Network Working Group                                             N. So
Internet Draft                                                 A. Malis
Intended Status: Informational                               D. McDysan
Expires: September 2010                                         Verizon
                                                                L. Yong
                                                                 Huawei
                                                              F. Jounay
                                                         France Telecom
                                                              Y. Kamite
                                                                    NTT
                                                          March 5, 2010



                  Framework for MPLS Over Composite Link
                    draft-so-yong-rtgwg-cl-framework-01


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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Abstract

   This document describes a framework for managing aggregated traffic
   over a composite link. A composite link consists of a group of non-
   homogenous links that have the same forward adjacency and can be
   considered as a single TE link or an IP link used for MPLS. The
   document primarily focuses on MPLS data plane and control plane
   traffic over a composite link and composite link advertisement within
   IGP. MPLS traffic can be set up by either RSVP-TE or LDP signaling.
   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...................................................2
   2. Conventions used in this document..............................3
   2.1. Acronyms.....................................................3
   2.2. Terminology..................................................4
   3. Composite Link Framework.......................................4
   3.1. Composite Link Architecture..................................4
   3.2. Interior Functions...........................................6
   3.2.1. Functions specific to LSP flows with TE information........7
   3.2.2. Functions specific to LSP flows without TE information.....7
   3.2.3. Functions for LSP flows with and without TE information....7
   3.3. Exterior Functions...........................................8
   3.3.1. Composite Link Advertisement and Component Link Setup......8
   3.3.2. Functions specific to LSP flows with TE information........8
   3.3.3. Functions specific to LSP flows without TE information.....8
   3.3.4. Functions to LSP flows with and without TE information.....9
   4. Applicability..................................................9
   4.1. Single-Layer Scenarios.......................................9
   4.2. Multi-Layer Scenario........................................10
   5. Security Considerations.......................................10
   6. IANA Considerations...........................................11
   7. References....................................................11
   7.1. Normative References........................................11
   7.2. Informative References......................................11
   8. Acknowledgments...............................................12



1. Introduction

   This document describes a framework of Composite Link in IP/MPLS
   network. Single link and link bundle [RFC4201] have been widely used
   in today's IP/MPLS networks. A link bundle bundles a group of
   homogeneous links as a TE link to make routing approach more
   scalable. A composite link allows bundling non-homogenous links


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   together as a single logical link. The motivations for using a
   composite link are descried in the document [CL Requirement]. This
   document states composite link framework in the context of MPLS
   network with MPLS control plane.

   A composite link is a single logical link 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. To achieve the better component link utilization and
   avoid component link congestion, the document describes some new
   aspects on the traffic flow assignment to component links. The
   document also describes the advertisement of a composite link as a
   routing interface in MPLS control plane and the addition of component
   links to a composite link.

   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.  Acronyms

      BW: Bandwidth

      ECMP: Equal Cost Multi-Path

      FRR: Fast Re-Route

      LAG: Link Aggregation Group

      LDP: Label Distribution Protocol

      LSA: Link State Advertisements

      LSP: Label Switched Path

      MPLS: Multi-Protocol Label Switching

      OAM: Operation, Administration, and Management

      PDU: Protocol Data Unit

      PE: Provider Edge device



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      RSVP: ReSource reserVation Protocol

      RTD: Real Time Delay

      TE: Traffic Engineering

      VRF: Virtual Routing and Forwarding

2.2. Terminology

   Composite Link: a group of component links, which can be considered
   as a single MPLS TE link or as a single IP link used for MPLS.

   Component Link: a physical link (e.g., Lambda, Ethernet PHY, SONET/
   SDH, OTN, etc.) with packet transport capability, or a logical link
   (e.g., MPLS LSP, Ethernet VLAN, MPLS-TP LSP, etc.)

   Connection: An aggregation of traffic flows which are treated
   together as a single unit by Composite Link Interior Functions for
   the purpose of routing onto a specific component link and measuring
   traffic volume.

   Exterior Functions: These are performed by an MPLS router that makes
   a composite link useable by the network via control protocols, or by
   an MPLS router that interacts with other routers to dynamically
   configure a component link within a composite link. These functions
   are those that interact via routing and/or signaling protocols with
   other routers in the same layer network or other layer networks.

   Interior Functions: Actions performed by the MPLS routers directly
   connected by a composite link. This includes the determination of the
   component link on which a traffic flow is placed. This is local
   implementation.

