rame
`Technology and Practice
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 1 of 24
`
`

`

`FRAME RELAY
`
`TECHNOLOGY AND PRACTICE
`
`Jeff T. Buckwalter, Ph.D .
`
`• TT
`
`ADDISON-WESLEY
`Boston • San Francisco • New York • Toronto • Montreal
`London • Munich • Paris • Madrid
`Capetown • Sydney • Tokyo • Singapore • Mexico City
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 2 of 24
`
`

`

`Many of the designations used by manufacturers and sellers to distinguish their products are claimed
`as trademarks. Where those designations appear in this book and Addison Wesley Longman, Inc., was
`aware of a trademark claim, the designations have been printed with initial capital letters.
`
`The author and publisher have taken care in preparation of this book, but make no expressed or
`implied warranty of any kind and assume no responsibility for errors or omissions. No liability is
`assumed for incidental or consequential damages in connection with or arising out of the use of the
`information or programs contained herein.
`
`The publisher offers discounts on this book when ordered in quantity for special sales. For more
`information, please contact:
`
`Pearson Education Corporate Sales Division
`201 W. 103rd Street
`Indianapolis, IN 46290
`(800) 428-5331
`corpsales@pearsoned.com
`
`Library of Congress Cataloging-in-Publication Data
`
`Buckwalter, Jeff T.
`Frame relay : technology and practice I Jeff T. Buckwalter.
`p. cm.
`Includes bibliographical references and index.
`ISBN 0-201-48524-9
`.
`1. Frame relay (Data transmission) 2. Computer networks.
`TK5105.38 B83 1999
`004.6'6-dc21
`
`I. Title.
`
`99-051438
`CIP
`
`Copyright © 2000 by Addison Wesley Longman, Inc.
`
`All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or
`transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or other(cid:173)
`wise, without the prior written permission of the publisher. Printed in the United States of America.
`Published simultaneously in Canada,
`
`Text printed on recycled and acid-free paper.
`ISBN 0201485249
`04 03 02 01
`2 3 4 5 6 7 MA
`2nd Printing
`January 2002
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 3 of 24
`
`

`

`Chapter lIJ
`
`Introduction
`
`This chapter introduces changes in the business and technical communities
`that are driving demand for new communications services-in particular,
`frame relay services. An understanding of these trends provides a context
`for evaluating frame relay and other emerging technologies.
`We introduce a simple block diagram for a frame relay network and
`briefly discuss the basic components. Frame relay networks will be dis(cid:173)
`cussed in much more depth in later chapters.
`Next, we describe the major benefits of frame relay technology. These
`benefits are why frame relay has become so popular within the last
`few years. For balance, we also describe the major disadvantages of the
`technology.
`Lastly, we briefly discuss the relation of frame relay to other technolo(cid:173)
`gies. We point out its major advantages and disadvantages as compared to
`leased lines, ATM, X.25, switched digital fa,cilities, virtual private networks
`(VPNs), and other emerging technologies. These comparisons will be dis-
`,
`cussed further in later chapters.
`
`Driving Forces for Frame Relay
`
`Frame relay has been one of the major success stories in the data commu(cid:173)
`nications arena. From its introduction in the early 1990s, the combination
`of frame relay products and services has grown rapidly to an estimated $15
`billion in annual global revenues in the year 2000 [VerticalSG99]. Growth
`rates have often been over 100% per year. Why?
`
`1
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 4 of 24
`
`

