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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 5212

  Network Working Group                              Kohei Shiomoto (NTT)
  Internet Draft                          Dimitri Papadimitriou (Alcatel)
                                      Jean-Louis Le Roux (France Telecom)
                                               Martin Vigoureux (Alcatel)
                                                  Deborah Brungard (AT&T)
  
  Expires: December 2006                                        June 2006
  
                Requirements for GMPLS-based multi-region and
                       multi-layer networks (MRN/MLN)
  
                   draft-ietf-ccamp-gmpls-mln-reqs-01.txt
  
  
  Status of this Memo
  
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     This Internet-Draft will expire on December 2006.
  
  
     Copyright Notice
  
     Copyright (C) The Internet Society (2006).
  
  Abstract
  
     Most of the initial efforts on Generalized MPLS (GMPLS) have been
     related to environments hosting devices with a single switching
     capability. The complexity raised by the control of such data
     planes is similar to that seen in classical IP/MPLS networks.
  
     By extending MPLS to support multiple switching technologies, GMPLS
     provides a comprehensive framework for the control of a multi-
  
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     layered network of either a single switching technology or multiple
     switching technologies. In GMPLS, a switching technology domain
     defines a region, and a network of multiple switching types is
     referenced in this document as a multi-region network (MRN). When
     referring in general to a layered network, which may consist of
     either a single or multiple regions, this document uses the term,
     Multi-layer Network (MLN). This draft defines a framework for GMPLS
     based multi-region/multi-layer networks and lists a set of
     functional requirements.
  
  Table of Contents
  
     1. Introduction...................................................2
     2. Conventions used in this document..............................4
     3. Positioning....................................................4
     3.1. Data plane layers and control plane regions..................5
     3.2. Service layer networks.......................................5
     3.3. Vertical and Horizontal interaction and integration..........6
     4. Key concepts of GMPLS-based MLNs and MRNs......................7
     4.1. Interface Switching Capability...............................7
     4.2. Multiple Interface Switching Capabilities....................8
     4.2.1. Networks with multi-switching-type-capable hybrid nodes....8
     4.3. Integrated Traffic Engineering (TE) and Resource Control.....9
     4.3.1. Triggered signaling.......................................10
     4.3.2. FA-LSP....................................................10
     4.3.3. Virtual network topology (VNT)............................11
     5. Requirements..................................................11
     5.1. Scalability.................................................11
     5.2. LSP resource utilization....................................12
     5.2.1. FA-LSP release and setup..................................12
     5.2.2. Virtual TE-Link...........................................13
     5.3. LSP Attribute inheritance...................................14
     5.4. Verification of the LSP.....................................14
     5.5. Disruption minimization.....................................14
     5.6. Stability...................................................15
     5.7. Computing paths with and without nested signaling...........16
     5.8. Handling single-switching and multi-switching-type-capable
     nodes............................................................17
     5.9. Advertisement of the available adaptation resource..........17
     6. Security Considerations.......................................17
     7. References....................................................18
     7.1. Normative Reference.........................................18
     7.2. Informative References......................................18
     8. Author's Addresses............................................19
     9. Intellectual Property Considerations..........................20
     10. Full Copyright Statement.....................................20
  
  1. Introduction
  
  
  
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     Generalized MPLS (GMPLS) extends MPLS to handle multiple switching
     technologies: packet switching, layer-two switching, TDM switching,
     wavelength switching, and fiber switching (see [RFC3945]). The
     Interface Switching Capability (ISC) concept is introduced for
     these switching technologies and is designated as follows: PSC
     (packet switch capable), L2SC (Layer-2 switch capable), TDM (Time
     Division Multiplex capable), LSC (lambda switch capable), and FSC
     (fiber switch capable).
  
     Service providers may operate networks where multiple different
     switching technologies exist. The representation, in a GMPLS
     control plane, of a switching technology domain is referred to as a
     region [RFC4206].
  
     A switching type describes the ability of a node to forward data of
     a particular data plane technology, and uniquely identifies a
     network region. A layer describes a data plane switching
     granularity level (e.g. VC4, VC-12). A data plane layer is
     associated with a region in the control plane (e.g. VC4 associated
     to TDM, IP associated to PSC). However, more than one data plane
     layer can be associated to the same region (e.g. both VC4 and VC12
     are associated to TDM). Thus, a control plane region, identified by
     its switching type value (e.g. TDM), can itself be sub-divided into
     smaller granularity based on the bandwidth that defines the "data
     plane switching layers" e.g. from VC-11 to VC4-256c. The Interface
     Switching Capability Descriptor (ISCD) [RFC4202], identifying the
     interface switching type, the encoding type and the switching
     bandwidth granularity, enable the characterization of the
     associated layers.
  
     A network comprising transport nodes with multiple data plane
     layers of either the same ISC or different ISCs, controlled by a
     single GMPLS control plane instance is called a Multi-Layer Network
     (MLN). To differentiate a network supporting LSPs of different
     switching technologies (ISCs) from a single region network, a
     network supporting more than one switching technology is called a
     Multi-Region Network (MRN). All MRNs are MLNs, by definition.
  
