Stupid Question: B8ZS on an AMI T1 1

[ISDNman]

Hey folks. I am familiar with the basics of AMI and AMI with Zero Substitution.

I am being told by a vendor it is OK to run B8ZS on a T1 configured for AMI.

This makes sense since the end user equipment would should handle this on both ends.

However, if this is the case it seems very odd that virtually every piece of gear I have used that supports b8ZS also supports AMI. It would seem to me that if an "AMI Line" will take either then equipment would not support the inferior AMI.

I guess my theory is that at each repeater and at the DSX the equipment checks for correct ONEs density and has to know which to look for?

I don't think running B8ZS is going to work on this AMI circuit, but I'd like to know if this is true and why.

Thanks folks

 

[artesian2000]

Here's what might happen. Yea you might be able to but if the bit stream runs to many 0's over the connection you're going to start clocking crc's on the line. You could run AMI over a B8ZS line but not the other way around. Depending on the application you could get CSU to convert the AMI on the line to B8ZS on the drop side but I still think you;re opening yourself up to issues. I've done numerous voice t-1's with AMI on the drop and B8ZS on the line but never the other was around.

 

[SYQUEST]

Artesian2000 is absolutely correct! I used to order all my DS1s as SF/D4-B8ZS, and the Telco craftpeople always seemed to miss this on the D4 Channel Bank when they set the options on the LIUs. Then the errors would slowly increase. I even had one telco D4 crash the DS1 because of the errors when channel 24 was inuse.

The reason I used B8ZS on SF/D4 at the time was because ESF equipment was more expensive than the non ESF type, and B8ZS gives you the clear channel for 64k DDS, and I was using lots of NT DE4E channel banks. At the time NT did not make an ESF Line Driver Unit or one with that option. This was prior to the DE4E Smart CB.

Never had an issue with the OIUs (Office Repeater Unit) or the field repeaters on poles or in manholes. Those were transparent to line code. The better CSUs either have an option to set or it was transparent. It has been transparent in most NIUs since the early 1990s.

But ISDNman, to go one step further, let me say this: now depending on the DS1 design and what apparatus the provider is terminating the circuit on, could be a factor. The DS1 pipe in and of itself can handle ANY DS1 format, but the stuff on either end is going to determine what format you can actually use. So your provider is partially correct in what he said.

So if you are going to take advantage of this, be careful and test throughly what ever you do!

T-Berds NEVER LIE!

....JIM....