The present invention relates to a method of authentication for Media
Gateway, comprising: setting up an initial key for validating initial
digital signatures between a Media Gateway and a Media Gateway
Controller; generating a new shared key having a specific lifetime by
performing signaling communication between said Media Gateway and said
Media Gateway Controller with said initial key; authenticating calls and
responses between said Media Gateway and said Media Gateway Controller
with said new shared key; and updating said shared key between said Media
Gateway and said Media Gateway Controller if the lifetime of said shared
key is expired. The invention can authenticate each call, update the
shared key periodically, and prevent calling invalidly effectively.