TEAS Working Group Haomian Zheng
Internet Draft Xianlong Luo
Category: Informational Huawei Technologies
Yang Zhao
China Mobile
Yunbin Xu
CAICT
Sergio Belotti
Dieter Beller
Nokia
Expires: June 6, 2019 December 6, 2018
Interworking of GMPLS Control and Centralized Controller System
draft-zheng-teas-gmpls-controller-inter-work-02
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 issue from multi-
domain, multi-vendor and multi-technology. An example of such
centralized architecture is 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
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
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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
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This Internet-Draft will expire on June 6, 2019.
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Conventions used in this document
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 Interwork with Centralized Controller System. 5
3. Link Management Protocol .................................... 6
4. Routing Options ............................................. 6
4.1. OSPF-TE ................................................ 6
4.2. ISIS-TE ................................................ 7
4.3. Netconf/RESTconf ....................................... 7
5. Path Computation ............................................ 7
5.1. Constraint-based Path Computing in GMPLS Control ....... 7
5.2. Path Computation Element (PCE) ......................... 7
6. Signaling Options ........................................... 8
6.1. RSVP-TE ................................................ 8
7. Interworking Scenarios ...................................... 8
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7.1. Topology Collection & Synchronization .................. 8
7.2. Multi-domain/layer Service Provisioning ................ 9
7.3. Recovery ............................................... 9
7.4. Controller Reliability ................................ 10
8. Manageability Considerations ............................... 10
9. Security Considerations .................................... 10
10. IANA Considerations........................................ 10
11. References ................................................ 11
11.1. Normative References ................................. 11
11.2. Informative References ............................... 12
12. Authors' Addresses ........................................ 14
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. More generic description for
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. Central 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
central 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 central 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
GMPLS control plane. This document describes how GMPLS control
interworks with centralized controller system in transport network.
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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 controller can also collect 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 controllers applying these
protocols communicate with each other to exchange resource
information and establish Label Switched Paths (LSPs). In this way,
controllers 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 such as ACTN
[RFC8453]. In centralized controller systems, a controller is aware
of the network topology and is responsible for provisioning incoming
service requests. In ACTN, multiple abstraction levels are designed
and controllers at different levels implement different functions.
This kind of abstraction enables multi-vendor, multi-domain, and
multi-technology control.
For example in ACTN, an MDSC coordinates several PNCs controlling
different domains. Each PNC provides a topological view of the
domain it controls, which can be abstracted, to the MDSC, so that
the MDSC learns the topology of the network encompassing multiple
domains. When a multi-domain service request arrives at the MDSC,
the MDSC first computes an end-to-end path based on the abstracted
topology view provided by the PNCs. Then, the MDSC splits this path
to multiple segment according to domain boundaries and allocate each
segment to corresponding PNC for detailed path computation and LSP
segment setup. When each PNC has reported the establishment of its
LSP segment, the multi-domain service is established.
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2.3. GMPLS Control Interwork with Centralized Controller System
The ACTN framework [RFC8453] defines a hierarchical controller
architecture and describes how these controllers communicate with
each other in order to control a multi-domain transport network. The
controllers at the different levels in the hierarchy typically
perform network abstraction of the domain they control and provide
an abstracted view of their domain to the controller at the next
level in the hierarchy. The controllers at the different
hierarchical levels also interact with each other during end-to-end
service establishment, which can span multiple domains. Within each
domain, GMPLS control can be applied to each NE. The bottom-level
central controller like PNC can act as a NE to collect network
information and initiate LSP. Figure 1 shows an example of GMPLS
interworking with ACTN.
+----------+
| MDSC |
+----------+
^ ^
| |
+---------+ +---------+
| RESTConf / YANG models |
V V
+---------+ +---------+
| PNC | | PNC |
+---------+ +---------+
^ ^ ^ ^
| | | |
OSPF-TE| |PCEP OSPF-TE| |PCEP
Netconf| | Netconf| |
V V V V
.-------------. Inter- .-------------.
/ \ domain / \
| LMP | link | LMP |
| OSPF-TE ========== OSPF-TE |
| RSVP-TE | | RSVP-TE |
\ / \ /
`------------` `------------`
GMPLS domain GMPLS domain
Figure 1: Example of GMPLS interworks with ACTN
In Figure 1, each domain has the GMPLS control plane enabled at the
physical network level. The PNC can listen to the IGP routing
protocol messages (OSPF LSAs for example) that the GMPLS control
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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 [TE-topo] 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 topology graph of
the multi-domain network, and can use it for path computation. To
setup a service, the MDSC can exploit Yang tunnel model together
with the technology-specific YANG model augmentations.
3. Link Management Protocol
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 property. In this way, link
resources, which are fundamental resources in the network, are
discovered by both ends of the link.
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 centralized controller system, central controller can be placed
at the GMPLS network and passively receive the information flooded
in the network. In this way, the central 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
protocol has been extended to support technology-specific routing.
