Applicability of Abstraction and Control of Traffic Engineered Networks (ACTN) to Packet Optical Integration (POI)
draft-ietf-teas-actn-poi-applicability-06
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| Authors | Fabio Peruzzini , Jean-Francois Bouquier , Italo Busi , Daniel King , Daniele Ceccarelli | ||
| Last updated | 2022-03-07 | ||
| Replaces | draft-peru-teas-actn-poi-applicability | ||
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draft-ietf-teas-actn-poi-applicability-06
TEAS Working Group Fabio Peruzzini
Internet Draft TIM
Intended status: Informational Jean-Francois Bouquier
Vodafone
Italo Busi
Huawei
Daniel King
Old Dog Consulting
Daniele Ceccarelli
Ericsson
Expires: September 2022 March 7, 2022
Applicability of Abstraction and Control of Traffic Engineered
Networks (ACTN) to Packet Optical Integration (POI)
draft-ietf-teas-actn-poi-applicability-06
Abstract
This document considers the applicability of Abstraction and Control
of TE Networks (ACTN) architecture to Packet Optical Integration
(POI)in the context of IP/MPLS and optical internetworking. It
identifies the YANG data models being defined by the IETF to support
this deployment architecture and specific scenarios relevant for
Service Providers.
Existing IETF protocols and data models are identified for each
multi-layer (packet over optical) scenario with a specific focus on
the MPI (Multi-Domain Service Coordinator to Provisioning Network
Controllers Interface)in the ACTN architecture.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
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Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction...................................................3
1.1. Terminology...............................................5
2. Reference network architecture.................................7
2.1. Multi-domain Service Coordinator (MDSC) functions.........9
2.1.1. Multi-domain L2/L3 VPN network services.............11
2.1.2. Multi-domain and multi-layer path computation.......14
2.2. IP/MPLS Domain Controller and NE Functions...............17
2.3. Optical Domain Controller and NE Functions...............19
3. Interface protocols and YANG data models for the MPIs.........19
3.1. RESTCONF protocol at the MPIs............................19
3.2. YANG data models at the MPIs.............................20
3.2.1. Common YANG data models at the MPIs.................20
3.2.2. YANG models at the Optical MPIs.....................21
3.2.3. YANG data models at the Packet MPIs.................21
3.3. PCEP.....................................................22
4. Inventory, service and network topology discovery.............23
4.1. Optical topology discovery...............................25
4.2. Optical path discovery...................................26
4.3. Packet topology discovery................................27
4.4. SR-TE path discovery.....................................27
4.5. Inter-domain link discovery..............................28
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4.5.1. Cross-layer link discovery..........................29
4.5.2. Inter-domain IP link discovery......................31
4.6. Multi-layer IP link discovery............................33
4.6.1. Single-layer intra-domain IP links..................36
4.7. LAG discovery............................................38
4.8. L2/L3 VPN network services discovery.....................38
4.9. Inventory discovery......................................38
5. Establishment of L2/L3 VPN network services with TE requirements
.................................................................38
5.1. Optical Path Computation.................................40
5.2. Multi-layer IP link Setup................................41
5.3. SR-TE Path Setup and Update..............................42
6. Conclusions...................................................43
7. Security Considerations.......................................44
8. Operational Considerations....................................44
9. IANA Considerations...........................................44
10. References...................................................44
10.1. Normative References....................................44
10.2. Informative References..................................46
Appendix A. OSS/Orchestration Layer...........................49
A.1. MDSC NBI................................................49
Appendix B. Multi-layer and multi-domain resiliency...........52
B.1. Maintenance Window......................................52
B.2. Router port failure.....................................52
Acknowledgments..................................................53
Contributors.....................................................53
Authors' Addresses...............................................55
1. Introduction
The complete automation of the management and control of Service
Providers transport networks (IP/MPLS, optical, and microwave
transport networks) is vital for meeting emerging demand for high-
bandwidth use cases, including 5G and fiber connectivity services.
The Abstraction and Control of TE Networks (ACTN) architecture and
interfaces facilitate the automation and operation of complex optical
and IP/MPLS networks through standard interfaces and data models.
This allows a wide range of of network services that can be requested
by the upper layers fulfilling almost any kind of service level
requirements from a network perspective (e.g. physical diversity,
latency, bandwidth, topology, etc.)
