[VoIP] Switcher in training

[Steph Kerman]

Small commercially built crossbar exchanges do exist.  Building a small 
XB exchange is feasible but difficult because the marker circuit, which 
controls the operation of the switch or switches, is pretty complex and 
requires a variety of special purpose relays with different coil and 
contact characteristics.  Building a small XB exchange using stored 
program control with a PC or other CPU board might be a more practical 
solution if you're not put off by the notion of mixed technologies and 
have programming skills or are willing to learn.  But even with stored 
program control, you will need to build at least two different types of 
trunk ciruits to accomplish a complete exchange.  Again, the more you 
are willing to resort to the use of electronic components in the trunk 
circuits over conventional all-relay designs, the more feasible the 
task.  The use of stored program control also simplifies the trunk 
circuits, improving the feasibility in this way too.

Perhaps the smallest commercially built crossbar exchange is the 
Ericsson ARD624 PAX, with 16 lines and 2 links (connecting paths).  It 
weighs 100 lbs and stands about 36" tall with a footprint of 18" x 12" 
or less.  I own one and can share scans of some of the documents.  The 
larger 30 line 4 link ARD636 is about 24" wide, similar height and 
proportionately heavier but certainly nothing that would stress standard 
floor load capacities of any structure fit for occupany.

I also own an NEC PABX equipped for 40 lines.  This is about 42" wide, 
60" tall, 24" deep and probably weighs 400-600 lbs: much much less than 
a piano.  This exchange uses conventional WECo-style 20-vertical 
crossbar switches.

Finding a abandoned XB PAX or PABX is certainly something to be hoped 
for but not something you can count on.  Small PAXs seem to have been 
quite few and far between even at the height of their use.  There were 
many many very nice quality Japanese built PABXs installed during the 
1970s so it's more likely to find one of them.  But even they do not 
turn up frequently and many of them were the larger systems occupying 
considerably more floor space and weight than the ones I described.

Steph

Frank Hansche wrote:
> Good afternoon, all.
>
> I am in the beginning stages of building an Asterisk switch, then 
> ultimately an legacy switch.
>
> I have an extensive background in electronics and computers, and I 
> have worked in microwave radio as well as operating a medium sized 
> System 75. I've read the documentation on Asterisk and, combined with 
> my System 75 knowledge, I feel pretty confident about putting up an 
> Asterisk PBX/tandem. When I start to put my legacy switch together, I 
> will most likely reach out to the group for some help.
>
> One question I do have is about crossbar switches. Is there equipment 
> available to build a small switch? I live in a typical Northwest tract 
> home, and floor load is an issue. I don't know if my floor will hold a 
> larger switch. Any information will be most helpful.
>
> Oh yeah, I was also in broadcasting as a DJ and broadcast engineer. 
> East Hill Radio is my other spot of electronic and computer insanity!
>
> Thank you for reading!Frank Hanschewww.easthillradio.comSupport 
> community radio!
>