draft-ietf-pce-inter-layer-frwk-04.txt   draft-ietf-pce-inter-layer-frwk-05.txt 
Network Working Group Eiji Oki Network Working Group E. Oki
Internet Draft NTT Internet Draft NTT
Category: Informational Jean-Louis Le Roux Category: Informational J-L Le Roux
Expires: January 2008 France Telecom Expires: March 2008 France Telecom
Adrian Farrel A. Farrel
Old Dog Consulting Old Dog Consulting
September 2007
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-04.txt draft-ietf-pce-inter-layer-frwk-05.txt
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents months and may be updated, replaced, or obsoleted by other
at any time. It is inappropriate to use Internet- Drafts as documents at any time. It is inappropriate to use Internet- Drafts
reference material or to cite them other than as "work in progress." as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Abstract Abstract
A network may comprise multiple layers. It is important to globally A network may comprise multiple layers. It is important to
optimize network resource utilization, taking into account all globally optimize network resource utilization, taking into
layers, rather than optimizing resource utilization at each layer account all layers, rather than optimizing resource utilization at
independently. This allows better network efficiency to be achieved each layer independently. This allows better network efficiency to
through a process that we call inter-layer traffic engineering. The be achieved through a process that we call inter-layer traffic
Path Computation Element (PCE) can be a powerful tool to achieve engineering. The Path Computation Element (PCE) can be a powerful
inter-layer traffic engineering. tool to achieve inter-layer traffic engineering.
This document describes a framework for applying the PCE-based This document describes a framework for applying the PCE-based
architecture to inter-layer Multiprotocol Label Switching (MPLS) and architecture to inter-layer Multiprotocol Label Switching (MPLS)
Generalized MPLS (GMPLS) traffic engineering. It provides and Generalized MPLS (GMPLS) traffic engineering. It provides
suggestions for the deployment of PCE in support of multi-layer suggestions for the deployment of PCE in support of multi-layer
networks. This document also describes network models where PCE networks. This document also describes network models where PCE
performs inter-layer traffic engineering, and the relationship performs inter-layer traffic engineering, and the relationship
between PCE and a functional component called the Virtual Network between PCE and a functional component called the Virtual Network
Topology Manager (VNTM). Topology Manager (VNTM).
Table of Contents Table of Contents
1. Introduction....................................................2 1. Introduction....................................................3
1.1. Terminology..................................................3 1.1. Terminology..................................................4
2. Inter-Layer Path Computation....................................3 2. Inter-Layer Path Computation....................................4
3. Inter-layer Path Computation Models.............................5 3. Inter-layer Path Computation Models.............................6
3.1. Single PCE Inter-Layer Path Computation......................5 3.1. Single PCE Inter-Layer Path Computation......................6
3.2. Multiple PCE Inter-Layer Path Computation....................5 3.2. Multiple PCE Inter-Layer Path Computation....................7
3.3. General Observations.........................................6 3.3. General Observations.........................................9
4. Inter-Layer Path Control........................................7 4. Inter-Layer Path Control........................................9
4.1. VNT Management...............................................7 4.1. VNT Management...............................................9
4.2. Inter-Layer Path Control Models..............................7 4.2. Inter-Layer Path Control Models..............................9
4.2.1. Cooperation Model Between PCE and VNTM.....................7 4.2.1. PCE-VNTM Cooperation Model................................10
4.2.2. Higher-Layer Signaling Trigger Model.......................9 4.2.2. Higher-Layer Signaling Trigger Model......................12
4.2.3. Examples of Multi-Layer ERO...............................11 4.2.3. NMS-VNTM Cooperation Model................................15
5. Choosing Between Inter-Layer Path Control Models...............11 4.2.4. Possible Combinations of Inter-Layer Path Computation and
5.1. VNTM Functions:.............................................11 Inter-Layer Path Control Models....................................17
5.2. Border LSR Functions:.......................................12 5. Choosing Between Inter-Layer Path Control Models...............18
5.3. Complete Inter-Layer LSP Setup Time:........................12 5.1. VNTM Functions:.............................................18
5.4. Network Complexity..........................................12 5.2. Border LSR Functions:.......................................19
5.5. Separation of Layer Management..............................13 5.3. Complete Inter-Layer LSP Setup Time:........................20
6. Security Considerations........................................13 5.4. Network Complexity..........................................20
7. Acknowledgment.................................................14 5.5. Separation of Layer Management..............................21
8. References.....................................................14 6. Manageability Considerations...................................21
8.1. Normative Reference.........................................14 6.1. Control of Function and Policy..............................22
8.2. Informative Reference.......................................14 6.1.1. Control of Inter-Layer Computation Function...............22
9. Authors' Addresses.............................................14 6.1.2. Control of Per-Layer Policy...............................22
10. Intellectual Property Statement..............................15 6.1.3. Control of Inter-Layer Policy.............................22
6.2. Information and Data Models.................................23
6.3. Liveness Detection and Monitoring...........................23
6.4. Verifying Correct Operation.................................24
6.5. Requirements on Other Protocols and Functional Components...24
6.6. Impact on Network Operation.................................25
7. Security Considerations........................................25
8. Acknowledgments................................................26
Oki et al Expires March 2008 2
9. References.....................................................26
9.1. Normative Reference.........................................26
9.2. Informative Reference.......................................27
10. Authors・Addresses...........................................28
11. Intellectual Property Statement..............................28
1. Introduction 1. Introduction
A network may comprise multiple layers. These layers may represent A network may comprise multiple layers. These layers may represent
separations of technologies (e.g., packet switch capable (PSC), time separations of technologies (e.g., packet switch capable (PSC),
division multiplex (TDM), or lambda switch capable (LSC)) [RFC3945], time division multiplex (TDM), or lambda switch capable (LSC))
separation of data plane switching granularity levels (e.g., PSC-1, [RFC3945], separation of data plane switching granularity levels
PSC-2, VC4, or VC12) [MLN-REQ], or a distinction between client and (e.g., PSC-1, PSC-2, VC4, or VC12) [MLN-REQ], or a distinction
server networking roles. In this multi-layer network, Label Switched between client and server networking roles. In this multi-layer
Paths (LSPs) in a lower layer are used to carry higher-layer LSPs network, Label Switched Paths (LSPs) in a lower layer are used to
across the lower-layer network. The network topology formed by carry higher-layer LSPs across the lower-layer network. The
lower-layer LSPs and advertised as traffic engineering links (TE network topology formed by lower-layer LSPs and advertised as
links) to the higher layer is called the Virtual Network Topology traffic engineering links (TE links) to the higher layer is called
(VNT) [MLN-REQ]. the 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
inter-layer traffic engineering. This includes mechanisms allowing call inter-layer traffic engineering. This includes mechanisms
the computation of end-to-end paths across layers (known as inter- allowing the computation of end-to-end paths across layers (known
layer path computation), and mechanisms for control and management as inter-layer path computation), and mechanisms for control and
of the Virtual Network Topology (VNT) by setting up and releasing management of the Virtual Network Topology (VNT) by setting up and
LSPs in the lower layers [MLN-REQ]. releasing LSPs in the lower layers [MLN-REQ].
Inter-layer traffic engineering is included in the scope of the Path Inter-layer traffic engineering is included in the scope of the
Computation Element (PCE)-based architecture [RFC4655], and PCE can Path Computation Element (PCE)-based architecture [RFC4655], and
provide a suitable mechanism for resolving inter-layer path PCE can provide a suitable mechanism for resolving inter-layer
computation issues. path computation issues.
Oki et al Expires January 2008 2
PCE Communication Protocol requirements for inter-layer traffic PCE Communication Protocol requirements for inter-layer traffic
engineering are set out in [PCE-INTER-LAYER-REQ]. engineering are set out in [PCE-INTER-LAYER-REQ].
This document describes a framework for applying the PCE-based This document describes a framework for applying the PCE-based
architecture to inter-layer traffic engineering. It provides architecture to inter-layer traffic engineering. It provides
suggestions for the deployment of PCE in support of multi-layer suggestions for the deployment of PCE in support of multi-layer
networks. This document also describes network models where PCE networks. This document also describes network models where 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
management of the VNT, and called the Virtual Network Topology and management of the VNT, called the Virtual Network Topology
Manager (VNTM). Manager (VNTM).
