Metro Ethernet

Label Switching in a Nonpacket World

MPLS networks consist of LSRs connected via circuits called label switched paths (LSPs). To establish an LSP, a signaling protocol is required. Between two adjacent LSRs, an LSP is locally identified by a short, fixed-length identifier called a label, which is only significant between these two LSRs. When a packet enters an MPLS-based packet network, it is classified according to its forwarding equivalency class and, possibly, additional rules, which together determine the LSP along which the packet must be sent. For this purpose, the ingress LSR attaches an appropriate label to the packet and forwards the packet to the next hop. The label itself is a shim layer header, a virtual path identifier/virtual channel ...