Last-mile connectivity, a term that's familiar to any company that connects its private network to the Internet, refers to the critical link between a site and a carrier (i.e., the link between a private network and the Internet backbone). Until recently, companies depended on carriers and their landlines for last-mile connectivity. Now, satellite-based network services have developed to the point that their speed and cost make them a viable alternative to terrestrial links, and Tachyon is a leader in this field.
Overcoming Latency
Commercial use of satellites for telephone, television, and other types of data transmission has occurred for decades. Commercial use of satellites for high-rate TCP/IP data transmission, however, is relatively new. Typically, satellite communication has inherent latency that doesn't mix well with network protocols such as TCP/IP, which is optimized for low-latency LANs. Marrying these technologies was a major accomplishment that Tachyon achieved while remaining within the bounds of the open standards on which TCP/IP is based. Thus, you can plug the Tachyon Extended Enterprise Network Access service system into your LAN without worrying about nonstandard protocols or hardware that might not interoperate with your network.
The basic problems with satellite communication include the sheer distance of most satellites from the earth; TCP/IP's default slow start, window size, and acknowledgment frequency; the inherent noise levels of a satellite link; and ever-changing atmospheric conditions. To mitigate these concerns, Tachyon developed new signal modulation schemes, optimized communications protocols, and specialized satellite radio technologies. The result is a reliable, satellite-based broadband circuit that's robust enough for enterprise customer needs. The initial setup price is steep, but the monthly fee is close to that of an average terrestrial T1 circuit.
Testing the Tachyon
I used the Tachyon system in the Windows & .NET Magazine Lab for 3 months. After I filled out a site survey form, an installer showed up with the equipment. The elliptical satellite dish connects to the indoor unit with a pair of coaxial cables. The indoor unit is an appliance with two network interfaces. One is a proprietary interface for the satellite dish, and the other is a standard 10/100 Ethernet card with an RJ-45 connector. The unit has a Web interface for configuration, but it's password protected and isn't typically accessible by the customer. The system installer and the Tachyon support staff are the only people who configure the indoor unit.
With its standard Ethernet interface, the Tachyon system was a breeze to set up on the network. I received one routable IP address from Tachyon, which I assigned to the external interface of my firewall.
The performance of the Tachyon system was generally good. I could definitely sense more latency over the satellite connection than over a standard landline. Tachyon uses a Web proxy service that prefetches Web content from sites that you visit, which helps when you explore one Web site but not when you browse many sites. The inherent latency of a satellite connection is greatest when you initially establish a connection to a site, so the protocol enhancements that Tachyon uses are more evident during downloading activities than during casual browsing. I wasn't surprised to experience the best performance with FTP because latency isn't a concern with UDP. Average cumulative performance in the lab was approximately 79 percent of the advertised speed (i.e., 1.544Mbps down, 256Kbps up).
Overall, the Tachyon satellite service performed well. Because of the high price for setup compared with traditional carrier services, Tachyon might not be the best choice for companies whose proximity to carrier infrastructure assures them relatively inexpensive WAN links. However, for companies in remote areas or those that need last-mile redundancy that's independent of landlines, Tachyon provides a service well worth the cost.
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