Network Working Group E. Oki
Internet Draft NTT
Category: Informational J-L Le Roux
Expires: June 2008 France Telecom
A. Farrel
Old Dog Consulting
January 2008
Framework for PCE-Based Inter-Layer MPLS and GMPLS Traffic
Engineering
draft-ietf-pce-inter-layer-frwk-06.txt
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Abstract
A network may comprise multiple layers. It is important to
globally optimize network resource utilization, taking into
account all layers, rather than optimizing resource utilization at
each layer independently. This allows better network efficiency to
be achieved through a process that we call inter-layer traffic
engineering. The Path Computation Element (PCE) can be a powerful
tool to achieve inter-layer traffic engineering.
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This document describes a framework for applying the PCE-based
architecture to inter-layer Multiprotocol Label Switching (MPLS)
and Generalized MPLS (GMPLS) traffic engineering. It provides
suggestions for the deployment of PCE in support of multi-layer
networks. This document also describes network models where PCE
performs inter-layer traffic engineering, and the relationship
between PCE and a functional component called the Virtual Network
Topology Manager (VNTM).
Table of Contents
1. Introduction....................................................3
1.1. Terminology..................................................4
2. Inter-Layer Path Computation....................................4
3. Inter-layer Path Computation Models.............................6
3.1. Single PCE Inter-Layer Path Computation......................6
3.2. Multiple PCE Inter-Layer Path Computation....................7
3.3. General Observations.........................................9
4. Inter-Layer Path Control........................................9
4.1. VNT Management...............................................9
4.2. Inter-Layer Path Control Models..............................9
4.2.1. PCE-VNTM Cooperation Model................................10
4.2.2. Higher-Layer Signaling Trigger Model......................12
4.2.3. NMS-VNTM Cooperation Model................................15
4.2.4. Possible Combinations of Inter-Layer Path Computation and
Inter-Layer Path Control Models....................................17
5. Choosing Between Inter-Layer Path Control Models...............18
5.1. VNTM Functions:.............................................18
5.2. Border LSR Functions:.......................................19
5.3. Complete Inter-Layer LSP Setup Time:........................20
5.4. Network Complexity..........................................20
5.5. Separation of Layer Management..............................21
6. Stability Considerations.......................................21
7. Manageability Considerations...................................22
7.1. Control of Function and Policy..............................23
7.1.1. Control of Inter-Layer Computation Function...............23
7.1.2. Control of Per-Layer Policy...............................23
7.1.3. Control of Inter-Layer Policy.............................23
7.2. Information and Data Models.................................24
7.3. Liveness Detection and Monitoring...........................24
7.4. Verifying Correct Operation.................................25
7.5. Requirements on Other Protocols and Functional Components...25
7.6. Impact on Network Operation.................................26
8. Security Considerations........................................26
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9. Acknowledgments................................................27
10. References...................................................27
10.1. Normative Reference.........................................27
10.2. Informative Reference.......................................28
11. Authors' Addresses...........................................29
12. Intellectual Property Statement..............................29
1. Introduction
A network may comprise multiple layers. These layers may represent
separations of technologies (e.g., packet switch capable (PSC),
time division multiplex (TDM), or lambda switch capable (LSC))
[RFC3945], separation of data plane switching granularity levels
(e.g., PSC-1, PSC-2, VC4, or VC12) [MLN-REQ], or a distinction
between client and server networking roles. In this multi-layer
network, Label Switched Paths (LSPs) in a lower layer are used to
carry higher-layer LSPs across the lower-layer network. The
network topology formed by lower-layer LSPs and advertised as
traffic engineering links (TE links) to the higher layer is called
the Virtual Network Topology (VNT) [MLN-REQ].
It may be effective to optimize network resource utilization
globally, i.e., taking into account all layers, rather than
optimizing resource utilization at each layer independently. This
allows better network efficiency to be achieved and is what we
call inter-layer traffic engineering. This includes mechanisms
allowing the computation of end-to-end paths across layers (known
as inter-layer path computation), and mechanisms for control and
management of the Virtual Network Topology (VNT) by setting up and
releasing LSPs in the lower layers [MLN-REQ].
