Question

We have a DSL , how can we calculate the available bandwidth so that we can shape the packet, We can assume the bandwidth to be 100mbps on the ethernet interface
However, in DSL devices, the train rate(Bandwidth rate ) is varies according to different situation.
How can i get the available bandwidth rate(from varies)?.
Any method is there for getting the available bandwidth value?

Answer 1

“Bandwidth” is not something you can determine for a single computer. As a minimum you need to specify both endpoints. Even your assumption of 100 mbps on Ethernet may be wrong, as the cable or the other endpoint may not be capable of the full transfer rate. Usually this is done by Quality of Service functionality incorporated into the network transfer, and it is not an easy thing to do.

In our multiplayer game (using UDP) we have used Packet Pair Probing successfully, and even if it is not universal, it was the most reliable from all methods we have tried. I am afraid it is out of scope of this answer to describe it in more detail, but this answer gives quite good description of something very similar in easy to understand terms:

Basically, if you start from zero bandwidth and increase bandwidth use, latency very slowly increases – until you hit about 90% of your bandwidth. Then latency goes through the roof, up to another plateau, after which it again increases slowly.