TEAS Working Group Haomian Zheng
Internet Draft Yi Lin
Category: Informational Huawei Technologies
Yang Zhao
China Mobile
Yunbin Xu
CAICT
Dieter Beller
Nokia
Expires: August 12, 2024 February 9, 2024
Interworking of GMPLS Control and Centralized Controller Systems
draft-ietf-teas-gmpls-controller-inter-work-13
Abstract
Generalized Multi-Protocol Label Switching (GMPLS) control allows
each network element (NE) to perform local resource discovery,
routing and signaling in a distributed manner.
On the other hand, with the development of software-defined
transport networking technology, a set of NEs can be controlled via
centralized controller hierarchies to address the issues from multi-
domain, multi-vendor, and multi-technology. An example of such
centralized architecture is Abstraction and Control of Traffic
Engineered Networks (ACTN) controller hierarchy described in RFC
8453.
Instead of competing with each other, both the distributed and the
centralized control plane have their own advantages, and should be
complementary in the system. This document describes how the GMPLS
distributed control plane can interwork with a centralized
controller system in a transport network.
Status of this Memo
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Table of Contents
1. Introduction ................................................. 3
2. Overview ..................................................... 4
2.1. Overview of GMPLS Control Plane ......................... 4
2.2. Overview of Centralized Controller System ............... 4
2.3. GMPLS Control Interworking with a Centralized Controller
System ....................................................... 5
3. Discovery Options ............................................ 7
3.1. LMP ..................................................... 7
4. Routing Options .............................................. 7
4.1. OSPF-TE ................................................. 7
4.2. ISIS-TE ................................................. 8
4.3. NETCONF/RESTCONF ........................................ 8
5. Path Computation ............................................. 8
5.1. Controller-based Path Computation ....................... 8
5.2. Constraint-based Path Computing in GMPLS Control ........ 8
5.3. Path Computation Element (PCE) .......................... 8
6. Signaling Options ............................................ 9
6.1. RSVP-TE ................................................. 9
7. Interworking Scenarios ....................................... 9
7.1. Topology Collection & Synchronization ................... 9
7.2. Multi-domain Service Provisioning ...................... 10
7.3. Multi-layer Service Provisioning ....................... 13
7.3.1. Multi-layer Path Computation ...................... 14
7.3.2. Cross-layer Path Creation ......................... 16
7.3.3. Link Discovery .................................... 17
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7.4. Recovery ............................................... 17
7.4.1. Span Protection ................................... 18
7.4.2. LSP Protection .................................... 18
7.4.3. Single-domain LSP Restoration ..................... 18
7.4.4. Multi-domain LSP Restoration ...................... 19
7.4.5. Fast Reroute ...................................... 23
7.5. Controller Reliability ................................. 23
8. Manageability Considerations ................................ 24
9. Security Considerations ..................................... 24
10. IANA Considerations......................................... 24
11. References ................................................. 24
11.1. Normative References .................................. 24
11.2. Informative References ................................ 26
12. Contributors ............................................... 28
13. Authors' Addresses ......................................... 29
1. Introduction
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] extends
MPLS to support different classes of interfaces and switching
capabilities such as Time-Division Multiplex Capable (TDM), Lambda
Switch Capable (LSC), and Fiber-Switch Capable (FSC). Each network
element (NE) running a GMPLS control plane collects network
information from other NEs and supports service provisioning through
signaling in a distributed manner. A more generic description of
Traffic-engineering networking information exchange can be found in
[RFC7926].
On the other hand, Software-Defined Networking (SDN) technologies
have been introduced to control the transport network in a
centralized manner. Centralized controllers can collect network
information from each node and provision services to corresponding
nodes. One of the examples is the Abstraction and Control of Traffic
Engineered Networks (ACTN) [RFC8453], which defines a hierarchical
architecture with Provisioning Network Controller (PNC), Multi-
domain Service Coordinator (MDSC) and Customer Network Controller
(CNC) as centralized controllers for different network abstraction
levels. A Path Computation Element (PCE) based approach has been
proposed as Application-Based Network Operations (ABNO) in
[RFC7491].
In such centralized controller architectures, GMPLS can be applied
for the NE-level control. A centralized controller may support GMPLS
enabled domains and may interact with a GMPLS enabled domain where
the GMPLS control plane does the service provisioning from ingress
to egress. In this case the centralized controller sends the request
to the ingress node and does not have to configure all NEs along the
path through the domain from ingress to egress thus leveraging the
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GMPLS control plane. This document describes how GMPLS control
interworks with a centralized controller system in a transport
network.
2. Overview
In this section, overviews of GMPLS control plane and centralized
controller system are discussed as well as the interactions between
the GMPLS control plane and centralized controllers.
2.1. Overview of GMPLS Control Plane
GMPLS separates the control plane and the data plane to support
time-division, wavelength, and spatial switching, which are
significant in transport networks. For the NE level control in
GMPLS, each node runs a GMPLS control plane instance.
Functionalities such as service provisioning, protection, and
restoration can be performed via GMPLS communication among multiple
NEs. At the same time, the GMPLS control plane instance can also
collect information about node and link resources in the network to
construct the network topology and compute routing paths for serving
service requests.
Several protocols have been designed for GMPLS control [RFC3945]
including link management [RFC4204], signaling [RFC3471], and
routing [RFC4202] protocols. The GMPLS control plane instances
applying these protocols communicate with each other to exchange
resource information and establish Label Switched Paths (LSPs). In
this way, GMPLS control plane instances in different nodes in the
network have the same view of the network topology and provision
services based on local policies.
2.2. Overview of Centralized Controller System
With the development of SDN technologies, a centralized controller
architecture has been introduced to transport networks. One example
architecture can be found in ACTN [RFC8453]. In such systems, a
controller is aware of the network topology and is responsible for
provisioning incoming service requests.
Multiple hierarchies of controllers are designed at different levels
implementing different functions. This kind of architecture enables
multi-vendor, multi-domain, and multi-technology control. For
example, a higher-level controller coordinates several lower-level
controllers controlling different domains, for topology collection
and service provisioning. Vendor-specific features can be abstracted
between controllers, and a standard API (e.g., generated from
RESTCONF/YANG) is used.