`

`2
`
`Chapter 1
`
`Introduction
`
`The Need for Frame Relay
`
`For a number of years, managers of wide area networks (WANs) have
`had several needs on their wish lists. Frame relay technology was devel(cid:173)
`oped to specifically address these needs, which are
`
`• A higher performance packet technology
`• Integration of traffic from both legacy and LAN applications over
`the same physical network
`• Simpler network management
`• More reliable networks
`• Lower network costs
`
`We now explore each one.
`
`A Higher Performance Packet Technology
`"High performance" means high throughput, low delay, and high efficiency.
`Good throughput and delay are requirements for a wide area network. High
`efficiency is desirable in order to obtain good return on investment.
`Network managers have seen a dramatic increase in the volume of data
`traffic over the years. Some of the reasons for this, such as LAN internet(cid:173)
`working and the shift from text to graphics, we will discuss in the next sub(cid:173)
`section. The result has been a need to handle much higher throughput, in
`bits per second, than previously.
`In addition to the need for higher raw throughput, network managers
`also need low network delay, especially across the wide area network. Low
`delay (also known as latency) is necessary in part because of the expecta(cid:173)
`tions that LAN users' have for very fast response time. Typically, users do
`not care and do not want to know whether the resources they are using are
`on their qwn LAN or on a distant one. In either case, they want fast re(cid:173)
`sponse time, even though it is technically much harder to provide it across
`the wide area.
`Lastly, network managers need a technology that efficiently handles
`bursty traffic. Most data traffic is bursty, meaning that an end user may
`want to transfer a 10-Mbyte file across the network and then do no more
`transfers for 20 minutes. This tends to produce very high circuit utiliza(cid:173)
`tions for short periods of time, then no utilization at all for long periods of
`tim.~, resulting in a low average circuit utilization. (For our purposes, circuit
`utilization is the percentage of time the circuit is busy.) Network managers
`find it hard to cost-justify an expensive long-distance circuit that may be
`busy for only 5% of the time on the average. For that reason, they need a
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 5 of 24
`
`

`

`l·
`
`Driving Forces for Frame Relay
`
`3
`
`technology that will handle bursty traffic as efficiently as possible, by
`maintaining a high average circuit utilization when possible. We will ex(cid:173)
`plore this performance issue more thoroughly in Chapter 11, Design of
`·
`Frame Relay Networks.
`Circuit-switched technologies, such as Tl/El lines or ISDN lines, all of
`which use time division multiplexing, are notoriously inefficient for trans(cid:173)
`porting bursty data traffic. (See the Glossary for brief explanations of Tl;
`El, and ISDN.) They are much better for transporting low-volume, contirt(cid:173)
`uous data streams, such as voice or video. Hence, network managers have
`a need for a packet-switching technology as an alternative to the less effi(cid:173)
`cient circuit-switching technologies.
`In general, frame relay is a high-performance technology with good
`throughput and acceptable delay. It is also relatively efficient, for two tech(cid:173)
`nical reasons: its ability to statistically multiplex many logical connections
`over the same physical circuit and its ability to "burst" extra data into the
`network. More on these two issues in Chapter 3, Frame Relay Architecture,
`and Chapter 5, Frame Relay Virtual Circuits ..
`
`Traffic Integration
`Historically, in many companies one department, often called Manage(cid:173)
`ment Information Systems (MIS), built and supported the centralized MIS
`applications. These applications, which were and still are missibn critical,
`were often based on IBM's Systems Network Architecture (SNA) and are
`now often called legacy applications, although the term "legacy" also more
`generally refers to any older application. In contrast to the wide area net(cid:173)
`works that support SNA, LANs were often built, supported, and intercon(cid:173)
`nected by whatever departments needed the connectivity. This resulted in
`many companies developing parallel networks, one for the LAN file trarts:(cid:173)
`fers and one for the MIS applications. With the current competitive busi(cid:173)
`ness environment and the emphasis on cost justification, there is increasing
`pressure to consolidate these LAN and legacy networks.
`Frame relay technology is able to consolidate both types of data traffic
`over the same physical network. In addition, under certain conditions
`voice and video traffic can also be carried over a frame relay network (see
`Chapter 12, Voice over Fra:r;ne Relay). This consolidation is often called
`network convergence.
`'-'.t?
`
`Simpler Network Management
`Network management has become increasingly complex. This is due to
`such factors as
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 6 of 24
`
`

