Cisco press application acceleration and WAN optimization fundamentals jul 2007 ISBN 1587053160

He hasextensive experience in the content delivery network CDNmarket, focusing on enterprise and service provider contentdelivery and application optimization needs.. Provide high-perfor

Application Acceleration and WAN Optimization Fundamentals

by Ted Grevers Jr.; Joel Christner - CCIE No 15311

Publisher: Cisco Press Pub Date: July 06, 2007 Print ISBN-10: 1-58705-316-0 Print ISBN-13: 978-1-58705-316-0 Pages: 384

Table of Contents | Index

Overview

IT organizations face pressure to increase productivity, improveapplication performance, support global collaboration, improvedata protection, and minimize costs In today's WAN-centeredenvironments, traditional LAN-oriented infrastructure

approaches are insufficient to meet these goals ApplicationAcceleration and WAN Optimization Fundamentals introduces abetter solution: integrating today's new generation of

accelerator solutions to efficiently and effectively scale networksbeyond traditional capabilities while improving performance andminimizing costs through consolidation

Ted Grevers and Joel Christner begin by reviewing the

challenges network professionals face in delivering applications

to globally distributed workforces You learn how acceleratorsare transforming application business models, enabling IT

departments to centralize and consolidate resources while alsodelivering consistently superior performance

Grevers and Christner show how to identify network consumers,prioritize traffic, and guarantee appropriate throughput and

response times to business-critical applications You learn how

to use quality of service techniques such as packet classificationand marking and traffic policing, queuing, scheduling, and

shaping

optimization services into your network and for optimizing

content delivery The authors show how to address applicationprotocol-related performance problems that cannot be resolvedthrough compression or flow optimization alone In the finalchapter, the authors walk you through several real-world

scenarios for utilizing accelerator technology

Ted Grevers, Jr., is the solution manager for the Cisco® VideoIPTV Systems Test and Architecture (C-VISTA) team He hasextensive experience in the content delivery network (CDN)market, focusing on enterprise and service provider contentdelivery and application optimization needs

Joel Christner, CCIE® No 15311, is the manager of technicalmarketing for the Cisco Application Delivery Business Unit

(ADBU) He has extensive experience with application protocols,acceleration technologies, LAN/WAN infrastructure, and storagenetworking Grevers and Christner are key contributors to thedesign and architecture of Cisco application delivery and

application acceleration solutions

Provide high-performance access to remote data, content,video, rich media, and applications

Identify performance barriers arising from networks,

protocols, operating systems, hardware, file systems, andapplications

Employ application-specific acceleration components to

mitigate the negative impact of latency and bandwidth

This book is part of the Cisco Press® Fundamentals Series

Books in this series introduce networking professionals to newnetworking technologies, covering network topologies, sampledeployment concepts, protocols, and management techniques.Category: Cisco Press/Networking

Covers: Network Optimization

Application Acceleration and WAN Optimization Fundamentals

by Ted Grevers Jr.; Joel Christner - CCIE No 15311

Publisher: Cisco Press

Pub Date: July 06, 2007

Print ISBN-10: 1-58705-316-0 Print ISBN-13: 978-1-58705-316-0 Pages: 384

Hardware Barriers to Application Performance

Summary

Chapter 3 Aligning Network Resources with Business Priority

Employing Quality of Service

Understanding Accelerator Control Features and IntegrationSummary

Using CDN Calculation Tools

Chapter 6 Overcoming Transport and Link Capacity LimitationsUnderstanding Transport Protocol Limitations

Understanding Transmission Control Protocol FundamentalsOvercoming Transport Protocol Limitations

Command Grill Corporation: Improving HTTP ApplicationPerformance

This book provides foundational information about applicationacceleration and WAN optimization techniques and technologies.Every effort has been made to make this book as complete and

as accurate as possible, but no warranty or fitness is implied.The information is provided on an "as is" basis The authors,Cisco Press, and Cisco Systems, Inc., shall have neither liabilitynor responsibility to any person or entity with respect to anyloss or damages arising from the information contained in thisbook or from the use of the discs or programs that may

accompany it

The opinions expressed in this book belong to the author andare not necessarily those of Cisco Systems, Inc

