Abbreviations

 

ASM   Availability state machine

ATM   Asynchronous transfer mode

BIP      Bit Interleaved Parity

CR-LDP constraint-based routing LDP

DLCI   Data Link Connection Identifier

DoS     Denial of Service

E-LSP EXP-Inferred-PSC LSP [21]

ER       Explicit Routing

FEC     Forwarding Equivalence Classes

FFS     For Further Study

FTN    FEC-To-NHLFE

LIB      Label Information Bases

L-LSP Label-Only-Inferred-PSC LSP [21]

LSP     Label Switched Path

LSR     Label Switching Router

MIB     Management Information Base

MPLS  Multi Protocol Layer Switching

NHLFE Next-Hop Label Forwarding Entry

NMS   Network Management System.

OAM   Operation Administration and Maintenance

PDU    Protocol data unit

PHB    Per Hop Behavior

QoS     Quality of Service

RSVP  Resource ReSerVation Protocol

RSVP-TE        RSVP Extensions for Traffic Engineering

SLA     Service Level Agreement

SNMP Simple Network Management Protocol

TLV     Type/Length/Value

TTSI    Trail Termination Source Identifier

VCI     virtual circuit identifier

VPI      virtual path identifier

 


Terms

Backup entity – This is a collective term for the protection LSP of the protection switching mechanism and the backup segment for the fast rerouting mechanism.

 

Bi-Directional: Two LSRs that use LDP to exchange label/FEC mapping information are known as "LDP Peers" with respect to that information and we speak of there being an "LDP Session" between them. A single LDP session allows each peer to learn the other's label mappings; i.e., the protocol is bi-directional [8].

 

Control plane: The MPLS Control Plane is responsible for populating and maintaining the LFIB. [52]

 

Data-plane: See user-plane.

 

Dedicated OAM Cells: Packets containing OAM information that are dedicated to be sent at a periodic basis.

 

Egress: Point of exit from an MPLS context or domain. The egress of an LSP is the logical point at which the determination to pop a label associated with an LSP is made. The label may actually be popped at the LSR making this determination or at the one prior to it (in the penultimate hop pop case). Egress from MPLS in general is the point at which the last label is removed (resulting in removal of the label stack). [49]

 

Ingress: Point at which an MPLS context or domain is entered. The ingress of an LSP is the point at which a label is pushed onto the label stack (possibly resulting in the creation of the label stack). [49]

 

LSP Tunnel: An LSP tunnel is an LSP with a well-defined source (ingress point) and sink (egress point).  From an architectural viewpoint an LSP tunnel at layer N is equivalent to an LSP trail at layer N.  However, the term ‘tunnel’ implies that it is supporting some higher layer client entity, which could be either a higher level LSP trail or (for the highest level LSP trail) a higher level network layer protocol such as IP. [21a]

 

Label switching: Switching based on use of labels. [49]

 

Label Switching Router (LSR): A device that participates in one or more routing protocols and uses the route information derived from routing protocol exchanges to drive LSP setup and maintenance. Such a device typically distributes labels to peers and uses these labels (when provided as part of data presented for forwarding) to forward label-encapsulated L3 packets. In general, an LSR may or may not be able to forward non-label-encapsulated data and provide ingress/egress to LSPs (that is, to perform what is frequently referred to as the label edge router, or LER, function).

 

Network Management System (NMS): System responsible for managing at least part of a network (Network Cell). An NMS is generally a reasonably powerful and well-equipped computer such as an engineering workstation. NMSs communicate with agents to help keep track of network statistics and resources.

 

Per Hop Behavior: A Differentiated Services behavioral definition. A PHB is defined at a node by the combination of a Differentiated Services Code Point (DSCP) and a set of configured behaviors. [49]

 

Penultimate hop: A process by which the peer immediately upstream of the egress LSR is asked to pop a label prior to forwarding the packet to the egress LSR. Using LDP, this is done by assigning the special value of the implicit Null label. This allows the egress to push the work of popping the label to its upstream neighbor, possibly allowing for a more optimal processing of the remaining packet. Note that this can be done because once the label has been used to determine the next-hop information for the last hop, the label is no longer useful. Using PHP is helpful because it allows the packet to be treated as an unlabeled packet by the last hop. Using PHP, it is possible to implement an "LSR" that never uses labels. [49]

 

Redundancy: When a backbone network has more than one links between its routers, thus making different ways traffic can be sent to the same destination, we say that the backbone has link redundancy. If the backbone has one or more alternative LSP(s) between the edge routers for a given LSP, we say that the backbone has LSP redundancy. A low degree of redundancy means that the network normally uses most of its links, whilst a high degree of redundancy means that the network normally uses few of its links.