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2.3. GMPLS Control Interworking with a Centralized Controller System
Besides GMPLS and the interactions among the controller hierarchies,
it is also necessary for the controllers to communicate with the
network elements. Within each domain, GMPLS control can be applied
to each NE. The bottom-level centralized controller can act as an NE
to collect network information and initiate LSPs. Figure 1 shows an
example of GMPLS interworking with centralized controllers (ACTN
terminologies are used in the figure).
+-------------------+
| Orchestrator |
| (MDSC) |
+-------------------+
^ ^ ^
| | |
+-------------+ | +-------------+
| |RESTCONF/YANG models |
V V V
+-------------+ +-------------+ +-------------+
|Controller(N)| |Controller(G)| |Controller(G)|
| (PNC) | | (PNC) | | (PNC) |
+-------------+ +-------------+ +-------------+
^ ^ ^ ^ ^ ^
| | | | | |
NETCONF| |PCEP NETCONF| |PCEP NETCONF| |PCEP
/YANG | | /YANG | | /YANG | |
V V V V V V
.----------. Inter- .----------. Inter- .----------.
/ \ domain / \ domain / \
| | link | LMP | link | LMP |
| |======| OSPF-TE |======| OSPF-TE |
| | | RSVP-TE | | RSVP-TE |
\ / \ / \ /
`----------` `----------` `----------`
Non-GMPLS domain 1 GMPLS domain 2 GMPLS domain 3
Figure 1: Example of GMPLS/non-GMPLS interworking with Controllers
Figure 1 shows the scenario with two GMPLS domains and one non-GMPLS
domain. This system supports the interworking among non-GMPLS
domain, GMPLS domain and the controller hierarchies.
For domain 1, the network elements were not enabled with GMPLS so
the control is purely from the controller, via NETCONF/YANG and/or
PCEP.
For domains 2 and 3:
- Each domain has the GMPLS control plane enabled at the physical
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network level. The PNC can exploit GMPLS capabilities implemented
in the domain to listen to the IGP routing protocol messages (OSPF
LSAs, for example) that the GMPLS control plane instances are
disseminating into the network and thus learn the network
topology. For path computation in the domain with PNC implementing
a PCE, PCCs (e.g. NEs, other controller/PCE) use PCEP to ask the
PNC for a path and get replies. The MDSC communicates with PNCs
using, for example REST/RESTCONF based on YANG data models. As a
PNC has learned its domain topology, it can report the topology to
the MDSC. When a service arrives, the MDSC computes the path and
coordinates PNCs to establish the corresponding LSP segment.
- Alternatively, the NETCONF protocol can be used to retrieve
topology information utilizing the, e.g., [RFC8795] Yang model and
the technology-specific YANG model augmentations required for the
specific network technology. The PNC can retrieve topology
information from any NE (the GMPLS control plane instance of each
NE in the domain has the same topological view), construct the
topology of the domain, and export an abstracted view to the MDSC.
Based on the topology retrieved from multiple PNCs, the MDSC can
create a topology graph of the multi-domain network, and can use
it for path computation. To set up a service, the MDSC can
exploit, e.g., [TE-Tunnel] Yang model together with the
technology-specific YANG model augmentations.
This document focuses on the interworking between GMPLS and the
centralized controller system, including:
- The interworking between the GMPLS domains and the centralized
controllers (including the orchestrator, if it exists) controlling
the GMPLS domains.
- The interworking between a non-GMPLS domain (which is controlled
by a centralized controller system) and a GMPLS domain, through
the controller hierarchy architecture.
For convenience, this document uses the following terminologies for
the controller and the orchestrator:
- Controller(G): A domain controller controlling a GMPLS domain (the
controller(G) of the GMPLS domains 2 and 3 in Figure 1);
- Controller(N): A domain controller controlling a non-GMPLS domain
(the controller(N) of the non-GMPLS domain 1 in Figure 1);
- H-Controller(G): A domain controller controlling the higher-layer
GMPLS domain, in the context of multi-layer networks;
- L-Controller(G): A domain controller controlling the lower-layer
GMPLS domain, in the context of multi-layer networks;
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- H-Controller(N): A domain controller controlling the higher-layer
non-GMPLS domain, in the context of multi-layer networks;
- L-Controller(N): A domain controller controlling the lower-layer
non-GMPLS domain, in the context of multi-layer networks;
- Orchestrator(MD): An orchestrator used to orchestrate the multi-
domain networks;
- Orchestrator(ML): An orchestrator used to orchestrate the multi-
layer networks.
3. Discovery Options
In GMPLS control, the link connectivity needs to be verified between
each pair of nodes. In this way, link resources, which are
fundamental resources in the network, are discovered by both ends of
the link.
3.1. LMP
Link management protocol (LMP) [RFC4204] runs between a pair of
nodes and is used to manage TE links. In addition to the setup and
maintenance of control channels, LMP can be used to verify the data
link connectivity and correlate the link properties.
4. Routing Options
In GMPLS control, link state information is flooded within the
network as defined in [RFC4202]. Each node in the network can build
the network topology according to the flooded link state
information. Routing protocols such as OSPF-TE [RFC4203] and ISIS-TE
[RFC5307] have been extended to support different interfaces in
GMPLS.
In a centralized controller system, the centralized controller can
be placed in the GMPLS network and passively receive the information
flooded in the network. In this way, the centralized controller can
construct and update the network topology.
4.1. OSPF-TE
OSPF-TE is introduced for TE networks in [RFC3630]. OSPF extensions
have been defined in [RFC4203] to enable the capability of link
state information for GMPLS network. Based on this work, OSPF has
been extended to support technology-specific routing. The routing
protocol for OTN, WSON and optical flexi-grid networks are defined
in [RFC7138], [RFC7688] and [RFC8363], respectively.
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4.2. ISIS-TE
ISIS-TE is introduced for TE networks in [RFC5305] and is extended
to support GMPLS routing functions [RFC5307], and has been updated
to [RFC7074] to support the latest GMPLS switching capability and
Types fields.
4.3. NETCONF/RESTCONF
NETCONF [RFC6241] and RESTCONF [RFC8040] protocols are originally
used for network configuration. These protocols can also be used for
topology retrieval by using topology-related YANG models, such as
[RFC8345] and [RFC8795]. These protocols provide a powerful
mechanism for notification of topology changes to the client.
5. Path Computation
5.1. Controller-based Path Computation
Once a controller learns the network topology, it can utilize the
available resources to serve service requests by performing path
computation. Due to abstraction, the controllers may not have
sufficient information to compute the optimal path. In this case,
the controller can interact with other controllers by sending, for
example, Yang Path Computation requests [PAT-COMP] or PCEP, to
compute a set of potential optimal paths and then, based on its own
constraints, policy and specific knowledge (e.g. cost of access
link) can choose the more feasible path for e2e service path setup.