     MLNs can be categorized according to the distribution of the ISCD
     values amongst the LSRs:
     - Each LSR may support just one ISCD, and the MLN may be comprised
       of LSRs that support different ISCDs. Such LSRs are known as
       single-switching-type-capable LSRs.
     - Each LSR may support more than one ISCD at the same time so that
       the network containing these LSR is an MLN. Such LSRs are known
       as multi-switching-type-capable LSRs, and can be further
       classified as either "simplex" or "hybrid" nodes as defined in
       Section 4.2.
     - The MLN may be constructed from any combination of single-
       switching-type-capable LSRs and multi-switching-type-capable
  
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       LSRs.
  
     Since GMPLS provides a comprehensive framework for the control of
     different switching capabilities, a single GMPLS instance may be
     used to control the MLN enabling rapid service provisioning and
     efficient traffic engineering across all switching capabilities. In
     such networks, TE Links are consolidated into a single Traffic
     Engineering Database (TED). Since this TED contains the information
     relative to all the different regions and layers existing in the
     network, a path across multiple regions or layers can be computed
     using this TED. Thus optimization of network resources can be
     achieved across the whole MLN.
  
     Consider, for example, a MRN consisting of packet-switch capable
     routers and TDM cross-connects. Assume that a packet LSP is routed
     between source and destination packet-switchi capable routers, and
     that the LSP can be routed across the PSC-region (i.e. utilizing
     only resources of the packet region topology). If the performance
     objective for the LSP is not satisfied, new TE links may be created
     between the packet-switch capable routers across the TDM-region
     (for example, VC-12 links) and the LSP can be routed over those TE
     links. Further, even if the LSP can be successfully established
     across the PSC-region, TDM hierarchical LSPs across the TDM region
     between the packet-switch capable routers may be established and
     used if doing so is necessary to meet the operator's objectives for
     network resources availability (e.g., link bandwidth, or adaptation
     ports between regions) across the regions. The same considerations
     hold when VC4 LSPs are provisioned to provide extra flexibility for
     the VC12 and/or VC11 layers in an MLN.
  
     This document describes the requirements to support multi-
     region/multi-layer networks. There is no intention to specify
     solution-specific elements in this document. The applicability of
     existing GMPLS protocols and any protocol extensions to the MRN/MLN
     will be addressed in separate documents [MRN-EVAL].
  
  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 RFC 2119
     [RFC2119].
  
  3. Positioning
  
     A multi-region network (MRN) is always a multi-layer network (MLN)
     since the network devices on region boundaries bring together
     different ISCs. A MLN, however, is not necessarily a MRN since
     multiple layers could be fully contained within a single region.
  
  
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     For example, VC12, VC4, and VC4-4c are different layers of the TDM
     region.
  
  3.1. Data plane layers and control plane regions
  
     A data plane layer is a collection of network resources capable of
     terminating and/or switching data traffic of a particular format.
     These resources can be used for establishing LSPs or connectionless
     traffic delivery. For example, VC-11 and VC4-64c represent two
     different layers.
  
     From the control plane viewpoint, an LSP region is defined as a set
     of one or more data plane layers that share the same type of
     switching technology, that is, the same switching type. For example,
     VC-11 and VC-4 layers are part of the same TDM region. The
     currently defined regions are: PSC, L2SC, TDM, LSC, and FSC regions.
     Hence, an LSP region is a technology domain (identified by the ISC
     type) for which data plane resources (i.e. data links) are
     represented into the control plane as an aggregate of TE
     information associated with a set of links (i.e. TE links). For
     example VC-11 and VC4-64c capable TE links are part of the same TDM
     region. Multiple layers can thus exist in a single region network.
  
     Note also that the region may produce a distinction within the
     control plane. Layers of the same region share the same switching
     technology and, therefore, use the same set of technology-specific
     signaling objects within the control plane, but layers from
     different regions may use different technology-specific objects or
     encodings. This means that there is a control plane discontinuity
     when crossing a region boundary.
  
  
  
  3.2. Service layer networks
  
     A service provider's network may be divided into different service
     layers. The customer's network is considered from the provider's
     perspective as the highest service layer. It interfaces to the
     highest service layer of the service provider's network.
     Connectivity across the highest service layer of the service
     provider's network may be provided with support from successively
     lower service layers. Service layers are realized via a hierarchy
     of network layers located generally in several regions and commonly
     arranged according to the switching capabilities of network devices.
  
     For instance some customers purchase Layer 1 (i.e. transport)
     services from the service provider, some Layer 2 (e.g. ATM), while
     others purchase Layer 3 (IP/MPLS) services. The service provider
     realizes the services by a stack of network layers located within
     one or more network regions. The network layers are commonly
  
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     arranged according to the switching capabilities of the devices in
     the networks. Thus, a customer network may be provided on top of
     the GMPLS-based multi-region/multi-layer network. For example, a
     Layer 1 service (realized via the network layers of TDM, and/or LSC,
     and/or FSC regions) may support a Layer 2 network (realized via ATM
     VP/VC) which may itself support a Layer 3 network (IP/MPLS region).
     The supported data plane relationship is a data-plane client-server
     relationship where the lower layer provides a service for the
     higher layer using the data links realized in the lower layer.
  
     Services provided by a GMPLS-based multi-region/multi-layer network
     are referred to as "Multi-region/Multi-layer network services". For
     example, legacy IP and IP/MPLS networks can be supported on top of
     multi-region/multi-layer networks. It has to be emphasized that
     delivery of such diverse services is a strong motivator for the
     deployment of multi-region/multi-layer networks.
  