Trademark Acknowledgments

All terms mentioned in this book that are known to be

trademarks or service marks have been appropriately

capitalized Cisco Press or Cisco Systems, Inc., cannot attest tothe accuracy of this information Use of a term in this book

content particular to your business, training goals, marketingfocus, and branding interests For more information, please

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At Cisco Press, our goal is to create in-depth technical books ofthe highest quality and value Each book is crafted with careand precision, undergoing rigorous development that involvesthe unique expertise of members from the professional

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Readers' feedback is a natural continuation of this process Ifyou have any comments regarding how we could improve thequality of this book, or otherwise alter it to better suit yourneeds, you can contact us through e-mail at

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Technical Editors: Jim French, Zach Seils, Steve Wasko Book and Cover Designer: Louisa Adair

Fax: +31 0 20 357 1100

Cisco has more than 200 offices worldwide Addresses, phonenumbers, and fax numbers are listed on the Cisco Website at

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©2007 Cisco Systems, Inc All rights reserved CCVP, the Ciscologo, and the Cisco Square Bridge logo are trademarks of CiscoSystems, Inc.; Changing the Way We Work, Live, Play, and

SlideCast, SMARTnet, StackWise, The Fastest Way to IncreaseYour Internet Quotient, and TransPath are registered

trademarks of Cisco Systems, Inc and/or its affiliates in theUnited States and certain other countries

All other trademarks mentioned in this document or Website arethe property of their respective owners The use of the wordpartner does not imply a partnership relationship between Ciscoand any other company (0609R)

Dedications

This book is dedicated to Kathleen, my wife, and our threewonderful children, Ella, Teddy III, and Garon

—Ted Grevers, Jr

This book is dedicated to my beautiful wife Christina, our

—Joel Christner

including Cisco Wide Area Application Services (WAAS) and

Application and Content Networking Services (ACNS) Theseresponsibilities include creating white papers, presentations,training, competitive analysis, and collateral; enabling sales;and driving product requirements and strategic direction withthe product management team Before joining the ADBU, Joelwas a member of the storage networking advanced technologyteam within Cisco Joel is a graduate student at Columbia

University working toward a master's degree in computer

science He holds a bachelor of science degree in electronicsengineering technology Joel lives with his wife in San Jose, CA

Jim French, CCIE No 4074, has more than 9 years of

experience at Cisco, 13 years of experience in information

technologies, and more than 13 years of experience fatheringhis wonderful son Brian Jim has held the position of Cisco

Distinguished System Engineer since early 2003 and holds CCIEand CISSP certifications Since joining Cisco, he has focused onrouting, switching, voice, video, security, storage, content, andapplication networking Most recently, Jim has been helping

customers to decrease upfront capital investments in

application infrastructure, reduce application operational costs,speed application time to market, increase application touchpoints (interactions), increase application availability, and

improve application performance Working with Cisco marketingand engineering, Jim has been instrumental in driving new

features and acquisitions into Cisco products to make customerssuccessful Jim received a BSEE degree from Rutgers University,College of Engineering, in 1987 and later went on to attain anMBA from Rutgers Graduate School of Management in 1994 Inhis spare time, Jim enjoys family, friends, running, basketball,biking, traveling, and laughing

Zach Seils, CCIE No 7861, is a technical leader in Cisco

Advanced Services Data Center Networking Practice Zach's

focus is the design and deployment of Cisco WAAS solutions forthe largest enterprise customers with Cisco He is also

frequently engaged with partners and internal Cisco engineersworldwide to advise on the design, implementation, and

troubleshooting of Cisco WAAS He also works closely with theApplication Delivery Business Unit (ADBU) on product

networking for large corporations Graduating in 1995 from

Central Michigan University, Steve has spent time deployingclient/server environments for 10 years with EDS, IBM,

Microsoft, and Cisco While at Microsoft, Steve was also a seniorproduct manager for Microsoft's Windows Server Division

Steve's industry certifications include Cisco Storage NetworkingSolutions Design Specialist, Novell Certified NetWare Engineer(CNE), and Microsoft Certified Systems Engineer (MCSE)

would have gone insane trying to find a balance between family,work, and writing time Thank you for being there for me

