PCE Working Group Xian Zhang
Internet Draft Haomian Zheng
Category: Standards track Huawei Technologies
Oscar Gonzales de Dios
Victor Lopez
Telefonica I+D
Yunbin Xu
CAICT
Expires: April 24, 2020 October 24, 2019
Extensions to the Path Computation Element Protocol (PCEP) to Support
Resource Sharing-based Path Computation
draft-zhang-pce-resource-sharing-11
Abstract
Resource sharing in a network means two or more Label Switched Paths
(LSPs) use common pieces of resource along their paths. This can
help save network resources and is useful in scenarios such as LSP
recovery or when two LSPs do not need to be active at the same time.
A Path Computation Element (PCE) is responsible for path computation
with such requirement.
Existing extensions to the Path Computation Element Protocol (PCEP)
allow one path computation request for an LSP to be associated with
other (existing) LSPs through the use of the PCEP Association
Object.
This document extends PCEP in order to support resource-sharing-
based path computation as another use of the Association Object to
enable better efficiency in the computation and in the resultant
paths and network resource usage.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on April 24, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction and Motivation .................................. 3
1.1. Requirements Language ................................... 4
2. Motivation ................................................... 5
2.1. Single Domain Use Case .................................. 5
2.2. Multiple Layers/Domains Use Case ........................ 6
2.3. Bulk Path Computation Use Case .......................... 8
3. Extensions to PCEP ........................................... 9
3.1. Association Group and Type .............................. 9
3.2. Resource Sharing TLV ................................... 10
3.3. Processing Rules ....................................... 11
4. Implementation Status ....................................... 12
5. Manageability Considerations ................................ 12
5.1. Control of Function and Policy ......................... 12
5.2. Information and Data Models ............................ 12
5.3. Liveness Detection and Monitoring ...................... 13
5.4. Verify Correct Operations .............................. 13
5.5. Requirements on Other Protocols ........................ 13
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5.6. Impact on Network Operations ........................... 13
6. Security Considerations ..................................... 13
7. IANA Considerations ......................................... 14
7.1. Association Object Type Indicators ..................... 14
7.2. PCEP TLV Definitions ................................... 14
8. References .................................................. 15
8.1. Normative References ................................... 15
8.2. Informative References ................................. 15
9. Acknowledgements ............................................ 16
10. Contributor's Address ...................................... 16
11. Authors' Addresses ......................................... 17
1. Introduction and Motivation
A Path Computation Element (PCE) is a way to provide path
computation function, and it is especially useful in the scenarios
where complex constraints and/or a demanding amount of computation
resource are required [RFC4655]. The development of PCE
standardization has evolved from stateless to stateful. A stateful
PCE has access to the LSP database information of the networks it
serves as a computation engine [RFC8231]. Unless specified, this
document assumes a PCE mentioned is a stateful PCE.
Resource sharing denotes that two or more Label Switched Paths
(LSPs) share common pieces of resource, (such as a common time slot
of a link in an Optical Transport Network (OTN)). This is usually
useful in the scenario where only one of the LSPs is active and the
benefit is to save network resources. A simple example of this is
dynamically calculating a recovery LSP for an existing LSP
undergoing a link failure. Note that resource sharing can be worked
out using a stateless PCE, but the mechanism may be complex and is
out the scope of this document.
This document considers the requirement that a new LSP may request
for resource sharing with one or multiple existing LSPs. Furthermore,
if there is resource sharing between a new LSP and existing an LSP,
the two LSPs cannot be used to carry traffic simultaneously, the new
LSP will take over the traffic from the existing LSP.
In a single domain, this is a common requirement in the recovery
cases especially in order to increase traffic resilience against
failure while reducing the amount of network resource used for
recovery purposes [RFC4428].
The current protocol supporting the communication between a PCE and
a Path Computation Client (PCC), i.e. PCE Protocol (PCEP), allows
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for re-optimization of an existing LSP [RFC5440]. This is achieved
by setting the R bit in the Request Parameter (RP) object, together
with some additional information if applicable, in the Path
Computation Request (PCReq) message sent from a PCC to the PCE. To
support this type of resource sharing, a PCC needs to ask a PCE to
compute a new path with the constraints of sharing resource with one
or multiple existing LSPs. It is worth noting the "resource sharing"
in this draft not only means one LSP re-using the same links of
another LSP, but also the same slice of bandwidth in the network.
