draft-ietf-pce-inter-layer-frwk-02.txt   draft-ietf-pce-inter-layer-frwk-03.txt 
Network Working Group Eiji Oki Network Working Group Eiji Oki
Internet Draft NTT Internet Draft NTT
Category: Informational Jean-Louis Le Roux Category: Informational Jean-Louis Le Roux
Expires: April 2007 France Telecom Expires: September 2007 France Telecom
Adrian Farrel Adrian Farrel
Old Dog Consulting Old Dog Consulting
October 2006
Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic
Engineering Engineering
draft-ietf-pce-inter-layer-frwk-02.txt draft-ietf-pce-inter-layer-frwk-03.txt
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Abstract Abstract
A network may comprise of multiple layers. It is important to A network may comprise multiple layers. It is important to globally
globally optimize network resources utilization, taking into optimize network resource utilization, taking into account all
account all layers, rather than optimizing resource utilization at layers, rather than optimizing resource utilization at each layer
each layer independently. This allows better network efficiency to independently. This allows better network efficiency to be achieved
be achieved through a process that we call inter-layer traffic through a process that we call inter-layer traffic engineering. The
engineering. The Path Computation Element (PCE) can be a powerful Path Computation Element (PCE) can be a powerful tool to achieve
tool to achieve inter-layer traffic engineering. inter-layer traffic engineering.
This document describes a framework for applying the PCE-based path This document describes a framework for applying the PCE-based
computation architecture to inter-layer MPLS and GMPLS traffic architecture to inter-layer Multiprotocol Label Switching (MPLS) and
engineering. It provides suggestions for the deployment of PCE in Generalized MPLS (GMPLS) traffic engineering. It provides
support of multi-layer networks. This document also describes suggestions for the deployment of PCE in support of multi-layer
network models where PCE performs inter-layer traffic engineering, networks. This document also describes network models where PCE
and the relationship between PCE and a functional component called performs inter-layer traffic engineering, and the relationship
the Virtual Network Topology Manager (VNTM). between PCE and a functional component called the Virtual Network
Topology Manager (VNTM).
Table of Contents Table of Contents
1. Terminology.....................................................2 1. Terminology.....................................................2
2. Introduction....................................................2 2. Introduction....................................................2
3. Inter-Layer Path Computation....................................3 3. Inter-Layer Path Computation....................................3
4. Inter-layer Path Computation Models.............................5 4. Inter-layer Path Computation Models.............................5
4.1. Single PCE Inter-Layer Path Computation......................5 4.1. Single PCE Inter-Layer Path Computation......................5
4.2. Multiple PCE Inter-Layer Path Computation....................6 4.2. Multiple PCE Inter-Layer Path Computation....................5
4.3. General observations.........................................7 4.3. General Observations.........................................6
5. Inter-Layer Path Control........................................7 5. Inter-Layer Path Control........................................7
5.1. VNT Management...............................................8 5.1. VNT Management...............................................7
5.2. Inter-Layer Path Control Models..............................8 5.2. Inter-Layer Path Control Models..............................7
5.2.1. Cooperation model between PCE and VNTM.....................8 5.2.1. Cooperation Model Between PCE and VNTM.....................7
5.2.2. Higher-Layer Signaling Trigger Model......................10 5.2.2. Higher-Layer Signaling Trigger Model.......................9
5.2.3. Examples of multi-layer ERO...............................12 5.2.3. Examples of Multi-Layer ERO...............................11
6. Choosing between inter-layer path control models...............12 6. Choosing Between Inter-Layer Path Control Models...............11
6.1. VNTM functions:.............................................13 6.1. VNTM Functions:.............................................11
6.2. Border LSR functions:.......................................13 6.2. Border LSR Functions:.......................................12
6.3. Complete inter-layer LSP setup time:........................13 6.3. Complete Inter-Layer LSP Setup Time:........................12
6.4. Network complexity..........................................14 6.4. Network Complexity..........................................12
7. Security Considerations........................................14 6.5. Separation of Layer Management..............................13
8. Acknowledgment.................................................15 7. Security Considerations........................................13
9. References.....................................................15 8. Acknowledgment.................................................14
9.1. Normative Reference.........................................15 9. References.....................................................14
9.2. Informative Reference.......................................15 9.1. Normative Reference.........................................14
10. Authors' Addresses...........................................16 9.2. Informative Reference.......................................14
11. Intellectual Property Statement..............................16 10. Authors' Addresses...........................................15
11. Intellectual Property Statement..............................15
1. Terminology 1. Terminology
This document uses terminology from the PCE-based path computation This document uses terminology from the PCE-based path computation
architecture [RFC4655] and also common terminology from Multi architecture [RFC4655] and also common terminology from Multi
Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS (GMPLS) Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS (GMPLS)
[RFC3945] and Multi-Layer Networks [MLN-REQ]. [RFC3945] and Multi-Layer Networks [MLN-REQ].
2. Introduction 2. Introduction
A network may comprise of multiple layers. These layers may A network may comprise multiple layers. These layers may represent
represent separations of technologies (e.g., packet switch capable separations of technologies (e.g., packet switch capable (PSC), time
(PSC), time division multiplex (TDM) lambda switch capable (LSC)) division multiplex (TDM), or lambda switch capable (LSC)) [RFC3945],
[RFC3945], separation of data plane switching granularity levels separation of data plane switching granularity levels (e.g., PSC-1,
(e.g. PSC-1, PSC-2, VC4, VC12) [MLN-REQ], or a distinction between PSC-2, VC4, or VC12) [MLN-REQ], or a distinction between client and
client and server networking roles. In this multi-layer network, server networking roles. In this multi-layer network, Label Switched
Label Switched Paths (LSPs) in a lower layer are used to carry Paths (LSPs) in a lower layer are used to carry higher-layer LSPs
higher-layer LSPs across the lower-layer network. The network across the lower-layer network. The network topology formed by
lower-layer LSPs and advertised to the higher layer is called a
Oki et al Expires April 2007 2 Virtual Network Topology (VNT) [MLN-REQ].
topology formed by lower-layer LSPs and advertised to the higher
layer is called a Virtual Network Topology (VNT) [MLN-REQ].
It may be effective to optimize network resource utilization It may be effective to optimize network resource utilization
globally, i.e. taking into account all layers, rather than globally, i.e., taking into account all layers, rather than
optimizing resource utilization at each layer independently. This optimizing resource utilization at each layer independently. This
allows better network efficiency to be achieved and is what we call allows better network efficiency to be achieved and is what we call
inter-layer traffic engineering. This includes mechanisms allowing inter-layer traffic engineering. This includes mechanisms allowing
the computation of end-to-end paths across layers (known as inter- the computation of end-to-end paths across layers (known as inter-
layer path computation), and mechanisms for control and management layer path computation), and mechanisms for control and management
of the VNT by setting up and releasing LSPs in the lower layers of the Virtual Network Topology (VNT) by setting up and releasing
[MLN-REQ]. LSPs in the lower layers [MLN-REQ].
Inter-layer traffic engineering is included in the scope of the Oki et al Expires September 2007 2
PCE-based path computation architecture [RFC4655], and PCE can Inter-layer traffic engineering is included in the scope of the Path
Computation Element (PCE)-based architecture [RFC4655], and PCE can
provide a suitable mechanism for resolving inter-layer path provide a suitable mechanism for resolving inter-layer path
computation issues. computation issues.
PCE Communication Protocol requirements for inter-layer traffic PCE Communication Protocol requirements for inter-layer traffic
engineering are set forth in [PCE-INTER-LAYER-REQ]. engineering are set forth in [PCE-INTER-LAYER-REQ].