Path computation is one of the key objectives in various types of
controllers. In the given architecture, it is possible for different
components that have the capability to compute the path.
5.2. Constraint-based Path Computing in GMPLS Control
In GMPLS control, a routing path may be computed by the ingress node
([RFC3473]) based on the ingress node Traffic Engineering Database
(TED). In this case, constraint-based path computation is performed
according to the local policy of the ingress node.
5.3. Path Computation Element (PCE)
PCE has been introduced in [RFC4655] as a functional component that
provides services to compute paths in a network. In [RFC5440], the
path computation is accomplished by using the TED, which maintains a
view of the link resources in the network. The emergence of PCE
efficiently improves the quality of network planning and offline
computation, but there is a risk that the computed path may be
infeasible if there is a diversity requirement, because stateless
PCE has no knowledge about the former computed paths.
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To address this issue, stateful PCE has been proposed in [RFC8231].
Besides the TED, an additional LSP Database (LSP-DB) is introduced
to archive each LSP computed by the PCE. In this way, PCE can easily
figure out the relationship between the computing path and former
computed paths. In this approach, PCE provides computed paths to
PCC, and then PCC decides which path is deployed and when to be
established.
With PCE-Initiated LSPs [RFC8281], PCE is allowed to trigger the PCC
to perform setup, maintenance, and teardown of the PCE-initiated LSP
under the stateful PCE model. This would allow a dynamic network
that is centrally controlled and deployed.
In a centralized controller system, the PCE can be implemented in a
centralized controller, and the centralized controller performs path
computation according to its local policies. On the other hand, the
PCE can also be placed outside of the centralized controller. In
this case, the centralized controller acts as a PCC to request path
computation to the PCE through PCEP. One of the reference
architecture can be found in [RFC7491].
6. Signaling Options
Signaling mechanisms are used to set up LSPs in GMPLS control.
Messages are sent hop by hop between the ingress node and the egress
node of the LSP to allocate labels. Once the labels are allocated
along the path, the LSP setup is accomplished. Signaling protocols
such as RSVP-TE [RFC3473] have been extended to support different
interfaces in GMPLS.
6.1. RSVP-TE
RSVP-TE is introduced in [RFC3209] and extended to support GMPLS
signaling in [RFC3473]. Several label formats are defined for a
generalized label request, a generalized label, suggested label and
label sets. Based on [RFC3473], RSVP-TE has been extended to support
technology-specific signaling. The RSVP-TE extensions for OTN, WSON,
optical flexi-grid network are defined in [RFC7139], [RFC7689], and
[RFC7792], respectively.
7. Interworking Scenarios
7.1. Topology Collection & Synchronization
Topology information is necessary on both network elements and
controllers. The topology on a network element is usually raw
information, while the topology on the controller can be either raw
or abstracted. Three different abstraction methods have been
described in [RFC8453], and different controllers can select the
corresponding method depending on application.
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When there are changes in the network topology, the impacted network
elements need to report changes to all the other network elements,
together with the controller, to sync up the topology information.
The inter-NE synchronization can be achieved via protocols mentioned
in Sections 3 and 4. The topology synchronization between NEs and
controllers can either be achieved by routing protocols OSPF-
TE/PCEP-LS in [PCEP-LS] or NETCONF protocol notifications with YANG
model.
7.2. Multi-domain Service Provisioning
Based on the topology information on controllers and network
elements, service provisioning can be deployed. Plenty of methods
have been specified for single domain service provisioning, such as
using PCEP and RSVP-TE.
Multi-domain service provisioning would require coordination among
the controller hierarchies. Given the service request, the end-to-
end delivery procedure may include interactions at any level (i.e.
interface) in the hierachy of the controllers (e.g. MPI and SBI for
ACTN). The computation for a cross-domain path is usually completed
by controllers who have a global view of the topologies. Then the
configuration is decomposed into lower-level controllers, to
configure the network elements to set up the path.
A combination of the centralized and distributed protocols may be
necessary for the interaction between network elements and
controller. Several methods can be used to create the inter-domain
path:
1) With end-to-end RSVP-TE session:
In this method, all the domains need to support the RSVP-TE protocol
and thus need to be GMPLS domains. The Controller(G) of the source
domain triggers the source node to create the end-to-end RSVP-TE
session, and the assignment and distribution of the labels on the
inter-domain links are done by the border nodes of each domain,
using RSVP-TE protocol. Therefore, this method requires the
interworking of RSVP-TE protocols between different domains.
There are two possible methods:
1.1) One single end-to-end RSVP-TE session
In this method, an end-to-end RSVP-TE session from the source node
to the destination node will be used to create the inter-domain
path. A typical example would be the PCE Initiation scenario, in
which a PCE message (PCInitiate) is sent from the controller(G) to
the source node, and then trigger an RSVP procedure along the path.
Similarly, the interaction between the controller and the source
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node of the source domain can be achieved by NETCONF protocol with
corresponding YANG models, and then completed by running RSVP among
the network elements.
1.2) LSP Stitching
The LSP stitching method defined in [RFC5150] can also be used to
create the end-to-end LSP. I.e., when the source node receives an
end-to-end path creation request (e.g., using PCEP or NETCONF
protocol), the source node starts an end-to-end RSVP-TE session
along the end points of each LSP segment (refers to S-LSP in
[RFC5150]) of each domain, to assign the labels on the inter-domain
links between each pair of neighbor S-LSPs, and stitch the end-to-
end LSP to each S-LSP. See Figure 2 as an example. Note that the S-
LSP in each domain can be either created by its Controller(G) in
advance, or created dynamically triggered by the end-to-end RSVP-TE
session.
