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Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints the labels identify established paths between endpoints. MPLS can encapsulate packets of various network protocols, hence the multiprotocol component of the name. MPLS supports a range of access technologies, including T1/E1, ATM, Frame Relay, and DSL.
A multilayer switch (MLS) is a computer networking device that switches on OSI layer 2 like an ordinary network switch and provides extra functions on higher OSI layers. The MLS was invented by engineers at Digital Equipment Corporation.
The Resource Reservation Protocol (RSVP) is a transport layer protocol designed to reserve resources across a network using the integrated services model. RSVP operates over an IPv4 or IPv6 and provides receiver-initiated setup of resource reservations for multicast or unicast data flows. It does not transport application data but is similar to a control protocol, like Internet Control Message Protocol (ICMP) or Internet Group Management Protocol (IGMP). RSVP is described in RFC 2205.
Label Distribution Protocol (LDP) is a protocol in which routers capable of Multiprotocol Label Switching (MPLS) exchange label mapping information. Two routers with an established session are called LDP peers and the exchange of information is bi-directional. LDP is used to build and maintain label-switched path (LSP) databases that are used to forward traffic through MPLS networks.
Virtual Private LAN Service (VPLS) is a way to provide Ethernet-based multipoint to multipoint communication over IP or MPLS networks. It allows geographically dispersed sites to share an Ethernet broadcast domain by connecting sites through pseudowires. The term sites includes multiplicities of both servers and clients. The technologies that can be used as pseudo-wire can be Ethernet over MPLS, L2TPv3 or even GRE. There are two IETF standards track RFCs describing VPLS establishment.
Bidirectional Forwarding Detection (BFD) is a network protocol that is used to detect faults between two routers or switches connected by a link. It provides low-overhead detection of faults even on physical media that doesn't support failure detection of any kind, such as Ethernet, virtual circuits, tunnels and MPLS label-switched paths.
In IP-based computer networks, virtual routing and forwarding (VRF) is a technology that allows multiple instances of a routing table to co-exist within the same router at the same time. One or more logical or physical interfaces may have a VRF and these VRFs do not share routes therefore the packets are only forwarded between interfaces on the same VRF. VRFs are the TCP/IP layer 3 equivalent of a VLAN. Because the routing instances are independent, the same or overlapping IP addresses can be used without conflicting with each other. Network functionality is improved because network paths can be segmented without requiring multiple routers.
Penultimate hop popping (PHP) is a function performed by certain routers in an MPLS enabled network. It refers to the process whereby the outermost label of an MPLS tagged packet is removed by a label switch router (LSR) before the packet is passed to an adjacent label edge router (LER). The benefit is that the LSR has to do a label lookup anyway and it doesn't make a difference whether this results in a label swap or pop. However, for the LER this saves one cycle of label lookup.
Constraint-based Routing Label Distribution Protocol (CR-LDP) is a control protocol used in some computer networks. As of February 2003, the IETF MPLS working group deprecated CR-LDP and decided to focus purely on RSVP-TE.
A Layer 2 MPLS VPN is a term in computer networking. It is a method that Internet service providers use to segregate their network for their customers, to allow them to transmit data over an IP network. This is often sold as a service to businesses.
Resource Reservation Protocol - Traffic Engineering (RSVP-TE) is an extension of the Resource Reservation Protocol (RSVP) for traffic engineering. It supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature of the packet streams they want to receive. RSVP runs on both IPv4 and IPv6.
An ingress router is a label switch router that is a starting point (source) for a given label-switched path (LSP). An ingress router may be an egress router or an intermediate router for any other LSP(s). Hence the role of ingress and egress routers is LSP specific. Usually, the MPLS label is attached with an IP packet at the ingress router and removed at the egress router, whereas label swapping is performed on the intermediate routers. However, in special cases the ingress router could be pushing label in label stack of an already existing MPLS packet. Note that, although the ingress router is the starting point of an LSP, it may or may not be the source of the under-lying IP packets.
In MPLS, a label with the value of 1 represents the router alert label. This label value is legal anywhere in the label stack except at the bottom. When a received packet contains this label value at the top of the label stack, it is delivered to a local software module for processing. The actual forwarding of the packet is determined by the label beneath it in the stack. However, if the packet is forwarded further, the Router Alert Label should be pushed back onto the label stack before forwarding. The use of this label is analogous to the use of the "Router Alert" option in IPv4 packets. Since this label cannot occur at the bottom of the stack, it is not associated with a particular network layer protocol.
Provider Backbone Bridge Traffic Engineering (PBB-TE) is a computer networking technology specified in IEEE 802.1Qay, an amendment to the IEEE 802.1Q standard. PBB-TE adapts Ethernet to carrier class transport networks. It is based on the layered VLAN tags and MAC-in-MAC encapsulation defined in IEEE 802.1ah, but it differs from PBB in eliminating flooding, dynamically created forwarding tables, and spanning tree protocols. Compared to PBB and its predecessors, PBB-TE behaves more predictably and its behavior can be more easily controlled by the network operator, at the expense of requiring up-front connection configuration at each bridge along a forwarding path. PBB-TE Operations, Administration, and Management (OAM) is usually based on IEEE 802.1ag. It was initially based on Nortel's Provider Backbone Transport (PBT).
Forwarding may refer to:
A forwarding information base (FIB), also known as a forwarding table or MAC table, is most commonly used in network bridging, routing, and similar functions to find the proper output network interface controller to which the input interface should forward a packet. It is a dynamic table that maps MAC addresses to ports. It is the essential mechanism that separates network switches from Ethernet hubs. Content-addressable memory (CAM) is typically used to efficiently implement the FIB, thus it is sometimes called a CAM table.
Label switching is a technique of network relaying to overcome the problems perceived by traditional IP-table switching. Here, the switching of network packets occurs at a lower level, namely the data link layer rather than the traditional network layer.
An egress router is a label switch router that is an end point (drain) for a given label-switched path (LSP). An egress router may be an ingress router or an intermediate router for any other LSP(s). Hence the role of egress and ingress routers is LSP specific. Usually, the MPLS label is attached with an IP packet at the ingress router and removed at the egress router, whereas label swapping is performed on the intermediate routers.
Generalized Multi-Protocol Label Switching (GMPLS) is a protocol suite extending MPLS to manage further classes of interfaces and switching technologies other than packet interfaces and switching, such as time-division multiplexing, layer-2 switching, wavelength switching and fiber-switching.
Path protection in telecommunications is an end-to-end protection scheme used in connection oriented circuits in different network architectures to protect against inevitable failures on service providers’ network that might affect the services offered to end customers. Any failure occurred at any point along the path of a circuit will cause the end nodes to move/pick the traffic to/from a new route. Finding paths with protection, especially in elastic optical networks, was considered a difficult problem, but an efficient and optimal algorithm was proposed.
References
- MPLS FAQ For Beginners: What is a Forwarding Equivalence Class (FEC)?
- Understanding the Role of FECs in MPLS
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