RTGWG                                                 C. Villamizar, Ed.
Internet-Draft                                                OCCNC, LLC
Intended status: Informational                           D. McDysan, Ed.
Expires: September 23, 2013 January 12, 2014                                        Verizon
                                                                 S. Ning
                                                     Tata Communications
                                                                A. Malis
                                                                 Verizon
                                                                 L. Yong
                                                              Huawei USA
                                                          March 22,
                                                           July 11, 2013

          Requirements for Composite Links Advanced Multipath in MPLS Networks
                   draft-ietf-rtgwg-cl-requirement-10
                   draft-ietf-rtgwg-cl-requirement-11

Abstract

   There is often

   This document provides a need to provide large aggregates set of bandwidth that
   are best provided using parallel links between routers or requirements for Advanced Multipath
   in MPLS LSR.
   In core networks there Networks.

   Advanced Multipath is often no alternative since the aggregate
   capacities of core networks today far exceed the capacity of a single
   physical link or single packet processing element.

   The presence of parallel links, with each link potentially comprised formalization of multiple layers has resulted multipath techniques
   currently in additional requirements.  Certain
   services may benefit from being restricted to use in IP and MPLS networks and a subset set of the
   component links or a specific component link, where component link
   characteristics, such as latency, differ.  Certain services require
   that an LSP be treated as atomic and avoid reordering.  Other
   services will continue extensions to require only that reordering not occur
   within a microflow as is current practice.
   existing multipath techniques.

Status of this Memo

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   This Internet-Draft will expire on September 23, 2013. January 12, 2014.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4  3
   2.  Assumptions  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4  3
   3.  Definitions  . . . . . . . . . . . . . . . . .  Functional Requirements  . . . . . . . .  4
   4.  Network Operator Functional Requirements . . . . . . . . . . .  5
     4.1.  6
     3.1.  Availability, Stability and Transient Response . . . . . .  5
     4.2.  6
     3.2.  Component Links Provided by Lower Layer Networks . . . . .  6
     4.3.  7
     3.3.  Parallel Component Links with Different Characteristics  .  8
   5.
   4.  Derived Requirements . . . . . . . . . . . . . . . . . . . . . 10
   6. 11
   5.  Management Requirements  . . . . . . . . . . . . . . . . . . . 11
   7. 12
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8. 13
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   9. 13
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   10. 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  ITU-T G.800 Composite Link Definitions and
                Terminology . . . . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

1.  Introduction

   The purpose of this document is to describe why network operators
   require certain functions in order to solve certain business problems
   (Section 2).  The intent

   There is to first describe why things often a need to be
   done in terms of functional provide large aggregates of bandwidth that
   are best provided using parallel links between routers or carrying
   traffic over multiple MPLS LSP.  In core networks there is often no
   alternative since the aggregate capacities of core networks today far
   exceed the capacity of a single physical link or single packet
   processing element.

   The presence of parallel links, with each link potentially comprised
   of multiple layers has resulted in additional requirements.  Certain
   services may benefit from being restricted to a subset of the
   component links or a specific component link, where component link
   characteristics, such as latency, differ.  Certain services require
   that an LSP be treated as atomic and avoid reordering.  Other
   services will continue to require only that reordering not occur
   within a microflow as is current practice.

   The purpose of this document is to clearly enumerate a set of
   requirements related to the protocols and mechanisms that provide
   MPLS based Advanced Multipath.  The intent is to first provide a set
   of functional requirements that are as independent as possible of
   protocol specifications (Section 4). 3).  For certain functional
   requirements this document describes a set of derived protocol
   requirements (Section 4) and management requirements (Section 5).  Appendix A provides a summary of
   G.800 terminology used to define a composite link.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Assumptions

   Any statement which requires the solution to support some new
   functionality through use of [RFC2119] keywords, SHOULD be
   interpretted as follows.  The services supported include pseudowire based services (RFC 3985
   [RFC3985]), including VPN services, Internet traffic encapsulated by
   at least one MPLS label (RFC 3032 [RFC3032]), and dynamically
   signaled MPLS (RFC 3209 [RFC3209] or RFC 5036 [RFC5036]) implementation either MUST or MPLS-TP
   LSPs (RFC 5921 [RFC5921]).  The MPLS LSPs supporting these services
   may be point-to-point, point-to-multipoint, SHOULD
   support the new functionality depending on the use of either MUST or multipoint-to-
   multipoint.

