draft-ietf-pce-inter-layer-frwk-05.txt   draft-ietf-pce-inter-layer-frwk-06.txt 
Network Working Group E. Oki Network Working Group E. Oki
Internet Draft NTT Internet Draft NTT
Category: Informational J-L Le Roux Category: Informational J-L Le Roux
Expires: March 2008 France Telecom Expires: June 2008 France Telecom
A. Farrel A. Farrel
Old Dog Consulting Old Dog Consulting
September 2007 January 2008
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-05.txt draft-ietf-pce-inter-layer-frwk-06.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
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4.2.2. Higher-Layer Signaling Trigger Model......................12 4.2.2. Higher-Layer Signaling Trigger Model......................12
4.2.3. NMS-VNTM Cooperation Model................................15 4.2.3. NMS-VNTM Cooperation Model................................15
4.2.4. Possible Combinations of Inter-Layer Path Computation and 4.2.4. Possible Combinations of Inter-Layer Path Computation and
Inter-Layer Path Control Models....................................17 Inter-Layer Path Control Models....................................17
5. Choosing Between Inter-Layer Path Control Models...............18 5. Choosing Between Inter-Layer Path Control Models...............18
5.1. VNTM Functions:.............................................18 5.1. VNTM Functions:.............................................18
5.2. Border LSR Functions:.......................................19 5.2. Border LSR Functions:.......................................19
5.3. Complete Inter-Layer LSP Setup Time:........................20 5.3. Complete Inter-Layer LSP Setup Time:........................20
5.4. Network Complexity..........................................20 5.4. Network Complexity..........................................20
5.5. Separation of Layer Management..............................21 5.5. Separation of Layer Management..............................21
6. Manageability Considerations...................................21 6. Stability Considerations.......................................21
6.1. Control of Function and Policy..............................22 7. Manageability Considerations...................................22
6.1.1. Control of Inter-Layer Computation Function...............22 7.1. Control of Function and Policy..............................23
6.1.2. Control of Per-Layer Policy...............................22 7.1.1. Control of Inter-Layer Computation Function...............23
6.1.3. Control of Inter-Layer Policy.............................22 7.1.2. Control of Per-Layer Policy...............................23
6.2. Information and Data Models.................................23 7.1.3. Control of Inter-Layer Policy.............................23
6.3. Liveness Detection and Monitoring...........................23 7.2. Information and Data Models.................................24
6.4. Verifying Correct Operation.................................24 7.3. Liveness Detection and Monitoring...........................24
6.5. Requirements on Other Protocols and Functional Components...24 7.4. Verifying Correct Operation.................................25
6.6. Impact on Network Operation.................................25 7.5. Requirements on Other Protocols and Functional Components...25
7. Security Considerations........................................25 7.6. Impact on Network Operation.................................26
8. Acknowledgments................................................26 8. Security Considerations........................................26
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9. References.....................................................26 9. Acknowledgments................................................27
9.1. Normative Reference.........................................26 10. References...................................................27
9.2. Informative Reference.......................................27 10.1. Normative Reference.........................................27
10. Authors・Addresses...........................................28 10.2. Informative Reference.......................................28
11. Intellectual Property Statement..............................28 11. Authors' Addresses...........................................29
12. Intellectual Property Statement..............................29
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), separations of technologies (e.g., packet switch capable (PSC),
time division multiplex (TDM), or lambda switch capable (LSC)) time division multiplex (TDM), or lambda switch capable (LSC))
[RFC3945], separation of data plane switching granularity levels [RFC3945], separation of data plane switching granularity levels
(e.g., PSC-1, PSC-2, VC4, or VC12) [MLN-REQ], or a distinction (e.g., PSC-1, PSC-2, VC4, or VC12) [MLN-REQ], or a distinction
between client and server networking roles. In this multi-layer between client and server networking roles. In this multi-layer
network, Label Switched Paths (LSPs) in a lower layer are used to network, Label Switched Paths (LSPs) in a lower layer are used to
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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 between PCE and a functional component in charge of the control
and management of the VNT, called the Virtual Network Topology and management of the VNT, called the Virtual Network Topology
Manager (VNTM). Manager (VNTM).
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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 Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS
(GMPLS) [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 This section describes key topics of inter-layer path computation
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----- ----- ----- ----- ----- ----- ----- -----
| 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 1A Simple Example of a Multi-Layer Network. Figure 1: A Simple Example of a Multi-Layer Network.
Consider, for instance, the two-layer network shown in Figure 1, Consider, for instance, the two-layer network shown in Figure 1,
where the higher-layer network is a packet-based IP/MPLS or GMPLS where the higher-layer network is a packet-based IP/MPLS or GMPLS
network (LSRs H1, H2, H3, and H4), and the lower-layer network 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 (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 LSR in the higher-layer network (H1) tries to set up an LSP to an
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egress LSR (H4) also in the higher-layer network across the egress LSR (H4) also in the higher-layer network across the
lower-layer network, and needs a path in the higher-layer network. lower-layer network, and needs a path in the higher-layer network.
However, suppose that there is no TE link in the higher-layer However, suppose that there is no TE link in the higher-layer
network between the border LSRs located on the boundary between network between the border LSRs located on the boundary between
the higher-layer and lower-layer networks (H2 and H3). Suppose the higher-layer and lower-layer networks (H2 and H3). Suppose
also that the ingress LSR does not have topology visibility into also that the ingress LSR does not have topology visibility into
the lower layer. If a single-layer path computation is applied for the lower layer. If a single-layer path computation is applied for
the higher-layer, the path computation fails because of the the higher-layer, the path computation fails because of the
missing TE link. On the other hand, inter-layer path computation 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 is able to provide a route in the higher-layer (H1-H2-H3-H4) and a
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for use in RSVP-TE 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
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as the TE link identifiers of the hierarchical LSPs when as the TE link identifiers of the hierarchical LSPs when
advertised as TE links in the higher-layer network. The TE link advertised as TE links in the higher-layer network. The TE link
may be a regular TE link that is actually established, or a 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 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 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- 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 layer LSP. Note that the path of a virtual TE link is not
necessarily known in advance, and this may require a further necessarily known in advance, and this may require a further
(lower-layer) path computation. (lower-layer) path computation.
