I have subscribed for a broadband plan for 2Mbps. However there is considerable inconsistencies between the promised speed and the actual download speeds. For instance the maximum download speeds I get is about 300Kbps. Why this disparity? Is the speeds lost to attenuation or is the 2Mbps a shared line accessed by multiple subscribers?
Line speeds are measured in decimal bits per second. Data speeds are measured in binary bytes per second. The download speed you are getting is 300KB/s, not Kbps. Let's do the math:
2Mbps (line speed) = 2,000,000 bits per second
2,000,000 bits per second = 2,000,000/8 bytes per second = 250,000 bytes per second
250,000 bytes per second / 1024 bytes per KiB = 244KB/s (data rate)
The line has to carry control and address information as well as data. Typically, the peak true data rate is about 95% of the line rate, so you'd expect 244*.95 or 232KB/s to be the peak data rate for a line with a 2Mbps line rate.
You are almost certainly mixing bits and bytes. 300 kB/s (kilobytes per second) equals 2.4 Mb/s (Megabits per second), or slightly more than your stated plan bandwidth.