   The locations
   SHOULD in a network where these the requirements apply are a Label
   Edge Router (LER) statement.  The implementation SHOULD in
   most or a Label Switch Router (LSR) as defined all cases allow any new functionality to be individually
   enabled or disabled through configuration.  A service provider or
   other deployment MAY choose to enable or disable any feature in RFC
   3031 [RFC3031]. their
   network, subject to implementation limitations on sets of features
   which can be disabled.

2.  Definitions
   Multipath
       The IP DSCP cannot term multipath includes all techniques in which

       1.  Traffic can take more than one path from one node to a
           destination.

       2.  Individual packets take one path only.  Packets are not
           subdivided and reassembled at the receiving end.

       3.  Packets are not resequenced at the receiving end.

       4.  The paths may be:

           a.  parallel links between two nodes, or

           b.  may be specific paths across a network to a destination
               node, or

           c.  may be links or paths to an intermediate node used to
               reach a common destination.

       The paths need not have equal capacity.  The paths may or may not
       have equal cost in a routing protocol.

   Advanced Multipath
       Advanced Multipath meets the requirements defined in this
       document.  A key capability of advanced multipath is the support
       of non-homogeneous component links.

   Composite Link
       The term Composite Link had been a registered trademark of Avici
       Systems, but was abandoned in 2007.  The term composite link is
       now defined by the ITU in [ITU-T.G.800].  The ITU definition
       includes multipath as defined here, plus inverse multiplexing
       which is explicitly excluded from the definition of multipath.

   Inverse Multiplexing
       Inverse multiplexing either transmits whole packets and
       resequences the packets at the receiving end or subdivides
       packets and reassembles the packets at the receiving end.
       Inverse multiplexing requires that all packets be handled by a
       common egress packet processing element and is therefore not
       useful for flow very high bandwidth applications.

   Component Link
       The ITU definition of composite link in [ITU-T.G.800] and the
       IETF definition of link bundling in [RFC4201] both refer to an
       individual link in the composite link or link bundle as a
       component link.  The term component link is applicable to all
       forms of multipath.  The IEEE uses the term member rather than
       component link in Ethernet Link Aggregation [IEEE-802.1AX].

   Client LSP
       A client LSP is an LSP which has been set up over a server layer.
       In the context of this discussion, a client LSP is a LSP which
       has been set up over a multipath as opposed to an LSP
       representing the multipath itself or any LSP supporting a
       component links of that multipath.

   Flow
       A sequence of packets that should be transferred in order on one
       component link of a multipath.

   Flow identification since L3VPN
   requires Diffserv transparency (see RFC 4031 5.5.2 [RFC4031]),
       The label stack and other information that uniquely identifies a
       flow.  Other information in
   general flow identification may include an IP
       header, pseudowire (PW) control word, Ethernet MAC address, etc.
       Note that a client LSP may contain one or more Flows or a client
       LSP may be equivalent to a Flow.  Flow identification is used to
       locally select a component link, or a path through the network operators do not rely on
       toward the DSCP of Internet
   packets.

3.  Definitions

   ITU-T G.800 Based Composite and Component Link Definitions:
       Section 6.9.2 destination.

   Load Balance
       Load split, load balance, or load distribution refers to
       subdividing traffic over a set of ITU-T-G.800 [ITU-T.G.800] defines composite and component links as summarized in Appendix A.  The following
       definitions for composite and such that load
       is fairly evenly distributed over the set of component links and
       certain packet ordering requirements are derived from met.  Some existing
       techniques better acheive these objectives than others.

   Performance Objective
       Numerical values for performance measures, principally
       availability, latency, and intended delay variation.  Performance
       objectives may be related to Service Level Agreements (SLA) as
       defined in RFC2475 or may be consistent with the cited ITU-T G.800
       terminology.

       Composite Link:  A composite link is a logical link composed of a
           set of parallel point-to-point component strictly internal.  Performance
       objectives may span links, where all
           links in the set share the same endpoints. edge-to-edge, or end-to-end.
       Performance objectives may span one provider or may span multiple
       providers.