   Traffic Flow: A set of packets with a common identifier and
   characteristics that is used by Composite link interior functions to
   place the set of packets on the same component link. Identifiers can
   be an MPLS label stack or any combination of IP addresses and
   protocol types for routing, signaling, and management packets.

   Virtual Interface: Composite link is advertised as an interface in
   IGP

3. Composite Link Framework

3.1. Composite Link Architecture

   [ITU-T G.800] defines Composite Link as: multiple parallel links
   between the same subnetworks can be bundled together into a single
   composite link. Each component link 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


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   information using different server layer trails thus the sequence of
   symbols crossing this link may not be preserved. This definition
   implies that a composite link appears as a single logical link
   between two nodes and the component links in a composite link can
   have the same or different properties such as latency and capacity.
   Composite link framework 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, or can be a logical
   link configured on a LSP [LSP Hierarchy].  Even if the transport
   technology implementing the component links is identical, the
   characteristics (e.g., bandwidth, latency) of the component links may
   differ.

   Composite Link can apply to MPLS network. As shown in Figure 1, the
   composite link may carry LSP traffic flows and control plane 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 between two connected routers 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.

   Composite link relies on its component links to carry the traffic. An
   important framework concept is the connection shown in Figure 1. The
   connection only exists within the composite link and is controlled by
   the composite link function. At the transmitting end (R1 in Figure
   1), composite link maps a set of traffic flows including control
   plane packets into one connection and routes the connection on a
   specific component link. This method enables connection based routing
   over component links and traffic volume measurement on a per
   connection basis. As a result, it guarantees the ordering per traffic
   flow. One component link may carry one or more connections. At the
   receiving end (R2 in Figure 1), composite link receives traffic flows
   from its component links and sends them to MPLS forwarding engine
   like a regular link. Note that a special case of this model is where
   a single flow is mapped to a single connection.














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              Management Plane
          Configuration and Measurement <------------+
                     ^                               |
                     |                               |
                     |                               |
                     |                               |
             +-------+-+                           +-+-------+
             |       | |                           | |       |
        CP Packets   V |                           | V     CP Packets
             |  V  +-+-+     Component Link 1      +-+-+  ^  |
             |  |  |   |===========================|   |  |  |
             |  +--|-|*|****** connections ********|*|-|--+  |
           ~~|~~>~~|~| |===========================| |~|~~>~~|~~
     LSP   ~~|~~>~~|~| |     Component Link 2      | |~|~~>~~|~~ LSP
     Traffic~|~~>~~|~| |===========================| |~|~~>~~|Traffic
     Flows ~~|~~>~~|~|*|****** connections ********|*|~|~~>~~|~ Flows
           ~~|~~>~~|~| |===========================| |~|~~>~~|~~
           ~~|~~>~~|~| |     Component Link 3      | |~|~~>~~|~~
           ~~|~~>~~|~| |===========================| |~|~~>~~|~~
             |     | |*|****** connections ********|*| |     |
             |     | | |===========================|   |     |
             |     +---+                           +---+     |
             +---------+                           +---------+
                   !   !                           !   !
                   !   !<---- Component Links ---->!   !
                   !<------- Composite Link ---------->!


                Figure 1  Composite Link Architecture Model


4.

4.1. Interior Functions

   The interior functions are implemented within the interior of MPLS
   routers connected via a composite link. This includes local
   determination of the component link on which a traffic flow is
   placed, i.e. the flow to the interface mapping. Although this
   assignment is local, management configuration for some aspects of
   these interior functions is important to achieve operational
   consistency.

   As described in section 3.1, the Interior Functions map traffic flows
   to a connection and route connections to component links based on
   traffic flow parameters, connection parameters, and component link
   parameters. The connection parameters may be calculated from the
   parameters of the flows mapped to the connection or may derive from
   the measurement of the traffic volume on the connection plus
   configured connection parameters via the management plane.




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   A component link in a composite link may fail independently. The
   interior functions are able to detect component link failure and re-
   assign impacted flows to other active component links. When a
   composite link can't recover some impacted flows, it notifies control
   plane about the flows. 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.
   This action ensures the remaining traffic is transported properly.

   The interior functions provide component link fault notification and
   composite link fault notification upon the failure of a component
   link or a composite link. Component link fault notification is sent
   to the management plane. Composite link fault notification is sent to
   the control plane and management plane. Composite link allows
   operator to trace which component link a LSP is assigned to.