`

`4
`
`Chapter 1
`
`Introduction
`
`• Mergers and acquisitions among companies, which result in the
`merging of disparate networks
`• More types of traffic that must be carried, such as digitized voice and
`images
`• The proliferation of "new" protocols, such as ATM, while "old" pro(cid:173)
`tocols, such as IBM's Bisynch, continue to live on despite attempts to
`eradicate them.
`• Deregulation of the com.m.unications industry, which has led to in(cid:173)
`creased product and services choices for network managers
`
`These factors, combined with pressure to control costs and a shortage of
`trained network staff, have created a need for simpler network manage(cid:173)
`ment. Some network managers have responded by outsourcing pieces of
`their management or at least making increasing use of carriers' services.
`When frame relay is used in a network, overall network management
`usually becomes simpler. This issue is discussed more fully in Chapter 8,
`Network Management.
`
`More Reliable Networks
`As companies have become more dependent on their networks, the need
`for overall reliability has increased. Companies want high availability and
`long mean time between failure (MTBF), both for individual components
`and for the network as a whole. Having any potential single point of fail(cid:173)
`ure becomes a great concern.
`
`Lower Network Costs
`As the traffic volume on networks has increased, and the need for higher
`performance networks has grown, so has the cost of paying for the net(cid:173)
`work. Network managers are under pressure to keep costs from escalating.
`In keeping with the corporate trend toward downsizing, they need to do
`more with less.
`As we will see in the later section on the benefits of frame relay, the use
`of frame relay technology often leads to lower costs.1
`
`1The term "frame relay" is used in at least tht~e related ways. It refers to a particular type of packet(cid:173)
`switching technology. It also refers to a set of standards (protocols) that describe how a company
`interfaces its equipment to a frame relay network. And it refers to a set of services offered by pub(cid:173)
`lic frame relay service providers. The context usually makes it clear which is the appropriate
`meaning.
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 7 of 24
`
`

`

`Driving Forces for Frame Relay
`
`5
`
`Accelerators for the Growth of Frame Relay
`
`Equipment vendors and service providers saw that a "fast packet" tech(cid:173)
`nology, such as frame relay, could help satisfy the needs of network
`managers discussed above. Frame relay technology could improve perfor(cid:173)
`mance, integrate traffic types, and simplify network management, all for a
`reasonable price.
`However, several trends also have accelerated the growth and accep(cid:173)
`tance of frame relay far beyond its being just another technology. In the
`communications arena these trends are
`
`• A shift to /1 cleaner" digital networks
`• Increasingly intelligent network devices
`• Experience with packet networks
`• Availability of ISDN standards as a basis for frame relay
`• A shift from the centrality of voice to the centrality of data commu(cid:173)
`nications
`• Increasing use of LANs and client/ server computing
`• Increasing use of digitized voice and video, multimedia, and digital
`imaging
`• Increasing importance of computer networks for businesses
`
`Shift to Cleaner Digital Networks
`During the 1980s, sophisticated fiber optic networks were installed
`throughout the United States. Fiber optic lines significantly increase the
`quality of transmissions, resulting in far lower error rates for packets sent
`across the network.
`Cleaner digital circuits allow frame relay to dramatically simplify the
`processing of errors, as Chapter 3, Frame Relay Architecture, will show.
`
`Increasingly Intelligent Network Devices
`The often quoted Moore's Law states that computer chip complexity dou(cid:173)
`bles roughly every 18 months [Newton98]. Compounded over many years,
`this evolution has led to vast increases in the processing power of both
`end-user devices (custome~;premises equipment) and network devices,
`such as switches. Intelligenf"end-user devices, such as routers and access
`concentrators, have taken over much of the error processing that used to
`be performed within the network itself. Thus, the frame relay network pro(cid:173)
`tocot which does only simple error processing, -can function well in this
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 8 of 24
`
`