Packet Optical Integration (POI) is an advanced use case of traffic
engineering. In wide-area networks, a packet network based on the
Internet Protocol (IP), and often Multiprotocol Label Switching
(MPLS) or Segment Routing (SR), is typically realized on top of an
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optical transport network that uses Dense Wavelength Division
Multiplexing (DWDM)(and optionally an Optical Transport Network
(OTN)layer).
In many existing network deployments, the packet and the optical
networks are engineered and operated independently. As a result,
there are technical differences between the technologies (e.g.,
routers compared to optical switches) and the corresponding network
engineering and planning methods (e.g., inter-domain peering
optimization in IP, versus dealing with physical impairments in DWDM,
or very different time scales). In addition, customers needs can be
different between a packet and an optical network, and it is not
uncommon to use different vendors in both domains. The operation of
these complex packet and optical networks is often siloed, as these
technology domains require specific skills sets.
The packet/optical network deployment and operation separation are
inefficient for many reasons. Both capital expenditure (CAPEX) and
operational expenditure (OPEX) could be significantly reduced by
integrating the packet and the optical networks. Multi-layer online
topology insight can speed up troubleshooting (e.g., alarm
correlation) and network operation (e.g., coordination of maintenance
events), multi-layer offline topology inventory can improve service
quality (e.g., detection of diversity constraint violations) and
multi-layer traffic engineering can use the available network
capacity more efficiently (e.g., coordination of restoration). In
addition, provisioning workflows can be simplified or automated as
needed across layers (e.g., to achieve bandwidth-on-demand or to
perform activities during maintenance windows).
ACTN framework enables this complete multi-layer and multi-vendor
integration of packet and optical networks through Multi-Domain
Service Coordinator (MDSC) and packet and optical Provisioning
Network Controllers (PNCs).
In this document, critical scenarios for POI are described from the
packet service layer perspective and identified the required
coordination between packet and optical layers to improve POI
deployment and operation. Precise definitions of scenarios can help
with achieving a common understanding across different disciplines.
The focus of the scenarios are multi-domain packet networks operated
as a client of optical networks.
This document analyses the case where the packet networks support
multi-domain SR-TE paths and the optical networks could be either a
DWDM network or an OTN network (without DWDM layer) or multi-layer
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OTN/DWDM network. DWDM networks could be either fixed-grid or
flexible-grid.
Multi-layer and multi-domain scenarios, based on reference network
described in section 2, and very relevant for Service Providers, are
described in section 4 and in setion 5.
For each scenario, existing IETF protocols and data models,
identified in section 3.1 and section 3.2, are analysed with
particular focus on the MPI in the ACTN architecture.
For each multi-layer scenario, the document analyzes how to use the
interfaces and data models of the ACTN architecture.
A summary of the gaps identified in this analysis is provided in
section 6.
Understanding the level of standardization and the possible gaps will
help assess the feasibility of integration between packet and optical
DWDM domains (and optionally OTN layer) in an end-to-end multi-vendor
service provisioning perspective.
1.1. Terminology
This document uses the ACTN terminology defined in [RFC8453]
In addition this document uses the following terminology.
Customer service:
the end-to-end service from CE to CE
Network service:
the PE to PE configuration including both the network service layer
(VRFs, RT import/export policies configuration) and the network
transport layer (e.g. RSVP-TE LSPs). This includes the
configuration (on the PE side) of the interface towards the CE
(e.g. VLAN, IP adress, routing protocol etc.)
Port:
the physical entity that transmits and receives physical signals
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Interface:
a physical or logical entity that transmits and receives traffic
Link:
an association between two interfaces that can exchange traffic
directly
Ethernet link:
a link between two Ethernet interfaces
IP link:
a link between two IP interfaces
Cross-layer link:
an Ethernet link between an Ethernet interface on a router and an
Ethernet interface on an optical NE
Intra-domain single-layer Ethernet link:
an Ethernet link between between two Ethernet interfaces on
physically adjacent routers that belong to the same P-PNC domain
Intra-domain single-layer IP link:
an IP link supported by an intra-domain single-layer Ethernet link
Inter-domain single-layer Ethernet link:
an Ethernet link between between two Ethernet interfaces on
physically adjacent routers which belong to different P-PNC domains
Inter-domain single-layer IP link:
an IP link supported by an inter-domain single-layer Ethernet link.