Oki et al Expires March 2008 3
1.1. Terminology 1.1. 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
[RFC3945] and Multi-Layer Networks [MLN-REQ]. (GMPLS) [RFC3945] and Multi-Layer Networks [MLN-REQ].
2. Inter-Layer Path Computation 2. Inter-Layer Path Computation
This section describes key topics of inter-layer path computation in This section describes key topics of inter-layer path computation
MPLS and GMPLS networks. in MPLS and GMPLS networks.
[RFC4206] defines a way to signal a higher-layer LSP, which has an [RFC4206] defines a way to signal a higher-layer LSP, which has an
explicit route that includes hops traversed by LSPs in lower layers. explicit route that includes hops traversed by LSPs in lower
The computation of end-to-end paths across layers is called Inter- layers. The computation of end-to-end paths across layers is
Layer Path Computation. called Inter-Layer 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 topology of the lower-layer, particularly in an information on the topology of the lower-layer, particularly in an
overlay or augmented model deployment, and hence may not be able to overlay or augmented model deployment, and hence may not be able
compute an end-to-end path across layers. to compute an end-to-end path across layers.
PCE-based Inter-Layer Path Computation, consists of using one or PCE-based Inter-Layer Path Computation, consists of using one or
more PCEs to compute an end-to-end path across layers. This could be more PCEs to compute an end-to-end path across layers. This could
achieved by a single PCE path computation where the PCE has topology be achieved by a single PCE path computation where the PCE has
information about multiple layers and can directly compute an end- topology information about multiple layers and can directly
to-end path across layers considering the topology of all of the compute an end-to-end path across layers considering the topology
layers. Alternatively, the inter-layer path computation could be of all of the layers. Alternatively, the inter-layer path
performed as a multiple-PCE computation where each member of a set computation could be performed as a multiple-PCE computation where
of PCEs has information about the topology of one or more layers each member of a set of PCEs has information about the topology of
(but not all layers), and the PCEs collaborate to compute an end-to- one or more layers (but not all layers), and the PCEs collaborate
end path. to compute an end-to-end path.
Consider, for instance, a two-layer network where the higher-layer ----- ----- ----- -----
network is a packet-based IP/MPLS or GMPLS network, and the lower- | LSR |--| LSR |................| LSR |--| LSR |
layer network is a GMPLS optical network. An ingress LSR in the | H1 | | H2 | | H3 | | H4 |
higher-layer network tries to set up an LSP to an egress LSR also in ----- -----\ /----- -----
the higher-layer network across the lower-layer network, and needs a \----- -----/
path in the higher-layer network. However, suppose that there is no | LSR |--| LSR |
TE link in the higher-layer network between the border LSRs located | L1 | | L2 |
on the boundary between the higher-layer and lower-layer networks. ----- -----
Suppose also that the ingress LSR does not have topology visibility
into the lower layer. If a single-layer path computation is applied Figure 1 ・A Simple Example of a Multi-Layer Network.
for the higher-layer, the path computation fails because of the
missing TE link. On the other hand, inter-layer path computation is Consider, for instance, the two-layer network shown in Figure 1,
able to provide a route in the higher-layer and a suggestion that a where the higher-layer network is a packet-based IP/MPLS or GMPLS
lower-layer LSP be set up between the border LSRs. network (LSRs H1, H2, H3, and H4), and the lower-layer network
(LSRs, H2, L1, L2, and H3) is a GMPLS optical network. An ingress
LSR in the higher-layer network (H1) tries to set up an LSP to an
Oki et al Expires March 2008 4
egress LSR (H4) also in the higher-layer network across the
lower-layer network, and needs a path in the higher-layer network.
However, suppose that there is no TE link in the higher-layer
network between the border LSRs located on the boundary between
the higher-layer and lower-layer networks (H2 and H3). Suppose
also that the ingress LSR does not have topology visibility into
the lower layer. If a single-layer path computation is applied for
the higher-layer, the path computation fails because of the
missing TE link. On the other hand, inter-layer path computation
is able to provide a route in the higher-layer (H1-H2-H3-H4) and a
suggestion that a lower-layer LSP be set up between the border
LSRs (H2-L1-L2-H3).
Oki et al Expires January 2008 3
Lower-layer LSPs that are advertised as TE links into the higher- Lower-layer LSPs that are advertised as TE links into the higher-
layer network form a Virtual Network Topology (VNT) that can be used layer network form a Virtual Network Topology (VNT) that can be
for routing higher-layer LSPs. Inter-layer path computation for end- used for routing higher-layer LSPs. Inter-layer path computation
to-end LSPs in the higher-layer network that span the lower-layer for end-to-end LSPs in the higher-layer network that span the
network may utilize the VNT, and PCE is a candidate for computing lower-layer network may utilize the VNT, and PCE is a candidate
the paths of such higher-layer LSPs within the higher-layer network. for computing the paths of such higher-layer LSPs within the
Alternatively, the PCE-based path computation model can: 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 referred information gathered from more than one layer. This mode is
to as Single PCE Computation in [RFC4655]. referred 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
with PCEs responsible for each layer. This mode is referred to as with PCEs responsible for each layer. This mode is referred to as
Multiple PCE Computation with inter-PCE communication in [RFC4655]. Multiple PCE Computation with inter-PCE communication in [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 border LSR that is the entry point to a new end and each transit border LSR that is the entry point to a new
layer. This mode is referred to as Multiple PCE Computation (without layer. This mode is referred to as Multiple PCE Computation
inter-PCE communication) in [RFC4655]. This option utilizes per- (without inter-PCE communication) in [RFC4655]. This option
layer path computation performed independently by successive PCEs. utilizes per-layer path computation performed independently by
successive PCEs.
The PCE invoked by the head-end LSR computes a path that the LSR can The PCE invoked by the head-end LSR computes a path that the LSR
use to signal an MPLS-TE or GMPLS LSP once the path information has can use to signal an MPLS-TE or GMPLS LSP once the path
been converted to an Explicit Route Object (ERO) for use in RSVP-TE information has been converted to an Explicit Route Object (ERO)
signaling. There are two options. 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 lower-layer LSPs to be already established lower-layer LSPs or lower-layer LSPs to be
established on demand. That is, the resulting ERO includes sub- established on demand. That is, the resulting ERO includes sub-
object(s) corresponding to lower-layer hierarchical LSPs expressed object(s) corresponding to lower-layer hierarchical LSPs expressed
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.
The second case is that the PCE computes a path that includes a Oki et al Expires March 2008 5
loose hop that spans the lower-layer network. The higher layer path as the TE link identifiers of the hierarchical LSPs when
computation selects which lower layer network to use, and selects advertised as TE links in the higher-layer network. The TE link
the entry and exit points from that lower-layer network, but does may be a regular TE link that is actually established, or a
not select the path across the lower-layer network. A transit LSR virtual TE link that is not established yet (see [MLN-REQ]). If it
that is the entry point to the lower-layer network is expected to is a virtual TE link, this triggers a setup attempt for a new
expand the loose hop (either itself or relying on the services of a lower-layer LSP when signaling reaches the head-end of the lower-
PCE). The path expansion process on the border LSR may result either layer LSP. Note that the path of a virtual TE link is not
in the selection of an existing lower-layer LSP, or in the necessarily known in advance, and this may require a further
computation and setup of a new lower-layer LSP. (lower-layer) path computation.
- Option 2: Multi-layer path. The PCE computes a "multi-layer" path, The second case is that the PCE computes a path that includes a
i.e., a path that includes TE links from distinct layers [RFC4206]. loose hop that spans the lower-layer network. The higher layer
Such a path can include the complete path of one or more lower-layer path computation selects which lower layer network to use, and
LSPs that already exist or are not yet established. In the latter selects the entry and exit points from that lower-layer network,
but does not select the path across the lower-layer network. A
transit LSR that is the entry point to the lower-layer network 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.
Oki et al Expires January 2008 4 - Option 2: Multi-layer path. The PCE computes a "multi-layer"
case, the signaling of the higher-layer LSP will trigger the path, i.e., a path that includes TE links from distinct layers
establishment of the lower-layer LSPs. [RFC4206]. Such a path can include the complete path of one or
more lower-layer LSPs that already exist or are not yet
established. In the latter case, the signaling of the higher-layer
LSP will trigger the establishment of the lower-layer LSPs.