   A composite link Component Link may itself be a component of another composite link, but only
           a strict hierarchy of links is allowed.

       Component Link:  A point-to-point physical link (including (where a
   "physical link" includes one or more link layer plus a physical
   layer) or a logical link that preserves ordering in the steady state.
   A component link may have transient out of order events, but such
   events must not exceed the network's
           specific NPO.  Examples of Performance Objectives.  For
   example, a physical compoent link are: any set may be comprised of
           link layers over a WDM wavelength or any supportable
   combination of Ethernet PHY, PPP, SONET or OTN over a
           physical link.  Examples of a logical link are: MPLS LSP,
           Ethernet VLAN, MPLS-TP LSP.  A set of link layers supported over pseudowire is a logical link that appears to the client
           to be a physical link.

   Flow:  A sequence of packets that must be transferred in order on one
       component link.

   Flow identification:  The label stack and other information that
       uniquely identifies a flow.  Other information in flow
       identification may include an IP header, PW control word,
       Ethernet MAC address, etc.  Note that an LSP may contain one or
       more Flows physical layer or an LSP over logical sub-
   layers, including those providing physical layer emulation.

   The ingress and egress of a multipath may be equivalent to a Flow.  Flow
       identification is used midpoint LSRs with
   respect to locally select a component link, or given client LSP.  A midpoint LSR does not participate
   in the signaling of any clients of the client LSP.  Therefore, in
   general, multipath endpoints cannot determine requirements of clients
   of a
       path client LSP through participation in the network toward signaling of the destination.

   Network Performance Objective (NPO):  Numerical values for
       performance measures, principally availability, latency, clients
   of the client LSP.

   The term Advanced Multipath is intended to be used within the context
   of this document and
       delay variation.  See the related documents,
   [I-D.ietf-rtgwg-cl-use-cases] for more
       details.

4.  Network Operator and [I-D.ietf-rtgwg-cl-framework] and
   any other related document.  Other advanced multipath techniques may
   in the future arise.  If the capabilities defined in this document
   become commonplace, they would no longer be considered "advanced".
   Use of the term "advanced multipath" outside this document, if
   refering to the term as defined here, should indicate Advanced
   Multipath as defined by this document, citing the current document
   name.  If using another definition of "advanced multipath", documents
   may optionally clarify that they are not using the term "advanced
   multipath" as defined by this document if clarification is deemed
   helpful.

3.  Functional Requirements

   The Functional Requirements in this section are grouped in
   subsections starting with the highest priority.

4.1.

3.1.  Availability, Stability and Transient Response

   Limiting the period of unavailability in response to failures or
   transient events is extremely important as well as maintaining
   stability.  The transient period between some service disrupting
   event and the convergence of the routing and/or signaling protocols
   MUST occur within a time frame specified by NPO Performance Objective
   values.
   [I-D.ietf-rtgwg-cl-use-cases] provides references

   FR#1  An advanced multipath MAY be announced in conjunction with
         detailed parameters about its component links, such as
         bandwidth and latency.  The advanced multipath SHALL behave as
         a summary of
   service types requiring a range of restoration times.

   FR#1 single IGP adjacency.

   FR#2  The solution SHALL provide a means to summarize some routing
         advertisements regarding the characteristics of a composite
         link an advanced
         multipath such that the routing updated protocol converges mechanisms maintain
         convergence times within the timeframe needed to meet or no
         significantly exceed existing Performance Objective for
         convergence on the same network or convergence on a network performance objective.  A
         composite link CAN be announced in conjunction
         with detailed
         parameters about its component links, such as bandwidth and
         latency.  The composite link SHALL behave as a single IGP
         adjacency.

   FR#2 similar topology.

   FR#3  The solution SHALL ensure that all possible restoration operations happen
         within the timeframe needed to meet the NPO.
         The solution may need to specify a means for aggregating
         signaling the timeframe needed to meet this requirement.

   FR#3 existing Performance
         Objective for restoration time on the same network or
         restoration time on a network with a similar topology.