`

`6
`
`Chapter 1
`
`Introduction
`
`environment by handing off the heavyweight error detection and correc(cid:173)
`tion to the end-user devices.
`In addition, the increase in processing power has produced inexpensive
`network switches, such as frame relay switches, that can handle large
`amounts of traffic.
`
`Experience with Packet Networks
`In many ways, frame relay is the next evolutionary step beyond X.25
`packet switching. As we will see in Chapter 3, Frame Relay Architecture,
`there are many similarities, and some vital differences, between the two.
`Thus, years of experience with X.25, and with its relative, the Internet Pro(cid:173)
`tocol (IP), have made it easier for networkers to learn about and feel com(cid:173)
`fortable with frame relay.
`
`A vailabi/ity of /SDN Standards as a Basis for Frame Relay
`ISDN standards were the basis for the frame relay standards. In 1988 the
`ITU-T Recommendation I.122, now called Framework for Frame Mode Bearer
`Services, introduced the frame relay protocol as a part of the ISDN stan(cid:173)
`dards. In particular, the ISDN D channel protocol, ITU-T Q.921, which is
`used by ISDN equipment to set up calls, was the basis for much of the
`frame relay work. Since then, ANSI, ITU-T, and other organizations have
`picked up and extended the frame relay standards. (More about these
`organizations in Chapter 2, Who's Who in Frame Relay.)
`Around 1990, when equipment vendors were looking for a newer,
`higher performance packet-switching technology, they were attracted to
`the careful and substantial ISDN work that had already been done.
`
`Shift from the Centrality of Voice to the Centrality
`of Data Communications
`Historically, wide area data communications were an add on to the exist(cid:173)
`ing well-established analog voice communications network. During the
`1990s the trend has reversed. The handling of voice traffic is rapidly
`becoming less of a standard for justifying corporate co:rruriunications net(cid:173)
`works, while data communications ,demands are soaring. The data com(cid:173)
`munications market is increasing af'a rate of about 25% per year, while the
`voice market is increasing at less than 5% per year.
`This shift from analog to digital traffic has helped the growth of frame
`relay, which is a digital protocot by increasing the amount of digital traf(cid:173)
`fic that must be carried.
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 9 of 24
`
`

`

`Frame Relay Network Basics
`
`7
`
`Increasing Use of LANs and Client/Server Computing
`LANs have grown up from a local resource-sharing method to an inter(cid:173)
`connected infrastructure that supports a client/ server environment. Appli(cid:173)
`cations that run on LANs typically have expectations of quick response
`time and the ability to handle large quantities of data. The advent of mul(cid:173)
`timedia makes the demand for communications capacity all the greater.
`The interconnection of high-speed LANs over a low-speed WAN poses
`problems for LAN-based applications.
`Frame relay has enjoyed growth because of its ability to cost-effectively
`interconnect LANs at a reasonable performance level.
`
`Increasing Use of Digitized Voice and Video, Multimedia,
`and Digital Imaging
`From the Web to corporate intranets to new Windows operating systems,
`we see increasing emphasis on digitized voice, video, and images. This
`trend is fueled in part by more powerful compression algorithms, such as
`MPEG-2, which make the handling of large data files more feasible. The
`vastly increased processing power of microprocessors, as discussed above,_
`also allows larger files.
`Digitized multimedia files are large. Frame relay technology helps han(cid:173)
`dle the huge traffic volumes.
`
`\
`
`Increasing Importance of Computer Networks for Businesses
`Computer communication is becoming ever more critical throughout the
`entire organization. Failure of the network can have disastrous conse(cid:173)
`quences for the business. For many companies, frame relay technology is a
`piece of the answer for building reliable networks.
`
`Frame Relay Network Basics
`
`Here we briefly discuss a diagram (Figure 1.1) that illustrates the simplest
`case of a frame relay network. We will discuss more complex frame relay
`scenarios in later chapters; however, this diagram is the one to keep in
`mind as the ''basic" design lao/put.
`Descriptions of the six components of a typical frame relay network
`follow.
`
`Frame relay customer premises equipment (CPE), which converts
`the user's data into frames that are compatible with the frame relay
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 10 of 24
`
`

`

`8
`
`Chapter 1
`
`Introduction
`
`•
`
`FIGURE 1.1 Basics of a Frame Relay Network. A frame relay network has five major physical
`components and one "virtual" component.
`
`interface standards. The access equipment may be a router, a frame
`relay access device (FRAD), a front end processor, or any other frame
`relay DTE. Usually, the same frame relay access equipment may be
`used with either private frame relay networks or public frame relay
`services.
`
`Access line, which connects the customer's equipment to a port on the
`frame relay switch. The access facility2 must be appropriate for the port
`speed and is usually a 56/64-Kbps or a Tl/El link. When a fractional
`Tl/El is desired, a full Tl/El is still generally used for access, although
`the unused portion may transpbrt other traffic. At the customer's site, a
`standard data service unit/ channel service unit (DSU I CSU) is used to
`
`2The terms "line," "circuit," "link," and "facility" are used interchangeably when describing the
`access line.
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 11 of 24
`
`