Inter-layer traffic engineering is included in the scope of the
Path Computation Element (PCE)-based architecture [RFC4655], and
PCE can provide a suitable mechanism for resolving inter-layer
path computation issues.
PCE Communication Protocol requirements for inter-layer traffic
engineering are set out in [PCE-INTER-LAYER-REQ].
This document describes a framework for applying the PCE-based
architecture to inter-layer traffic engineering. It provides
suggestions for the deployment of PCE in support of multi-layer
networks. This document also describes network models where PCE
performs inter-layer traffic engineering, and the relationship
between PCE and a functional component in charge of the control
and management of the VNT, called the Virtual Network Topology
Manager (VNTM).
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1.1. Terminology
This document uses terminology from the PCE-based path computation
architecture [RFC4655] and also common terminology from Multi
Protocol Label Switching (MPLS) [RFC3031], Generalized MPLS
(GMPLS) [RFC3945] and Multi-Layer Networks [MLN-REQ].
2. Inter-Layer Path Computation
This section describes key topics of inter-layer path computation
in MPLS and GMPLS networks.
[RFC4206] defines a way to signal a higher-layer LSP, which has an
explicit route that includes hops traversed by LSPs in lower
layers. The computation of end-to-end paths across layers is
called Inter-Layer Path Computation.
A Label Switching Router (LSR) in the higher-layer might not have
information on the topology of the lower-layer, particularly in an
overlay or augmented model deployment, and hence may not be able
to compute an end-to-end path across layers.
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 achieved by a single PCE path computation where the PCE has
topology information about multiple layers and can directly
compute an end-to-end path across layers considering the topology
of all of the layers. Alternatively, the inter-layer path
computation could be performed as a multiple-PCE computation where
each member of a set of PCEs has information about the topology of
one or more layers (but not all layers), and the PCEs collaborate
to compute an end-to-end path.
----- ----- ----- -----
| LSR |--| LSR |................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 1: A Simple Example of a Multi-Layer Network.
Consider, for instance, the two-layer network shown in Figure 1,
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
(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
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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).
Lower-layer LSPs that are advertised as TE links into the higher-
layer network form a Virtual Network Topology (VNT) that can be
used for routing higher-layer LSPs. Inter-layer path computation
for end-to-end LSPs in the higher-layer network that span the
lower-layer network may utilize the VNT, and PCE is a candidate
for computing the paths of such higher-layer LSPs within the
higher-layer network. Alternatively, the PCE-based path
computation model can:
- Perform a single computation on behalf of the ingress LSR using
information gathered from more than one layer. This mode is
referred to as Single PCE Computation in [RFC4655].
- Compute a path on behalf of the ingress LSR through cooperation
with PCEs responsible for each layer. This mode is referred to as
Multiple PCE Computation with inter-PCE communication in [RFC4655].
- 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
layer. This mode is referred to as Multiple PCE Computation
(without inter-PCE communication) in [RFC4655]. This option
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 use to signal an MPLS-TE or GMPLS LSP once the path
information has been converted to an Explicit Route Object (ERO)
for use in RSVP-TE signaling. There are two options.
- Option 1: Mono-layer path.
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
option. In the first case the PCE computes a path that includes
already established lower-layer LSPs or lower-layer LSPs to be
established on demand. That is, the resulting ERO includes sub-
object(s) corresponding to lower-layer hierarchical LSPs expressed
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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
loose hop that spans the lower-layer network. The higher layer
path computation selects which lower layer network to use, and
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.
- Option 2: Multi-layer path. The PCE computes a "multi-layer"
path, i.e., a path that includes TE links from distinct layers
[RFC4206]. Such a path can include the complete path of one or
more lower-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
As stated in Section 2, two PCE modes defined in the PCE
architecture can be used to perform inter-layer path computation.
They are discussed in the sections that follow.
3.1. Single PCE Inter-Layer Path Computation
In this model Inter-layer path computation is performed by a
single PCE that has topology visibility into all layers. Such a
PCE is called a multi-layer PCE.
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
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
computation across layers (single PCE path computation). For
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
lower layer LSP from H2 to H3, already in existence or not yet
established.
