Patricia Seybold Group
`E-Business Thought Leaders
`
`Network Caching Guide
`Optimizing Web Content Delivery
`
`By Michael A. Goulde
`March 1999
`
`Prepared for Inktomi Corporation
`
`85 Devonshire Street, 5th Floor, Boston, MA 02109 • Phone 617.742.5200 • Fax 617.742.1028 • www.psgroup.com
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`Table of Contents
`
`Executive Summary .............................................................................................1
`Importance of the Web.....................................................................................1
`Problems Caused by the Web’s Success ...........................................................1
`Caching Improves Performance........................................................................2
`Caching Supports Advanced Applications........................................................3
`Traffic Server Meets Caching Requirements ....................................................3
`Traffic Server Is a Strategic Application Platform ............................................5
`Conclusion.......................................................................................................5
`Introduction: The Business Case for Caching .......................................................6
`Economics and the Internet ..............................................................................6
`Barriers to Growth ...........................................................................................7
`Caching Overcomes Barriers............................................................................8
`Who Benefits from Caching? ...........................................................................9
`Quantifying the Benefits ................................................................................10
`Caching Basics...................................................................................................13
`Caching Internet Content ...............................................................................13
`How Caching Reduces Bandwidth Requirements...........................................14
`Key Requirements a Cache Must Address ......................................................15
`Cache Server Deployment..................................................................................16
`Designing a Cache Architecture: Cache Configuration Options......................16
`Identifying Ideal Cache Locations..................................................................20
`Capacity Planning for Caching.......................................................................27
`Designing Cache-Friendly Web Content ........................................................27
`Inktomi Traffic Server: Taking Caching to a New Level ....................................29
`Traffic Server Design Goals...........................................................................29
`Differentiating Features..................................................................................30
`Summary and Conclusions.................................................................................37
`
`Glossary of Terms..............................................................................................39
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`Illustrations
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`Illustration 1. Growth of the Web.........................................................................6
`
`Illustration 2. Network Traffic with and Without Caching....................................8
`
`Illustration 3. Bandwidth Savings.......................................................................11
`
`Illustration 4. Transparent Caching with Layer 4 Switch ....................................17
`
`Illustration 5. Transparent Caching with WCCP.................................................18
`
`Illustration 6. Cache Deployment Options..........................................................21
`
`Illustration 7. Point of Presence..........................................................................21
`
`Illustration 8. Network Aggregation Point..........................................................23
`
`Illustration 9. International Gateway ..................................................................24
`
`Illustration 10. Web Hosting Environment .........................................................25
`
`Illustration 11. Last Mile Implementations .........................................................26
`
`Illustration 12. Corporate Gateway.....................................................................26
`
`Illustration 13. Inktomi Traffic Server Architecture............................................31
`
`Illustration 14. Traffic Server Management Statistics .........................................32
`
`Cache Server Feature Checklist..........................................................................37
`
`Inktomi and the Inktomi logo are registered trademarks of Inktomi Corporation. Traffic Server is a trademark of Inktomi.
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`Network Caching Guide
`Optimizing Web Content Delivery
`
`Executive Summary
`
`Importance of the Web
`
`The creation of the World Wide Web was one of the most important events in the
`history of information technology. Whether measured by amount of content
`reachable over the Web or by the number of users accessing that content, the Web
`continues growing at an incredible rate ten years after it was first invented.
`Estimates are that by 2001, the number of Web users will be greater than 175
`million. One of the largest Internet Service Providers estimates that network
`traffic is doubling every 90 days as graphics, audio, and video become more
`common. The Web has penetrated households throughout the United States faster
`than any other technology in history, including the telephone, television, and
`VCR.
`
`The Web’s explosive growth has placed enormous stress on the capacity of the
`Internet, spurring massive investment on the part of carriers and network service
`providers in order to expand Internet capacity from the backbone all the way to
`homes and businesses. At the same time the Internet is becoming the network of
`choice for many types of business applications, spurring additional growth and
`increased load. The Internet is becoming a major, albeit distributed, center for
`commerce of all types. An increasing proportion of Internet traffic is in the form
`of business-to-business and business-to-consumer E-commerce transactions.
