MPLS stands for "Multi-Protocol Label Switching" packet-switching VPN technology. After MPLS VPN is used, incoming data packets are assigned a "label" by a "label edge router (LER)". Such labeled packets are forwarded along a "label switch path (LSP)". Along a LSP, each "label switch router (LSR)" forwards a packet based solely on the instructions of the label. At each hop, the LSR strips off the existing label and applies a new label which tells the next hop how to forward the packet. Finally, the LER at the destination system removes the label and delivers the packet to the destined address.
In a MPLS network, LSP is enforced at every hop along the data path such that a secure path is provided across an IP cloud. Specific IP tunnels can be created throughout MPLS network for individual customer, without the need for encryption or end-user applications. LSP paths are designed for their traffic characteristics, as such, they are very similar to ATM path engineering.
LSPs are not restricted to a particular Layer 2 technology but can be flexibly applied to multiple Layer 2 transports such as ATM, Frame Relay or Ethernet. In this way, MPLS enables LSPs to become end-to-end circuits.
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