[Asterisk-Users] E1/T1 failover hardware

[Jon Pounder]

> Warning ! I know zip about electronics.

why not just use a multipole relay ?

a 4pole double throw relay gives you 4 sets of contacts for the 2x tx and
2x rx wires. if you want to control with a bit in a parallel port, use
something like a uln2003 relay driver (if the coil current is low enough),
or a couple discrete transistors with the right gain and power handling.

use the 12vdc out of a spare drive connector to power the relay.

I would use one relay rather than 2 dpdt ones so that the switches are
mechanically locked together and if one relay sticks you don't get a weird
combination of circuits connected. Nothing will break, and the phone cops
won't likely bother you if this does happen, but it could be real annoying
and hard to diagnose if it does.

This is basically the electromechanical equivalent of you pulling one
cable and plugging in another (which is what I was going to do with some
T1 routers), except, I found the TXPort.

This actually is meant for failing between telco circuits, but works just
fine working failing between CPE instead. it actually has csus, reframers,
clock generator etc, as well as the "relay" circuit I describe to do the
switchover. it actually samples the lines and uses some intelligence to
see which to switch to. The device is "obsolete" so you'll only find it
surplus now, and its t1 only as far as I know but there is probably E1
gear around that does the same thing. I bought mine for $20 so it was not
even worth thinking about my own setup for that price, but they were
listed at up to $3000 when new.




>
> I've been looking for a device to handle the switching of an E1
> connection from one Asterisk box to another in the event of a
> catastrophic server failure.  All of the solutions I've seen so far have
> been designed to handle the situation where the telco line faults so
> that the local PBX can switch to a secondary E1.
>
> I've come across this application note :
>
> http://www.maxim-ic.com/appnotes.cfm/appnote_number/2857
>
> which describes "T1/E1/J1, N+1 Redundancy With Analog Switches"
>
> These parts are obviously designed to be built into E1 boards - hence, I
> think, the protection circuitry.
>
> Here's the question, then :  what (apart from jumping through regulatory
> hoops) is to stop a simple array of MOSFETS (and a bit of control
> circuitry) implementing a failover switch controlled (say) by a pin on a
> serial or parallel port ?
>
> jd
>
> --
>
> John Daragon                                          john at argv.co.uk
> argv[0] limited
> Lambs Lawn Cottage,  Staple Fitzpaine,  Taunton,  TA3 5SL,  UK
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>
>
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Jon Pounder

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