Broadband Internet

In order to understand MPLS (Multiprotocol Label Switching), you first need to know it's not a service, but a technique. This technique is used for sending such services as IP VPNs, Metro Ethernet and optical services. While carriers design MPLS network backbones, the actual services businesses purchase are not called MPLS, instead go by the names IP VPN, Metro Ethernet or any other name the industry decides to label it at the time.

Labeling packets are the main concept behind MPLS. Standard routed IP networks consist of each router independently deciding where to send the packet each time the packet arrives at the router. This decision is based entirely on the packet's network-layer header.

When a packet arrives in the network, it gets matched up with a specific forwarding equivalence class (FEC) that attaches a short bit sequence (label) to the packet. Tables for each router in the network are then used for identifying how packets of a specific FEC type are to be handled. Header analysis is no longer necessary once the packet enters the network. Instead, a new FEC is made each time the label is used by the routers to index into a table.

Tables allow an MPLS network to consistently sort packets based on their individual characteristics (i.e., packets coming from certain ports or packets carrying data for certain applications). While a challenging task, packets carrying real-time traffic (i.e., voice and video) can be given priority over other applications by assigning them to low-latency routes within the network. The important thing to remember is labels are used for "attaching" more infomation to each packet than what the routers originally had.