      4.1.1. Functions specific to LSP flows with TE information

   When a composite link is deployed in a MPLS-TE network, LSPs are
   signaled by RSVP-TE protocol. The protocol message contains LSP
   parameters like BW, setting/holding priority, latency, etc. The
   composite link will take these parameters into account when assigning
   LSP to a connection and a connection to a component link.

      4.1.2. Functions specific to LSP flows without TE information

   When a composite link is deployed in a non-TE MPLS network, LSPs are
   signaled by LDP. LDP message does not provide LSP TE information.
   These LSPs can be mapped to local configured connections with minimum
   bandwidth, maximum bandwidth, preemption priority, and holding
   priority parameters. The interior function measures the traffic
   volume on the connection and derives the BW parameter for the
   connection. The interior functions use these parameters to assign the
   connection to a component link.

   When the connection bandwidth exceeds the component link capacity,
   the interior functions are able to reassign the traffic flows to
   other connections that are over different component links.

      4.1.3. Functions for LSP flows with and without TE information

   When a composite link carries LSPs that are signaled by LDP or RSVP-
   TE, the interior functions separates them into different connections
   that have independent parameters. If there is a shortage of capacity
   in a composite link, interior functions perform preemption, rerouting
   or termination of flows based on the traffic flow priority.








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4.2. Exterior Functions

   The Exterior Functions have the aspects that are applicable exterior
   to the connected MPLS routers. These exterior functions apply to
   routing and signaling protocols. Protocol solutions are for further
   study.

      4.2.1. Composite Link Advertisement and Component Link Setup

   In IGP, a composite Link is advertised as a single virtual routable
   interface between two connected routers, which forms routing and
   forwarding adjacency between the connected routers. A composite link
   must be advertised as a link in IGP.[RFC2328] The interface
   parameters for the composite link can be pre-configured by operator
   or be derived from its component links. Composite link latency may be
   advertised for other routers to perform route computation.

   A composite link may contain the set of component links. A component
   link may be configured by operator or signaled by the control plane.
   In both cases, it is necessary to convey component link parameters to
   the composite link.

   When a component link is supported by lower layer network as
   described in section 4.2, 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.

   Composite link advertisement and component link setup requirements
   are specified in [CL Requirement]

      4.2.2. Functions specific to LSP flows with TE information

   When RSVP-TE [RFC3209] signals a LSP over a composite link, the
   composite link takes the signaled LSP parameters as the flow
   parameters and sends the PATH message to the downstream router of the
   composite link. The downstream router selects the LSP label that is
   used over the composite link and sends RESV message with the label
   info. to the upstream LSR.  The forward engine at the upstream LSR
   will push the label into the LSP packets. Composite link interior
   functions map the label to a connection that is assigned to a
   component link.

   When a composite link is advertised as a TE link in MPLS-TE network
   [RFC3630], composite link capacity is advertised. It is possible to
   advertise multiple capacities and latencies to reflect individual
   component link property. [CL requirement]

      4.2.3. Functions specific to LSP flows without TE information

   When LDP [RFC5036] is used to signal LSPs over a composite link, a
   LDP session has to be established between two LSRs connected via a


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   composite link. When signaling a LSP for a FEC over the composite
   link, the upstream LSR sends label request message to the downstream
   LSR, the downstream LSR selects a label for the FEC and sends the
   label mapping message back to the upstream LSR.

      4.2.4. Functions to LSP flows with and without TE information

   When there is a shortage of capacity in a composite link which
   supports LSP flows with and without TE information, interior
   functions are able to perform preemption, rerouting or termination of
   flows to ensure transport quality, the exterior functions are able to
   inform LSR control plan preempted flows. Thus the control plan
   informs the LSP head-end if it is singled by RSVP-TE or prunes label
   distribution for the LSP that is singled by LDP.

5. Applicability

   A composite link may be deployed between two Ps, P and PE, and two
   PEs. Two routers connected via a composite link forms forwarding
   adjacency and routing adjacency. It can be used in MPLS-TE only, MPLS
   non-TE only, or combined environment.

   In MPLS-TE application, the composite link is advertised as a link in
   IGP and a TE link in IGP TE extension that uses either OSPF-TE or IS-
   IS-TE. RSVP-TE signaling protocol is used to establish a LSP. TE
   tunnel and private line are examples of applications.

