CCAMP Working Group I. Busi (Ed.)
Internet Draft Huawei
Intended status: Informational D. King
Lancaster University
Expires: December 2017 July 03, 2017
Transport Northbound Interface Use Cases
draft-tnbidt-ccamp-transport-nbi-use-cases-02
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Abstract
Transport network domains, including Optical Transport Network (OTN)
and Wavelength Division Multiplexing (WDM) networks, are typically
deployed based on a single vendor or technology platforms. They are
often managed using proprietary interfaces to dedicated Element
Management Systems (EMS), Network Management Systems (NMS) and
increasingly Software Defined Network (SDN) controllers.
A well-defined open interface to each domain management system or
controller is required for network operators to facilitate control
automation and orchestrate end-to-end services across multi-domain
networks. These functions may be enabled using standardized data
models (e.g. YANG), and appropriate protocol (e.g., RESTCONF).
This document describes the key use cases and requirements for
transport network control and management. It reviews proposed and
existing IETF transport network data models, their applicability,
and highlights gaps and requirements.
Table of Contents
1. Introduction..................................................3
2. Conventions used in this document.............................3
3. Use Case 1: Single-domain with single-layer...................3
3.1. Reference Network........................................3
3.1.1. Single Transport Domain - OTN Network...............4
3.2. Topology Abstractions....................................6
3.3. Service Configuration....................................7
3.3.1. ODU Transit.........................................7
3.3.2. EPL over ODU........................................8
3.3.3. Other OTN Client Services...........................8
3.3.4. EVPL over ODU.......................................9
3.3.5. EVPLAN and EVPTree Services.........................9
3.3.6. Virtual Network Services............................9
3.4. Multi-functional Access Links............................9
3.5. Protection Scenarios.....................................9
3.5.1. Linear Protection...................................10
4. Use Case 2: Single-domain with multi-layer....................11
5. Use Case 3: Multi-domain with single-layer....................11
6. Use Case 4: Multi-domain and multi-layer......................11
7. Security Considerations.......................................11
8. IANA Considerations...........................................11
9. References....................................................11
9.1. Normative References.....................................11
9.2. Informative References...................................11
10. Acknowledgments..............................................12
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1. Introduction
A common open interface to each domain controller/management system
is pre-requisite for network operators to control multi-vendor and
multi-domain networks and enable also service provisioning
coordination/automation. This can be achieved by using standardized
YANG models, used together with an appropriate protocol (e.g.,
RESTCONF).
This document assumes a reference architecture, including
interfaces, based on the Abstraction and Control of Traffic-
Engineered Networks (ACTN), defined in [ACTN-Frame].
The focus of the current version is on the MPI (interface between
the Multi Domain Service Coordinator (MDSC) and a Physical Network
Controller (PNC), controlling a transport network domain).
The relationship between the current IETF YANG models and the type
of ACTN interfaces can be found in [ACTN-YANG].
The ONF Technical Recommendations for Functional Requirements for
the transport API, may be found in [ONF TR-527].
Furthermore, ONF transport API multi-layer examples may be found in
[ONF GitHub].
This document describes use cases that could be used for analyzing
the applicability of the existing models defined by the IETF for
transport networks
Considerations about the CMI (interface between the Customer Network
Controller (CNC) and the MDSC) are for further study.
2. Conventions used in this document
For discussion in future revisions of this document.
3. Use Case 1: Single-domain with single-layer
3.1. Reference Network
The current considerations discussed in this document are based on
the following reference networks:
- single transport domain: OTN network
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It is expected that future revisions of the document will include
additional reference networks.
3.1.1. Single Transport Domain - OTN Network
Figure 1 shows the network physical topology composed of a single-
domain transport network providing transport services to an IP
network through five access links.
................................................
: IP domain :
: .............................. :
: : ........................ : :
: : : : : :
: : : S1 -------- S2 ------ C-R4 :
: : : / | : : :
: : : / | : : :
: C-R1 ------ S3 ----- S4 | : : :
: : : \ \ | : : :
: : : \ \ | : : :
: : : S5 \ | : : :
: C-R2 -----+ / \ \ | : : :
: : : \ / \ \ | : : :
: : : S6 ---- S7 ---- S8 ------ C-R5 :
: : : / : : :
: C-R3 -----+ : : :
: : : Transport domain : : :
: : : : : :
:........: :......................: :........:
Figure 1 Reference network for Use Case 1
The IP and transport (OTN) domains are respectively composed by five
routers C-R1 to C-R5 and by eight ODU switches S1 to S8. The
transport domain acts as a transit domain providing connectivity to
the IP layer.