This may occur when an LSP is required for re-routing, or online re-
optimization. Current PCEP specifications do not provide such
function. More specifically, this document describes the resource
sharing issue during the procedure when a new LSP is required to
replace an existing LSP for use together with Make-before-break
(MBB) described in [RFC3209].
As mentioned in [RFC8231], the PLSP-ID provides a unique identifier
for an LSP during a PCEP session between PCC and PCE. Such
identification is helpful in supporting the resource sharing
requirement for stateful PCEs because it greatly simplifies the
operation of a PCC. Instead of the PCC determining all the resources
to be shared, the PCC can request that the PCE share the resources
of a specific LSP: the stateful PCE is able to determine those
resource itself.
Resource sharing can also be required in an inter-layer PCEP
session. This is similar to the previous requirement. However, it is
more complex and therefore deserves a more detailed explanation
here.
In a multi-layer network, LSPs in a lower layer are used to carry
higher-layer LSPs across the lower-layer network [RFC5623].
Therefore, the resource sharing constraints in the higher layer
might actually relate to resource sharing in the lower layer. Thus,
it is useful to consider how this can be achieved and whether
additional extensions are needed using the models defined in
[RFC5623].
In the next sections, use cases are provided to show what
information needs to be exchanged to fulfill these requirements.
This memo then provides extensions to PCEP to enable this function.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
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BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Motivation
2.1. Single Domain Use Case
There are two potential cases that request resource to be shared:
restoration and re-optimization. Figure 1 shows a single domain
network with a stateful PCE, and is used as an example for the
resource sharing application.
+--------------+
| |
| Stateful PCE |
| |
+--------------+
+------+ +------+ +------+
| N1 +----------+ N2 +-----X---+ N3 |
+--+---+ +---+--+ +---+--+
| | |
| +---------+ |
| | |
| +------+ +------+ |
+-----+ N5 +----------+ N4 +-----+
+------+ +------+
Figure 1: A Single Domain Example
LSP0 (existing): N1-N2-N3
LSP1 (restoration): N1-N2-N4-N3
LSP2 (re-optimization): N1-N5-N4-N3
For the failure restoration, we can assume a working LSP (LSP0)
exists in the network. When there is failure on the link N2-N3, it
is desired to set up a restoration path for this working LSP.
Suppose N1 serves as the PCC and sends a request to the stateful PCE
for such an LSP. Before sending the request, N1 may need to check
what policy should be applied for the restoration. For example, it
might value resource sharing and prefer to share as much resource
with the working LSP as possible and specify this policy in the
PCReq message. Given such policy, a probable outcome from the path
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computation would be LSP1, which shares the link 'N1-N2' with the
existing LSP.
Re-optimization does not usually result from a specific failure in
the network, but takes place on a stable network when more optimal
paths may have become available. Thus switching from the existing
LSP to the new LSP happens with live traffic. An example can be
found in Figure 1 without failure on the link N2-N3. Instead, an
online re-optimization is needed for the working LSP (LSP0) from the
stateful PCE. In such cases, the best choice is to set up a backup
LSP for the working LSP with totally separate routing (for example,
LSP2), and move the traffic to that backup LSP. After that, the
working LSP can be torn down, which will not result in any
interruption during the optimization procedure. This can actually be
implemented with existing PCEP mechanisms. However, if there is no
such separate path, existing PCEP mechanisms will return an error. A
secondary option for this case is to set up an LSP and complete re-
optimization with resource sharing, even if some interruption is
introduced.
In the example from Figure 1 it is assumed that the restored LSP or
re-optimized LSP have the same source and destination nodes. But in
some applications there is no restriction for this assumption, i.e.,
after an LSP is failed, it can be restored as a new LSP with
different source/destination.
In the use cases above it is also assumed that the characteristics
of the restored LSP or re-optimized LSP are unchanged. However, it
is possible to have parameter changes during the resource sharing
computation. For example, the bandwidth of the request LSP may be
different from the existing LSP, while resource sharing is still
preferred by the PCC. The PCE should consider the sharing request
together with the policy and available resources in the network.
Details can be found in Section 3.3.
