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: April 2006                                        October 2005
                Requirements for GMPLS-based multi-region and
                       multi-layer networks (MRN/MLN)
  Status of this Memo
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     Copyright Notice
     Copyright (C) The Internet Society (2005).
     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. Services.....................................................5
     3.3. Vertical and Horizontal interaction and integration..........6
     4. Key concepts of GMPLS-based MLNs and MRNs......................6
     4.1. Interface Switching Capability...............................7
     4.2. Multiple Interface Switching Capabilities....................7
     4.2.1. Networks with multi-switching capable hybrid nodes.........8
     4.3. Integrated Traffic Engineering (TE) and Resource Control.....9
     4.3.1. Triggered signaling........................................9
     4.3.2. FA-LSP....................................................10
     4.3.3. Virtual network topology (VNT)............................10
     5. Service networks provided over MRN/MLN........................11
     6. Requirements..................................................11
     6.1. Scalability.................................................11
     6.2. LSP resource utilization....................................12
     6.2.1. FA-LSP release and setup..................................12
     6.2.2. Virtual TE-Link...........................................12
     6.3. LSP Attribute inheritance...................................14
     6.4. Verification of the LSP.....................................14
     6.5. Disruption minimization.....................................14
     6.6. Stability...................................................14
     6.7. Computing paths with and without nested signaling...........15
     6.8. Handling single-switching and multi-switching type capable
     6.9. Advertisement of the available adaptation resource..........16
     7. Security Considerations.......................................17
     8. References....................................................17
     8.1. Normative Reference.........................................17
     8.2. Informative References......................................18
     9. Author's Addresses............................................18
     10. Intellectual Property Considerations.........................19
     11. 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 [HIER].
     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) [GMPLS-RTG], 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).
     MRNs can be categorized according to the distribution of the
     switching type values amongst the LSRs:
     - Network elements are single switching capable LSRs and
       different types of LSRs form the network.
     - Network elements are multi-switching capable LSRs i.e. nodes
       hosting at least more than one switching capability. Multi-
     switching capable LSRs are further
       classified as "simplex" and "hybrid" nodes (see Section 4.2).
     - Any combination of the above two elements. A network composed
       of both single and multi-switching capable LSRs.
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     Since GMPLS provides a comprehensive framework for the control of
     different switching capabilities, a single GMPLS instance may be
     used to control the MRNs/MLNs 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/layers existing in the
     network, a path across multiple regions/layers can be computed
     using this TED. Thus optimization of network resources can be
     achieved across multiple regions/layers.
     Consider, for example, a MRN consisting of IP/MPLS routers and TDM
     cross-connects. Assume that a packet LSP is routed between source
     and destination IP/MPLS routers, and that the LSP can be routed
     across the PSC-region (i.e. utilizing only resources of the IP/MPLS
     level topology). If the performance objective for the LSP is not
     satisfied, new TE links may be created between the IP/MPLS routers
     across the TDM-region (for example, VC-12 links) and the LSP can be
     routed over those links. Further, even if the LSP can be
     successfully established across the PSC-region, TDM hierarchical
     LSPs across the TDM region between the IP/MPLS routers may be
     established and used if doing so enables meeting an operator's
     objectives on network resources available (e.g. link bandwidth, and
     adaptation port between regions) across the multiple regions. The
     same considerations hold when VC4 LSPs are provisioned to provide
     extra flexibility for the VC12 and/or VC11 layers in a 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",
     this document are to be interpreted as described in RFC 2119
  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.
     For example, VC12, VC4, and VC4-4c are different layers of the TDM
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  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 several data plane layers that share the same type of
     switching technology, that is, the same switching type. 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 is a control plane only concept. That is,
     layers of the same region share the same switching technology and,
     therefore, need the same set of technology specific signaling
  3.2. Services
     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
     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 One service (realized via the network layers of TDM, and/or
     LSC, and/or FSC regions) may support a Layer Two network (realized
     via ATM VP/VC) which may itself support a Layer Three network
     (IP/MPLS region). The supported data plane relationship is a data-
     plane client-server relationship where the lower layer provides a
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     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.
