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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