`Estimates of the economic impact of E-commerce over the next few years range
`from tens of billions to hundreds of billions of dollars. In any event, the Web is
`well on its way to becoming a major tool to people who conduct business all over
`the world. The expanding importance of the Web as a stimulant for world
`economic growth means that it must be a safe, reliable, predictable, and
`affordable place to do business.
`
`Problems Caused by the Web’s Success
`
`The enormous success of the Web as a source of information and as a platform for
`E-commerce has led to serious problems. Users’ expectations for a fruitful and
`enjoyable experience browsing the Web are often met with frustration and
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`annoyance because of slow performance and unreliable connections. Web sites
`take a long time to access and pages seemingly take forever to download. Cynics
`claim that WWW stands for “World Wide Wait.” Many people despair as to the
`prospects for improvement in the foreseeable future. Companies using the Internet
`to conduct business need more reliable performance as well.
`
`One of the major problems lies in the inherently inefficient nature of the Web.
`Every user seeking to view specific content must obtain it directly from the server
`that is the point of origin for that content. This is like everyone having to fly to
`Hollywood to see the latest movie. There is no distribution mechanism designed
`into the Web that is analogous to the system of movie theaters that place first-run
`movies in your hometown. Internet bandwidth is not an unlimited resource. All
`too often, users consume all available capacity. Since it is not possible to have
`dedicated, point-to-point bandwidth allocated to users, congestion is bound to
`occur. Special events, whether planned or unplanned, cause unpredictable peaks
`in bandwidth usage. As broadband access to home and work becomes more
`widespread, even greater pressure is placed on total available bandwidth. Added
`to bandwidth constraints is the fact that, as Internet use increases, servers are
`becoming overloaded and can’t handle the load.
`
`Simply adding more bandwidth to the Internet backbone isn’t the solution. First,
`all the bandwidth added to date has barely kept pace with Internet growth.
`Second, whether the bandwidth is being added to the backbone that spans the
`globe or the last mile between an Internet Service Provider and a household or
`office, the cost of delivering more bandwidth is extremely high. Adding
`bandwidth also just tends to move the bottleneck, rather than eliminating it. Other
`solutions must be sought to provide improved performance and to make the
`medium more predictable for users. Otherwise the Web will not fully realize its
`potential as an information resource and a vehicle for global trade.
`
`Caching Improves Performance
`
`One way to improve performance and make it more predictable is to minimize the
`variability introduced by long trips across the Internet from the content source to
`the user’s browser. By storing frequently accessed content at a location closer to
`the user, a great deal of latency and unpredictable delay in the Internet can be
`eliminated. The technique for doing this is called caching. Caching is a means of
`storing content objects from a Web server closer to the user, where they can be
`retrieved more quickly. The storehouse of objects, including text pages, images,
`and other content, is called a Web cache (pronounced cash).
`
`Caching has long been used in computer design. Data that are frequently used by
`the central processing unit (CPU) are stored in very fast memory, sometimes right
`on the CPU chip, thereby reducing the latency for reading those data and reducing
`the frequency with which a CPU has to read data from a slower disk drive.
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`Network caching, while a newer concept, is based on exactly the same principle
`and has the same benefit of cost-effectively improving the user experience.
`
`Caching also provides a way to distribute content closer to users in the same way
`that Hollywood distributes movies to local theatres, where each showing is
`viewed by many theatergoers rather than just one. This makes movies accessible
`to more people and easier to get to. Caching provides direct benefits to the end
`user in terms of reduced latency of Web page download (the time you have to
`wait before anything starts to happen) and faster download speeds (the time it
`takes for all the downloading to finish). But caching also provides benefits to
`network service providers. By storing, or caching, Web content that users request
`from remote servers locally, fewer of these requests have to be sent out over the
`Internet to be fulfilled. As a result, the access provider maintaining a cache has its
`upstream bandwidth requirements reduced. This reduces the bandwidth the
`service provider has to purchase in order to provide its customers with a
`satisfactory Web experience.
`
`Caching also provides several benefits in a Web hosting environment in which an
`access provider hosts Web sites for many customers. It can reduce the impact of
`traffic spikes caused by high-interest content and also serve as the basis for a
`variety of value-added services, such as providing additional capacity, guaranteed
`service levels, and replication services.
