Date: Tue, 7 Apr 1998 08:26:23 +1000 (EST) From: "Daniel O'Callaghan" <danny@panda.hilink.com.au> To: Glen Foster <gfoster@gfoster.com> Cc: chrism@keyworld.net, Anthony.Barlow@europe.simoco.com, freebsd-isp@FreeBSD.ORG, freebsd@plinet.com Subject: Re: Bandwidth limiter for services? Message-ID: <Pine.BSF.3.91.980407081431.313C-100000@panda.hilink.com.au> In-Reply-To: <199804062152.RAA10319@gfoster.intr.net>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, 6 Apr 1998, Glen Foster wrote: > This is speculation on my part based on scanty evidence. I wish > Dennis would 'fess up and describe the logic behind his code in this > forum. I've written a bandwidth limiter which works fairly basically. Unfortunately I lost it and have not had time to rewrite it. I'll describe *my* logic and maybe someone will pick it up and run with it. * A 64 kbps line has a throughput of 8 kBytes/second, thus each packet will take packet_len/8192 seconds to traverse the link. A 1024 byte packet will take 125 ms to traverse the link. * Since a packet takes < 1 ms to traverse a decent FreeBSD box with ethernet cards on each side, a packet which is to travel at a notional 64 kbps must be delayed in transit by (packet_len/8.192 - 1) ms, if the queue is empty. * If there is already a packet in the queue, the newly arrived packet must be scheduled for transmission (packet_len/8.192 - 1) ms after the last packet in the queue is due to be sent. You can see that the above effectively simulates what actually happens in a router which converts from your ISPs backbone ethernet/whatever to your 64 kbps ISDN link. My bandd used divert sockets, so traffic of a certain type could be sent through it - anything ipfw can test for. It should be noted that the system above will work best when there is a separate instance of bandd limiting traffic in the opposite direction, as per real life 64k lines. The above example is for 64kbps. Adjust accordingly. Danny To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.BSF.3.91.980407081431.313C-100000>