Without you, Chapter 1 would still be a blinking cursor on a

blank page, and the kids would be running the house

Ella, "Baby E," and Teddy, "Mein Theo," we have a lot of catch-up time ahead of us at the playground Who wants to be theline leader? "Monsieur Garon," although you will be just a yearold when this work is published, you've been kind to Kathleenand I during my many late nights of writing Who would havethought that 4 hours of sleep would be such a wonderful thing?Thank you, babies

If I were to choose one word to describe Joel Christner duringthe process of co-authoring this book, it would be "dedicated."I've never worked with anyone at Cisco as dedicated as you,Joel Your dedication and commitment to excellence made co-authoring this book a joy Joel, you are a rock star

From Joel Christner:

I would like to first thank my wife, Christina Christina, you

have been patient, supportive, and loving through this entireprocess, and I cannot find the words or expressions to thank

I would also like to give special thanks to you, the reader, forpurchasing and reading this book Ted and I both hope you find

it to be of value to you, and look forward to your feedback andcomments on improving it

I'd also like to give thanks to a few teams within Cisco To theteam within ADBU, you are all a blessing, and it has been anhonor and a privilege to work with such an amazing,

aggressive, quality-oriented, and customer-focused team Tothe Data Center and Application Networking Services advancedtechnology teams, I thank each of you for doing an outstandingjob and helping position Cisco as a leader in application

networking services

Numerous thanks to each of the technical reviewers, Steve

Wasko, Zach Seils, and Jim French, for their countless hours inreviewing this book and helping me and Ted improve its quality,accuracy, and readability You are all three a pleasure to workwith, brilliantly insightful, and we appreciate everything you doand have done

A tremendous thank you to the production team, Dayna Isley,Karen Gettman, Kristin Weinberger, and Christopher Cleveland.Thank you for helping to "shape the experience." Working withyou has been great, and I look forward to doing it again verysoon!

Last, and certainly not least, I'd like to thank my co-author TedGrevers, Jr Ted, working with you on this project has been

great I thank you for being a good friend, a mentor, and forgiving me the opportunity to join ADBU and work under yourguidance

[View full size image]

Command Syntax Conventions

The conventions used to present command syntax in this bookare the same conventions used in the IOS Command Reference.The Command Reference describes these conventions as

follows:

Boldface indicates commands and keywords that are

entered literally as shown In actual configuration examplesand output (not general command syntax), boldface

Square brackets [ ] indicate optional elements

Braces { } indicate a required choice

Braces within brackets [{ }] indicate a required choicewithin an optional element.

Over the years, I have often taught myself a new technology bydelving into the most complex aspects of the technology

supporting a globally distributed workforce By leveraging theirdiverse backgrounds and experience, Joel and Ted have

provided a unique perspective into the fundamental

technologies that define this rapidly evolving market And bytaking a solution-centric approach, they are empowering thereader with the knowledge necessary to weave WAN

optimization and application acceleration solutions into the

fabric of today's complex IT infrastructures

Businesses are just beginning to understand the potential ofWAN optimization and application acceleration solutions As

these solutions take on an increasingly relevant role in the

scalability and efficiency of the IT infrastructure, understandingthe fundamental technologies will be invaluable I would

Cisco Systems, Inc.

IT organizations face a number of increasing pressures to

increase productivity, improve application performance, provideinfrastructure conducive to global collaboration, improve

posture toward data protection and compliance, and minimizecosts across the board These pressures come largely as a

result of initiatives to increase availability and resiliency in

times of an "always on" business driven by the Internet, naturaldisasters, acts of war, and increasing competition The challenge

is that the corporate workforce continues to become more

global, and the characteristics of WANs are dramatically

different from those of LANs Simply consolidating infrastructureprovides better support for global collaboration, cost reduction,and better posture toward data protection and compliance, butdoes so at the cost of performance and productivity Adding

servers to the infrastructure potentially can improve

performance but does so at the cost of capital and operationalexpenditure, data protection, and complexity

