[Computers/Telecom] Anyone know where I can find information about line timings?

[Nadiar]

I'm looking for specific information about the various line timing systems, but haven't been able to find anything specific. I'll find lots of "This is how we do AMI" or "This is 8ZBS" but I'm looking for a break down of all of the different sets.

Tzaka, and help?

[Lysandor]

I'm looking for specific information about the various line timing systems, but haven't been able to find anything specific. I'll find lots of "This is how we do AMI" or "This is 8ZBS" but I'm looking for a break down of all of the different sets.

Tzaka, and help?

Well, most of my direct experience with accessing this kind of info comes from Internal AT&T documents, which I no longer possess, and couldn't really share with you if I did.

That said, I have a pretty good grasp of the situation, and am glad to answer whatever questions you have to the best of my ability, but I will need to know what exactly you are trying to do.

In a nutshell (as of 2002) AMI is more compatible with various pieces of end user / customer hardware, while B8ZS is more suited to newer Multiplexors, smartjacks and CSU / DSU's. The simple reason is that AMI doesnt handle data very well -- if at all.

Another thing to consider, is due to syncronization issues, you only get 56kbps per channel of throughput on a D4/AMI circuit, where B8ZS allows you the full use of 64kbps. This may not sound like a big deal, but over 24 channels (a typical T1), or several T3's (28 T1's) it can really add up. Basically -- AMI is older technology, and primarily suited to voice transmissions, while B8ZS is a newer technology, and is suitable for voice / data / video.

[Nadiar]

So thats 2, but there is at least 1 more =p

And yes, I understand the basics, I'm just hoping for a more detailed version that includes the bit flips.

I can't remember the exact details, but as I remember it, the bit flips work something like this:
0000 0000 -> 0000 000-1-1
1111 1111 -> 1-11-1 1-11-1
1010 1010 -> 1010 1010

I just don't remember the special cases and exact patterns =(

[Coren]

I'm looking for specific information about the various line timing systems, but haven't been able to find anything specific. I'll find lots of "This is how we do AMI" or "This is 8ZBS" but I'm looking for a break down of all of the different sets.

You confused me with "line timing" here... I'm used to read the term "line code" for AMI, 8ZBS, etc.

Anyways, maybe this is a good starting point:
Wikipedia knows it all!

[Nadiar]

It appears the one I am looking for would fall under Modified AMI. Which doesn't exist.

I can't remember the name, all I remember is it uses a 'trick' to use AMI without dropping all 0's.

[Lysandor]

So thats 2, but there is at least 1 more =p

And yes, I understand the basics, I'm just hoping for a more detailed version that includes the bit flips.

I can't remember the exact details, but as I remember it, the bit flips work something like this:
0000 0000 -> 0000 000-1-1
1111 1111 -> 1-11-1 1-11-1
1010 1010 -> 1010 1010

I just don't remember the special cases and exact patterns =(

Are you talking about SS7 signaling for SDN / ISDN?

That and "Frame Relay" which isnt technically a signalling arrangement, though it is a point to point protocol.

The only other one I can think of off hand is "unframed", which relies on translations at each end, using specialized equipment. Intercepting that pretty much guarantees that you will intercept only meaningless 0's and 1's. That was typically only used in government facilities -- IIRC.

[Lysandor]

It appears the one I am looking for would fall under Modified AMI. Which doesn't exist.

I can't remember the name, all I remember is it uses a 'trick' to use AMI without dropping all 0's.

Huh, never heard of that one. But my father is on his way over for dinner. Ill ask him what he knows about it. He was a Comm Tech for 24 years to my 7.

EDIT: Here is a link to a guy who has a way to make AMI channels run at 64kbps.

http://yarchive.net/phone/b8zs.html

IF that is what your looking for, the information is near the bottom. It's a little out of my area of expertise, but apparantly possible.

[Coren]

Looking at B8ZS, it *is* a modified AMI, which avoids 8 0s by violating AMI.

The way I read the page, B8ZS uses AMI in general, but replaces 8 0s with a special pattern of 000V10V1, where V is an AMI violation.
I.e., if the most recent previous Mark of AMI was coded as +1, the 8 0s code as:
0, 0, 0, +1 (V!), -1, 0, -1 (V!), +1
Similar, if the mrpMoA was a -1, it would be:
0, 0, 0, -1 (V!), +1, 0, +1 (V!), -1

Just my interpretation...

[Nadiar]

I don't remember which site I was looking at that had something weird, but thanks for the links =p

I'm a network guy, and shouldn't have anything to do with this, but there is a LEC up here that basically refuses to do any work, so what we end up doing is guiding them through troubleshooting steps, and thus I've kind of been crash coursing in Line testing =(