Since the telephone wires can carry high speed data why is it that my 56kbs modem data transmission rates seem to be limited 4 to 7 kbs. Why can we can never approach the 56kbs capacity?

Answer 1

This is a long question, and the answer is even longer. Let me try to keep it short: First, the fact that the telephone wire can carry highspeed broadband internet signals up to 20Mbps based on today's technology is irrelevant to the use of a traditional 56kbps modem. These modems use a different technology, and currently peak at around 56kbps. Whatever the nominal line speed is (56kbps in this case), and irrespective of the technology in use (PSTN modem, DSL, etc), however, the resulting observed data throughput is always less: First, there is a simple but classic mistake. When downloading data from the Internet, the current data rate is often displayed in kBps (also KBps), that is, kilo bytes per second. One byte equals 8 (or more) bits on the line. A 56kbps modem is rated at 56 kilobits per second. As a rule of thumb, you expect no more than 56/8=7 kilobytes per second actual effective throughput. Other factors further limit the effective data throughput: each portion of data travels in an envelope, which carries addressing information and other administrative details, much like a postal envelope. This overhead is added to each packet, and unavoidable. Other factors include transmission errors and recovery (retries, etc), or -on some technologies- different ways by which the Internet connection is shared with other users. A cable modem, for example, accesses the Internet through a coaxial cable that is shared with many other houses in the same street. If all neighbours use a cable modem at the same time, each individual's throughput will be throttled. Last not least, even on a very high-performant Internet access, you'd still need to send data to or obtain data from a remote site that can actually handle the same speed. If you traverse half the globe to access, for example, a US site from Europe, you'll have latencies in the order of (typically) more than 60ms for each data packet to reach the other continent alone.