Knowledge gathered from BSNL tech guy:
59.XX.XX.XX IPs are on NIB-1, 117.XX.XX.XX IPs are on NIB-2. NIB-1 uses older hardware, they are more rebust but unable to implement FUP. If anyone takes FUP based plans on NIB-1, either the connection will stand on a particular speed, or the SNR will increase so much that the line will become unstable.
i again complained in exchange, i will wait till end of this month and wait for the bill to come,to confirm plan change.
Then i can fight with exchange people for 4mbps speed