Ok, not having anything better to do this afternoon, i decided to learn exactly how"port binding" works. I am posting this for the benfit of others who might be interested. Its not too technical and you get a fairly good idea.This is how UTstarcom(DSLAM equipment provider to BSNL) defines port-binding as( i think it calls it iSMART)"Operator A offers both flat-fee DSL service to residential customers and to business customers such as Internet cafes.All services are based on PPPoE authentication and utilize common B-RAS. To prevent residential customers fromusing their home accounts at an Internet cafe, the operator has to bind the subscriber’s username and password to theirhome DSL port. This way, residential DSL subscribers can use their logon information to gain Internet access at home,but not at an Internet café or at the home of another residential customer. In this application, the DSLAM is requiredto insert home-port identity information along with the PPP authentication packet." B-RAS stands for broadband remote access server. Its used to authenticate subscribers. And this is what UTStarcom says regarding the "home port" in the above para "iSmart inserts home-port identity information into the PAP authentication packet and relays the information to thePPPoE server. Home-port identity information includes the AN-2000 node ID as well as the shelf, slot and port indexof the home port. This information is inserted into the username field of the PAP authentication request. The operatorcan provision the system to replace the original username with home-port identity information, or to append thehome-port information in front of the original username. Each DSL port can be independently provisioned to turniSmart on or off and, if turned on, to either replace the username or append the home-port to the original username" The An-2000 is the DSLAM model number.Hope this helped you understanding port binding a little better. 