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In Figure 2, the network is comprised of two layers. LSRs H1, H2, In Figure 2, the network is comprised of two layers. LSRs H1, H2,
H3, 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.
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----- -----
| 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 |
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one layer (resulting in a size reduction for the Traffic one layer (resulting in a size reduction for the Traffic
Engineering Database (TED)). 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.
Figure 3 shows multiple PCE inter-layer computation with inter-PCE Figure 3 shows multiple PCE inter-layer computation with inter-PCE
communication. There is one PCE in each layer. The PCEs from each 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
田onsult・with PCE Lo to compute paths across the lower layer. PCE "consult" with PCE Lo to compute paths across the lower layer. PCE
Lo is responsible for path computation in the lower layer. A Lo is responsible for path computation in the lower layer. A
simple example of cooperation between the PCEs could be as simple example of cooperation between the PCEs could be as
follows: 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 - PCE Hi selects H2 as the entry point to the lower layer, and H3
as 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.
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----- -----
| PCE | | PCE |
| Hi | | Hi |
--+-- --+--
| |
----- ----- | ----- ----- ----- ----- | ----- -----
| LSR |--| LSR |............|...........| LSR |--| LSR | | LSR |--| LSR |............|...........| LSR |--| LSR |
| H1 | | H2 | | | H3 | | H4 | | H1 | | H2 | | | H3 | | H4 |
----- -----\ --+-- /----- ----- ----- -----\ --+-- /----- -----
\ | PCE | / \ | PCE | /
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\ ----- / \ ----- /
\ / \ /
\----- -----/ \----- -----/
| LSR |--| LSR | | LSR |--| LSR |
| L1 | | L2 | | L1 | | L2 |
----- ----- ----- -----
Figure 4: Multiple PCE Inter-layer Path Computation without Inter- Figure 4: Multiple PCE Inter-layer Path Computation without Inter-
PCE Communication PCE Communication
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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 with cooperating mono-layer PCEs, because there is no requirement
to 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 layersTE 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 - As the single PCE inter-layer path computation model uses more
TE topology information in one computation than is used by PCEs in TE topology information in one computation than is used by PCEs in
the Multiple PCE path computation model, it requires more the Multiple PCE path computation model, it requires more
computation 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 border nodes or links be examined. This is relatively simple in
the single PCE inter-layer path computation model because the PCE the single PCE inter-layer path computation model because the PCE
has full visibility ・the computation is similar to the has full visibility -
- the computation is similar to the
computation within a single domain of a single layer. In the computation within a single domain of a single layer. In the
multiple PCE inter-layer path computation model, backward multiple PCE inter-layer path computation model, backward
recursive techniques described in [BRPC] could be used, by recursive techniques described in [BRPC] could be used, by
considering layers as separate domains. 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
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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 functional element that A VNT Manager (VNTM) is defined as a functional element that
manages and controls the VNT. PCE and VNT Manager are distinct manages and controls the VNT. PCE and VNT Manager are distinct
functional 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
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4.2.1. PCE-VNTM Cooperation Model 4.2.1.
PCE-VNTM Cooperation Model
----- ------ ----- ------
| PCE |--->| VNTM | | PCE |--->| VNTM |
----- ------ ----- ------
^ : ^ :
: : : :
: : : :
v V v V
----- ----- ----- ----- ----- ----- ----- -----
| LSR |----| LSR |................| LSR |----| LSR | | LSR |----| LSR |................| LSR |----| LSR |
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established to support future LSP requests. Messages from PCE to established to support future LSP requests. Messages from PCE to
VNTM contain information about the higher-layer demand (from H2 to VNTM contain information about the higher-layer demand (from H2 to
H3), and may include a suggested path in the lower layer (if the H3), and may include a suggested path in the lower layer (if the
PCE has visibility into the lower layer network). VNTM uses local PCE has visibility into the lower layer network). VNTM uses local
policy and possibly management/configuration input to determine policy and possibly management/configuration input to determine
how to process the suggestion from PCE, and may request an ingress 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 (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 LSR (H2) may themselves use a PCE with visibility into the lower
layer to compute the path of this new LSP. layer to compute the path of this new LSP.
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When the higher-layer PCE fails to compute a path and notifies When the higher-layer PCE fails to compute a path and notifies
VNTM, it may wait for the lower-layer LSP to be set up and VNTM, it may wait for the lower-layer LSP to be set up and
advertised as a TE link. PCE may have a timer. After TED is advertised as a TE link. PCE may have a timer. After TED is
updated within a specified duration, PCE will know a new TE link. 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- 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 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 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 timely manner, or that the PCE will be notified by VNTM that no
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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 Step 3: PCE suggests to VNTM that a new TE link connecting H2 and
H3 would be useful. The PCE notifies VNTM that it will be waiting H3 would be useful. The PCE notifies VNTM that it will be waiting
for the TE link to be created. VNTM considers whether lower-layer for the TE link to be created. VNTM considers whether lower-layer
LSPs should be established if necessary and if acceptable within LSPs should be established if necessary and if acceptable within
VNTMs policy constraints. VNTM's 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 Step 6: If the lower-layer LSP setup is successful, the ingress
LSR notifies VNTM that the LSP is complete and supplies the tunnel LSR notifies VNTM that the LSP is complete and supplies the tunnel
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Step 8: PCE notices the new TE link advertisement and recomputes Step 8: PCE notices the new TE link advertisement and recomputes
the 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 includes the already-established lower layer-LSP as a single hop
in the higher layer. The higher-layer route is specified as H1-H2- in the higher layer. The higher-layer route is specified as H1-H2-
H3-H4, where all hops are strict. H3-H4, where all hops are strict.
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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.
