used topology descriptions for the most common topologies
(see Figure 2-1).
Tree
Bus
Ring
Figure 2-1. Network Topologies
Star
Hub
1706n01
2-4 The Classification of Networks
Bus
Tree
Overview of Networking
The bus topology uses a single common cable or link (coaxial cable, broadcast
radio frequency) to connect the stations of the network to one another. The bus
topology is strictly an Ethernet phenomenon, and is frequently encountered in
existing Ethernet environments. Stations connect to the common media through a
series of taps, located a specified distance from one another along the common
cable, and only one station may successfully transmit onto the common media at
any one time. Bus topologies are noted for their simplicity, but are notoriously
difficult to troubleshoot. In addition, a failure of the bus media itself, due to
disruption or poor configuration, causes the network to cease functioning.
The tree topology arranges links and stations into distinct hierarchies in order to
allow greater control and troubleshooting. In order to function well, networks
using tree topologies must incorporate some form of “traffic control,”
determining when traffic is allowed to travel up and down the branches of the
tree. Similar to a well-defined chain of command, the tree topology shields
disparate network groups from affecting each other.
Ring
The tree topology also facilitates much more straightforward troubleshooting
procedures. The main downfall of the tree topology is its own organization. If
there is a failure on one of the branches of the tree, every branch that forks from
that point of failure becomes unable to communicate with the rest of the network.
The ring topology connects every station on the network to every other station in
the network in a contiguous circle. Most common in the Token Ring and FDDI
network technologies (discussed later), ring topologies rely on well-defined rules
of transmission and reception in order to function. Stations are connected in a
definite series, with information going from one station to the next in a
pre-defined order. Since each station is expecting transmissions from the station
before it and sending transmissions only to the station following it, ring
topologies can be made to incorporate automatic fault location and recovery
procedures.
The Classification of Networks 2-5
Overview of Networking
Star
The star topology consists of a number of individual stations which communicate
through a common central point. Similar to the bus topology, star topology
network stations all share a single common interface. In place of a section of cable,
however, the common central point in star topology networks is often a
concentrator device, or “hub.” Each station connects to the hub through its own
physical interface, and many concentrators incorporate their own troubleshooting
and monitoring functions, allowing network managers to determine faulty
stations and remove them from the concentrator without disrupting the
remaining network. Unfortunately, a failure of the concentrator can lead to the
same disabling of the network that can occur in bus topologies.
Hybrid
Any network topology that incorporates elements of two or more of the
previously discussed topologies is a hybrid. For example, a tree that led down to a
series of buses (the ‘leaves’) would be a hybrid called a “tree of buses.” A ring
topology network with a series of concentrators acting as stations on the ring
would be called a “ring of stars.” As networks grow to encompass more and more
of a facility’s needs, topologies tend to hybridize in order to fulfill the individual
needs of workgroups and departments.
Network Technologies
While a topology describes the way a network is physically laid out, the network
technology defines how the devices that make up the network receive and
transmit information, deal with faults and problems, and control the actual
operation of the network. The technology of the network can be seen as the Rules
of Order that will be followed at the meeting. These concrete and binding rules
will determine who may speak, at what time, for how long, to whom, in what
language, and so on. The technology determines how problems are identified and
what methods may be used to resolve them. If arm wrestling is going to be
considered a valid means of breaking a deadlock between two sides in a vote, the
rules of order must clearly state that, as well as provide the rules for arm
wrestling.
There are several commonly-encountered technologies in networking. Among the
most common of the ‘client-server’ (non mainframe-terminals) technologies are
Ethernet, Token Ring, and the Fiber Distributed Data Interface (FDDI). These
network technologies and their operation are individually described in their own
chapters later in this document.
2-6 The Classification of Networks
Media
Overview of Networking
The term media has come to mean several different things in today’s English
language. For the purposes of networking, media always refers to the physical
entity that is used for the purposes of transmitting and receiving the impulses
that make up data exchange. While in some networks, radio frequencies and
nationwide telephone service providers are considered to be media, the term
most commonly refers to the physical chunks of cable that connect one network
device to another. In the meeting metaphor, media is simply the communications
system that is to be used, be it speech, writing, or tin-can telephone.