Conversely to resource sharing, it may also be required to apply a
disjoint constraint for the path computation. [ietf-pce-association-
diversity] discusses the solution under such a scenario, which is a
companion work to this document.
2.2. Multiple Layers/Domains Use Case
As Discussed in Section 3 of [RFC5623], there are three models for
inter-layer path computation. They are single PCE computation,
multiple PCE with inter-PCE communication, and multiple PCE without
inter-PCE communication. For the single PCE computation, the process
would be similar to that of the use case in Section 2.1.
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An inter-layer path computation example is shown in Figure 2. Assume
an LSP (LSP1: H2-H3) has been established already, visible as H2-H3
from the view of the higher-layer PCE, and as H2-L1-L2-H3 from the
global view (or from the view of the lower-layer PCE). A new request
is received by H2 to establish a new LSP (LSP2: from H2 to H5),
given the constraint that it can share resources with LSP1. This
requirement is possible if only one of the LSPs needs to be active
and resource sharing is the target.
-----
.................................| LSR |
.: | H5 |
.: /-----
.: / |
----- -----.: ----- -----/ |
| LSR |--| LSR |.......................| LSR |--| LSR | /
| H1 | | H2 | | H3 | | H4 | /
----- -----\ /----- ----- /
\ / /
\ / /
\ / /
\ / /
\----- -----/ /
| LSR |-| LSR | /
| L1 | | L2 | /
----- -----\ /
| \ /
| \ /
| \ /
----- \-----/
| LSR |-----------| LSR |
| L3 | | L4 |
----- -----
Figure 2: A Two-layer Network Example
If the model of multiple PCEs with inter-PCE communication is
employed, the path computation request sent by H2 to higher-layer
PCE will be forwarded to lower-layer PCE since there is no resource
readily available in the higher layer. So it leaves the lower-layer
PCE to compute a path in the lower layer in order to support the
higher layer request. In this case, the lower-layer PCE is required
to compute a path between H2 and H5 under the constraint that it can
share the resource with that of LSP1. At this moment the lower-layer
PCE has knowledge of the explicit route of LSP1 (H2-L1-L2-H3), and
therefore can map the lower layer LSP with the higher-layer one. So
when the lower-layer PCE computes the path for LSP2, it can consider
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the resource used by LSP1 as available with higher priority. For
example, the lower-layer PCE may choose H2-L1-L2-L4-H5 as the
computation result. On the other hand, if the path computation
policy is to have a separate path with LSP1, the lower-layer PCE may
choose H2-L1-L3-L4-H5.
During this procedure the higher-layer PCE can only use information
about LSP1 (such as its five-tuple LSP information). An issue to
solve is how the lower-layer PCE can resolve this information to the
actual resource usage in its own layer, i.e. the lower layer. This
could be solved by the edge LSR (L1) reporting this higher-lower LSP
correlation to the lower-layer PCE as part of the LSP information
during the LSP state synchronization process. If needed, it can be
updated later when there is a change in this information.
Alternatively, the lower-layer PCE can get this information from
other sources, such as a network management system, where this
information should be stored.
If the model of multiple PCEs without inter-PCE communication is
employed, the path computation request in the lower layer will be
initiated by the border LSR node, i.e., L1. The process would be
similar to that of the previous scenario. A point worth noting is
that the border LSR node may be able to resolve the higher layer LSP
information itself, such as by mapping it to the corresponding LSP
in the lower layer, in this way the lower-layer PCE does not need to
perform this function. Otherwise, the mapping method mentioned above
can still be used.
2.3. Bulk Path Computation Use Case
There is a potential need for resource sharing during bulk path
computation, especially the processing of the "sticky resources" in
[RFC7399]. It would be useful to specify the resources that can be
shared among different paths, i.e., the bandwidth information.
Considering the H-PCE architecture in [ietf-pce-stateful-hpce], when
the parent PCE asks for a single path across a few domains, such a
request may become a bulk path computation to a certain child PCE.
Figure 3 shows an example of 3 domains. The parent PCE will select
one of these path for establishment.