     A customer network may be provided on top of a server GMPLS-based
     MRN/MLN which is operated by a service provider. For example, a
     pure IP and/or an IP/MPLS network can be provided on top of GMPLS-
     based packet over optical networks [IW-MIG-FW]. The relationship
     between the networks is a client/server relationship and, such
     services are referred to as "MRN/MLN services". In this case, the
     customer network may form part of the MRN/MLN, or may be partially
     separated, for example to maintain separate routing information but
     retain common signaling.
  
  
  3.3. Vertical and Horizontal interaction and integration
  
     Vertical interaction is defined as the collaborative mechanisms
     within a network element that is capable of supporting more than
     one layer and of realizing the client/server relationships between
     them. Protocol exchanges between two network controllers managing
     different regions or layers are also a vertical interaction.
     Integration of these interactions as part of the control plane is
     referred to as vertical integration. Thus, this refers thus to the
     collaborative mechanisms within a single control plane instance
     driving multiple network layers. Such a concept is useful in order
     to construct a framework that facilitates efficient network
     resource usage and rapid service provisioning in carrier's networks
     that are based on multiple layers, switching technologies, or ISCDs.
  
     Horizontal interaction is defined as the protocol exchange between
     network controllers that manage transport nodes within a given
     layer or region (i.e. nodes with the same switching capability).
     For instance, the control plane interaction between two TDM network
     elements switching at OC-48 is an example of horizontal interaction.
     GMPLS protocol operations handle horizontal interactions within the
     same routing area. The case where the interaction takes place
  
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     across a domain boundary, such as between two routing areas within
     the same network layer, is currently being evaluated as part of the
     inter-domain work [Inter-domain], and is referred to as horizontal
     integration. Thus horizontal integration refers to the
     collaborative mechanisms between network partitions and/or
     administrative divisions such as routing areas or autonomous
     systems.
  
     This distinction needs further clarification when administrative
     domains match layer boundaries. Horizontal interaction is extended
     to cover such cases. For example, the collaborative mechanisms in
     place between two lambda switching capable areas relate to
     horizontal integration. On the other hand, the collaborative
     mechanisms in place in a network that supports IP/MPLS over TDM
     switching could be described as vertical and horizontal integration
     in the case where each network belongs to a separate routing area.
  
  4. Key concepts of GMPLS-based MLNs and MRNs
  
     A network comprising transport nodes with multiple data plane
     layers of either the same ISC or different ISCs, controlled by a
     single GMPLS control plane instance, is called a Multi-Layer
     Network (MLN). A sub-set of MLNs consists of networks supporting
     LSPs of different switching technologies (ISCs). A network
     supporting more than one switching technology is called a Multi-
     Region Network (MRN).
  
  4.1. Interface Switching Capability
  
     The Interface Switching Capability (ISC) is introduced in GMPLS to
     support various kinds of switching technology in a unified way
     [RFC4202]. An ISC is identified via a switching type.
  
     A switching type (also referred to as the switching capability
     type) describes the ability of a node to forward data of a
     particular data plane technology, and uniquely identifies a network
     region. The following ISC types (and, hence, regions) are defined:
     PSC, L2SC, TDM, LSC, and FSC. Each end of a data link (more
     precisely, each interface connecting a data link to a node) in a
     GMPLS network is associated with an ISC.
  
     The ISC value is advertised as a part of the Interface Switching
     Capability Descriptor (ISCD) attribute (sub-TLV) of a TE link end
     associated with a particular link interface [RFC4202]. Apart from
     the ISC, the ISCD contains information, including the encoding type,
     the bandwidth granularity, and the unreserved bandwidth on each of
     eight priorities at which LSPs can be established. The ISCD does
     not "identify" network layers, it uniquely characterizes
     information associated to one or more network layers.
  
  
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     TE link end advertisements may contain multiple ISCDs. This can be
     interpreted as advertising a multi-layer (or multi-switching) TE
     link end. That is, the TE link end is present in multiple layers.
  
  4.2. Multiple Interface Switching Capabilities
  
     In an MLN, network elements may be single-switching or multi-
     switching-type-capable nodes. Single-switching type capable nodes
     advertise the same ISC value as part of their ISCD sub-TLV(s) to
     describe the termination capabilities of their TE Link(s). This
     case is described in [RFC4202].
  
     Multi-switching-type-capable LSRs are classified as "simplex" or
     "hybrid" nodes. Simplex and hybrid nodes are categorized according
     to the way they advertise these multiple ISCs:
  
     - A simplex node can terminate links with different switching
     capabilities each of them connected to the node by a single link
     interface. So, it advertises several TE Links each with a single
     ISC value as part of its ISCD sub-TLVs. For example, an LSR with
     PSC and TDM links each of which is connected to the LSR via single
     interface.
  
     - A hybrid node can terminate links with different switching
     capabilities terminating on the same interface. So, it advertises
     at least one TE Link containing more than one ISCDs with different
     ISC values. For example, a node comprising of PSC and TDM links,
     which are interconnected via internal links. The external
     interfaces connected to the node have both PSC and TDM capability.
  