While media can conceivably be any system of physically transmitting the
impulses indicating the zeroes and ones of electronic data, there are a number of
media common to most networks. Unshielded Twisted Pair cabling, or UTP, is a
commonly-used media in networks. UTP is small-gauge, inexpensive cabling
made up of a series of copper strands which are twisted together inside the
insulating jacket, in the same manner as many telephone cables are. Several
Ethernet networks use telephone-grade UTP as their primary media. Other
common media include coaxial cable, fiber optics (both Light Emitting Diode and
Laser driven), Shielded Twisted Pair (STP), and specific technology-related cable
types such as the Attachment Unit Interface (AUI) cable defined in the Ethernet
technology specification.
It is important to note that some media are not supported by some technologies.
For example; neither the Token Ring nor FDDI standards support the use of
coaxial cables. Each technology will define what media it supports, and to what
extent. Some technologies are very demanding of certain types of media, and all
technologies place limitations on the extent to which a particular media may be
used. These limitations, for the purposes of designing networks, are discussed in
greater detail within the chapters providing individual descriptions of the major
networking technologies, as well as in the Charts and Tables section at the end of
this Networking Guide.
This guide does not intend to describe in detail the procedures for cable
installation and testing. Characteristic properties of the individual media and any
special installation-related information that should be kept in mind during
planning will be presented. This information should be used to assist the selection
of a media based on the needs of a specific location to be networked.
To provide a rough footing, a brief description of each of the cabling media to be
referred to within this Networking Guide follows.
Do not run electrically conductive cabling (cable media with
metal strands or shielding) between buildings. Exposed
conductive cabling is susceptible to lightning strikes.
The Classification of Networks 2-7
Overview of Networking
Thick Coaxial Cable
Thick coaxial cable (also known as thick Ethernet cable, “thicknet”, or 10BASE5
cable) is a cable constructed with a single solid core, which carries the network
signals, and a series of layers of shielding and insulator material. The shielding of
thick coaxial cable consists of four stages. The outermost shield is a braided metal
screen. Working inward, the second stage shield is usually a metal foil, but in
some brands of coaxial cable may be made up of a second screen. The third stage
consists of a second braided shield followed by the fourth stage, a second foil
shield. The various shields are separated by non-conductive insulator materials.
Foil Shield
Solid Core
Outer
Jacket
Insulator
Braided Shield
1706n02
Figure 2-2. Thick Coaxial Cable Cross-Section
Thick coaxial cable is a media used exclusively in Ethernet installations,
commonly as a backbone media. Transceivers (devices designed to TRANSmit
and reCIEVE network signals) are connected to the cable at specified distances
from one another, and standard transceiver (AUI) cables connect these
transceivers to the network devices.
Due to the extensive shielding, thick coaxial cable is highly resistant to electrical
interference by outside sources such as lighting, machinery, etc. Because of the
bulkiness and limited flexibility of the cable (typically 0.405 inch in diameter or
thicker), thick coaxial cable is primarily used as a backbone media and is placed in
cable runways or laid above ceiling tiles to keep it out of the way. The 10BASE5
standard, which standardizes minimum and maximum characteristics for
Ethernet networks using thick coaxial cable, specifies a maximum cable length of
500meters (1,640 ft).
Thick coaxial cable is designed to be accessed as a shared media. Multiple
transceivers can be attached to the thick coaxial cable at multiple points along the
cable itself.
2-8 The Classification of Networks
Thin Coaxial Cable
Overview of Networking
Thin coaxial cable (also known as thin Ethernet cable, “thinnet,” “cheapernet,”
RG58 A/U, BNC or 10BASE2 cable) is a less shielded, and thus less expensive,
type of coaxial cabling. Also used exclusively for Ethernet networks, thin coaxial
cable is smaller, lighter, and more flexible than thick coaxial cable. The cable itself
resembles (but is not identical to) television coaxial cable.
Thin coaxial cable is made up of a single outer copper shield, which may be
braided or foil, a layer beneath that of non-conductive dielectric material, and a
stranded center conductor. This shielding makes thin coaxial cable resistant to
electromagnetic interference as the shielding of thick coaxial cable does, but does
not provide the same extent of protection. Thin coaxial cable can be run to a
maximum length of 185 meters (606.7 ft.).
