Multiprotocol Label Switching (MPLS) is a standards-based approach to packet-forwarding first introduced to the Internet Engineering Task Force (IETF) in 1996. The core idea is that a group of packets requiring similar forwarding treatment, a “Forwarding Equivalence Class (FEC)”, can be associated with a label, which is used to make forwarding decisions for those packets. MPLS speeds network traffic flow and increases network quality of service (QoS) by reducing time required for a router to look up the address of the next node in the packet-forwarding sequence. The protocol operates at "Layer 2.5" between traditional definitions of Layer 2 (Data Link Layer) and Layer 3 (Network Layer) in an Open Systems Interconnection (OSI) Model.
Cisco engineers, including Cisco Fellows Bruce Davie, Tony Li, and Yakov Rekhter, and Cisco Distinguished Engineers Eric Rosen and George Swallow, proposed "Tag Switching", which combined ideas from other industry players as the basis of MPLS architecture. This simple, yet powerful idea has many applications, such as enabling service providers to provide layer 3 VPN services. Rosen and Rekhter described this application in 1999 as Informational RFC 2547, later standardized by the IETF as RFC 4364.
In addition, MPLS is used for “traffic engineering,” controlling the paths over which traffic flows, in ways not easily possible with traditional IP routing. Another application is "pseudo-wire emulation," developed and standardized by Cisco Distinguished Engineer Luca Martini. This approach enables SONET, Frame Relay, and Ethernet traffic over MPLS and Internet Protocol (IP) networks.
MPLS was recently recognized as a “successful” standard by the IETF, based on its maturity and adoption, and Cisco experts have led efforts to standardize MPLS for more than 13 years. For example, Swallow has chaired the MPLS Working Group since 1996 and developed a consensus protocol that combined features from several vendors' work to “produce the best technical solution for customers,” according to Davie. Since its inception, MPLS technology has continued to develop, leading to additional working groups chaired by Cisco engineers.
Cisco thought leaders continue to contribute to MPLS and to new areas: Swallow continues to lead the MPLS Working Group; Davie is involved in video and content networking; and Rosen has worked extensively on the support of multicast in MPLS VPNs.
Bruce Davie’s talk on the Future of MPLS at the MPLS Ethernet World Congress, February, 2009 discusses “Where does MPLS go now?” Davie concludes that MPLS is a critical piece of infrastructure for service providers, and the next challenge is to move from being core technology to achieve more scale and high resilience in the face of link and node failures.