3. Inter-layer Path Computation Models 3. Inter-layer Path Computation Models
As stated in Section 2, two PCE modes defined in the PCE As stated in Section 2, 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 in the sections that follow. They are discussed in the sections that follow.
3.1. Single PCE Inter-Layer Path Computation 3.1. 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
PCE that has topology visibility into all layers. Such a PCE is single PCE that has topology visibility into all layers. Such a
called a multi-layer PCE. PCE is called a multi-layer PCE.
In Figure 1, the network is comprised of two layers. LSRs H1, H2, H3, In Figure 2, the network is comprised of two layers. LSRs H1, H2,
and H4 belong to the higher layer, and LSRs H2, H3, L1, and L2 H3, and H4 belong to the higher layer, and LSRs H2, H3, L1, and L2
belong to the lower layer. The PCE is a multi-layer PCE that has belong to the lower layer. The PCE is a multi-layer PCE that has
visibility into both layers. It can perform end-to-end path visibility into both layers. It can perform end-to-end path
computation across layers (single PCE path computation). For computation across layers (single PCE path computation). For
instance, it can compute an optimal path H1-H2-L1-L2-H3-H4, for a instance, it can compute an optimal path H1-H2-L1-L2-H3-H4, for a
higher layer LSP from H1 to H4. This path includes the path of a higher layer LSP from H1 to H4. This path includes the path of a
lower layer LSP from H2 to H3, already in existence or not yet lower layer LSP from H2 to H3, already in existence or not yet
established. established.
Oki et al Expires March 2008 6
----- -----
| 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 2: Single PCE Inter-Layer Path Computation
visibility
3.2. Multiple PCE Inter-Layer Path Computation 3.2. 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
topology visibility restricted to its own layer. Some providers may has topology visibility restricted to its own layer. Some
want to keep the layer boundaries due to factors such as providers may want to keep the layer boundaries due to factors
organizational and/or service management issues. The choice for such as organizational and/or service management issues. The
multiple PCE computation instead of single PCE computation may also choice for multiple PCE computation instead of single PCE
be driven by scalability considerations, as in this mode a PCE only computation may also be driven by scalability considerations, as
needs to maintain topology information for one layer (resulting in a in this mode a PCE only needs to maintain topology information for
size reduction for the Traffic Engineering Database (TED)). one layer (resulting in a 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.
In Figure 2, there is one PCE in each layer. The PCEs from each Figure 3 shows multiple PCE inter-layer computation with inter-PCE
communication. 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 田onsult・with PCE Lo to compute paths across the lower layer. PCE
Lo is responsible for path computation in the lower layer. A
Oki et al Expires January 2008 5 simple example of cooperation between the PCEs could be as
Lo is responsible for path computation in the lower layer. A simple follows:
example of cooperation between the PCEs could be as follows:
- LSR H1 sends a request for a path H1-H4 to PCE Hi - LSR H1 sends a request for a path H1-H4 to PCE Hi
- PCE Hi selects H2 as the entry point to the lower layer, and H3 as - PCE Hi selects H2 as the entry point to the lower layer, and H3
the exit point. as the exit point.
- PCE Hi requests a path H2-H3 from PCE Lo. - PCE Hi requests a path H2-H3 from PCE Lo.
- PCE Lo returns H2-L1-L2-H3 to PCE Hi. - PCE Lo returns H2-L1-L2-H3 to PCE Hi.
- PEC Hi is now able to compute the full path (H1-H2-L1-L2-H3-H4) - PEC Hi is now able to compute the full path (H1-H2-L1-L2-H3-H4)
and return it to H1. and return it to H1.
Of course more complex cooperation may be required if an optimal Of course more complex cooperation may be required if an optimal
end-to-end path is desired. end-to-end path is desired.
Oki et al Expires March 2008 7
----- -----
| PCE | | PCE |
| Hi | | Hi |
--+-- --+--
| |
----- ----- | ----- ----- ----- ----- | ----- -----
| LSR |--| LSR |............|...........| LSR |--| LSR | | LSR |--| LSR |............|...........| LSR |--| LSR |
| H1 | | H2 | | | H3 | | H4 | | H1 | | H2 | | | H3 | | H4 |
----- -----\ --+-- /----- ----- ----- -----\ --+-- /----- -----
\ | PCE | / \ | PCE | /
\ | Lo | / \ | Lo | /
\ ----- / \ ----- /
\ / \ /
\----- -----/ \----- -----/
| LSR |--| LSR | | LSR |--| LSR |
| L1 | | L2 | | L1 | | L2 |
----- ----- ----- -----
Figure 2 : Cooperating Mono-Layer PCEs - Multiple PCEs with single- Figure 3: Multiple PCE Inter-Layer Path Computation with Inter-PCE
layer visibility Communication
Figure 4 shows multiple PCE inter-layer path computation without
inter-PCE communication. As described in Section 2, separate path
computations are performed on behalf of the TE-LSP head-end and
each transit border LSR that is the entry point to a new layer.
-----
| PCE |
| Hi |
-----
----- ----- ----- -----
| LSR |--| LSR |........................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ ----- /----- -----
\ | PCE | /
\ | Lo | /
\ ----- /
\ /
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 4: Multiple PCE Inter-layer Path Computation without Inter-
PCE Communication
Oki et al Expires March 2008 8
3.3. General Observations 3.3. General Observations
- Depending on implementation details, the time to perform inter- - Depending on implementation details, the time to perform inter-
layer path computation in the Single PCE inter-layer path layer path computation in the Single PCE inter-layer path
computation model may be less than that of the Multiple PCE model computation model may be less than that of the Multiple PCE model
with cooperating mono-layer PCEs, because there is no requirement to with cooperating mono-layer PCEs, because there is no requirement
exchange messages between cooperating PCEs. to exchange messages between cooperating PCEs.
- When TE topology for all layer networks is visible within one - 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
topology information in one computation than is used by PCEs in the TE topology information in one computation than is used by PCEs in
Multiple PCE path computation model, it requires more computation the Multiple PCE path computation model, it requires more
power and memory. 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
single PCE inter-layer path computation model because the PCE has the single PCE inter-layer path computation model because the PCE
full visibility - the computation is similar to the computation has full visibility ・the computation is similar to the
computation within a single domain of a single layer. In the
Oki et al Expires January 2008 6 multiple PCE inter-layer path computation model, backward
within a single domain of a single layer. In the multiple PCE inter- recursive techniques described in [BRPC] could be used, by
layer path computation model, backward recursive techniques considering layers as separate domains.
described in [BRPC] could be used, by considering layers as separate
domains.
4. Inter-Layer Path Control 4. Inter-Layer Path Control
4.1. VNT Management 4.1. 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 were provisioned across the lower- might be resolved if new LSPs were provisioned across the lower-
layer network. Furthermore, the modification, re-organization and layer network. Furthermore, the modification, re-organization and
new provisioning of lower-layer LSPs may enable better utilization new provisioning of lower-layer LSPs may enable better utilization
of lower-layer network resources given the demands of the higher- of lower-layer network resources given the demands of the higher-
layer network. In other words, the VNT needs to be controlled or layer network. In other words, the VNT needs to be controlled or
managed in cooperation with inter-layer path computation. managed 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 functional element that
and controls the VNT. PCE and VNT Manager are distinct functional manages and controls the VNT. PCE and VNT Manager are distinct
elements that may or may not be co-located. functional elements that may or may not be co-located.
4.2. Inter-Layer Path Control Models 4.2. Inter-Layer Path Control Models
4.2.1. Oki et al Expires March 2008 9
Cooperation Model Between PCE and VNTM 4.2.1. PCE-VNTM Cooperation Model
----- ------ ----- ------
| 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 |
----- ----- ----- -----
Figure 3: Cooperation Model Between PCE and VNTM Figure 5: PCE-VNTM Cooperation Model
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 network, networks. LSRs H1, H2, H3, and H4 belong to the higher-layer
LSRs H2, L1, L2, and H3 belong to the lower-layer network, as shown network, LSRs H2, L1, L2, and H3 belong to the lower-layer network,
in Figure 3. Consider that H1 requests PCE to compute an inter-layer as shown in Figure 5. The case of single PCE inter-layer path
path between H1 and H4. There is no TE link in the higher-layer computation is considered here to explain the cooperation model
between H2 and H3 before the path computation request fails. But the between PCE and VNTM, but multiple PCE path computation with or
PCE may provide information to the VNT Manager responsible for the without inter-PCE communication can also be applied to this model.
