This field should be assigned as a unique member number within a redundancy group. The value 0 always indicates a secondary member. Primary members should have numbers which are higher than secondary members. Note: This definition of member values, including the use of the value 0 for the secondary member allows compatibility with existing 1:n SONET APS channel numbering. Yet the numbering definition has also been expanded to allow support for the most general m:n redundancy architectures.