[asterisk-users] Slightly OT:CSU on Digium cards, and it's requirement

[Jon Pounder]

Quoting C F <shmaltz at gmail.com>:

> Do the Digium cards have a built in CSU?
> Is a CSU an FCC requirement? or just a carrier requirement?

if you expect things to work you need one regardless of regulations,  
yes the digium cards have it built in, as do most modern t1 cards.

if the "T1" terminates in something that looks like a scsi connector  
you have an hssi interface most likely, if it terminates in an rj45,  
especially if it has status lights, you most likely have yourself a  
csu built in, sometimes you'll have a db15 instead of the rj45  
depending on the country it was designed for but it still works the  
same if you just get a passive adapter to get to the connector type  
you need (or make one, t1 speed is a 1/8th of the slowest ethernet so  
construction technique is not too critical if you ever made an  
ethernet cable)


coming in from the raw copper pair this is what needs to be there :

telco supplied "pairgain" box which is normally an HDSL modem that  
gets you from a type of dsl circuit to a 2 pair T1 / DS1 circuit  
(don't confuse DSL and DS ONE in this sentence)

that is the actual demarcation point.

then comes your csu/(dsu)
This is the point where remote loopback tests can be done without  
actually talking to the guts of your hardware, telco can normally do  
it to their box as well but when they do a line test they loop to your  
csu normally.

next comes a serial interface of some sort, in a more modern setup its  
indivisible from the csu, in the old days you had a physical  
synchronous serial cable between running at t1 clock speed.

Where its separate the serial port is also known as an hssi connection  
or high speed serial interface.


So without the csu in the mix converting the t1 channel frame encoding  
down to the actual serial data, you have no way to talk to the channel.

its like saying I have a usb port, do I really need the ethernet  
dongle in order to plug it into an ethernet jack ? Then again some  
hardware has an ethernet jack right on it, but it still has all the  
same ethernet hardware as the dongle in there somewhere even if there  
is no physical usb path between the pci bus and the ethernet, it still  
accomplishes the same thing.

the csu is sort of like the part of the modem where the start and stop  
bits are added into the actual data before hitting the actual modem  
proper where the bits are converted to tones, we don't generally make  
the distinction on that part of the circuit since the rest is useless  
without it.









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Jon Pounder

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