Source : Free On-Line Dictionary of Computing

Multiprotocol Label Switching
     
         (MPLS) A {packet switching} {protocol} developed
        by the {IETF}.  Initially developed to improve switching
        speed, other benefits are now seen as being more important.
     
        MPLS adds a 32-{bit} label to each {packet} to improve
        {network} efficiency and to enable {routers} to direct
        {packets} along predefined routes in accordance with the
        required {quality of service}.  The label is added when the
        {packet} enters the MPLS {network}, and is based on an
        analysis of the {packet} {header}.  The label contains
        information on the route along which the {packet} may travel,
        and the {forwarding equivalence class} (FEC) of the {packet}.
        Packets with the same {FEC} are routed through the {network}
        in the same way.
     
        Routers make forwarding decisions based purely on the contents
        of the label.  This simplifies the work done by the {router},
        leading to an increase in speed.  At each {router}, the label
        is replaced with a new label, which tells the next {router}
        how to forward the {packet}.  The label is removed when the
        {packet} leaves the MPLS {network}.
     
        Modern {ASIC}-based routers can look up routes fast enough to
        make the speed increase less important.  However, MPLS still
        has some benefits.  The use of {FEC}s allows {QoS} levels to
        be guaranteed, and MPLS allows {IP} {tunnel}s to be created
        through a {network}, so that {VPN}s can be implemented without
        {encryption}.
     
        {MPLS Resource Center (http://www.mplsrc.com/)}.
     
        [RFC 3031]
     
        (2002-04-14)