+------------------------+
| Orchestrator(MD) |
+-----------+------------+
|
+---------------+ +------V-------+ +---------------+
| Controller(G) | | Controller(G)| | Controller(G) |
+-------+-------+ +------+-------+ +-------+-------+
| | |
+--------V--------+ +-------V--------+ +--------V--------+
|Client | | | | Client|
|Signal Domain 1| | Domain 2 | |Domain 3 Signal|
| | | | | | | |
|+-+-+ | | | | +-+-+|
|| | | +--+ +--+| |+--+ +--+ +--+| |+--+ +--+ | | ||
|| | | | | | || || | | | | || || | | | | | ||
|| ******************************************************** ||
|| | | | | || || | | | | || || | | | | ||
|+---+ +--+ +--+| |+--+ +--+ +--+| |+--+ +--+ +---+|
+-----------------+ +----------------+ +-----------------+
| . . . . . . |
| .<-S-LSP 1->. .<- S-LSP 2 -->. .<-S-LSP 3->. |
| . . . . |
|-------------->.---->.------------->.---->.-------------->|
|<--------------.<----.<-------------.<----.<--------------|
| End-to-end RSVP-TE session for LSP stitching |
Figure 2: LSP stitching
2) Without end-to-end RSVP-TE session:
In this method, each domain can be a GMPLS domain or a non-GMPLS
domain. Each controller (may be a Controller(G) or a Controller(N))
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is responsible to create the path segment within its domain. The
border node does not need to communicate with other border nodes in
other domains for the distribution of labels on inter-domain links,
so end-to-end RSVP-TE session through multiple domains is not
required, and the interworking of RSVP-TE protocol between different
domains is not needed.
Note that path segments in the source domain and the destination
domain are "asymmetrical" segments, because the configuration of
client signal mapping into server layer tunnel is needed at only one
end of the segment, while configuration of server layer cross-
connect is needed at the other end of the segment. See the example
in Figure 3.
+------------------------+
| Orchestrator(MD) |
+-----------+------------+
|
+---------------+ +------V-------+ +---------------+
| Controller | | Controller | | Controller |
+-------+-------+ +------+-------+ +-------+-------+
| | |
+--------V--------+ +-------V--------+ +--------V--------+
|Client Domain 1| | Domain 2 | | Domain 3 Client|
|Signal | | | | Signal|
| | Server layer| | | | | |
| | tunnel | | | | | |
|+-+-+ ^ | | | | +-+-+|
|| | | +--+ |+--+| |+--+ +--+ +--+| |+--+ +--+ | | ||
|| | | | | || || || | | | | || || | | | | | ||
|| ******************************************************** ||
|| | | | | || . || | | | | || . || | | | | ||
|+---+ +--+ +--+| . |+--+ +--+ +--+| . |+--+ +--+ +---+|
+-----------------+ . +----------------+ . +-----------------+
. . . .
.<-Path Segment 1->.<--Path Segment 2-->.<-Path Segment 3->.
Figure 3: Example of asymmetrical path segment
The PCEP / GMPLS protocols should support creation of such
asymmetrical segments.
Note also that mechanisms to assign the labels in the inter-domain
links also need to be considered. There are two possible methods:
2.1) Inter-domain labels assigned by NEs:
The concept of Stitching Label that allows stitching local path
segments was introduced in [RFC5150] and [sPCE-ID], in order to form
the inter-domain path crossing several different domains. It also
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describes the Backward-Recursive PCE-Based Computation (BRPC) and
Hierarchical Path Computation Element (H-PCE) PCInitiate procedure,
i.e., the ingress node of each downstream domain assigns the
stitching label for the inter-domain link between the downstream
domain and its upstream neighbor domain, and this stitching label
will be passed to the upstream neighbor domain by PCE protocol,
which will be used for the path segment creation in the upstream
neighbor domain.
2.2) Inter-domain labels assigned by controller:
If the resources of inter-domain links are managed by the
orchestrator(MD), each domain controller can provide to the
orchestrator(MD) the list of available labels (e.g. timeslots if OTN
is the scenario) using the IETF Topology YANG model and related
technology specific extension. Once the orchestrator(MD) has
computed the E2E path, RSVP-TE or PCEP can be used in the different
domains to setup related segment tunnel consisting with label inter-
domain information, e.g. for PCEP the label Explicit Route Object
(ERO) can be included in the PCInitiate message to indicate the
inter-domain labels, so that each border node of each domain can
configure the correct cross-connect within itself.
7.3. Multi-layer Service Provisioning
GMPLS can interwork with centralized controller system in multi-
layer networks.
+----------------+
|Orchestrator(ML)|
+------+--+------+
| | Higher-layer Network
| | .--------------------.
| | / \
| | +--------------+ | +--+ Link +--+ |
| +-->| H-Controller +----->| | |**********| | |
| +--------------+ | +--+ +--+ |
| \ . . /
| `--.------------.---`
| . .
| .---.------------.---.
| / . . \
| +--------------+ | +--+ +--+ +--+ |
+----->| L-Controller +----->| | ============== | |
+--------------+ | +--+ +--+ +--+ |
\ H-LSP /
`-------------------`
Lower-layer Network
Figure 4: GMPLS-controller interworking in multi-layer networks
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An example with two layers of network is shown in Figure 4. In this
example, the GMPLS control plane is enabled in at least one layer
network (otherwise it is out of scope of this document), and
interworks with the controller of its domain (H-Controller and L-
Controller, respectively). The Orchestrator(ML) is used to
coordinate the control of the multi-layer network.
7.3.1. Multi-layer Path Computation
[RFC5623] describes three inter-layer path computation models and
four inter-layer path control models:
- 3 Path computation:
o Single PCE path computation model
o Multiple PCE path computation with inter-PCE communication
model
o Multiple PCE path computation without inter-PCE communication
model
- 4 Path control:
o PCE-VNTM cooperation model
o Higher-layer signaling trigger model
o NMS-VNTM cooperation model (integrated flavor)
o NMS-VNTM cooperation model (separate flavor)
Section 4.2.4 of [RFC5623] also provides all the possible
combinations of inter-layer path computation and inter-layer path
control models.
To apply [RFC5623] in multi-layer network with GMPLS-controller
interworking, the H-Controller and the L-Controller can act as the
PCE Hi and PCE Lo respectively, and typically, the Orchestrator(ML)
can act as a Virtual Network Topology Manager (VNTM) because it has
the abstracted view of both the higher-layer and lower-layer
networks.