This document describes a framework for applying the PCE-based path This document describes a framework for applying the PCE-based
computation architecture to inter-layer traffic engineering. It architecture to inter-layer traffic engineering. It provides
provides suggestions for the deployment of PCE in support of multi- suggestions for the deployment of PCE in support of multi-layer
layer networks. This document also describes network models where networks. This document also describes network models where PCE
PCE performs inter-layer traffic engineering, and the relationship performs inter-layer traffic engineering, and the relationship
between PCE and a functional component in charge of the control and between PCE and a functional component in charge of the control and
management of the VNT, and called the Virtual Network Topology management of the VNT, and called the Virtual Network Topology
Manager (VNTM). Manager (VNTM).
3. Inter-Layer Path Computation 3. Inter-Layer Path Computation
This section describes key topics of inter-layer path computation This section describes key topics of inter-layer path computation in
in MPLS and GMPLS networks. MPLS and GMPLS networks.
[RFC4206] defines a way to signal a higher-layer LSP, whose [RFC4206] defines a way to signal a higher-layer LSP, whose explicit
explicit route includes hops traversed by LSPs in lower layers. The route includes hops traversed by LSPs in lower layers. The
computation of end-to-end paths across layers is called Inter-Layer computation of end-to-end paths across layers is called Inter-Layer
Path Computation. Path Computation.
A Label Switching Router (LSR) in the higher-layer might not have A Label Switching Router (LSR) in the higher-layer might not have
information on the lower-layer topology, particularly in an overlay information on the topology of the lower-layer, particularly in an
or augmented model, and hence may not be able to compute an end-to- overlay or augmented model deployment, and hence may not be able to
end path across layers. compute an end-to-end path across layers.
PCE-based inter-layer path computation, consists of relying on one
or more PCEs to compute an end-to-end path across layers. This
could be achieved by rely on a single PCE path computation where
the PCE has topology information about multiple layers and can
directly compute an end-to-end path across layers considering the
topology of all of the layers. Alternatively, the inter-layer path
computation could be performed as a multiple PCE computation where
each member of a set of PCEs have information about the topology of
Oki et al Expires April 2007 3 PCE-based inter-layer path computation, consists of using one or
one or more layers, but not all layers, and collaborate to compute more PCEs to compute an end-to-end path across layers. This could be
an end-to-end path. achieved by a single PCE path computation where the PCE has topology
information about multiple layers and can directly compute an end-
to-end path across layers considering the topology of all of the
layers. Alternatively, the inter-layer path computation could be
performed as a multiple PCE computation where each member of a set
of PCEs has information about the topology of one or more layers
(but not all layers), and the PCEs collaborate to compute an end-to-
end path.
Consider, for instance, a two-layer network where the higher-layer Consider, for instance, a two-layer network where the higher-layer
network is a packet-based IP/MPLS network or GMPLS network and the network is a packet-based IP/MPLS or GMPLS network, and the lower-
lower-layer network is a GMPLS optical network. An ingress LSR in layer network is a GMPLS optical network. An ingress LSR in the
the higher-layer network tries to set up an LSP to an egress LSR higher-layer network tries to set up an LSP to an egress LSR also in
also in the higher-layer network across the lower-layer network, the higher-layer network across the lower-layer network, and needs a
and needs a path in the higher-layer network. However, suppose that path in the higher-layer network. However, suppose that there is no
there is no Traffic Engineering (TE) link between border LSRs, Traffic Engineering (TE) link in the higher-layer network between
which are located on the boundary between the higher-layer and border LSRs, which are located on the boundary between the higher-
lower-layer networks, and that the ingress LSR does not have layer and lower-layer networks, and that the ingress LSR does not
topology visibility in the lower layer. If a single-layer path have topology visibility into the lower layer. If a single-layer
computation is applied for the higher-layer, the path computation path computation is applied for the higher-layer, the path
fails. On the other hand, inter-layer path computation is able to computation fails because of the missing TE link. On the other hand,
provide a route in the higher-layer and a suggestion that a lower- inter-layer path computation is able to provide a route in the
layer LSP be setup between border LSRs, considering both layers' TE higher-layer and a suggestion that a lower-layer LSP be set up
topologies. between border LSRs.
Lower-layer LSPs form a Virtual Network Topology (VNT), which can Oki et al Expires September 2007 3
be used for routing higher-layer LSPs or to carry IP traffic. Lower-layer LSPs that are advertised as TE links into the higher-
Inter-layer path computation for end-to-end LSPs in the higher- layer network form a Virtual Network Topology (VNT), which can be
layer network that span the lower-layer network may utilize the VNT, used for routing higher-layer LSPs. Inter-layer path computation for
and PCE is a candidate for computing the paths of such higher-layer end-to-end LSPs in the higher-layer network that span the lower-
LSPs within the higher-layer network. The PCE-based path layer network may utilize the VNT, and PCE is a candidate for
computation model can: computing the paths of such higher-layer LSPs within the higher-
layer network. Alternatively, the PCE-based path computation model
can:
- Perform a single computation on behalf of the ingress LSR using - Perform a single computation on behalf of the ingress LSR using
information gathered from more than one layer. This mode is information gathered from more than one layer. This mode is referred
referred to as Single PCE Computation in [RFC4655]. to as Single PCE Computation in [RFC4655].
- Compute a path on behalf of the ingress LSR through cooperation - Compute a path on behalf of the ingress LSR through cooperation
between PCEs responsible for each layer. This mode is referred to with PCEs responsible for each layer. This mode is referred to as
as Multiple PCE Computation with inter-PCE communication in Multiple PCE Computation with inter-PCE communication in [RFC4655].
[RFC4655].
- Perform separate path computations on behalf of the TE-LSP head- - Perform separate path computations on behalf of the TE-LSP head-
end and each transit LSR that is the entry point to a new layer. end and each transit border LSR that is the entry point to a new
This mode is referred to as Multiple PCE Computation (without layer. This mode is referred to as Multiple PCE Computation (without
inter-PCE communication) in [RFC4655]. This option utilizes per- inter-PCE communication) in [RFC4655]. This option utilizes per-
layer path computation performed independently by successive PCEs. layer path computation performed independently by successive PCEs.
The PCE computes and returns a path to the PCC that the PCC can use The PCE invoked by the head-end LSR computes a path that the LSR can
to build an MPLS or GMPLS LSP once converted to an Explicit Route use to signal an MPLS-TE or GMPLS LSP once the path information has
Object (ERO) for use in RSVP-TE signaling. There are two options. been converted to an Explicit Route Object (ERO) for use in RSVP-TE
signaling. There are two options.
- Option 1: Mono-layer path. - Option 1: Mono-layer path.
The PCE computes a "mono-layer" path, i.e., a path that includes The PCE computes a "mono-layer" path, i.e., a path that includes
only TE links from the same layer. There are two cases for this only TE links from the same layer. There are two cases for this
option. In the first case the PCE computes a path that includes option. In the first case the PCE computes a path that includes
already established lower-layer LSPs or expected lower-layer LSPs already established lower-layer LSPs or lower-layer LSPs to be
to be established: that is the resulting ERO includes sub-object(s) established on demand. That is, the resulting ERO includes sub-
corresponding to lower-layer hierarchical LSPs expressed as the TE object(s) corresponding to lower-layer hierarchical LSPs expressed
link identifiers, which can be numbered or unnumbered ones, of the as the TE link identifiers of the hierarchical LSPs when advertised
as TE links in the higher-layer network. The TE link may be a
regular TE link that is actually established, or a virtual TE link
that is not established yet (see [MLN-REQ]). If it is a virtual TE
link, this triggers a setup attempt for a new lower-layer LSP when
signaling reaches the head-end of the lower-layer LSP. Note that the
path of a virtual TE link is not necessarily known in advance, and
this may require a further (lower-layer) path computation.