  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 switching capability and of realizing the client/server
     relationships between them. Protocol exchanges between two network
     controllers managing different regions are also a vertical
     interaction. Integration of these interactions as part of the
     control plane is referred to as vertical integration. The latter
     refers thus to the collaborative mechanisms within a single control
     plane instance driving multiple switching capabilities. 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
     switching technologies.
     In a strict sense, horizontal interaction is defined as the
     protocol exchange between network controllers that manage transport
     nodes within a given region (i.e. nodes with the same switching
     capability). For instance, the control plane interaction between
     two LSC network elements is an example of horizontal interaction.
     GMPLS protocol operations handle horizontal interactions within the
     same routing area. The case where the interaction takes place
     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 gets blurred when administrative domains
     match layer boundaries. Horizontal interaction is extended to cover
     such case. 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 area.
  4. Key concepts of GMPLS-based MLNs and MRNs
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     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
     [GMPLS-ROUTING]. An ISC is identified via a switching type.
     A switching type (also referred to as the switching capability
     types) 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. Apart from the ISC,
     the ISCD contains information, such as 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.
     TE link end advertisements may contain multiple ISCDs. This can be
     interpreted as advertising a multi-layer (or multi-switching) TE
     link end.
  4.2. Multiple Interface Switching Capabilities
     In a 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 [GMPLS-ROUTING].
     Multi-switching capable LSRs are classified as "simplex" and
     "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
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     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
     - 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 capable hybrid nodes
     The network contains at least one hybrid node, zero or more simplex
     nodes, and a set of single switching 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 two PSC and TDM
     links (Link1 and Link2 respectively). It also has 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,
     Link2 and provide through them 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        |     :
                          :           ----------      :
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                               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).
     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 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 layer(s)
     (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
     - provisioning of end-to-end LSPs with dynamic triggering of FA
     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.
     There is a full spectrum of options to control how FA LSPs are
     dynamically established. It 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 signaling perspective, there are two alternatives to
     establish lower layer FA LSP: static and dynamic.  Decision will be
     made either by the operator or automatically  using features like
     TE auto-mesh, for instance. 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".
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  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
     [HIER]. 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 FA-LSP. The TE-link
     associated to an FA-LSP is called an FA. An FA has the special
     characteristic of not requiring a routing adjacency (peering)
     between its ends yet still guaranteeing control plane connectivity
     between the FA-LSP ends based on a signaling adjacency. A FA is a
     useful and powerful tool for improving the scalability of GMPLS
     Traffic Engineering (TE) capable networks.
     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 [HIER]. 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
  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 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 VNT. The virtual
     network topology is configured by setting up or tearing down the
     LSC 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 change, topology configuration change, signaling
     request from the upper layer, and network failure. 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
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     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. Service networks provided over MRN/MLN
     A customer network may be provided on top of a server MRN/MLN
     network (such as a transport network) which is operated by a
     service provider. For example legacy IP or IP/MPLS networks can be
     provided on top of GMPLS packet or optical networks [IW-MIG-FW].
     The relationship between the networks is a client/server
     relationship and, such services are referred to as "MRN/MLN
     The customer network may be provided either as part of the MRN/MLN
     or in a separate network instance distinct from the MRN/MLN. There
     could also be an administrative boundary between the customer
     network and the MRN/MLN operated by the service provider. All
     requirements described in this document SHOULD be applicable if
     there is an administrative boundary between the customer network
     and the MRN/MLN operated by service provider.
     Impact on the customer network design, operation, and
     administration SHOULD be minimized. For instance, the design for
     address assignment and IGP area division should be kept independent
     from the underlying MRN/MLN.
     The MRN/MLN SHOULD provide mechanisms to allow an administrative
     boundary between the customer network and the MRN/MLN.
