Indicates this tunnel's directionality and role, using values such as out(0), outbidir(1), in(2), hwbidir(3), inbidir(4), transuni(5), transbi(6), and transbih(7), covering unidirectional and bidirectional tunnels both at endpoints and at transit nodes. Note the source MIB's prose description lists the meanings in a different order than the numeric SYNTAX values are declared, so the exact enum-to-meaning mapping should be confirmed against a live device rather than assumed from the text alone; values other than out(0) are only meaningful when mplsTunnelLSPEncoding is non-zero.