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-----
| PCE |
-----
----- ----- ----- -----
| LSR |--| LSR |................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 2: Single 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 topology visibility restricted to its own layer. Some
providers may want to keep the layer boundaries due to factors
such as organizational and/or service management issues. The
choice for multiple PCE computation instead of single PCE
computation may also be driven by scalability considerations, as
in this mode a PCE only needs to maintain topology information for
one layer (resulting in a size reduction for the Traffic
Engineering Database (TED)).
These PCEs are called mono-layer PCEs. Mono-layer PCEs collaborate
to compute an end-to-end optimal path across layers.
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
Hi is responsible for computations in the higher layer and may
"consult" with PCE Lo to compute paths across the lower layer. PCE
Lo is responsible for path computation in the lower layer. A
simple example of cooperation between the PCEs could be as
follows:
- 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 the exit point.
- PCE Hi requests a path H2-H3 from PCE Lo.
- PCE Lo returns H2-L1-L2-H3 to PCE Hi.
- PEC Hi is now able to compute the full path (H1-H2-L1-L2-H3-H4)
and return it to H1.
Of course more complex cooperation may be required if an optimal
end-to-end path is desired.
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-----
| PCE |
| Hi |
--+--
|
----- ----- | ----- -----
| LSR |--| LSR |............|...........| LSR |--| LSR |
| H1 | | H2 | | | H3 | | H4 |
----- -----\ --+-- /----- -----
\ | PCE | /
\ | Lo | /
\ ----- /
\ /
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 3: Multiple PCE Inter-Layer Path Computation with Inter-PCE
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
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3.3. General Observations
- Depending on implementation details, the time to perform inter-
layer path computation in the Single PCE inter-layer path
computation model may be less than that of the Multiple PCE model
with cooperating mono-layer PCEs, because there is no requirement
to exchange messages between cooperating PCEs.
- When TE topology for all layer networks is visible within one
routing domain, the single PCE inter-layer path computation model
may be adopted because a PCE is able to collect all layers' TE
topologies by participating in only one routing domain.
- As the single PCE inter-layer path computation model uses more
TE topology information in one computation than is used by PCEs in
the Multiple PCE path computation model, it requires more
computation power and memory.
When there are multiple candidate layer border nodes (we may say
that the higher layer is multi-homed), optimal path computation
requires that all the possible paths transiting different layer
border nodes or links be examined. This is relatively simple in
the single PCE inter-layer path computation model because the PCE
has full visibility -
- the computation is similar to the
computation within a single domain of a single layer. In the
multiple PCE inter-layer path computation model, backward
recursive techniques described in [BRPC] could be used, by
considering layers as separate domains.
4. Inter-Layer Path Control
4.1. VNT Management
As a result of inter-layer path computation, a PCE may determine
that there is insufficient bandwidth available in the higher-layer
network to support this or future higher-layer LSPs. The problem
might be resolved if new LSPs were provisioned across the lower-
layer network. Furthermore, the modification, re-organization and
new provisioning of lower-layer LSPs may enable better utilization
of lower-layer network resources given the demands of the higher-
layer network. In other words, the VNT needs to be controlled or
managed in cooperation with inter-layer path computation.
A VNT Manager (VNTM) is defined as a functional element that
manages and controls the VNT. PCE and VNT Manager are distinct
functional elements that may or may not be co-located.
4.2. Inter-Layer Path Control Models
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4.2.1.
PCE-VNTM Cooperation Model
----- ------
| PCE |--->| VNTM |
----- ------
^ :
: :
: :
v V
----- ----- ----- -----
| LSR |----| LSR |................| LSR |----| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 5: PCE-VNTM Cooperation Model
A multi-layer network consists of higher-layer and lower-layer
networks. LSRs H1, H2, H3, and H4 belong to the higher-layer
network, LSRs H2, L1, L2, and H3 belong to the lower-layer network,
as shown in Figure 5. The case of single PCE inter-layer path
computation is considered here to explain the cooperation model
between PCE and VNTM, but multiple PCE path computation with or
without inter-PCE communication can also be applied to this model.
Consider that H1 requests the PCE to compute an inter-layer path
between H1 and H4. There is no TE link in the higher-layer between
H2 and H3 before the path computation request, so the request
fails. But the PCE may provide information to the VNT Manager
responsible for the lower layer network that may help resolve the
situation for future higher-layer LSP setup.
