This just gets more confusing as I find more info. I was looking at this
doc:
http://ext1.ttc.com/library/pdfs/fund_ds3.pdf
It's an interesting read, but like most other info I'm finding, it deals
with the base assumption that the DS3 is being used to multiplex 28
T1's. The doc talks about 'C-bit' (used for bit-stuffing and something
similar to T1 FDL) on a per-DS1 basis. I noticed the Cisco doc below does
the same thing.
I think I'm just lost here. Anyhow, I'll order unframed and pick c-bit,
and then do some testing when I get the line to see that alarms happen and
whatnot.
Thanks all,
Charles
On Wed, 6 Sep 2000 lf@elemental.net wrote:
> Charles,
>
> Quoting Charles Sprickman (spork@inch.com):
>
> > It's a bit off-topic, but does anyone have any recommendations (including
> > the why's) on whether I should order this framed or unframed? I see the
> > PA-T3 seems to support either mode of operation, but there are no
> > explanations as to what the advantages/disadvantages of unframed/c-bit/m13
> > modes of operation are. Do I lose alarm functionality if I go
> > unframed? If I go framed is there a preference for either c-bit or m13?
> >
> > And if anyone has pointers to a good doc detailing the various framing
> > types and all that would be appreciated...
>
> I just stumbled across this by accident on Cisco.Com after reading
> your email (it assumes an external DSU, but the last paragraph
> is still interesting):
>
> --------------8<--------------------------------------------------------------
> Q: Does Cisco have an official preference as to the line coding to use on
> DS-3 lines?. Options are Cbit or M 13. There doesn't seem to be a reason why
> it would not work with either. I'm assuming that it is similar to DS-1, in
> which case line coding is transparent to the router and we don't care,
> right?
>
> A: It doesn't matter what the coding is since the Cisco interface doesn't
> actually "see" the line. Our interface is the T3 DSU, which has to worry
> about the formatting and coding on the network line.
>
> The vendor of the DSU (e.g. T3 Plus) might not support both. If the DSU
> supports both, Cbit is preferred for improved maintenance options.
>
> Cbit is used when you want to use inband signaling for things like network
> management, similar to the Facility Data Link (FDL) of the T1. It is a
> 21-bit field. Cbit is part of the M13 frame, which is like the T1 frame,
> except it is called an M frame. The "13" represents a DS1 to DS3
> multiplexer, hence M13.
>
> [http://www.cisco.com/warp/customer/116/11.html]
> --------------8<--------------------------------------------------------------
>
> Cheers,
> Lars.
> --
> Lars Fenneberg, lf@elemental.net (private), lf@mcs-cityline.net (work)
>
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