     Additionally TE link advertisements issued by a simplex or a hybrid
     node may need to provide information about the node's internal
     adaptation capabilities between the switching technologies
     supported. That is, the node's capability to perform layer border
     node functions.
  
  
  4.2.1. Networks with multi-switching-type-capable hybrid nodes
  
     The network contains at least one hybrid node, zero or more simplex
     nodes, and a set of single-switching-type-capable nodes.
  
     Figure 5a shows an example hybrid node. The hybrid node has two
     switching elements (matrices), which support, for instance, TDM and
     PSC switching respectively. The node terminates a PSC and a TDM
     link (Link1 and Link2 respectively). It also has an internal link
     connecting the two swtching elements.
  
     The two switching elements are internally interconnected in such a
     way that it is possible to terminate some of the resources of, say,
  
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     Link2 and provide adaptation for PSC traffic received/sent over the
     PSC interface (#b). This situation is modeled in GMPLS by
     connecting the local end of Link2 to the TDM switching element via
     an additional interface realizing the termination/adaptation
     function. Two ways are possible to set up PSC LSPs. Available
     resource advertisement e.g. Unreserved and Min/Max LSP Bandwidth
     should cover both two ways.
  
                               Network element
                          .............................
                          :            --------       :
                          :           |  PSC   |      :
              Link1 -------------<->--|#a      |      :
                          :  +--<->---|#b      |      :
                          :  |         --------       :
                TDM       :  |        ----------      :
                +PSC      :  +--<->--|#c  TDM   |     :
              Link2 ------------<->--|#d        |     :
                          :           ----------      :
                          :............................
  
                               Figure 5a. Hybrid node.
  
  
  4.3. Integrated Traffic Engineering (TE) and Resource Control
  
     In GMPLS-based multi-region/multi-layer networks, TE Links are
     consolidated into a single Traffic Engineering Database (TED) for
     use by the single control plane instance. Since this TED contains
     the information relative to all the layers of all regions in the
     network, a path across multiple layers (possibly crossing multiple
     regions) can be computed using the information in this TED. Thus
     optimization of network resources across the multiple layers of the
     same region and across multiple regions can be achieved.
  
     These concepts allow for the operation of one network layer over
     the topology (that is, TE links) provided by other network layers
     (for example, the use of a lower layer LSC LSP carrying PSC LSPs).
     In turn, a greater degree of control and inter-working can be
     achieved, including (but not limited too):
     - dynamic establishment of Forwarding Adjacency LSPs (see Section
     4.3.3)
     - provisioning of end-to-end LSPs with dynamic triggering of FA
     LSPs
  
     Note that in a multi-layer/multi-region network that includes
     multi-switching-type-capable nodes, an explicit route used to
     establish an end-to-end LSP can specify nodes that belong to
     different layers or regions. In this case, a mechanism to control
     the dynamic creation of FA LSPs may be required.
  
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     There is a full spectrum of options to control how FA LSPs are
     dynamically established. The process can be subject to the control
     of a policy, which may be set by a management component, and which
     may require that the management plane is consulted at the time that
     the FA LSP is established. Alternatively, the FA LSP can be
     established at the request of the control plane without any
     management control.
  
  4.3.1. Triggered signaling
  
     When an LSP crosses the boundary from an upper to a lower layer, it
     may be nested into a lower layer FA LSP that crosses the lower
     layer. From a signaling perspective, there are two alternatives to
     establish the lower layer FA LSP: static (pre-provisioned) and
     dynamic (triggered).  Pre-provisioned FA-LSP will be initiated
     either by the operator or automatically using features like TE
     auto-mesh [AUTO-MESH]. If such a lower layer LSP does not already
     exist, the LSP may be established dynamically. Such a mechanism is
     referred to as "triggered signaling".
  
  4.3.2. FA-LSP
  
     Once an LSP is created across a layer, it can be used as a data
     link in an upper layer.
  
     Furthermore, it can be advertised as a TE-link, allowing other
     nodes to consider the LSP as a TE link for their path computation
     [RFC4206]. An LSP created either statically or dynamically by one
     instance of the control plane and advertised as a TE link into the
     same instance of the control plane is called a Forwarding adjacency
     LSP (FA-LSP). The TE-link as which the FA-LSP is advertised is
     called an FA. An FA has the special characteristic of not requiring
     a routing adjacency (peering) between its end points yet still
     guaranteeing control plane connectivity between the FA-LSP end
     points based on a signaling adjacency. A FA is a useful and
     powerful tool for improving the scalability of GMPLS Traffic
     Engineering (TE) capable networks since multiple higher layer LSPs
     may be nested (aggregated) over a single FA-LSP.
  
     The aggregation of LSPs enables the creation of a vertical (nested)
     LSP Hierarchy. A set of FA-LSPs across or within a lower layer can
     be used during path selection by a higher layer LSP. Likewise, the
     higher layer LSPs may be carried over dynamic data links realized
     via LSPs (just as they are carried over any "regular" static data
     links). This process requires the nesting of LSPs through a
     hierarchical process [RFC4206]. The TED contains a set of LSP
     advertisements from different layers that are identified by the
     ISCD contained within the TE link advertisement associated with the
     LSP [RFC4202].
  
