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

[dave o'leary]

At 10:16 AM 1/18/2005 -0800, Michael K. Smith wrote:
>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

either will work, but they should definitely be consistent end to end
(both the equipment and the circuit settings).  It is probably clock
slips that you are seeing that cause the errors.  In addition to the
discussion that Michael pointed you to below, here is another useful
reference page:

http://www.protocols.com/pbook/ds3.htm

You can ignore the latter part of the page which refers to the ATM specific
mapping.  The physical layer framing info on the first half of the page
is relevant.

                                         dave

> > 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
>
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