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 |
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adequate connectivity. If the PCE has inter-layer visibility it adequate connectivity. If the PCE has inter-layer visibility it
may return a path that includes hops in the lower layer (H1-H2-L1- may return a path that includes hops in the lower layer (H1-H2-L1-
L2-H3-H4), but if it has no visiblity into the lower layer, it may L2-H3-H4), but if it has no visiblity into the lower layer, it may
return a path with a loose hop from H2 to H3 (H1-H2-H3(loose)-H4). return a path with a loose hop from H2 to H3 (H1-H2-H3(loose)-H4).
The former is a multi-layer path, and the latter a mono-layer path The former is a multi-layer path, and the latter a mono-layer path
that includes loose hops. that includes loose hops.
In the higher-layer signaling trigger model with a multi-layer In the higher-layer signaling trigger model with a multi-layer
path, the LSP route supplied by the PCE includes the route of a path, the LSP route supplied by the PCE includes the route of a
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lower-layer LSP that is not yet established. A border LSR that is lower-layer LSP that is not yet established. A border LSR that is
located at the boundary between the higher-layer and lower-layer located at the boundary between the higher-layer and lower-layer
networks (H2 in this example) receives a higher-layer signaling networks (H2 in this example) receives a higher-layer signaling
message, notices that the next hop is in the lower-layer network, message, notices that the next hop is in the lower-layer network,
starts to setup the lower-layer LSP as described in [RFC4206]. starts to setup the lower-layer LSP as described in [RFC4206].
Note that these actions depends on a policy being applied at the Note that these actions depends on a policy being applied at the
border LSR. An example procedure of the signaling trigger model border LSR. An example procedure of the signaling trigger model
with a multi-layer path is as follows. 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.
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On the other hand, in the signaling trigger model with a mono- On the other hand, in the signaling trigger model with a mono-
layer path, a higher-layer LSP route includes a loose hop to layer path, a higher-layer LSP route includes a loose hop to
traverse the lower-layer network between the two border LSRs. A traverse the lower-layer network between the two border LSRs. A
border LSR that receives a higher-layer signaling message needs to border LSR that receives a higher-layer signaling message needs to
determine a path for a new lower-layer LSP. It applies local determine a path for a new lower-layer LSP. It applies local
policy to verify that a new LSP is acceptable and then either policy to verify that a new LSP is acceptable and then either
consults a PCE with responsibility for the lower-layer network or consults a PCE with responsibility for the lower-layer network or
computes the path by itself, and initiates signaling to establish computes the path by itself, and initiates signaling to establish
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the lower-layer LSP. Again, it is possible that a suitable lower- the lower-layer LSP. Again, it is possible that a suitable lower-
layer LSP has already been established (or become available). In layer LSP has already been established (or become available). In
this case, the border LSR may select such a lower-layer LSP this case, the border LSR may select such a lower-layer LSP
without the need to signal a new LSP provided that the existing without the need to signal a new LSP provided that the existing
lower-layer LSP satisfies the explicit route in the higher-layer lower-layer LSP satisfies the explicit route in the higher-layer
signaling request. Since the higher-layer signaling request used a signaling request. Since the higher-layer signaling request used a
loose hop without specifying any specifics of the path within the loose hop without specifying any specifics of the path within the
lower-layer network, the border LSR has greater freedom to choose lower-layer network, the border LSR has greater freedom to choose
a lower-layer LSP than in the previous example. 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. acceptable and then initiates establishment of a lower-layer LSP.
It 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
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| |
L6--L7 L6--L7
\ \
H5--H6 H5--H6
Figure 7: Example of a Multi-Layer Network Figure 7: Example of a Multi-Layer Network
Examples of multi-layer EROs are explained using Figure 7. It is Examples of multi-layer EROs are explained using Figure 7. It is
described how lower-layer LSP setup is performed in the higher- described how lower-layer LSP setup is performed in the higher-
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layer signaling trigger model using an ERO that can include 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 2. The next subobject is a strict hop to L1 followed by a loose
hop to H3. hop to H3.
3. The next subobjects are a series of hops (strict or loose) in 3. The next subobjects are a series of hops (strict or loose) in
the 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 4.2.3.
NMS-VNTM Cooperation Model
----- -----
| NMS | | NMS |
| | ----- | | -----
----- | PCE | ----- | PCE |
^ ^ | Hi | ^ ^ | Hi |
: : ----- : : -----
: : ^ : : ^
: : : : : :
: : : : : :
skipping to change at line 740 skipping to change at line 745
| VNTM |<-->| PCE | | LSR |--| LSR | | VNTM |<-->| PCE | | LSR |--| LSR |
| | | Lo | | L1 | | L2 | | | | Lo | | L1 | | L2 |
------ ----- ----- ----- ------ ----- ----- -----
Figure 8: NMS-VNTM Cooperation Model Figure 8: NMS-VNTM Cooperation Model
Figure 8 show the Network Management System (NMS)-VNTM cooperation Figure 8 show the Network Management System (NMS)-VNTM cooperation
model. The NMS manages the upper layer. The case of multiple PCE model. The NMS manages the upper layer. The case of multiple PCE
computation without inter-PCE communication is used to explain the computation without inter-PCE communication is used to explain the
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NMS-VNTM cooperation model here, but single PCE path computation NMS-VNTM cooperation model here, but single PCE path computation
could also be applied to this model. Note that multiple PCE path could also be applied to this model. Note that multiple PCE path
computation with inter-PCE communication does not fit in with this computation with inter-PCE communication does not fit in with this
model. model.
The NMS requests a head-end LSR (H1 in this example) to set up a 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 higher-layer LSP between head-end and tail-end LSRs without
specifying any route. The head-end LSR, which is a PCC, requests 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- 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 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 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. 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 The notification may include the information that there is no TE
link between the border LSRs. link between the border LSRs.
Note that it is equally valid for the higher-layer PCE to be 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, 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 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 cannot be provisioned owing to the lack of a TE link between H2
and H3. and H3.
