By positioning content near the network's edge, CDNs reduce the latency associated with the Internet's multiple routers and slow peering points. Using cache devices or servers strategically located in ISP PoPs (points of presence), public CDNs mirror original content from subscribers and make it available near end users. The result is more accessible content and faster delivery. Companies such as CacheFlow, F5 Networks, Network Appliance and Volera present a similar way for enterprise networks to reduce the bandwidth requirements and costs associated with the generally slow Internet access points and WAN links for remote campuses.

This technology becomes critical as enterprises realize the full benefits of creating, using and reusing valuable content. In a recent survey of 150 enterprises, Aberdeen Group found that 45 percent intend to buy a content- or document-management application. The HTRC Group estimates that the North American market for eCDN products will grow 72.6 percent per year to reach $625 million by 2004. Clearly, companies realize it makes no sense to create content if you can't deliver it.

The savings realized by creating and developing content once and reusing it across the enterprise is apparent. By enhancing the content with rich media, enterprises also can upgrade the quality of experience for employees, improve corporate communications and deliver training materials that improve the learning process.

Companies can use eCDNs to Webcast videos of enterprisewide meetings and corporate events, eliminating a boatload of employee travel costs. ECDNs also let organizations update training materials in real time for immediate distribution. The same benefits can apply to instructor-led training. For example, in the past two years, IBM moved 70 percent of its training online for an annual savings of $200 million (see NewMonday.com: IBM saves ý200m a year).

Branching Out

Most enterprises have centrally located data centers with high-capacity Web and application servers linked to back-end storage devices. In turn, the data centers serve branch or regional offices via the Internet or dedicated WAN links. Although 56- and 128-Kbps links are sufficient for transmiting and receiving e-mail, documents and static Web pages, they become saturated when many users demand rich media.

Just 10 branch employees accessing a streamed training video encoded at 150 Kbps from a central server can eat up the bandwidth of a 1.54-Mbps T1 line and saturate the branch-office access point. Such traffic may prevent other applications from running if they regularly traverse the WAN link. It also may jack up bandwidth costs if your only solution is to add capacity. Furthermore, other bursty TCP-based traffic may cause higher percentages of lost packets, raising jitter rates and latency, and degrading the quality of the stream.

Because it's so costly, increasing bandwidth to accommodate streaming traffic is not the answer. Monthly WAN bandwidth will set you back about $800 per Mbps in North America. At that rate, a T1 line costs about $1,250 per month (see "Content Networking and Edge Services: Leveraging the Internet for Profit"). If rich media has a future in your enterprise, you need more options than "feeds and speeds." Rather than increase pipe size, eCDNs help decrease bandwidth needs.

Using caching technology at the network's edge, eCDNs let user transactions begin and end over a corporate LAN without ever traversing the Internet or a WAN link to the central data center. If you keep in mind the $800-per-Mbps transfer rate for a T1, it's easy to see the cost savings. Not only can eCDN providers cache frequently used files for reuse, they can also pre-position content close to users. As our review of eCDNs (Volera Makes You Cache-Rich Quick") shows, this not only reduces the amount of information that traverses costly links but improves application response time.