- Satellite Technology: Overview in 200 Words or Fewer
- Is Satellite Right for All Applications?
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Is Satellite Right for All Applications?
As I stated earlier, a geosynchronous satellite orbits 23,500 miles above the earth—or about a 50,000-mile round trip for a conversation. Light travels at 186,000 miles per second. On paper, at least, that equates to a little more than one-quarter second of delay. That’s enough to become noticeable before one even considers other things that can "slow a circuit down" such as latency in I/P and other protocols, as well as capacitive and reactive components in circuits. The effect of this becomes apparent in the example below, in what I consider to be my all-time favorite telecommunications practical joke: listening to someone in the shop talk to themselves. It goes like this:
While at a U.S. Air Force AUTOVON hub in Japan in the late 1970s, we had access to Model 490L Autovon switch. (Boy, now some of you really know I am dating myself). The switch was connected by inter-switch trunks to other switches worldwide. We would begin by jacking in directly to a satellite trunk from Japan to one of the international gateway hubs in Hawaii or California. From there, the call would progress via the commercial AT&T network across the United States, adding additional delay, to one of the international gateway hubs on the east coast. There was nothing in the network to prevent its picking up a second (or sometimes a third) satellite hop at this point that terminated in the U.K., Germany, Turkey, Italy, or anywhere else we had another switch.
We dialed up a loop back.
The call had by then traversed two or three satellite hops from Turkey, all the way back to Japan. By the time it got there, there was often a delay of two seconds or more. We would then patch the link to the home phone of any supervisor, which at that particular moment was not held in high esteem. At 3 AM. Picture the scenario:
Hello? (Silence)Hello? (Silence)
Hello?
About to hang up, but then HIS "hello" comes back at him—on a 1970s vintage analog circuit going 100,000 miles he could not tell it was his voice; only that it sounded like an international call. The next two or three minutes were invariably hilarious as the poor victim tried to establish contact with himself!
Victim: Hello? Response: Hello?Victim: Who is this? Response: Hello?
Victim: Who is this? Response: Hello?
Victim: Who is this? Response: Who is this? (Now the "who is this" is coming back!)
After a few minutes of this, they eventually figured it out and went back to bed—but during the time we would usually have it on a speaker in the shop for everyone to enjoy. It was funnier than the Abbott and Costello’s "Who’s On First?" routine.
The point that I am trying to make is that delays in satellite transmission can obviously affect voice communications. How much delays affect data that previously used a landline should be a topic of discussion between you and the satellite vendor. If your equipment sends out short "blocks" of data before expecting an acknowledgment from the far end, however, it affects performance more over a satellite than long blocks will. Absent these kinds of concerns, which can be addressed by the satellite vendor, satellite can be a remarkable disaster recovery vehicle. Here’s why:
- Ubiquitous coverage. A group of satellites can cover virtually the entire surface of the earth.
- Instant infrastructure. Satellite service can be quickly provisioned to in areas in which there is no terrestrial infrastructure.
- Independent of terrestrial infrastructure. Satellite service can provide additional bandwidth—on a diverse path—to provide redundancy as well as overflow capability during peak usage periods.
- Temporary networks. As stated above, people like the military and Department of Homeland Security find satellite to be the only practical, short-term solution for getting critical information into and out of an area.
- Rapid provisioning of services. Satellite services can be deployed quickly anywhere within the "footprint" of a satellite.
- Disaster recovery. In times of widespread disaster such as hurricanes, earthquakes, or tsunamis, solutions provided via satellite may be more available and more reliable than land-based connections.
If you are looking for a great reference and "easy read" on this topic, download or order the First Responder’s Guide to Satellite Communications, published by the Satellite Industry Association (SIA).
I’ll be back again soon with more tips on how satellite communications can add immeasurably to your organization’s capability to recover after a disaster, including some actual examples of successful configurations. In the meantime, good luck in your planning and your pursuits!