In computer networking and telecommunications, Multi Protocol Label Switching (MPLS) is a data-carrying mechanism that 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 designed to 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.

Multi-Protocol Label Switching (MPLS) is a network standard adopted by the Internet Engineering Task Force. Under this protocol a premises router, known as a Label Edge Router (LER), appends a 32-bit label to a packet header that passes critical instructions to other routers in an IP network. The MPLS label contains information on how to 1) establish a switched path through an IP network 2) identify packets that share a common classification for transport and 3) prioritize the Quality of Service (QoS) the packets should receive. Once the LER forwards a packet to the network the carrier’s Label Switch Router (LSR) reads the packet label and switches the packet to the next LSR on its path to the destination address. Notice that MPLS allows the carrier to switch, a layer 2 function, packets that are layer 3 datagrams. The ability to switch packets enables an MPLS network to move packets more quickly than would be possible with a traditional routing protocol. The LSRs simply read the label to determine the switch path for the packets, instead of matching the packet’s IP address to a routing table.

MPLS has a superior method for handling network congestion that helps the enterprise WAN achieve a high level of performance for time sensitive applications. The QoS parameter in the packet label identifies packets with a high priority for switching through the network. When network traffic heats up the LSRs spot the packets with high value QoS and move them to the front of the line for switching. Lower value QoS packets get buffered until the traffic situation eases. This way voice and video packets flow through the WAN without delay, even when the network is congested, while email packets get passed when traffic levels permit.

The Benefits of Multi-Protocol Line Switching

• MPLS switches traffic more rapidly than previous routing protocols.
• MPLS supports voice and video by applying QoS to time sensitive packets.
• MPLS supports mesh topologies by self-defining optimal routes between sites.
• MPLS creates a private WAN over existing carrier IP backbones, thereby reducing overall network investment.

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