On 4 May 2015, at 11:41, Paolo Valente <[email protected]> wrote:
> Thanks for this extra information and suggestions. Just to be certain that I > am not missing anything: I am assuming that also the observed delay you > mention is the delay observed from outside endpoints, and not the total delay > that one would obtain by adding also the queueing delays inside end points > (which, in my case, is one of the unobservable quantities). Paolo, this is where the difference between ∆Q|G, ∆Q|S and ∆Q|V are important - the extraction of the ∆Q|G and ∆Q|S establishes the structural delay, differences from that structural delay are caused by the contention for the onward transmission resources. > Il giorno 04/mag/2015, alle ore 12:28, Jonathan Morton > <[email protected]> ha scritto: > >> Generally, the minimum observed delay will correspond to the case when both >> inbound and outbound queues are empty throughout the path. This delay should >> correspond to basic propagation and forwarding delays, which can't be >> reduced further without altering some aspect of the network. >> >> Higher observed delays than this will tend to correspond to one or both of >> the buffers at the bottleneck being persistently filled. To work out which >> one, you'll need to estimate the network load in each direction. This is of >> course easiest if you can see all or most of the traffic passing the >> bottleneck link, or if you yourself are participating in that load, but it's >> probably possible in some other situations if you get creative. >> >> To determine that bloat is NOT present, you need to observe delays that are >> close to the baseline unloaded condition, while also being fairly sure that >> the bottleneck link is saturated in the relevant direction. >> >> The most reliable indication of link saturation is to observe ECN marked >> packets, which will only normally be produced by an AQM algorithm signalling >> link congestion (where both endpoints of the flow have negotiated ECN >> support). A slightly less reliable indication of saturation is to observe >> lost packets, either via retransmission or ack patterns, especially if they >> occur in bursts or at remarkably regular intervals. >> >> - Jonathan Morton > > > -- > Paolo Valente > Algogroup > Dipartimento di Fisica, Informatica e Matematica > Via Campi, 213/B > 41125 Modena - Italy > homepage: http://algogroup.unimore.it/people/paolo/ > _______________________________________________ Bloat mailing list [email protected] https://lists.bufferbloat.net/listinfo/bloat
