On my GT-P3100 I can login to internet through Wi-Fi but cannot connect to internet through mobile data connection, when wi- fi is not available.Kindly suggest what is required.

Does it have a SIM installed? If so, does the account it is associated with have a data plan? What about tablet configuration? Have you enabled data roaming? In this last case, it may be that the 3g/4g/lte plan provider is not available in your area in which case data roaming would be required (and costly).

Sim is installed, yes it has a data plan, as a matter of fact when wi-fi was not installed I was loging on to net with the data plan. Also data roaming is enabled.