+-------+
/| P-PCE |\
/ +---+---+ \
/ | \
/ | \
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/ | \
/ | \
/ | \
/ | \
+-----/+ +---+---+ +\------+
|C-PCE1| |C-PCE2 | |C-PCE3 |
+------+ +-------+ +-------+
/ | \
--------------- ----------------------- -------------
/ \ / \ / \
| +---+ +---+ | | +---+ +---+ +---+ | | +---+ +---+ |
| | A +-----+ B +-+--+--+ D +---+ E +---+ H +-+--+-+ J +----+ L | |
| +-\-+ +---+ | | +---+ +---+ +--\+ | | +---+ +-/-+ |
| \ | | / \ | | / |
| \ | | / \| | / |
| \ +---+ | | +---+ / |\\| +---+/ |
| \+ C +-+--+--+ G +/ | |----| K | |
\ +---+/ \ +---+ / \ +---+ /
---------------- ----------------------- --------------
Figure 3: Bulk Request example with Hierarchical PCEs
A 3-domain example is shown in Figure 3, with the hierarchical PCE
architecture. In this example nodes A/B/C belong to domain 1, nodes
D/E/G/H belong to domain 2, and nodes J/K/L belong to domain 3.
Inter-domain links are B-D/C-G between domains 1 and 2, and H-J/H-K
between domains 2 and 3. Given a path computation request from A to
L, a bulk request from P-PCE would be helpful to understand whether
it is possible to have different combinations on the inter-domain
links. However, the resources on some specific links become 'sticky'
and have to be indicated as 'sharing allowed' to avoid unnecessary
resource competition. For example, both the route A-B-D-E-H-J-L and
A-C-G-E-H-K-L are qualified, but these routes are competing for the
resource on the link E-H and cannot be established simultaneously,
so there must be one route failed to be reported to P-PCE. Given the
indication of allowing resource sharing on the link E-H, both of
these routes can be reported for P-PCE's decision, and there will
not be any competition as the P-PCE understands that only one path
needs to be set up.
3. Extensions to PCEP
3.1. Association Group and Type
According to the definition in [ietf-pce-association-group], the
association group is used to associate multiple LSPs into one group
for further path computation considerations, such as disjointness
and resource sharing. An association ID will be used to identify the
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resource sharing group. An association type that described
disjointness has been defined in [ietf-pce-association-diversity].
In this document, a new association type is defined as follows:
Association type = TBD1 ("Sharing Association Type").
A sharing group should have multiple LSPs. The number of LSPs and
the criteria for how LSPs share among each other are dependent on
local policy.
3.2. Resource Sharing TLV
The PCEP Resource Sharing group MAY carry the following TLV. It MAY
be carried within a PCReq message from the network element (or other
PCCs) so as to indicate the desired resource sharing requirements to
be applied by the stateful PCE during path computation.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = TBD2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |B|S|N|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following flags are defined:
* L (Link share) bit: when set, this flag indicates that the PCE
should prioritize the links shared by existing LSPs within the
sharing group for path computation.
* N (Node share) bit: when set, this flag indicates that the PCE
should prioritize the nodes shared by existing LSPs within the
sharing group for path computation.
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* S (SRLG share) bit: when set, this flag indicates that the PCE
should set the SRLG (Shared Risk Link Group) of the computed LSP to
the same as existing LSPs within the sharing group for path
computation.
* B (Bandwidth share) bit: when set, this flag indicates that the
PCE should prioritize the bandwidth to be shared by LSPs within the
sharing group for bulk path computation.
It is worth noting that there can be multiple flags set which may
conflict with each. In this scenario, the result for path
computation will be dependent on the policy of PCE.
Optional TLVs may be needed to indicate the LSPs with which the
resource is shared. If multiple LSPs are required, the PCE may need
to consider different sharing policies, which is implementation
dependent and may result in a different computing result. The
selection policy among multiple computation result is out of the
scope of this document.
3.3. Processing Rules
To request a path allowing resource sharing with one or multiple
existing LSPs, a PCC includes a Resource Sharing TLV in the
Association Group Object in any kind of path computation request
message, such as the PCReq, PCUpd, or PCInitiate messages specified
in [RFC8231] and [RFC8281].
On receipt of a PCEP message with a Resource Sharing TLV, a stateful
PCE MUST proceed as follows:
- If the Resource Sharing TLV is unknown/unsupported, the PCE will
follow procedures defined in [RFC5440]. That is, the PCE sends a
PCErr message with error type 26 (Association Error) and error
value 6 (Association Information Mismatch), and the related path
computation request is discarded.
