asterisk users - Feb 2009 - what is the effect of high LBO settings?

I'm working on an Asterisk system with all of it's PRI ports configured
with
the LBO setting at 5, like this:

    span=3,0,5,esf,b8zs

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. Does anybody
know  what audio effects could this possibly have with short cabling? 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?

Brandon.
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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