`
`Caching Supports Advanced Applications
`
`By the very nature of their design and function, cache servers offer unique
`opportunities for supporting advanced applications. Because a cache server is an
`intermediary between the Internet and the client, it can serve as a transformation
`point, converting the original content into different languages, formats, or media
`for delivery. A cache server can take a rich graphical page, distill the text content,
`and deliver it to a special pager or other handheld device. A cache server can
`translate pages from one language to another. Caches can become intermediate
`storage points for large, complex content such as streaming video and other
`multimedia. But not every caching product can provide a platform for these
`applications. Cache server programmability is a key feature that unleashes these
`benefits.
`
`Traffic Server Meets Caching Requirements
`
`Inktomi Traffic Server addresses all of the requirements for a high-performance,
`high-capacity, reliable, and flexible caching solution. It is designed to be used at
`various locations throughout the network, providing optimal performance for
`users and optimal bandwidth utilization for network service providers. Flexible
`configuration options allow Traffic Server to reduce the frequency with which
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`browser requests have to travel all the way to the origin server in order to be
`fulfilled.
`
`Inktomi designed Traffic Server with several specific goals in mind:
`
`• Deliver high performance across a broad range of loads
`
`•
`
`Implement caches at the highest levels of network traffic, handle extremely
`high volumes of requests, and cache extremely large amounts of data
`
`• Provide reliable operation that meets or exceeds the reliability of the services
`being cached
`
`• Minimize the cost of administering, maintaining, and operating large caching
`systems
`
`Traffic Server has several unique features that set Inktomi’s product apart from
`most other caching products. These include:
`
`• Traffic Server is built on standard hardware and standard system software,
`reducing the cost of ownership and taking advantage of new hardware and
`software designs (including large SMP computers).
`
`• Traffic Server is designed with the protocol and API support necessary to
`make it an ideal platform for value-added services.
`
`• Traffic Server’s Object Store is a specially designed storage mechanism
`optimized for rapid retrieval of cached objects.
`
`• Traffic Server’s DataFlow processing structure allows for efficient processing
`of incoming network streams in parallel with processing requests for data.
`
`•
`
`Inktomi’s clustering technology uniquely provides high capacity, high
`availability, and scalability for meeting
`increasingly demanding
`load
`conditions along with required capabilities for cluster management.
`
`In addition, Inktomi has been a leader in supporting industry protocols and
`formats, including:
`
`•
`•
`•
`•
`
`Industry’s first cache support for streaming media (RTSP) with RealNetworks
`Industry’s first integrated support for Usenet News (NNTP)
`Industry’s first third-party support for Cisco’s WCCP protocol
`Industry’s first HTTP 1.1 compliant cache
`
`Compared to other caching products on the market, Inktomi Traffic Server has an
`edge in having been designed from the outset to provide the highest performance
`and extensibility in the most demanding conditions.
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`Traffic Server Is a Strategic Application Platform
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`Network Caching Guide
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`Traffic Server is a key component that Internet access and Web hosting service
`providers, large electronic commerce sites, and large corporate networks consider
`an integral part of their network architectures. Inktomi’s product is designed to be
`flexible in how it is configured and deployed, making it suitable for a range of
`applications.
`
`Using Traffic Server to cache network data makes it possible to provide users
`with an optimal experience and predictable response times. With typical cache hit
`rates, the user experience has a higher quality of service (QoS). Improved QoS
`provides significant benefits to ISPs, content providers, and corporate sites. Better
`QoS results in higher customer loyalty and retention. It helps create a stronger
`brand equity, both for the access provider and for content providers. Content
`providers who ensure that their content is amply cached throughout the network,
`close to users, will ultimately see more visitors accessing their content.
`
`In addition to the benefits users receive, network service providers benefit from
`implementing Traffic Server because of the flexibility, ease of configuration,
`management of complex environments, and ability to offer new and differentiated
`services. Investments in bandwidth can be proactively managed, providing
`insurance against unpredictable peak loads and assuring more consistent
`performance for hosted sites. Customer satisfaction increases, creating a much
`higher customer retention rate and delivering a higher payback on the customer
`acquisition investment.
`
`The Internet and the World Wide Web will continue to grow and provide the
`foundation for an expanding share of global commerce. Growth is partially
`dependent on the quality of the experience that users and businesses have.