Table 1 shows all possible combinations of path computation and path
control models in multi-layer network with GMPLS-controller
interworking:
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Table 1: Combinations of path computation and path control models
---------------------------------------------------------
| Path computation |Single PCE | Multiple | Multiple |
| \ | (Not | PCE with | PCE w/o |
| Path control |applicable)| inter-PCE | inter-PCE |
|---------------------+-----------+-----------+-----------|
| PCE-VNTM | ...... | | |
| cooperation | . -- . | Yes | Yes |
| | . . | | |
|---------------------+--.----.---+-----------+-----------|
| Higher-layer | . . | | |
| signaling trigger | . -- . | Yes | Yes |
| | . . | | |
|---------------------+--.----.---+-----------+-----------|
| NMS-VNTM | . . | .........|....... |
| cooperation | . -- . | .Yes | No . |
| (integrated flavor) | . . | . | . |
|---------------------+--.----.---+--.--------+------.----|
| NMS-VNTM | . . | . | . |
| cooperation | . -- . | .No | Yes. |
| (separate flavor) | ...... | .........|....... |
---------------------+----|------+--------|--+-----------
V V
Not applicable because Typical models to be used
there are multiple PCEs
Note that:
- Since there is one PCE in each layer network, the path computation
model "Single PCE path computation" is not applicable.
- For the other two path computation models "Multiple PCE with
inter-PCE" and "Multiple PCE w/o inter-PCE", the possible
combinations are the same as defined in [RFC5623]. More
specifically:
o The path control models "NMS-VNTM cooperation (integrated
flavor)" and "NMS-VNTM cooperation (separate flavor)" are the
typical models to be used in multi-layer network with GMPLS-
controller interworking. This is because in these two models,
the path computation is triggered by the Network Management
System (NMS) or VNTM. And in the centralized controller system,
the path computation requests are typically from the
Orchestrator(ML) (acts as VNTM).
o For the other two path control models "PCE-VNTM cooperation"
and "Higher-layer signaling trigger", the path computation is
triggered by the NEs, i.e., NE performs PCC functions. These
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two models are still possible to be used, although they are not
the main methods.
7.3.2. Cross-layer Path Creation
In a multi-layer network, a lower-layer LSP in the lower-layer
network can be created, which will construct a new link in the
higher-layer network. Such lower-layer LSP is called Hierarchical
LSP, or H-LSP for short, see [RFC6107].
The new link constructed by the H-LSP can then be used by the
higher-layer network to create new LSPs.
As described in [RFC5212], two methods are introduced to create the
H-LSP: the static (pre-provisioned) method and the dynamic
(triggered) method.
1) Static (pre-provisioned) method
In this method, the H-LSP in the lower-layer network is created in
advance. After that, the higher-layer network can create LSPs using
the resource of the link constructed by the H-LSP.
The Orchestrator(ML) is responsible to decide the creation of H-LSP
in the lower-layer network if it acts as a VNTM. It then requests
the L-Controller to create the H-LSP via, for example, MPI interface
under the ACTN architecture. See Section 3.3.2 of [TE-Tunnel].
If the lower-layer network is a GMPLS domain, the L-Controller(G)
can trigger the GMPLS control plane to create the H-LSP. As a
typical example, the PCInitiate message can be used for the
communication between the L-Controller and the source node of the H-
LSP. And the source node of the H-LSP can trigger the RSVP-TE
signaling procedure to create the H-LSP, as described in [RFC6107].
If the lower-layer network is a non-GMPLS domain, other methods may
be used by the L-Controller(N) to create the H-LSP, which is out of
scope of this document.
2) Dynamic (triggered) method
In this method, the signaling of LSP creation in the higher-layer
network will trigger the creation of H-LSP in the lower-layer
network dynamically, if it is necessary. Therefore, both the higher-
layer and lower-layer networks need to support the RSVP-TE protocol
and thus need to be GMPLS domains.
In this case, after the cross-layer path is computed, the
Orchestrator(ML) requests the H-Controller(G) for the cross-layer
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LSP creation. As a typical example, the MPI interface under the ACTN
architecture could be used.
The H-Controller(G) can trigger the GMPLS control plane to create
the LSP in the higher-layer network. As a typical example, the
PCInitiate message can be used for the communication between the H-
Controller(G) and the source node of the Higher-layer LSP, as
described in Section 4.3 of [RFC8282]. At least two sets of ERO
information should be included to indicate the routes of higher-
layer LSP and lower-layer H-LSP.
The source node of the Higher-layer LSP follows the procedure
defined in Section 4 of [RFC6001], to trigger the GMPLS control
plane in both higher-layer network and lower-layer network to create
the higher-layer LSP and the lower-layer H-LSP.
On success, the source node of the H-LSP should report the
information of the H-LSP to the L-Controller(G) via, for example,
PCRpt message.
7.3.3. Link Discovery
If the higher-layer network and the lower-layer network are under
the same GMPLS control plane instance, the H-LSP can be a Forwarding
Adjacency LSP (FA-LSP). Then the information of the link constructed
by this FA-LSP, called Forwarding Adjacency (FA), can be advertised
in the routing instance, so that the H-Controller can be aware of
this new FA. [RFC4206] and the following updates to it (including
[RFC6001] and [RFC6107]) describe the detailed extensions to support
advertisement of an FA.
If the higher-layer network and the lower-layer network are under
separate GMPLS control plane instances, or one of the layer networks
is a non-GMPLS domain, after an H-LSP is created in the lower-layer
network, the link discovery procedure will be triggered in the
higher-layer network to discover the information of the link
constructed by the H-LSP. LMP protocol defined in [RFC4204] can be
used if the higher-layer network supports GMPLS. The information of
this new link will be advertised to the H-Controller.
7.4. Recovery
The GMPLS recovery functions are described in [RFC4426]. Span
protection, end-to-end protection and restoration, are discussed
with different protection schemes and message exchange requirements.
Related RSVP-TE extensions to support end-to-end recovery is
described in [RFC4872]. The extensions in [RFC4872] include
protection, restoration, preemption, and rerouting mechanisms for an
end-to-end LSP. Besides end-to-end recovery, a GMPLS segment
recovery mechanism is defined in [RFC4873], which also intends to be
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compatible with Fast Reroute (FRR) (see [RFC4090] which defines
RSVP-TE extensions for the FRR mechanism, and [RFC8271] which
described the updates of GMPLS RSVP-TE protocol for FRR of GMPLS TE-
LSPs).
7.4.1. Span Protection
Span protection refers to the protection of the link between two
neighboring switches. The main protocol requirements include:
- Link management: Link property correlation on the link protection
type;
- Routing: announcement of the link protection type;
- Signaling: indication of link protection requirement for that LSP.
GMPLS already supports the above requirements, and there are no new
requirements in the scenario of interworking between GMPLS and
centralized controller system.
7.4.2. LSP Protection
The LSP protection includes end-to-end and segment LSP protection.
