NETWORK DESIGN The following excerpt was taken from the Xensei Corporation web site at www.xensei.com. It describes the Xensei network that Jeff designed and built while the company was under his management. This excerpt was intended as a sales tool, and therefore is a somewhat simplified overview of the network, but it does show many of the key features of this advanced network design.

Technical Advantage

Xensei is a facilities based hosting provider. That means that unlike many web hosting companies, Xensei owns its own backbone network and servers, ensuring the ability to consistently deliver reliable, high performance services to its customers.

Xensei's backbone network is fully redundant, providing reliable, 24 hour a day Internet connectivity, never interrupted by equipment failures, power outages, or other network mishaps:

Figure 1. Simplified view of Xensei's Fault-Tolerant, Load Balanced Network

Key Features of Xensei's Fault-Tolerant, Load Balanced Network Design:

1. Xensei's Internet transit (connectivity) is purchased from multiple, distinct Network Service Providers (NSPs) with strong traffic exchange agreements, providing Xensei customers with direct connectivity to most of the Internet, while avoiding congested public traffic exchange points.

   In addition to Xensei's primary transit connections, Xensei also maintains direct traffic exchange arrangements with over twenty other local and regional ISPs, providing the fastest possible delivery of traffic to nearby destinations.

2. Xensei maintains fully redundant border routers, which can continue to provide full Internet connectivity to Xensei's customers even in the event of a complete failure of any router or transit connection.

3. Xensei maintains fully redundant core routers, which can continue to provide full connectivity within Xensei's own backbone network even in the event of a complete failure of any router or internal network link.

4. (Not shown on diagram) The OSPF (Open Shortest Path First) and BGP4 (Border Gateway Protocol) routing protocols are utilized by Xensei's border and core routers as well as Xensei's terminal servers and critical hosts, to provide dynamic, secure, fault-tolerant, load-balanced multi-path routing, both within Xensei's own backbone network, and to and from other Internet backbone networks. This allows failures in any part of our internal network, or beyond Xensei's network, to be detected and routed around automatically, within seconds, ensuring that service won't be interrupted by an unexpected failure.

5. Redundant, load balanced network segments utilizing state of the art layer-2 switching technology are maintained to provide multiple paths for moving data quickly in and out of Xensei's backbone network. Xensei's internal networks are all 100Mbps or faster.

6. (Not shown on diagram) Xensei utilizes fault-tolerant RAID disk subsystems in its servers, and maintains on-site spares within its NOC (Network Operations Center) for all critical server components. These on-site spares ensure rapid restoration of services should a critical component fail, even in the unlikely event of a failure of all components of a redundant system.

7. (Not shown on diagram) Xensei's NOC is powered by fully redundant UPS (Uninterruptable Power Supply) power. Each 2200 VA UPS is capable of providing backup power for an extended period of time, and key components such as Xensei's core and border routers are supplied with power interleaved from both UPS power sources, thus providing network redundancy even in the event of a UPS failure.

When choosing a site to host your organization's web presence, or when deciding how to connect your organization to the Internet, the above features are all important considerations. Will your site be available if your provider's backbone connection fails? Will it be available if a router or server goes down? Will you be able to receive your mail under these conditions, or if a mail or DNS server fails? At Xensei, we're proud to be able to answer yes when asked any of these questions.