As with thick coaxial cable, thin coaxial cable allows multiple devices to connect
to a single cable. Up to 30 transceivers may be connected to a single length of thin
coaxial cable, spaced a minimum of 0.5 meter from one another. Connections to
the cable are typically made using T-connectors, which provide taps for
additional runs of coaxial cable to workstations or network devices. T-connectors,
as shown in Figure 2-3, below, provide three RG58 connections, two of which
attach to RG58 female connectors on the cable itself and one of which is used for
connection to the male RG58 connection of a transceiver or Desktop Network
Interface Card on a workstation.
Front
Side
Bottom
1706n03
Figure 2-3. Thin Coaxial Cable T-Connector
The Classification of Networks 2-9
Overview of Networking
Attachment Unit Interface (AUI)
Attachment Unit Interface cable (referred to hereafter as AUI cable, but which
may also be called office transceiver cable or standard transceiver cable in other
publications) is a shielded, multistranded cable that is used to connect Ethernet
network devices to Ethernet transceivers. AUI cable should be used for no other
purpose.
AUI cable is made up of four individually shielded pairs of wire surrounded by
an overall cable shielding sheath. The gauge of the internal cables determines the
thickness and relative flexibility of the AUI cable. Heavy-gauge AUI cable
(containing pairs of wire of 20 or 22 AWG wire) is capable of reaching a maximum
distance of 50 meters (164 ft.) between transceivers and the network device, but is
thick, and somewhat inflexible. The lighter-gauge AUI cable (consisting of 28
AWG wire) is thinner and much more flexible, but can only be run to a maximum
distance of 16.5 meters (54.1 ft.).
Unshielded Twisted Pair (UTP)
Unshielded Twisted Pair cabling (referred to here as UTP, but also may be termed
copper wire, 10BASE-T wire, Category 3, 4, or 5 Ethernet wire, telephone cable, or
twisted pair without shielded or unshielded qualifier) is commonly made up of
two or, ideally, four pairs of 22, 24 or 26 AWG unshielded copper solid or stranded
wires. These pairs of wires are twisted together throughout the length of the
cable. The twisting of associated pairs helps to reduce the interference of the other
strands of wire throughout the cable. UTP cable used in network installations is
the same type of cable used in the installation of telephone lines within buildings.
Tx+
Tx-
RxRx+
1706n04
Figure 2-4. UTP Pair Association
As UTP cabling already exists in many facilities, and as it is inexpensive, available
in bulk and easy to install, the use of twisted pair cabling is often a significant
savings over the use of other media in a networking installation. As UTP cabling
is an accepted media in all common network technologies, it is considered a
somewhat ‘future-proof’ media. In opposition to a length of thin coaxial cable,
which can only be used for Ethernet communications between devices, UTP
cabling could initially be used for Ethernet, then be used to support Token Ring
and FDDI network equipment as the network grew.
2-10 The Classification of Networks
UTP cabling is differentiated by the quality of the cable. UTP is divided into
Categories, which indicate the relative quality of the materials used and the
processes used to manufacture the cables. The categories used in LANs range
from Category 3 to Category 5, with Category 5 being the highest quality.
Shielded Twisted Pair (STP)
Shielded Twisted Pair cabling (referred to in this document as STP, but also seen
as “IBM-type” cable or “shielded copper”) is a cable type which is constructed in
much the same fashion as UTP cabling (see Figure 2-4) but incorporates more
elaborate shielding methods. These cables are most commonly used in Token
Ring networks.
As with UTP cable, STP cable consists of two or more pairs of wire. Each wire is
shielded with a layer of insulation, twisted together with a related wire, then
bundled with the other pairs and wrapped in a metal foil. The metal foil provides
additional resistance to the effects of external electrical fields produced by
electrical equipment or other cabling.
STP cabling, like UTP cabling, is divided into groups based on fitness for a
particular purpose. Where UTP referred to Categories of cable, STP cabling is
divided into “types.” These types are based on the IBM Cabling System, and are
often labeled “IBM Type 1 STP.” IBM Type 1 cable is usually the highest quality,
incorporating several layers of shielding and made with heavy-gauge wire, while
Types 6 and 9 STP are usually best suited for use as short jumper cables in
low-interference areas.