The NMS may now suggest (or request) to the VNTM that a lower- The NMS may now suggest (or request) to the VNTM that a lower-
layer LSP between the border LSRs could be established and could layer LSP between the border LSRs could be established and could
be advertised as a TE link in the higher layer to support future be advertised as a TE link in the higher layer to support future
higher-layer LSP requests. The communication between the NMS and higher-layer LSP requests. The communication between the NMS and
the VNTM may be performed in an automatic manner or in a manual 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 manner, and is a key interaction between layers that may also be
separate administrative domains. Thus, this communication is separate administrative domains. Thus, this communication is
skipping to change at line 791 skipping to change at line 797
between H1 and H4. between H1 and H4.
Thus, cooperation between the high layer and lower layer is Thus, cooperation between the high layer and lower layer is
performed though communication between NMS and VNTM. An example of performed though communication between NMS and VNTM. An example of
such a procedure of the NSM-VNTM cooperation model is as follows such a procedure of the NSM-VNTM cooperation model is as follows
using the example network in Figure 6. using the example network in Figure 6.
Step 1: NMS requests a head-end LSR (H1) to set up a higher-layer Step 1: NMS requests a head-end LSR (H1) to set up a higher-layer
LSP between H1 and H4 without specifying any route. LSP between H1 and H4 without specifying any route.
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Step 2: H1 (PCC) requests PCE to compute a path between H2 and H3. 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 Step 3: The path computation fails because there is no TE link
across the lower-layer network. across the lower-layer network.
Step 4: H1 (PCC) notifies NMS. The notification may include an Step 4: H1 (PCC) notifies NMS. The notification may include an
indication that there is no TE link between H2 and H4. indication that there is no TE link between H2 and H4.
Step 5: NMS suggests (or requests) to VNTM that a new TE link 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 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 it will be waiting for the TE link to be created. VNTM considers
whether lower-layer LSPs should be established if necessary and if whether lower-layer LSPs should be established if necessary and if
acceptable within VNTMs policy constraints. acceptable within VNTM's policy constraints.
Step 6: VNTM requests the lower-layer PCE for path computation. Step 6: VNTM requests the lower-layer PCE for path computation.
Step 7: VNTM requests the ingress LSR in the lower-layer network Step 7: VNTM requests the ingress LSR in the lower-layer network
(H2) to establish a lower-layer LSP. The request message includes (H2) to establish a lower-layer LSP. The request message includes
a lower-layer LSP route obtained from the lower-layer PCE a lower-layer LSP route obtained from the lower-layer PCE
responsible for the lower-layer network. responsible for the lower-layer network.
Step 5: H2 signals the lower-layer LSP. Step 5: H2 signals the lower-layer LSP.
skipping to change at line 834 skipping to change at line 840
Step 9: NMS again requests H1 to set up a higher-layer LSP between Step 9: NMS again requests H1 to set up a higher-layer LSP between
H1 and H4. H1 and H4.
Step 10: H1 requests the higher-layer PCE to compute a path and Step 10: H1 requests the higher-layer PCE to compute a path and
obtains a successful result that includes the higher-layer route obtains a successful result that includes the higher-layer route
that is specified as H1-H2-H3-H4, where all hops are strict. 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 Step 11: H1 initiates signaling with the computed path H2-H3-H4 to
establish the higher-layer LSP. establish the higher-layer LSP.
4.2.4. Possible Combinations of Inter-Layer Path Computation and 4.2.4.
Possible Combinations of Inter-Layer Path Computation and
Inter-Layer Path Control Models Inter-Layer Path Control Models
Table 1 summarizes the possible combinations of inter-layer path Table 1 summarizes the possible combinations of inter-layer path
computation and inter-layer path control models. There are three computation and inter-layer path control models. There are three
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inter-layer path computation models: the single PCE path inter-layer path computation models: the single PCE path
computation model; the multiple PCE path computation with inter- computation model; the multiple PCE path computation with inter-
PCE communication model; and the multiple PCE path computation PCE communication model; and the multiple PCE path computation
without inter-PCE communication model. There are also three inter- without inter-PCE communication model. There are also three inter-
layer path control models: the PCE-VNTM cooperation model; the layer path control models: the PCE-VNTM cooperation model; the
higher-layer signaling trigger model; and the NMS-VNTM cooperation higher-layer signaling trigger model; and the NMS-VNTM cooperation
model. All the combinations between inter-layer path computation model. All the combinations between inter-layer path computation
and path control models, except for the combination of the and path control models, except for the combination of the
multiple PCE path computation with inter-layer PCE communication multiple PCE path computation with inter-layer PCE communication
model and the NMS-VNTM cooperation model are possible. model and the NMS-VNTM cooperation model are possible.
skipping to change at line 889 skipping to change at line 896
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:
VNTM functions are required in both the PCE-VNTM cooperation model VNTM functions are required in both the PCE-VNTM cooperation model
and the NMS-VNTM model. In 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
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and a border LSR. Communications between a higher-layer PCE and and a border LSR. Communications between a higher-layer PCE and
the VNTM are event notifications and may use SNMP notifications the VNTM are event notifications and may use SNMP notifications
from the PCE MIB modules [PCE-MIB]. Note that communications from from the PCE MIB modules [PCE-MIB]. Note that communications from
the PCE to the VNTM do not have any acknowledgements. the PCE to the VNTM do not have any acknowledgements.
VNTM-LSR communication can use existing GMPLS-TE MIB modules VNTM-LSR communication can use existing GMPLS-TE MIB modules
[RFC4802]. In the NMS-VNTM cooperation model, communications are [RFC4802]. In the NMS-VNTM cooperation model, communications are
required between NMS and VNTM, between VNTM and a lower-layer PCE, required between NMS and VNTM, between VNTM and a lower-layer PCE,
and between VNTM and a border LSR. NMS-VNTM communications, which and between VNTM and a border LSR. NMS-VNTM communications, which
are out of scope of this document, may use proprietary or standard are out of scope of this document, may use proprietary or standard
skipping to change at line 938 skipping to change at line 945
layer Path message uses a multi-layer path, the border LSR must layer Path message uses a multi-layer path, the border LSR must
judge whether lower-layer signaling is needed. judge whether lower-layer signaling is needed.