Intra-domain multi-layer Ethernet link:
an Ethernet link supported by two cross-layer links and an optical
tunnel in between
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Intra-domain multi-layer IP link:
an IP link supported an intra-domain multi-layer Ethernet link
2. Reference network architecture
This document analyses several deployment scenarios for Packet and
Optical Integration (POI) in which ACTN hierarchy is deployed to
control a multi-layer and multi-domain network, with two optical
domains and two packet domains, as shown in Figure 1:
+----------+
| MDSC |
+-----+----+
|
+-----------+-----+------+-----------+
| | | |
+----+----+ +----+----+ +----+----+ +----+----+
| P-PNC 1 | | O-PNC 1 | | O-PNC 2 | | P-PNC 2 |
+----+----+ +----+----+ +----+----+ +----+----+
| | | |
| \ / |
+-------------------+ \ / +-------------------+
CE1 / PE1 BR1 \ | / / BR2 PE2 \ CE2
o--/---o o---\-|-------|--/---o o---\--o
\ : : / | | \ : : /
\ : PKT domain 1 : / | | \ : PKT domain 2 : /
+-:---------------:-+ | | +-:---------------:--+
: : | | : :
: : | | : :
+-:---------------:------+ +-------:---------------:--+
/ : : \ / : : \
/ o...............o \ / o...............o \
\ optical domain 1 / \ optical domain 2 /
\ / \ /
+------------------------+ +--------------------------+
Figure 1 - Reference Network
The ACTN architecture, defined in [RFC8453], is used to control this
multi-layer and multi-domain network where each Packet PNC (P-PNC) is
responsible for controlling its packet domain and where each Optical
PNC (O-PNC) in the above topology is responsible for controlling its
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optical domain. The packet domains controlled by the P-PNCs can be
Autonomous Systems (ASes), defined in [RFC1930], or IGP areas, within
the same operator network.
The routers between the packet domains can be either AS Boundary
Routers (ASBR) or Area Border Router (ABR): in this document, the
generic term Border Router (BR) is used to represent either an ASBR
or an ABR.
The MDSC is responsible for coordinating the whole multi-domain
multi-layer (packet and optical) network. A specific standard
interface (MPI) permits MDSC to interact with the different
Provisioning Network Controller (O/P-PNCs).
The MPI interface presents an abstracted topology to MDSC hiding
technology-specific aspects of the network and hiding topology
details depending on the policy chosen regarding the level of
abstraction supported. The level of abstraction can be obtained based
on P-PNC and O-PNC configuration parameters (e.g., provide the
potential connectivity between any PE and any BR in an SR-TE
network).
In the reference network of Figure 1, it is assumed that:
o The domain boundaries between the packet and optical domains are
congruent. In other words, one optical domain supports
connectivity between routers in one and only one packet domain;
o There are no inter-domain physical links between optical domains.
Inter-domain physical links exist only:
o between packet domains (i.e., between BRs belonging to
different packet domains): these links are called inter-domain
Ethernet or IP links within this document;
o between packet and optical domains (i.e., between routers and
optical NEs): these links are called cross-layer links within
this document;
o between customer sites and the packet network (i.e., between
CE devices and PE routers): these links are called access
links within this document.
o All the physical interfaces at inter-domain links are Ethernet
physical interfaces.
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Although the new optical technologies (e.g., QSFP-DD ZR 400G) allows
providing DWDM pluggable interfaces on the routers, the deployment of
those pluggable optics is not yet widely adopted by the operators.
The reason is that most operators are not yet ready to manage packet
and optical networks in a single unified domain. The analysis of the
unified use case is outside the scope of this draft.
This document analyses scenarios where all the multi-layer IP links,
supported by the optical network, are intra-domain (intra-AS/intra-
area), such as PE-BR, PE-P, BR-P, P-P IP links. Therefore the inter-
domain IP links are always single-layer links supported by Ethernet
physical links.
The analysis of scenarios with multi-layer inter-domain IP links is
outside the scope of this document.
Therefore, if inter-domain links between the optical domains exist,
they would be used to support multi-domain optical services, which
are outside the scope of this document.
The optical network elements (NEs) within the optical domains can be
ROADMs or OTN switches, with or without an integrated ROADM function.
2.1. Multi-domain Service Coordinator (MDSC) functions
The MDSC in Figure 1 is responsible for multi-domain and multi-layer
coordination across multiple packet and optical domains, as well as
to provide multi-layer/multi-domain L2/L3 VPN network services
requested by an OSS/Orchestration layer.
From an implementation perspective, the functions associated with
MDSC and described in [RFC8453] may be grouped in different ways.
