This chapter describes Multiprotocol Label Switching (MPLS) technologies, which enable networks to perform traffic engineering, resident communication, virtual private networking, Ethernet emulation, and so on. First, an overview of MPLS is provided. Next, the functions and mechanisms of MPLS are described. Finally, MPLS applicabilities are discussed.
A key purpose of MPLS is to provide a tunneling mechanism that uses labels. MPLS is an Internet Engineering Task Force (IETF) standard intended to enhance the forwarding performance and traffic engineering intelligence of packet-based networks including Asynchronous Transfer Mode (ATM) and Internet Protocol (IP). MPLS communication is connection oriented, while IP datagram communication is connectionless. In the connection-oriented communication, a connection is established before starting communication. In connectionless communication, communication immediately starts by exchanging datagrams between source and destination hosts without establishing a connection. MPLS carries IP and non-IP payloads, and can operate over any data link layer. The layer of MPLS is considered to be between the data link layer (layer 2) and the network layer (layer 3). MPLS separates the control plane from the forwarding plane. MPLS enables the IP control plane to run on devices that cannot understand IP or recognize packet boundaries. The architecture of MPLS is discussed in more detail in .