An explanation of the packet-pair probing algorithm in plain language

Net开发者_如何转开发worked applications often benefit from the ability to estimate the bandwidth between two end-points on the Internet. This may be advantageous not only for rate control purposes, but also in isolating preferred connections where a number of alternatives exist.

Although there are a couple of rigorous treatments of packet-pair probing, a summary of the high-level principles and salient points, covering both the how and the why of the method would be very beneficial; even if only to serve as a bootstrap to more in-depth study.

Any pointers to implementations or usage of packet-pair probing that serve as good examples would also be much appreciated.

Update: I found some good soft introduction material in a usenix paper derived from work on the nettimer tool - in particular the discussion concerning use of cross-talk filters and sampling windows for increased agility make a lot of sense.

About high-level principles: traditional means of estimating bandwidth send one packet to target and wait for it to return, then send another packet and wait for return, etc... in a sequential way. Then one computes some kind of average/median of the total time of the return trip per k-byte (or any other unit). This information is then used against the theoretical maximum bandwidth (when available) to estimate the available unused bandwidth.

Packet-pair probing send a group of packets to the target at once (i.e., in a parallel way) and wait for them to return. Then a kind of average/median is computed too and evaluated against the maximum theoretical bandwidth.

If you send more packets at once, you are disturbing the system you are trying to measure and you have to take this into account in your estimations, but it goes faster than the one-by-one method and feels more like a snapshot. The bottom question is: what's the trade-off between measurement accuracy and speed of measurement in both cases? Is there any value in this trading?

I have written a program for bandwidth estimation using packet pair method. If anyone wants to have a look at it, will be happy to share it..

EDIT:

Here, is how, I had implemented it in a class assignment,

https://github.com/npbendre/Bandwidth-Estimation-using-Packet-Pair-Probing-Algorithm

Hope this helps!