|
North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Is anyone actually USING IP QoS?
[email protected] wrote: >>Please. Caching is _at least_ as efficient as multicasting (multicasting >>_is_ caching, with zero retention time) - w/o associated security and >>scalability problems. >>research or data to support these assertions? Just bare logics (a lost art in the modern datacom world, i guess). Make this gedunkenexperiment: take each mcast packet replicating point and replace it with a cache with very small retention time. The thing will replicate data in exactly the same way; and the packets will flow along the same paths. Therefore it is _at least_ as efficient. (Note that i do not consider possibility of building mcast trees dependent on traffic or bandwidth reservation - the algorithmic complexity involved makes that an intractable problem (it is believed to be NP-complete in general case); even the best heuristic algorithms for such planning place it beyond realm of computable for the networks fraction of size of present Internet). >and how does caching magically negate security and scalability concerns? Caching is not employing any routing information exchange. Therefore it is a) oblivious to the state of other caches or to the changes in network topology and b) is invulnerable to the bogus routing information and flap-like DoS attacks. >what tools are you using to do content replication/management that scale to >thousands of hosts/caches? 99% of Web content is write-once. It does not need any fancy management. The remaining 1% can be delivered end-to-end. (BTW, i do consider intelligent cache-synchronization development efforts seriously misguided; there's a much simpler and much more scalable solution to the cache performance problem. If someone wants to invest, i'd like to talk about it :) >even if i assume caching is as efficient, or >more so, than multicast, i'm still just trading one set of >security/scalability concerns for others. caching is no more a silver >bullet than multicast. It is not that caching is a silver bullet, it is rather that multicating is unuseable at a large scale. >i won't deny the potential scalability problems but i think your >generalizing/oversimplifying to say caching just works and has no security >or scalability concerns. Well, philosophical note: science is _all_ about generalizing. For an inventor of perpetuum mobile the flat refusal of a modern physicist to look into details to assert that it will not work sure looks as an oversimplifying. After all, the details of actual construction sure are a lot more complex than the second law of thermodynamics. In this case, i just do not care to go into details of implementations. The L2/L3 mcasting is not scalable and _cannot be made_ scalable for reasons having nothing to do with deficiencies of protocols. Caching algorithms do not have similar limitations, solely because they do not rely on distributed computations. So they have a chance of working. Of course, nothing "just works". --vadim PS To those who point that provider ABC already sells mcast service: there's an old saying at NASA that with enough thrust even pigs can fly. However, no reactively propulsed hog is likely to make it to an orbit all on its own.
|