1. Both the service- and network-related functions are collapsed into
a single, monolithic implementation, dealing with the end customer
service requests received from the CMI (Customer MDSC Interface)
and adapting the relevant network models. An example is represented
in Figure 2 of [RFC8453].
2. An implementation can choose to split the service-related and the
network-related functions into different functional entities, as
described in [RFC8309] and in section 4.2 of [RFC8453]. In this
case, MDSC is decomposed into a top-level Service Orchestrator,
interfacing the customer via the CMI, and into a Network
Orchestrator interfacing at the southbound with the PNCs. The
interface between the Service Orchestrator and the Network
Orchestrator is not specified in [RFC8453].
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3. Another implementation can choose to split the MDSC functions
between an "higher-level MDSC" (MDSC-H) responsible for packet and
optical multi-layer coordination, interfacing with one Optical
"lower-level MDSC" (MDSC-L), providing multi-domain coordination
between the O-PNCs and one Packet MDSC-L, providing multi-domain
coordination between the P-PNCs (see for example Figure 9 of
[RFC8453]).
4. Another implementation can also choose to combine the MDSC and the
P-PNC functions together.
In the current service provider's network deployments, at the North
Bound of the MDSC, instead of a CNC, typically there is an
OSS/Orchestration layer. In this case, the MDSC would implement only
the Network Orchestration functions, as in [RFC8309] and described in
point 2 above. Therefore, the MDSC is dealing with the network
services requests received from the OSS/Orchestration layer.
The functionality of the OSS/Orchestration layer and the interface
toward the MDSC are usually operator-specific and outside the scope
of this draft. Therefore, this document assumes that the
OSS/Orchestrator requests the MDSC to set up L2/L3 VPN network
services through mechanisms that are outside the scope of this
document.
There are two prominent workflow cases when the MDSC multi-layer
coordination is initiated:
o Initiated by a request from the OSS/Orchestration layer to setup
L2/L3 VPN network services that requires multi-layer/multi-domain
coordination;
o Initiated by the MDSC itself to perform multi-layer/multi-domain
optimizations and/or maintenance activities (e.g. rerouting LSPs
with their associated services when putting a resource, like a
fibre, in maintenance mode during a maintenance window).
Unlike service fulfillment, these workflows are not related to a
network service provisioning request being received from
the OSS/Orchestration layer.
The latter workflow cases are outside the scope of this document.
This document analyses the use cases where multi-layer coordination
is triggered by a network service request received from the
OSS/Orchestration layer.
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2.1.1. Multi-domain L2/L3 VPN network services
Figure 2 provides an example of an hub & spoke multi-domain L2/L3 VPN
with three PEs where the hub PE (PE13) and one spoke PE (PE14) are
within the same packet domain and the other spoke PE (PE23) is within
a different packet domain.
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------
| CE13 |___________________
------ ) __________________
( | ) ( )
( | PE13 P15 BR11 ) ( BR21 P24 )
( ____ ___ ____ ) ( ____ ___ )
( / H \ _ _ _ / \ _ _ / \ _)_ _ _(_ / \ _ _ _ / \ )
( \____/... \___/ \____/ ) ( \____/ \___/ )
( :..... ) ( | )
( ____ :__ ____ ) ( ____ _|__ )
( / S \...../ \._._./ \__________/ \._._._._./ S \ )
( \____/ \___/ \____/ ) ( \____/ \____/ )
( | ) ( | )
( | PE14 P16 BR12 ) ( BR22 PE23 | )
( | ) ( | )
------ ) ( ------
| CE14 | ___________________) (_____________| CE23 |
------ ------
_____________________________ ___________________
( ) ( )
( ____ ____ ) ( ____ )
( /NE11\ __ _ _ _ _ /NE12\ ) ( /NE21\ _ _ )
( \____/.. \____/ ) ( \____/ \ )
( | :..... ...: \ ) ( / \ )
( _|__ :__: \____ ) ( ___/ __\_ )
( /NE13\_ _ /NE14\ _ _ _ /NE15\ ) ( /NE22\ _ _ _ /NE23\ )
( \____/ \____/ \____/ ) ( \____/ \____/ )
( ) ( )
(_____________________________) (___________________)
optical domain 1 optical domain 2
H / S = Hub VRF / Spoke VRF
____ = Inter-domain interconnections
..... = SR policy Path 1
_ _ _ = SR policy Path 2
Figure 2 - Multi-domain L3VPN example
There are many options to implement multi-domain L2/L3 VPNs,
including:
1. BGP-LU (seamless MPLS)
2. Inter-domain RSVP-TE
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3. Inter-domain SR-TE
This document provides an analysis of the inter-domain SR-TE option.
