In which two ways does SGSN detect and know when GGSN has restarted? (Choose two.)
A. change in recovery value in echo response
B. change in recovery value in PDU notification request from GGSN to SGSN
C. change in recovery value in Update PDP Context Request from GGSN to SGSN
D. when the sequence number in a response message is different from that of the request message
E. when the TEID value in response in GTP header is different from that of the request message