`

`Frame Relay Network Basics
`
`9
`
`terminate the access circuit. (See Chapter 4, Connecting to the Network,
`for more about access options and DSU/CSUs.)
`Port connection on the frame relay switch, which is the point of entry
`into the frame relay backbone network and is usually associated with
`an individual site. A single port connection will support multiple logi(cid:173)
`cal connections to many different remote locations (as discussed in
`Chapter 5, Frame Relay Virtual Circuits). The purpose of the port con(cid:173)
`nection is to dynamically allocate netWork capacity to meet the chang(cid:173)
`ing needs of users. The connection is defined in terms of speed. The
`most common speeds available range from 56/64 Kbps to 1.544 Mbps
`(2.048 Mbps in Europe), although higher speeds are available.3
`Frame relay switch, which does the actual processing and routing of
`the frames once they enter the network. The frame may transit one or
`more intermediate switches before it reaches the destination switch.
`The switching equipment may be a specialized frame relay switch, an
`I/O card on a Tl/El multiplexer, or a packet switch that also supports
`frame relay as long as it implements the frame relay interface stan(cid:173)
`dards. A frame relay switch may be part of a private network or part of
`a public frame relay service.
`Backbone trunks, which connect the frame relay switches within a
`frame relay network. The backbone circuits are often Tl or T3 lines.
`(See the Glossary for T3.) They are meshed to provide alternate routes
`though the network. For public frame relay services, the backbone is
`handled completely by the carrier and is not seen by the user. In fact, for
`the major carriers the backbone is actually an A TM network rather than
`meshed trunks.4 For public frame relay networks, the combination of
`frame relay switches and backbone facilities is often called the frame
`relay cloud, perhaps because the user's frames seem to disappear into
`the fog and then magically reappear on the other side.
`
`3Lower port speeds are typically quoted as multiples of 56 Kbps or 64 Kbps. The port speed will
`be a multiple of 56 Kbps if the speed of the access line is a multiple of 56 Kbps; and similarly for
`the 64-Kbps case. However, for a Tl access line some service providers quote the port speed as
`1.544 Mbps, which is the raw speed of the circuit, with framing bits included (see the Glossary for
`more about Tl). Other service providers quote the port speed as 1.536 Mbps, which is the usable
`speed of the Tl circuit after framing b}t,s have been excluded. The relevant calculation is 24 chan(cid:173)
`nels x 64 Kbps per channel= 1.536 Mbps. Similarly, for El access circuits the port speed is some(cid:173)
`times quoted as 2.048 Mbps (raw rate) or as 1.920 Mbps (usable capacity; 30 channels x 64 Kbps per
`channel= 1.920 Mbps). Some service providers duck the issue of exact Tl port speed by quoting
`"Tl speed" or just "1.5 Mbps."
`4Some carriers are also beginning to send frame relay traffic over IP VPNs based on Multiprotocol
`Label Switching (MPLS). See [Wex99] for a survey.
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 12 of 24
`
`

`

`10
`
`Chapter 1 . Introduction
`
`Virtual circuits, which are the "nonphysical" component of a frame
`relay network. Sometimes also called virtual connections or logical
`connections, they are the frame· relay equivalent of dedicated physical
`lines. A virtual circuit appears to the user as a physical link, but no
`actual bandwidth is allocated to it-hence, it is "virtual." Two types of
`virtual circuits exist, permanent virtual circuits (PVCs), which are the
`most common, and switched virtual circuits (SVCs). When PVCs are
`used, the network operator assigns the end points of the circuits at the
`time of circuit provisioning. With SVCs the virtual circuit is set up
`dynamically, in real time, much as a phone call is set up. More on this
`in Chapter 5, Frame Relay Virtual Circuits.
`
`Benefits and Limitations of Frame Relay
`
`Frame relay technology is one solution to some of the problems that cor(cid:173)
`porate network managers are facing.
`
`·
`
`Benefits
`
`In this subsection we outline its typical benefits. These benefits are of
`course related to the needs of network managers discussed earlier. In later
`chapters we elaborate on how users can design their networks to achieve
`them. In other chapters, after we have discussed more details of frame
`relay technology, we will outline its technical advantages (Table 1.1).
`
`Cost Reductions
`Tariff Savings. For public frame relay services, the cost of frame relay
`connections is usually lower than that of equivalent dedicated leased lines,
`
`TABLE 1.1 The Benefits and Disadvantages of Frame Relay
`
`Costs
`Complexity
`
`Flexibility
`Performance
`Upgrade capability
`Traffic reporting
`
`jJ_
`jJ_
`,:'-\. 11
`11
`11
`11
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 13 of 24
`
`

