CONTENT DELIVERY NETWORKS
Blowing Away Web Delays -- Content delivery providers claim they can blast Web pages to end-users. Are they just blowing smoke?
Angela M. Pugh
data.com
Give 'em what they want, when they want it. The strategy for serving up Web content really is that simple: Customers expect their pages immediately, and if they don't see them that soon they'll waste no time searching elsewhere. Trouble is, speedy delivery over today's sluggish Internet links is a tall order. And every frustrated surfer who cuts to another site is another potential customer lost.
But three providers say they can deliver content quickly enough to keep the page views (and revenues) high. They build so-called content delivery networks (CDNs)-installing servers on ISP nets all over the world so that content is as close to customers as possible. On top of that, they place probes and agents all along the 'Net to gather information on congestion-and build a virtual weather map of conditions that they can use to send traffic along the quickest path. Throw in caching and mirroring, these providers say, and it can all add up to a 50 percent increase in performance over typical in-house solutions. And performance is only part of the package: Corporate customers also save money since they don't have to add bandwidth every time things slow down. "It's more cost-effective," says Monty Mullig, vice president of CNN Internet Technologies (Atlanta), which is using the Freeflow service from Akamai Technologies Inc. (Cambridge, Mass.).
Still, as with any new service, net architects need to weigh all the factors before signing on. For one thing, CDNs aren't built into every ISP network-so traffic still stands a chance of being held up, depending on the route it takes. For another, no providers handle all types of content-and none take care of e-commerce.
Aside from keeping those things in mind, corporate customers should also get the full scoop on geographic coverage, as well as network coverage (how many content servers it has on how many ISP backbones). Pore over the architectural details too; find out just how the agents, probes, and caching and mirroring features work to boost performance. Also ask the obvious question: Just what kind of content does the provider handle? Look into the servers, too, and check whether the provider changes URLs to affect customers' brand identity. Remember that the availability of service-level agreements (SLAs) and the pricing specifics can play a big part in the final decision.
Table of Content
Aside from Akamai, Adero Inc. (Cambridge, Mass.) and Sandpiper Networks Inc. (Thousand Oaks, Calif.) are now selling content delivery services (see Table 1). If statistics are to be believed, their timing is right. A survey conducted by research firm Jupiter Communications LLC (New York) showed that 47 percent of end-users who experience technical problems the first time they try connecting to a Web site will simply go to another-and 9 percent of that number will never return.
The three providers have several things in common. First, they can deliver content to users in real time. Second, they furnish logs and traffic statistics. Third, they offer online monitoring via Web-based GUIs and allow customers to keep tabs on the CDN. Finally, they allow customers to update content directly and at will, rather than forcing them to schedule updates.
But that's about where the similarity ends. Geographic coverage, for one thing, varies. Akamai claims coverage in 25 countries, Adero in 19, and Sandpiper in 7. Akamai plans to be in 30 countries by the end of the year, and Sandpiper in 15.
Adero, which is hoping to expand to 30 countries, says it's focusing on the international market-either U.S. companies that have large amounts of traffic from overseas, or international companies that have a lot of Web traffic from the U.S. Why? The need for content delivery services is more pressing outside the U.S., according to Oliver Jones, vice president of engineering for Adero. U.S. networks are "hyperconnnected," meaning there are many routes from a Web server to an end-user. But internationally, the 'Net is more hierarchical, Jones says, and performance is lower. Adero thinks it can give those customers a 20 percent to 300 percent performance increase.
Server Setup
But geographic coverage is only one factor. Net architects also should find out on how many networks providers colocate their servers. Akamai is in the lead on this front, claiming 1,200 servers on 25 networks-with plans for "thousands" of servers on 60 networks. Sandpiper claims 800 servers on 25 networks, with plans to expand to 1,000 servers on 30. Adero has 25 servers on 25 networks, with plans for 40 on 40 by the end of the year.
There's more to keep in mind. Potential customers should also take into account the number of other customers a provider has. The more there are, the greater the number of users sharing the network. Akamai claims to have 40 corporate customers; Sandpiper, 25; and Adero, 12.
Delivery Details
Of course, coverage and servers are only part of the picture. Net architects would also be wise to learn exactly what these providers do-and how they do it.
Akamai and Sandpiper offer two delivery options: delivery of all customer content, or delivery of just the bandwidth-intensive material like graphics. (Customers deliver the "lighter" text portion from their own Web servers.) Adero delivers all content.
