Problem with the sgsnemu of OsmoGGSN

Dear all I am facting the following problems and hope you can help me: - At present, I have two GGSN nodes(such as A and B), I also hava a sgsnemu node which is connected to GGSN-A and hold a PDP context, now I want to connect this PDP context to GGSN-B to simulate the handover of mobile devices between different base stations. How can I do it? - And I I wonder if sgsnemu can generate “Update PDP Context Request” message. Thanks and regards Arthur