Tuesday, March 20, 2007

ShoreTel's Brainy Voice Switches Avoid Outages

Enterprise VoIP telephone systems have a lot to live up to. Traditional TDM based telephony has a development history spanning many decades of refinement. The gold standard of system availability is commonly accepted as "five nines" or 99.999% uptime. Any replacement for PBX and Centrex based phone systems has this lofty expectation to contend with.

ShoreTel takes on the reliability challenge with an approach used by high reliability military and aerospace systems. It's redundant distributed processing. The principle is to avoid putting all your apples in one basket. Murphy's Law says that if there is a single component that can take your system down, that's the one that's going to fail and probably at the worst possible time. Designers of high reliability systems avoid single point failures. If something goes wrong, there needs to be another piece of equipment that can take up the slack.

Actually, that's the way the Internet was designed. There are many routers, each with many routes to choose from, distributed over a wide geographical area. You can cut any line or knock out any router and the Internet will automatically compensate. The worst that happens is that traffic will slow if demand exceeds the resources available.

ShoreTel's ShoreGear Voice Switches aren't single point PBX phone systems. The switches are designed to communicate and coordinate with each other to create an IP PBX phone system that is distributed throughout the company. If you knock out one of the switches or it is unreachable due to a local network failure, its peers will take over its tasks to ensure that call processing continues uninterrupted. The same is true of IP phones being handled by that switch. They automatically fail over to another switch at the site.

What about trunk line faults? Multiple ShoreGear-T1 switches will provide PSTN connectivity even if one T1 or ISDN PRI line goes down. Outgoing calls will be picked up by the working ShoreGear gateways.

System expansion is accomplished by adding additional ShoreGear Voice Switches to the network as demand for phones and phone lines increases. This includes adding additional business sites on the network. As more switches are added, they peer to provide a robust distributed phone system.

The design of the ShoreGear Voice Switches is geared to support five-nines availability. The boxes are completely solid state, using flash memory rather than mechanical hard disk drives to store data. The operating system is a high reliability embedded real-time control OS called VxWorks from WindRiver Systems rather than the standard PC or server operating system.

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