For both cases:
- In the provisioning phase:
In both single-domain and multi-domain scenarios, the disjoint
path computation can be done by the centralized controller system,
as it has the global topology and resource view. And the path
creation can be done by the procedure described in Section 7.2.
- In the protection switchover phase:
In both single-domain and multi-domain scenarios, the existing
standards provide the distributed way to trigger the protection
switchover. For example, data plane Automatic Protection Switching
(APS) mechanism described in [G.808.1], [RFC7271] and [RFC8234],
or GMPLS Notify mechanism described in [RFC4872] and [RFC4873]. In
the scenario of interworking between GMPLS and centralized
controller system, using these distributed mechanisms rather than
centralized mechanism (i.e., the controller triggers the
protection switchover) can significantly shorten the protection
switching time.
7.4.3. Single-domain LSP Restoration
- Pre-planned LSP protection (including shared-mesh restoration):
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In pre-planned protection, the protecting LSP is established only
in the control plane in the provisioning phase, and will be
activated in the data plane once failure occurs.
In the scenario of interworking between GMPLS and centralized
controller system, the route of protecting LSP can be computed by
the centralized controller system. This takes the advantage of
making better use of network resource, especially for the resource
sharing in shared-mesh restoration.
- Full LSP rerouting:
In full LSP rerouting, the normal traffic will be switched to an
alternate LSP that is fully established only after failure
occurrence.
As described in [RFC4872] and [RFC4873], the alternate route can
be computed on demand when failure occurrence, or pre-computed and
stored before failure occurrence.
In a fully distributed scenario, the pre-computation method offers
faster restoration time, but has the risk that the pre-computed
alternate route may become out of date due to the changes of the
network.
In the scenario of interworking between GMPLS and centralized
controller system, the pre-computation of the alternate route
could take place in the centralized controller (and may be stored
in the controller or the head-end node of the LSP). In this way,
any changes in the network can trigger the refreshment of the
alternate route by the centralized controller. This makes sure
that the alternate route will not become out of date.
7.4.4. Multi-domain LSP Restoration
A working LSP may traverse multiple domains, each of which may or
may not support GMPLS distributed control plane.
In the case that all the domains support GMPLS, both the end-to-end
rerouting method and the domain segment rerouting method could be
used.
In the case that only some of the domains support GMPLS, the domain
segment rerouting method could be used in those GMPLS domains. For
other domains which do not support GMPLS, other mechanisms may be
used to protect the LSP segments, which are out of scope of this
document.
1) End-to-end rerouting:
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In this case, failure that occurs on the working LSP inside any
domain or on the inter-domain links will trigger the end-to-end
restoration.
In both pre-planned and full LSP rerouting, the end-to-end
protecting LSP could be computed by the centralized controller
system, and could be created by the procedure described in Section
7.2. Note that the end-to-end protecting LSP may traverse different
domains from the working LSP, depending on the result of multi-
domain path computation for the protecting LSP.
+----------------+
|Orchestrator(MD)|
+-------.--------+
............................................
. . . .
+----V-----+ +----V-----+ +----V-----+ +----V-----+
|Controller| |Controller| |Controller| |Controller|
| (G) 1 | | (G) 2 | | (G) 3 | | (G) 4 |
+----.-----+ +-------.--+ +-------.--+ +----.-----+
. . . .
+----V--------+ +-V-----------+ . +-------V-----+
| Domain 1 | | Domain 2 | . | Domain 4 |
|+---+ +---+| |+---+ +---+| . |+---+ +---+|
|| ===/~/======/~~~/================================ ||
|+-*-+ +---+| |+---+ +---+| . |+---+ +-*-+|
| * | +-------------+ . | * |
| * | . | * |
| * | +-------------+ . | * |
| * | | Domain 3 <... | * |
|+-*-+ +---+| |+---+ +---+| |+---+ +-*-+|
|| ************************************************* ||
|+---+ +---+| |+---+ +---+| |+---+ +---+|
+-------------+ +-------------+ +-------------+
====: Working LSP ****: Protecting LSP /~/: Failure
Figure 5: End-to-end restoration
2) Domain segment rerouting:
2.1) Intra-domain rerouting:
If failure occurs on the working LSP segment in a GMPLS domain, the
segment rerouting ([RFC4873]) could be used for the working LSP
segment in that GMPLS domain. Figure 6 shows an example of intra-
domain rerouting.
The intra-domain rerouting of a non-GMPLS domain is out of scope of
this document.
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+----------------+
|Orchestrator(MD)|
+-------.--------+
............................................
. . . .
+----V-----+ +----V-----+ +----V-----+ +----V-----+
|Controller| |Controller| |Controller| |Controller|
| (G) 1 | |(G)/(N) 2 | |(G)/(N) 3 | |(G)/(N) 4 |
+----.-----+ +-------.--+ +-------.--+ +----.-----+
. . . .
+----V--------+ +-V-----------+ . +-------V-----+
| Domain 1 | | Domain 2 | . | Domain 4 |
|+---+ +---+| |+---+ +---+| . |+---+ +---+|
|| ===/~/=========================================== ||
|+-*-+ +-*-+| |+---+ +---+| . |+---+ +---+|
| * * | +-------------+ . | |
| * * | . | |
| * * | +-------------+ . | |
| * * | | Domain 3 <... | |
|+-*-+ +-*-+| |+---+ +---+| |+---+ +---+|
|| ********* || || | | || || | | ||
|+---+ +---+| |+---+ +---+| |+---+ +---+|
+-------------+ +-------------+ +-------------+
====: Working LSP ****: Rerouting LSP segment /~/: Failure
Figure 6: Intra-domain segment rerouting
2.2) Inter-domain rerouting:
If intra-domain segment rerouting failed (e.g., due to lack of
resource in that domain), or if failure occurs on the working LSP on
an inter-domain link, the centralized controller system may
coordinate with other domain(s), to find an alternative path or path
segment to bypass the failure, and then trigger the inter-domain
rerouting procedure. Note that the rerouting path or path segment
may traverse different domains from the working LSP.
The domains involved in the inter-domain rerouting procedure need to
be GMPLS domains, which support the RSVP-TE signaling for the
creation of rerouting LSP segment.
For inter-domain rerouting, the interaction between GMPLS and
centralized controller system is needed:
- Report of the result of intra-domain segment rerouting to its
Controller(G), and then to the Orchestrator(MD). The former one
could be supported by the PCRpt message in [RFC8231], while the
latter one could be supported by the MPI interface of ACTN.
