Monday, February 27, 2006

Washington State Emergency Agency to Use Satellite VoIP

Written by Robert Poe

Washington state's Emergency Management Division has deployed an emergency communication system using VoIP connections over satellites.

The system makes it possible for emergency personnel to talk to each other even when they're on opposite sides of the mountain range that divides the state. That geographical barrier makes it hard to use the VHF radio links that emergency agencies typically depend on.

The system, provided by Last Mile Networks using technology from FreelineUSA, connects a remote trailer to a National Guard central communications building via satellite links similar to those used to deliver commercial "dish" TV. The trailer, which operates at the disaster site, contains communications equipment and various backup power supplies, including a satellite dish and FreelineUSA IP node with softswitch capabilities.

The current configuration of the system provides eight simultaneous IP voice channels. It can also provide video links, using non-blocking architecture to make sure the video streams don't knock the voice links off the air.

VoIP technology gained attention for emergency communications following the widespread damage to conventional networks caused by Hurricane Katrina.

However, VoIP communication via satellite has been rare, mainly due to the significant delays resulting from the need for signals to travel to and from high-orbiting satellites. Such delays can run from 650 milliseconds to 1.2 seconds, according to Robert Simkavitz, president and CEO of FreelineUSA, which supplied key networking equipment used in both the remote and command center sites.

FreelineUSA uses specialized techniques to deal with the problems caused by such delays, such as the tendency of VoIP networks to drop calls when there are no packet transmissions for a certain length of time. Testing has shown the system to work with up to three-second delays, Simkavitz says.

Satellite delays are also disconcerting to callers, which is one reason for the near-complete migration of commercial international phone traffic from satellites to optical fiber cables.
One in-flight Internet communication system for airliners uses Iridium and other satellites to provide air-to-ground links.


Iridium's 66 so-called low earth-orbit, or LEO, satellites orbit at heights of only 780 kilometers. That means they produce considerably less delay than the geostationary satellites used to provide TV and other types of communications services. Geostationary satellites, so named because they remain in a fixed location above the earth, orbit at over 35,000 km.

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