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 Consider that H1 requests the PCE to compute an inter-layer path
path computation and is unable to supply a path because there is no between H1 and H4. There is no TE link in the higher-layer between
TE link between H2 and H3. The computation fails, but PCE suggests H2 and H3 before the path computation request, so the request
to VNTM that a lower-layer LSP (H2-H3) could be established to fails. But the PCE may provide information to the VNT Manager
support future LSP requests. Messages from PCE to VNTM contain responsible for the lower layer network that may help resolve the
situation for future higher-layer LSP setup.
Oki et al Expires January 2008 7 The roles of PCE and VNTM are as follows. PCE performs inter-layer
information about the higher-layer demand (from H2 to H3). VNTM uses path computation and is unable to supply a path because there is
local policy and possibly management/configuration input to no TE link between H2 and H3. The computation fails, but PCE
determine how to process the suggestion from PCE, and may request an suggests to VNTM that a lower-layer LSP (H2-H3) could be
ingress LSR (e.g. H2) to establish a lower-layer LSP. VNTM or the established to support future LSP requests. Messages from PCE to
ingress LSR (H2) may themselves use a PCE with visibility into the VNTM contain information about the higher-layer demand (from H2 to
lower layer to compute the path of this new LSP. H3), and may include a suggested path in the lower layer (if the
PCE has visibility into the lower layer network). VNTM uses local
policy and possibly management/configuration input to determine
how to process the suggestion from PCE, and may request an ingress
LSR (e.g. H2) to establish a lower-layer LSP. VNTM or the ingress
LSR (H2) may themselves use a PCE with visibility into the lower
layer to compute the path of this new LSP.
When the higher-layer PCE fails to compute a path and notifies VNTM, Oki et al Expires March 2008 10
it may wait for the lower-layer LSP to be set up and advertised as a When the higher-layer PCE fails to compute a path and notifies
TE link. It could then compute the complete end-to-end path for the VNTM, it may wait for the lower-layer LSP to be set up and
higher-layer LSP and return the result to the PCC. In this case, the advertised as a TE link. PCE may have a timer. After TED is
PCC may be kept waiting for some time, and it is important that the updated within a specified duration, PCE will know a new TE link.
It could then compute the complete end-to-end path for the higher-
layer LSP and return the result to the PCC. In this case, the PCC
may be kept waiting for 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, or that the PCE will be notified by VNTM that no new timely manner, or that the PCE will be notified by VNTM that no
LSP will become available. In any case, if the PCE decides to wait, new LSP will become available. In any case, if the PCE decides to
it must operates a timeout. An example of such a cooperative wait, it must operates a timeout. An example of such a cooperative
procedure between PCE and VNTM is as follows using the exmaple procedure between PCE and VNTM is as follows using the example
network in Figure 3. network in Figure 4.
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.
Step 2: The path computation fails because there is no TE link Step 2: The path computation fails because there is no TE link
across the lower-layer network. across the lower-layer network.
Step 3: PCE suggests to VNTM that a new TE link connecting H2 and H3 Step 3: PCE suggests to VNTM that a new TE link connecting H2 and
would be useful. The PCE notifies VNTM that it will be waiting for H3 would be useful. The PCE notifies VNTM that it will be waiting
the TE link to be created. VNTM considers whether lower-layer LSPs for the TE link to be created. VNTM considers whether lower-layer
should be established if necessary and if acceptable within VNTM's LSPs should be established if necessary and if acceptable within
policy constraints. VNTM痴 policy constraints.
Step 4: VNTM requests an ingress LSR in the lower-layer network Step 4: VNTM requests an ingress LSR in the lower-layer network
(e.g., H2) to establish a lower-layer LSP. The request message may (e.g., H2) to establish a lower-layer LSP. The request message may
include a lower-layer LSP route obtained from the PCE responsible include a lower-layer LSP route obtained from the PCE responsible
for the lower-layer network. for the lower-layer network.
Step 5: The ingress LSR signals to establish the lower-layer LSP. Step 5: The ingress LSR signals to establish the lower-layer LSP.
Step 6: If the lower-layer LSP setup is successful, the ingress LSR Step 6: If the lower-layer LSP setup is successful, the ingress
notifies VNTM that the LSP is complete and supplies the tunnel LSR notifies VNTM that the LSP is complete and supplies the tunnel
information. information.
Step 7: The ingress LSR (H2) advertises the new LSP as a TE link in Step 7: The ingress LSR (H2) advertises the new LSP as a TE link
the higher-layer network routing instance. in the higher-layer network routing instance.
Step 8: PCE notices the new TE link advertisement and recomputes the Step 8: PCE notices the new TE link advertisement and recomputes
requested path. the requested path.
Step 9: 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 as a single hop in includes the already-established lower layer-LSP as a single hop
the higher layer. The higher-layer route is specified as H1-H2-H3-H4, in the higher layer. The higher-layer route is specified as H1-H2-
where all hops are strict. H3-H4, where all hops are strict.
Oki et al Expires March 2008 11
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.
Oki et al Expires January 2008 8 4.2.2. Higher-Layer Signaling Trigger Model
4.2.2.
Higher-Layer Signaling Trigger Model
----- -----
| PCE | | PCE |
----- -----
^ ^
: :
: :
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 6: Higher-layer Signaling Trigger Model
Figure 4 shows the higher-layer signaling trigger model. As in the Figure 6 shows the higher-layer signaling trigger model. The case
case described in Section 4.2.1, consider that H1 requests PCE to of single PCE path computation is considered to explain the
compute a path between H1 and H4. There is no TE link in the higher- higher-layer signaling trigger model here, but multiple PCE path
layer between H2 and H3 before the path computation request. computation with/without inter-PCE communication can also be
applied to this model.
As in the case described in Section 4.2.1, consider that H1
requests PCE to compute a path between H1 and H4. There is no TE
link in the higher-layer between H2 and H3 before the path
computation request.
PCE is unable to compute a mono-layer path, but may judge that the PCE is unable to compute a mono-layer path, but may judge that the
establishment of a lower-layer LSP between H2 and H3 would provide establishment of a lower-layer LSP between H2 and H3 would provide
adequate connectivity. If the PCE has inter-layer visibility it may adequate connectivity. If the PCE has inter-layer visibility it
return a path that includes hops in the lower layer (H1-H2-L1-L2-H3- may return a path that includes hops in the lower layer (H1-H2-L1-
H4), but if it has no visiblity into the lower layer, it may return L2-H3-H4), but if it has no visiblity into the lower layer, it may
a path with a loose hop from H2 to H3 (H1-H2-H3(loose)-H4). The return a path with a loose hop from H2 to H3 (H1-H2-H3(loose)-H4).
former is a multi-layer path, and the latter a mono-layer path that The former is a multi-layer path, and the latter a mono-layer path
includes loose hops. 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
the LSP route supplied by the PCE includes the route of a lower- path, the LSP route supplied by the PCE includes the route of a
layer LSP that is not yet established. A border LSR that is located
at the boundary between the higher-layer and lower-layer networks Oki et al Expires March 2008 12
(H2 in this example) receives a higher-layer signaling message, lower-layer LSP that is not yet established. A border LSR that is
notices that the next hop is in the lower-layer network, starts to located at the boundary between the higher-layer and lower-layer
setup the lower-layer LSP as described in [RFC4206]. Note that these networks (H2 in this example) receives a higher-layer signaling
actions depends on a policy being applied at the border LSR. An message, notices that the next hop is in the lower-layer network,
example procedure of the signaling trigger model with a multi-layer starts to setup the lower-layer LSP as described in [RFC4206].
path is as follows. Note that these actions depends on a policy being applied at the
border LSR. An example procedure of the signaling trigger model
with a multi-layer path is as follows.
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
that a new lower-layer LSP needs to be established. judges 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
specified as H1-H2-L1-L2-H3-H4, where all hops are strict. be 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.
