Editing Multiprotocol Label Switching (section)

==Comparisons==
MPLS can make use of existing ATM network or Frame Relay infrastructure, as its labeled flows can be mapped to ATM or Frame Relay virtual-circuit identifiers, and vice versa.

===Frame Relay===
[[Frame Relay]] aimed to make more efficient use of existing physical resources, which allow for the underprovisioning of data services by [[telecommunications companies]] (telcos) to their customers, as clients were unlikely to be utilizing a data service 100 percent of the time. Consequently, [[oversubscription]] of capacity by the telcos, while financially advantageous to the provider, can directly affect overall performance.

Telcos often sold Frame Relay to businesses looking for a cheaper alternative to [[dedicated line]]s; its use in different geographic areas depended greatly on governmental and telecommunication companies' policies.

Many customers migrated from Frame Relay to MPLS over IP or Ethernet, which in many cases reduced costs and improved manageability and performance of their wide area networks.<ref>{{Cite web|url=http://www.icact.org/upload/2010/0264/20100264_finalpaper.pdf|title=A Study on Any Transport over MPLS (AToM)|last=Tran Cong Hung, Le Quoc Cuong, Tran Thi Thuy Mai|date=10 Feb 2019|website=International Conference on Advanced Communications Technology|access-date=5 February 2020}}</ref>

===Asynchronous Transfer Mode===
While the underlying protocols and technologies are different, both MPLS and [[Asynchronous Transfer Mode|ATM]] provide a connection-oriented service for transporting data across computer networks. In both technologies, connections are signaled between endpoints, the connection state is maintained at each node in the path, and encapsulation techniques are used to carry data across the connection. Excluding differences in the signaling protocols (RSVP/LDP for MPLS and [[PNNI]] for ATM) there still remain significant differences in the behavior of the technologies.

The most significant difference is in the transport and encapsulation methods. MPLS is able to work with variable-length packets while ATM uses fixed-length (53 bytes) cells. Packets must be segmented, transported and re-assembled over an ATM network using an adaptation layer, which adds significant complexity and overhead to the data stream. MPLS, on the other hand, simply adds a label to the head of each packet and transmits it on the network.

Differences exist, as well, in the nature of the connections. An MPLS connection (LSP) is unidirectional, allowing data to flow in only one direction between two endpoints. Establishing two-way communications between endpoints requires a pair of LSPs be established. Because two LSPs are used, data flowing in the forward direction may use a different path from data flowing in the reverse direction. ATM point-to-point connections (virtual circuits), on the other hand, are [[Two-way communication|bidirectional]], allowing data to flow in both directions over the same path.{{efn|Both SVC and PVC ATM connections are bidirectional.<ref>[[ITU-T]] I.150 3.1.3.1</ref>}}

Both ATM and MPLS support tunneling of connections inside connections. MPLS uses label stacking to accomplish this while ATM uses ''virtual paths''. MPLS can stack multiple labels to form tunnels within tunnels. The ATM virtual path indicator (VPI) and virtual circuit indicator (VCI) are both carried together in the cell header, limiting ATM to a single level of tunneling.

The biggest advantage that MPLS has over ATM is that it was designed from the start to be complementary to IP. Modern routers can support both MPLS and IP natively across a common interface allowing network operators great flexibility in [[network design]] and operation. ATM's incompatibilities with IP require complex adaptation, making it comparatively less suitable for today's predominantly IP networks.