Reliability
Building a system you can count on, no matter what.
Satellite networks provide one of the most reliable means of communications available. Like other telecommunications, it is rated by its “availability’, or the percentage of time (per month or year) that the service works correctly.
How availability relates to outage (Down-time)/month:
|
Availability |
Service Outage per Month |
Service Outage per Month |
| |
Minutes |
Hours |
|
99.000% |
432 |
7.2 |
|
99.900% |
43.2 |
0.72 |
|
99.990% |
4.32 |
0.072 |
|
99.999% |
0.432 |
0.0072 |
Here’s a little perspective on reliability.
A typical communications service like telephone or cable TV delivers approximately 99.9% availability, or 43 minutes of service down-time per month. Because it happens in spurts, it isn’t very noticeable to the average subscriber (unless, of course, it happens right when you need it most).
IT managers speak in terms of “five nines” (99.999%) availability, or less than one half a minute of outage per month. This is extremely hard to achieve in any real-world electronic system. For most practical networks and computer systems, the cost of backup and fault-tolerant systems needed to achieve this is prohibitive.
While an availability of 99%, with 432 minutes of outage per month, would seem to be unacceptable—it’s the goal sought for cellular telephone and other terrestrial wireless services. However, the real availability of cellular service is 95% or less.
Typical Satellite Reliability
|
Type |
Reliability |
Outage Min./Month |
|
Direct-to-home TV |
99.5% |
43.2 |
|
VSAT data services |
99.9% to 99.95% |
21.6 to 43.2 |
|
Telephone services |
99.95% |
21.6 |
Failure?
Once in orbit, many satellties operate for periods that are years in excess of their expected useful life. Still, unexpected partial or total failure may occur. Sometimes the failure can be anticipated and users moved to alternative capacity before losing service.
Why Satellite Service Fails and How It’s Restored.
|
Service Failure Cause |
Solution/Prevention |
|
On-board component failure |
•Redundant equipment (spares)
•Changing frequency to a different transponder |
|
User equipment failure |
•Maintenance action |
|
Link outage due to rain |
•Proper engineering and equipment selection; or use of land-based network backup |
|
Operator or equipment errors at teleport (hub) |
•Addressed by teleport operator; have necessary backup equipment available |
|
Radio frequency interference (RFI) unexpectedly jams signal |
•Generally caused by operator error or equipment malfunction; following good practice and having provided full contact information details are best prevention |
Choosing a Specific Satellite
The foundation of satellite reliability is the quality and performance of the satellite itself. Each satellite has:
So consider the past performance of a particular satellite when making a selection. Be sure to discuss reliability with the satellite operator.