   FR#4  The solution SHALL provide a mechanism to select a path for a
         flow across a network that contains a number of paths comprised
         of pairs of nodes connected by composite links advanced multipath in such a way
         as to automatically distribute the load over the network nodes
         connected by composite links advanced multipaths while meeting all of the other
         mandatory requirements stated above.  The solution SHOULD work
         in a manner similar to that of current networks without any
         composite link
         advanced multipath protocol enhancements when the
         characteristics of the individual component links are
         advertised.

   FR#4

   FR#5  If extensions to existing protocols are specified and/or new
         protocols are defined, then the solution SHOULD provide a means
         for a network operator to migrate an existing deployment in a
         minimally disruptive manner.

   FR#5

   FR#6  Any automatic LSP routing and/or load balancing solutions MUST NOT oscillate such that performance observed by users changes
         such oscillate.  Some change
         in path MAY occur.  The solution MUST ensure that an NPO is violated. path
         stability and traffic reordering continue to meet Performance
         Objective on the same network or on a network with a similar
         topology.  Since oscillation may cause reordering, there MUST
         be means to control the frequency of changing the component
         link over which a flow is placed.

   FR#6

   FR#7  Management and diagnostic protocols MUST be able to operate
         over composite links. advanced multipaths.

   Existing scaling techniques used in MPLS networks apply to MPLS
   networks which support Composite Links. Advanced Multipaths.  Scalability and
   stability are covered in more detail in
   [I-D.ietf-rtgwg-cl-framework].

4.2.

3.2.  Component Links Provided by Lower Layer Networks

   Case 3 as defined in [ITU-T.G.800] involves a

   A component link
   supporting an MPLS may be supported by a lower layer network over another network.  For
   example, the lower layer network
   (e.g., may be a circuit switched network or another
   MPLS network (e.g., MPLS-TP)).  The lower layer network may change
   the latency (and/or other performance parameters) seen by the MPLS layer network.  Network
   Operators have NPOs of which some components are based on performance
   parameters. client
   layer.  Currently, there is no protocol for the lower layer network
   to inform the higher layer network of a change in a performance
   parameter.  Communication of the latency performance parameter is a
   very important requirement.  Communication of other performance
   parameters (e.g., delay variation) is desirable.

   FR#7   In order to support network NPOs and provide acceptable user
          experience, the

   FR#8   The solution SHALL specify a protocol means to allow a lower
          layer server network to communicate latency to the higher
          layer client network.

   FR#8

   FR#9   The precision of latency reporting SHOULD be configurable.  A
          reasonable default SHOULD be provided.  Implementations SHOULD
          support precision of at least 10% of the one way latencies for
          latency of 1 ms or more.

   FR#9

   FR#10  The solution SHALL provide a means to limit the latency to
          meet a Performance Objective target on a per LSP flow basis between nodes within a network to meet an NPO
          target when the path between these nodes contains one or more
          pairs
          group of nodes connected via a composite link. flow basis, where flows or groups of flows are
          identifiable in the forwarding plane and are signaled using in
          the control plane or set up using the management plane.

          The NPOs Performance Objectives differ across the services, and
          some services have different NPOs Performance Objectives for
          different QoS classes, for example, one QoS class may have a
          much larger latency bound than another.  Overload can occur
          which would violate an NPO a Performance Objective parameter (e.g.,
          loss) and some remedy to handle this case for a composite link an advanced
          multipath is required.

   FR#10

   FR#11  If the total demand offered by traffic flows exceeds the
          capacity of the composite link, advanced multipath, the solution SHOULD define
          a means to cause the LSPs for some traffic flows or groups of flows to move
          to some other point in the network that is not congested.
          These "preempted LSPs" flows" may not be restored if there is no
          uncongested path in the network.

   The intent is to measure the predominant latency in uncongested
   service provider networks, where geographic delay dominates and is on
   the order of milliseconds or more.  The argument for including
   queuing delay is that it reflects the delay experienced by
   applications.  The argument against including queuing delay is that
   it if used in routing decisions it can result in routing instability.
   This tradeoff is discussed in detail in
   [I-D.ietf-rtgwg-cl-framework].

4.3.