The analysis of other options is outside the scope of this draft.
It is also assumed that:
o each packet domain in Figure 2 is implementing SR-TE and the
stitching between two domains is done using end-to-end/multi-
domain SR-TE;
o the bandwidth of each intra-domain SR-TE path is managed by its
respective P-PNC;
o binding SID is used for the end-to-end SR-TE path stitching;
o each packet domain in Figure 2 is using TI-LFA, with SRLG
awareness, for local protection within each domain.
In this scenario, one of the key MDSC functions is to identify the
multi-domain/multi-layer SR-TE paths to be used to carry the L2/L3
VPN traffic between PEs belonging to different packet domains and to
relay this information to the P-PNCs, to ensure that the PEs'
forwarding tables (e.g., VRF) are properly configured to steer the
L2/L3 VPN traffic over the intended multi-domain/multi-layer SR-TE
paths.
The selection of the SR-TE path should take into account the TE
requirements and the binding requirements for the L2/L3 VPN network
service.
In general the binding requirements for a network service (e.g L2/L3
VPN), can be summarized within three cases:
1. The customer is asking for VPN isolation dynamically creating
and binding tunnels to the service such that they are not shared
by others services (e.g. VPN).
The level of isolation can be different:
a) Hard isolation with deterministic latency that means L2/L3
VPN requiring a set of dedicated TE Tunnels (neither
sharing with other services nor competing for bandwidth
with other tunnels) providing deterministic latency
performances
b) Hard isolation but without deterministic characteristics
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c) Soft isolation that means the tunnels associated with L2/L3
VPN are dedicated to that but can compete for bandwidth
with other tunnels.
2. The customer does not ask isolation,and could request a VPN
service where associated tunnels can be shared across multiple
VPNs.
For each SR-TE path required to support the L2/L3 VPN network
service, it is possible that:
1. A SR-TE path that meets the TE and binding requirements already
exist in the network.
2. An existing SR-TE path could be modified (e.g., through bandwidth
increase) to meet the TE and binding requirements:
a. The SR-TE path characteristics can be modified only in the
packet layer.
b. One or more new underlay optical tunnels need to be setup to
support the requested changes of the overlay SR-TE paths
(multi-layer coordination is required).
3. A new SR-TE path needs to be setup to meet the TE and binding
requirements:
a. The new SR-TE path reuses existing underlay optical tunnels;
b. One or more new underlay optical tunnels need to be setup to
support the setup of the new SR-TE path (multi-layer
coordination is required).
2.1.2. Multi-domain and multi-layer path computation
When a new SR-TE path needs to be setup, the MDSC is also responsible
to coordinate the multi-layer/multi-domain path computation.
Depending on the knowledge that MDSC has of the topology and
configuration of the underlying network domains, three approaches for
performing multi-layer/multi-domain path computation are possible:
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1. Full Summarization: In this approach, the MDSC has an abstracted
TE topology view of all of its, packet and optical, underlying
domains.
In this case, the MDSC does not have enough TE topology
information to perform multi-layer/multi-domain path computation.
Therefore the MDSC delegates the P-PNCs and O-PNCs to perform
local path computation within their respective controlled domains
and it uses the information returned by the P-PNCs and O-PNCs to
compute the optimal multi-domain/multi-layer path.
This approach presents an issue to P-PNC, which does not have the
capability of performing a single-domain/multi-layer path
computation, since it can not retrieve the topology information
from the O-PNCs nor delegate the O-PNC to perform optical path
computation.
A possible solution could be to include a CNC function within the
P-PNC to request the MDSC multi-domain optical path computation,
as shown in Figure 10 of [RFC8453].
Another solution could be to rely on the MDSC recursive hierarchy,
as defined in section 4.1 of [RFC8453], where, for each IP and
optical domain pair, a "lower-level MDSC" (MDSC-L) provides the
essential multi-layer correlation and the "higher-level MDSC"
(MDSC-H) provides the multi-domain coordination.
In this case, the MDSC-H can get an abstact view of the underlying
multi-layer domain topologies from its underlying MDSC-L. Each
MDSC-L gets the full view of the IP domain topology from P-PNC and
can get an abstracted view of the optical domain topology from its
underlying O-PNC. In other words, topology abstraction is possible
at the MPIs between MDSC-L and O-PNC and between MDSC-L and MDSC-
H.