Oki et al Expires January 2008 9 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 H2-L1-L2-
along the specified lower-layer route of H2-L1-L2-H3. That is, the H3. That is, the border LSR recognizes the hops within the
border LSR recognizes the hops within the explicit route that apply explicit route that apply to the lower-layer network, verifies
to the lower-layer network, verifies with local policy that a new with local policy that a new LSP is acceptable, and establishes
LSP is acceptable, and establishes the required lower-layer LSP. the required lower-layer LSP. Note that it is possible that a
Note that it is possible that a suitable lower-layer LSP has already suitable lower-layer LSP has already been established (or become
been established (or become available) between the time that the available) between the time that the computation was performed and
computation was performed and the moment when the higher-layer the moment when the higher-layer signaling message reached the
signaling message reached the border LSR. In this case, the border border LSR. In this case, the border LSR may select such a lower-
LSR may select such a lower-layer LSP without the need to signal a layer LSP without the need to signal a new LSP provided that the
new LSP provided that the lower-layer LSP satisfies the explicit lower-layer LSP satisfies the explicit route in the higher-layer
route in the higher-layer signaling request. signaling request.
Step 6: After the lower-layer LSP is established, the higher-layer Step 6: After the lower-layer LSP is established, the higher-layer
signaling continues along the specified higher-layer route of H2-H3- signaling continues along the specified higher-layer route of H2-
H4 using hierarchical signaling [RFC4206]. H3-H4 using hierarchical signaling [RFC4206].
On the other hand, in the signaling trigger model with a mono-layer On the other hand, in the signaling trigger model with a mono-
path, a higher-layer LSP route includes a loose hop to traverse the layer path, a higher-layer LSP route includes a loose hop to
lower-layer network between the two border LSRs. A border LSR that traverse the lower-layer network between the two border LSRs. A
receives a higher-layer signaling message needs to determine a path border LSR that receives a higher-layer signaling message needs to
for a new lower-layer LSP. It applies local policy to verify that a determine a path for a new lower-layer LSP. It applies local
new LSP is acceptable and then either consults a PCE with policy to verify that a new LSP is acceptable and then either
responsibility for the lower-layer network or computes the path by consults a PCE with responsibility for the lower-layer network or
itself, and initiates signaling to establish the lower-layer LSP. computes the path by itself, and initiates signaling to establish
Again, it is possible that a suitable lower-layer LSP has already
been established (or become available). In this case, the border LSR Oki et al Expires March 2008 13
may select such a lower-layer LSP without the need to signal a new the lower-layer LSP. Again, it is possible that a suitable lower-
LSP provided that the existing lower-layer LSP satisfies the layer LSP has already been established (or become available). In
explicit route in the higher-layer signaling request. Since the this case, the border LSR may select such a lower-layer LSP
higher-layer signaling request used a loose hop without specifying without the need to signal a new LSP provided that the existing
any specifics of the path within the lower-layer network, the border lower-layer LSP satisfies the explicit route in the higher-layer
LSR has greater freedom to choose a lower-layer LSP than in the signaling request. Since the higher-layer signaling request used a
previous example. loose hop without specifying any specifics of the path within the
lower-layer network, the border LSR has greater freedom to choose
a lower-layer LSP than in the previous example.
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. It acceptable and then initiates establishment of a lower-layer LSP.
either consults a PCE with responsibility for the lower-layer It 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.
Finally, note that a virtual TE link may have been advertised into 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- 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 H2-H3-H4 where all the hops are strict. But when the higher-layer
signaling message reaches the layer border node H2 (that was signaling message reaches the layer border node H2 (that was
responsible for advertising the virtual TE link) it realizes that responsible for advertising the virtual TE link) it realizes that
the TE link does not exist yet, and signals the necessary LSP across the TE link does not exist yet, and signals the necessary LSP
the lower-layer network using its own path determination (just as across the lower-layer network using its own path determination
for a loose hop in the higher layer) before continuing with the (just as for a loose hop in the higher layer) before continuing
higher-layer signaling. with the higher-layer signaling.
Oki et al Expires January 2008 10
4.2.3.
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 a Multi-Layer Network Figure 7: Example of a Multi-Layer Network
This section describes how lower-layer LSP setup is performed in the Examples of multi-layer EROs are explained using Figure 7. It is
higher-layer signaling trigger model using an ERO that can include described how lower-layer LSP setup is performed in the higher-
Oki et al Expires March 2008 14
layer signaling trigger model using an ERO that can include
subobjects in both the higher and lower layers. It gives rise to subobjects in both the higher and lower layers. It gives rise to
several options for the ERO when it reaches the last LSR in the several options for the ERO when it reaches the last LSR in 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
to H3. hop to H3.
3. The next subobjects are a series of hops (strict or loose) in the 3. The next subobjects are a series of hops (strict or loose) in
lower-layer network followed by H3. For example, {L1(strict), the 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 example, the lower layer can utilize any LSP tunnel In the first example, the lower layer can utilize any LSP tunnel
that will deliver the end-to-end LSP to H3. In the third case, the that will deliver the end-to-end LSP to H3. In the third case, the
lower layer must select an LSP tunnel that traverses L3 and L5. lower layer must select an LSP tunnel that traverses L3 and L5.
However, this does not mean that the lower layer can or should use However, this does not mean that the lower layer can or should use
an LSP from L1 to L3 and another from L3 to L5. an LSP from L1 to L3 and another from L3 to L5.
4.2.3. NMS-VNTM Cooperation Model
-----
| NMS |
| | -----
----- | PCE |
^ ^ | Hi |
: : -----
: : ^
: : :
: : :
: v v
: ------ ----- ----- ------
: | LSR |--| LSR |........................| LSR |--| LSR |
: | H1 | | H2 | | H3 | | H4 |
: ------ -----\ /----- ------
: ^ \ /
: : \ /
: -------- \ /
v : \ /
------ ----- \----- -----/
| VNTM |<-->| PCE | | LSR |--| LSR |
| | | Lo | | L1 | | L2 |
------ ----- ----- -----
Figure 8: NMS-VNTM Cooperation Model
Figure 8 show the Network Management System (NMS)-VNTM cooperation
model. The NMS manages the upper layer. The case of multiple PCE
computation without inter-PCE communication is used to explain the
Oki et al Expires March 2008 15
NMS-VNTM cooperation model here, but single PCE path computation
could also be applied to this model. Note that multiple PCE path
computation with inter-PCE communication does not fit in with this
model.
The NMS requests a head-end LSR (H1 in this example) to set up a
higher-layer LSP between head-end and tail-end LSRs without
specifying any route. The head-end LSR, which is a PCC, requests
the higher-layer PCE to compute a path between head-end and tail-
end LSRs. There is no TE link in the higher-layer between border
LSRs (H2 and H3 in this example). When the PCE fails to compute a
path, it informs the PCC (i.e. head-end LSR) that notifies the NMS.
The notification may include the information that there is no TE
link between the border LSRs.
Note that it is equally valid for the higher-layer PCE to be
consulted by the NMS rather than by the head-end LSR. In this case,
the result is the same ・the NMS discovers that an end-to-end LSP
cannot be provisioned owing to the lack of a TE link between H2
and H3.
The NMS may now suggest (or request) to the VNTM that a lower-
layer LSP between the border LSRs could be established and could
be advertised as a TE link in the higher layer to support future
higher-layer LSP requests. The communication between the NMS and
the VNTM may be performed in an automatic manner or in a manual
manner, and is a key interaction between layers that may also be
separate administrative domains. Thus, this communication is
potentially a point of application of administrative, billing, and
security policy. The NMS may wait for the lower-layer LSP to be
set up and advertised as a TE link, or may reject the operator's
request for the service that requires the higher-layer LSP with a
suggestion that the operator tries again later.
The VNTM requests the lower-layer PCE to compute a path, and then
requests H2 to establish a lower-layer LSP. Alternatively, the
VNTM may make a direct request to H2 for the LSP, and H2 may
consult the lower-layer PCE. After the NMS is informed or notices
that the lower-layer LSP has been established, it can request the
head-end LSR (H1) to set up the higher-layer end-to-end LSP
between H1 and H4.
Thus, cooperation between the high layer and lower layer is
performed though communication between NMS and VNTM. An example of
such a procedure of the NSM-VNTM cooperation model is as follows
using the example network in Figure 6.
Step 1: NMS requests a head-end LSR (H1) to set up a higher-layer
LSP between H1 and H4 without specifying any route.
