Editing Multiprotocol Label Switching (section)

==Role and functioning==
In an MPLS network, labels are assigned to data packets. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. This allows one to create end-to-end circuits across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particular [[OSI model]] [[data link layer]] (layer 2) technology, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic. Multiprotocol label switching belongs to the family of [[packet-switched network]]s.

MPLS operates at a layer that is generally considered to lie between traditional definitions of OSI Layer 2 ([[data link layer]]) and Layer 3 ([[network layer]]), and thus is often referred to as a ''layer 2.5'' protocol. It was designed to provide a unified data-carrying service for both [[Telecommunication circuit|circuit]]-based clients and packet-switching clients which provide a [[datagram]] service model. It can be used to carry many different kinds of traffic, including IP [[packet (information technology)|packets]], as well as native [[Asynchronous Transfer Mode]] (ATM), [[Frame Relay]], [[Synchronous Optical Networking]] (SONET) or [[Ethernet]].

A number of different technologies were previously deployed with essentially identical goals, such as Frame Relay and ATM. Frame Relay and ATM use ''labels'' to move [[Frame (networking)|frames]] or cells through a network. The header of the Frame Relay frame and the ATM cell refers to the [[virtual circuit]] that the frame or cell resides on. The similarity between Frame Relay, ATM, and MPLS is that at each hop throughout the network, the ''label'' value in the header is changed. This is different from the [[IP routing|forwarding of IP packets]].<ref>{{cite book|title=MPLS Fundamentals|isbn=978-1587051975|last1=Ghein|first1=Luc De|year=2007|publisher=Cisco Press }}</ref> MPLS technologies have evolved with the strengths and weaknesses of ATM in mind. MPLS is designed to have lower overhead than ATM while providing [[connection-oriented service]]s for variable-length frames, and has replaced much use of ATM in the market.<ref>{{cite book|title=Applied Data Communications (A Business-Oriented Approach)|isbn=0471346403|last1=Goldman|first1=James E.|last2=Rawles|first2=Phillip T.|date=12 January 2004|publisher=Wiley }}</ref> MPLS dispenses with the cell-switching and signaling-protocol baggage of ATM. MPLS recognizes that small ATM cells are not needed in the core of modern networks, since modern optical networks are fast enough that even full-length 1500-byte packets do not incur significant real-time queuing delays.{{efn|The desire to minimize [[network latency]] e.g., to support voice traffic was the motivation for the small-cell nature of ATM.}} At the same time, MPLS attempts to preserve the [[teletraffic engineering|traffic engineering]] (TE) and [[out-of-band control]] that made Frame Relay and ATM attractive for deploying large-scale networks.