This read-write OCTET STRING is the member individual-address bitmap for an SMDS group address, where a SET request's first byte specifies the operation (1 for deleting, 2 for adding) followed by the actual bitmap bytes, with the most significant bit corresponding to local individual address ID 1; a GET response returns just the bitmap itself. This is the mechanism for managing group membership: an admin adds or removes individual addresses from a multicast group by sending a specially-prefixed SET rather than simply writing a full replacement bitmap. An engineer adding individual address ID 5 to an existing SMDS multicast group would SET smdsaddrMemberAddrMap with a leading byte of 2 (add) followed by a bitmap with bit 5 set, rather than trying to rewrite the entire membership list.