`

`Benefits and Limitations of Frame Relay
`
`11
`
`typically by 20% to 50%. This is due, in part, to the ability of frame relay
`networks to statistically multiplex many PVCs over a single physical line.
`(Statistical multiplexing is discussed more fully in Chapter 5, Frame Relay
`Virtual Circuits.) Thus, more logical .connections can be supported by a
`given physical line, which is more cost effective for the carrier. The same
`economics work for private frame relay networks also.
`However, we shouldn't overgeneralize about pricing. In the United
`States, frame relay pricing is usually not distance sensitive. Hence, the
`price advantage of frame relay is more apparent only for longer distances.
`In other countries, because of regulatory policies, frame relay may actually
`be priced higher than equivalent leased lines.
`
`Wide Area Circuit Savings. Since frame relay allows many logical con(cid:173)
`nections to be shared over the same physical circuit, the number of physi(cid:173)
`cal circuits can often be reduced, particularly for highly meshed networks.
`
`Equipment Savings. For the same reason that the number of physical cir(cid:173)
`cuits can be reduced, the number of wide area network ports to remote
`locations can be reduced, often significantly. Thus, smaller and less expen(cid:173)
`sive routers may be feasible. Fewer physical circuits also translate into a
`reduction in the number of DSU /CSUs needed.
`
`Local Access Savings. Again, for the same reason that the number of
`physical circuits and the number of ports can be reduced, the number of
`local access circuits can be reduced. Here, the local access circuits include
`the local connections to long-distance leased lines. In addition, separate
`applications, such as LANs and IBM's SNA and possibly voice, can often
`be consolidated into a single network, further reducing the number of local
`access circuits.
`
`Savings Example. As an illustration of the potential savings described
`above, consider Figure l.2(a). We have 5 routers that are fully meshed,
`requiring a total of 10 long-distance leased lines, 20 router WAN ports, 20
`DSU /CSUs, and 20 different local access circuits. Assume that the local
`access circuits connect to long-distance leased lines at a long-distance car(cid:173)
`rier's point of presence (POP-), In Figure l.2(b ), we have the same 5 routers,
`but only 5 total router WAKf ports, 5 DSU/CSUs, and 5 local access cir(cid:173)
`cuits. The 10 long distance leased lines have been replaced by 10 PVCs,
`which are "logical," not "physical." The equipment within the provider's
`frame relay network, such as DSU /CSUs, frame relay switches, and
`trunks, is the responsibility of the service provider. Although the reduction
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 14 of 24
`
`

`

`12
`
`Chapter 1
`
`Introduction
`
`Router
`
`Router
`
`(a) Fully Meshed Router Network
`
`(b) Fully Meshed Frame Relay Network
`
`FIGURE 1.2 Example of Savings When Using Frame Relay. Fully meshed leased line networks
`need more CPE than fully meshed frame relay networks.
`
`in the amount of equipment is more noticeable than the tariff savings in
`our example, the reduction in monthly recurring charges typically pro(cid:173)
`duces a greater savings in the long run.
`With more routers in a fully meshed configuration, the savings only be(cid:173)
`come more drainatic.5
`
`5However, no one builds large fully meshed router networks based on leased lines because the
`costs increase as the square of the number of routers. Large router networks are partially meshed,
`often with a hierarchical structure.
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 15 of 24
`
`