Oki et al Expires April 2007 4 The second case is that the PCE computes a path that includes a
hierarchical LSPs when advertised as TE links in the higher-layer loose hop that spans the lower-layer network. The higher layer path
network. The TE link may be a regular TE link that is actually computation selects which lower layer network to use, and selects
established, or a virtual TE link that is not established yet (see the entry and exit points from that lower-layer network, but does
[MLN-REQ]). If it is a regular TE link, this does not trigger new not select the path across the lower-layer network. A transit LSR
lower-layer LSP setup, but the utilization of existing lower-layer that is the entry point to the lower-layer network is expected to
LSPs. If it is a virtual TE link, this triggers a new lower-layer expand the loose hop (either itself or relying on the services of a
LSP setup (provided that there are available resources in the lower PCE). The path expansion process on the border LSR may result either
layer). A transit LSR corresponding to the entry point of the in the selection of an existing lower-layer LSP, or in the
virtual TE link is expected to trigger the new lower-layer LSP computation and setup of a new lower-layer LSP.
setup. Note that the path of a virtual TE link is not necessarily
known in advance, and this may require path computation either on
the entry point or on a PCE. The second case is that the PCE
computes a path that includes loose hop(s). The higher layer path
would select which lower layer paths to use and would select the
entry and exit points from those layers, but would not select the
path across the layers. A transit LSR corresponding to the entry
point is expected to expand the loose hop (either itself or relying
on the services of a PCE). The path expansion process on the border
LSR may result either in the selection of an existing lower-layer
LSP, or in the computation and setup of a new lower-layer LSP.
- Option 2: Multi-layer path. The PCE computes a "multi-layer" path, - Option 2: Multi-layer path. The PCE computes a "multi-layer" path,
i.e. a path that includes TE links from distinct layers [RFC4206]. i.e., a path that includes TE links from distinct layers [RFC4206].
Such a path can include the complete path of one or more lower- Such a path can include the complete path of one or more lower-layer
layer LSPs that already exist or are not yet established. In the LSPs that already exist or are not yet established. In the latter
latter case, the signaling of the higher-layer LSP will trigger the
Oki et al Expires September 2007 4
case, the signaling of the higher-layer LSP will trigger the
establishment of the lower-layer LSPs. establishment of the lower-layer LSPs.
4. Inter-layer Path Computation Models 4. Inter-layer Path Computation Models
As stated in Section 3, two PCE modes defined in the PCE As stated in Section 3, two PCE modes defined in the PCE
architecture can be used to perform inter-layer path computation. architecture can be used to perform inter-layer path computation.
They are discussed below. They are discussed below.
4.1. Single PCE Inter-Layer Path Computation 4.1. Single PCE Inter-Layer Path Computation
In this model Inter-layer path computation is performed by a single In this model Inter-layer path computation is performed by a single
PCE that has topology visibility in all layers. Such a PCE is PCE that has topology visibility into all layers. Such a PCE is
called a multi-layer PCE. called a multi-layer PCE.
In Figure 1, the network is comprised of two layers. LSR H1, H2, H3 In Figure 1, the network is comprised of two layers. LSRs H1, H2, H3,
and H4 belong to the higher layer, and LSRs L1 and L2 belong to the and H4 belong to the higher layer, and LSRs H2, H3, L1, and L2
lower layer. The PCE is a multi-layer PCE that has visibility into belong to the lower layer. The PCE is a multi-layer PCE that has
both layers. It can perform end-to-end path computation across visibility into both layers. It can perform end-to-end path
layers (single PCE path computation). For instance, it can compute computation across layers (single PCE path computation). For
an optimal path H2-L1-L2-H3-H4, for a higher layer LSP from H1 to instance, it can compute an optimal path H1-H2-L1-L2-H3-H4, for a
H4. This path includes the path of a lower layer LSP from H2 to H3, higher layer LSP from H1 to H4. This path includes the path of a
already established or not. lower layer LSP from H2 to H3, already in existence or not yet
established.
Oki et al Expires April 2007 5
----- -----
| PCE | | PCE |
----- -----
----- ----- ----- ----- ----- ----- ----- -----
| LSR |--| LSR |................| LSR |--| LSR | | LSR |--| LSR |................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 | | H1 | | H2 | | H3 | | H4 |
----- -----\ /----- ----- ----- -----\ /----- -----
\----- -----/ \----- -----/
| LSR |--| LSR | | LSR |--| LSR |
| L1 | | L2 | | L1 | | L2 |
----- ----- ----- -----
Figure 1 : Multi-Layer PCE - A single PCE with multi-layer Figure 1 : Multi-Layer PCE -
- A single PCE with multi-layer
visibility visibility
4.2. Multiple PCE Inter-Layer Path Computation 4.2. Multiple PCE Inter-Layer Path Computation
In this model there is at least one PCE per layer, and each PCE has In this model there is at least one PCE per layer, and each PCE has
topology visibility restricted to its own layer. Some providers may topology visibility restricted to its own layer. Some providers may
want to keep the layer boundaries due to other factors such as want to keep the layer boundaries due to factors such as
organizational and/or service management issues. The choice for organizational and/or service management issues. The choice for
multiple PCE computation instead of single PCE computation may also multiple PCE computation instead of single PCE computation may also
be driven by scalability considerations, as in this mode a PCE only be driven by scalability considerations, as in this mode a PCE only
needs to maintain topology information of one layer (TED size needs to maintain topology information for one layer (resulting in a
reduction). size reduction for the Traffic Engineering Database (TED)).
These PCEs are called mono-layer PCEs. Mono-layer PCEs collaborate These PCEs are called mono-layer PCEs. Mono-layer PCEs collaborate
to compute an end-to-end optimal path across layers. to compute an end-to-end optimal path across layers.
Oki et al Expires September 2007 5
In Figure 2, there is one PCE in each layer. The PCEs from each In Figure 2, there is one PCE in each layer. The PCEs from each
layer collaborate to compute an end-to-end path across layers. PCE layer collaborate to compute an end-to-end path across layers. PCE
Hi is responsible for computations in the higher layer and may Hi is responsible for computations in the higher layer and may
"consult" with PCE Lo to compute paths across the lower layer. PCE "consult" with PCE Lo to compute paths across the lower layer. PCE
Lo is responsible for path computation in the lower layer. A simple Lo is responsible for path computation in the lower layer. A simple
example of cooperation between the PCEs could be: PCE Hi requests a example of cooperation between the PCEs could be as follows:
path H2-H3 from PCE Lo. Of course more complex cooperation may be - LSR H1 sends a request for a path H1-H4 to PCE Hi
required if an end-to-end optimal path is desired. - PCE Hi selects H2 as the entry point to the lower layer, and H3 as
the exit point.
- PCE Hi requests a path H2-H3 from PCE Lo.
- PCE Lo returns H2-L1-L2-H3 to PCE Hi.
- PEC Hi is able to compute the full path (H1-H2-L1-L2-H3-H4) and
return it to H1.
Of course more complex cooperation may be required if an optimal
end-to-end path is desired.
