[c-nsp] Re: DS3 framing: M13 vs. C-bit

[Michael K. Smith]

On 1/18/05 9:40 AM, "John Neiberger" <John.Neiberger at efirstbank.com> wrote:

> I don't have  a lot of experience with DS3s and I have a minor problem
> that I need some help with. We have a point-to-point DS3 with both
> endpoints set to M13 framing (Cisco 7513 PA-T3+ and a Kentrox IDSU).
> This link involves two service providers. Qwest says that we are
> provisioned for M13, as well. However, Time Warner at the other end of
> the link seems to think we're provisioned for C-bit. My question is
> this: does that matter?
> 
> We see a highly intermittent burst of errors from time to time but
> other than that we don't see a problem. It can run for days or weeks
> without a single error and then we'll see a blip of a couple thousand
> errors, after which it runs cleanly again. Is it possible that this
> problem is caused because of c-bit being used on the Time Warner side of
> that part of the link?
> 
> We have three potential courses of action:
> 
> 1. Get Time Warner to switch to M13
> 2. Get Qwest to switch to c-bit and change our end devices to c-bit
> 3. Do nothing since the errors are brief and infrequent
> 
> What do you think? Could the framing mismatch cause a problem, perhaps
> similar to an AMI/B8ZS mismatch in the DS1 world?
> 
Here is a pretty good discussion of C-Bit vs. M1-3 from the archives.

http://puck.nether.net/lists/cisco-nsp/2393.html

I'm a bit surprised you can get the DS-3 to talk end-to-end with two
different framing types.  I would bet there are more than two circuits in
play here.  I have always heard C-Bit and B3ZS for Framing/Line-encoding on
a data circuit.  I *think* MI-3 is more for DS-1 over DS-3 purposes.

Mike