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The routing protocol for OTN, WSON and optical flexi-grid network
are defined in [RFC7138], [RFC7688] and [RFC8363], respectively.
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. Besides, these protocols can also be
used for topology retrieval by using topology-related YANG models,
such as [RFC8345] and [TE-topo]. These protocols provide a powerful
mechanism for notification that permits to notify the client about
topology changes.
5. 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 MDSC may not have sufficient
information to compute the optimal path. In this case, the MDSC can
interact with different domain controllers by sending Yang Path
Computation requests [PAT-COMP] 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 service e2e 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.
5.1. Constraint-based Path Computing in GMPLS Control
In GMPLS control, a routing path is computed by the ingress node
[RFC3473] and is based on the ingress node TED. Constraint-based
path computation is performed according to the local policy of the
ingress node.
5.2. Path Computation Element (PCE)
PCE has been introduced in [RFC4655] as a functional component that
provides services to compute path in a network. In [RFC5440], the
path computation is accomplished by using the Traffic Engineering
Database (TED), which maintains the link resources in the network.
The emergence of PCE efficiently improve the quality of network
planning and offline computation, but there is a risk that the
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computed path may be infeasible if there is a diversity requirement,
because stateless PCE has no knowledge about the former computed
paths.
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.
In PCE Initiation [RFC8281], PCE is allowed to trigger the PCC to
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 centralized controller system, the PCE can be implement in a
central controller, and the central controller performs path
computation according to its local policies. On the other hand, the
PCE can also be placed outside of the central controller. In this
case, the central controller acts as a PCC to request path
computation to the PCE through PCEP.
6. Signaling Options
Signaling mechanisms are used to setup 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 network element is usually raw
information, while the topology on the controller can be either raw
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or abstracted. Three different abstraction methods have been
described in [RFC8453], and different controllers can select the
corresponding method depending on application.
When there are changes in the network topology, the impacted network
element(s) 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 section 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 with YANG model.
7.2. Multi-domain/layer 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/layer service provisioning would request coordination
among the controller hierarchies. Given the service request, the
end-to-end delivery procedure may include interactions on MPI and
SBI. The computation for a cross-domain/layer path is usually
completed by MDSC, who has a global view of the topologies. Then the
configuration is decomposed into lower layer controllers, including
both MDSC and PNCs, 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. A typical example would be the PCE Initiation scenario,
in which a PCE message (PCInitiate) is sent from the controller to
the first-end node, and then trigger a RSVP procedure along the
path. Similarly, the interaction between the controller and the
ingress node of a domain can be achieved by Netconf protocol with
corresponding YANG models, and then completed by running RSVP among
the network elements.
7.3. Recovery
The GMPLS recovery functions are described in [RFC4426]. Two models,
span protection and 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]. By
introducing secondary record route objects, LSP segment can be
switched to another path like fast reroute [RFC4090].
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For the recovery with controllers, timely interaction between
controller and network elements are required. Usually the re-routing
can be decomposed into path computation and delivery, the controller
can take some advantage in the path computation due to the global
topology view. And the delivery can be achieved by the procedure
described in section 7.2.
7.4. Controller Reliability
Given the important role in the network, the reliability of
controller is critical. Once a controller is shut down, the network
should operate as well. It 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.
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 applies 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.
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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.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, 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.
[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.
[RFC8453] Ceccarelli, D. and Y. Lee, "Framework for Abstraction and
Control of Traffic Engineered Networks", RFC 8453, August
2018.
11.2. Informative References
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
[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.
[RFC4426] Lang, J., Ed., Rajagopalan, B., Ed., and D.
Papadimitriou, Ed., "Generalized Multi-Protocol Label
witching (GMPLS) Recovery Functional Specification", RFC
4426, March 2006.
[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.
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[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.
[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.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231, September 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.
[TE-topo] Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H.,
Gonzalez De Dios, O., "YANG Data Model for Traffic
Engineering (TE) Topologies", draft-ietf-teas-yang-te-
topo-18, work in progress.
[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-04, 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.
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12. Authors' Addresses
Haomian Zheng
Huawei Technologies
F3 R&D Center, Huawei Industrial Base,
Bantian, Longgang District,
Shenzhen 518129 P.R.China
Email: zhenghaomian@huawei.com
Xianlong Luo
Huawei Technologies
F3 R&D Center, Huawei Industrial Base,
Bantian, Longgang District,
Shenzhen 518129 P.R.China
Email: luoxianlong@huawei.com
Yunbin Xu
CAICT
Email: xuyunbin@ritt.cn
Yang Zhao
China Mobile
Email: zhaoyangyjy@chinamobile.com
Sergio Belotti
Nokia
Email: sergio.belotti@nokia.com
Dieter Beller
Nokia
Email: Dieter.Beller@nokia.com
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