Description: This object indicates which ports belong to the same multicast group, on a per-VLAN basis. Each multicast group has an octet string to indicate the port map. The most significant bit represents the lowest numbered port, and the least significant bit represents the highest numbered port. Thus, each port of the switch is represented by a single bit within the value of this object. If that bit has a value of '1' then that port is included in the set of ports; the port is not included if its bit has a value of '0'(Note that the setting of the bit corresponding to the port from which a frame is received is irrelevant). The 4 octets represent one unit port according to its logical port. If the unit has less than 32 ports, other ports will be set to 0.