   In MPLS non-TE application, the composite link is advertised as a
   link within the IGP that uses either OSPF or IS-IS as routing
   protocol. In this case, LDP signaling protocol is used to establish a
   LSP. L3VPN is the most popular application for this case.

   In the hybrid application, the composite link is advertised as a link
   and a TE link within IGP by using different types of LSA and both
   RSVP-TE and LDP signaling for LSP establishment, as described in
   section 3.

5.1. Single-Layer Scenarios

   The component links of Figure 1 applies to at least the scenarios
   illustrated in Figure 2.  The component links may be physical or
   logical, or supported by different technologies. In the first
   scenario, a set of physical links connect adjacent (P) routers
   (R1/R2).

   In the second scenario, a set of logical links connect adjacent (P or
   PE) routers over other equipment (i.e., R3/R4) that may implement
   RSVP-TE signaled MPLS tunnels which may be in the same IGP as R1/R2.
   In this case, R3/R4 provides a TE-LSP segment of TE-LSP from R1 and
   R2. In another case, R3/R4 are in different IGP from R1/R2, R3 and R4
   provide connectivity for R1 and R2. The connectivity provides a



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   component link in the composite link of R1/R2. R3 and P4 may
   implement MPLS-TP.



    +-------+                 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 Types

5.2. Multi-Layer Scenario

   In the third scenario in Figure 2, GMPLS lower layer LSPs (e.g.,
   Fiber, Wavelength, TDM) as determined by a lower layer network in a
   multi-layer network deployment as illustrated by R5/R6. In this case,
   R5 and R6 would usually not be part of the same IGP as R1/R2 and may
   have a static interface, or may have a signaling but not a routing
   association with R1 and R2. Note that in scenarios 2 and 3 when the
   intermediate routers are not part of the same IGP as R1/R2 (i.e., can
   be viewed as operating at a lower layer) that the characteristics of
   these links (e.g., latency) may change dynamically, and there is an
   operational desire to handle this type of situation in a more
   automated fashion than is currently possible with existing protocols.
   Note that this problem currently occurs with a single lower-layer
   link in existing networks and it would be desirable for the solution
   to handle the case of a single lower-layer component link as well.
   Note that the interfaces at R1 and R2 are associated with these
   different component links can be configured with IP addresses or use
   unnumbered links as an interior, local function since the individual
   component links are not advertised as the virtual interface.

6. Security Considerations

   The solution is a local function on the router to support traffic
   engineering management over multiple parallel links.  It does not



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   introduce a security risk for control plane and data plane.

   The solution could change the frequency of routing update messages
   and therefore could change routing convergence time. The solution
   MUST provide controls to dampen the frequency of such changes so as
   to not destabilize routing protocols.

7. IANA Considerations

   IANA actions to provide solutions are for further study.

8. References

8.1. Normative References

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

   [RFC2328] Moy, J., "OSPF Version 2", RFC 2328, April 1998.

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

   [RFC3630]  Katz, D., "Traffic Engineering (TE) Extension to OSPF
   Version 2", RFC 3630, September 2003.

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

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



8.2. Informative References

   [Entropy Label] Kompella, K. and S. Amante, "The Use of Entropy
   Labels in MPLS Forwarding", November 2008, Work in Progress

   [LSP Hierarchy] Shiomoto, K. and A. Farrel, "Procedures for
   Dynamically               Signaled Hierarchical Label Switched
   Paths", November 2008, Work in Progress

   [Soft Preemption] Meyer, M. and J. Vasseur, "MPLS Traffic Engineering
   Soft Preemption", February 2009, Work in Progress

   [CL Requirement] So, N. and Yong, L, "Requirements for MPLS Over
   Composite Link", Oct. 2009, Work in Progress





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9. Acknowledgments

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

   This document was prepared using 2-Word-v2.0.template.dot.















































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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

      Frederic Jounay
      France Telecom
      2, avenue Pierre-Marzin
      22307 Lannion Cedex,
      FRANCE
      Email: frederic.jounay@orange-ftgroup.com

      Yuji Kamite
      NTT Communications Corporation
      Granpark Tower
      3-4-1 Shibaura, Minato-ku
      Tokyo  108-8118
      Japan
      Email: y.kamite@ntt.com









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