One big problem with QoS is that most application programmer have no clue as to how to specify QoS related parameters. A few years ago, when I put on my application programmer's hat [pretending I had an MPEG-1 stream to pump out] and looked at the ATM UNI 3.0 specification, I found that (a) I could not really understand the meaning of roughly 1/4 of the parameters and (b) for many of the parameters I understood, I was not at all sure what were the appropriate values to use. In general, most of the multi-media stuff uses some sort of compression algorithm. Unless one have a good understanding of the nitty gritty of the algorithm, one would be somewhat hard pressed to set values. For pre-generated pre-compressed material, one can at least run the material once and monitor its network characteristic. However, translating those characteristic to jitter control parameters is still non-trivial. With real time compression, the challenge is much trickier. So, if the application programmers have a hard time specifying QoS ...... Non application based QoS may be more practical. Hence if I pay for a 3Mbps service from my ISP, I want to ensure that I can get 3Mbps from my end of the pipe to any edge of the ISPs backbone. I will be a bit annoyed if the 3Mbps is only between my end of the pipe to a totally over subscribed and under provisioned POP! If my ISP have a real meaningful SLA with me, I suspect they will being doing real traffic engineering in their access and backbone routers to support the contracted QoS. That could be relatively straight forward as long as the QoS parameters are not too funky (definitely no mention of jitter). Another related type of QoS that is more practical and likely to be done is relative QoS in the form of if I have a 3Mbps pipe to the ISP, the CEO is going to get preferential service to the mail room clerk etc. Such QoS does not seem to be too complex to do at the CPE edge router, again, as long as one does not try to get too fancy and as long as it is relative. Regards, John Leong -- --------------------------------------------------------- Bell Labs Research johnleong@research.bell-labs.com 4995 Patrick Henry Dr. Tel: 408-567-4459 Santa Clara, CA 95054 Fax: 408-567-4448