The behavior of the transport domain is the same whether the
ingress/egress nodes in the IP domain, supporting an IP service, are
directly attached to the transport domain or there are other routers
in between the ingress/egress nodes of the IP domain and the routers
directly attached to the transport network.
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+-----+
| CNC |
+-----+
|
|CMI I/F
|
+-----------------------+
| MDSC |
+-----------------------+
|
|MPI I/F
|
+-------+
| PNC |
+-------+
|
-----
( )
( OTN )
( Physical )
( Network )
( )
-----
Figure 2 Controlling Hierarchy for Use Case 1
The mapping of the client IP traffic on the physical link between
the routers and the transport network is made in the IP routers only
and is not controlled by the transport PNC and is transparent to the
transport nodes.
The control plane architecture follows the ACTN architecture and
framework document [ACTN-Frame]. The Client Controller act as a
client with respect to the Multi-Domain Service Coordinator (MDSC)
via the Controller-MDSC Interface (CMI). The MDSC is connected to a
plurality of Physical Network Controllers (PNCs), one for each
domain, via a MDSC-PNC Interface (MPI). Each PNC is responsible
only for the control of its domain and the MDSC is the only entity
capable of multi-domain functionalities as well as of managing the
inter-domain links. The key point of the whole ACTN framework is
detaching the network and service control from the underlying
technology and help the customer express the network as desired
by business needs. Therefore, care must be taken to keep minimal
dependency on the CMI (or no dependency at all) with respect to
the network domain technologies. The MPI instead requires some
specialization according to the domain technology.
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In this section, we address the case of an IP and a Transport PNC
having respectively an IP a Transport MPI. The interface within
the scope of this document is the Transport MPI while the IP Network
MPI is out of its scope and considerations about the CMI are for
further study.
3.2. Topology Abstractions
There are multiple methods to abstract a network topology. This
document assumes the abstraction method defined in [RFC7926]:
Abstraction is the process of applying policy to the available TE
information within a domain, to produce selective information that
represents the potential ability to connect across the domain.
Thus, abstraction does not necessarily offer all possible
connectivity options, but presents a general view of potential
connectivity according to the policies that determine how the
domain's administrator wants to allow the domain resources to be
used.
[TE-Topo] describes a YANG base model for TE topology without any
technology specific parameters. Moreover, it defines how to abstract
for TE-network topologies.
[ACTN-Abstraction] provides the context of topology abstraction in
the ACTN architecture and discusses a few alternatives for the
abstraction methods for both packet and optical networks. This is an
important consideration since the choice of the abstraction method
impacts protocol design and the information it carries. According
to [ACTN-Abstraction], there are three types of topology:
o White topology: This is a case where the Physical Network
Controller (PNC) provides the actual network topology to the
Multi-domain Service Coordinator (MDSC) without any hiding or
filtering. In this case, the MDSC has the full knowledge of the
underlying network topology.
o Black topology: The entire domain network is abstracted as a
single virtual node with the access/egress links without
disclosing any node internal connectivity information.
o Grey topology: This abstraction level is between black topology
and white topology from a granularity point of view. This is
abstraction of TE tunnels for all pairs of border nodes. We may
further differentiate from a perspective of how to abstract
internal TE resources between the pairs of border nodes:
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- Grey topology type A: border nodes with a TE links between
them in a full mesh fashion.
- Grey topology type B: border nodes with some internal
abstracted nodes and abstracted links.
For single-domain with single-layer use-case, the white topology may
be disseminated from the PNC to the MDSC in most cases. There may be
some exception to this in the case where the underlay network may
have complex optical parameters, which do not warrant the
distribution of such details to the MDSC. In such case, the topology
disseminated from the PNC to the MDSC may not have the entire TE
information but a streamlined TE information. This case would incur
another action from the MDSC's standpoint when provisioning a path.
The MDSC may make a path compute request to the PNC to verify the
feasibility of the estimated path before making the final
provisioning request to the PNC, as outlined in [Path-Compute].
Topology abstraction for the CMI is for further study (to be
addressed in future revisions of this document).
3.3. Service Configuration
In the following use cases, the Multi Domain Service Coordinator
(MDSC) needs to be capable to request service connectivity from the
transport Physical Network Controller (PNC) to support IP routers
connectivity. The type of services could depend of the type of
physical links (e.g. OTN link, ETH link or SDH link) between the
routers and transport network.
