By JIM RAY
Network World

The Internet's latency and unreliability is largely due to its decentralized architecture. After all, the Internet is essentially a federation of networks making a best-effort attempt at delivering content. While network technology is improving at a rapid rate, the average request for a Web page still traverses about 17 terrestrial network exchange points, each of which can cause additional delay or lose packets.

Using satellite rather than terrestrial transmission can reduce the number of exchange points and improve network reliability and performance.

Satellite technology is an ideal match for content delivery networks, which replicate and distribute Web content to multiple facilities in dispersed locations. When users request that content it is served locally, rather than from an origin server located far away.

Because satellite networks are inherently multicast-enabled, they achieve significant economies of scale when simultaneously distributing content to multiple locations. A satellite-based content delivery infrastructure includes:

Popularity-based caching - Every downlink facility or point of presence is equipped with multicast-enabled network caches that locally store popular Web objects as they are requested by end users. These appliances increase network performance and reliability, and conserve upstream bandwidth. Multicast-enabled caches are essential for satellite networks to complete multicast push of content.

The caches operate via one-way IP over satellite with an asymmetrical terrestrial return link and via two-way IP over very small aperture terminal for the most flexibility. In two-way mode, caches would need to offer HTTP acceleration to mitigate the impact of satellite round-trip latency on the TCP protocol.

Scalable and reliable streaming media delivery - Scalable streaming media supports all major formats, including Windows Media, MP-3 and MPEG-1. Today's streaming solutions are being sized to distribute up to 20,000 simultaneous 300K bit/sec broadband streams from the edge downlink facility or other downstream node to end users.

While on-demand streaming is forecast to comprise the lion's share of the streaming market, live streaming is crucial to some applications, such as real-time sporting events and live corporate addresses. Also, live streaming is a core competency of satellite service providers, as the content must be sourced from its origin, and satellite networks avoid the majority of bottlenecks in terrestrial networks.

Traffic management - Directing both global and local traffic to optimal nodes is essential. Globally, end users requesting content are directed to the node in the service provider's network that can best serve the request quickly and reliably. While this can be highly dependent on geographic location, other deciding factors include the current workload on each node and the traffic congestion between each node and the end user. Locally, switches and load balancers use a variety of techniques to spread the workload evenly among available servers, or to direct particular traffic types to the appropriate device for optimal handling.

Intelligent content distribution and management - This component orchestrates the centralized distribution of content to remote nodes and incorporates reliable multicast techniques to guarantee the quality of distributed content, check for distribution errors, manage versions of content and automatically update nodes with fresh content. Combining this intelligent multicast content push with the unicast content pull derived from user re-quests provides the opportunity to create tiered services through local content hosting and insures high quality of service.

Content-oriented features - These capabilities, including user authentication and billing integration, are the application-level technologies that turn access service providers into content-driven services. While today's Internet is primarily a terrestrial network, many satellite service providers and operators are moving quickly to offer content delivery services.

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