`Inktomi Traffic Server is helping network service providers and corporate
`network administrators provide optimal performance and responsiveness in this
`complex environment. Traffic Server also provides a foundation for advanced
`applications that will emerge as the Internet and Web continue to mature.
`
`Conclusion
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`Introduction: The Business Case for Caching
`
`Economics and the Internet
`
`The Internet and the World Wide Web that was built on it have been experiencing
`explosive growth (see Illustration 1). Between 1994 and 1997 the increase in the
`number of people accessing the Web, the number of Web sites, the amount of
`content available, and the amount of data being transferred over the Internet was
`almost immeasurable. International Data Corporation (IDC) estimates from 1997
`to 2001 the number of Web users will have tripled, to more than 175 million. IDC
`also estimates that the Web is growing by more than a million pages a day and
`will reach 1.5 billion pages by the year 2000. Current estimates indicate that
`network traffic is doubling every 90 days as graphics, audio, and video become
`more common. In addition, new uses for the Web have emerged, including E-
`commerce sites, portal sites, destination sites, and comparison shopping sites.
`
`Illustration 1. Growth, both in the number of Web users and the amount of content those users are
`accessing, is predicted to accelerate after the turn of the century. This will place a tremendous load on
`the Internet and potentially impact users’ quality of service experience.
`
`After an initial period of skepticism as to whether the Web would ever have real
`economic value or just be eye candy, there is little doubt today that the Web
`represents one of the major sources of economic growth in the world. Depending
`on the source, estimates for the value of commerce that will take place over the
`Web vary tremendously, ranging from tens of billions to hundreds of billions of
`dollars. Whatever the figure turns out to be in actuality, it is clear that the Web is
`rapidly becoming a significant global marketplace.
`
`For the foreseeable future, the Web will continue to grow in several dimensions.
`The number of users will continue to increase. The number of Web sites will
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`Barriers to Growth
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`Network Caching Guide
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`continue to increase. The amount of Web content available will continue to
`increase. And the amount of traffic that the Internet will have to carry in order to
`support this growth will continue to increase. But can the Web and the Internet
`grow forever? Is there some limit, either technical, economic, social, or otherwise,
`that will cause the Web’s growth to stall before it reaches its maximum potential?
`And if so, what can be done to prevent that from occurring?
`
`One of the most likely barriers to continued growth of the Internet and E-
`commerce is the growing frustration on the part of many users with an Internet
`that is slow to transfer information to their browsers and takes an insufferably
`long time to download content to their machines. There are many sources of
`frustration for users, including:
`
`• Slow Connection Speeds. Slow connections mean slow downloads. The
`maximum speed at which a user can connect to the Internet is limited by the
`types of access offered in his geographic area and how much he can afford, or
`is willing, to pay.
`
`• Unpredictable Performance across the Internet. As users connect at higher
`and higher speeds, the path to the Web server across the public Internet may
`not keep up with the user’s connection speed.
`
`• Limitations in Available Bandwidth. As Internet traffic increases, the
`capacity of the Internet infrastructure has to be built out to handle the
`additional load. That build-out will lag behind user demand for the foreseeable
`future.
`
`• Web Sites that Are Overwhelmed with Traffic. Many popular Web sites are
`not engineered to handle the loads they experience. Sometimes this is because
`of poor planning, but other times it is due to unexpected popularity.
`
`The result is that users are subject to long waits while a page begins loading and
`long delays while the page finishes downloading.
`
`Addressing these problems takes more than just huge investments on the part of
`network service providers. Even at high levels of capital expenditures today,
`service providers are just barely keeping up with growing bandwidth demand.
`Increasing bandwidth alone cannot address the Quality of Service (QoS) issues.
`Greater bandwidth cannot address network latency and bandwidth cannot
`accelerate overloaded or slow origin servers. Other solutions are required.
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`Caching Overcomes Barriers
`
`Caching is an approach that improves QoS for users while improving the
`economics for network service providers. Caching entails storing frequently
`accessed Web content closer to users, thereby reducing the number of hops that
`must be traversed in order retrieve content that resides on a remote site. This
`approach is not unlike the system that exists with Hollywood movies. Movie fans
`aren’t required to travel to Hollywood to view a movie; the movies are sent to
`local theatres where people can view them at their leisure. Placing Web or other
`network content close to users in the form of a network cache is basically the
`same idea.
