It is a simplification of the ATM concept based on the realization that small cells are not needed in the core of modern networks, as modern optical networks (as of 2001) are so fast (at speeds of 10 Gbits/s and well beyond) that even full-length 1500 byte packets do not incur significant queuing delays.
At the same time, it attempts to preserve the ideas of traffic engineering and out-of-band control that made ATM attractive for deploying large scale networks.
MPLS works by encapsulating packets with a very simple MPLS header that specifies a virtual circuit 'label'. This can then be used for routing without the router looking inside the cell, and so enables protocol independent packet forwarding that does not need to look at a protocol-dependent [routing table]?.
However, the routing protcols used to determine which tags get routed where are quite different to those used in ATM.
However, MPLS can make use of existing ATM network infrastructure, as its labeled flows can be simply mapped to ATM virtual circuit identifiers.
MPLS is currently in use in large networks, even though it is still (as of 2001) undergoing IETF standardization.
In practice, MPLS is mainly used to route IP and Ethernet traffic.
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