1. A method of processing a packet in a multi-protocol label switching-transport profile (MPLS-TP) network, comprising: classifying an input packet, and extracting or generating at least a packet transport layer (PTL) index through a lookup according to the classification result; performing a lookup for determining a next hop using the extracted or generated PTL index, and acquiring service-specific lookup results; checking whether the input packet is a multicast packet, transmitting the packet after extracting an output (O)-port group from the input packet and extracting O-port-specific PTL indexes through loopback when the input packet is a multicast packet, and checking whether an LS has been generated when the input packet is not a multicast packet; and when it is checked that an LS has been generated, transmitting the packet after generating the LS loopback header, encapsulating the generated LS loopback header, and extracting a next PTL index, and when it is checked that no LS has been generated, checking whether a label operation is a label pop operation.