Overview of Networking
Fiber Optics
Fiber optic cable is a high performance media constructed of glass or plastic
which uses pulses of light as a transmission method. Because fiber optics do not
use electrical charges to pass data, they are free from the possibility of interference
due to proximity to electrical fields. This, combined with the extremely low rate of
signal degradation and dB loss makes fiber optics able to traverse extremely long
distances. The actual maximums are dependant upon the technology being used,
but distances upwards of 2 kilometers (1.2 miles) are not uncommon.
The Classification of Networks 2-11
Overview of Networking
Fiber optic cabling is made up of a glass strand, the core, which allows for the
easy transmission of light; the cladding, a glass layer around the core which helps
keep the light within the core; and a plastic buffer which protects the cable.
Cladding
There are two basic types of fiber optics: multimode and single mode. The names
come from the types of light used in the transmission process.
Multimode Fiber Optics
Multimode fiber optic cabling uses inexpensive Light Emitting Diodes (LEDs) to
produce the signals that travel through the core of the cable. Due to the nature of
the LED, the signal produced is made up of a number of differing wavelengths of
light, fired outward from the center of the LED. Not all the rays of light enter the
fiber, and those that do often do so at an angle, which reduces the amount of
distance the signal can effectively cover.
Single Mode Fiber Optics
Single mode fiber optics, driven by the concentrated beams of light which can
only be produced by lasers, are constructed in the same fashion as multimode
fiber optics, but may use a narrower core strand. The use of lasers to drive the
signal greatly increases the expense involved in producing single mode fiber optic
devices as opposed to multimode fiber optic devices. The expense involved in
single mode fiber optic equipment often causes it to be reserved for applications
requiring its ability to traverse much greater distances than multimode fiber
optics.
Transmissive Core
PVC Buffer (Jacketing)
Figure 2-5. Fiber Optic Cable Cross-Section
1706n05
Single mode fiber optics and their hardware can transmit and receive signals at
distances of 3 kilometers (1.8 miles) or more. As such, it is often best reserved for
extremely long-distance LAN communications.
NOTE
2-12 The Classification of Networks
While the media is capable of supporting these distances, the
technology being used may not be able to function with a link of
that distance. Be sure to remain within the maximum distances and
limitations imposed on any network technology by the appropriate
IEEE or ANSI standard.
Interoperability and Standards Bodies
Interoperability, the Ideal of Networking
Ideally, all devices placed on any network should be able to transfer information
in a usable fashion and understandable format to any other station. For some
time, however, this was not always the case. Different companies, even within the
same industry, have different ways of designing, developing, and constructing
their products. Different views of how a network should operate led to radically
different products and methods of networking. These early networking
implementations were specific to one particular vendor, and would often only
work in homogenous environments, where all components used in the network
were produced by that single vendor. This method of networking locked
customers into relying on a single vendor for all of their networking needs,
current and future, which could lead to problems if the network implementation
was unsatisfactory. Ripping out all of your present networking equipment in
order to use the proprietary solution of another vendor can become an extremely
costly proposition.
Overview of Networking
To combat this, the idea of interoperability grew in popularity. Ideally,
interoperability means that the networking devices of Vendor X can
communicate, problem-free, with the networking devices of Vendor Y.
Standards and Compliance
Interoperability requires the following of standards, distinct rules and finite
margins within which network operation and performance must be kept. If a
network does not meet the minimums, or exceeds the maximums of the
networking standard that the industry uses, it is said to be “out of specifications,”
and may not operate at an acceptable level. For example, the Token Ring network
standard specifies the maximum number of stations that may be placed on one
network, or “ring.” If this number of stations is exceeded, the network will suffer
erratic performance and may cease to function correctly. By providing a single
definition for the maximum number of stations per ring, the Token Ring standard
allows devices from multiple vendors to operate in the same fashion.
Standards are defined by committee, through the operation of standards
institutes. Standards institutes are made up of personnel from several firms in the
industry who volunteer their time and effort. These volunteers work to compose
and ratify an acceptable standard, which, when accepted and ratified, will need to
at least be met by any product that refers to itself as “standards-compliant.”
Products that are not standards-compliant may cause or experience
interoperability problems when operating in a standards-based network. Of
course, even in a fully standards-based network, there may still be problems.
Most vendors in the industry, realizing the importance of providing a flexible and
open network to all customers, seek to eliminate any interoperability problems
they notice.
