In IP routing each packet travels from one router to the next, each router makes an independent forwarding decision for that packet. That is each router analyses packet header, and each router runs a network layer routing algorithm. Each router independently chooses a next hop for the packet, based on its analysis and the results of running the routing algorithm.
In conventional IP forwarding a particular router will typically consider two packets to be in the same FEC(forward equivalence class) if there is some address prefix X in that router’s routing table such that X is the largest match for each packets destination address. As the packet traverses the network each hop in turn reexamines the packet and assigns it to the FEC.
Almost all protocols deployed today are based on algorithms designed to obtain the shortest path in the network for packet traversal and do not make into account of additional metrics (such as delay and congestion), which can further decreases the network performance. To speed up the forwarding scheme, a GMPLS device uses labels rather than address matching to determine the next hop for the received packet.

GMPLS is an extended framework of MPLS protocol. Generalized MPLS provides not also the packet switching but also switching in time slot domain(TDM), wavelength domain(DWDM),and space domain(fiber). In
MPLS the assignment of a particular packet to a particular FEC is done just once, as the packet enters the network. The FEC to which the packet is assigned and is encoded as a short fixed length value known as a label. When a packet is forwarded to its next hop, the label is sent along with it that is the packets are labeled before they are forwarded. GMPLS is a significant and challenging concept for next generation data and optical networks. By eliminating the two layers, ATM and SONET/SDH, GMPLS provides interoperable, scalable and parallel development of IP over DWDM network architecture.

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