As described in section 3.1.1, the control of different adaptations
inside IP routers, C-Ri (PKT -> foo) and C-Rj (foo -> PKT), are
assumed to be performed by means that are not under the control of,
and not visible to, transport PNC. Therefore, these mechanisms are
outside the scope of this document.
3.3.1. ODU Transit
This use case assumes that the physical link interconnecting IP
routers and transport network is an OTN link.
The physical/optical interconnection is supposed to be a pre-
configured and not exposed via MPI to MDSC.
If we consider the case of a 10Gb IP link between C-R1 to C-R3,we
need to instantiate an ODU2 end-to-end connection between C-R1 and
C-R3, crossing transport nodes S3, S5, and S6.
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The traffic flow between C-R1 and C-R3 can be summarized as:
C-R1 (PKT -> ODU2), S3 (ODU2), S5 (ODU2), S6 (ODU2),
C-R3 (ODU2 -> PKT)
The MDSC should be capable via MPI interface to request the setup of
ODU2 transit service with enough information that can permit
transport PNC to instantiate and control the ODU2 segment through
nodes S3, S5, S6.
3.3.2. EPL over ODU
This use case assumes that the physical link interconnecting IP
routers and transport network is an Ethernet link.
If we consider the case of a 10Gb IP link between C-R1 to C-R3, we
need to instantiate an EPL service between C-R1 and C-R3 supported
by an ODU2 end-to-end connection between S3 and S6, crossing
transport node S5.
The traffic flow between C-R1 and C-R3 can be summarized as:
C-R1 (PKT -> ETH), S3 (ETH -> ODU2), S5 (ODU2),
S6 (ODU2 -> ETH), C-R3 (ETH-> PKT)
The MDSC should be capable via MPI i/f to request the setup of EPL
service with enough information that can permit transport PNC to
instantiate and control the ODU2 end-to-end connection through nodes
S3, S5, S6, as well as the adaptation functions inside S3 and S6:
S3&S6 (ETH -> ODU2) and S9&S6 (ODU2 -> ETH).
3.3.3. Other OTN Client Services
[ITU-T G.709-2016] defines mappings of different client layers into
ODU. Most of them are used to provide Private Line services over
an OTN transport network supporting a variety of types of physical
access links (e.g., Ethernet, SDH STM-N, Fibre Channel,
InfiniBand,).
This use case assumes that the physical links interconnecting IP
routers and transport network are any one of these possible options.
If we consider the case of a 10Gb IP link between C-R1 to C-R3
using SDH physical links, we need to instantiate an STM-64 Private
Line service between C-R1 and C-R3 supported by an ODU2 end-to-end
connection between S3 and S6, crossing transport node S5.
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The traffic flow between C-R1 and C-R3 can be summarized as:
C-R1 (PKT -> STM-64), S3 (STM-64 -> ODU2), S5 (ODU2),
S6 (ODU2 -> STM-64), C-R3 (STM-64 -> PKT)
The MDSC should be capable via MPI i/f to request the setup of an
STM-64 Private Line service with enough information that can permit
transport PNC to instantiate and control the ODU2 end-to-end
connection through nodes S3, S5, S6, as well as the adaptation
functions inside S3 and S6: S3&S6 (STM-64 -> ODU2) and S9&S3 (STM-64
-> PKT).
3.3.4. EVPL over ODU
For future revision.
3.3.5. EVPLAN and EVPTree Services
For future revision.
3.3.6. Virtual Network Services
For future revision.
3.4. Multi-functional Access Links
For future revision.
3.5. Protection Scenarios
The MDSC needs to be capable to request the transport PNC to
configure protection when requesting the setup of the connectivity
services described in section 3.3.
[Editor's note (for DT discussion):] Should we describe only
protection or also restoration scenarios?
Since in this use case it is assumed that switching is performed
only in one layer, the OTN ODU layer, for all the services defined
in section 3.3, protection can only be provided at that same layer.
Resiliency mechanisms on the access link are considered outside the
scope of this use case.
[Editor's note (for DT discussion):] I think that scenarios with
access link resiliency could be seen as being multi-domain and/or
multi-layer. For further discussion with DT members.
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3.5.1. Linear Protection
It is possible to protect any service defined in section 3.3 from
failures within the OTN transport domain by configuring a linear
protection group, as defined in [ITU-T G.808.1], in the data plane
between node S3 and node S6.
[Editor's note:] Check for IETF references about protection
definitions.
The OTN linear protection group can be configured to operate as 1+1
unidirectional, 1+1 bidirectional (to check) or 1:n bidirectional,
as defined in [ITU-T G.808.1] and [ITU-T G.873.1].
