At 12:28 AM 5/24/01 -0400, nrf wrote: >But this makes much less sense in a PVC environment, where the circuits are, >well, permanent. For example, for PVC's I understand that you set up a >circuit with a given QoS. Then, what if, when you have stuff to send, that >QoS you thought you had is just not available at that time? > >This same question can be extended to SVC's. Let's say you created an SVC >with a certain QoS. Then, something bad happens, like one of the ATM >switches dies, and rerouting occurs, and the QoS of that SVC can no longer >be fulfilled. What happens now? Does the call just die? Or is it kept, >but at reduced QoS (and if so, then what was the point of stipulating the >QoS in the first place)? > >Am I just way off base here? The way I understood it, treat the PVC as whatever QoS mechanism it has. If someone gives you a UBR PVC, when the bandwidth starts going, you are the first pile of cells to drop. If everyone is UBR, then every can get dropped, just like Frame Relay, etc. If you got 5 guys with UBRs and one guy with a CBR, the UBRs all die first, before the CBR does. If all of them are CBR, they will all start dying "evenly." No such thing as a free lunch, so no such thing as free bandwidth, SOMEONE must PAY for the oversubscription done. OR the ATM Switch will pre-calculate the CBR PVCs and never let you generate such a CBR in which they can oversubscribe the link. In the end, QoS does not give someone more bandwidth per se, they might give them more prioritized bandwidth, so if they oversubscribe, if you do not have a special QoS setup, they are just as "doomed" as the guy with the other medium. QoS is about dealing with limited resources effectively, does not really replace getting just more raw bandwidth, just helps hold off buying that new upgrade and keeping some guys happy. (well, latency is a different issue, in which QoS is mandatory and raw bandwidth does not help, but sounds like you were talking about normal data) -Carroll Kong Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=5730&t=5730 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