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- Report of inter-domain link failure to the two Controllers (e.g.,
Controller(G) 1 and Controller(G) 2 in Figure 7) by which the two
ends of the inter-domain link are controlled respectively, and
then to the Orchestrator(MD). The former one could be done as
described in Section 7.1 of this document, while the latter one
could be supported by the MPI interface of ACTN.
- Computation of rerouting path or path segment crossing multi-
domains by the centralized controller system (see [PAT-COMP]);
- Creation of rerouting LSP segment in each related domain. The
Orchestrator(MD) can send the LSP segment rerouting request to the
source Controller(G) (e.g., Controller(G) 1 in Figure 7) via MPI
interface, and then the Controller(G) can trigger the creation of
rerouting LSP segment through multiple GMPLS domains using GMPLS
rerouting signaling. Note that the rerouting LSP segment may
traverse a new domain which the working LSP does not traverse
(e.g., Domain 3 in Figure 7).
+----------------+
|Orchestrator(MD)|
+-------.--------+
..................................................
. . . .
+-----V------+ +-----V------+ +-----V------+ +-----V------+
| Controller | | Controller | | Controller | | Controller |
| (G) 1 | | (G) 2 | | (G) 3 | | (G)/(N) 4 |
+-----.------+ +------.-----+ +-----.------+ +-----.------+
. . . .
+-----V-------+ +----V--------+ . +------V------+
| Domain 1 | | Domain 2 | . | Domain 4 |
|+---+ +---+| |+---+ +---+| . |+---+ +---+|
|| | | || || | | || . || | | ||
|| ============/~/========================================== ||
|| * | | || || | | * || . || | | ||
|+-*-+ +---+| |+---+ +-*-+| . |+---+ +---+|
| * | +----------*--+ . | |
| * | ***** . | |
| * | +----------*-----V----+ | |
| * | | *Domain 3 | | |
|+-*-+ +---+| |+---+ +-*-+ +---+| |+---+ +---+|
|| * | | || || | | * | | || || | | ||
|| ******************************* | | || || | | ||
|| | | || || | | | | || || | | ||
|+---+ +---+| |+---+ +---+ +---+| |+---+ +---+|
+-------------+ +---------------------+ +-------------+
====: Working LSP ****: Rerouting LSP segment /~/: Failure
Figure 7: Inter-domain segment rerouting
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7.4.5. Fast Reroute
[RFC4090] defines two methods of fast reroute, the one-to-one backup
method and the facility backup method. For both methods:
1) Path computation of protecting LSP:
In Section 6.2 of [RFC4090], the protecting LSP (detour LSP in one-
to-one backup, or bypass tunnel in facility backup) could be
computed by the Point of Local Repair (PLR) using, for example,
Constraint-based Shortest Path First (CSPF) computation. In the
scenario of interworking between GMPLS and centralized controller
system, the protecting LSP could also be computed by the centralized
controller system, as it has the global view of the network
topology, resource and information of LSPs.
2) Protecting LSP creation:
In the scenario of interworking between GMPLS and centralized
controller system, the Protecting LSP could still be created by the
RSVP-TE signaling protocol as described in [RFC4090] and [RFC8271].
In addition, if the protecting LSP is computed by the centralized
controller system, the Secondary Explicit Route Object defined in
[RFC4873] could be used to explicitly indicate the route of the
protecting LSP.
3) Failure detection and traffic switchover:
If a PLR detects that failure occurs, it may significantly shorten
the protection switching time by using the distributed mechanisms
described in [RFC4090] to switch the traffic to the related detour
LSP or bypass tunnel, rather than in a centralized way.
7.5. Controller Reliability
Given the important role in the network, the reliability of
controller is critical. If the controller is shut down or
disconnected from the network, it is highly desirable that all of
the services currently provisioned in the network continue to
function and carry traffic. Furthermore, protection switching to
pre-established paths should also function. Additionally, it is
desirable to provide protection mechanisms, such as redundancy, so
that full operational control can be maintained even when one
instance of the controller fails. This can be either achieved by
controller back up or functionality back up. There are several of
controller backup or federation mechanisms in the literature. It is
also more reliable to have some function back up in the network
element, to guarantee the performance in the network.
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8. Manageability Considerations
Each entity in the network, including both controllers and network
elements, should be managed properly as it will interact with other
entities. The manageability considerations in controller hierarchies
and network elements still apply respectively. For the protocols
applied in the network, manageability is also requested.
The responsibility of each entity should be clarified. The control
of function and policy among different controllers should be
consistent via proper negotiation process.
9. Security Considerations
This document provides the interwork between the GMPLS and
controller hierarchies. The security requirements in both system
still apply respectively. Protocols referenced in this document also
have various security considerations, which is also expected to be
satisfied.
Other considerations on the interface between the controller and the
network element are also important. Such security includes the
functions to authenticate and authorize the control access to the
controller from multiple network elements. Security mechanisms on
the controller are also required to safeguard the underlying network
elements against attacks on the control plane and/or unauthorized
usage of data transport resources.
10. IANA Considerations
This document requires no IANA actions.
11. References
11.1. Normative References
[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.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630, September
2003.
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[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC4206] Kompella, K. and Rekhter Y., "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC4872] Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
Ed., "RSVP-TE Extensions in Support of End-to-End
Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC 4872, May 2007.
[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
"GMPLS Segment Recovery", RFC 4873, May 2007.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC6001] Papadimitriou D., Vigoureux M., Shiomoto K., Brungard D.
and Le Roux JL., "Generalized MPLS (GMPLS) Protocol
Extensions for Multi-Layer and Multi-Region Networks
(MLN/MRN)", RFC 6001, October 2010.
[RFC6107] Shiomoto K. and Farrel A., "Procedures for Dynamically
Signaled Hierarchical Label Switched Paths", RFC 6107,
February 2011.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder J., Bierman A.,
"Network Configuration Protocol (NETCONF)", RFC 6241, June
2011.
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[RFC7074] Berger, L. and J. Meuric, "Revised Definition of the GMPLS
Switching Capability and Type Fields", RFC 7074, November
2013.
[RFC7491] King, D., Farrel, A., "A PCE-Based Architecture for
Application-Based Network Operations", RFC7491, March
2015.