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     If a lower layer LSP is not advertised as an FA, it can still be
     used to carry higher layer LSPs across the lower layer. For example,
     if the LSP is set up using triggered signaling, it will be used to
     carry the higher layer LSP that caused the trigger. Further, the
     lower layer remains available for use by other higher layer LSPs
     arriving at the boundary.
  
  
  4.3.3. Virtual network topology (VNT)
  
     A set of one or more of lower-layer LSPs provides information for
     efficient path handling in upper-layer(s) of the MLN, or, in other
     words, provides a virtual network topology (VNT) to the upper-
     layers. For instance, a set of LSPs, each of which is supported by
     an LSC LSP, provides a virtual network topology to the layers of a
     PSC region, assuming that the PSC region is connected to the LSC
     region. Note that a single lower-layer LSP is a special case of the
     VNT. The virtual network topology is configured by setting up or
     tearing down the lower layer LSPs. By using GMPLS signaling and
     routing protocols, the virtual network topology can be adapted to
     traffic demands.
  
     Reconfiguration of the virtual network topology may be triggered by
     traffic demand changes, topology configuration changes, signaling
     requests from the upper layer, and network failures. For instance,
     by reconfiguring the virtual network topology according to the
     traffic demand between source and destination node pairs, network
     performance factors, such as maximum link utilization and residual
     capacity of the network, can be optimized [MAMLTE]. Reconfiguration
     is performed by computing the new VNT from the traffic demand
     matrix and optionally from the current VNT. Exact details are
     outside the scope of this document. However, this method may be
     tailored according to the service provider's policy regarding
     network performance and quality of service (delay, loss/disruption,
     utilization, residual capacity, reliability).
  
  5.Requirements
  
  5.1. Scalability
  
     The MRN/MLN relies on a unified traffic engineering and routing
     model. The TED in each LSR is populated with TE-links from all
     layers of all regions. This may lead to a huge amount of
     information that has to be flooded and stored within the network.
     Furthermore, path computation times, which may be of great
     importance during restoration, will depend on the size of the TED.
  
     Thus MRN/MLN routing mechanisms MUST be designed to scale well with
     an increase of any of the following:
  
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      - Number of nodes
      - Number of TE-links (including FA-LSPs)
      - Number of LSPs
      - Number of regions and layers
      - Number of ISCDs per TE-link.
  
     Further, design of the routing protocols MUST NOT prevent TE
     information filtering based on ISCDs. Signaling protocol SHOULD be
     able to operate on partial TE information.
  
  
  5.2. LSP resource utilization
  
     It MUST be possible to utilize network resources efficiently.
     Particularly, resource usage in all layers SHOULD be optimized as a
     whole (i.e., across all layers), in a coordinated manner, (i.e.,
     taking all layers into account). The number of lower-layer LSPs
     carrying upper-layer LSPs SHOULD be minimized (Note that multiple
     LSPs MAY be used for load balancing). Unneccesary lower-layer LSPs,
     which would not carry any traffic by rerouting the traffic over it
     to alternative lower-layer LSPs, SHOULD be avoided.
  
  5.2.1. FA-LSP release and setup
  
     Statistical multiplexing can only be employed in PSC and L2SC
     regions. A PSC or L2SC LSP may or may not consume the maximum
     reservable bandwidth of the FA LSP that carries it. On the other
     hand, a TDM, or LSC LSP always consumes a fixed amount of bandwidth
     as long as it exists (and is fully instantiated) because
     statistical multiplexing is not available.
  
     If there is low traffic demand, some FA LSPs that do not carry any
     LSP MAY be released so that lower-layer resources are released.
     Note that if a small fraction of the available bandwidth of an FA-
     LSP is still in use, the nested LSPs can also be re-routed to other
     FA-LSPs (optionally using the make-before-break technique) to
     complete free up the FA-LSP. Alternatively, the FA LSPs MAY be
     retained for future use. Release or retention of underutilized FA
     LSPs is a policy decision.
  
     As part of the re-optimization process, the solution MUST allow
     rerouting of an FA LSP while keeping interface identifiers of
     corresponding TE links unchanged. Further, this process MUST be
     possible while the FA LSP is carrying traffic (higher layer LSPs)
     with minimal disruption to the traffic.
  
     Additional FA LSPs MAY also be created based on policy, which might
     consider residual resources and the change of traffic demand across
     the region. By creating the new FA LSPs, the network performance
     such as maximum residual capacity may increase.
  
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     As the number of FA LSPs grows, the residual resource may decrease.
     In this case, re-optimization of FA LSPs MAY be invoked according
     to policy.
  
     Any solution MUST include measures to protect against network
     destabilization caused by the rapid setup and teardown of LSPs as
     traffic demand varies near a threshold.
  
  5.2.2. Virtual TE-Link
  
     It may be considered disadvantageous to fully instantiate (i.e.
     pre-provision) the set of lower layer LSPs that provide the VNT
     since this might reserve bandwidth that could be used for other
     LSPs in the absence of the upper-layer traffic.
  
