re:[Diffserv-interest] DiffServ over ATM
"Jeff Norman" <jnorman@nortelnetworks.com> Thu, 30 August 2001 15:53 UTC
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Date: Thu, 30 Aug 2001 11:52:12 -0400
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From: Jeff Norman <jnorman@nortelnetworks.com>
Reply-To: Jeff Norman <jnorman@nortelnetworks.com>
Subject: re:[Diffserv-interest] DiffServ over ATM
To: John Tillberg <John.E.Tillberg@telia.se>
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John, I know others may disagree or agree with me, but IMHO, queuing on multiple queues based on IP QoS/CoS/DiffServ and then queuing on another set of multiple queues based on ATM service categories is somewhat redundant. Typically it's one or the other, or if both do exist then the ATM queues should be applying back-pressure onto the IP queues such that packets can get differentiated and conditioned by the IP queues as well. It looks like to me in your situation, the back-pressure isn't happening. Best Regards, --Jeff In message "[Diffserv-interest] DiffServ over ATM", John Tillberg writes: >Hello DiffServers! >I'm currently doing some simulations (using Opnet) of IP over ATM where I >use WFQ to differentiate between two separate traffic classes on a network >with low bandwidth links (2 Mbps). It appears that the WFQ mechanism doesn't >have any significant impact on the performance of the network. No matter how >I tune the weights, or even if I overload some of the links, I get almost >zero delay for both of my queues. However I do get delay on the ATM layer >(and I am aware of that I have to map my IP QoS classes onto proper ATM QoS >classes). I presume this is because the forwarding speed on the IP layer is >much higher than the bandwidth of the network. Hence every (conforming) >incoming packet will receive service on the IP layer (i.e. sent down to the >lower layers) right away even if there is a state of congestion on the ATM >layer. Have I misunderstood the matter? If not: Is this the same case for >DiffServ? Does the effect of the IP-packet scheduler get "disabled" in a >similar manner when you run DiffServ over ATM? >Yours Sincerely > >John Tillberg > >********************************************************************* >John Tillberg >Telia Research AB Phone: +46 8-713 82 07 >Wireless Solutions Fax: +46 8-713 81 49 >Vitsandsgatan 9 Mobile: +46 702-43 43 90 >SE-123 86 Farsta Email: John.E.Tillberg@telia.se >Sweden > >******************************************************************** > > >_______________________________________________ >Diffserv-interest mailing list >Diffserv-interest@ietf.org >http://www1.ietf.org/mailman/listinfo/diffserv-interest > _______________________________________________ Diffserv-interest mailing list Diffserv-interest@ietf.org http://www1.ietf.org/mailman/listinfo/diffserv-interest
- re:[Diffserv-interest] DiffServ over ATM Jeff Norman
- Re: [Diffserv-interest] DiffServ over ATM Brian E Carpenter