In the PCE-VNTM cooperation model and the NMS-VNTM model, no In the PCE-VNTM cooperation model and the NMS-VNTM model, no
additional function for triggered signaling is required in border additional function for triggered signaling is required in border
LSRs except when virtual TE links are used. Therefore, if these LSRs except when virtual TE links are used. Therefore, if these
additional functions are not supported in border LSRs, where a additional functions are not supported in border LSRs, where a
border LSR is controlled by VNTM to set up a lower-layer LSP, the border LSR is controlled by VNTM to set up a lower-layer LSP, the
cooperation model has to be chosen. cooperation model has to be chosen.
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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, NSM and VNTM, and VNTM and LSR. In the PCE-VNTM PCE, PCE and VNTM, NSM and VNTM, and VNTM and LSR. In the PCE-VNTM
cooperation model and the NMS-VNTM model, the additional cooperation model and the NMS-VNTM model, the additional
communication steps are required compared with the higher-layer communication steps are required compared with the higher-layer
signaling trigger model. On the other hand, the cooperation model signaling trigger model. On the other hand, the cooperation model
provides better control at the cost of a longer service setup time. provides better control at the cost of a longer service setup time.
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In the single PCE model an end-to-end path can be found in a In the single PCE model an end-to-end path can be found in a
single computation because there is full visibility into both single computation because there is full visibility into both
layers and all possible paths through all layer interconnects can layers and all possible paths through all layer interconnects can
be considered. 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.
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When non-cooperating mono-layer PCEs, each of which is in a When non-cooperating mono-layer PCEs, each of which is in a
separate layer, are used with the triggered LSP model, it is not separate layer, are used with the triggered LSP model, it is not
possible to determine the best border LSRs, and connectivity possible to determine the best border LSRs, and connectivity
cannot even be guaranteed. In this case, signaling crankback cannot even be guaranteed. In this case, signaling crankback
techniques [CRANK] can be used to eventually achieve connectivity, techniques [CRANK] can be used to eventually achieve connectivity,
but optimality is far harder to achieve. In this model, a PCE that but optimality is far harder to achieve. In this model, a PCE that
is requested by an ingress LSR to compute a path expects a border is requested by an ingress LSR to compute a path expects a border
LSR to setup a lower-layer path triggered by high-layer signaling LSR to setup a lower-layer path triggered by high-layer signaling
when there is no TE link between border LSRs. when there is no TE link between border LSRs.
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small demand in the higher layer to tie up valuable resources in small demand in the higher layer to tie up valuable resources in
the lower layer. 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 coordination point for all lower layer LSPs and can be closely
tied to a human operator as well as to policy and billing. Such a tied to a human operator as well as to policy and billing. Such a
model can also be achieved using triggered signaling. model can also be achieved using triggered signaling.
6. Manageability Considerations 6. Stability Considerations
Inter-layer traffic engineering needs to be managed and operated
correctly to avoid introducing instability problems.
Lower-layer LSPs are likely, by the nature of the technologies
used in layered networks, to be of considerably higher capacity
than the higher-layer LSPs. This has the benefit of allowing
multiple higher-layer LSPs to be carried across the lower-layer
network in a single lower-layer LSP. However, when a new lower-
layer LSP is set up to support a request for a higher-layer LSP
because there is no suitable route in the higher-layer network, it
may be the case that a very large LSP is established in support of
a very small traffic demand. Further, if the higher-layer LSP is
short-lived, the requirement for the lower-layer LSP will go away
Oki et al Expires June 2008 21
leaving it either in-place but unused, or requiring it to be torn
down. This may cause excessive tie-up of unused lower-layer
network resources, or may introduce instability into the lower-
layer network. It is important that appropriate policy controls or
configuration features are available so that demand-led
establishment of lower-layer LSPs (the so-called "bandwidth on
demand") is filtered according to the requirements of the lower-
layer network.
When a higher-layer LSP is requested to be set up, a new lower-
layer LSP may be established if there is no route with the
requested bandwidth for the higher-layer LSP. After the lower-
layer LSP is established, existing high-layer LSPs could be re-
routed to use the newly established lower-layer LSP if using the
lower-layer LSP provides a better route than that taken by the
existing LSPs. This re-routing may result in lower utilization of
other lower-layer LSPs that used to carry the existing higher-
layer LSPs. When the utilization of a lower-layer LSP drops below
a threshold (or drops to zero), the LSP is deleted according to
lower-layer network policy. But consider that some other new
higher-layer LSP may be requested at once requiring the
establishment or re-establishment of a lower-layer LSP. This, in
turn, may cause higher-layer re-routing making other lower-layer
LSPs under-utilized, in a cyclic manner. This behavior makes the
higher-layer network unstable.
Inter-layer traffic engineering needs to avoid network instability
problems. To solve the problem, network operators may have some
constraints achieved through configuration or policy, where inter-
layer path control actions such as re-routing and deletion of
lower-layer LSPs are not easily allowed. For example, threshold
parameters for the actions are determined so that hysteresis
control behavior can be performed.
7. Manageability Considerations
Inter-layer MPLS or GMPLS traffic engineering must be considered Inter-layer MPLS or GMPLS traffic engineering must be considered
in the light of administrative and management boundaries that are in the light of administrative and management boundaries that are
likely to coincide with the technology layer boundaries. That is, likely to coincide with the technology layer boundaries. That is,
each layer network may possibly be under separate management each layer network may possibly be under separate management
control with different policies applied to the networks, and control with different policies applied to the networks, and
specific policy rules applied at the boundaries between the layers. specific policy rules applied at the boundaries between the layers.
Management mechanisms are required to make sure that inter-layer Management mechanisms are required to make sure that inter-layer
traffic engineering can be applied without violating the policy traffic engineering can be applied without violating the policy
and administrative operational procedures used by the network and administrative operational procedures used by the network
operators. operators.