 

Reliability: When a backbone network has more than one links between its routers, and the network has mechanisms for detecting link errors and route around the affected area, we say that the network has high link reliability. If the backbone has one or more alternative LSP(s) between the edge routers for a given LSP and the network has mechanisms for detecting LSP errors, we say that the LSPs have high LSP reliability.

 

Router: A device used to forward packets at the network (L3) layer. [49]

 

Service Level Agreement (SLA): SLA is a contract between network providers and customers that services the providers should provide. This can be the amount of server uptime in percentage, the amount of users that can be served simultaneously or similar.

 

Type-Length-Value (TLV): An object description with highly intuitive meaning; that is, the object consists of three fields: type, length, and value. Type gives the semantic meaning of the value, length gives the number of bytes in the value field (that may be fixed by the type), and value consists of length bytes of data in a format consistent with type. This object format is used in LDP and several other protocols [49].

 


Trail: A generic transport entity at layer N which is composed of a client payload (which can be a packet from a client at higher layer N-1) with specific overhead added at layer N to ensure the forwarding integrity of the server transport entity at layer N. This is a more general term for LSP at ITU-T. [21]

 

Trail termination point: A source or sink point of a trail at layer N, at which the trail overhead is added or removed respectively.  A trail termination point must have a unique means of identification within the layer network. [21a]

 

Upstream: Direction from which traffic is expected to arrive. This applies to a specific forwarding equivalence class. [49]

 

User-plane: This refers to the set of traffic forwarding components through which traffic flows. CV OAM packets are periodically inserted into this traffic flow to monitor the health of those forwarding components. The user-plane is also sometimes called the data-plane (especially in IETF). Note that control-plane protocols (eg for signalling or routing) and management-plane protocols will require their own user-plane, and their user-plane may or may not be congruent (to varying degrees) with the traffic bearing user-plane [21].


     References

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[4]     Bill Michael
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[17]   ITU-T Study Group 13
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[18]   Larry L. Peterson and Bruce S. Davie
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[19]   Postel, J.
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[21]   ITU-T Study Group 13
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[21a] ITU-T Study Group 13
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[22]   E. Rosen, D. Tappan, G. Fedorkow, Y. Rekhter, D. Farinacci, T. Li, A. Conta
MPLS Label Stack Encoding, RFC 3032, IETF Network Working Group, January 2001
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[26]   D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G. Swallow
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[28]   Cheenu Srinivasan, Arun Viswanathan, Thomas D. Nadeau
Multiprotocol Label Switching (MPLS) Traffic Engineering Management Information Base, Internet Draft, WORK IN PROGRES, IETF Network Working Group, January 2002, expires July 2002
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[29]   R. Hinden, S. Deering
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[30]   Case, J., Fedor, M. , Schoffstall, M., and Davin, C.
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[32]   ITU-T Study Group 13
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[33]   Rosen, E., Viswanathan, A., Callon, R.,
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[34]   S. Deering and R. Hinden
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[39]   F. Kastenholz,
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[45] Information Sciences Institute, University of Southern California,
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[46]   T. Socolofsky, C. Kale
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[48]   P. Almquist, F. Kastenholz,
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[49]   The MPLS Resource Center
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[50]   The 10 Gigabit Ethernet Alliance
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[51]   Cisco Systems, Inc
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[52]   Vivek Alwayn
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MECHANISMS FOR OAM ON MPLS IN LARGE IP BACKBONE NETWORKS (c) 2002 Hallstein Lohne, Johannes Vea, a graduate thesis written for AUC/ERICSSON