Oki et al Expires April 2007 6
----- -----
| PCE | | PCE |
| Hi | | Hi |
--+-- --+--
| |
----- ----- | ----- ----- ----- ----- | ----- -----
| LSR |--| LSR |............|...........| LSR |--| LSR | | LSR |--| LSR |............|...........| LSR |--| LSR |
| H1 | | H2 | | | H3 | | H4 | | H1 | | H2 | | | H3 | | H4 |
----- -----\ --+-- /----- ----- ----- -----\ --+-- /----- -----
\ | PCE | / \ | PCE | /
skipping to change at line 325 skipping to change at line 330
\ ----- / \ ----- /
\ / \ /
\----- -----/ \----- -----/
| LSR |--| LSR | | LSR |--| LSR |
| L1 | | L2 | | L1 | | L2 |
----- ----- ----- -----
Figure 2 : Cooperating Mono-Layer PCEs - Multiple PCEs with single- Figure 2 : Cooperating Mono-Layer PCEs - Multiple PCEs with single-
layer visibility layer visibility
4.3. General observations 4.3. General Observations
- Depending on implementation details, inter-layer path computation - Depending on implementation details, inter-layer path computation
time in the Single PCE inter-layer path computation model may be time in the Single PCE inter-layer path computation model may be
less than that of the Multiple PCE model with cooperating mono-
layer PCEs, because there is no requirement to exchange messages
between cooperating PCEs.
- When TE topology for all layered networks is visible within one Oki et al Expires September 2007 6
less than that of the Multiple PCE model with cooperating mono-layer
PCEs, because there is no requirement to exchange messages between
cooperating PCEs.
- When TE topology for all layer networks is visible within one
routing domain, the single PCE inter-layer path computation model routing domain, the single PCE inter-layer path computation model
may be adopted because a PCE is able to collect all layers' TE may be adopted because a PCE is able to collect all layers' TE
topologies by participating in only one routing domain. topologies by participating in only one routing domain.
- As the single PCE inter-layer path computation model uses more TE - As the single PCE inter-layer path computation model uses more TE
topology information than is used by PCEs in the Multiple PCE path topology information than is used by PCEs in the Multiple PCE path
computation model, it requires more computation power and memory. computation model, it requires more computation power and memory.
When there are multiple candidate layer border nodes (we may say When there are multiple candidate layer border nodes (we may say
that the higher layer is multi-homed), optimal path computation that the higher layer is multi-homed), optimal path computation
requires that all the possible paths transiting different layer requires that all the possible paths transiting different layer
border nodes or links be examined. This is relatively simple in the border nodes or links be examined. This is relatively simple in the
single PCE inter-layer path computation model because the PCE has single PCE inter-layer path computation model because the PCE has
full visibility - the computation is similar to the computation full visibility -
within a single domain of a single layer. In the multiple PCE - the computation is similar to the computation
inter-layer path computation model, backward recursive techniques within a single domain of a single layer. In the multiple PCE inter-
described in [BRPC] could be used, by considering layers as layer path computation model, backward recursive techniques
separate domains. described in [BRPC] could be used, by considering layers as separate
domains.
5. Inter-Layer Path Control 5. Inter-Layer Path Control
Oki et al Expires April 2007 7
5.1. VNT Management 5.1. VNT Management
As a result of inter-layer path computation, a PCE may determine As a result of inter-layer path computation, a PCE may determine
that there is insufficient bandwidth available in the higher-layer that there is insufficient bandwidth available in the higher-layer
network to support this or future higher-layer LSPs. The problem network to support this or future higher-layer LSPs. The problem
might be resolved if new LSPs are provisioned across the lower- might be resolved if new LSPs were provisioned across the lower-
layer network. Further, the modification, re-organization and new layer network. Further, the modification, re-organization and new
provisioning of lower-layer LSPs may enable better utilization of provisioning of lower-layer LSPs may enable better utilization of
lower-layer network resources given the demands of the higher-layer lower-layer network resources given the demands of the higher-layer
network. In other words, the VNT needs to be controlled or managed network. In other words, the VNT needs to be controlled or managed
in cooperation with inter-layer path computation. in cooperation with inter-layer path computation.
A VNT Manager (VNTM) is defined as a network element that manages A VNT Manager (VNTM) is defined as a network element that manages
and controls the VNT. PCE and "VNT Management" are distinct and controls the VNT. PCE and VNT Managemer are distinct functional
functions that may or may not be co-located. To describe each elements that may or may not be co-located.
function clearly, VNTM is considered as a functional element in
this draft.
5.2. Inter-Layer Path Control Models 5.2. Inter-Layer Path Control Models
5.2.1. Cooperation model between PCE and VNTM 5.2.1. Cooperation Model Between PCE and VNTM
----- ------ ----- ------
| PCE |--->| VNTM | | PCE |--->| VNTM |
----- ------ ----- ------
^ : ^ :
: : : :
: : : :
v V v V
----- ----- ----- ----- ----- ----- ----- -----
| LSR |----| LSR |................| LSR |----| LSR | | LSR |----| LSR |................| LSR |----| LSR |
| H1 | | H2 | | H3 | | H4 | | H1 | | H2 | | H3 | | H4 |
----- -----\ /----- ----- ----- -----\ /----- -----
\----- -----/ \----- -----/
| LSR |--| LSR | | LSR |--| LSR |
| L1 | | L2 | | L1 | | L2 |
Oki et al Expires September 2007 7
----- ----- ----- -----
Figure 3: Cooperation model between PCE and VNTM Figure 3: Cooperation Model Between PCE and VNTM
A multi-layer network consists of higher-layer and lower-layer A multi-layer network consists of higher-layer and lower-layer
networks. LSRs H1, H2, H3, and H4 belong to the higher-layer networks. LSRs H1, H2, H3, and H4 belong to the higher-layer network,
network, LSRs H2, L1, L2, and H3 belong to the lower-layer network, LSRs H2, L1, L2, and H3 belong to the lower-layer network, as shown
as shown in Figure 3. Consider that H1 requests PCE to compute an in Figure 3. Consider that H1 requests PCE to compute an inter-layer
inter-layer path between H1 and H4. There is no TE link in the path between H1 and H4. There is no TE link in the higher-layer
higher-layer between H2 and H3 before the path computation request. between H2 and H3 before the path computation request fails. But the
PCE may provide information to the VNT Manager responsible for the
lower layer network that may help resolve the situation for future
higher-layer LSP setup.
The roles of PCE and VNTM are as follows. PCE performs inter-layer The roles of PCE and VNTM are as follows. PCE performs inter-layer
path computation and is unable to supply a path because there is no path computation and is unable to supply a path because there is no
TE link between H2 and H3. The computation fails, but PCE suggests TE link between H2 and H3. The computation fails, but PCE suggests
to VNTM that a lower-layer LSP (H2-H3) should be established to to VNTM that a lower-layer LSP (H2-H3) could be established to
support future LSP requests. VNTM uses local policy and possibly support future LSP requests. Messages from PCE to VNTM contain
management/configuration input to determine how to process the information about the higher-layer demand (from H2 to H3). VNTM uses
suggestion from PCE, and may request an ingress LSR (e.g. H2) to local policy and possibly management/configuration input to
determine how to process the suggestion from PCE, and may request an
Oki et al Expires April 2007 8 ingress LSR (e.g. H2) to establish a lower-layer LSP. VNTM or the
establish a lower-layer LSP. VNTM or the ingress LSR (H2) may use a ingress LSR (H2) may themselves use a PCE with visibility into the
PCE with visibility into the lower layer to compute the path of lower layer to compute the path of this new LSP.
this new LSP.