- If the Resource Sharing TLV is extracted correctly, the PCE MUST
apply the requested resource sharing requirement.
The procedure of setting flags follows the rules defined in Section
3.1. The flags in the Resource Sharing TLV may be locally configured
on the requesting nodes via external entities, such as a network
management system or the entity that imposes the resource sharing
requirement.
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It is worth noting that the Resource Sharing TLV can be used
together with other path indication objects like the IRO/XRO, with
different objectives. The first difference is, the use of the
Resource Sharing TLV is to set up an alternative path, instead a new
path. It is also dependent on the knowledge held be the PCC, e.g.,
if the PCC has full knowledge of the path information and has a
strong preference on the route, it may send the request message with
an IRO to specify the route. On the other hand, if the PCC does not
know how the path should go but just wants to set up a new LSP to
replace the old one, it may use the Resource Sharing TLV instead of
an IRO. The second difference is that the Resource Sharing TLV is a
loose requirement. For example, if the constraint specified in an
IRO/XRO in an A-Z path computation request cannot be satisfied, the
reply message from PCE to PCC would be unsuccessful. However it is
still possible to have a path from the A-Z. If the target
node/link/SRLG/Bandwidth is set in the Resource Sharing TLV rather
than an IRO, the PCE may feedback a path from A-Z that does not
share the target specified in the Resource Sharing TLV.
4. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942].
Currently the authors are not aware of any implementations.
5. Manageability Considerations
All manageability requirements and considerations listed in
[RFC5440] and [RFC8231] apply to the PCEP protocol extensions
defined in this document. In addition, requirements and
considerations listed in this section apply.
5.1. Control of Function and Policy
A PCE or PCC implementation MUST allow operator-configured
associations and SHOULD allow setting of the resource sharing TLV
(Section 3.4) as described in this document.
5.2. Information and Data Models
An implementation SHOULD allow the operator to view the resource
sharing configured or created dynamically. Further implementation
SHOULD allow to view resource sharing associations reported by each
peer, and the current set of LSPs in the association. The PCEP YANG
module [ietf-pce-pcep-yang] includes association groups information.
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5.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
5.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440] and [RFC8231].
5.5. Requirements on Other Protocols
Mechanisms defined in this document do not imply any new
requirements on other protocols. The configuration on local policy
may be accomplished by other protocols, such as Netconf.
5.6. Impact on Network Operations
Mechanisms defined in [RFC5440] and [RFC8231] also apply to PCEP
extensions defined in this document.
6. Security Considerations
Security of PCEP is discussed in [RFC5440] and [RFC6952]. The
extensions in this document do not change the fundamentals of
security for PCEP.
However, the introduction of the Resource Sharing TLV in the
Association Group Object provides a vector that may be used to probe
for information from a network. For example, a PCC that wants to
discover the path of an LSP with which it is not involved can issue
a request message with a Resource Sharing TLV and may be able to get
back quite a lot of information about the path of the LSP through
issuing multiple such requests for different endpoints and analyzing
the received results. To protect against this, a PCE SHOULD be
configured with access and authorization controls such that only
authorized PCCs (for example, those within the network) can make
computation requests, only specifically authorized PCCs can make
requests for resource sharing, and such requests relating to
specific LSPs are further limited to a select few PCCs. How such
access controls and authorization is managed is outside the scope of
this document, but it will at the least include Access Control
Lists.
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Furthermore, a PCC must be aware that setting up an LSP that shares
resources with another LSP may be a way of attacking the other LSP,
for example by depriving it of the resources it needs to operate
correctly. Thus it is important that, both in PCEP and the
associated signaling protocols, only authorized resource sharing is
allowed.
