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
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