If the PCE cannot compute a path for the higher-layer LSP without When the higher-layer PCE fails to compute a path and notifies VNTM,
the establishment of a further lower-layer LSP, the PCE may notify it may wait for the lower-layer LSP to be set up and advertised as a
VNTM and wait for the lower-layer LSP to be set up and advertised TE link. It could then compute the complete end-to-end path for the
as a TE link. It can then compute the complete end-to-end path for higher-layer LSP and return the result to the PCC. In this case, the
the higher-layer LSP and return the result to the PCC. In this case, PCC may be kept waiting for some time, and it is important that the
the PCC may be kept waiting some time, and it is important that the
PCC understands this. It is also important that the PCE and VNTM PCC understands this. It is also important that the PCE and VNTM
have an agreement that the lower-layer LSP will be set up in a have an agreement that the lower-layer LSP will be set up in a
timely manner, the PCE operates a timeout, or the PCE will be timely manner, or that the PCE will be notified by VNTM that no new
notified by VNTM that no new LSP will become available. An example LSP will become available. In any case, if the PCE decides to wait,
of such a cooperative procedure between PCE and VNTM is as follows. it must operates a timeout. An example of such a cooperative
procedure between PCE and VNTM is as follows using the exmaple
network in Figure 3.
Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4. Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4.
In the request, it indicates that inter-layer path computation is
allowed.
Step 2: As a result of the inter-layer path computation, PCE judges Step 2: The path computation fails because there is no TE link
that a new lower-layer LSP needs to be established. across the lower-layer network.
Step 3: PCE suggests to VNTM that a new lower-layer LSP should be Step 3: PCE suggests to VNTM that a new TE link connecting H2 and H3
would be useful. VNTM considers whether lower-layer LSPs should be
established if necessary and if acceptable within VNTM's policy established if necessary and if acceptable within VNTM's policy
constraints. The inter-layer path route computed by PCE may include constraints. The PCE notifies VNTM that it will be waiting for the
one or more virtual TE links. If PCE knows the inclusion of the TE link to be created.
virtual TE link(s) in the inter-layer route, PCE may suggest VNTM
that the corresponding new lower-layer LSP(s) should be established.
Otherwise, new lower-layer LSP(s) may be setup according to the
higher-layer signaling trigger model.
In the above description, it is assumed that a higher layer LSP is
supported by a single lower layer LSP. However, in case of VCAT,
several lower layer LSPs may be used to transport a single higher
layer LSP.
Step 4: VNTM requests an ingress LSR (e.g. H2) to establish a Step 4: VNTM requests an ingress LSR in the lower-layer network
lower-layer LSP. The request message may include a pre-computed (e.g., H2) to establish a lower-layer LSP. The request message may
lower-layer LSP route obtained from the PCE responsible for the include a lower-layer LSP route obtained from the PCE responsible
lower-layer network. for the lower-layer network.
Step 5: The ingress LSR starts signaling to establish a lower-layer Step 5: The ingress LSR signals to establish the lower-layer LSP.
LSP.
Step 6: If the lower-layer LSP setup is completed, the ingress LSR Step 6: If the lower-layer LSP setup is successful, the ingress LSR
notifies VNTM that the LSP is complete and supplies the tunnel notifies VNTM that the LSP is complete and supplies the tunnel
information. information.
Step 7: VNTM replies to PCE to inform it that the lower-layer LSP Oki et al Expires September 2007 8
is now established, and includes the lower-layer tunnel information. Step 7: The ingress LSR (H2) advertises the new LSP as a TE link in
Alternatively, PCE may get to know about the existence of the the higher-layer network routing instance.
lower-layer LSP when a new TE link in the higher-layer
Oki et al Expires April 2007 9 Step 8: PCE notices the new TE link advertisement and recomputes the
corresponding to the lower-layer LSP is advertised to PCE through requested path.
the IGP.
Step 8: PCE replies to H1 (PCC) with a computed higher-layer LSP Step 9: PCE replies to H1 (PCC) with a computed higher-layer LSP
route. The computed path is categorized as a mono-layer path that route. The computed path is categorized as a mono-layer path that
includes the already-established lower layer-LSP. The higher-layer includes the already-established lower layer-LSP as a single hop in
route is specified as H2-H3-H4, where all hops are strict. the higher layer. The higher-layer route is specified as H1-H2-H3-H4,
where all hops are strict.
Step 9: H1 initiates signaling with the computed path H2-H3-H4 to Step 9: H1 initiates signaling with the computed path H2-H3-H4 to
establish the higher-layer LSP. establish the higher-layer LSP.
5.2.2. Higher-Layer Signaling Trigger Model 5.2.2. Higher-Layer Signaling Trigger Model
----- -----
| PCE | | PCE |
----- -----
^ ^
skipping to change at line 496 skipping to change at line 494
v v
----- ----- ----- ----- ----- ----- ----- -----
| LSR |----| LSR |................| LSR |--| LSR | | LSR |----| LSR |................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 | | H1 | | H2 | | H3 | | H4 |
----- -----\ /----- ----- ----- -----\ /----- -----
\----- -----/ \----- -----/
| LSR |--| LSR | | LSR |--| LSR |
| L1 | | L2 | | L1 | | L2 |
----- ----- ----- -----
Figure 4: Higher-layer signaling trigger model Figure 4: Higher-layer Signaling Trigger Model
Figure 4 shows the higher-layer signaling trigger model. As in the Figure 4 shows the higher-layer signaling trigger model. As in the
case described in section 5.2.1, consider that H1 requests PCE to case described in Section 5.2.1, consider that H1 requests PCE to
compute an inter-layer path between H1 and H4. There is no TE link compute a path between H1 and H4. There is no TE link in the higher-
in the higher-layer between H2 and H3 before the path computation layer between H2 and H3 before the path computation request.
request.
If PCE judges that a lower-layer LSP needs to be established based PCE is unable to compute a mono-layer path, but may judge that the
on the inter-layer path computation result, a lower-layer LSP is establishment of a lower-layer LSP between H2 and H3 would provide
established during the higher-layer signaling procedure. After PCE adequate connectivity. If the PCE has inter-layer visibility it may
completes inter-layer path computation, PCE sends a reply message return a path that includes hops in the lower layer (H1-H2-L1-L2-H3-
including explicit route to the ingress LSR (PCC). There are two H4), but if it has no visiblity into the lower layer, it may return
ways to express the higher-layer LSP route, which are a multi-layer a path with a loose hop from H2 to H3 (H1-H2-H3(loose)-H4). The
path and a mono-layer path that includes loose hop(s). former is a multi-layer path, and the latter a mono-layer path that
includes loose hops.
In the higher-layer signaling trigger model with a multi-layer path, In the higher-layer signaling trigger model with a multi-layer path,
a high-layer LSP route includes a route for a lower-layer LSP that the LSP route supplied by the PCE includes the route of a lower-
is not yet established. An LSR that is located at the boundary layer LSP that is not yet established. A border LSR that is located
between the higher-layer and lower-layer networks, called a border at the boundary between the higher-layer and lower-layer networks
LSR, receives a higher-layer signaling message and then may start (H2 in this example) receives a higher-layer signaling message,
to setup the lower-layer LSP. Note that it depends on a policy at notices that the next hop is in the lower-layer network, starts to
the border LSR whether the higher-layer signaling triggers a lower- setup the lower-layer LSP as described in [RFC4206]. Note that these
layer LSP setup. An example procedure of the signaling trigger actions depends on a policy at the border LSR. An example procedure
model with a multi-layer path is as follows. of the signaling trigger model with a multi-layer path is as follows.
Oki et al Expires April 2007 10 Oki et al Expires September 2007 9
Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4. Step 1: H1 (PCC) requests PCE to compute a path between H1 and H4.
The request indicates that inter-layer path computation is allowed. The request indicates that inter-layer path computation is allowed.
Step 2: As a result of the inter-layer path computation, PCE judges Step 2: As a result of the inter-layer path computation, PCE judges
that a new lower-layer LSP needs to be established. that a new lower-layer LSP needs to be established.