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2. Partial summarization: In this approach, the MDSC has full
visibility of the TE topology of the packet network domains and an
abstracted view of the TE topology of the optical network domains.
The MDSC then has only the capability of performing multi-
domain/single-layer path computation for the packet layer (the
path can be computed optimally for the two packet domains).
Therefore, the MDSC still needs to delegate the O-PNCs to perform
local path computation within their respective domains and it uses
the information received by the O-PNCs, together with its TE
topology view of the multi-domain packet layer, to perform multi-
layer/multi-domain path computation.
3. Full knowledge: In this approach, the MDSC has the complete and
enough detailed view of the TE topology of all the network domains
(both optical and packet).
In such case MDSC has all the information needed to perform multi-
domain/multi-layer path computation, without relying on PNCs.
This approach may present, as a potential drawback, scalability
issues and, as discussed in section 2.2. of [PATH-COMPUTE],
performing path computation for optical networks in the MDSC is
quite challenging because the optimal paths depend also on
vendor-specific optical attributes (which may be different in the
two domains if they are provided by different vendors).
This document analyses scenarios where the MDSC uses the partial
summarization approach to coordinate multi-domain/multi-layer path
computation.
Typically, the O-PNCs are responsible for the optical path
computation of services across their respective single domains.
Therefore, when setting up the network service, they must consider
the connection requirements such as bandwidth, amplification,
wavelength continuity, and non-linear impairments that may affect the
network service path.
The methods and types of path requirements and impairments, such as
those detailed in [OIA-TOPO], used by the O-PNC for optical path
computation are not exposed at the MPI and therefore out of scope for
this document.
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2.2. IP/MPLS Domain Controller and NE Functions
As highlighted in section 2.1.1, SR-TE is used in the packet domain.
Each domain, corresponding to either an IGP area or an Autonomous
System (AS) within the same operator network, is controlled by a
packet domain controller (P-PNC).
P-PNCs are responsible to setup the SR-TE paths between any two PEs
or BRs in their respective controlled domains, as requested by MDSC,
and to provide topology information to the MDSC.
With reference to Figure 2, a bidirectional SR-TE path from PE13 in
domain 1 to PE23 in domain 2 requires the MDSC to coordinate the
actions of:
o P-PNC1 to push a SID list to PE13 including the Binding SID
associated to the SR-TE path in Domain 2 with PE23 as the target
destination (forward direction);
o P-PNC2 to push a SID list to PE23 with including the Binding SID
associated to the SR-TE path in Domain 1 with PE13 as the target
destination (reverse direction).
With reference to Figure 3, P-PNCs are then responsible:
1. To expose to MDSC their respective detailed TE topology
2. To perform single-layer single-domain local SR-TE path
computation, when requested by MDSC between two PEs (for single-
domain end-to-end SR-TE path) or between PEs and BRs for an inter-
domain SR-TE path selected by MDSC;
3. To configure the ingress PE or BR router in their respective
domain with the SID list associated with an SR-TE path;
4. To configure finally the VRF and PE-CE interfaces (Service access
points) of the intra-domain and inter-domain network services
requested by the MDSC.
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+------------------+ +------------------+
| | | |
| P-PNC1 | | P-PNC2 |
| | | |
+--|-----------|---+ +--|-----------|---+
| 1.SR-TE | 2.VPN | 1.SR-TE | 2.VPN
| Policy | Provisioning | Policy | Provisioning
| Config | | Config |
V V V V
+---------------------+ +---------------------+
CE / PE SR-TE path 1 BR\ / BR SR-TE path 2 PE \ CE
o--/---o..................o--\-----/--o..................o---\--o
\ / \ /
\ Domain 1 / \ Domain 2 /
+---------------------+ +---------------------+
End-to-end SR-TE path
<------------------------------------------------->
Figure 3 Domain Controller & NE Functions
When requesting the setup of a new SR-TE path, the MDSC provides the
P-PNCs with the explicit path to be created or modified. In other
words, the MDSC can communicate to the P-PNCs the full list of nodes
involved in the path (strict mode). In this case, the P-PNC is just
responsible to push to headend PE or BR the list of SIDs to create
that explicit SR-TE path.
For scalability purposes, in large packet domains, where multiple
engineered paths are available between any two nodes, the MDSC can
request a loose path, together with per-domain TE constraints, to
allow the P-PNC selecting the intra-domain SR-TE path meeting these
constraints.