Application acceleration and WAN optimization are powerful

technologies incorporated into accelerator solutions that aredesigned to help IT professionals intelligently deploy, in centralmanaged facilities, an infrastructure that provides performancemetrics for remote users that foster productivity, job

satisfaction, and global collaboration Accelerator solutions

enable high-performance access to remote information such asfiles, content, video, rich media, applications, and more Thesesolutions can help IT organizations satisfy requirements fromusers, management, and regulatory bodies simultaneously

Goals and Methods

The application acceleration and WAN optimization market isbecoming increasingly relevant in today's IT climate because ofthe immediate and tangible benefits that such solutions provide

to IT organizations With such a dynamic market being bornbefore our eyes, the authors realize that a book dedicated to

available today, and have insight into how many of these

solutions are designed While each vendor's implementation isunique, and this book simply cannot scale to discuss all of theimplementations, the concept discussed in this book and

purpose discussed of each implementation remains constant, as

an example of how the foundational components are designedand interact with other components within the solution

Who Should Read This Book?

This book is intended for anyone who is interested in learningabout the foundational components of application accelerationand WAN optimization, including IT directors, network

managers, application infrastructure engineers, and systemsengineers It is assumed that you have a high-level

understanding of the end-to-end application architectures andprotocols found within many enterprise and commercial

companies It is also assumed that you understand basic

networking principals, including routing, switching, quality ofservice (QoS), and network monitoring Unlike other books thatdive into the abyss of device- and version-specific

implementation guidelines and configurations, this book focuses

on the technologies at large, looking at the numerous

components that comprise a WAN optimization and applicationacceleration solution at a technology architecture level

Although this book could be read cover to cover, it is designed

to be flexible and allow you to easily move between chaptersand sections of chapters to cover just the material that you aremost interested in

This book has seven chapters covering the following topics:

Chapter 1, "Strategic Information Technology Initiatives,"introduces the challenges faced by IT organizations and

business at large, setting the tone for the relevance andimportance of WAN optimization and application

acceleration solutions

Chapter 2, "Barriers to Application Performance," builds

upon the first chapter and examines what are the

fundamental barriers to application performance in WANenvironments and the need for a holistic solution to

application performance

Chapter 3, "Aligning Network Resources with Business

Priority," discusses how the network is the platform thattouches all aspects of an organization and why it serves asthe foundation for an infrastructure conducive to applicationperformance

Chapter 4, "Overcoming Application-Specific Barriers,"

discusses how accelerators can work within the context ofspecific application protocols to improve user performanceand efficiency over the WAN while minimizing bandwidthconsumption These topics, along with those presented inChapter 5, are commonly viewed together as applicationacceleration

Chapter 5, "Content Delivery Networks," examines how

accelerators can be leveraged to ensure that the right

information is available in the right location at the right timethrough intelligent acquisition and distribution of

Limitations," examines application-agnostic techniques forimproving application performance and efficiency over theWAN through integration at the transport layer These topicsinclude compression, data suppression, and transport

protocol optimization and are commonly referred to as WANoptimization

Chapter 7, "Examining Accelerator Technology Scenarios,"shows four scenarios of how WAN optimization and

application acceleration solutions have provided benefit tofour customer environments

The book concludes with two appendixes:

Appendix A, "Common Ports and Assigned Applications,"serves as a quick reference guide for ports that are

commonly used in today's diverse network environment.Appendix B, "Ten Places for More Information," provideslinks to external locations on the Internet to help you

further your knowledge on the topics discussed in this work

territory Today, with advances in information technology, larger

a workforce that is distributed globally Supporting the

applications that the distributed workforce must access to

perform their daily tasks to drive productivity, revenue, andcustomer satisfaction has become a major business-impactingfactor Although this book does not address the process of

employee management in a distributed workforce environment,

it does address the IT aspects that directly impact the ability ofemployees to function efficiently in a distributed workforce

environment

This chapter introduces fundamental concepts related to

applications, distributed servers, and wide-area networks

(WAN) in a distributed workforce environment It also explainshow IT departments have had to modify their business models

to support a distributed workforce

Managing Applications

Software applications have become critical to an employee'sproductivity in today's workplace, driving greater competitiveadvantage and improving key business metrics Utility