Step 3: PCE replies to H1 (PCC) with a computed multi-layer route Step 3: PCE replies to H1 (PCC) with a computed multi-layer route
including higher-layer and lower-layer LSP routes. The route may be including higher-layer and lower-layer LSP routes. The route may be
specified as H2-L1-L2-H3-H4, where all hops are strict. specified as H1-H2-L1-L2-H3-H4, where all hops are strict.
Step 4: H1 initiates higher-layer signaling using the computed Step 4: H1 initiates higher-layer signaling using the computed
explicit router of H2-L1-L2-H3-H4. explicit router of H2-L1-L2-H3-H4.
Step 5: The border LSR (H2) that receives the higher-layer Step 5: The border LSR (H2) that receives the higher-layer signaling
signaling message starts lower-layer signaling to establish a message starts lower-layer signaling to establish a lower-layer LSP
lower-layer LSP along the specified lower-layer route of L1-L2-H3. along the specified lower-layer route of H2-L1-L2-H3. That is, the
That is, the border LSR recognizes the hops within the explicit border LSR recognizes the hops within the explicit route that apply
route that apply to the lower-layer network, verifies with local to the lower-layer network, verifies with local policy that a new
policy that a new LSP is acceptable, and establishes the required LSP is acceptable, and establishes the required lower-layer LSP.
lower-layer LSP. Note that it is possible that a suitable lower- Note that it is possible that a suitable lower-layer LSP has already
layer LSP has been established (or become available) between the been established (or become available) between the time that the
time that the computation was performed and the moment when the
higher-layer signaling message reached the border LSR. In this case,
the border LSR may select such a lower-layer LSP without the need
to signal a new LSP provided that the lower-layer LSP satisfies the
explicit route in the higher-layer signaling request.
Step 6: After the lower-layer LSP is established, the higher-layer
signaling continues along the specified higher-layer route of H2-
H3-H4.
On the other hand, in the signaling trigger model with a mono-layer
path, a higher-layer LSP route includes a loose or strict hop to
traverse the lower-layer network between the two border LSRs. In
the strict hop case, a virtual TE link may be advertised, but a
lower-layer LSP is not setup. A border LSR that receives a higher-
layer signaling message needs to determine a path for a new lower-
layer LSP. It applies local policy to verify that a new LSP is
acceptable and then either consults a PCE with responsibility for
the lower-layer network or computes the path by itself, and
initiates signaling to establish a lower-layer LSP. Again, it is
possible that a suitable lower-layer LSP has been established (or
become available) between the time that the higher-layer
computation was performed and the moment when the higher-layer computation was performed and the moment when the higher-layer
signaling message reached the border LSR. In this case, the border signaling message reached the border LSR. In this case, the border
LSR may select such a lower-layer LSP without the need to signal a LSR may select such a lower-layer LSP without the need to signal a
new LSP provided that the lower-layer LSP satisfies the explicit new LSP provided that the lower-layer LSP satisfies the explicit
route in the higher-layer signaling request. Since the higher-layer route in the higher-layer signaling request.
Step 6: After the lower-layer LSP is established, the higher-layer
signaling continues along the specified higher-layer route of H2-H3-
H4 using hierarchical signaling [RFC4206].
On the other hand, in the signaling trigger model with a mono-layer
path, a higher-layer LSP route includes a loose hop to traverse the
lower-layer network between the two border LSRs. A border LSR that
receives a higher-layer signaling message needs to determine a path
for a new lower-layer LSP. It applies local policy to verify that a
new LSP is acceptable and then either consults a PCE with
responsibility for the lower-layer network or computes the path by
itself, and initiates signaling to establish the lower-layer LSP.
Again, it is possible that a suitable lower-layer LSP has already
been established (or become available). In this case, the border LSR
may select such a lower-layer LSP without the need to signal a new
LSP provided that the lower-layer LSP satisfies the explicit route
in the higher-layer signaling request. Since the higher-layer
signaling request used a loose hop without specifying any specifics signaling request used a loose hop without specifying any specifics
of the path within the lower-layer network, the border LSR has of the path within the lower-layer network, the border LSR has
greater freedom to choose a lower-layer LSP than in the previous greater freedom to choose a lower-layer LSP than in the previous
example. example.
Oki et al Expires April 2007 11
The difference between procedures of the signaling trigger model The difference between procedures of the signaling trigger model
with a multi-layer path and a mono-layer path is Step 5. Step 5 of with a multi-layer path and a mono-layer path is Step 5. Step 5 of
the signaling trigger model with a mono layer path is as follows: the signaling trigger model with a mono layer path is as follows:
Step 5' The border LSR (H2) that receives the higher-layer Step 5': The border LSR (H2) that receives the higher-layer
signaling message applies local policy to verify that a new LSP is signaling message applies local policy to verify that a new LSP is
acceptable and then initiates establishment of a lower-layer LSP. acceptable and then initiates establishment of a lower-layer LSP. It
It either consults a PCE with responsibility for the lower-layer either consults a PCE with responsibility for the lower-layer
network or computes the route by itself to expand the loose hop network or computes the route by itself to expand the loose hop
route in the higher-layer path. route in the higher-layer path.
5.2.3. Examples of multi-layer ERO Oki et al Expires September 2007 10
Finally, note that a virtual TE link may have been advertised into
the higher-layer network. This causes the PCE to return a path H1-
H2-H3-H4 where all the hops are strict. But when the higher-layer
signaling message reaches the layer border node H2 (that was
responsible for advertising the virtual TE link) it realizes that
the TE link does not exist yet, and signals the necessary LSP across
the lower-layer network using its own path determination (just as
for a loose hop in the higher layer) before continuing with the
higher-layer signaling.
5.2.3. Examples of Multi-Layer ERO
PCE PCE
^ ^
: :
: :
V V
H1--H2 H3--H4 H1--H2 H3--H4
\ / \ /
L1==L2==L3--L4--L5 L1==L2==L3--L4--L5
| |
| |
L6--L7 L6--L7
\ \
H5--H6 H5--H6
Figure 5 Example of multi-layer network Figure 5: Example of a Multi-Layer Network
This section describes how lower-layer LSP setup is performed in This section describes how lower-layer LSP setup is performed in the
the higher-layer signaling trigger model using an ERO that can higher-layer signaling trigger model using an ERO that can include
include subobjects in both the higher and lower layers. It gives subobjects in both the higher and lower layers. It gives rise to
rise to several options for the ERO when it reaches the last LSR in several options for the ERO when it reaches the last LSR in the
the higher layer network (H2). higher layer network (H2).
1. The next subobject is a loose hop to H3 (mono layer ERO). 1. The next subobject is a loose hop to H3 (mono layer ERO).
2. The next subobject is a strict hop to L1 followed by a loose hop 2. The next subobject is a strict hop to L1 followed by a loose hop
to H3. to H3.
3. The next subobjects are a series of hops (strict or loose) in 3. The next subobjects are a series of hops (strict or loose) in the
the lower-layer network followed by H3. For example, {L1(strict), lower-layer network followed by H3. For example, {L1(strict),
L3(loose), L5(loose), H3(strict)} L3(loose), L5(loose), H3(strict)}
In the first, the lower layer can utilize any LSP tunnel that will In the first example, the lower layer can utilize any LSP tunnel
deliver the end-to-end LSP to H3. In the third case, the lower that will deliver the end-to-end LSP to H3. In the third case, the
layer must select an LSP tunnel that traverses L3 and L5. However, lower layer must select an LSP tunnel that traverses L3 and L5.
this does not mean that the lower layer can or should use an LSP However, this does not mean that the lower layer can or should use
from L1 to L3 and another from L3 to L5. an LSP from L1 to L3 and another from L3 to L5.