So how do those options work in practice? Say a user is downloading content from the Web site of a company that delivers its own text but leaves the graphics to a CDN operator (see Figure 1). The user's browser locates the company site by sending a request to the local DNS (domain name service) server, which returns the IP address of the site and transparently makes the connection-just as with any ordinary Web request. When the user reaches the company Web site, the text portion of the content is delivered-but the browser is also redirected to a CDN, which delivers the nontext data.
It's worth noting that even when Akamai is delivering the full mix of text and graphics, the Web request is still routed via its customer's Web server. But Adero and Sandpiper go about it a bit differently. Yes, the initial request goes to the DNS server-but what's returned is the IP address of the server on the CDN that can deliver the content. The origin server (that is, the company's) is eliminated altogether, which both companies claim augments performance.
Probing Questions
Next up in the content delivery decision process are the specific methods providers use to improve performance once requests have reached the CDN.
All three say they use proprietary software algorithms-running either on server agents or standalone probes-to route incoming requests for content over the most efficient path on the Internet, and to the server that is best able to handle them. (Probes sit on such ISP devices as routers, while agents typically reside on servers.)
Their algorithms base their routing decisions on three types of information. First, they measure the load and availability of their own servers. Second, they measure the geographical proximity of users to the available servers in the CDN. Third, they monitor the 'Net for congestion and outages, using that data to build a weather map of performance. "You need probes on ISPs outside of your own network to gain a more realistic view of real performance on the Internet," says Leo Spiegel, CEO of Sandpiper.
Adero uses both probes and agents to gather information. Its 25 probes use dial-up accounts to measure response times for end-users; its agents gather information on such metrics as latency , as well as data culled from public databases that gather stats on the Internet, to form its map.
Sandpiper's probes do the same thing by gathering data on about 25 variables, ranging from packet loss and latency to static network topology and peering relationships. Akamai calls its agents "monitors," and says they gather data on the performance of the public Internet as well as the performance of its own network. Akamai claims to have monitors on all 1,200 of its servers. Sandpiper has 150 probes. Adero has 25 probes and 25 agents.
Cache and Wary
Caching is another technique providers rely on to boost performance. When content is delivered, it's also cached in the CDN provider's server. The provider furnishes statistics on hits to content publishers so they can see how many people are requesting their sites.
Many ISPs cache content, which Joe Laszlo, an analyst with Jupiter, says "is a problem. Control of the content is taken out of the content publisher's hands. They want everyone to get the same picture, and with some ISP caches, it's unclear how often a site is updated," he says. In addition, companies have no way to see how many people have looked at their sites, information that's important when setting advertising rates.
But all of the content delivery providers say they can update content in real-time-so only the freshest content is served. They do so by looking at traffic logs from inside the ISP caches via proprietary algorithms. Adero says its caches and ISP caches can be configured as peers, talking to each other via ICP (Internet caching protocol).
With Akamai and Sandpiper, the ISP caches essentially become part of the content delivery network. The caches can talk to each other via proprietary software. This integration benefits the CDN provider, the ISP, the Web site owner, and the end-user. CDN providers can update content for their customers in the ISP cache and can offer them hit statistics. The ISP benefits because it doesn't have to go all the way back to the origin server to update content (saving money on bandwidth). The Web site owner doesn't have to worry that old content is in ISP caches, and end-users get the content faster. Adero and Sandpiper use Traffic Server from Inktomi Corp. (San Mateo, Calif.) for caching, while Akamai uses its proprietary algorithms. "It costs less because it was developed internally," says Kieran Taylor, senior product manager for Akamai.
Net architects may also want to look into mirroring, which allows providers to send copies of content to multiple servers on their networks. They typically use mirroring to push content if it's popular or frequently requested.
Adero uses a mirroring product from Webspective Software Inc. (Needham, Mass.), while Sandpiper uses proprietary algorithms (and says it will look into a possible partnership with a mirroring vendor in the future). Akamai doesn't offer mirroring, saying it hasn't seen huge demand-but it nonetheless is considering supporting it later this year.
The Character of Their Content
Of course, the best performance in the world means nothing if a provider doesn't handle the specific types of content a customer has. While all deliver graphics, downloadable media, streaming media, software downloads, and text, there are some distinctions to make (see Table 2). Sandpiper and Akamai, for example, can both deliver authenticated content-including cookies, digital certificates, and password-protected sites. Adero doesn't, but says it has plans to do so.