  6. Requirements
  6.1. 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:
      - Number of nodes
      - Number of TE-links (including FA-LSPs)
      - Number of LSPs
      - Number of regions and layers
      - Number of ISCDs per TE-link.
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  6.2. 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, (ie taking
     all layers into account). The number of lower-layer LSPs carrying
     upper-layer LSPs SHOULD be minimized as much as possible (Note that
     multiple LSPs may be used for load balance) . Unneccesary lower-
     layer LSPs SHOULD be avoided.
  6.2.1. 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, which do not carry
     any LSP may be released so that resources are released. Note that
     if a small fraction of the available bandwidth is still under use,
     the nested LSPs can also be re-routed optionally using the make-
     before-break technique. Alternatively, the FA LSPs may be retained
     for future usage. Release or retention of underutilized FA LSPs is
     a policy decision.
     As part of the re-optimization process, the solution MUST allow
     rerouting of FA LSPs while keeping interface identifiers of
     corresponding TE links unchanged.
     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.
     As the number of FA LSPs grows, the residual resource may decrease.
     In this case, re-optimization of FA LSPs MAY be invoked according
     the policy.
     Any solution MUST include measures to protect against network
     destabilization caused by the rapid set up and tear down of LSPs as
     traffic demand varies near a threshold.
  6.2.2. Virtual TE-Link
     It may be considered disadvantageous to fully instantiate (i.e.
     pre-provision) the set of lower layer LSPs since this may reserve
     bandwidth that could be used for other LSPs in the absence of the
     upper-layer traffic.
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     However, in order to provision upper-layer LSPs across the lower-
     layer, the LSPs MAY still be advertised into the upper-layer as
     though they had been fully established. Such TE links that
     represent the possibility of an underlying LSP are termed "virtual
     TE-link". Note that this is not a mandatory (MUST) requirement
     since even if there are no LSPs advertised to the higher layer, it
     is possible to route an upper layer LSP into a lower layer based on
     the lower layer's TE-links and making assumptions that proper
     hierarchical LSPs in the lower layer will be dynamically created as
     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 it has not been established.
     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 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 across the lower
     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.
     Virtual TE-links MAY be modified dynamically (by adding or removing
     virtual TE links) 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 configured
     SHOULD be well-engineered.
     How to design the VNT and how to manage it are out of scope of this
     document and will be treated in a companion document on solution.
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  6.3. 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.
  6.4. Verification of the LSP
     When the LSP is created, it SHOULD be verified that it has been
     established before it can be used by an upper layer LSP. Note, this
     is not within the GMPLS capability scope for non-PSC interfaces.
  6.5. Disruption minimization
     When reconfiguring the VNT according to a change in traffic demand,
     the upper-layer LSP might be disrupted. Such disruption MUST be
     When residual resource decreases to a certain level, some 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 LSPs 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).
  6.6. Stability
     The 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.
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     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
     and/or deletion of several LSPs.
     Creation and deletion of LSPs MAY be triggered by adjacent layers
     or through operational actions to meet traffic demand change,
     topology change, signaling request from the upper layer, and
     network failure. Routing robustness SHOULD be traded with
     adaptability with respect to the change of incoming traffic
     A full mesh of LSPs MAY be created between every pair of border
     nodes of the PSC region. The merit of a full mesh of PSC TE-LSPs is
     that it provides stability to the PSC-level routing. That is, the
     forwarding table of an PSC-LSR is not impacted by re-routing
     changes within the lower-layer (e.g., TDM layer). Further, there is
     always full PSC reachability and immediate access to bandwidth to
     support PSC LSPs. 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 wasting if LSP with a certain amount
     of reserved bandwidth is used.
     Note that the use of virtual TE-links solves the bandwidth wasting
     issue, and may reduce the control plane overload.
  6.7. 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 computing
     the path. 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 TE database 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 TE database 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.
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     The upper-layer signaling request may contain a loose ERO, and the
     boundary node is responsible for creation of the lower-layer FA-LSP.
