My ISP says it provides up to 512kbps but  yet all i get is 20kbp. i tried changing my os thinking it might be a flaw in my windows 7 os but nothing improved.could someone please explain me why this is happening and a good site or a book where i can learn about networking. Thanks in advance. :)

your prolly looking a...

There are several factors that limit the goodput you are getting.  The first three are related to TCP, part of a stack of protocols used by most hosts on the Internet to communicate with each other.   Roughly, the three factors are: 1. OS configuration of the TCP window size, both at the sending end and the receiving end.  The receiver window size essentially limits how much data you can receive per second so that the OS is not overwhelmed.  Modern OS should set this size to a sufficient large value so it is unlikely that this is the cause. 2. Packet loss.  Two main reasons for packet loss are: (a) congestion in the network.  When too many packets are sent through the same link in the network, buffers in router can overflow, causing packet loss.  (b) If you are using the Internet over wireless channel, then packet loss can occur due to noise in the channel.  The TCP congestion control algorithm takes packet loss as a signal of congestion in the network, and so slow down sending to clear up the congestion.  3. Round-trip time.  The longer it takes for your computer and the sender to communicate, the lower the goodput is going to get. TCP does not continuously send data into the network, but rather send a little bit at a time, waiting for the receiver to acknowledge that data is received properly before it sends more.  If the round-trip time between the sender and the receiver is too long, then it takes longer for the acknowledgement to reach the sender, delaying sending of new data. Other factors include throttling by ISPs, bottleneck at the sender, and limits of the physical medium.  You can search for many information about these topics online.  If you want a good undergraduate-level textbook to learn about Computer Networking, I would recommend the book by Kurose and Ross, http://www.aw-bc.com/kurose_ross/.

To clarify 's answer: make sure you are comparing bits to bits and not "bytes" (8x bits).  20KBytes/sec = 160Kbits/sec. Is that what is happening?

1. As the first commenter stated: "Up to 512kbps" really does only mean that the maximum you will ever get is that, and no minimum will be given.  At least this is the official statement I ever get from an ISP. 2. With DSL, the distance from your residence to the local Branch office (DSLAM) is actually very important once you are far enough.  The maximum listed is 18,000 ft (5460m) and that is measured in the wire used, not the direct distance ("as the crow flies"). http://computer.howstuffworks.com/vdsl1.htm Anecdotal but true: My place is ~15000ft  from the DSLAM (this was measured by a technician), and I can only get ~30kbps out of the 1Mbps rate.

May be you are looking at the download speed and saying it's 20kbps. Download Speed = (approx) 1/8 of advertised speed  =256 / 8 = 32 kbps