     However, in order to allow path computation of upper-layer LSPs
     across the lower-layer, the lower-layer LSPs MAY be advertised into
     the upper-layer as though they had been fully established, but
     without actually establishing them. Such TE links that represent
     the possibility of an underlying LSP are termed "virtual TE-link".
     It is an implementation choice at a boundary node whether to create
     virtual TE-links, and the choice if available MUST be under the
     control of operator policy. Note that there is no requirement to
     support the creation of virtual TE-links, since real TE-links (with
     established LSPs) may be used, and even if there are no TE-links
     (virtual or real) advertised to the higher layer, it is possible to
     route a higher layer LSP into a lower layer on the assumptions that
     proper hierarchical LSPs in the lower layer will be dynamically
     created (triggered) as needed.
  
     If an upper-layer LSP that makes use of a virtual TE-Link is set up,
     the underlying LSP MUST be immediately signaled in the lower layer.
  
     If virtual TE-Links are used in place of pre-established LSPs, the
     TE-links across the upper-layer can remain stable using pre-
     computed paths while wastage of bandwidth within the lower-layer
     and unnecessary reservation of adaptation ports at the border nodes
     can be avoided.
  
     The concept of the VNT can be extended to allow the virtual TE-
     links to form part of the VNT. The combination of the fully
     provisioned TE-links and the virtual TE-links defines the VNT
     provided by the lower layer.
  
     The solution SHOULD provide operations to facilitate the build-up
     of such virtual TE-links, taking into account the (forecast)
     traffic demand and available resource in the lower-layer.
  
  
  
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     Virtual TE-links MAY be modified dynamically (by adding or removing
     virtual TE links, or chancing their capacity) according to the
     change of the (forecast) traffic demand and the available resource
     in the lower-layer.
  
     Any solution MUST include measures to protect against network
     destabilization caused by the rapid changes in the virtual network
     topology as traffic demand varies near a threshold.
  
     The VNT can be changed by setting up and/or tearing down virtual TE
     links as well as by modifying real links (i.e. the fully
     provisioned LSPs).
  
     The maximum number of virtual TE links that can be defined SHOULD
     be configurable.
  
     How to design the VNT and how to manage it are out of scope of this
     document.
  
  5.3. LSP Attribute inheritance
  
     TE-Link parameters SHOULD be inherited from the parameters of the
     LSP that provides the TE-link, and so from the TE-links in the
     lower layer that are traversed by the LSP.
     These include:
     - Interface Switching Capability
     - TE metric
     - Maximum LSP bandwidth per priority level
     - Unreserved bandwidth for all priority levels
     - Maximum Reservable bandwidth
     - Protection attribute
     - Minimum LSP bandwidth (depending on the Switching Capability)
  
     Inheritance rules MUST be applied based on specific policies.
     Particular attention should be given to the inheritance of TE
     metric (which may be other than a strict sum of the metrics of the
     component TE links at the lower layer) and protection attributes.
  
  5.4. Verification of the LSP
  
     When a lower layer LSP is established for use as a data link by a
     higher layer, the LSP MAY be verified for correct connectivity and
     data integrity. Such mechanisms are data technology-specific and
     are beyond the scope of this document, but may be coordinated
     through the GMPLS control plane.
  
  
  5.5. Disruption minimization
  
  
  
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     When reconfiguring the VNT according to a change in traffic demand,
     the upper-layer LSP might be disrupted. Such disruption to the
     upper layers MUST be minimized.
  
     When residual resource decreases to a certain level, some lower
     layer LSPs MAY be released according to local or network policies.
     There is a trade-off between minimizing the amount of resource
     reserved in the lower layer and disrupting higher layer traffic
     (i.e. moving the traffic to other TE-LSPs so that some LSPs can be
     released). Such traffic disruption MAY be allowed but MUST be under
     the control of policy that can be configured by the operator. Any
     repositioning of traffic MUST be as non-disruptive as possible (for
     example, using make-before-break).
  
  5.6. Stability
  
     Path computation is dependent on the network topology and
     associated link state. The path computation stability of an upper
     layer may be impaired if the VNT changes frequently and/or if the
     status and TE parameters (TE metric for instance) of links in the
     virtual network topology changes frequently.
  
     In this context, robustness of the VNT is defined as the capability
     to smooth changes that may occur and avoid their propagation into
     higher layers. Changes of the VNT may be caused by the creation,
     deletion, or modification of several LSPs.
  
     Creation, deletion and modification of LSPs MAY be triggered by
     adjacent layers or through operational actions to meet traffic
     demand changes, topology changes, signaling requests from the upper
     layer, and network failures. Routing robustness SHOULD be traded
     with adaptability with respect to the change of incoming traffic
     requests.
  
     A full mesh of LSPs MAY be created between every pair of border
     nodes of the higher layer. The merit of a full mesh of PSC TE-LSPs
     is that it provides stability to the higher layer routing. That is,
     the TED or forwarding table used in the higher layer of an PSC-LSR
     is not impacted by routing changes within the lower-layer (e.g.,
     TDM layer). Further, there is always full PSC reachability and
     immediate access to bandwidth to support LSPs in the higher layer.
     But it also has significant drawbacks, since it requires the
     maintenance of n^2 RSVP-TE sessions, which may be quite CPU and
     memory consuming (scalability impact). Also this may lead to
     significant bandwidth wastage if LSPs with a certain amount of
     reserved bandwidth are used.
     Note that the use of virtual TE-links solves the bandwidth wastage
     issue, and may reduce the control plane overload.
  
