It seems to me that in fact there was some sort of oversubscription was going on, as the core ATM switches seemed to be overloaded and were queuing cells, thereby causing you latency. (If that is not what happened, then what else could have caused the increase in latency, maybe a cut in a link followed by rerouting?). But anyway, it seems like the QoS stipulations were violated (your latency was greater than whatever you contracted for). But the traffic still went through, right? The ATM call wasn't just rejected simply because the QoS was no longer being fulfilled, is that true? You see, I'm trying to assess what really is the relationship between ATM and QoS. Every proponent of ATM says that it has great QoS features. This makes perfect sense during SVC setup, where an edge router may make a SSCP call request for an SVC setup with a given QoS, and that request is either rejected or accepted, based on available resources. If accepted, the core ATM switches are then obliged to fulfill that QoS for the life of the SVC. 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? ""Circusnuts"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > I don't know that you can oversubscribe ATM like you would picture say > Frame-Relay or an ISP POP. The PVC's are generally allocated & the > bandwidth is usually carved-out. SLA's are generally well defines & the > circuits are watched (ATM Probes, NOC, SNMP) when you purchase DS3's & OC > links. We turned up new OC's in the South West & the very first symptoms > of oversubscription weren't with throughput, but latency. Malfunctioning > Apps & network management tell all... > > Phil > > ----- Original Message ----- > From: nrf > To: > Sent: Wednesday, May 23, 2001 9:03 PM > Subject: Exactly what happens in ATM when QoS cannot be fulfilled? [7:5658] > > > > I am interested in exactly what happens in a real world, ATM WAN > > environment, where the ATM has been provisioned from a major telco (AT&T > or > > MCI, let's say). So let's ignore SVC's and PNNI and that kind of thing, > > because hardly any telcos use that stuff anyways, and deal only with PVC's > > > > For example, let's say I got some routers attached to this ATM cloud, > > through PVC's. I have decided to contract for, say, a stringent CBR CoS > > because I am running real-time video. > > > > Now, I would presume that the telco has most likely overprovisioned its > ATM > > core, in order to earn more revenue, such that the telco can meet its SLA > > most of the time, but not all the time. > > > > So exactly what is the sequence of events when the telco ATM switches are > > unable to meet the CoS requirements of the ATM "call"? I would imagine > that > > traffic-policing and CAC would come into play. But could somebody provide > a > > precise sequence of events that would occur? Would an error message be > seen > > on the router? > > > > Thanx > > FAQ, list archives, and subscription info: > http://www.groupstudy.com/list/cisco.html > > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=5680&t=5680 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
