This attribute describes the source of a chassis identifier. The enumeration 'chassisComponent(1)' represents a chassis identifier based on the value of entPhysicalAlias object (defined in IETF RFC 2737) for a chassis component (i.e., an entPhysicalClass value of 'chassis(3)'). The enumeration 'interfaceAlias(2)' represents a chassis identifier based on the value of ifAlias object (defined in IETF RFC 2863) for an interface on the containing chassis. The enumeration 'portComponent(3)' represents a chassis identifier based on the value of entPhysicalAlias object (defined in IETF RFC 2737) for a port or backplane component (i.e., entPhysicalClass value of 'port(10)' or 'backplane(4)'), within the containing chassis. The enumeration 'macAddress(4)' represents a chassis identifier based on the value of a unicast source address (encoded in network byte order and IEEE 802.3 canonical bit order), of a port on the containing chassis as defined in IEEE Std 802-2001. The enumeration 'networkAddress(5)' represents a chassis identifier based on a network address, associated with a particular chassis. The encoded address is actually composed of two fields. The first field is a single octet, representing the IANA AddressFamilyNumbers value for the specific address type, and the second field is the network address value. The enumeration 'interfaceName(6)' represents a chassis identifier based on the value of ifName object (defined in IETF RFC 2863) for an interface on the containing chassis. The enumeration 'local(7)' represents a chassis identifier based on a locally defined value.