The roles of PCE and VNTM are as follows. PCE performs inter-layer
path computation and is unable to supply a path because there is
no TE link between H2 and H3. The computation fails, but PCE
suggests to VNTM that a lower-layer LSP (H2-H3) could be
established to support future LSP requests. Messages from PCE 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
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.
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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
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.
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
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 LSP will become available. In any case, if the PCE decides to
wait, it must operates a timeout. An example of such a cooperative
procedure between PCE and VNTM is as follows using the example
network in Figure 4.
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
across the lower-layer network.
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
for the TE link to be created. VNTM considers whether lower-layer
LSPs should be established if necessary and if acceptable within
VNTM's policy constraints.
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
include a lower-layer LSP route obtained from the PCE responsible
for the lower-layer network.
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 notifies VNTM that the LSP is complete and supplies the tunnel
information.
Step 7: The ingress LSR (H2) advertises the new LSP as a TE link
in the higher-layer network routing instance.
Step 8: PCE notices the new TE link advertisement and recomputes
the requested path.
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
includes the already-established lower layer-LSP as a single hop
in the higher layer. The higher-layer route is specified as H1-H2-
H3-H4, where all hops are strict.
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Step 9: H1 initiates signaling with the computed path H2-H3-H4 to
establish the higher-layer LSP.
4.2.2.
Higher-Layer Signaling Trigger Model
-----
| PCE |
-----
^
:
:
v
----- ----- ----- -----
| LSR |----| LSR |................| LSR |--| LSR |
| H1 | | H2 | | H3 | | H4 |
----- -----\ /----- -----
\----- -----/
| LSR |--| LSR |
| L1 | | L2 |
----- -----
Figure 6: Higher-layer Signaling Trigger Model
Figure 6 shows the higher-layer signaling trigger model. The case
of single PCE path computation is considered to explain the
higher-layer signaling trigger model here, but multiple PCE path
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
establishment of a lower-layer LSP between H2 and H3 would provide
adequate connectivity. If the PCE has inter-layer visibility it
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
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
that includes loose hops.
In the higher-layer signaling trigger model with a multi-layer
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
located at the boundary between the higher-layer and lower-layer
networks (H2 in this example) receives a higher-layer signaling
message, notices that the next hop is in the lower-layer network,
starts to setup the lower-layer LSP as described in [RFC4206].
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.
The request indicates that inter-layer path computation is allowed.
Step 2: As a result of the inter-layer path computation, PCE
judges that a new lower-layer LSP needs to be established.
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 specified as H1-H2-L1-L2-H3-H4, where all hops are strict.
Step 4: H1 initiates higher-layer signaling using the computed
explicit router of H2-L1-L2-H3-H4.
Step 5: The border LSR (H2) that receives the higher-layer
signaling message starts lower-layer signaling to establish a
lower-layer LSP along the specified lower-layer route of H2-L1-L2-
H3. That is, the border LSR recognizes the hops within the
explicit route that apply to the lower-layer network, verifies
with local policy that a new LSP is acceptable, and establishes
the required lower-layer LSP. Note that it is possible that a
suitable lower-layer LSP has already been established (or become
available) between the time that the computation was performed and
the moment when the higher-layer signaling message reached the
border LSR. In this case, the border LSR may select such a lower-
layer LSP without the need to signal a new LSP provided that the
lower-layer LSP satisfies the explicit route in the higher-layer
signaling request.
Step 6: After the lower-layer LSP is established, the higher-layer
signaling continues along the specified higher-layer route of H2-
H3-H4 using hierarchical signaling [RFC4206].
On the other hand, in the signaling trigger model with a mono-
layer path, a higher-layer LSP route includes a loose hop to
traverse the lower-layer network between the two border LSRs. A
border LSR that receives a higher-layer signaling message needs to
determine a path for a new lower-layer LSP. It applies local
policy to verify that a new LSP is acceptable and then either
consults a PCE with responsibility for the lower-layer network or
computes the path by itself, and initiates signaling to establish
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the lower-layer LSP. Again, it is possible that a suitable lower-
layer LSP has already been established (or become available). In
this case, the border LSR may select such a lower-layer LSP
without the need to signal a new LSP provided that the existing
lower-layer LSP satisfies the explicit route in the higher-layer
signaling request. Since the higher-layer signaling request used a
loose hop without specifying any specifics 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
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:
Step 5': The border LSR (H2) that receives the higher-layer
signaling message applies local policy to verify that a new LSP is
acceptable and then initiates establishment of a lower-layer LSP.