[Editor's note (for DT discussion):] The most common protection
mechanism used in OTN networks is 1+1 unidirectional. Should we
consider also the other cases?
In these scenarios, a working transport entity and a protection
transport entity, as defined in [ITU-T G.808.1], should be
configured in the data plane:
Working transport entity: S3 -> S5 -> S6
Protection transport entity: S3 -> S4 -> S6 -> S7 -> S6
Requirements about how the MDSC could be capable to request the
transport PNC to configure the protection group are for further
study.
[Editor's note:] Need to discuss whether MDSC should decide that
linear protection is needed and whether it should be 1+1 or 1:1 or
whether the transport PNC can take this decision based on other
information provided by MDSC (or whether both options are possible).
The Transport PNC should be capable to report to the MDSC which is
the active transport entity, as defined in [ITU-T G.808.1], in the
data plane.
Given the fast dynamic of protection switching operations in the
data plane (50ms recovery time), this reporting is not expected to
be in real-time.
It is also worth noting that with unidirectional protection
switching, e.g., 1+1 unidirectional, the active transport entity may
be different in the two directions.
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4. Use Case 2: Single-domain with multi-layer
For future revision.
5. Use Case 3: Multi-domain with single-layer
For future revision.
6. Use Case 4: Multi-domain and multi-layer
For future revision.
7. Security Considerations
For further study.
8. IANA Considerations
This document requires no IANA actions.
9. References
9.1. Normative References
[RFC7926] Farrel, A. et al., "Problem Statement and Architecture for
Information Exchange between Interconnected Traffic-
Engineered Networks", BCP 206, RFC 7926, July 2016.
[ITU-T G.709-2016] G.808.1 G.709 (06/16), "Interfaces
for the optical transport network", June 2016.
[ITU-T G.808.1] ITU-T Recommendation G.808.1, "Generic protection
switching - Linear trail and subnetwork protection", May
2014.
[ITU-T G.873.1] ITU-T Recommendation G.873.1, "Optical transport
network (OTN): Linear protection", May 2014.
[ACTN-Frame] Ceccarelli, D., Lee, Y. et al., "Framework for
Abstraction and Control of Transport Networks", draft-
ietf-teas-actn-framework, work in progress.
[ACTN-Abstraction] Lee, Y. et al., "Abstraction and Control of TE
Networks (ACTN) Abstraction Methods", draft-lee-teas-actn-
abstraction, work in progress.
9.2. Informative References
[TE-Topo] Liu, X. et al., "YANG Data Model for TE Topologies",
draft-ietf-teas-yang-te-topo, work in progress.
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[ACTN-YANG] Zhang, X. et al., "Applicability of YANG models for
Abstraction and Control of Traffic Engineered Networks",
draft-zhang-teas-actn-yang, work in progress.
[Path-Compute] Busi, I., Belotti, S. et al., " Yang model for
requesting Path Computation", draft-busibel-teas-yang-
path-computation, work in progress.
[ONF TR-527] ONF Technical Recommendation TR-527, "Functional
Requirements for Transport API", June 2016.
[ONF GitHub] ONF Open Transport (SNOWMASS)
https://github.com/OpenNetworkingFoundation/Snowmass-
ONFOpenTransport
10. Acknowledgments
The authors would like to thank all members of the Transport NBI
Design Team involved in the definition of use cases, gap analysis
and guidelines for using the IETF YANG models at the Northbound
Interface (NBI) of a Transport SDN Controller.
The authors would like to thank Xian Zhang, Anurag Sharma, Sergio
Belotti, Tara Cummings, Michael Scharf, Karthik Sethuraman, Oscar
Gonzalez de Dios, Hans Bjursrom and Italo Busi for having initiated
the work on gap analysis for transport NBI and having provided
foundations work for the development of this document.
This document was prepared using 2-Word-v2.0.template.dot.
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Authors' Addresses
Italo Busi (Editor)
Huawei
Email: italo.busi@huawei.com
Daniel King (Editor)
Lancaster University
Email: d.king@lancaster.ac.uk
Sergio Belotti
Nokia
Email: sergio.belotti@nokia.com
Gianmarco Bruno
Ericsson
Email: gianmarco.bruno@ericsson.com
Young Lee
Huawei
Email: leeyoung@huawei.com
Victor Lopez
Telefonica
Email: victor.lopezalvarez@telefonica.com
Carlo Perocchio
Ericsson
Email: carlo.perocchio@ericsson.com
Haomian Zheng
Huawei
Email: zhenghaomian@huawei.com
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