In such a case it is mandatory that P-PNC signals back to the MDSC
which path it has chosen so that the MDSC keeps track of the relevant
resources utilization.
An example of that comes from Figure 2. The SR-TE path requested by
the MDSC touches PE13 - P16 - BR12 - BR21 - PE23. P-PNC2 knows of two
possible paths with the same topology metric, e.g. BR21 - P24 - PE23
and BR21 - BR22 - PE23, but with different load. It may prefer then
to steer the traffic on the latter because it is less loaded.
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This exception is mentioned here for the sake of completeness but
since the network considered in this document does not fall in this
scenario, in the rest of the paper the assumption is that the MDSC
always provides the explicit list of SID(s) to the P-PNCs to setup or
modify the SR-TE path.
2.3. Optical Domain Controller and NE Functions
The optical network provides the underlay connectivity services to
IP/MPLS networks. The packet and optical multi-layer coordination is
done by the MDSC, as shown in Figure 1.
The O-PNC is responsible to:
o provide to the MDSC an abstract TE topology view of its underlying
optical network resources;
o perform single-domain local path computation, when requested by
the MDSC;
o perform optical tunnel setup, when requested by the MDSC.
The mechanisms used by O-PNC to perform intra-domain topology
discovery and path setup are usually vendor-specific and outside the
scope of this document.
Depending on the type of optical network, TE topology abstraction,
path computation and path setup can be single-layer (either OTN or
WDM) or multi-layer OTN/WDM. In the latter case, the multi-layer
coordination between the OTN and WDM layers is performed by the
O-PNC.
3. Interface protocols and YANG data models for the MPIs
This section describes general assumptions applicable at all the MPI
interfaces, between each PNC (Optical or Packet) and the MDSC, to
support the scenarios discussed in this document.
3.1. RESTCONF protocol at the MPIs
The RESTCONF protocol, as defined in [RFC8040], using the JSON
representation defined in [RFC7951], is assumed to be used at these
interfaces. In addition, extensions to RESTCONF, as defined in
[RFC8527], to be compliant with Network Management Datastore
Architecture (NMDA) defined in [RFC8342], are assumed to be used as
well at these MPI interfaces and also at MDSC NBI interfaces.
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3.2. YANG data models at the MPIs
The data models used on these interfaces are assumed to use the YANG
1.1 Data Modeling Language, as defined in [RFC7950].
3.2.1. Common YANG data models at the MPIs
As required in [RFC8040], the "ietf-yang-library" YANG module defined
in [RFC8525] is used to allow the MDSC to discover the set of YANG
modules supported by each PNC at its MPI.
Both Optical and Packet PNCs use the following common topology YANG
data models at the MPI:
o The Base Network Model, defined in the "ietf-network" YANG module
of [RFC8345];
o The Base Network Topology Model, defined in the "ietf-network-
topology" YANG module of [RFC8345], which augments the Base
Network Model;
o The TE Topology Model, defined in the "ietf-te-topology" YANG
module of [RFC8795], which augments the Base Network Topology
Model.
Both Optical and Packet PNCs use the common TE Tunnel Model, defined
in the "ietf-te" YANG module of [TE-TUNNEL], at the MPI.
All the common YANG data models are generic and augmented by
technology-specific YANG modules, as described in the following
sections.
Both Optical and Packet PNCs also use the Ethernet Topology Model,
defined in the "ietf-eth-te-topology" YANG module of [CLIENT-TOPO],
which augments the TE Topology Model with Ethernet technology-
specific information.
Both Optical and Packet PNCs use the following common notifications
YANG data models at the MPI:
o Dynamic Subscription to YANG Events and Datastores over RESTCONF
as defined in [RFC8650];
o Subscription to YANG Notifications for Datastores updates as
defined in [RFC8641].
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PNCs and MDSCs are compliant with subscription requirements as stated
in [RFC7923].
3.2.2. YANG models at the Optical MPIs
The Optical PNC uses at least one of the following technology-
specific topology YANG data models, which augment the generic TE
Topology Model:
o The WSON Topology Model, defined in the "ietf-wson-topology" YANG
module of [RFC9094];
o the Flexi-grid Topology Model, defined in the "ietf-flexi-grid-
topology" YANG module of [Flexi-TOPO];
o the OTN Topology Model, as defined in the "ietf-otn-topology" YANG
module of [OTN-TOPO].