Oki et al Expires March 2008 16
Step 2: H1 (PCC) requests PCE to compute a path between H2 and H3.
Step 3: The path computation fails because there is no TE link
across the lower-layer network.
Step 4: H1 (PCC) notifies NMS. The notification may include an
indication that there is no TE link between H2 and H4.
Step 5: NMS suggests (or requests) to VNTM that a new TE link
connecting H2 and H3 would be useful. The NMS notifies VNTM that
it will be waiting for the TE link to be created. VNTM considers
whether lower-layer LSPs should be established if necessary and if
acceptable within VNTM痴 policy constraints.
Step 6: VNTM requests the lower-layer PCE for path computation.
Step 7: VNTM requests the ingress LSR in the lower-layer network
(H2) to establish a lower-layer LSP. The request message includes
a lower-layer LSP route obtained from the lower-layer PCE
responsible for the lower-layer network.
Step 5: H2 signals the lower-layer LSP.
Step 6: If the lower-layer LSP setup is successful, H2 notifies
VNTM that the LSP is complete and supplies the tunnel information.
Step 7: H2 advertises the new LSP as a TE link in the higher-layer
network routing instance.
Step 8: VNTM notifies NMS that the underlying lower-layer LSP has
been set up, and NMS notices the new TE link advertisement.
Step 9: NMS again requests H1 to set up a higher-layer LSP between
H1 and H4.
Step 10: H1 requests the higher-layer PCE to compute a path and
obtains a successful result that includes the higher-layer route
that is specified as H1-H2-H3-H4, where all hops are strict.
Step 11: H1 initiates signaling with the computed path H2-H3-H4 to
establish the higher-layer LSP.
4.2.4. Possible Combinations of Inter-Layer Path Computation and
Inter-Layer Path Control Models
Table 1 summarizes the possible combinations of inter-layer path
computation and inter-layer path control models. There are three
Oki et al Expires March 2008 17
inter-layer path computation models: the single PCE path
computation model; the multiple PCE path computation with inter-
PCE communication model; and the multiple PCE path computation
without inter-PCE communication model. There are also three inter-
layer path control models: the PCE-VNTM cooperation model; the
higher-layer signaling trigger model; and the NMS-VNTM cooperation
model. All the combinations between inter-layer path computation
and path control models, except for the combination of the
multiple PCE path computation with inter-layer PCE communication
model and the NMS-VNTM cooperation model are possible.
Table 1: Possible Combinations of Inter-Layer Path Computation and
Inter-Layer Path Control Models.
----------------------------------------------------
| Path computation | Single | Multiple | Multiple |
| \ | PCE | PCE with | PCE w/o |
| Path control | | inter-PCE | inter-PCE |
|----------------------------------------------------|
| PCE-VNTM | Yes | Yes | Yes |
| cooperation | | | |
|----------------------------+-----------+-----------|
| Higher-layer | Yes | Yes | Yes |
| signaling trigger | | | |
|----------------------------------------------------|
| NMS-VNTM | No* | No | Yes |
| cooperation | | | |
-------------------+--------+-----------+-----------
*Note that, in case of NSM-VNTM cooperation and single PCE inter-
layer path computation, the PCE function used by NMS and VNTM may
be collocated, but it will operate on separate TEDs.
5. Choosing Between Inter-Layer Path Control Models 5. 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 may be chosen by a network operator in different appropriate model may be chosen by a network operator in different
deployment scenarios taking all these considerations into account. deployment scenarios taking all these considerations into account.
5.1. VNTM Functions: 5.1. VNTM Functions:
In the cooperation model, VNTM functions are required. In this model, VNTM functions are required in both the PCE-VNTM cooperation model
and the NMS-VNTM model. In the PCE-VNTM cooperation model,
communications are required between PCE and VNTM, and between VNTM communications are required between PCE and VNTM, and between VNTM
and a border LSR. VNTM-LSR communication can rely on existing GMPLS-
TE MIB modules. PCE-VNTM communication will be detailed in further Oki et al Expires March 2008 18
revisions of this document. and a border LSR. Communications between a higher-layer PCE and
the VNTM are event notifications and may use SNMP notifications
from the PCE MIB modules [PCE-MIB]. Note that communications from
the PCE to the VNTM do not have any acknowledgements.
VNTM-LSR communication can use existing GMPLS-TE MIB modules
[RFC4802]. In the NMS-VNTM cooperation model, communications are
required between NMS and VNTM, between VNTM and a lower-layer PCE,
and between VNTM and a border LSR. NMS-VNTM communications, which
are out of scope of this document, may use proprietary or standard
interfaces, some of which, for example, are standardized in TM
Forum. Communications between VNTM and a lower-layer PCE use PCEP
[PCEP]. VNTM-LSR communications are the same as in the PCE-VNTM
cooperation model.
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.
Oki et al Expires January 2008 11
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 far harder to apply in the trigger model since it requires that is far harder to apply in the trigger model since it requires
the coordination of policy between multiple border LSRs. the coordination of policy between multiple border LSRs.
5.2. Border LSR Functions: 5.2. 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
some additional functions. It needs to trigger lower-layer signaling have some additional functions. It needs to trigger lower-layer
when a higher-layer path message suggests that lower-layer LSP setup signaling when a higher-layer path message suggests that lower-
is necessary. Note that, if virtual TE links are used, the border layer LSP setup is necessary. Note that, if virtual TE links are
LSRs must be capable of triggered signaling. used, the border LSRs must be capable of triggered signaling.
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 a loose hop, the border LSR receiving the Path message or specifies a loose hop, the border LSR receiving the Path
must obtain a lower-layer route either by consulting a PCE or by message must obtain a lower-layer route either by consulting a PCE
using its own computation engine. If the ERO in the higher-layer or by using its own computation engine. If the ERO in the higher-
Path message uses a multi-layer path, the border LSR must judge layer Path message uses a multi-layer path, the border LSR must
whether lower-layer signaling is needed. judge whether lower-layer signaling is needed.
In the cooperation model, no additional function for triggered In the PCE-VNTM cooperation model and the NMS-VNTM model, no
signaling is required in border LSRs except when virtual TE links additional function for triggered signaling is required in border
are used. Therefore, if these additional functions are not supported LSRs except when virtual TE links are used. Therefore, if these
in border LSRs, where a border LSR is controlled by VNTM to set up a additional functions are not supported in border LSRs, where a
lower-layer LSP, the cooperation model has to be chosen. border LSR is controlled by VNTM to set up a lower-layer LSP, the
cooperation model has to be chosen.
Oki et al Expires March 2008 19
5.3. Complete Inter-Layer LSP Setup Time: 5.3. Complete Inter-Layer LSP Setup Time:
The complete inter-layer LSP setup time includes inter-layer path The complete inter-layer LSP setup time includes inter-layer path
computation, signaling, and the communication time between PCC and computation, signaling, and the communication time between PCC and
PCE, PCE and VNTM, and VNTM and LSR. In the cooperation model, the PCE, PCE and VNTM, NSM and VNTM, and VNTM and LSR. In the PCE-VNTM
additional communication steps are required compared with the cooperation model and the NMS-VNTM model, the additional
higher-layer signaling trigger model. On the other hand, the communication steps are required compared with the higher-layer
cooperation model provides better control at the cost of a longer signaling trigger model. On the other hand, the cooperation model
service setup time. provides better control at the cost of a longer 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 of layer signaling starts to when it is completed, is more than that
the cooperation model except when a virtual TE link is included. of the cooperation model except when a virtual TE link is included.
This is because the former model requires lower-layer signaling to This is because the former model requires lower-layer signaling to
take place during the higher-layer signaling. A higher-layer ingress take place during the higher-layer signaling. A higher-layer
LSR has to wait for more time until the higher-layer signaling is ingress LSR has to wait for more time until the higher-layer
completed. A higher-layer ingress LSR is required to be tolerant of signaling is completed. A higher-layer ingress LSR is required to
longer path setup times. be tolerant of longer path setup times.
5.4. Network Complexity 5.4. 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 routed layer boundaries is non-trivial. The higher layer LSP must be
to the correct layer border nodes to achieve optimality in both routed to the correct layer border nodes to achieve optimality in
layers. both layers.