applications are those that are pervasive across all employees

in an enterprise (or subscribers in a service provider network).Utility applications generally include e-mail, file, print, portal,search, voice, video, collaboration, and similar applications.Applications are no longer limited to simple word processing orspreadsheet applications Critical business tools now range fromthe simple web browser to applications that support functionssuch as e-mail, video on demand (VoD), database applications,and streaming media Applications, with the exception of Voiceover IP (VoIP) and streaming media, now drive the majority oftraffic that traverses most WAN connections today in the

enterprise These applications evolved from a centralized

client/server model to a distributed architecture, which nowincludes client workstations, personal digital assistants (PDAs),printers, remote desktop terminals, and even telephones

possibilities

Although maintaining a distributed workforce has many

benefits, such as having knowledgeable employees closer tocustomers, these benefits cannot be realized without facing alist of challenges Acquisitions, mergers, outsourcing, and

diverse employee responsibilities are all contributors that force

IT organizations to deal with a distributed workforce

Acquisitions and mergers create a unique set of challenges

because common application platform "religions" need to beagreed upon, and the demands of corporate communicationincrease Outsourcing creates not only network security

concerns, but also several application-level challenges that

require access to applications that might be housed in a

corporate data center across potentially distant security

boundaries Lastly, diverse employee responsibilities createunique branch challenges, based on the role and expected

output of each employee within a remote branch location

In each of the previously mentioned scenarios, application

performance becomes harder to effectively maintain as thedistance between the user and applications grows As networklinks increase to span larger geographies, so does the amount

of latency due to the amount of time needed to transmit datafrom point to point across the network Coupling the limitations

of physics with application inefficiencies, commonly called

application chatter, leads to exponentially slower response

times than what would be encountered on a local-area network(LAN) While bandwidth capacity might continue to increase forsuch long-distance connections, applications and content

continue to become more robust and rich-media centric Theneed for greater bandwidth capacity will always outpace thecapacities currently available These variables, and many

others, impact the overall performance of not just the

application, but also the employee

If you ask a network administrator why a specific application

application manager, she might say it is the network that iscausing slow application performance Who is right in this

situation? Many times, they are both right This section

describes testing new applications in the work environment andreducing application latency as methods of improving the

usability of applications in a distributed environment

Testing New Applications

Most enterprises have a structured testing model for the

introduction of a new application into the work environment.Many times, the new application is written to meet an

enterprise customer's business objective: process the data

input by the user, and save the processed data in a definedlocation New application testing typically occurs within the

customer's controlled lab environment A common test

configuration includes a couple client workstations, a server,and a switched network environment This type of testing

environment proves the application's offering abilities but manytimes does not demonstrate the limitations the application

brings to the end user who is based in a remote branch office

on the other side of a slow WAN link In many cases, these

limitations are not discovered until a production pilot, or if theapplication is deployed en masse

Figure 1-1 shows a simple application test environment, whichincludes an application server, switch, and two clients

Figure 1-1 Simple Application Test Environment

Client-based application caching is not enough to overcome theobstacles that are introduced when accessing centralized

applications and the associated data over the WAN Althoughapplication caches do aid in the overall performance for a givenuser, they do not address all of the limitations imposed by

application inefficiency, physics, the exponential increase in

need for capacity, and the growing geographically distributedworkforce

Two applications common to the distributed workforce are

Microsoft Outlook and Internet Explorer Both applications allowthe user or application administrator to define a certain amount

of client disk space for application caching The application

cache on the client workstation operates independently of theapplication server that hosts the data the client is requesting,providing a better-performing application experience

Microsoft Outlook retains a copy of the user's mailbox on the

to access all of the user's mail locally On-disk access reducesthe application's frequent reactive dependency on the WAN;Outlook seeks new mail periodically, appending the new mail tothe locally cached copy of the user's mailbox

