In 1996 a group from Ipsilon Networks proposed a "flow management protocol". Their "IP Switching" technology, which was defined only to work over ATM, did not achieve market dominance. Cisco Systems, introduced a related proposal, not restricted to ATM transmission, called "Tag Switching". It was a Cisco proprietary proposal, and was renamed "Label Switching".It was handed over to the Internet Engineering Task Force (IETF) for open standardization. The IETF work involved proposals from other vendors, and development of a consensus protocol that combined features from several vendors' work.
One original motivation was to allow the creation of simple high-speed switches, since for a significant length of time it was impossible to forward IP packetsentirely in hardware. However, advances in VLSI have made such devices possible. Therefore the advantages of MPLS primarily revolve around the ability to support multiple service models and perform traffic management. MPLS also offers a robust recovery framework that goes beyond the simple protection rings of synchronous optical networking (SONET/SDH).
Multiprotocol Label Switching (MPLS) is amechanism in high-performance telecommunications networks which directs and carries data from one network node to the next with the help of labels. MPLS makes it easy to create virtual links between distant nodes. It can encapsulate packets of various network protocols.
MPLS is a highly scalable, protocol agnostic, data-carrying mechanism. In an MPLS network, data packets are assigned labels.Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. This allows one to create end-to-end circuits across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particular data link layer technology, such as Asynchronous Transfer Mode (ATM), Frame Relay, Synchronous OpticalNetworking (SONET) or Ethernet, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. MPLS belongs to the family of packet-switched networks.
MPLS operates at an OSI model layer that is generally considered to lie between traditional definitions of layer 2 (data link layer) and layer 3 (network layer), and thus is often referred to as a "layer 2.5" protocol. It was designedto provide a unified data-carrying service for both circuit-based clients and packet-switching clients which provide a datagram service model. It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and Ethernet frames.
A number of different technologies were previously deployed with essentially identical goals, such as Frame Relay and ATM. MPLStechnologies have evolved with the strengths and weaknesses of ATM in mind. Many network engineers agree that ATM should be replaced with a protocol that requires less overhead, while providing connection-oriented services for variable-length frames. MPLS is currently replacing some of these technologies in the marketplace. It is highly possible that MPLS will completely replace thesetechnologies in the future, thus aligning these technologies with current and future technology needs.
In particular, MPLS dispenses with the cell-switching and signaling-protocol baggage of ATM. MPLS recognizes that small ATM cells are not needed in the core of modern networks, since modern optical networks (as of 2008) are so fast (at 40 Gbit/s and beyond) that even full-length 1500 byte packets do notincur significant real-time queuing delays (the need to reduce such delays — e.g., to support voice traffic — was the motivation for the cell nature of ATM).
At the same time, MPLS attempts to preserve the traffic engineering and out-of-band control that made frame relay and ATM attractive for deploying large-scale networks.
While the traffic management benefits of migrating to MPLS are quite...