  
  
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  5.7. Computing paths with and without nested signaling
  
     Path computation MAY take into account LSP region and layer
     boundaries when computing a path for an LSP. For example, path
     computation MAY restrict the path taken by an LSP to only the links
     whose interface switching capability is PSC.
  
     Interface switching capability is used as a constraint in path
     computation. For example, a TDM-LSP is routed over the topology
     composed of TE links of the same TDM layer. In calculating the path
     for the LSP, the TED MAY be filtered to include only links where
     both end include requested LSP switching type. In this way
     hierarchical routing is done by using a TED filtered with respect
     to switching capability (that is, with respect to particular layer).
  
     If triggered signaling is allowed, the path computation mechanism
     MAY produce a route containing multiple layers/regions. The path is
     computed over the multiple layers/regions even if the path is not
     "connected" in the same layer as the endpoints of the path exist.
     Note that here we assume that triggered signaling will be invoked
     to make the path "connected", when the upper-layer signaling
     request arrives at the boundary node.
  
     The upper-layer signaling request may contain an ERO that includes
     only hops in the upper layer, in which case the boundary node is
     responsible for triggered creating of the lower-layer FA-LSP using
     a path of its choice, or for the selection of any available lower
     layer LSP as a data link for the higher layer. This mechanism is
     appropriate for environments where the TED is filtered in the
     higher layer, where separate routing instances are used per layer,
     or where administrative policies prevent the higher layer from
     specifying paths through the lower layer.
  
     Obviously, if the lower layer LSP has been advertised as a TE link
     (virtual or real) into the higher layer, then the higher layer
     signaling request may contain the TE link identifier and so
     indicate the lower layer resources to be used. But in this case,
     the path of the lower layer LSP can be dynamically changed by the
     lower layer at any time.
  
     Alternatively, the upper-layer signaling request may contain an ERO
     specifying the lower layer FA-LSP route. In this case, the boundary
     node is responsible for decision as to which it should use the path
     contained in the strict ERO or it should re-compute the path within
     in the lower-layer.
  
     Even in case the lower-layer FA-LSPs are already established, a
     signaling request may also be encoded as loose ERO. In this
     situation, it is up to the boundary node to decide whether it
  
  
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     should a new lower-layer FA-LSP or it should use the existing
     lower-layer FA-LSPs.
  
     The lower-layer FA-LSP can be advertised just as an FA-LSP in the
     upper-layer or an IGP adjacency can be brought up on the lower-
     layer FA-LSP.
  
  
  5.8. Handling single-switching and multi-switching-type-capable
      nodes
  
     The MRN/MLN can consist of single-switching-type-capable and multi-
     switching-type-capable nodes. The path computation mechanism in the
     MLN SHOULD be able to compute paths consisting of any combination
     of such nodes.
  
     Both single-switching-type-capable and multi-switching-type-capable
     (simplex or hybrid) nodes could play the role of layer boundary.
     MRN/MLN Path computation SHOULD handle TE topologies built of any
     combination of nodes
  
  5.9. Advertisement of the available adaptation resource
  
     A hybrid node SHOULD maintain resources and advertise the resource
     information on its internal links, the links required for vertical
     (layer) integration. Likewise, path computation elements SHOULD be
     prepared to use the availability of termination/adaptation
     resources as a constraint in MRN/MLN path computations to reduce
     the higher layer LSP setup blocking probability because of the lack
     of necessary termination/ adaptation resources in the lower
     layer(s).
  
     The advertisement of the adaptation capability to terminate LSPs of
     lower-region and forward traffic in the upper-region is REQUIRED,
     as it provides critical information when performing multi-region
     path computation.
  
     The mechanism SHOULD cover the case where the upper-layer links
     which are directly connected to upper-layer switching element and
     the ones which are connected through internal links between upper-
     layer element and lower-layer element coexist (See section 4.2.1).
  
  
  6. Security Considerations
  
     The current version of this document does not introduce any new
     security considerations as it only lists a set of requirements. In
     the future versions, new security requirements may be added.
  
  
  
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  7. References
  
  7.1. Normative Reference
  
     [RFC2119]       Bradner, S., "Key words for use in RFCs to
                      Indicate Requirement Levels", BCP 14, RFC 2119,
                      March 1997.
  
     [RFC3979]       Bradner, S., "Intellectual Property Rights in IETF
                      Technology", BCP 79, RFC 3979, March 2005.
  
     [RFC4202]  K.Kompella and Y.Rekhter, "Routing Extensions in
                   Support of Generalized Multi-Protocol Label
                   Switching (GMPLS)," RFC4202, October 2005.
  
     [Inter-domain]  A.Farrel, J-P. Vasseur, and A.Ayyangar, "A
                   framework for inter-domain MPLS traffic
                   engineering," draft-ietf-ccamp-inter-domain-
                   framework, work in progress.
  
     [RFC4206]  K.Kompella and Y.Rekhter, "Label Switched Paths (LSP)
                   Hierarchy with Generalized Multi-Protocol Label
                   Switching (GMPLS) Traffic Engineering (TE),"
                   RFC4206, Oct. 2005.
  
     [STITCH]   Ayyangar, A. and Vasseur, JP., "Label Switched Path
                   Stitching with Generalized MPLS Traffic Engineering",
                   draft-ietf-ccamp-lsp-stitching, work in progress.
  