Interoperability and Standards Bodies 2-13
Overview of Networking
The most common Local Area Networking technologies (Ethernet, Token Ring,
and FDDI) have standards ratified and in place for their operation and
configuration. ATM, still in the draft stages in some aspects, is operating under a
working interim standard, which is intended to allow ATM equipment to be
produced which will be compatible with future ATM standards. The standards
bodies that this document is concerned with and the standards they oversee are
listed below:
Standards Committee Technology Standard Code
Table 2-1. Networking Standards Bodies
Institute of Electrical and
Electronic Engineers (IEEE)
American National Standards
Institute
ATM Forum Asynchronous Transfer Mode UNI V3.0
Ethernet IEEE 802.3
Token Ring IEEE 802.5
Fiber Distributed Data Interface (FDDI) ANSI X3T9.5
The OSI Model, Basis of Standards
The International Organization for Standardization (ISO) Open Systems
Interconnect (OSI) Model provides a framework for the development of system
connection standards by defining a consistent hierarchy of rules. The OSI model
defines where the needed tasks of system interconnection are performed but not
how they are performed. How tasks are performed on a given layer is determined
by the protocols, or rules, written for that particular network based on the OSI
model. The layers may be implemented in hardware, software, or both. Each layer
in a network based on the OSI model performs specific types of functions
required for proper system interconnection.
2-14 Interoperability and Standards Bodies
Overview of Networking
There are seven layers in the OSI Model (see Figure 2-6). They begin with the
Physical Layer and end with the Application Layer. Each layer provides services
to the layer above it. As the seventh layer is the ‘topmost’ layer, it servers the user
directly, and is considered the top of the OSI model.
Application
7.
Presentation
6.
Session
5.
Transport
4.
Network
3.
Data Link
2.
Physical
1.
1706n06
Figure 2-6. OSI Model
Layer Seven: Application
The Application Layer is the user’s interface with the network. This layer directly
interacts with user application programs to provide access to the network. All
other layers exist to support the requirements of the Application layer. The
Application layer is usually involved with network-oriented end-user tasks such
as electronic mail, network file transfers, and collaborative document preparation.
Layer Six: Presentation
The Presentation Layer deals with data translation and code conversion between
devices with different data formats (i.e. ASCII to EBCDIC). This layer also handles
translation between differing device types and file formats, as well as data
encryption and decryption services. In the transmit mode, the presentation layer
passes information from the application layer to the Session layer after it has
appropriately modified or converted the data. In the receive mode, the
Presentation layer works in reverse passing information from the Session layer to
the Application layer.
Layer Five: Session
The Session layer manages the communications dialogue between two
communicating devices. The Session layer establishes rules for initiating and
terminating communications between devices and can provide error recovery.
Interoperability and Standards Bodies 2-15
Overview of Networking
Layer Four: Transport
The Transport layer deals with the optimization of data transfer from source to
destination by managing network data flow and implementing the quality of
service requested by the Session layer. The Transport layer determines the packet
size requirements for transmission based on the amount of data to be sent and the
maximum packet size allowed by the network architecture. If the data to be sent is
larger than the maximum packet size allowed on the network, the Transport layer
is responsible for dividing the data into acceptable sizes and sequencing each
packet for transmission.
When receiving data from the Network layer, the Transport layer ensures that the
data is received in order and checks for duplicate and lost packets. If data is
received out of order, the Transport layer correctly orders the data and passes the
data up to the Session layer for additional processing.
Layer Three: Network
The Network layer accepts data from the Transport layer and adds the
appropriate information to the packet to provide proper network routing and
some level of error control. Data is formatted by this layer for the appropriate
communications method, such as IP, IPX, or X.25.
Layer Two: Data Link
The Data Link layer is involved with transmission, error detection, and flow
control of the data. The major function of the Data Link layer is to act as a shield
for the higher layers of the OSI model, controlling the actual processes of
transmission and reception. Error detection and control of the Physical layer are
the primary functions of this layer, ensuring that data received by the upper
layers is error-free. For purposes of understanding networking, it is useful to
divide the Data Link layer into two sub-layers; the Logical Link Control layer and
the Media Access Control layer (see Figure 2-7).
Application
7.
Presentation
6.
Session
5.
Transport
4.
Network
3.
Data Link
2.
Physical
1.
Figure 2-7. Data Link Layer
Logical Link Control
Media Access Control
1706n07
2-16 Interoperability and Standards Bodies
Loading...