It either consults a PCE with responsibility for the lower-layer
network or computes the route by itself to expand the loose hop
route in the higher-layer path.
Finally, note that a virtual TE link may have been advertised into
the higher-layer network. This causes the PCE to return a path H1-
H2-H3-H4 where all the hops are strict. But when the higher-layer
signaling message reaches the layer border node H2 (that was
responsible for advertising the virtual TE link) it realizes that
the TE link does not exist yet, and signals the necessary LSP
across the lower-layer network using its own path determination
(just as for a loose hop in the higher layer) before continuing
with the higher-layer signaling.
PCE
^
:
:
V
H1--H2 H3--H4
\ /
L1==L2==L3--L4--L5
|
|
L6--L7
\
H5--H6
Figure 7: Example of a Multi-Layer Network
Examples of multi-layer EROs are explained using Figure 7. It is
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
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
higher layer network (H2).
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 to H3.
3. The next subobjects are a series of hops (strict or loose) in
the lower-layer network followed by H3. For example, {L1(strict),
L3(loose), L5(loose), H3(strict)}
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
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
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
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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.
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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's 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
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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
This section compares the cooperation model between PCE and VNTM,
and the higher-layer signaling trigger model, in terms of VNTM
functions, border LSR functions, higher-layer signaling time, and
complexity (in terms of number of states and messages). An
appropriate model may be chosen by a network operator in different
deployment scenarios taking all these considerations into account.
5.1. VNTM Functions:
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
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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
required, and no such communications are required.
If VNTM functions are not supported in a multi-layer network, the
higher-layer signaling trigger model has to be chosen.
The inclusion of VNTM functionality allows better coordination of
cross-network LSP tunnels and application of network-wide policy
that is far harder to apply in the trigger model since it requires
the coordination of policy between multiple border LSRs.
5.2. Border LSR Functions:
In the higher-layer signaling trigger model, a border LSR must
have some additional functions. It needs to trigger lower-layer
signaling when a higher-layer path message suggests that lower-
layer LSP setup is necessary. Note that, if virtual TE links are
used, the border LSRs must be capable of triggered signaling.
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 must obtain a lower-layer route either by consulting a PCE
or by using its own computation engine. If the ERO in the higher-
layer Path message uses a multi-layer path, the border LSR must
judge whether lower-layer signaling is needed.
In the PCE-VNTM cooperation model and the NMS-VNTM model, no
additional function for triggered signaling is required in border
LSRs except when virtual TE links are used. Therefore, if these
additional functions are not supported in border LSRs, where a
border LSR is controlled by VNTM to set up a lower-layer LSP, the
cooperation model has to be chosen.
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5.3. Complete Inter-Layer LSP Setup Time:
The complete inter-layer LSP setup time includes inter-layer path
computation, signaling, and the communication time between PCC and
PCE, PCE and VNTM, NSM and VNTM, and VNTM and LSR. In the PCE-VNTM
cooperation model and the NMS-VNTM model, the additional
communication steps are required compared with the higher-layer
signaling trigger model. On the other hand, the cooperation model
provides better control at the cost of a longer service setup time.
Note that, in terms of higher-layer signaling time, in the higher-
layer signaling trigger model, the required time from when higher-
layer signaling starts to when it is completed, is more than that
of the cooperation model except when a virtual TE link is included.
This is because the former model requires lower-layer signaling to
take place during the higher-layer signaling. A higher-layer
ingress LSR has to wait for more time until the higher-layer
signaling is completed. A higher-layer ingress LSR is required to
be tolerant of longer path setup times.
5.4. Network Complexity
If the higher and lower layer networks have multiple interconnects
then optimal path computation for end-to-end LSPs that cross the
layer boundaries is non-trivial. The higher layer LSP must be
routed to the correct layer border nodes to achieve optimality in
both layers.
