From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dimitris Kotsonis Date: Mon, 06 Dec 2004 11:54:56 +0000 Subject: Re: [LARTC] Shaping traffic on heavily oversubscribed links? Message-Id: <41B44890.4090401@comkey.spark.net.gr> List-Id: References: <41A5A31B.8010901@expertron.co.za> In-Reply-To: <41A5A31B.8010901@expertron.co.za> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lartc@vger.kernel.org Justin Schoeman wrote: > Hi all, > > I am having some fun with traffic shaping, and have run into an > interesting situation. Here is South Africa, most internet links are > heavily oversubscribed, which means that in most cases the local link > is _not_ the bottleneck, and shaping on the local link does not help > that much... > We have the same problem in DSL lines here in Greece. I have found that while the average efective speed on such lines varies, tha average rate of packets is more or less constant. I have a theory for this. I believe that the routers that forward the traffic on congested lines - on ISPs and on the ATM circuits at the telcoms - don't take the extra time needed to calculate the size of the packets and distribute the traffic on a per packet basis. This leads to a 'fairness' among the end receivers based on packets/sec instead of bandwidth. To be more specific. In my ADSL line I usually achieve between 20-30 pps (measured with MRTG). With an average packet size of 1500 this is 20-45 kbytes/sec. But packets sizes close to the MTU are found on single ftp/http connections and pretty much nowehere else. Packet sizes of 400 to 500 are more realistic, especially when p2p programs are involved. 20-30 packets give 8-10kbytes/sec. You can expect even less when using voip programs which utilize smaller packets. If you find that single a FTP session tends to get more bandwidth thatn p2p programs or multiuser traffic then you have a simillar problem to our own. I would suggest that you setup MRTG to monitor packets to research further into this. > Does anybody have some tips on shaping such links? How can you get > interractive traffic if you don't know how much bandwidth to reserve > for it? How can you give fair access to a link if you don't know what > the link capacity is? > Well, I am working on one. Since I can't shape bandwidth because it flactuates erratically with time and usage I decided to shape packets. I have created a new queueing discipline based on TBF which uses packets instead of bytes for its tokens and I am allocating a constant packet/sec rate on each user of my ADSL line. A better solution would be to create an HTB alike packet-based qdisc for dynamic shaping. If you find that you have the some problem as me and you want to experiment with a packet-based TBF qdisc I can send you a patch for linux-2.6.8 and iproute2 in this list. I would like to here your thought on this anyway ... Dimitris _______________________________________________ LARTC mailing list / LARTC@mailman.ds9a.nl http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/