Date: Wed, 6 Dec 1995 14:25:45 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Cc: terry@lambert.org, hackers@freebsd.org Subject: Re: How big are queues on a typical router ? Message-ID: <199512062125.OAA01948@phaeton.artisoft.com> In-Reply-To: <199512061932.UAA18137@labinfo.iet.unipi.it> from "Luigi Rizzo" at Dec 6, 95 08:32:28 pm
next in thread | previous in thread | raw e-mail | index | archive | help
> > > I am asking because during some tests (on a connection which > > > apparently goes through a ~256Kbit/s line) I experienced large > > > packet losses, yet an upper bound on the RTT of about 1.2s compared > > > to a lower bound of ~.3s . This makes me think that the queue on > > > the routers is about 1s-worth of data (approx 32KB). Is this correct ? > > > > The RTT value you have is the minimum pool retention time for a > > successful transit of the router. > > > > This time dictates the number of packets, maximum, you can see in a > > given interval, and thus how much memory (what pool size) would be > > required. > > sorry I don't get this. If it takes 1.2s for a full transit, the amount of memory that a pool would need to contain to guarantee that the pool does not overflow is the number of packets that can be in the router at one time times the maximum packet size. > > It sounds like your router is simply overleaded by 20%. > > nor i can understand where the 20% comes from, how it relates to the > loss rate measured by a (20-minutes long) sequence of pings, and if > it is reasonable that this is a steady-state situation. You said an upper bound of 1.2s on the RTT and if the queue is 1s as you think, then 1.2/1.0 = 1.2 = 120% capacity = overloaded by 20%. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199512062125.OAA01948>