3.3.  Parallel Component Links with Different Characteristics

   Corresponding to Case 1 of [ITU-T.G.800], as

   As one means to provide high availability, network operators deploy a
   topology in the MPLS network using lower layer networks that have a
   certain degree of diversity at the lower layer(s).  Many techniques
   have been developed to balance the distribution of flows across
   component links that connect the same pair of nodes.  When the path
   for a flow can be chosen from a set of candidate nodes connected via composite links,
   advanced multipaths, other techniques have been developed.  Refer to
   the Appendices in [I-D.ietf-rtgwg-cl-use-cases] for a description of
   existing techniques and a set of references.

   FR#11

   FR#12  The solution SHALL measure traffic on a labeled flows or groups of traffic flow
          flows and dynamically select the component link on which to
          place this flow traffic in order to balance the load so that no
          component link in the composite link advanced multipath between a pair of
          nodes is overloaded.

   FR#12

   FR#13  When a traffic flow is moved from one component link to
          another in the same composite link advanced multipath between a set of nodes
          (or sites), it MUST be done so in a minimally disruptive
          manner.

   FR#13

   FR#14  Load balancing MAY be used during sustained low traffic
          periods to reduce the number of active component links for the
          purpose of power reduction.

   FR#14

   FR#15  The solution SHALL provide a means to identify flows whose
          rearrangement frequency needs to be bounded by a configured
          value.

   FR#15
          value and MUST provide a means to bound the rearrangement
          frequency for these flows.

   FR#16  The solution SHALL provide a means that communicates whether
          the flows within an client LSP can be split across multiple
          component links.  The solution SHOULD provide a means to
          indicate the flow identification field(s) which can be used
          along the flow path which can be used to perform this
          function.

   FR#16

   FR#17  The solution SHALL provide a means to indicate that a traffic
          flow shall select will traverse a component link with the minimum latency
          value.

   FR#17

   FR#18  The solution SHALL provide a means to indicate that a traffic
          flow shall select will traverse a component link with a maximum acceptable
          latency value as specified by protocol.

   FR#18

   FR#19  The solution SHALL provide a means to indicate that a traffic
          flow shall select will traverse a component link with a maximum acceptable
          delay variation value as specified by protocol.

   FR#19

   FR#20  The solution SHALL provide a means local to a node that
          automatically distributes flows across the component links in
          the composite link advanced multipath such that NPOs Performance Objectives are met.

   FR#20
          met as described in prior requirements.

   FR#21  The solution SHALL provide a means to distribute flows from a
          single client LSP across multiple component links to handle at
          least the case where the traffic carried in an client LSP
          exceeds that of any component link in the composite link. advanced multipath.
          As defined in
          section 3, Section 2, a flow is a sequence of packets that must
          should be transferred on one component link.

   FR#21 link and should be
          transferred in order.

   FR#22  The solution SHOULD support the use case where a composite
          link an advanced
          multipath itself is a component link for a higher order composite
          link.
          advanced multipath.  For example, a composite link an advanced multipath
          comprised of MPLS-TP bi-
          directional bi-directional tunnels viewed as logical
          links could then be used as a component link in yet another composite link
          advanced multipath that connects MPLS routers.

   FR#22

   FR#23  The solution MUST support an optional means for client LSP
          signaling to bind an a client LSP to a particular component link
          within a
          composite link. an advanced multipath.  If this option is not
          exercised, then an a client LSP that is bound to a composite link an advanced
          multipath may be bound to any component link matching all
          other signaled requirements, and different directions of a
          bidirectional client LSP can be bound to different component
          links.

   FR#23

   FR#24  The solution MUST support a means to indicate that both
          directions of co-routed bidirectional client LSP MUST be bound
          to the same component link.

   A minimally disruptive change implies that as little disruption as is
   practical occurs.  Such a change can be achieved with zero packet
   loss.  A delay discontinuity may occur, which is considered to be a
   minimally disruptive event for most services if this type of event is
   sufficiently rare.  A delay discontinuity is an example of a
   minimally disruptive behavior corresponding to current techniques.

   A delay discontinuity is an isolated event which may greatly exceed
   the normal delay variation (jitter).  A delay discontinuity has the
   following effect.  When a flow is moved from a current link to a
   target link with lower latency, reordering can occur.  When a flow is
   moved from a current link to a target link with a higher latency, a
   time gap can occur.  Some flows (e.g., timing distribution, PW
   circuit emulation) are quite sensitive to these effects.  A delay
   discontinuity can also cause a jitter buffer underrun or overrun
   affecting user experience in real time voice services (causing an
   audible click).  These sensitivities may be specified in an NPO. a
   Performance Objective.