Where the lower layer LSPs are advertised into the higher layer
network as TE links, the computation can be resolved in the higher
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 as TE links into the higher layer network, and this
might be a function for a VNT Manager component. Similarly,
attention should be given to the fact that the LSPs crossing the
lower-layer network might share points of common failure (e.g.,
they might traverse the same link in the lower-layer network) and
the shared risk link groups (SRLGs) for the TE links advertised in
the higher-layer must be set accordingly.
In the single PCE model an end-to-end path can be found in a
single computation because there is full visibility into both
layers and all possible paths through all layer interconnects can
be considered.
Where PCEs cooperate to determine a path, an iterative computation
model such as [BRPC] can be used to select an optimal path across
layers.
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When non-cooperating mono-layer PCEs, each of which is in a
separate layer, are used with the triggered LSP model, it is not
possible to determine the best border LSRs, and connectivity
cannot even be guaranteed. In this case, signaling crankback
techniques [CRANK] can be used to eventually achieve connectivity,
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
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
Many network operators may want to provide a clear separation
between the management of the different layer networks. In some
cases, the lower layer network may come from a separate commercial
arm of an organization or from a different corporate body entirely.
In these cases, the policy applied to the establishment of LSPs in
the lower-layer network and to the advertisement of these LSPs as
TE links in the higher-layer network will reflect commercial
agreements and security concerns (see next section). Since the
capacity of the LSPs in the lower-layer network are likely to be
significantly larger than those in the client higher-layer network
(multiplex-server model), the administrator of the lower-layer
network may want to exercise caution before allowing a single
small demand in the higher layer to tie up valuable resources in
the lower layer.
The necessary policy points for this separation of administration
and management are more easily achieved through the VNTM approach
than by using triggered signaling. In effect, the VNTM is the
coordination point for all lower layer LSPs and can be closely
tied to a human operator as well as to policy and billing. Such a
model can also be achieved using triggered signaling.
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
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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
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.
Management mechanisms are required to make sure that inter-layer
traffic engineering can be applied without violating the policy
and administrative operational procedures used by the network
operators.
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7.1. Control of Function and Policy
7.1.1.
Control of Inter-Layer Computation Function
PCE implementations that are capable of supporting inter-layer
computations should provide a configuration switch to allow
support of inter-layer path computations to be enabled or disabled.
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.
7.1.2.
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.
7.1.3.
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 (see Section 6). 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
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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.
7.2. 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].
7.3. 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
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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.
7.4. 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.
7.5. 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,
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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.
7.6. 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.
8. 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
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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
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.
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,
Jean-Francois Peltier, Young Lee, Ina Minei, and Jean-Philippe
Vasseur for their useful comments.
10. References
10.1. Normative Reference
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC 3031, January
2001.
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draft-ietf-pce-inter-layer-frwk-06.txt January 2008
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
Architecture", RFC 3945, October 2004.
[RFC4206] K. Kompella and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching (GMPLS)
Traffic Engineering (TE)", RFC 4206, October 2005.
10.2. Informative Reference
[MLN-REQ] K. Shiomoto et al., "Requirements for GMPLS-based multi-
region networks (MRN)", draft-ietf-ccamp-gmpls-mln-reqs (work in
progress).
[PCE-INTER-LAYER-REQ] E. Oki et al., "PCC-PCE Communication
Requirements for Inter-Layer Traffic Engineering’’, draft-ietf-pce-
inter-layer-req (work in progress).
[BRPC] JP. Vasseur et al., "A Backward Recursive PCE-based
Computation (BRPC) procedure to compute shortest inter-domain
Traffic Engineering Label Switched Paths", draft-ietf-pce-brpc
(work in progress).
[CRANK] A. Farrel et al., "Crankback Signaling Extensions for MPLS
and GMPLS RSVP-TE", RFC 4920, July 2007.
[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.
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draft-ietf-pce-inter-layer-frwk-06.txt January 2008
[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).
11. Authors' Addresses
Eiji Oki
NTT
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: oki.eiji@lab.ntt.co.jp
Jean-Louis Le Roux
France Telecom R&D,
Av Pierre Marzin,
22300 Lannion, France
Email: jeanlouis.leroux@orange-ftgroup.com
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
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