Which option describes the message that establishes the direct tunnel between RNC and
GGSN?

A.
SGSN context request/response and modify PDP context request/response

B.
SGSN: Initiated update PDP context request/response and RAB assignment
request/response

C.
GGSN: Initiated update PDP context request/response and RAB assignment
request/response

D.
SGSN: Initiated update PDP context request/response and modify PDP context
request/response