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6.1. Control of Function and Policy 7.1. Control of Function and Policy
6.1.1. Control of Inter-Layer Computation Function 7.1.1.
Control of Inter-Layer Computation Function
PCE implementations that are capable of supporting inter-layer PCE implementations that are capable of supporting inter-layer
computations should provide a configuration switch to allow computations should provide a configuration switch to allow
support of inter-layer path computations to be enabled or disabled. support of inter-layer path computations to be enabled or disabled.
When a PCE is capable of, and configured for, inter-layer path When a PCE is capable of, and configured for, inter-layer path
computation, it should advertise this capability as described in computation, it should advertise this capability as described in
[PCE-INTER-LAYER-REQ], but this advertisement may be suppressed [PCE-INTER-LAYER-REQ], but this advertisement may be suppressed
through a secondary configuration option. through a secondary configuration option.
6.1.2. Control of Per-Layer Policy 7.1.2.
Control of Per-Layer Policy
Where each layer is operated as a separate network, the operators Where each layer is operated as a separate network, the operators
must have control over the policies applicable to each network, must have control over the policies applicable to each network,
and that control should be independent of the control of policies and that control should be independent of the control of policies
for other networks. for other networks.
Where multiple layers are operated as part of the same network, Where multiple layers are operated as part of the same network,
the operator may have a single point of control for an integrated the operator may have a single point of control for an integrated
policy across all layers, or may have control of separate policies policy across all layers, or may have control of separate policies
for each layer. for each layer.
6.1.3. Control of Inter-Layer Policy 7.1.3.
Control of Inter-Layer Policy
Probably the most important issue for inter-layer traffic Probably the most important issue for inter-layer traffic
engineering is inter-layer policy. This may cover issues such as engineering is inter-layer policy. This may cover issues such as
under what circumstances a lower layer LSP may be established to under what circumstances a lower layer LSP may be established to
provide connectivity in the higher layer network. Inter-layer provide connectivity in the higher layer network. Inter-layer
policy may exist to protect the lower layer (high capacity) policy may exist to protect the lower layer (high capacity)
network from very dynamic changes in micro-demand in the higher network from very dynamic changes in micro-demand in the higher
layer network. It may also be used to ensure appropriate billing layer network (see Section 6). It may also be used to ensure
for the lower layer LSPs. appropriate billing for the lower layer LSPs.
Inter-layer policy SHOULD include the definition of the points of Inter-layer policy SHOULD include the definition of the points of
connectivity between the network layers, the inter-layer TE model connectivity between the network layers, the inter-layer TE model
to be applied (for example, the selection between the models to be applied (for example, the selection between the models
described in this document), and the rules for path computation described in this document), and the rules for path computation
and LSP setup. Where inter-layer policy is defined, it MUST be and LSP setup. Where inter-layer policy is defined, it MUST be
used consistently throughout the network, and SHOULD be made used consistently throughout the network, and SHOULD be made
available to the PCEs that perform inter-layer computation so that available to the PCEs that perform inter-layer computation so that
appropriate paths are computed. Mechanisms for providing policy appropriate paths are computed. Mechanisms for providing policy
information to PCEs are discussed in [PCE-POLICY]. information to PCEs are discussed in [PCE-POLICY].
VNTM may provide a suitable functional component for the VNTM may provide a suitable functional component for the
implementation of inter-layer policy. Use of VNTM allows the implementation of inter-layer policy. Use of VNTM allows the
administrator of the lower layer network to apply inter-layer administrator of the lower layer network to apply inter-layer
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policy without making that policy public to the operator of the policy without making that policy public to the operator of the
higher layer network. Similarly, a cooperative PCE model (with or higher layer network. Similarly, a cooperative PCE model (with or
without inter-PCE communication) allows separate application of without inter-PCE communication) allows separate application of
policy during the selection of paths. policy during the selection of paths.
6.2. Information and Data Models 7.2. Information and Data Models
Any protocol extensions to support inter-layer computations MUST Any protocol extensions to support inter-layer computations MUST
be accompanied by the definition of MIB objects for the control be accompanied by the definition of MIB objects for the control
and monitoring of the protocol extensions. These MIB object and monitoring of the protocol extensions. These MIB object
definitions will conventionally be placed in a separate document definitions will conventionally be placed in a separate document
from that which defines the protocol extensions. The MIB objects from that which defines the protocol extensions. The MIB objects
MAY be provided in the same MIB module as used for the management MAY be provided in the same MIB module as used for the management
of the base protocol that is being extended. of the base protocol that is being extended.
Note that inter-layer PCE functions SHOULD, themselves, be Note that inter-layer PCE functions SHOULD, themselves, be
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Where there are communications between a PCE and VNTM, additional Where there are communications between a PCE and VNTM, additional
MIB modules MAY be necessary to manage and model these MIB modules MAY be necessary to manage and model these
communications. On the other hand, if these communications are communications. On the other hand, if these communications are
provided through MIB notifications, then those notifications MUST provided through MIB notifications, then those notifications MUST
form part of a MIB module definition. form part of a MIB module definition.
Policy Information Base (PIB) modules MAY also be appropriate to Policy Information Base (PIB) modules MAY also be appropriate to
meet the requirements as described in Section 6.1 and [PCE-POLICY]. meet the requirements as described in Section 6.1 and [PCE-POLICY].
6.3. Liveness Detection and Monitoring 7.3. Liveness Detection and Monitoring
Liveness detection and monitoring is required between PCEs and Liveness detection and monitoring is required between PCEs and
PCCs, and between cooperating PCEs as described in [RFC4657]. PCCs, and between cooperating PCEs as described in [RFC4657].
Inter-layer traffic engineering does not change this requirement. Inter-layer traffic engineering does not change this requirement.
Where there are communications between a PCE and VNTM, additional Where there are communications between a PCE and VNTM, additional
liveness detection and monitoring MAY be required to allow the PCE liveness detection and monitoring MAY be required to allow the PCE
to know whether the VNTM has received its information about failed to know whether the VNTM has received its information about failed
path computations and desired TE links. path computations and desired TE links.
