0                                  31
                |     MPLS Label Stack entry        |
                +--------+--------+--------+--------+
                |     MPLS Label Stack entry        |
                +--------+--------+--------+--------+
      xSPL      |       Extension Label (XL)        | <--+
                +--------+--------+--------+--------+    |--- cSPL
      eSPL      |           Extended SPL            | <--+
                +--------+--------+--------+--------+
                |  MPLS Label Stack entry (cont.)   |