Microsoft Internet Explorer supports configurable storage andlocation options for cached Internet and intranet content Thebrowser cache stores copies of any objects that do not containheader settings that prohibit the caching of objects for lateruse Commonly cached objects include graphics files, Java

objects, and sound files associated with web pages A cachedobject is effective only if the object is requested two or moretimes Users and application administrators have the option ofincreasing or decreasing the amount of space allowed for

cached content, ranging from as little as 1 MB to as much as 32

GB of on-disk storage

In Microsoft Outlook and Microsoft Internet Explorer, applicationcaching is effective only for the application being cached andonly for the user where the application caching is configured.Access to any content or object that does not reside within theclient's local application cache must traverse the WAN Not allapplication traffic can be cached by the client's local applicationcache

territory Today, with advances in information technology, larger

a workforce that is distributed globally Supporting the

applications that the distributed workforce must access to

perform their daily tasks to drive productivity, revenue, andcustomer satisfaction has become a major business-impactingfactor Although this book does not address the process of

employee management in a distributed workforce environment,

it does address the IT aspects that directly impact the ability ofemployees to function efficiently in a distributed workforce

environment

This chapter introduces fundamental concepts related to

applications, distributed servers, and wide-area networks

(WAN) in a distributed workforce environment It also explainshow IT departments have had to modify their business models

to support a distributed workforce

Managing Applications

Software applications have become critical to an employee'sproductivity in today's workplace, driving greater competitiveadvantage and improving key business metrics Utility

applications are those that are pervasive across all employees

in an enterprise (or subscribers in a service provider network).Utility applications generally include e-mail, file, print, portal,search, voice, video, collaboration, and similar applications.Applications are no longer limited to simple word processing orspreadsheet applications Critical business tools now range fromthe simple web browser to applications that support functionssuch as e-mail, video on demand (VoD), database applications,and streaming media Applications, with the exception of Voiceover IP (VoIP) and streaming media, now drive the majority oftraffic that traverses most WAN connections today in the

enterprise These applications evolved from a centralized

client/server model to a distributed architecture, which nowincludes client workstations, personal digital assistants (PDAs),printers, remote desktop terminals, and even telephones

possibilities

Although maintaining a distributed workforce has many

benefits, such as having knowledgeable employees closer tocustomers, these benefits cannot be realized without facing alist of challenges Acquisitions, mergers, outsourcing, and

diverse employee responsibilities are all contributors that force

IT organizations to deal with a distributed workforce

Acquisitions and mergers create a unique set of challenges

because common application platform "religions" need to beagreed upon, and the demands of corporate communicationincrease Outsourcing creates not only network security

concerns, but also several application-level challenges that

require access to applications that might be housed in a

corporate data center across potentially distant security

boundaries Lastly, diverse employee responsibilities createunique branch challenges, based on the role and expected

output of each employee within a remote branch location

In each of the previously mentioned scenarios, application

performance becomes harder to effectively maintain as thedistance between the user and applications grows As networklinks increase to span larger geographies, so does the amount

of latency due to the amount of time needed to transmit datafrom point to point across the network Coupling the limitations

of physics with application inefficiencies, commonly called

application chatter, leads to exponentially slower response

times than what would be encountered on a local-area network(LAN) While bandwidth capacity might continue to increase forsuch long-distance connections, applications and content

continue to become more robust and rich-media centric Theneed for greater bandwidth capacity will always outpace thecapacities currently available These variables, and many

others, impact the overall performance of not just the

application, but also the employee

If you ask a network administrator why a specific application

application manager, she might say it is the network that iscausing slow application performance Who is right in this

situation? Many times, they are both right This section

describes testing new applications in the work environment andreducing application latency as methods of improving the

usability of applications in a distributed environment

Testing New Applications

Most enterprises have a structured testing model for the

introduction of a new application into the work environment.Many times, the new application is written to meet an

enterprise customer's business objective: process the data

input by the user, and save the processed data in a definedlocation New application testing typically occurs within the

customer's controlled lab environment A common test

configuration includes a couple client workstations, a server,and a switched network environment This type of testing

environment proves the application's offering abilities but manytimes does not demonstrate the limitations the application

brings to the end user who is based in a remote branch office

on the other side of a slow WAN link In many cases, these

limitations are not discovered until a production pilot, or if theapplication is deployed en masse

Figure 1-1 shows a simple application test environment, whichincludes an application server, switch, and two clients

