. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
 . Outer Encapsulating Header ...                                .
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
 . ESP Header...                                                 .
 +---------------------------------------------------------------+
 |   [AGGFRAG sub-type/flags]   :           BlockOffset          |
 +---------------------------------------------------------------+
 :                  [Optional Congestion Info]                   :
 +---------------------------------------------------------------+
 |       DataBlocks ...                                          ~
 ~                                                               ~
 ~                                                               |
 +---------------------------------------------------------------|
 . ESP Trailer...                                                .
 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .