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Network Working Group                                             N. So
Internet Draft                                                 A. Malis
Intended Status: Informational                               D. McDysan
Expires: December 2011                                          Verizon
                                                                L. Yong
                                                                 Huawei
                                                          C. Villamizar
                                                               Infinera
                                                                  T. Li
                                                                  Cisco
                                                           June 9, 2011



     Composite Link Framework in Multi Protocol Label Switching (MPLS)
                    draft-so-yong-rtgwg-cl-framework-04


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Abstract

   This document specifies a composite link framework in MPLS network.
   A composite link consists of a group of homogenous or non-homogenous
   links that have the same forward adjacency and can be considered as
   a single TE link or an IP link in routing. A composite link relies
   on its component links to carry the traffic over the composite link.
   The document specifies composite link framework. Applicability is
   described for a single pair of MPLS-capable nodes, a sequence of
   MPLS-capable nodes, or a set of layer networks connecting MPLS-
   capable nodes.

Table of Contents

   1. Introduction...................................................3
   2. Conventions used in this document..............................3
      2.1. Terminology...............................................3
   3. Composite Link Framework.......................................4
   4. Composite Link in Control Plane................................6
   5. Composite Link in Data Plane...................................8
   6. Composite Link in Management Plane.............................9
   7. Security Considerations........................................9
   8. IANA Considerations............................................9
   9. References.....................................................9
      9.1. Normative References......................................9
      9.2. Informative References...................................10
   10. Acknowledgments..............................................10




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1. Introduction

   Composite link functional requirements are specified in [CL-REQ].
   This document specifies a framework of Composite Link in MPLS
   network to meet the requirements. Single link and LAG based link
   bundle have been widely used in today's MPLS networks. A link bundle
   [RFC4201] bundles a group of homogeneous links as a TE link to make
   routing approach more scalable. A composite link allows bundling
   non-homogenous links together as a single logical link. The
   motivations for using a composite link are descried in the document
   [CL-REQ]. This document describes composite link framework in the
   context of MPLS network with MPLS control plane.

   A composite link is a single logical link in MPLS network that
   contains multiple parallel component links between two routers.
   Unlike a link bundle [RFC4201], the component links in a composite
   link can have different properties such as cost or capacity. A
   composite link can transport aggregated traffic as other physical
   links from the network perspective and use its component links to
   carry the traffic internally.

   Specific protocol solutions are outside the scope of this document.



2. Conventions used in this document

   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 [RFC2119].

2.1. Terminology

   Composite Link:  A composite link is a logical link composed of a
   set of parallel point-to-point component links, where all links in
   the set share the same endpoints.  A composite 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 or 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 a physical link are: Lambda,
   Ethernet PHY, and OTN.  Examples of a logical link are: MPLS LSP,
   Ethernet VLAN, and MPLS-TP LSP.

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






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   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 or
   an LSP may be equivalent to a Flow.  Flow identification is used to
   locally select a component link, or a path through the network
   toward the destination.

   Network Performance Objective (NPO):  Numerical values for
   performance measures, principally availability, latency, and delay
   variation.  See Appendix A for more details.

3. Composite Link Framework

   A Composite Link in the context of MPLS network is a set of parallel
   links between two routers that form a single logical link within the
   network. Composite link model is illustrated in Figure 1, where a
   composite link is configured between routers R1 and R2.  The
   composite link has three component links.  Individual component
   links in a composite link may be supported by different transport
   technologies such as wavelength, Ethernet VLAN.  Even if the
   transport technology implementing the component links is identical,
   the characteristics (e.g., bandwidth, latency) of the component
   links may differ.

   As shown in Figure 1, the composite link may carry LSP traffic flows
   and control plane packets that appear as IP packets. A LSP may be
   established over the link by either RSVP-TE or LDP signaling
   protocols. All component links in a composite link have the same
   forwarding adjacency. The composite link forms one routing interface
   at the composite link end points for MPLS control plane. In other
   words, two routers connected via a composite link have forwarding
   adjacency and routing adjacency. Each component link only has
   significance to the composite link, i.e. it does not appear as a
   link in the control plane.



















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              Management Plane
          Configuration and Measurement <------------+
                     ^                               |
                     |                               |
             +-------+-+                           +-+-------+
             |       | |                           | |       |
        CP Packets   V |                           | V     CP Packets
             |  V    | |     Component Link 1      | |    ^  |
             |  |    |=|===========================|=|    |  |
             |  +----| |     Component Link 2      | |----+  |
             |       |=|===========================|=|       |
   Aggregated LSPs   | |                           | |       |
            ~|~~~~~~>| |     Component Link 3      | |~~~~>~~|~~
             |       |=|===========================|=|       |
             |       | |                           | |       |
             | LSR     |                           |    LSR  |
             +---------+                           +---------+
                     !                               !
                     !                               !
                     !<------ Composite Link ------->!


                Figure 1  Composite Link Architecture Model

   A component link in a composite link may be constructed in different
   ways.[CL-REQ] Figure 2 shows three common ways that may be deployed
   in a network.



      +-------+                 1. Physical Link             +-------+
      |     |-|----------------------------------------------|-|     |
      |     | |                                              | |     |
      |     | |     +------+                     +------+    | |     |
      |     | |     | MPLS |    2. Logical Link  | MPLS |    | |     |
      |     |.|.... |......|.....................|......|....|.|     |
      |     | |-----|  R3  |---------------------|  R4  |----| |     |
      |     | |     +------+                     +------+    | |     |
      |     | |                                              | |     |
      |     | |                                              | |     |
      |     | |     +------+                     +------+    | |     |
      |     | |     |GMPLS |    3. Logical Link  |GMPLS |    | |     |
      |     |.|. ...|......|.....................|......|....|.|     |
      |     | |-----|  R5  |---------------------|  R6  |----| |     |
      |       |     +------+                     +------+    |       |
      | R1    |                                              |    R2 |
      +-------+                                              +-------+
            |<------------- Composite Link ------------------->|

             Figure 2 Illustration of Component Link Variances




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   As shown, the first component link is configured with direct
   physical media wire. The second component link is a TE tunnel that
   traverses R3 and R4. Both R3 and R4 are the nodes in the MPLS. The
   third component link is formed by lower layer network that has GMPLS
   enabled. In this case, R5 and R6 are not the nodes controlled by the
   MPLS but provide the connectivity for the component link. Note: if
   two unidirectional LSPs are used to construct a component link, they
   MUST be co-routed.

   Composite link forms one logical link between connected routers and
   is used to carry aggregated traffic.[CL-REQ] Composite link relies
   on its component links to carry the traffic over the composite link.
   This means that a composite link maps incoming traffic into
   component links. The router (R1 in Figure 1) of composite link
   ingress maps a set of traffic flows including control plane packets
   to a specific component link.  The router (R2 in Figure 1) of
   composite link egress receives the packets from its component links
   and sends them to MPLS forwarding engine like a regular link. The
   traffic from R2 to R1 is distributed by the router R2.

   Traffic mapping to component links may be done by control plane,
   management plane, or data plane.[CL-REQ] The objectives are to keep
   the individual flow packets in sequence and meet its QoS criteria,
   do not overload any component link, and be able to perform local
   recovery when one of component link fails.[CL-REQ] Operator may have
   other objectives such as placing a bi-directional flow or LSP on the
   same component link in both direction, load balance over component
   links, composite link energy saving, and etc. A flow may be a LSP,
   or sub-LSP [MLSP], PW, a flow within PW [FAT-PW], entropy flow in
   LSP [ENTROPY].

4. Composite Link in Control Plane

   A composite Link is advertised as a single logical interface between
   two connected routers, which forms routing and forwarding adjacency
   between the routers in IGP. The interface parameters for the
   composite link can be pre-configured by operator or be derived from
   its component links. Composite link advertisement requirements are
   specified in [CL-REQ].

   In IGP-TE, a composite link is advertised as a single TE link
   between two connected routers. This is similar to a link bundle
   [RFC4201]. Link bundle applies to a set of homogenous component
   links. Composite link allows homogenous and non-homogenous component
   links. In order for route computing engine to calculate a proper
   path for a LSP, it is necessary for composite link to advertise the
   summarized available BW as well as the maximum BW for single LSP. If
   a composite link contains some non-homogeneous component links, the
   composite link also need to advertise the summarized BW and the
   maximum BW for single LSP per each homogeneous component link group.
   The protocol extension for composite link advertisement will be
   described in the separated draft.


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   Current IGP Link announcement protocol does not give such
   capability. The protocol only allows advertising one cost based TE
   metrics. RFC4201 only advertises a largest available BW for a link
   bundle that includes a set of homogenous component links. Signaling
   protocol does not allow signaling an aggregated LSP where its BW may
   be larger than the capacity of any component links. [ENTROPY]

   A composite link may contain the set of component links. A component
   link may be configured by operator or signaled by the control plane.
   If two unidirectional LSPs are used to construct a component link,
   they MUST be co-routed. In both cases, it is necessary to convey
   component link parameters to the composite link.[CL-REQ] In an often
   case, a component link is configured to carry traffic under normal
   operation; under some situation, operator may want to configure a
   component link as a link for local recovery purpose, in which the
   composite link should not count the component link TE parameters
   into the composite link TE parameters for the advertisement. However,
   the composite link may send the traffic over the component link when
   a component link failure occurs. The protocol extension for singling
   component link parameter is for further study. This capability is
   not supported in current protocol because a link bundle contains a
   set of homogenous links.

   When a component link is supported by lower layer network (third
   component link in figure 2), the control plane that the composite
   link resides is able to interoperate with the GMPLS or MPLS-TP
   control plane that lower layer network uses for component link
   addition and deletion.[CL-REQ]

   It is possible for operator to configure one or multiple interface
   (s) over a composite link.

   Both LDP [RFC5036] and RSVP-TE [RFC3209] can be used to signal a LSP
   over a composite link. The router of composite link ingress MUST
   place the LSP on the component link that meets the LSP criteria
   indicated in the signaling message. Since the composite link brings
   some unique characteristics, some signaling protocol extensions are
   expected to facilitate the composite link to place LSP to a proper
   component link. Several cases may be considered as below. Signaling
   extension for configuring such LSP is for further study.

   A composite link may contain non-homogeneous component links. The
   route computing engine may select one group of component links for a
   LSP, it is necessary for signaling protocol to be able to indicate
   which group of component links for signaled LSP. Composite link MUST
   place the LSP to the component link whose performance such as delay
   or jitter is equal or better than the required.

   Since composite link capacity is aggregated capacity and is larger
   than individual component link capacity, it is possible to signal a
   LSP whose BW is larger than individual component link capacity.[CL-
   REQ] Assumption is such LSP carrying an aggregated traffic.


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   When a bi-directional LSP request is signaled over a composite link,
   if the request indicates that the LSP must be placed on the same
   component link, the routers of the composite link MUST place the LSP
   traffic in both directions on a same component link.

   Individual component link may fail independently. Upon component
   link failure, a composite link needs to perform local recovery, i.e.
   use some available capacity in other component link to carry
   impacted traffic. Composite link may use LDP or RSVP-TE signaling
   protocol to facilitate the recovery process between two routers that
   composite resides. To avoid looped crankback, during the local
   recovery process, the composite link should advertise its available
   BW as zero; after finishing the local recovery, it should update its
   proper available BW in IGP.

5. Composite Link in Data Plane

   The traffic over a composite link is distributed over individual
   component links. Traffic dissemination may be determined by control
   plane, management plane, or data plane, and may be changed due to
   component link status change.[CL-REQ] The distribution function is
   local to the routers in which a composite link belongs to and is not
   specified here. However, if a bi-directional LSP is required to be
   placed on the same component link in both directions, the routers at
   both composite link end points need incorporation in determining the
   component link for the LSP. The protocol extension of that is for
   further study.

   When performing traffic placement, a composite link does not
   differentiate multicast traffic vs. unicast traffic.

   A component link in a composite link may fail independently. The
   routers at a composite link MUST maintain each component link
   status. Two routers may use the control plane to sync up a component
   link state. When a component link fails, the routers of a composite
   link MUST re-assign impacted flows to other active component links
   in minimal disruptive manner. This is local function and do not
   incorporate with LSP head-end routers. When a composite link is not
   able to transport all flows, it preempts some flows based upon local
   management configuration and informs the control plane on these
   preempted flows. The composite link MUST support soft preemption
   [RFC5712]. This action ensures the remaining traffic is transported
   properly. Note: as mentioned in section 4, in order to prevent
   lopped crankback symptom, when composite link performs local
   recovery process, it should advertise its available BW as zero; when
   the local process completes, the composite link should update its
   link state with the proper available BW.

   The composite link functions provide component link fault
   notification and composite link fault notification. Component link
   fault notification MUST be sent to the management plane. Composite



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   link fault notification MUST be sent to management plane and
   distribute via link state message in IGP.

   Operator may want to perform an optimization function such as load
   balance or energy saving over a composite link, which may conduct
   some traffic moving from one component link to another. The process
   MUST support locally and gracefully traffic movement process among
   component links. The protocol that facilitates this process between
   two composite link end points is for further study.

6. Composite Link in Management Plane

   Management Plane MUST keep tracking a composite link and its
   individual composite link status and configuration. Management Plane
   MUST be able to make any component link in a composite link active
   and de-activate in order to facilitate operation maintenance task.
   The routers of a composite link resides MUST perform the
   redistribution of the traffic flows on a de-activated link to other
   component links based on the traffic flow TE criteria.

   Management Plane MUST be able to configure a LSP over a composite
   link and be able to select a component link for the LSP.

   Management Plane MUST be able to trace which component link a LSP is
   assigned to and monitor individual component link and composite link
   performance.

   Management Plane MUST be able to ping individual component link
   within a composite link.

   Management Plane should build the proper commands to allow operator
   execute an optimization process.

7. Security Considerations

   For further study.

8. IANA Considerations

   IANA actions to provide solutions are for further study.

9. References

9.1. Normative References

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

   [RFC3209]  D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan, G.
   Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels,"   December
   2001



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   [RFC4201]  Kompella, K., "Link Bundle in MPLS Traffic Engineering",
   RFC 4201, March 2005.

   [RFC5036]  Andersson, L., "LDP Specification", RFC 5036 , October
   2007.

   [RFC5712]  Meyer, M., "MPLS Traffic Engineering Soft Preemption",
   January 2010.

9.2. Informative References

   [CL-REQ] Villamizar, C. and McDysan, D, "Requirements for MPLS Over
   Composite Link", Oct. 2010, Work in Progress

   [ENTROPY] Kompella, K. and S. Amante, "The Use of Entropy Labels in
   MPLS Forwarding", draft-ietf-mpls-entropy-label-00.txt, May 2011,
   Work in Progress

   [FAT-PW] Bryan, S., et. Al, "Flow Aware Transport of Pseudowire over
   an MPLS PSN", draft-ietf-pwe3-fat-pw-06, May. 2011, Work in progress

   [MLSP] Kompella, K. "Multi-path Label Switched Paths Signaled Using
   RSVP-TE", draft-kompella-mpls-rsvp-ecmp-00.txt, July 2010, Work in
   Progress

10. Acknowledgments

   Authors would like to thank Adrian Farrel, Fred Jounay, Yuji Kamite
   for his extensive comments and suggestions, Ron Bonica, Nabil Bitar,
   Eric Gray, Lou Berger, and Kireeti Kompella for their reviews and
   great suggestions.























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   Authors' Addresses

      So Ning
      Verizon
      2400 N. Glem Ave.,
      Richerdson, TX  75082
      Phone: +1 972-729-7905
      Email: ning.so@verizonbusiness.com


      Andrew Malis
      Verizon
      117 West St.
      Waltham, MA  02451
      Phone: +1 781-466-2362
      Email: andrew.g.malis@verizon.com

      Dave McDysan
      Verizon
      22001 Loudoun County PKWY
      Ashburn, VA  20147
      Email: dave.mcdysan@verizon.com


      Lucy Yong
      Huawei USA
      1700 Alma Dr. Suite 500
      Plano, TX  75075
      Phone: +1 469-229-5387
      Email: lucyyong@huawei.com

      Curtis Villamizar
      Infinera
      Email: cvillamizar@infinera.com

      Tony Li
      Cisco Systems
      Email: tony.li@tony.li
















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