Editing Multiprotocol Label Switching (section)

==Relationship to Internet Protocol==
MPLS works in conjunction with the Internet Protocol (IP) and its routing protocols, usually [[interior gateway protocol]]s (IGPs). MPLS LSPs provide dynamic, transparent virtual networks with support for traffic engineering, the ability to transport layer-3 (IP) VPNs with overlapping address spaces, and support for layer-2 [[pseudowire]]s using [[Pseudowire Emulation Edge-to-Edge]] (PWE3){{Ref RFC|3985}} that are capable of transporting a variety of transport payloads ([[IPv4]], [[IPv6]], ATM, Frame Relay, etc.). MPLS-capable devices are referred to as LSRs. The paths an LSR knows can be defined using explicit hop-by-hop configuration, or are dynamically routed by the [[Constrained Shortest Path First]] (CSPF) algorithm, or are configured as a loose route that avoids a particular IP address or that is partly explicit and partly dynamic.

In a pure IP network, the shortest path to a destination is chosen even when the path becomes congested. Meanwhile, in an IP network with MPLS Traffic Engineering CSPF routing, constraints such as the RSVP bandwidth of the traversed links can also be considered, such that the shortest path with available bandwidth will be chosen. MPLS Traffic Engineering relies upon the use of TE extensions to [[Open Shortest Path First]] (OSPF) or [[Intermediate System to Intermediate System]] (IS-IS) and RSVP. In addition to the constraint of RSVP bandwidth, users can also define their own constraints by specifying link attributes and special requirements for tunnels to route (or not to route) over links with certain attributes.<ref>{{cite book|title=MPLS Fundamentals|isbn=978-1587051975| pages=249–326|last1=Ghein|first1=Luc De|year=2007|publisher=Cisco Press }}</ref>

For end-users the use of MPLS is not visible directly, but can be assumed when doing a [[traceroute]]: only nodes that do ''full'' IP routing are shown as hops in the path, thus not the MPLS nodes used in between, therefore when you see that a packet ''hops'' between two very distant nodes and hardly any other ''hop'' is seen in that provider's network (or [[Autonomous System (Internet)|AS]]) it is very likely that network uses MPLS.

===MPLS local protection===
{{Main|MPLS local protection}}
In the event of a network element failure when recovery mechanisms are employed at the IP layer, restoration may take several seconds which may be unacceptable for real-time applications such as [[VoIP]].<ref name="aslam">{{Citation|author=Aslam |title=NPP: A Facility Based Computation Framework for Restoration Routing Using Aggregate Link Usage Information|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=16546516|version=QoS-IP 2005 : quality of service in multiservice IP network|date=2005-02-02|access-date=2006-10-27|postscript=.|display-authors=etal}}</ref><ref name="raza">{{Citation|author=Raza |title=IEEE International Conference on Communications, 2005. ICC 2005. 2005|chapter=Online routing of bandwidth guaranteed paths with local restoration using optimized aggregate usage information|volume=1|pages=201–207|version=IEEE-ICC 2005|postscript=.|display-authors=etal|doi=10.1109/ICC.2005.1494347|isbn=0-7803-8938-7|year=2005|s2cid=5659648}}</ref><ref name="LiLi">{{Citation|author=Li Li |title=Routing bandwidth guaranteed paths with local restoration in label switched networks|journal=IEEE Journal on Selected Areas in Communications|volume=23|issue=2|pages=437–449|version=IEEE Journal on Selected Areas in Communications|postscript=.|display-authors=etal|doi=10.1109/JSAC.2004.839424|year=2005|s2cid=195347236 }}</ref> In contrast, [[MPLS local protection]] meets the requirements of real-time applications with recovery times comparable to those of [[shortest path bridging]] networks or [[SONET]] rings of less than 50&nbsp;ms.<ref name="aslam"/><ref name="LiLi"/><ref name="Kodialam">{{Citation|author=Kodialam|title=Proceedings IEEE INFOCOM 2001. Conference on Computer Communications. Twentieth Annual Joint Conference of the IEEE Computer and Communications Society (Cat. No.01CH37213)|chapter=Dynamic Routing of Locally Restorable Bandwidth Guaranteed Tunnels using Aggregated Link Usage Information|volume=1|pages=376–385|version=IEEE Infocom. pp. 376–385. 2001|postscript=.|display-authors=etal|doi=10.1109/INFCOM.2001.916720|isbn=0-7803-7016-3|year=2001|s2cid=13870642}}</ref>