Restore-SPSite is not recognized as cmd error!!

Hello all,

I am trying to restore the spsite. I have followed the proper syntax:

Restore-SPSite http://xxxxxx:portnumber/ -Path E:\bakfiles\xxx.bak

I am running this cmd from windows powershell . My environment is SP-2010. And I get an error saying:

The term Restore-SPSite is not recognized as the name of cmdlet, function, script file ....

Please help

Rakesh murthy