When a lower layer LSP fails (perhaps because of the failure of a 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 lower layer network resource) or is torn down as a result of lower
layer network policy, the consequent change SHOULD be reported to layer network policy, the consequent change SHOULD be reported to
the higher layer as a change in the VNT, although inter-layer the higher layer as a change in the VNT, although inter-layer
policy MAY dictate that such a change is hidden from the higher policy MAY dictate that such a change is hidden from the higher
layer. The upper layer network MAY additionally operate data plane layer. The upper layer network MAY additionally operate data plane
failure techniques over the virtual TE links in the VNT in order failure techniques over the virtual TE links in the VNT in order
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to monitor the liveness of the connections, but it should be noted to monitor the liveness of the connections, but it should be noted
that if the virtual TE link is advertised but not yet established that if the virtual TE link is advertised but not yet established
as an LSP in the lower layer, such higher layer OAM techniques as an LSP in the lower layer, such higher layer OAM techniques
will report a failure. will report a failure.
6.4. Verifying Correct Operation 7.4. Verifying Correct Operation
The correct operation of the PCE computations and interactions are The correct operation of the PCE computations and interactions are
described in [RFC4657], [PCEP], etc., and does not need further described in [RFC4657], [PCEP], etc., and does not need further
discussion here. discussion here.
The correct operation of inter-layer traffic engineering may be The correct operation of inter-layer traffic engineering may be
measured in several ways. First, the failure rate of higher layer measured in several ways. First, the failure rate of higher layer
path computations owing to an absence of connectivity across the path computations owing to an absence of connectivity across the
lower layer may be observed as a measure of the effectiveness of 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 the VNT and MAY be reported as part of the data model described in
skipping to change at line 1175 skipping to change at line 1236
Management tools in the higher layer network SHOULD provide a view Management tools in the higher layer network SHOULD provide a view
of which TE links are provided using planned lower layer capacity of which TE links are provided using planned lower layer capacity
(that is, physical connectivity or permanent connections) and (that is, physical connectivity or permanent connections) and
which TE links are dynamic and achieved through inter-layer which TE links are dynamic and achieved through inter-layer
traffic engineering. Management tools in the lower layer SHOULD traffic engineering. Management tools in the lower layer SHOULD
provide a view of the use to which lower layer LSPs are put 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 including whether they have been set up to support TE links in a
VNT, and if so for which client network. VNT, and if so for which client network.
6.5. Requirements on Other Protocols and Functional Components 7.5. Requirements on Other Protocols and Functional Components
There are no protocols or protocol extensions defined in this There are no protocols or protocol extensions defined in this
document and so it is not appropriate to consider specific document and so it is not appropriate to consider specific
interactions with other protocols. It should be noted, however, interactions with other protocols. It should be noted, however,
that the objective of this document is to enable inter-layer that the objective of this document is to enable inter-layer
traffic engineering for MPLS-TE and GMPLS networks and so it is traffic engineering for MPLS-TE and GMPLS networks and so it is
assumed that the necessary features for inter-layer operation of assumed that the necessary features for inter-layer operation of
routing and signaling protocols are in existence or will be routing and signaling protocols are in existence or will be
developed. developed.
This document introduces roles for various network components (PCE, This document introduces roles for various network components (PCE,
LSR, NMS, and VNTM). Those components are all required to play LSR, NMS, and VNTM). Those components are all required to play
their part in order that inter-layer TE can be effective. That is, their part in order that inter-layer TE can be effective. That is,
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an inter-layer TE model that assumes the presence and operation of an inter-layer TE model that assumes the presence and operation of
any of these functional components obviously depends on those any of these functional components obviously depends on those
components to fulfill their roles as described in this document. components to fulfill their roles as described in this document.
6.6. Impact on Network Operation 7.6. Impact on Network Operation
The use of a PCE to compute inter-layer paths is expected to have The use of a PCE to compute inter-layer paths is expected to have
a significant and beneficial impact on network operations. Inter- a significant and beneficial impact on network operations. Inter-
layer traffic engineering of itself may provide additional layer traffic engineering of itself may provide additional
flexibility to the higher layer network while allowing the lower flexibility to the higher layer network while allowing the lower
layer network to support more and varied client networks in a more layer network to support more and varied client networks in a more
efficient way. Traffic engineering across network layers allows efficient way. Traffic engineering across network layers allows
optimal use to be made of network resources in all layers. optimal use to be made of network resources in all layers.
The use of PCE as described in this document may also have a The use of PCE as described in this document may also have a
beneficial effect on the loading of PCEs responsible for beneficial effect on the loading of PCEs responsible for
performing inter-layer path computation while facilitating a more performing inter-layer path computation while facilitating a more
independent operation model for the network layers. independent operation model for the network layers.
7. Security Considerations 8. Security Considerations
Inter-layer traffic engineering with PCE raises new security Inter-layer traffic engineering with PCE raises new security
issues in all three inter-layer path control models. issues in all three inter-layer path control models.
In the cooperation model between PCE and VNTM, when the PCE In the cooperation model between PCE and VNTM, when the PCE
determines that a new lower-layer LSP is desirable, communications determines that a new lower-layer LSP is desirable, communications
are needed between the PCE and VNTM and between VNTM and a border are needed between the PCE and VNTM and between VNTM and a border
LSR. In this case, these communications should have security LSR. In this case, these communications should have security
mechanisms to ensure authenticity, privacy and integrity of the mechanisms to ensure authenticity, privacy and integrity of the
information exchanged. In particular, it is important to protect information exchanged. In particular, it is important to protect
skipping to change at line 1240 skipping to change at line 1301
policy functions so that the VNTM behavior upon receiving policy functions so that the VNTM behavior upon receiving
notification from a higher-layer PCE can be controlled. notification from a higher-layer PCE can be controlled.
