When an ISP claims a broadband speed, they mention it in Kilo Bits Per Second (KBPS) and the download speed that you see on your Download Agent application is in Kilo Bytes Per Second (KBPS). 8 bites form 1 byte -> this means you need to convert what you see on yoru Download application's interface as a Download speed in the same units as Broadband Service provider claims it.
Another thing that none of the ISPs in India clearly mention, but that issue does exist and worst in case of Tata Indicomm and Tata Tele Services Internet service ... they term it as 1:8 compression ratio. This is the issue that indicates how far your Internet connection speed can fall down. 1:8 compression ratio comes into account when there are too many connections that claim data transfer over same data line via Router port. Indeed, this is a business trick based on the probability of how many times all the 8 possible connections will be up at a given time? Unfortunately there are some time slots that the possibility is quite high of having all 8 up and demanding and that's the reason why we face "busy hours" which as a customer we do not deserve since we are paying for full service.
The 1:8 compression ratio when comes in action, your acclaimed 256 KBPS gets divided by 8 and at a given time when all concurrent connections are demanding resources for data transfer, your effective speed of service will drop down to 32 Kilo Bits Per Seconds (which is just 4 Kilo Bytes Per Seconds!). This is good enough for checking emails and browsing websites and if the Load Balancing methods implemented at ISP's Server are good enough then this situation rarely persists for a longer period of time.
For a real 256 KBPS (now, you know what that B stands for here), always opt for the ISP plans that claim 2 MBPS connection speed. This way, you will surely get 2 MBPS divided by 8 = 256 KBPS even in worst case, else connection speed problems are bound to come in picture. In my area (Pune), BSNL offers a 2 MBPS plan which I've opted for and also have Tata Tele Services connection for backup purpose, i.e. if BSNL goes down (happens rarely). The BSNL speed is always far better than Tata's Internet speed as I've observed the same on Download Accelerator Plus software during morning 9.30 to 12.00 (and virtually during any time in a day really).
I hope my this answer will help you to understand some of the issues related to your broadband internet connection and take some proper decisions to rest assured that you're getting a desired internet connection speed!
Best Wishes!
-- Ruturaaj.