   As with any load balancing change, a change initiated for the purpose
   of power reduction may be minimally disruptive.  Typically the
   disruption is limited to a change in delay characteristics and the
   potential for a very brief period with traffic reordering.  The
   network operator when configuring a network for power reduction
   should weigh the benefit of power reduction against the disadvantage
   of a minimal disruption.

5.

4.  Derived Requirements

   This section takes the next step and derives high-level requirements
   on protocol specification from the functional requirements.

   DR#1  The solution SHOULD attempt to extend existing protocols
         wherever possible, developing a new protocol only if this adds
         a significant set of capabilities.

   DR#2  A solution SHOULD extend LDP capabilities to meet functional
         requirements (without using TE methods as decided in
         [RFC3468]).

   DR#3  Coexistence of LDP and RSVP-TE signaled LSPs MUST be supported
         on a composite link. an advanced multipath.  Other functional requirements should
         be supported as independently of signaling protocol as
         possible.

   DR#4  When the nodes connected via a composite link an advanced multipath are in the
         same MPLS network topology, the solution MAY define extensions
         to the IGP.

   DR#5  When the nodes are connected via a composite link an advanced multipath are in
         different MPLS network topologies, the solution SHALL NOT rely
         on extensions to the IGP.

   DR#6  The solution SHOULD support composite link advanced multipath IGP
         advertisement that results in convergence time better than that
         of advertising the individual component links.  The solution
         SHALL be designed so that it represents the range of
         capabilities of the individual component links such that
         functional requirements are met, and also minimizes the
         frequency of advertisement updates which may cause IGP
         convergence to occur.

         Examples of advertisement update triggering events to be
         considered include: client LSP establishment/release, changes
         in component link characteristics (e.g., latency, up/down
         state), and/or bandwidth utilization.

   DR#7  When a worst case failure scenario occurs, the number of
         RSVP-TE client LSPs to be resignaled will cause a period of
         unavailability as perceived by users.  The resignaling time of
         the solution MUST meet the NPO objective support protocol mechanisms meeting existing
         provider Performance Objective for the duration of
         unavailability.  The
         unavailability without significantly relaxing those existing
         Performance Objectives for the same network or for networks
         with similar topology.  For example, the processing load due to
         IGP readvertisement MUST NOT increase significantly and the
         resignaling time of the solution MUST NOT increase
         significantly as compared with current methods.

6.

5.  Management Requirements

   MR#1  Management Plane MUST support polling of the status and
         configuration of a composite link an advanced multipath and its individual composite
          link
         advanced multipath and support notification of status change.

   MR#2  Management Plane MUST be able to activate or de-activate any
         component link in a composite link an advanced multipath in order to facilitate
         operation maintenance tasks.  The routers at each end of a
          composite link an
         advanced multipath MUST redistribute traffic to move traffic
         from a de-activated link to other component links based on the
         traffic flow TE criteria.

   MR#3  Management Plane MUST be able to configure a client LSP over a
          composite link an
         advanced multipath and be able to select a component link for
         the client LSP.

   MR#4  Management Plane MUST be able to trace which component link a
         client LSP is assigned to and monitor individual component link
         and
          composite link advanced multipath performance.

   MR#5  Management Plane MUST be able to verify connectivity over each
         individual component link within a composite link. an advanced multipath.

   MR#6  Component link fault notification MUST be sent to the
         management plane.

   MR#7   Composite link  Advanced multipath fault notification MUST be sent to the
         management plane and distribute MUST be distributed via link state message
         in the IGP.

   MR#8  Management Plane SHOULD provide the means for an operator to
          initiate an optimization process.

   MR#9   An operator initiated optimization MUST be performed in a
          minimally disruptive manner as described in Section 4.3.

   MR#10  Any statement which requires the solution to support some new
          functionality through use of the words new functionality,
          SHOULD be interpretted as follows.  The implementation either
          MUST or SHOULD support the new functionality depending on the
          use of either MUST or SHOULD in the requirements statement.
          The implementation Plane SHOULD in most or all cases allow any new
          functionality provide the means for an operator to
         initiate an optimization process.