6. Choosing between inter-layer path control models 6. Choosing Between Inter-Layer Path Control Models
This section compares the cooperation model between PCE and VNTM, This section compares the cooperation model between PCE and VNTM,
and the higher-layer signaling trigger model, in terms of VNTM and the higher-layer signaling trigger model, in terms of VNTM
functions, border LSR functions, higher-layer signaling time, and functions, border LSR functions, higher-layer signaling time, and
complexity (in terms of number of states and messages). An complexity (in terms of number of states and messages). An
appropriate model is chosen, taking into all these considerations. appropriate model may be chosen by a network operator in different
deployment scenarios taking all these considerations into account.
Oki et al Expires April 2007 12 6.1. VNTM Functions:
6.1. VNTM functions:
In the cooperation model, VNTM functions are required. In this In the cooperation model, VNTM functions are required. In this model,
model, additional overhead communications between PCE and VNTM and communications are required between PCE and VNTM, and between VNTM
between VNTM and a border LSR are required. and a border LSR. VNTM-LSR communication can rely on existing
GMPLS-TE MIB modules. PCE-VNTM communication will be detailed in
further revisions of this document.
Oki et al Expires September 2007 11
In the higher-layer signaling trigger model, no VNTM functions are In the higher-layer signaling trigger model, no VNTM functions are
required, and no such communications are required. required, and no such communications are required.
If VNTM functions are not supported in a multi-layer network, the If VNTM functions are not supported in a multi-layer network, the
higher-layer signaling trigger model has to be chosen. higher-layer signaling trigger model has to be chosen.
The inclusion of VNTM functionality allows better coordination of The inclusion of VNTM functionality allows better coordination of
cross-network LSP tunnels and application of network-wide policy cross-network LSP tunnels and application of network-wide policy
that is not available in the trigger model. that is far harder to apply in the trigger model since it requires
the coordination of policy between multiple border LSRs.
6.2. Border LSR functions: 6.2. Border LSR Functions:
In the higher-layer signaling trigger model, a border LSR must have In the higher-layer signaling trigger model, a border LSR must have
some additional functions. It needs to trigger lower-layer some additional functions. It needs to trigger lower-layer signaling
signaling when a higher-layer path message suggests that lower- when a higher-layer path message suggests that lower-layer LSP setup
layer LSP setup is necessary. The triggering signaling is also is necessary. Note that, if virtual TE links are used, the border
required in the cooperation case when the VNTM support virtual TE LSRs must be capable of triggered signaling.
links. Note that, if only the cooperation model is applied, it is
required that a PCE knows whether a link is a regular TE link or
virtual TE link.
If the ERO in the higher-layer Path message uses a mono-layer path If the ERO in the higher-layer Path message uses a mono-layer path
or specifies loose hop, a border LSR receiving the Path message or specifies a loose hop, the border LSR receiving the Path message
MUST obtain a lower-layer route either by consulting PCE or by must obtain a lower-layer route either by consulting a PCE or by
using its own computation engine. If the ERO in the higher-layer using its own computation engine. If the ERO in the higher-layer
Path message uses multi-layer path, the border LSR MUST judge Path message uses a multi-layer path, the border LSR must judge
whether lower-layer signaling is needed. whether lower-layer signaling is needed.
In the cooperation model, no additional function for triggered In the cooperation model, no additional function for triggered
signaling in border LSRs is required except when virtual TE links signaling is required in border LSRs except when virtual TE links
are used. Therefore, if these additional functions are not are used. Therefore, if these additional functions are not supported
supported in border LSRs, the cooperation model, where a border LSR in border LSRs, where a border LSR is controlled by VNTM to set up a
is controlled by VNTM to set up a lower-layer LSP, has to be chosen. lower-layer LSP, the cooperation model has to be chosen.
6.3. Complete inter-layer LSP setup time: 6.3. Complete Inter-Layer LSP Setup Time:
Complete inter-layer LSP setup time includes inter-layer path Complete inter-layer LSP setup time includes inter-layer path
computation, signaling, and communication time between PCC and PCE, computation, signaling, and communication time between PCC and PCE,
PCE and VNTM, and VNTM and LSR. In the cooperation model, the PCE and VNTM, and VNTM and LSR. In the cooperation model, the
additional communication steps are required compared with the additional communication steps are required compared with the
higher-layer signaling trigger model. On the other hand, the higher-layer signaling trigger model. On the other hand, the
cooperation model provides better control at the cost of a longer cooperation model provides better control at the cost of a longer
service setup time. service setup time.
Note that, in terms of higher-layer signaling time, in the higher- Note that, in terms of higher-layer signaling time, in the higher-
layer signaling trigger model, the required time from when higher- layer signaling trigger model, the required time from when higher-
layer signaling starts to when it is completed, is more than that layer signaling starts to when it is completed, is more than that of
the cooperation model except when a virtual TE link is included.
Oki et al Expires April 2007 13 This is because the former model requires lower-layer signaling to
of the cooperation model except when any virtual TE link is take place during the higher-layer signaling. A higher-layer ingress
included. This is because the former model requires lower-layer LSR has to wait for more time until the higher-layer signaling is
signaling to take place during the higher-layer signaling. A completed. A higher-layer ingress LSR is required to be tolerant of
higher-layer ingress LSR has to wait for more time until the longer path setup times.
higher-layer signaling is completed. A higher-layer ingress LSR is
required to be tolerant of longer path setup times.
An appropriate model is chosen, taking into all of the above
considerations.
6.4. Network complexity 6.4. Network Complexity
If the higher and lower layer networks have multiple interconnects If the higher and lower layer networks have multiple interconnects
then optimal path computation for end-to-end LSPs that cross the then optimal path computation for end-to-end LSPs that cross the
layer boundaries is non-trivial. The higher layer LSP must be layer boundaries is non-trivial. The higher layer LSP must be routed
routed to the correct layer border nodes to achieve optimality in to the correct layer border nodes to achieve optimality in both
both layers. layers.
Oki et al Expires September 2007 12
Where the lower layer LSPs are advertised into the higher layer Where the lower layer LSPs are advertised into the higher layer
network as TE links, the computation can be resolved in the higher network as TE links, the computation can be resolved in the higher
layer network. Care needs to be taken in the allocation of TE layer network. Care needs to be taken in the allocation of TE
metrics (i.e., costs) to the lower layer LSPs as they are metrics (i.e., costs) to the lower layer LSPs as they are advertised
advertised as TE links into the higher layer network, and this as TE links into the higher layer network, and this might be a
might be an issue for a VNT Manager component. function for a VNT Manager component. Similarly, attention should be
given to the fact that the LSPs crossing the lower-layer network
might share points of common failure (e.g., they might traverse the
same link in the lower-layer network) and the shared risk link
groups (SRLGs) for the TE links advertised in the higher-layer must
be set accordingly.
In the single PCE model an end-to-end path can be found in a single In the single PCE model an end-to-end path can be found in a single
computation because there is full visibility into both layers and computation because there is full visibility into both layers and
all possible paths through all layer interconnects can be all possible paths through all layer interconnects can be considered.
considered.
Where PCEs cooperate to determine a path, an iterative computation Where PCEs cooperate to determine a path, an iterative computation
model such as [BRPC] can be used to select an optimal path across model such as [BRPC] can be used to select an optimal path across
layers. layers.