7. IANA Considerations
7.1. Association Object Type Indicators
IANA maintains a registry called the "Path Computation Element
Protocol (PCEP) Numbers" registry with a subregistry called the
"Association Type Field" subregistry. IANA is requested to make an
assignment from that subregistry as follows:
Object Name Object Reference
Class Type
------------------------------------------------------------
TBD1 Sharing-group Association Type [this document]
7.2. PCEP TLV Definitions
This document defines the following TLVs to support the resource
sharing scenario:
Value Name Reference
------------------------------------------------------------
TBD2 Resource-sharing TLV [this document]
IANA is requested to allocate the following bit numbers in the flag
spaces of Resource-sharing TLV:
Bit Flag name Reference
31 Link Share [this document]
30 Node Share [this document]
29 SRLG Share [this document]
28 Bandwidth Share [this document]
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001. <https://www.rfc-
editor.org/info/rfc3209>.
[RFC5440] Vasseur, J.-P., and Le Roux, JL., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009. <https://www.rfc-editor.org/info/rfc5440>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8231] Crabbe, E., Medved, J., Minei, I., and R. Varga, "PCEP
Extensions for Stateful PCE", RFC8231, June 2017.
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", RFC 8281, October 2017. <https://www.rfc-
editor.org/info/rfc8281>.
[ietf-pce-association-group] Minei, I., Crabbe E., Sivabalan S.,
Ananthakrishnan H., Dhody D., Tanaka Y., "PCEP Extensions
for Establishing Relationships Between Sets of LSPs", work
in progress.
[ietf-pce-association-diversity] Litkowski, S., Sivabalan, S.,
Barth, C., Dhody, D., "Path Computation Element
communication Protocol extension for signaling LSP
diversity constraint", work in progress.
8.2. Informative References
[RFC4428] Papadimitriou, D., Mannie., E., "Analysis of Generalized
Multi-Protocol Label Switching (GMPLS)-based Recovery
Mechanisms (including Protection and Restoration)",
RFC4428, March 2006. <https://www.rfc-
editor.org/info/rfc4428>.
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draft-zhang-pce-resource-sharing-11 October 2019
[RFC4655] Farrel, A., Vasseur, J.-P., and Ash, J., "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006. <https://www.rfc-editor.org/info/rfc4655>.
[RFC5623] Oki., E., Takeda, T., Le Roux, JL., Farrel, A., "Framework
for PCE-Based Inter-Layer MPLS and GMPLS Traffic
Engineering", RFC5623, September 2009. <https://www.rfc-
editor.org/info/rfc5623>.
[RFC6952] Jethanandani, M., Patel, K., Zheng, L., "Analysis of BGP,
LDP, PCEP, and MSDP Issues According to the Keying and
Authentication for Routing Protocols (KARP) Design Guide",
RFC6952, May 2013. <https://www.rfc-
editor.org/info/rfc6952>.
[RFC7399] Farrel, A., King, D., "Unanswered Questions in the Path
Computation Element Architecture", RFC7399, October 2014.
<https://www.rfc-editor.org/info/rfc7399>.
[RFC7942] Sheffer, Y., Farrel, A., "Improving Awareness of Running
Code: The Implementation Status Section", RFC7942, July
2016. <https://www.rfc-editor.org/info/rfc7942>.
[ietf-pce-stateful-hpce] Dhody, D., Lee, Y., Ceccarelli, D., Shin,
J., King, D., Gonzalez de Dios, O., "Hierarchical Stateful
Path Computation Element (PCE)", work in progress.
[ietf-pce-pcep-yang] Dhody, D., Hardwick, J., Beeram, V., Tantsura,
J., "A YANG Data Model for Path Computation Element
Communications Protocol(PCEP)", work in progress.
9. Acknowledgements
The authors would like to thank Adrian Farrel for his review and
valuable comments.
10. Contributor's Address
Dhruv Dhody
Huawei Technologies
Email: dhruv.dhody@huawei.com
Igor Bryskin
Huawei Technologies
Email: Igor.Bryskin@huawei.com
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11. Authors' Addresses
Xian Zhang
Huawei Technologies
Email: zhang.xian@huawei.com
Haomian Zheng
Huawei Technologies
Email: zhenghaomian@huawei.com
Oscar Gonzalez de Dios
Telefonica I+D/gCTIO
Distrito Telefonica
E-28050 Madrid, Spain
EMail: oscar.gonzalezdedios@telefonica.com
Victor Lopez
Telefonica I+D/gCTIO
Distrito Telefonica
E-28050 Madrid, Spain
EMail: victor.lopezalvarez@telefonica.com
Yunbin Xu
CAICT
xuyunbin@caict.ac.cn
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