   MR#9  An operator initiated optimization MUST be individually enabled or disabled through
          configuration.

7. performed in a
         minimally disruptive manner as described in Section 3.3.

6.  Acknowledgements

   Frederic Jounay of France Telecom and Yuji Kamite of NTT
   Communications Corporation co-authored a version of this document.

   A rewrite of this document occurred after the IETF77 meeting.
   Dimitri Papadimitriou, Lou Berger, Tony Li, the former WG chairs John
   Scuder and Alex Zinin, the current WG chair Alia Atlas, and others
   provided valuable guidance prior to and at the IETF77 RTGWG meeting.

   Tony Li and John Drake have made numerous valuable comments on the
   RTGWG mailing list that are reflected in versions following the
   IETF77 meeting.

   Iftekhar Hussain and Kireeti Kompella made comments on the RTGWG
   mailing list after IETF82 that identified a new requirement.
   Iftekhar Hussain made numerous valuable comments on the RTGWG mailing
   list that resulted in improvements to document clarity.

   In the interest of full disclosure of affiliation and in the interest
   of acknowledging sponsorship, past affiliations of authors are noted.
   Much of the work done by Ning So occurred while Ning was at Verizon.
   Much of the work done by Curtis Villamizar occurred while at
   Infinera.  Infinera continues to sponsor this work on a consulting
   basis.

8.

   Tom Yu and Francis Dupont provided the SecDir and GenArt reviews
   respectively.  Both reviews provided useful comments.  Lou Berger
   provided the RtgDir review which resulted in substantial
   clarification of terminology and document wording, particularly in
   the Abstract, Introduction, and Definitions sections.

7.  IANA Considerations

   This memo includes no request to IANA.

9.

8.  Security Considerations

   This document specifies a set of requirements.

   The requirements
   themselves do not pose a security threat.  If these requirements considerations for MPLS/GMPLS and for MPLS-TP are
   met using MPLS signaling as commonly practiced today with
   authenticated but unencrypted OSPF-TE, ISIS-TE,
   documented in [RFC5920] and RSVP-TE or LDP,
   then [RFC6941].  This document does not impact
   the requirement to provide additional information in this
   communication presents security of MPLS, GMPLS, or MPLS-TP.

   The additional information that could conceivably
   be gathered in a man-in-the-middle confidentiality breach.  Such an
   attack would require a capability to monitor this signaling either
   through a provider breach or access document requires does not
   provide significant additional value to provider physical transmission
   infrastructure.  A provider breach an attacker beyond the
   information already poses typically available from attacking a threat of numerous
   tpes routing or
   signaling protocol.  If the requirements of attacks which this document are met by
   extending an existing routing or signaling protocol, the security
   considerations of far more serious consequence.  Encrption the protocol being extended apply.  If the
   requirements of this document are met by specifying a new protocol,
   the signaling can prevent or render more difficult any
   confidentiality breach security considerations of that otherwise might occur by means new protocol should include an
   evaluation of access
   to provider physical transmission infrastructure.

10. what level of protection is required by the additional
   information specified in this document, such as data origin
   authentication.

9.  References

10.1.

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

10.2.

9.2.  Informative References

   [I-D.ietf-rtgwg-cl-framework]
              Ning, S., McDysan, D., Osborne, E., Yong, L., and C.
              Villamizar, "Composite Link Framework in Multi Protocol
              Label Switching (MPLS)", draft-ietf-rtgwg-cl-framework-01
              (work in progress), August 2012.

   [I-D.ietf-rtgwg-cl-use-cases]
              Ning, S., Malis, A., McDysan, D., Yong, L., and C.
              Villamizar, "Composite Link Use Cases and Design
              Considerations", draft-ietf-rtgwg-cl-use-cases-01 (work in
              progress), August 2012.

   [ITU-T.G.800]
              ITU-T, "Unified functional architecture of transport
              networks", 2007, <http://www.itu.int/rec/T-REC-G/
              recommendation.asp?parent=T-REC-G.800>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, January 2001.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., Cases and G. Swallow, "RSVP-TE: Extensions to RSVP Design
              Considerations", draft-ietf-rtgwg-cl-use-cases-01 (work in
              progress), August 2012.