When non-cooperating mono-layer PCEs, each of which is in each When non-cooperating mono-layer PCEs, each of which is in a separate
layer, are used with a triggered LSP model, it is not possible to layer, are used with the triggered LSP model, it is not possible to
determine the best border LSRs, and connectivity cannot even be determine the best border LSRs, and connectivity cannot even be
guaranteed. In this case, signaling crankback techniques [CRANK] guaranteed. In this case, signaling crankback techniques [CRANK] can
can be used to eventually achieve connectivity, but optimality is be used to eventually achieve connectivity, but optimality is far
far harder to achieve. In this model, a PCE that is requested to harder to achieve. In this model, a PCE that is requested by an
compute a path by an ingress LSR expects a border LSR to setup a ingress LSR to compute a path expects a border LSR to setup a lower-
lower-layer path triggered by high-layer signaling when there is no layer path triggered by high-layer signaling when there is no TE
TE link between border LSRs. link between border LSRs.
7. Security Considerations 6.5. Separation of Layer Management
Inter-layer traffic engineering with PCE may raise new security Many network operators may want to provide a clear separation
issues in both inter-layer path control models. between the management of the different layer networks. In some
cases, the lower layer network may come from a separate commercial
arm of an organization or from a different corporate body entirely.
In these cases, the policy applied to the establishment of LSPs in
the lower-layer network and to the advertisement of these LSPs as TE
links in the higher-layer network will reflect commercial agreements
and security concerns (see next section). Since the capacity of the
LSPs in the lower-layer network are likely to be significantly
larger than those in the client higher-layer network (multiplex-
server model), the administrator of the lower-layer network may want
to exercise caution before allowing a single small demand in the
higher layer to tie up valuable resources in the lower layer.
In the cooperation model between PCE and VNTM, when PCE judges a The necessary policy points for this separation of administration
new lower-layer LSP, communications between PCE and VNTM and and management are more easily achieved through the VNTM approach
between VNTM and a border LSR are needed. In this case, there are than by using triggered signaling. In effect, the VNTM is the
some security concerns that need to be addressed for these coordination point for all lower layer LSPs and can be closely tied
to a human operator as well as to policy and billing. Such a model
can also be achieved using triggered signaling.
Oki et al Expires April 2007 14 7. Security Considerations
communications. These communications should have some security
mechanisms to ensure authenticity, privacy and integrity. Inter-layer traffic engineering with PCE raises new security issues
in both inter-layer path control models.
Oki et al Expires September 2007 13
In the cooperation model between PCE and VNTM, when the PCE judges a
new lower-layer LSP, communications between PCE and VNTM and between
VNTM and a border LSR are needed. In this case, there are some
security concerns that need to be addressed for these communications.
These communications should have some security mechanisms to ensure
authenticity, privacy and integrity. In particular, it is important
to protect against false triggers for LSP setup in the lower-layer
network.
In the higher-layer signaling trigger model, there are several In the higher-layer signaling trigger model, there are several
security concerns. First, PCE may inform PCC, which is located in security concerns. First, PCE may inform PCC, which is located in
the higher-layer network, of multi-layer path information that the higher-layer network, of multi-layer path information that
includes an ERO in the lower-layer network, while the PCC may not includes an ERO in the lower-layer network, while the PCC may not
have TE topology visibility into the lower-layer network. This have TE topology visibility into the lower-layer network. This
raises a security concern, where lower-layer hop information is raises a security concern, where lower-layer hop information is
known to transit LSRs supporting a higher-layer LSP. Some security known to transit LSRs supporting a higher-layer LSP. Some security
mechanisms to ensure authenticity, privacy and integrity may be mechanisms to ensure authenticity, privacy and integrity may be used.
used.
Security issues may also exist when a single PCE is granted full Security issues may also exist when a single PCE is granted full
visibility of TE information that applies to multiple layers. visibility of TE information that applies to multiple layers.
8. Acknowledgment 8. Acknowledgment
We would like to thank Kohei Shiomoto, Ichiro Inoue, Julien Meuric, We would like to thank Kohei Shiomoto, Ichiro Inoue, Julien Meuric,
Jean-Francois Peltier, Young Lee, and Ina Minei for their useful Jean-Francois Peltier, Young Lee, and Ina Minei for their useful
comments. comments.
9. References 9. References
9.1. Normative Reference 9.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to indicate [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
requirements levels", RFC 2119, March 1997. Label Switching Architecture", RFC 3031, January 2001.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
Architecture", RFC 3945, October 2004. Architecture", RFC 3945, October 2004.
[RFC4206] Kompella, K., and Rekhter, Y., "Label Switched Paths [RFC4206] Kompella, K., and Rekhter, Y., "Label Switched Paths (LSP)
(LSP) Hierarchy with Generalized Multi-Protocol Label Switching Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS)
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005. Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4208] G. Swallow et al., "Generalized Multiprotocol Label
Switching (GMPLS) User-Network Interface (UNI): Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE) Support for the
Overlay Model", RFC 4208, October 2005.
[RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation [RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006. Element (PCE)-Based Architecture", RFC 4655, August 2006.
9.2. Informative Reference 9.2. Informative Reference
[RFC4657] J. Ash, J.L Le Roux et al., " Path Communication Element
(PCE) Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[RFC4674] JL Le Roux et al., "Requirements for Path Computation
Element (PCE) Discovery", RFC 4674, September 2006.
Oki et al Expires April 2007 15
[MLN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi- [MLN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi-
region networks (MRN)", draft-ietf-ccamp-gmpls-mln-reqs (work in region networks (MRN)", draft-ietf-ccamp-gmpls-mln-reqs (work in
progress). progress).
[PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication [PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication
Requirements for Inter-Layer Traffic Engineering", draft-ietf-pce- Requirements for Inter-Layer Traffic Engineering", draft-ietf-pce-
inter-layer-req (work in progress). inter-layer-req (work in progress).
[PCEP] JP. Vasseur et al, "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep
(work in progress).
[BRPC] JP. Vasseur et al., "A Backward Recursive PCE-based [BRPC] JP. Vasseur et al., "A Backward Recursive PCE-based
Computation (BRPC) procedure to compute shortest inter-domain Computation (BRPC) procedure to compute shortest inter-domain
Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc (work
(work in progress). in progress).
[CRANK] A. Farrel et al., "Crankback Signaling Extensions for MPLS [CRANK] A. Farrel et al., "Crankback Signaling Extensions for MPLS
and GMPLS RSVP-TE", draft-ietf-ccamp-crankback (work in progress). and GMPLS RSVP-TE", draft-ietf-ccamp-crankback (work in progress).
Oki et al Expires September 2007 14
10. Authors' Addresses 10. Authors' Addresses
Eiji Oki Eiji Oki
NTT NTT
3-9-11 Midori-cho, 3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan Musashino-shi, Tokyo 180-8585, Japan
Email: oki.eiji@lab.ntt.co.jp Email: oki.eiji@lab.ntt.co.jp
Jean-Louis Le Roux Jean-Louis Le Roux
France Telecom R&D, France Telecom R&D,
Av Pierre Marzin, Av Pierre Marzin,
22300 Lannion, France 22300 Lannion, France
Email: jeanlouis.leroux@orange-ft.com Email: jeanlouis.leroux@orange-ftgroup.com
Adrian Farrel Adrian Farrel
Old Dog Consulting Old Dog Consulting
Email: adrian@olddog.co.uk Email: adrian@olddog.co.uk
11. Intellectual Property Statement 11. Intellectual Property Statement
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Information on the procedures with respect to rights in RFC Information on the procedures with respect to rights in RFC
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Oki et al Expires April 2007 16
specification can be obtained from the IETF on-line IPR repository specification can be obtained from the IETF on-line IPR repository
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The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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Copyright Statement Copyright Statement
Copyright (C) The Internet Society (2006). This document is Copyright (C) The IETF Trust (2007).
subject to the rights, licenses and restrictions contained in BCP
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Oki et al Expires April 2007 17 Oki et al Expires September 2007 15
This document is subject to the rights, licenses and restrictions
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Oki et al Expires September 2007 16
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