The main security concern in the higher-layer signaling trigger The main security concern in the higher-layer signaling trigger
model is related to confidentiality. The PCE may inform a higher- model is related to confidentiality. The PCE may inform a higher-
layer PCC about a multi-layer path that includes an ERO in the layer PCC about a multi-layer path that includes an ERO in the
lower-layer network, but the PCC may not have TE topology lower-layer network, but the PCC may not have TE topology
visibility into the lower-layer network and might not be trusted visibility into the lower-layer network and might not be trusted
with this information. A loose hop across the lower-layer network with this information. A loose hop across the lower-layer network
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could be used, but this decreases the benefit of multi-layer could be used, but this decreases the benefit of multi-layer
traffic engineering. A better alternative may be to mask the traffic engineering. A better alternative may be to mask the
lower-layer path using a path key [PATH-KEY] that can be expanded lower-layer path using a path key [PATH-KEY] that can be expanded
within the lower-layer network. Consideration must also be given within the lower-layer network. Consideration must also be given
to filtering the recorded path information from the lower-layer to filtering the recorded path information from the lower-layer -
-
see [RFC4208], for example. see [RFC4208], for example.
Additionally, in the higher-layer signaling trigger model, Additionally, in the higher-layer signaling trigger model,
consideration must be given to the security of signaling at the consideration must be given to the security of signaling at the
inter-layer interface since the layers may belong to different inter-layer interface since the layers may belong to different
administrative or trust domains. administrative or trust domains.
The NMS-VNTM cooperation model introduces communication between The NMS-VNTM cooperation model introduces communication between
the NMS and the VNTM. Both of these components belong to the the NMS and the VNTM. Both of these components belong to the
management plane and the communication is out of scope for this management plane and the communication is out of scope for this
skipping to change at line 1267 skipping to change at line 1329
considered to address many security and policy concerns because considered to address many security and policy concerns because
the control and decision-making is placed within the sphere of the control and decision-making is placed within the sphere of
influence of the operator in contrast to the more dynamic influence of the operator in contrast to the more dynamic
mechanisms of the other models. However, the security issues have mechanisms of the other models. However, the security issues have
simply moved, and will require authentication of operators and of simply moved, and will require authentication of operators and of
policy. 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. Any visibility of TE information that applies to multiple layers. Any
access to the single PCE will immediately gain access to the access to the single PCE will immediately gain access to the
topology information for all network layers ・effectively, a topology information for all network layers -
- effectively, a
single security breach can expose information that requires single security breach can expose information that requires
multiple breaches in other models. multiple breaches in other models.
8. Acknowledgments Note that, as described in Section 6, inter-layer TE can cause
network stability issues, and this could be leveraged to attack
either the higher or lower layer network. Precautionary measures,
such as those described in Section 7.1.3, can be applied through
policy or configuration to dampen any network oscillations.
9. 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, Ina Minei, and Jean-Philippe
comments. Vasseur for their useful comments.
9. References 10. References
9.1. Normative Reference 10.1. Normative Reference
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, [RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC 3031, January "Multiprotocol Label Switching Architecture", RFC 3031, January
2001. 2001.
Oki et al Expires June 2008 27
[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] K. Kompella and Y. Rekhter, "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.
Oki et al Expires March 2008 26 10.2. Informative Reference
9.2. 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鋳, 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 Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc
(work 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", RFC 4920, July 2007. and GMPLS RSVP-TE", RFC 4920, July 2007.
skipping to change at line 1333 skipping to change at line 1403
Interface (UNI): Resource ReserVation Protocol-Traffic Engineering Interface (UNI): Resource ReserVation Protocol-Traffic Engineering
(RSVP-TE) Support for the Overlay Model", RFC 4208, October 2005. (RSVP-TE) Support for the Overlay Model", RFC 4208, October 2005.
[RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation [RFC4655] A. Farrel, JP. Vasseur and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006. Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4657] J. Ash and J.L. Le Roux (Ed.), "Path Computation Element [RFC4657] J. Ash and J.L. Le Roux (Ed.), "Path Computation Element
(PCE) Communication Protocol Generic Requirements", RFC 4657, (PCE) Communication Protocol Generic Requirements", RFC 4657,
September 2006. September 2006.
Oki et al Expires June 2008 28
[PCE-POLICY] Bryskin, I., Papadimitriou, P., and Berger, L., [PCE-POLICY] Bryskin, I., Papadimitriou, P., and Berger, L.,
"Policy-Enabled Path Computation Framework", draft-ietf-pce- "Policy-Enabled Path Computation Framework", draft-ietf-pce-
policy-enabled-path-comp, (work in progress). policy-enabled-path-comp, (work in progress).
[PCEP] JP. Vasseur et al, "Path Computation Element (PCE) [PCEP] JP. Vasseur et al, "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep communication Protocol (PCEP) - Version 1 -" draft-ietf-pce-pcep
(work in progress). (work in progress).
Oki et al Expires March 2008 27 11. Authors' Addresses
10. Authors・Addresses
Eiji Oki Eiji Oki
NTT NTT
3-9-11 Midori-cho, 3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan Musashino-shi, Tokyo 180-8585, Japan
Email: oki.eiji@lab.ntt.co.jp Email: oki.eiji@lab.ntt.co.jp
Jean-Louis Le Roux Jean-Louis Le Roux
France Telecom R&D, France Telecom R&D,
Av Pierre Marzin, Av Pierre Marzin,
22300 Lannion, France 22300 Lannion, France
Email: jeanlouis.leroux@orange-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
11. Intellectual Property Statement 12. Intellectual Property Statement
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to pertain to the implementation or use of the technology to pertain to the implementation or use of the technology
described in this document or the extent to which any license described in this document or the extent to which any license
under such rights might or might not be available; nor does it under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any represent that it has made any independent effort to identify any
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in RFC 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
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at http://www.ietf.org/ipr. at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other any copyrights, patents or patent applications, or other
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Oki et al Expires June 2008 29
to implement this standard. Please address the information to the to implement this standard. Please address the information to the
IETF at ietf-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
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FOR A PARTICULAR PURPOSE. FOR A PARTICULAR PURPOSE.
Copyright Statement Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
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
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Oki et al Expires March 2008 29 Oki et al Expires June 2008 30
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