[asterisk-users] ISDN config: LBO values

[Jaap Winius]

Quoting Tilghman Lesher <tlesher at digium.com>:

>> The value selected should almost always be zero. However, if the cable
>> is of a significant length, another value must be selected, but which
>> one? There are two columns: CSU and DSX-1. When is it appropriate to
>> use the one or the other to determine the correct LBO value?
>
> Each LBO value is a different amount of loss to be expected on the
> line, and therefore the signal is amplified a commensurate amount.
> What it really comes down to is what works for you.

That's the usual approach, but if I was still happy with it I would  
not have asked the question. According to the manual, the values are  
found in a table, but what good is that if you can't make any sense of  
it?

In the mean time, I've googled some more and found one text that  
suggests CSU and DSX-1 are both T1 trunk interface types, while  
another suggests that a DSX-1 is an interface that a CSU is attached to.

It seems to me that the table refers to two situations that used to  
(or maybe still do) occur in North America in which an ISDN card is be  
attached to a T1 trunk line via a CSU/DSU (the "DSX-1"), or only a  
CSU. In the latter case, the ISDN card must also act as a DSU.

Can anyone say is this is correct? Any further explanation would be welcome.

Cheers,

Jaap