Hi, Am 27.11.18 um 12:58 schrieb Luca Muscariello: > A buffer in a router is sized once. RTT varies. > So BDP varies. That’s as simple as that. > So you just cannot be always at optimum because you don’t know what RTT > you have at any time.
The endpoints can measure the RTT. Yes, it's probably a bit noisy and there are several practical problems such as congestion on the reverse path and multiple bottlenecks, but in general it's not impossible. > Lola si not solving that. No protocol could BTW. LoLa is exactly solving that. It measures RTTmin and effective RTT (and there are lots of other delay-based CC proposals doing that) and tries to control the overall queuing delay, even achieving RTT-independent flow rate fairness. > BTW I don’t see any formal proof about queue occupancy in the paper. It's not in the LoLa paper, it was in a different paper, but reviewers thought it was already common knowledge. Regards, Roland > On Tue 27 Nov 2018 at 12:53, Bless, Roland (TM) <roland.bl...@kit.edu > <mailto:roland.bl...@kit.edu>> wrote: > > Hi Luca, > > Am 27.11.18 um 12:01 schrieb Luca Muscariello: > > A BDP is not a large buffer. I'm not unveiling a secret. > > That depends on speed and RTT (note that typically there are > several flows with different RTTs sharing the same buffer). > The essential point is not how much buffer capacity is available, > but how much is actually used, because that adds queueing delay. > > > And it is just a rule of thumb to have an idea at which working point > > the protocol is working. > > No, one can actually prove that this is the best size for > loss-based CC with backoff factor of 0.5 (assuming a single flow). > > > In practice the protocol is usually working below or above that value. > > That depends on the protocol. > > > This is where AQM and ECN help also. So most of the time the > protocol is > > working at way > > below 100% efficiency. > > > My point was that FQ_codel helps to get very close to the optimum w/o > > adding useless queueing and latency. > > With a single queue that's almost impossible. No, sorry. Just > impossible. > > No, it's possible. Please read the TCP LoLa paper. > > Regards, > Roland > _______________________________________________ Bloat mailing list Bloat@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/bloat