Understanding MPLS

MPLS or Multiprotocol Label Switching is the new kid on the block among networking protocols. It promises to make networking more efficient. As the name suggests,MPLS uses labels to enhance data forwarding decisions. It provides applications such as Virtual Private Network (VPN), Quality of Service (QoS), Traffic Engineering (TE) and Asynchronous Transfer Mode (ATM) over MPLS (AToM). MPLS is an Internet Engineering Task Force (IETF) initiative that integrates Layer-2 information such as bandwidth and latency into Layer-3 (IP) and reduces the forwarding overhead on routers.

Cisco was the first to propose MPLS under the name 'Tag Switching,' which was then handed over to the IETF for standardisation and renamed 'Label switching.' The rationale behind MPLS was to create simple, high-speed switches which at one time was unthinkable. But advances in Very Large Scale Integration (VLSI) made it happen.The basic goals of MPLS are traffic management and supporting multiple service models.

MPLS combines the power of ATM and IP. It supports IP, ATM and Frame Relay L2 protocols, provides mechanisms for controlling and managing traffic flows of varying granularity, and converts IP addresses to simple, fixed-length labels.

The inner workings of MPLS

Packets entering an MPLS network are assigned a label by Label Edge Routers (LER). These labels contain information such as the IP header field, Layer-4 socket number information, and differentiated service, in addition to the destination address, bandwidth and delay. After the labelling is done and the information is saved, packets are routed to their corresponding Labelled Switch Paths (LSPs).

Here, outgoing labels are placed on the packets by the Label Switch Routers (LSR). Based on the data-stream type and customer accessing the Internet, network operators can divert and route traffic with the help of LSPs.