     [RFC4204]  J. Lang, "Link management protocol (LMP)," RFC4204,
                   October 2005.
  
     [RFC3945]  E.Mannie (Ed.), "Generalized Multi-Protocol Label
                   Switching (GMPLS) Architecture", RFC 3945, October
                   2004.
  
  7.2. Informative References
  
     [MAMLTE]     K. Shiomoto et al., "Multi-area multi-layer traffic
                   engineering using hierarchical LSPs in GMPLS
                   networks", draft-shiomoto-multiarea-te, work in
                   progress.
  
     [MRN-EVAL] Le Roux, J.L., Brungard, D., Oki, E., Papadimitriou, D.,
                   Shiomoto, K., Vigoureux, M.,"Evaluation of existing
                   GMPLS Protocols against Multi Layer and Multi Region
                   Networks (MLN/MRN)", draft-leroux-ccamp-gmpls-mrn-
                   eval, work in progress.
  
  
  
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     [IW-MIG-FW]   Shiomoto, K., Papadimitriou, D., Le Roux, J.L.,
                   Brungard, D., Oki, E., Inoue, I., " Framework for
                   IP/MPLS-GMPLS interworking in support of IP/MPLS to
                   GMPLS migration ", draft-ietf-ccamp-mpls-gmpls-
                   interwork-fmwk-00.txt, work in progress.
  
     [AUTO-MESH]   Vasseur, JP., Le Roux, JL., et al., "Routing
                   extensions for discovery of Multiprotocol (MPLS)
                   Label Switch Router (LSR) Traffic Engineering (TE)
                   mesh membership", draft-ietf-ccamp-automesh, work in
                   progress.
  
  
  
  8. Author's Addresses
  
     Kohei Shiomoto
     NTT Network Service Systems Laboratories
     3-9-11 Midori-cho,
     Musashino-shi, Tokyo 180-8585, Japan
     Email: shiomoto.kohei@lab.ntt.co.jp
  
     Dimitri Papadimitriou
     Alcatel
     Francis Wellensplein 1,
     B-2018 Antwerpen, Belgium
     Phone : +32 3 240 8491
     Email: dimitri.papadimitriou@alcatel.be
  
     Jean-Louis Le Roux
     France Telecom R&D,
     Av Pierre Marzin,
     22300 Lannion, France
     Email: jeanlouis.leroux@orange-ft.com
  
     Martin Vigoureux
     Alcatel
     Route de Nozay, 91461 Marcoussis cedex, France
     Phone: +33 (0)1 69 63 18 52
     Email: martin.vigoureux@alcatel.fr
  
     Deborah Brungard
     AT&T
     Rm. D1-3C22 - 200
     S. Laurel Ave., Middletown, NJ 07748, USA
     Phone: +1 732 420 1573
     Email: dbrungard@att.com
  
     Contributors
  
  
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     Eiji Oki (NTT Network Service Systems Laboratories)
     3-9-11 Midori-cho, Musashino-shi, Tokyo 180-8585, Japan
     Phone: +81 422 59 3441 Email: oki.eiji@lab.ntt.co.jp
  
     Ichiro Inoue (NTT Network Service Systems Laboratories)
     3-9-11 Midori-cho, Musashino-shi, Tokyo 180-8585, Japan
     Phone: +81 422 59 3441 Email: ichiro.inoue@lab.ntt.co.jp
  
     Emmanuel Dotaro (Alcatel)
     Route de Nozay, 91461 Marcoussis cedex, France
     Phone : +33 1 6963 4723 Email: emmanuel.dotaro@alcatel.fr
  
  9. Intellectual Property Considerations
  
     The IETF takes no position regarding the validity or scope of any
     Intellectual Property Rights or other rights that might be claimed
     to pertain to the implementation or use of the technology described
     in this document or the extent to which any license under such
     rights might or might not be available; nor does it represent that
     it has made any independent effort to identify any such rights.
     Information on the procedures with respect to rights in RFC
     documents can be found in BCP 78 and BCP 79.
  
     Copies of IPR disclosures made to the IETF Secretariat and any
     assurances of licenses to be made available, or the result of an
     attempt made to obtain a general license or permission for the use
     of such proprietary rights by implementers or users of this
     specification can be obtained from the IETF on-line IPR repository
     at http://www.ietf.org/ipr.
  
     The IETF invites any interested party to bring to its attention any
     copyrights, patents or patent applications, or other proprietary
     rights that may cover technology that may be required to implement
     this standard.  Please address the information to the IETF at ietf-
     ipr@ietf.org.
  
     The IETF has been notified by Tellabs Operations, Inc. of
     intellectual property rights claimed in regard to some or all of
     the specification contained in this document. For more information,
     see http://www.ietf.org/ietf/IPR/tellabs-ipr-draft-shiomoto-ccamp-
     gmpls-mrn-reqs.txt
  
  10. Full Copyright Statement
  
     Copyright (C) The Internet Society (2006). This document is subject
     to the rights, licenses and restrictions contained in BCP 78, and
     except as set forth therein, the authors retain all their rights.
  
     This document and the information contained herein are provided on
     an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
  
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     REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
     THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
     EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
     THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
     ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A
     PARTICULAR PURPOSE.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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