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Why Is MPLS Needed?

After the initial BOF meeting in December 1996, the MPLS WG convened in early 1997 and addressed four original problems:

  1. Layer 3 network layer routing scalability

  2. Forwarding performance increases

  3. Cell switched-based technologies integration

  4. Increased routing services delivery flexibility

These four problems are central to the current challenges facing internetworking today. These include integrating the various technologies that must coexist, evolving and scaling to include increased traffic and new equipment, and providing new functionality, including new Internet services and applications.

MPLS was originally envisioned as a technology that could improve the scaling of Layer 3 IP routing by avoiding the large number of "fully connected" routers that were required for the Internet core. It has since been shown that there are other ways to extend IP routing over such meshes.

Also, the argument that forwarding performance could be greatly improved because the table lookup for short, fixed-length labels is much quicker than the longest destination address match that is required for conventional IP routing has been mitigated by hardware solutions done in application-specific integrated circuits (ASICs) and field-programmable gate arrays (FPGAs). The IP header analysis that is required is no longer the computational bottleneck for router performance, and is now done at "wire speed."

Because many service providers employ an ATM-based backbone and offer FR access services, MPLS has an important new way of offering value-added IP services over these existing transports. The cell switching-based technologies of ATM and frame-based FR are being integrated, migrated, and in some cases, supplanted by standards-based IP solutions such as MPLS.

A great deal of interest has been generated for new applications such as QoS, TE, VPNs, and fast path restoral. There is also interest in integrating new technologies under the MPLS umbrella, including MPLS use in optical networking and switching, voice over MPLS, placing certain types of Layer 2 traffic over MPLS, and many others.

While MPLS is being developed to address these original concerns, the major driving force for promoting the technology is to offer a method of providing alternate routing to the best-effort, shortest path first (SPF) routing that is utilized by the conventional IP routing done today. New types of applications and services will have new requirements that demand updated techniques to offer proper QoS to users.

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