`
`In operation, requests for content originate from a user’s browser and are first
`directed to the caching server. If the content is currently contained in the cache
`and is up to date, the content is sent to the user without the browser’s request
`having to be sent on to the originating server. This can reduce the latency for the
`transfer of content and reduce the amount of time it takes to transfer the content to
`the user. It also reduces the amount of data the service provider has to retrieve
`upstream from the Internet to fulfill requests. The difference in bandwidth
`requirements in a cached and noncached environment is shown in Illustration 2.
`(A more detailed technical discussion of cache technology follows in the sections
`“Caching Basics” and “Cache Deployment”.)
`
`Illustration 2. Network traffic with and without caching. The amount of bandwidth required across the
`backbone in a non-cached network is significantly greater than in a network that has been configured
`with caching servers, since many requests can be fulfilled locally.
`
`Caching Is Well-
`Proven
`
`Caching is a concept that is well understood in computer hardware design.
`Modern microprocessors employ on-chip caches of high-speed memory to store
`frequently used instructions and data locally instead of having to read them from
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`Web Browser
`Caching
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`Network Caching
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`Network Caching Guide
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`slower memory. Computers implement several additional levels of caching,
`including RAM cache and even on-disk cache, all designed to reduce the latency
`for reading instructions and data and speeding up the transfer of data within the
`system. The basic principle behind caching is to store frequently accessed data in
`a location that can be accessed more quickly than it could from the data’s more
`permanent location. In the case of a system’s CPU, the permanent location is the
`disk. On the Web, the permanent location is the origin server somewhere out on
`the Internet.
`
`Web browsers also implement a form of caching, storing recently accessed Web
`content on the user’s hard disk and reading from that local cache of files instead
`of accessing the Internet. This works well when the user hits the “Back” and
`“Forward” buttons in their browser during a session, but it does nothing if the user
`is browsing a site for the first time.
`
`Neither the browser’s cache nor a Web server’s cache can address network
`performance issues. By placing a cache of Web content on the network between
`the user and the originating Web sites, the distance that commonly accessed
`content has to travel over the Internet is reduced, and users experience quicker
`response and faster performance. Network caching takes advantage of the fact that
`some content is accessed more frequently that other content. By implementing a
`caching solution, network service providers can provide a better Web experience
`to their customers while reducing the total requirement for high-bandwidth
`connections to the Internet.
`
`Caching servers optimize both system and network resources. Naturally, there are
`trade-offs. There are obvious costs associated with implementing a caching
`solution, such as the expenses associated with hardware and software,
`administration, and maintenance. But for the network service provider, these costs
`are offset by potential savings associated with building additional Internet
`connection bandwidth. In addition
`to savings, caching
`introduces many
`opportunities for new sources of revenue, including service-level guarantees and
`content
`transformation services. There are also hard-to-quantify benefits
`associated with reducing user frustration and providing a better customer
`experience. As the number of users accessing an increasing wealth of Web
`content continues to grow, it will become easier to demonstrate the economic
`benefits of caching, both in hard and soft terms.
`
`Who Benefits from Caching?
`
`The ultimate beneficiaries of caching are users. No matter the speed at which a
`user connects to his Internet Service Provider (ISP), the response time for
`retrieving content from any Web site varies over a wide range. Response time is a
`function of the total amount of bandwidth available at any point in time, the total
`amount of network traffic at any point in time, and the load being placed on a
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`target site by an unpredictable number of visitors. And it is impossible to predict
`when those peak loads will occur. Major news events, such as when the Starr
`Report was released or Iraq was bombed, lead to heavy traffic at key Web sites
`that may swamp those sites with more traffic than they can handle. As a result,
`performance deteriorates and users are not just frustrated, their confidence in the
`Web as a reliable source of information suffers.
`
`But this need not be the case. For example, AOL has added Inktomi Traffic
`Server caching to its network architecture. With the cache in place they are able to
`handle over two billion hits per day, and peak loads, such as those generated by
`the publishing of the Starr Report on AOL’s Web site, had little or no effect on
`the AOL user experience.
