From: Scott Vermillion (scott_ccie_list@it-ag.com)
Date: Fri Feb 29 2008 - 14:43:07 ARST
In a typical production environment (in my experience), you're likely going
to derive clock from your service provider (in other words, you're going to
be the DTE on both ends of the link and the carrier gear is the DCE on both
ends). So you don't set a clock rate at all. If you're doing back-to-back
stuff, though, and you're setting up an E1, IIRC you set the clock rate to
the full 2048 kpbs (likewise, you set your clock for a T-1 to 1544 vs 1536).
This config statement dictates the rate at which ones and zeros are signaled
on the wire and is thus not concerned with how many might be overhead and
how many might be payload.
As for the BW thing, no not spillover, per se - not directly I don't think.
But you're going to screw things up like QoS and possibly metric
calculations. For example, imagine if you were only signaling at 128 kbps
but you configured BW to be 512 kbps and then assigned 256 kbps to a
priority class (and then offered that much load to the circuit)? I think
you'd wind up with tail drop in your priority queue, which would be a lot
like not having a priority queue (then again, you'll always experience tail
drop if you offer twice the load that the circuit can handle!...hmmm).
Also, my guess in this case would be that you might end up with a PQ-like
behavior, with starvation of non-priority classes, as the router would
constantly be trying to service this over-subscribed priority queue. Not
really sure about that last one, though. I guess it comes down to the exact
mechanics of how the scheduler works. I just recently finished "Inside
Cisco IOS Software Architecture," which does cover QoS and so forth. But I
don't recall reading anything definitive as to what would happened in this
case. I guess most books don't cover what happens when you intentionally
hose something up pretty badly... ;~)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Sadiq Yakasai
Sent: Friday, February 29, 2008 8:30 AM
To: Radioactive Frog
Cc: Santi; John; ccielab@groupstudy.com
Subject: Re: hdlc clock rate
I like to think of clock rate referring to the actual rate at which
the bits are transmitted physically on the wire. Its a physical layer
attribute I wld say.
While configured bandwidth refers to the usable bandwidth to be
utilized by the protocol in question on the link.
But i keep thinkin, what happens when u configure a BW statement on a
link to a value higher than the actually clocking rate on the
interface? Does that result in dropped or spillage of traffic or what?
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