Go CCIE Go!! - A Cisco Certified Internetwork Expert

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?