[asterisk-users] ISDN config: LBO values

[Jaap Winius]

Quoting Tilghman Lesher <tlesher at digium.com>:

> http://www.digchip.com/datasheets/parts/datasheet/222/82V2088-pdf.php
>
> See pages 17-18 of the associated PDF.  While this is not the T1 framer chip
> used, the values are identical, which leads me to believe that these values
> are actually industry standard.

Well, maybe more like a defacto standard. But, it still doesn't  
explain when to use the different values in a software configuration,  
e.g. with Asterisk.

As a term, DSX-1 is confusing. One description can be found in the  
Wikipedia article for T-carrier, which says it stands for Digital  
Signal Crossconnect: "DS1 signals are interconnected typically at  
Central Office locations at a common metallic cross-connect point  
known as a DSX-1. ..."

On the other hand, articles like the following use DSX-1 to describe  
customer site connections:

* Adtran NetVanta T1 Access Router
   http://www.arcelect.com/netvanta_access_t1_router.htm

The diagram shows how two different NetVanta models can be used to  
connect a T-1 line to a PBX.

There's also this page:

* Primary Rate Interface ISDN Line Port
   http://www22.verizon.com/wholesale/solutions/solution/pri+rate+isdn.html

Near the end, under Detailed Information, it says:

     "PRI service consists of a 4-wire DSX-1 port associated
     with a local switching system and the 4-wire DSX-1
     cross-connect between the OTC DSX-1 termination and the
     local switching system DSX-1 termination.

     "PRI ports are DSX-1 interfaces that meet the electrical
     specifications in ANSI T1.102. PRI service and use B8ZS
     line code and the Extended Superframe Format (ESF)
     described in ANSI T1.403."

Again, the term DSX-1 is used to describe a CPE port. In such cases, I  
think it will probably be appropriate to use the "DSX-1" column in the  
LBO table.

Still, what's the difference between "CSU" and "DSX-1"??

Speculation:

Could it be that "CSU" refers to situations where there is no  
equipment of any kind between the demarcation point and the ISDN card?  
In such cases, the ISDN card will have an integrated CSU, and the  
length of the cable will be unknown (thousands of feet), but you can  
know the attenuation value in dB; either by measuring it, or by  
getting it from the telco.

This scenario may only occur in the United States.

On the other hand, "DSX-1" will refer to situations where the ISDN  
card is connected -- via a DSX-1 port and a cable of a known length --  
to an external CSU and/or DSU. In turn, this equipment is connected to  
the demarc.

This scenario may apply in all other situations, e.g. ISDN BRI cards  
that connect to an NT-1.

Does this sound reasonable?

Thanks,

Jaap