Figure 1-1 Simple Application Test Environment

Client-based application caching is not enough to overcome theobstacles that are introduced when accessing centralized

applications and the associated data over the WAN Althoughapplication caches do aid in the overall performance for a givenuser, they do not address all of the limitations imposed by

application inefficiency, physics, the exponential increase in

need for capacity, and the growing geographically distributedworkforce

Two applications common to the distributed workforce are

Microsoft Outlook and Internet Explorer Both applications allowthe user or application administrator to define a certain amount

of client disk space for application caching The application

cache on the client workstation operates independently of theapplication server that hosts the data the client is requesting,providing a better-performing application experience

Microsoft Outlook retains a copy of the user's mailbox on the

to access all of the user's mail locally On-disk access reducesthe application's frequent reactive dependency on the WAN;Outlook seeks new mail periodically, appending the new mail tothe locally cached copy of the user's mailbox

Microsoft Internet Explorer supports configurable storage andlocation options for cached Internet and intranet content Thebrowser cache stores copies of any objects that do not containheader settings that prohibit the caching of objects for lateruse Commonly cached objects include graphics files, Java

objects, and sound files associated with web pages A cachedobject is effective only if the object is requested two or moretimes Users and application administrators have the option ofincreasing or decreasing the amount of space allowed for

cached content, ranging from as little as 1 MB to as much as 32

GB of on-disk storage

In Microsoft Outlook and Microsoft Internet Explorer, applicationcaching is effective only for the application being cached andonly for the user where the application caching is configured.Access to any content or object that does not reside within theclient's local application cache must traverse the WAN Not allapplication traffic can be cached by the client's local applicationcache

In the 1990s, it was common to build a distributed networkarchitecture that involved deployment of application-specific orfunction-specific servers in each of the locations where userswere present High-speed WAN connectivity was consideredvery expensive by today's terms, often involving connectivity atrates less than 512 kilobits per second (kbps) To allow for

efficient access to applications and common, shared storage forcollaboration and other purposes, distributed servers located inbranch offices became commonplace, as illustrated in Figure 1-

2 Having distributed servers creates several challenges for the

IT organization, including a difficult path toward implementingreliable and secure data protection and recovery, timely onsiteservice and support, and efficient, centralized management

Figure 1-2 Traditional Distributed Server Architecture

[View full size image]

A common method for protecting data on distributed servers is

to leverage a form of direct-attached tape backup or sharedtape backup in each of the locations where servers are present.Tape cartridges have been used for years as a common and

party services, or even a local employee, will take the tape(s)offsite after each backup has been completed Although this is atrusted method, tapes can be stolen, misplaced, or lost in

trusted form of data protection As a common practice, third-transit, or can become defective Furthermore, some employeesmight not feel the same sense of urgency about manually

taking tapes offsite, which might lead to some or all of the

tapes never actually leaving the location

As an alternative to tape backups, centralized backups havebeen used, but at a cost that impacts the WAN itself Although it

implementations, these models call for a reliable and high-capacity WAN connection Such means of protecting data

perform best if the WAN is in a state of low utilization, such ascan be found if there are no other business transactions takingplace, commonly after hours Even in scenarios where the

amount of WAN capacity is high and link utilization is low,

performance might suffer due to other causes such as serverlimitations, latency, packet loss, or limitations within the

transport protocol

Centralized data protection is driven by a variety of forces

including lower cost of management and less capital

investment Another key driver of centralized data protection isregulation initiated by government agencies or compliance

agencies within a particular vertical These regulations includeSarbanes-Oxley (SOX) and the Health Insurance Portability andAccountability Act (HIPAA)

Providing Timely Remote Service and Support

Remote service and support is another challenge with a

distributed infrastructure; the further from the corporate datacenter the asset resides, the more costly the asset is to

support If a branch server fails, for instance, it is not

uncommon for the users in that branch to go without access totheir data or applications hosted on that server In some cases,users might be able to make changes to their workstations toaccess information from another repository, which might requirethem to be introduced to the WAN This can have disastrousimpact on user productivity and also cause increased levels ofWAN utilization, which might cause other applications and

services using the WAN to suffer as well

Using Centralized Management Methods

Several products exist today—either native to the operating