A multimedia gateway for enabling a remote device to access a local device located in a private network via a residential gateway of the private network is provided. The multimedia gateway includes: connecting means for connecting to the private network and a multimedia service network, first receiving means for receiving authentication information from the remote device over the private network, storing means for storing the authentication information in a memory, second receiving means for receiving a session invite message from the remote device over the multimedia service network, the session invite message including authentication information, and authenticating means for authenticating the remote device by determining whether or not the authentication information included in the session invite message has been stored in the memory by the storing means.