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 advertised metrics (i.e., costs) to the lower layer LSPs as they are
as TE links into the higher layer network, and this might be a advertised as TE links into the higher layer network, and this
function for a VNT Manager component. Similarly, attention should be might be a function for a VNT Manager component. Similarly,
attention should be given to the fact that the LSPs crossing the
Oki et al Expires January 2008 12 lower-layer network might share points of common failure (e.g.,
given to the fact that the LSPs crossing the lower-layer network they might traverse the same link in the lower-layer network) and
might share points of common failure (e.g., they might traverse the the shared risk link groups (SRLGs) for the TE links advertised in
same link in the lower-layer network) and the shared risk link the higher-layer must be set accordingly.
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
computation because there is full visibility into both layers and single computation because there is full visibility into both
all possible paths through all layer interconnects can be considered. layers and all possible paths through all layer interconnects can
be 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 a separate Oki et al Expires March 2008 20
layer, are used with the triggered LSP model, it is not possible to When non-cooperating mono-layer PCEs, each of which is in a
determine the best border LSRs, and connectivity cannot even be separate layer, are used with the triggered LSP model, it is not
guaranteed. In this case, signaling crankback techniques [CRANK] can possible to determine the best border LSRs, and connectivity
be used to eventually achieve connectivity, but optimality is far cannot even be guaranteed. In this case, signaling crankback
harder to achieve. In this model, a PCE that is requested by an techniques [CRANK] can be used to eventually achieve connectivity,
ingress LSR to compute a path expects a border LSR to setup a lower- but optimality is far harder to achieve. In this model, a PCE that
layer path triggered by high-layer signaling when there is no TE is requested by an ingress LSR to compute a path expects a border
link between border LSRs. LSR to setup a lower-layer path triggered by high-layer signaling
when there is no TE link between border LSRs.
5.5. Separation of Layer Management 5.5. Separation of Layer Management
Many network operators may want to provide a clear separation Many network operators may want to provide a clear separation
between the management of the different layer networks. In some between the management of the different layer networks. In some
cases, the lower layer network may come from a separate commercial cases, the lower layer network may come from a separate commercial
arm of an organization or from a different corporate body entirely. arm of an organization or from a different corporate body entirely.
In these cases, the policy applied to the establishment of LSPs in 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 the lower-layer network and to the advertisement of these LSPs as
links in the higher-layer network will reflect commercial agreements TE links in the higher-layer network will reflect commercial
and security concerns (see next section). Since the capacity of the agreements and security concerns (see next section). Since the
LSPs in the lower-layer network are likely to be significantly capacity of the LSPs in the lower-layer network are likely to be
larger than those in the client higher-layer network (multiplex- significantly larger than those in the client higher-layer network
server model), the administrator of the lower-layer network may want (multiplex-server model), the administrator of the lower-layer
to exercise caution before allowing a single small demand in the network may want to exercise caution before allowing a single
higher layer to tie up valuable resources in the lower layer. small demand in the higher layer to tie up valuable resources in
the lower layer.
The necessary policy points for this separation of administration The necessary policy points for this separation of administration
and management are more easily achieved through the VNTM approach and management are more easily achieved through the VNTM approach
than by using triggered signaling. In effect, the VNTM is the than by using triggered signaling. In effect, the VNTM is the
coordination point for all lower layer LSPs and can be closely tied coordination point for all lower layer LSPs and can be closely
to a human operator as well as to policy and billing. Such a model tied to a human operator as well as to policy and billing. Such a
can also be achieved using triggered signaling. model can also be achieved using triggered signaling.
6. Security Considerations 6. Manageability Considerations
Inter-layer traffic engineering with PCE raises new security issues Inter-layer MPLS or GMPLS traffic engineering must be considered
in both inter-layer path control models. in the light of administrative and management boundaries that are
likely to coincide with the technology layer boundaries. That is,
each layer network may possibly be under separate management
control with different policies applied to the networks, and
specific policy rules applied at the boundaries between the layers.
In the cooperation model between PCE and VNTM, when the PCE judges a Management mechanisms are required to make sure that inter-layer
new lower-layer LSP, communications between PCE and VNTM and between traffic engineering can be applied without violating the policy
VNTM and a border LSR are needed. In this case, there are some and administrative operational procedures used by the network
security concerns that need to be addressed for these communications. operators.
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.
Oki et al Expires January 2008 13 Oki et al Expires March 2008 21
In the higher-layer signaling trigger model, there are several 6.1. Control of Function and Policy
security concerns. First, PCE may inform PCC, which is located in
the higher-layer network, of multi-layer path information that 6.1.1. Control of Inter-Layer Computation Function
includes an ERO in the lower-layer network, while the PCC may not
have TE topology visibility into the lower-layer network. This PCE implementations that are capable of supporting inter-layer
raises a security concern, where lower-layer hop information is computations should provide a configuration switch to allow
known to transit LSRs supporting a higher-layer LSP. Some security support of inter-layer path computations to be enabled or disabled.
mechanisms to ensure authenticity, privacy and integrity may be used.
When a PCE is capable of, and configured for, inter-layer path
computation, it should advertise this capability as described in
[PCE-INTER-LAYER-REQ], but this advertisement may be suppressed
through a secondary configuration option.
6.1.2. Control of Per-Layer Policy
Where each layer is operated as a separate network, the operators
must have control over the policies applicable to each network,
and that control should be independent of the control of policies
for other networks.
Where multiple layers are operated as part of the same network,
the operator may have a single point of control for an integrated
policy across all layers, or may have control of separate policies
for each layer.
6.1.3. Control of Inter-Layer Policy
Probably the most important issue for inter-layer traffic
engineering is inter-layer policy. This may cover issues such as
under what circumstances a lower layer LSP may be established to
provide connectivity in the higher layer network. Inter-layer
policy may exist to protect the lower layer (high capacity)
network from very dynamic changes in micro-demand in the higher
layer network. It may also be used to ensure appropriate billing
for the lower layer LSPs.
Inter-layer policy SHOULD include the definition of the points of
connectivity between the network layers, the inter-layer TE model
to be applied (for example, the selection between the models
described in this document), and the rules for path computation
and LSP setup. Where inter-layer policy is defined, it MUST be
used consistently throughout the network, and SHOULD be made
available to the PCEs that perform inter-layer computation so that
appropriate paths are computed. Mechanisms for providing policy
information to PCEs are discussed in [PCE-POLICY].
VNTM may provide a suitable functional component for the
implementation of inter-layer policy. Use of VNTM allows the
administrator of the lower layer network to apply inter-layer
Oki et al Expires March 2008 22
policy without making that policy public to the operator of the
higher layer network. Similarly, a cooperative PCE model (with or
without inter-PCE communication) allows separate application of
policy during the selection of paths.
6.2. Information and Data Models
Any protocol extensions to support inter-layer computations MUST
be accompanied by the definition of MIB objects for the control
and monitoring of the protocol extensions. These MIB object
definitions will conventionally be placed in a separate document
from that which defines the protocol extensions. The MIB objects
MAY be provided in the same MIB module as used for the management
of the base protocol that is being extended.
Note that inter-layer PCE functions SHOULD, themselves, be
manageable through MIB modules. In general, this means that the
MIB modules for managing PCEs SHOULD include objects that can be
used to select and report on the inter-layer behavior of each PCE.
It MAY also be appropriate to provide statistical information that
reports on the inter-layer PCE interactions.
Where there are communications between a PCE and VNTM, additional
MIB modules MAY be necessary to manage and model these
communications. On the other hand, if these communications are
provided through MIB notifications, then those notifications MUST
form part of a MIB module definition.
Policy Information Base (PIB) modules MAY also be appropriate to
meet the requirements as described in Section 6.1 and [PCE-POLICY].
6.3. Liveness Detection and Monitoring
Liveness detection and monitoring is required between PCEs and
PCCs, and between cooperating PCEs as described in [RFC4657].
Inter-layer traffic engineering does not change this requirement.
Where there are communications between a PCE and VNTM, additional
liveness detection and monitoring MAY be required to allow the PCE
to know whether the VNTM has received its information about failed
path computations and desired TE links.
When a lower layer LSP fails (perhaps because of the failure of a
lower layer network resource) or is torn down as a result of lower
layer network policy, the consequent change SHOULD be reported to
the higher layer as a change in the VNT, although inter-layer
policy MAY dictate that such a change is hidden from the higher
layer. The upper layer network MAY additionally operate data plane
failure techniques over the virtual TE links in the VNT in order
Oki et al Expires March 2008 23
to monitor the liveness of the connections, but it should be noted
that if the virtual TE link is advertised but not yet established
as an LSP in the lower layer, such higher layer OAM techniques
will report a failure.
