Multiprotocol Label Switching (MPLS) is a data forwarding technology designed to speed up and shape traffic flows across enterprise WANs and service provider networks. MPLS increases the speed and controls the flow of network traffic. With MPLS, data is directed through a path via labels instead of requiring complex lookups in a routing table at every stop.
When data enters a traditional IP network, it moves among network nodes based on long network addresses. With this method, each router on which a data packet lands must make its own decision, based on routing tables, about the packet’s next stop on the network. MPLS, on the other hand, assigns a label to each packet to send it along a predetermined path. MPLS is considered a layer 2.5 networking protocol. Layer 2 carries IP packets over simple LANs or point-to-point WANs, while layer 3 uses internet-wide addressing and routing using IP protocols. MPLS sits in between, with additional features for data transport across the network.
MPLS network contains Label Edge Routers (LER) and Label Switch Routers (LSR). These routers are used for label-switched packet routing as well as understanding MPLS labels and receiving and transmitting the labeled packet (without reading IP header).
The structure of MPLS label is as follows:
It consist of four parts as Label value (20-bits), Experimental (3-bits), Bottom of stack ‘S’ (1-bit), Time to live ‘TTL’ (8-bits). The label-switched paths (LSPs), enable service providers to decide ahead of time the best way for certain types of traffic to flow within a private or public network.
Scalable and protocol independent, this technique works with Internet Protocol (IP), frame relay and Asynchronous Transport Mode (ATM). MPLS also supports creation of VPN (LAN & leased lines). MPLS networks are scalable and are used for real-time applications that need minimal latency.