Based on IP routes and control protocols, MPLS is a connection-oriented switching technology for the network layer. MPLS uses short and fixed-length labels at different link layers for packet encapsulation, and switches label based on the encapsulated labels.

MPLS has two planes: the control plane and the forwarding plane. The control plane is connectionless, featuring powerful and flexible routing functions to meet network requirements for a variety of new applications. This plane is mainly responsible for label distribution, setup of label forwarding tables, and setup and removal of label switched paths (LSPs). The forwarding plane is also called the data plane. It is connection-oriented and supports Layer 2 networks such as ATM and Ethernet networks. The forwarding plane adds or deletes IP packet labels, and forwards the packets according to the label forwarding table.

Purpose

In the packet domain, MPLS helps to set up MPLS tunnels to carry PWs that transmit a variety of services on a PSN in an end-to-end manner. These services include TDM, ATM, and Ethernet services. Figure 1 shows the typical MPLS application in the packet domain. In the figure, the services between the NodeBs and RNCs are transmitted by PW1 and PW2 carried by the MPLS tunnel.

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