`
`Caching solutions provide network service providers with an answer to the
`problem of users’ virtually insatiable demand for bandwidth. A network provider
`can build investment models that address connectivity requirements for
`customers, but there is no model that can help with determining how much
`upstream bandwidth should be invested in. More upstream bandwidth can bring
`Web content to users more quickly, but how much bandwidth has to be provided
`is hard to determine. Caching as much Web content as possible within the ISP
`while using modest amounts of upstream bandwidth is a way to give users what
`they demand without creating a black hole for bandwidth investment on the part
`of the ISP.
`
`Caching has several benefits for corporations. By providing a local cache for Web
`content, corporations can control how much Internet bandwidth is required to
`satisfy users. In addition, by using filtering mechanisms and access policies,
`employee use of the Web can be controlled and limited to activities that
`contribute to corporate functions.
`
`The AOL Experience
`
`Network Service
`Providers Benefit
`
`Corporations Benefit
`from Control
`
`Quantifying the Benefits
`Direct Benefits to
`Network Service
`Providers
`
`Caching solutions can help reduce or defer investment requirements for service
`providers. Benchmarks have shown that even modest cache hit rates (of
`approximately 30 to 40 percent in a moderately loaded network access point) can
`reduce the amount of outbound bandwidth that has to be configured by the
`equivalent of several T3 lines. This means that a provider can deliver more
`content to customers with less outlay for bandwidth, effectively providing more
`bandwidth per dollar. This allows service providers to better manage their
`network build-out, which is critical since it may not always be available to add.
`
`To get a sense of the magnitude of the possible economic benefits to network
`access providers, assume that one T3 line carries 45 Mbps of data and 40 percent
`of that is HTTP traffic. A conservative cache hit rate of 40 percent would take 40
`percent of Web traffic off the backbone. Caching additional protocols, such as
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`NNTP and FTP, would result in even greater savings. Just using HTTP traffic for
`this example, the access provider would have a 16 percent reduction in backbone
`traffic (0.40 x 0.40 = 0.16). If bandwidth costs are estimated at $1,000 per Mpbs
`per month, then a network cache in front of a metered T3 with Internet access can
`save an ISP $7,200 per month or $86,000 per year. For a large ISP with multiple
`T3 lines, these savings can add up quickly, as shown in Illustration 3.
`
`Illustration 3. A summary of the savings an ISP can realize by using caching servers.
`
`Indirect Benefits to
`Network Service
`Providers
`
`Benefits for
`E-Commerce
`
`ISPs that can provide improved performance and better QoS for their customers
`will, all other things being equal, have higher satisfaction ratings, which will lead
`to higher customer retention. For each customer retained, an ISP avoids the
`burdensome cost of customer acquisition and the front-end load of getting
`customers up and running. By reducing these costs, ISP profitability will be able
`to increase.
`
`Caching provides distinct benefits for end users in the form of an enhanced
`experience and better perceived value for their monthly access fees. Happy Web
`surfers benefit the entire industry. But the real benefits accrue to the E-commerce
`sites that these users visit. Users can visit more sites, do more shopping, and
`purchase more goods and services if content can be delivered and downloaded
`faster. If conservative forecasts of a $100 billion market for E-commerce are true
`and caching can reduce shopper abandonment by one percent, then caching will
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`Indirect Benefits to
`Web Sites
`
`Revenue
`Opportunities from
`Value Added
`Services
`
`have contributed $1 billion to E-commerce. This is a significant benefit to an
`emerging market.
`
`All sites have a stake in QoS, but E-commerce sites can suffer a direct revenue
`impact if visitors have a less than ideal experience. If a site is perceived as
`performing poorly, fewer visitors will stick around to place orders, fewer visitors
`will return, and the site’s brand equity is weakened. A site that users experience as
`providing good performance will build strong brand loyalty and attract new users
`by reputation. Although E-commerce sites themselves are not deployment targets
`for large scale caching servers, they have a vested interest in promoting caching
`throughout the Internet. They can benefit, however, by designing sites to work
`well with caching solutions. How this is done depends on the sophistication of the
`cache server. E-commerce providers will need to take a more active role in
`advocating sophisticated cachi