The MPLS-OPS Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] Re: ATM-LSR do they use OSPF/IS-IS or PNNI??
Hi Hansen, I agree with you in general...MPLS should be able to demonstrate similar capabilities to ATM QoS, but I think most people would agree there's a long way to go yet, especially for the routing protocols. There's also the problem that nobody is yet building LSRs that were designed for the job. They're all adaptations of either a router or an ATM switch design. Hard QoS architectures are hard to build. ATM got it right for the most part, but there would be a strong argument that the way ATM does QoS (on a VC basis) will not scale to networks as big as the Internet. With MPLS we can aggregate things nicely, but in my mind this is not QoS, it's CoS. The tradeoff we seem to be faced with is the "quality" of our QoS architecture vs its scalability. ATM also has the advantage that it's Connection Oriented from end to end. One of the reasons it can deliver such a hard QoS assurance was that the application itself is able to negotiate with the network to ask for the explicit QoS requirements, and to get the network's agreement that these resources were available. To duplicate this with MPLS we'd have to extend RSVP signalling to the host (or maybe to the voice gateway in a VoMPLS installation). I know this has been discussed, but is at a very early stage. Another advantage of ATM in terms of QoS is the fixed cell size. Any fixed-PDU technology will have the edge over a variable PDU technology when it comes to QoS. Before I ignite a cells vs frames debate let me say that I believe the (many) advantages of a variable length PDU infrastructure (especially at very high speeds) outweight the QoS benefits of fixed PDU. In other words, I'll go along with the assumption that if you're transmitting at a high enough speed, the CoS you can squeeze out of a variable PDU network will one day be "good enough" (if you over-provision the network sufficiently). Cheers, Geoff At 11:53 19/04/01 -0400, HANSEN CHAN wrote: >> But as I understand it, the added value from IP VPNs either comes from >> security (whether this is "isolational" in nature like an ATM or Frame >> Relay VPN, or "truly secure" as in the case of an ecrypted ATM or IPSec VPN >> is up to the user), or from "perceived service enhancement". The latter >> could be via a CoS mechanism, which MPLS can potentially offer, or from a >> hard QoS mechanism which can only be offered from... >> >> a: A TDM mechanism (like SONET/SDH, which is expensive). >> b: A native ATM service. >> c: An over-provisioned stat mux service (eg. IP), which is also expensive >> in the long term. > >Geoff, > >I agree with your points above. However, I don't think there is anything stop MPLS implemented with a hard QoS mechanism like ATM >has done. A good LSR with the necessary traffic management infrastructure (queuing and scheduling) can achieve the same level, if >not better QoS. > >Cheers, >Hansen > >------- >The MPLS-OPS Mailing List >Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml >Archive: http://www.mplsrc.com/mpls-ops_archive.shtml > ================================================================ Geoff Bennett Tel: (33) 497 21 43 62 Director of Technology, OCTO Fax: (33) 497 21 43 50 Marconi Gaia - Bat. E email: geoff.bennett@marconi.com BP 123 06903 SOPHIA ANTIPOLIS FRANCE ================================================================ ------- The MPLS-OPS Mailing List Subscribe/Unsubscribe: http://www.mplsrc.com/mplsops.shtml Archive: http://www.mplsrc.com/mpls-ops_archive.shtml
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