[RFC7926] Farrel, A., Drake, J., Bitar, N., Swallow, G., Ceccarelli,
D. and Zhang, X., "Problem Statement and Architecture for
Information Exchange between Interconnected Traffic-
Engineered Networks", RFC7926, July 2016.
[RFC8040] Bierman, A., Bjorklund, M., Watsen, K., "RESTCONF
Protocol", RFC 8040, January 2017.
[RFC8271] Taillon M., Saad T., Gandhi R., Ali Z. and Bhatia M.,
"Updates to the Resource Reservation Protocol for Fast
Reroute of Traffic Engineering GMPLS Label Switched
Paths", RFC 8271, October 2017.
[RFC8282] Oki E., Takeda T., Farrel A. and Zhang F., "Extensions to
the Path Computation Element Communication Protocol (PCEP)
for Inter-Layer MPLS and GMPLS Traffic Engineering", RFC
8282, December 2017.
[RFC8453] Ceccarelli, D. and Y. Lee, "Framework for Abstraction and
Control of Traffic Engineered Networks", RFC 8453, August
2018.
[RFC8795] Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H.,
Gonzalez De Dios, O., "YANG Data Model for Traffic
Engineering (TE) Topologies", RFC8795, August 2020.
11.2. Informative References
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, October 2005.
[RFC4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC 4204,
October 2005.
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[RFC4426] Lang, J., Ed., Rajagopalan, B., Ed., and D. Papadimitriou,
Ed., "Generalized Multi-Protocol Label witching (GMPLS)
Recovery Functional Specification", RFC 4426, March 2006.
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, J.P., Farrel, A.,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February, 2008.
[RFC5212] Shiomoto K., Papadimitriou D., Le Roux JL., Vigoureux M.
and Brungard D., "Requirements for GMPLS-Based Multi-
Region and Multi-Layer Networks (MRN/MLN)", RFC 5212, July
2008.
[RFC5623] Oki E., Takeda T., Le Roux JL. and Farrel A., "Framework
for PCE-Based Inter-Layer MPLS and GMPLS Traffic
Engineering", RFC 5623, September 2009.
[RFC7138] Ceccarelli, D., Ed., Zhang, F., Belotti, S., Rao, R., and
J. Drake, "Traffic Engineering Extensions to OSPF for
GMPLS Control of Evolving G.709 Optical Transport
Networks", RFC 7138, March 2014.
[RFC7139] Zhang, F., Ed., Zhang, G., Belotti, S., Ceccarelli, D.,
and K. Pithewan, "GMPLS Signaling Extensions for Control
of Evolving G.709 Optical Transport Networks", RFC 7139,
March 2014.
[RFC7271] Ryoo, J., Ed., Gray, E., Ed., van Helvoort, H.,
D'Alessandro, A., Cheung, T., and Osborne, E., "MPLS
Transport Profile (MPLS-TP) Linear Protection to Match the
Operational Expectations of Synchronous Digital Hierarchy,
Optical Transport Network, and Ethernet Transport Network
Operators", RFC 7271, June 2014.
[RFC7688] Lee, Y., Ed. and G. Bernstein, Ed., "GMPLS OSPF
Enhancement for Signal and Network Element Compatibility
for Wavelength Switched Optical Networks", RFC 7688,
November 2015.
[RFC7689] Bernstein, G., Ed., Xu, S., Lee, Y., Ed., Martinelli, G.,
and H. Harai, "Signaling Extensions for Wavelength
Switched Optical Networks", RFC 7689, November 2015.
[RFC7792] Zhang, F., Zhang, X., Farrel, A., Gonzalez de Dios, O.,
and D. Ceccarelli, "RSVP-TE Signaling Extensions in
Support of Flexi-Grid Dense Wavelength Division
Multiplexing (DWDM) Networks", RFC 7792, March 2016.
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[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231, September 2017.
[RFC8234] Ryoo, J., Cheung, T., van Helvoort, H., Busi, I. and Wen
G., "Updates to MPLS Transport Profile (MPLS-TP) Linear
Protection in Automatic Protection Switching (APS) Mode",
RFC 8234, August 2017.
[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.
[RFC8345] Clemm, A., Medved, J., Varga, R., Bahadur, N.,
Ananthakrishnan, H., Liu, X., "A YANG Data Model for
Network Topologies", RFC 8345, March 2018.
[RFC8363] Zhang, X., Zheng, H., Casellas, R., Dios, O., and D.
Ceccarelli, "GMPLS OSPF-TE Extensions in support of Flexi-
grid DWDM networks", RFC8363, February 2017.
[PAT-COMP] Busi, I., Belotti, S., Lopez, V., Gonzalez de Dios, O.,
Sharma, A., Shi, Y., Vilalta, R., Setheraman, K., "Yang
model for requesting Path Computation", draft-ietf-teas-
yang-path-computation, work in progress.
[PCEP-LS] Dhody, D., Lee, Y., Ceccarelli, D., "PCEP Extensions for
Distribution of Link-State and TE Information", draft-
dhodylee-pce-pcep-ls, work in progress.
[TE-Tunnel] Saad, T. et al., "A YANG Data Model for Traffic
Engineering Tunnels and Interfaces", draft-ietf-teas-yang-
te, work in progress.
[sPCE-ID] Dugeon, O. et al., "PCEP Extension for Stateful Inter-
Domain Tunnels", draft-ietf-pce-stateful-interdomain, work
in progress.
[G.808.1] ITU-T, "Generic protection switching - Linear trail and
subnetwork protection", G.808.1, May 2014.
12. Contributors
Xianlong Luo
Huawei Technologies
G1, Huawei Xiliu Beipo Village, Songshan Lake
Dongguan
Guangdong, 523808 China
Email: luoxianlong@huawei.com
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Sergio Belotti
Nokia
Email: sergio.belotti@nokia.com
13. Authors' Addresses
Haomian Zheng
Huawei Technologies
H1, Huawei Xiliu Beipo Village, Songshan Lake
Dongguan
Guangdong, 523808 China
Email: zhenghaomian@huawei.com
Yunbin Xu
CAICT
Email: xuyunbin@caict.ac.cn
Yang Zhao
China Mobile
Email: zhaoyangyjy@chinamobile.com
Dieter Beller
Nokia
Email: Dieter.Beller@nokia.com
Yi Lin
Huawei Technologies
H1, Huawei Xiliu Beipo Village, Songshan Lake
Dongguan
Guangdong, 523808 China
Email: yi.lin@huawei.com
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