`

`Benefits and Limitations of Frame Relay
`
`13
`
`Decreased Complexity
`Frame relay can simplify network architectures and reduce the number
`of leased lines, parallel networks, ports, and equipment. This translates
`into decreased complexity and lower operating costs. Also, frame relay
`providers typically offer the option of bundling everything together,
`including the equipment. Even if this option is not taken, a public carrier
`will assume a larger burden for network operations and availability. Net(cid:173)
`work administration and provisioning is often easier and faster than with
`traditional dedicated networks. Hence, it is often easier to manage growth
`of a frame relay network. ·
`
`Improved Performance
`By eliminating the packet layer processing of packet-switched and X.25
`networks (as discussed in Chapter 3, Frame Relay Architecture), frame
`relay gives higher throughputs. This is why it is often called a "fast packet"
`technology. Also, frame relay solutions often allow a higher level of direct
`connectivity (more meshing) between remote locations. Bypassing inter(cid:173)
`mediate network hubs can reduce congestion and decrease response times.
`In fairness, however, frame relay solutions will usually incur longer
`and more variable delays than equivalent leased line scenarios, although
`such delays are usually within acceptable limits. The delays may also be
`mitigated by more meshing, which reduces intermediate router hops.
`More on this in Chapter 11, Design of Frame Relay Networks.
`
`Increased Upgrade Capability
`Existing equipment can typically be upgraded to support frame relay stan(cid:173)
`dards rather easily. For instance, access devices often require only soft(cid:173)
`ware changes or simple hardware upgrades. This benefit is of more direct
`value to vendors, but can also spin off to customers. Upgrade capability is
`improved because the frame relay standards are well defined, coherent,
`and widely supported by equipment vendors and service providers.
`
`Improved Traffic Reporting
`Frame relay can measure, aKd report on traffic patterns, traffic amounts,
`peak traffic times, and so forth. For some networks, this information can
`give network managers their first view of what is really happening in the
`network.
`
`l
`
`e
`l,
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 16 of 24
`
`

`

`14
`
`Chapter 1
`
`Introduction
`
`Limitations
`
`Like every other networking technology, frame relay has limitations, as
`follows.
`
`• It is a shared-medium technology, which means there is inherent
`potential for a heavy user of the medium to create congestion for
`other users. This is true for any type of shared medium, such as Eth(cid:173)
`ernet or ATM, although good engineering can minimize the impact
`of congestion in the network. Congestion results in long, and vari(cid:173)
`able, delays for the user.
`• Like all packet networks, it introduces finite, though small, delays
`at the switching nodes, even when there is no congestion. Thus,
`although the signal propagation delay across a frame relay network
`will be about the same as across a leased line network, the total delay
`will be somewhat longer. More about this in Chapter 11, Design of
`Frame Relay Networks.
`• It was originally intended for data-only applications because it was
`designed for bursty, delay-tolerant, variable-block-size data. This envi(cid:173)
`ronment is the opposite of what is needed for good-quality voice.
`Voice can be carried, but not at consistent "toll quality." High-quality
`video is quite difficult, although lower-quality video is possible.
`• Typically, frame relay service providers offer only one class of ser(cid:173)
`vice to the customer. Thus, the frame relay network does not distin(cid:173)
`guish between voice and video traffic on the one hand and ordinary
`data traffic on the other. Nor does it distinguish between different
`types of data traffic, such as interactive versus file transfer. This one(cid:173)
`size-fits-all service may not be particularly appropriate for certain
`types of traffic, such as voice, which has tight delay requirements.
`Some carriers are offering different classes of frame relay service, but
`such differentiated service is not yet widespread.
`• In order to lay out a frame relay network, the designer must have
`some grasp of traffic in the network. Although it is possible to wing
`it, then collect traffic statistics from the frame relay devices after the
`network is built, and then redesign the network, the most efficient
`method is to know initially where traffic is going, how much, and
`what kinds.
`• For public frame relay networks only certain speeds are available,
`and this will depend on the carrier. Standard offerings are usually
`limited to a few sub-64-Kbps choices plus any increment of 64 Kbps
`up to 1.5 Mbps, or sometimes higher. These limitations are primarily
`
`Cisco Systems, Inc.
`Exhibit 1013
`Page 17 of 24
`
`

`

`Frame Relay and Other Networking Technologies
`
`15
`
`for marketing reasons, not technical constraints. However, in practice
`these limitations are not extremely troublesome.
`
`Frame Relay and Other Networking Technologies
`
`Frame relay is one of the technologies for solving the needs of wide area
`network managers discussed earlier.