   [IEEE-802.1AX]
              IEEE Standards Association, "IEEE Std 802.1AX-2008 IEEE
              Standard for LSP
              Tunnels", RFC 3209, December 2001. Local and Metropolitan Area Networks - Link
              Aggregation", 2006, <http://standards.ieee.org/getieee802/
              download/802.1AX-2008.pdf>.

   [ITU-T.G.800]
              ITU-T, "Unified functional architecture of transport
              networks", 2007, <http://www.itu.int/rec/T-REC-G/
              recommendation.asp?parent=T-REC-G.800>.

   [RFC3468]  Andersson, L. and G. Swallow, "The Multiprotocol Label
              Switching (MPLS) Working Group decision on MPLS signaling
              protocols", RFC 3468, February 2003.

   [RFC3985]  Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
              Edge (PWE3) Architecture", RFC 3985, March 2005.

   [RFC4031]  Carugi, M. and D. McDysan, "Service Requirements for Layer
              3 Provider Provisioned Virtual Private Networks (PPVPNs)",
              RFC 4031, April 2005.

   [RFC5036]  Andersson, L., Minei, I.,

   [RFC4201]  Kompella, K., Rekhter, Y., and B. Thomas, "LDP
              Specification", L. Berger, "Link Bundling
              in MPLS Traffic Engineering (TE)", RFC 5036, 4201, October 2007.

   [RFC5921]  Bocci, M., Bryant, S., Frost, D., Levrau, 2005.

   [RFC5920]  Fang, L., and L.
              Berger, "A "Security Framework for MPLS in Transport and GMPLS
              Networks", RFC 5921, 5920, July 2010.

Appendix A.  ITU-T G.800 Composite Link Definitions and Terminology

   Composite Link:
       Section 6.9.2 of ITU-T-G.800 [ITU-T.G.800] defines composite link
       in terms of three cases, of which the following two are relevant
       (the one describing inverse (TDM) multiplexing does not apply).
       Note that these case definitions are taken verbatim from section
       6.9, "Layer Relationships".

       Case 1:  "Multiple parallel links between the same subnetworks
           can be bundled together into a single composite link.  Each
           component of the composite link is independent in the sense
           that each component link is supported by a separate server
           layer trail.  The composite link conveys communication
           information using different server layer trails thus the
           sequence of symbols crossing this link may not be preserved.
           This is illustrated in Figure 14."

       Case 3:  "A link can also be constructed by a concatenation of
           component links and configured channel forwarding
           relationships.  The forwarding relationships must have a 1:1
           correspondence to the link connections that will be provided
           by the client link.  In this case, it is not possible to
           fully infer the status of the link by observing the server
           layer trails visible at the ends of the link.  This is
           illustrated in Figure 16."

   Subnetwork:  A set of one or more nodes (i.e., LER or LSR)

   [RFC6941]  Fang, L., Niven-Jenkins, B., Mansfield, S., and links.
       As a special case it can represent a site comprised of multiple
       nodes.

   Forwarding Relationship:  Configured forwarding between ports on a
       subnetwork.  It may be connectionless (e.g., IP, not considered
       in this draft), or connection oriented (e.g., MPLS signaled or
       configured).

   Component Link:  A topolological relationship between subnetworks
       (i.e., a connection between nodes), which may be a wavelength,
       circuit, virtual circuit or an MPLS LSP. R.
              Graveman, "MPLS Transport Profile (MPLS-TP) Security
              Framework", RFC 6941, April 2013.

Authors' Addresses

   Curtis Villamizar (editor)
   OCCNC, LLC

   Email: curtis@occnc.com

   Dave McDysan (editor)
   Verizon
   22001 Loudoun County PKWY
   Ashburn, VA  20147
   USA

   Email: dave.mcdysan@verizon.com

   So Ning
   Tata Communications

   Email: ning.so@tatacommunications.com

   Andrew Malis
   Verizon
   60 Sylvan Road
   Waltham, MA  02451
   USA

   Phone: +1 781-466-2362
   Email: andrew.g.malis@verizon.com
   Lucy Yong
   Huawei USA
   5340 Legacy Dr.
   Plano, TX  75025
   USA

   Phone: +1 469-277-5837
   Email: lucy.yong@huawei.com