     When the boundary node receives the signaling setup request and
     determines that it has to expand the loose ERO content by creating
     the lower-layer FA-LSP, it will create the lower layer FA-LSP
     accordingly. Once the lower-layer LSP is established, the ERO
     contents for the upper-layer signaling setup request are expanded
     to include the lower-layer FA-LSP and signaling setup for the
     upper-layer LSP are carried in-band of the lower-layer LSP.
     The upper-layer signaling request may contain a strict 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
     should a new lower-layer FA-LSP or it should use the existing
     lower-layer FA-LSPs.
     We should note that 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.
  6.8. Handling single-switching and multi-switching type capable
     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 capable and multi-switching (simplex or
     hybrid) capable nodes could play the role of layer boundary.
     MRN/MLN Path computation SHOULD handle TE topologies built of any
     combination of single switching, simplex and hybrid nodes
  6.9. 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
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     of necessary termination/ adaptation resources in the lower
     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).
  7. 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.
  8. References
  8.1. Normative Reference
     [RFC3979]       Bradner, S., "Intellectual Property Rights in IETF
                      Technology", BCP 79, RFC 3979, March 2005.
     [GMPLS-ROUTING] K.Kompella and Y.Rekhter, "Routing Extensions  in
                   Support of Generalized Multi-Protocol Label
                   Switching," draft-ietf-ccamp-gmpls-routing-09.txt,
                   October 2003 (work in progress).
     [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.
     [HIER]     K.Kompella and Y.Rekhter, "LSP hierarchy with
                   generalized MPLS TE," draft-ietf-mpls-lsp-hierarchy-
                   08.txt, work in progress, Sept. 2002.
     [STITCH]   Ayyangar, A. and Vasseur, JP., "Label Switched Path
                   Stitching with Generalized MPLS Traffic Engineering",
                   draft-ietf-ccamp-lsp-stitching, work in progress.
     [LMP]      J. Lang, "Link management protocol (LMP)," draft- ietf-
                   ccamp-lmp-10.txt (work in progress), October 2003.
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                draft-shiomoto-ccamp-gmpls-mrn-reqs-03.txt  October 2005
     [RFC3945]  E.Mannie (Ed.), "Generalized Multi-Protocol Label
                   Switching (GMPLS) Architecture", RFC 3945, October
  8.2. 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
     [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.
     [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-shiomoto-ccamp-mpls-gmpls-
                   interwork-fmwk-00.txt, work in progress.
  9. Author's Addresses
     Kohei Shiomoto
     NTT Network Service Systems Laboratories
     3-9-11 Midori-cho,
     Musashino-shi, Tokyo 180-8585, Japan
     Dimitri Papadimitriou
     Francis Wellensplein 1,
     B-2018 Antwerpen, Belgium
     Phone : +32 3 240 8491
     Jean-Louis Le Roux
     France Telecom R&D,
     Av Pierre Marzin,
     22300 Lannion, France
     Martin Vigoureux
     Route de Nozay, 91461 Marcoussis cedex, France
     Phone: +33 (0)1 69 63 18 52
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     Deborah Brungard
     Rm. D1-3C22 - 200
     S. Laurel Ave., Middletown, NJ 07748, USA
     Phone: +1 732 420 1573
     Eiji Oki (NTT Network Service Systems Laboratories)
     3-9-11 Midori-cho, Musashino-shi, Tokyo 180-8585, Japan
     Phone: +81 422 59 3441 Email:
     Ichiro Inoue (NTT Network Service Systems Laboratories)
     3-9-11 Midori-cho, Musashino-shi, Tokyo 180-8585, Japan
     Phone: +81 422 59 3441 Email:
     Emmanuel Dotaro (Alcatel)
     Route de Nozay, 91461 Marcoussis cedex, France
     Phone : +33 1 6963 4723 Email:
  10. 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
     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-
     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,
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  11. Full Copyright Statement
     Copyright (C) The Internet Society (2005). 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
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