None of the vendors can process e-commerce transactions. They can deliver images for catalogs, but when it comes to making a credit card transaction, the end-user has to go through the Web site owner's transaction server. "They can browse and do everything until checkout," says Adero's Jones. "Then they would go to a transaction server."
So what's the problem? Actually, there are two. The first has to do with security: In order to process a transaction, a server needs an authentication key, and that key would have to be distributed to all of a content delivery provider's servers.
The second has to do with the customer's financial applications (including billing and payment apps). In order for e-commerce transactions to be processed on multiple CDN servers, the apps would have to be running on all of the machines. According to Sandpiper, e-commerce software currently runs on the back-end of networks. He says that massively distributed databases need to come into existence before e-commerce transactions can be processed on CDNs.
That lack of support for e-commerce looms as a real drawback, according to some observers. "It's nice to serve pictures, but at some point it will be equally important to support the business that supports the site," says Peter Christy, principal analyst with Collaborative Research (Los Altos, Calif.).
Sandpiper and Adero say that over the long term, they will focus on processing e-commerce transactions. Akamai doesn't have the same aspirations. "We're not in the business of transaction processing," says Akamai's Taylor. "We're in the business of content delivery."
Even though their services can't process e-commerce transactions, Adero and Sandpiper say they can deliver forms for interactive Web polls and time-sensitive information, such as stock quotes. Akamai says it doesn't deliver stock quotes or interactive polls because they're largely based on HTML (hypertext markup language)-which Akamai doesn't deliver for many of its customers. However, it says it could deliver a graphic display, such as a pie chart, with the poll results.
Shared Problems?
Potential customers also need to know what types of servers the CDNs are using. Fast servers are an important part of delivering speedy performance-and dedicated servers are faster than shared. Trouble is, all three use shared servers.
Another important issue in choosing a content delivery service is whether the provider rewrites, or changes, Web site URLs to affect the company's brand identity. This is a concern for companies that don't want-end users to see the content delivery provider's name when they're viewing a Web page. For instance, say an end-user is looking at the Web site of a Akamai customer; the URLs of the images will say "akamaitech.net." If the images are delivered by Sandpiper or Adero, the end-user doesn't see the provider's name anywhere, since their customers give them partial control of their DNSs.
Akamai says it hasn't sensed that URL renaming is an issue-but at least one of its customers has. "We forced them to not change it to 'Akamaitech,' " says CNN Internet's Mullig.
Provider Promises
Given that one of the main benefits of content delivery services is better performance, net architects might be interested in just what providers do to back up their promises. Fortunately, all three vendors offer SLAs. Both Sandpiper and Akamai guarantee 100 percent uptime. If the guarantee is not met, the customer is given one day's credit. In addition, both those providers guarantee that they can deliver content with their services faster than customers can deliver it themselves.
Sandpiper's SLAs address three other areas as well. First, the provider guarantees that it will never serve old content. Second, it promises customers that they will receive daily traffic logs. Third, Sandpiper guarantees that corporate customers always will be able to monitor the activity on its Footprint network. If any of the SLAs are not met, the customer receives a one-day service credit.
So where is Adero on the SLA front? It offers them for uptime and response time, but it didn't have any other details when this issue went to press.
The Cost of Content
The bottom line is a big part of the decision-making process for net architects. That's why it's important to understand the pricing schemes for content delivery services.
Start with Sandpiper, which charges $2,000 per Mbit/s per month. Akamai charges $1,995 per Mbit/s per month. Both offer volume discounts. Adero, on the other hand, offers two types of pricing. In the first scheme, it charges per Mbit/s; in the second, it charges per region served. Bandwidth-based pricing ranges from $1,995 to $3,195 per Mbit/s per month, depending on the region served. Region-specific pricing ranges from $200 to $345 per month. The $200 per-region price includes delivery of 5,000 page views a day and 50 Mbytes of downloads per day for one region. In this model, Web site owners can decide which regions they want to use the service for, and Adero will serve the content to those areas only.
All the providers base their bandwidth pricing on the 95th percentile model. Here's what that means. Every 5 minutes (in the case of Sandpiper) or 12 minutes (in the case of Akamai), the provider gathers statistics on how much traffic is moving over its network for each of its customers. All of the samples are compiled, and the top 5 percent are thrown out. The customer's monthly charge is based on the next number, which is at the 95th percentile mark.