6.4. Verifying Correct Operation
The correct operation of the PCE computations and interactions are
described in [RFC4657], [PCEP], etc., and does not need further
discussion here.
The correct operation of inter-layer traffic engineering may be
measured in several ways. First, the failure rate of higher layer
path computations owing to an absence of connectivity across the
lower layer may be observed as a measure of the effectiveness of
the VNT and MAY be reported as part of the data model described in
Section 6.2. Second, the rate of change of the VNT (i.e., the rate
of establishment and removal of higher layer TE links based on
lower layer LSPs) may be seen as a measure of the correct planning
of the VNT and MAY also form part of the data model described in
Section 6.2. Third, network resource utilization in the lower
layer (both in terms of resource congestion, and in consideration
of under utilization of LSPs set up to support virtual TE links)
can indicate whether effective inter-layer traffic engineering is
being applied.
Management tools in the higher layer network SHOULD provide a view
of which TE links are provided using planned lower layer capacity
(that is, physical connectivity or permanent connections) and
which TE links are dynamic and achieved through inter-layer
traffic engineering. Management tools in the lower layer SHOULD
provide a view of the use to which lower layer LSPs are put
including whether they have been set up to support TE links in a
VNT, and if so for which client network.
6.5. Requirements on Other Protocols and Functional Components
There are no protocols or protocol extensions defined in this
document and so it is not appropriate to consider specific
interactions with other protocols. It should be noted, however,
that the objective of this document is to enable inter-layer
traffic engineering for MPLS-TE and GMPLS networks and so it is
assumed that the necessary features for inter-layer operation of
routing and signaling protocols are in existence or will be
developed.
This document introduces roles for various network components (PCE,
LSR, NMS, and VNTM). Those components are all required to play
their part in order that inter-layer TE can be effective. That is,
Oki et al Expires March 2008 24
an inter-layer TE model that assumes the presence and operation of
any of these functional components obviously depends on those
components to fulfill their roles as described in this document.
6.6. Impact on Network Operation
The use of a PCE to compute inter-layer paths is expected to have
a significant and beneficial impact on network operations. Inter-
layer traffic engineering of itself may provide additional
flexibility to the higher layer network while allowing the lower
layer network to support more and varied client networks in a more
efficient way. Traffic engineering across network layers allows
optimal use to be made of network resources in all layers.
The use of PCE as described in this document may also have a
beneficial effect on the loading of PCEs responsible for
performing inter-layer path computation while facilitating a more
independent operation model for the network layers.
7. Security Considerations
Inter-layer traffic engineering with PCE raises new security
issues in all three inter-layer path control models.
In the cooperation model between PCE and VNTM, when the PCE
determines that a new lower-layer LSP is desirable, communications
are needed between the PCE and VNTM and between VNTM and a border
LSR. In this case, these communications should have security
mechanisms to ensure authenticity, privacy and integrity of the
information exchanged. In particular, it is important to protect
against false triggers for LSP setup in the lower-layer network
since such falsification could tie up lower-layer network
resources (achieving a denial of service attack on the lower-layer
network and on the higher layer network that is attempting to use
it) and could result in incorrect billing for services provided by
the lower-layer network. Where the PCE MIB modules are used to
provide the notification exchanges between the higher-layer PCE
and the VNTM, SNMP v3 should be used to ensure adequate security.
Additionally, the VNTM should provide configurable or dynamic
policy functions so that the VNTM behavior upon receiving
notification from a higher-layer PCE can be controlled.
The main security concern in the higher-layer signaling trigger
model is related to confidentiality. The PCE may inform a higher-
layer PCC about a multi-layer path that includes an ERO in the
lower-layer network, but the PCC may not have TE topology
visibility into the lower-layer network and might not be trusted
with this information. A loose hop across the lower-layer network
Oki et al Expires March 2008 25
could be used, but this decreases the benefit of multi-layer
traffic engineering. A better alternative may be to mask the
lower-layer path using a path key [PATH-KEY] that can be expanded
within the lower-layer network. Consideration must also be given
to filtering the recorded path information from the lower-layer ・
see [RFC4208], for example.
Additionally, in the higher-layer signaling trigger model,
consideration must be given to the security of signaling at the
inter-layer interface since the layers may belong to different
administrative or trust domains.
The NMS-VNTM cooperation model introduces communication between
the NMS and the VNTM. Both of these components belong to the
management plane and the communication is out of scope for this
PCE document. Note that the NMS-VNTM cooperation model may be
considered to address many security and policy concerns because
the control and decision-making is placed within the sphere of
influence of the operator in contrast to the more dynamic
mechanisms of the other models. However, the security issues have
simply moved, and will require authentication of operators and of
policy.
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. Any
access to the single PCE will immediately gain access to the
topology information for all network layers ・effectively, a
single security breach can expose information that requires
multiple breaches in other models.
7. Acknowledgment 8. Acknowledgments
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.
8. References 9. References
8.1. Normative Reference 9.1. Normative Reference
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol [RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
Label Switching Architecture", RFC 3031, January 2001. "Multiprotocol 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 (LSP) [RFC4206] K. Kompella and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS) Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS)
Traffic Engineering (TE)", RFC 4206, October 2005. Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation Oki et al Expires March 2008 26
Element (PCE)-Based Architecture", RFC 4655, August 2006. 9.2. Informative Reference
8.2. Informative Reference
[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).
[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 (work Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc
in progress). (work 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", RFC 4920, July 2007.
9. Authors' Addresses [PCE-MIB] E. Stephan, "Definitions of Textual Conventions for Path
Computation Element", draft-ietf-pce-tc-mib.txt (work in progress).
[RFC4802] A. Farrel and T. Nadeau, "Generalized Multiprotocol
Label Switching (GMPLS) Traffic Engineering Management Information
Base", RFC 4802, February 2007.
[PATH-KEY] Bradford, R., Vasseur, JP., and Farrel, A., "Preserving
Topology Confidentiality in Inter-Domain Path Computation Using a
Key Based Mechanism", draft-ietf-pce-path-key, work in progress.
[RFC4208] Swallow, G., Drake, J., Ishimatsu, H., and Rekhter, Y.,
" 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
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4657] J. Ash and J.L. Le Roux (Ed.), "Path Computation Element
(PCE) Communication Protocol Generic Requirements", RFC 4657,
September 2006.
[PCE-POLICY] Bryskin, I., Papadimitriou, P., and Berger, L.,
"Policy-Enabled Path Computation Framework", draft-ietf-pce-
policy-enabled-path-comp, (work in progress).
[PCEP] JP. Vasseur et al, "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep
(work in progress).
Oki et al Expires March 2008 27
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
Oki et al Expires January 2008 14
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-ftgroup.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
10. Intellectual Property Statement 11. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed Intellectual Property Rights or other rights that might be claimed
to pertain to the implementation or use of the technology described to pertain to the implementation or use of the technology
in this document or the extent to which any license under such described in this document or the extent to which any license
rights might or might not be available; nor does it represent that under such rights might or might not be available; nor does it
it has made any independent effort to identify any such rights. represent that it has made any independent effort to identify any
Information on the procedures with respect to rights in RFC such rights. Information on the procedures with respect to rights
documents can be found in BCP 78 and BCP 79. in RFC documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this of such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr. at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention
copyrights, patents or patent applications, or other proprietary any copyrights, patents or patent applications, or other
rights that may cover technology that may be required to implement proprietary rights that may cover technology that may be required
this standard. Please address the information to the IETF at ietf- to implement this standard. Please address the information to the
ipr@ietf.org. IETF at ietf-ipr@ietf.org.
Disclaimer of Validity Disclaimer of Validity
This document and the information contained herein are provided on This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
Oki et al Expires March 2008 28
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE
ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE. FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
Oki et al Expires January 2008 15 Oki et al Expires March 2008 29
 End of changes. 112 change blocks. 
425 lines changed or deleted 937 lines changed or added

This html diff was produced by rfcdiff 1.34. The latest version is available from http://tools.ietf.org/tools/rfcdiff/