[asterisk-users] what is the effect of high LBO settings?

[Jared Smith]

On Fri, 2009-02-27 at 14:07 -0700, Brandon B. wrote:
> As of yet, I am unwilling to change the LBO to 0 to where it probably
> should be because the system is working and I'm not sure exactly what
> the LBO does. I'm aware some changes were made to deal with low audio
> levels. 

LBO stands for Line Built Out... it's essentially a measurement of the
distance between your demarcation point (d-marc/smart jack/NIU) and your
Asterisk box.  As you can see from a sample system.conf (from DAHDI) or
zaptel.conf (from Zaptel), it's an integer value from the following
table:

0: 0 db (CSU) / 0-133 feet (DSX-1)
1: 133-266 feet (DSX-1)
2: 266-399 feet (DSX-1)
3: 399-533 feet (DSX-1)
4: 533-655 feet (DSX-1)
5: -7.5db (CSU)
6: -15db (CSU)
7: -22.5db (CSU)

As I understand it, the LBO is effectively an attenuation value, with a
higher number meaning less attenuation.  This way, you don't get too hot
of a signal with a short cable, or two low of a signal on long cable.

Just how far is your Asterisk box from the demarcation point?

> Also, I am trying to cross connect with another Asterisk system with
> the normal LBO setting (i.e. span=1,1,0,esf,b8zs) but as of yet the
> systems aren't seeing each other at all. Could the side with the high
> LBO be confusing the other side somehow?

Shouldn't be... you did use a T1-crossover cable to cross-connect the
two Asterisk boxes, right?  I've got a little T1 cross-connect diagram
at http://www.asteriskdocs.org/cables/ if you need a reference.


-- 
Jared Smith
Digium, Inc. | Training Manager