Need an example? Say Acme Corp. is using Akamai's network to deliver content. Every 12 minutes, each of Akamai's servers measures how much of Acme's traffic is traveling over its network. All of those stats are fed back to a central location. At the end of the month, all of the measurements are put in descending order (10 Mbit/s, 9 Mbit/s, 8 Mbit/s, 7 Mbit/s, etc.). The top 5 percent are erased, and the company is charged based on the next number, say 5 Mbit/s.
All customers using this pricing scheme sign up for a certain committed aggregate information rate (CAIR), which is a guaranteed data rate they will use each month. For instance, if a company signs up for a 10 Mbit/s CAIR, it commits to that level of traffic and is charged based on that number. All of the vendors let customers burst over their CAIR levels.
All three vendors also give customers the option of increasing their CAIR on a daily basis. This way, a customer can utilize the volume discount and be charged a lower rate per Mbit/s if its traffic level has increased.
Delivery Downside
While CDN services may give net architects hope of better performance and cheaper bandwidth, there are a few problems to keep in mind. While all three providers want to expand coverage by entering as many ISP networks as possible, right now they're not really in all that many. And that means some end-users might be out of reach of a specific network-in which case they'll receive their content only from the nearest available server.
And while there's no doubt the services offer speedier content delivery, observers aren't so sure about how much of a market there can really be. "There seems to be a built-in limit to how much they can grow," says Jupiter's Laszlo. "Once they get past the top 20 or 50 Web sites, the value proposition to a Web site will be less clear. They need to make themselves attractive to smaller Web ventures." This is because traffic costs increase dramatically once a site goes above a certain threshold.
On top of that, the architecture of the public Internet might even place limits on just how good performance can be. That's why some of the providers are looking to add satellite delivery in the future, which would bypass the public Internet altogether (see "The Space Case"). But "future" is the key word here: Right now, none of them offer satellite delivery.
Nevertheless, proximity plays a major role in both performance and price-and that's the big benefit of content delivery services these providers are trumpeting. "If you can get content from a location closer to you, performance is almost always faster, and usually cheaper," says Christy of Collaborative Research.
-Angela M. Pugh is associate editor, WAN services for Data Communications and is based in New York. She can be reached at apugh@data.com.
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Read up on content delivery networks (CDNs) and related topics. Check out these URLs:
www.caching.com
The Web site for Collaborative Research, an analyst firm specializing in e-commerce and e-business infrastructure, features papers on CDNs and satellite services, as well as information on caching.
www.jup.com
Click here for the Web site of research firm Jupiter Communications LLC (New York). Visitors can view reports on such topics as content hosting, online commerce, and what consumers want from a Web site.
isp-lists.com/isp-caching
This list contains information that can help net architects get up to speed on the types of caching ISPs are using-ranging from Squid and proxy server solutions to new satellite caching systems.
www.inktomi.com/products/traffic
Net architects can visit this site for the specifics on Inktomi's Traffic Server, which two of the three CDNs use. It also features the Traffic Server Bandwidth Calculator, which shows net architects how much bandwidth they can save by caching content on their networks.
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Sidebar-
The Space Case
What's one surefire way to bypass congested terrestrial pipes when delivering content? Do it from space. Three providers rely on satellites to get the delivery through: iBeam Broadcasting Corp. (Sunnyvale, Calif.), Edgix Corp. (New York), and Skycache Inc. (Laurel, Md.). Satellite-based content delivery providers distribute data to servers in ISP POPs (points of presence) around the world. By using point-to-multipoint broadcasting, they can update thousands of servers by uploading the data to the satellite network just once.
All of the satellite providers claim to offer the same advantages as their earth-bound counterparts: better performance, along with the savings that come with not having to purchase as much bandwidth.
But are they cheaper than terrestrial CDN services? Maybe not. "During the ramp-up period, using terrestrial methods will be more cost-effective for the types of content Sandpiper, Akamai, and Adero are doing today," says Joe Laszlo, an analyst at Jupiter Communications LLC (New York).
Net architects also should keep in mind that satellite services don't deliver as many types of content as terrestrial CDNs. In addition, none of the satellite networks have been tested by a third party, so no provider claims can be corroborated. In fact, even the satellite providers themselves haven't revealed hard stats on just how much performance is improved.
Satellite delivery providers also have to overcome a sizable obstacle: the long-held perception of satellite technology as something that just hasn't proven itself. "The industry hasn't embraced satellite [as a transport medium] yet," admits Rangu Salgame, president and chief executive of Edgix. But he's hopeful, asserting that "this is changing."-A.M.P.
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