The optical PNC uses at least one of the following technology-
specific tunnel YANG data models, which augments the generic TE
Tunnel Model:
o The WSON Tunnel Model, defined in the "ietf-wson-tunnel" YANG
modules of [WSON-TUNNEL];
o the Flexi-grid Tunnel Model, defined in the "ietf-flexi-grid-
tunnel" YANG module of [Flexi-TUNNEL];
o the OTN Tunnel Model, defined in the "ietf-otn-tunnel" YANG module
of [OTN-TUNNEL].
The optical PNC can optionally use the generic Path Computation YANG
RPC, defined in the "ietf-te-path-computation" YANG module of
[PATH-COMPUTE].
Note that technology-specific augmentations of the generic path
computation RPC for WSON, Flexi-grid and OTN path computation RPCs
have been identified as a gap.
The optical PNC uses the Ethernet Client Signal Model, defined in the
"ietf-eth-tran-service" YANG module of [CLIENT-SIGNAL].
3.2.3. YANG data models at the Packet MPIs
The Packet PNC also uses at least the following technology-specific
topology YANG data models:
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o The L3 Topology Model, defined in the "ietf-l3-unicast-topology"
YANG module of [RFC8346], which augments the Base Network Topology
Model;
o the L3 specific data model including extended TE attributes (e.g.
performance derived metrics like latency), defined in "ietf-l3-te-
topology" and in "ietf-te-topology-packet" YANG modules of [L3-TE-
TOPO];
o the SR Topology Model, defined in the "ietf-sr-mpls-topology" YANG
module of [SR-TE-TOPO].
Need to check the need/applicability of the "ietf-l3-te-topology" in
this scenario since it is not described in [SR-TE-TOPO].
The packet PNC uses at least the following YANG data models:
o L3VPN Network Model (L3NM), defined in the "ietf-l3vpn-ntw" YANG
module of [RFC9182];
o L3NM TE Service Mapping, defined in the "ietf-l3nm-te-service-
mapping" YANG module of [TSM];
o L2VPN Network Model (L2NM), defined in the "ietf-l2vpn-ntw" YANG
module of [L2NM];
o L2NM TE Service Mapping, defined in the "ietf-l2nm-te-service-
mapping" YANG module of [TSM].
3.3. PCEP
[RFC8637] examines the applicability of a Path Computation Element
(PCE) [RFC5440] and PCE Communication Protocol (PCEP) to the ACTN
framework. It further describes how the PCE architecture applies to
ACTN and lists the PCEP extensions that are needed to use PCEP as an
ACTN interface. The stateful PCE [RFC8231], PCE-Initiation
[RFC8281], stateful Hierarchical PCE (H-PCE) [RFC8751], and PCE as a
central controller (PCECC) [RFC8283] are some of the key extensions
that enable the use of PCE/PCEP for ACTN.
Since the PCEP supports path computation in the packet and optical
networks, PCEP is well suited for inter-layer path computation.
[RFC5623] describes a framework for applying the PCE-based
architecture to interlayer (G)MPLS traffic engineering. Furthermore,
the section 6.1 of [RFC8751] states the H-PCE applicability for
inter-layer or POI.
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[RFC8637] lists various PCEP extensions that apply to ACTN. It also
lists the PCEP extension for optical network and POI.
Note that the PCEP can be used in conjunction with the YANG data
models described in the rest of this document. Depending on whether
ACTN is deployed in a greenfield or brownfield, two options are
possible:
1. The MDSC uses a single RESTCONF/YANG interface towards each PNC to
discover all the TE information and request TE tunnels. It may
either perform full multi-layer path computation or delegate path
computation to the underneath PNCs.
This approach is desirable for operators from an multi-vendor
integration perspective as it is simple, and we need only one type
of interface (RESTCONF) and use the relevant YANG data models
depending on the operator use case considered. Benefits of having
only one protocol for the MPI between MDSC and PNC have been
already highlighted in [PATH-COMPUTE].
4. The MDSC uses the RESTCONF/YANG interface towards each PNC to
discover all the TE information and requests the creation of TE
tunnels. However, it uses PCEP for hierarchical path computation.
As mentioned in Option 1, from an operator perspective, this
option can add integration complexity to have two protocols
instead of one, unless the RESTOCONF/YANG interface is added to an
existing PCEP deployment (brownfield scenario).
Section 4 and section 5 of this draft analyse the case where a single
RESTCONF/YANG interface is deployed at the MPI (i.e., option 1
above).
4. Inventory, service and network topology discovery
In this scenario, the MSDC needs to discover through the underlying
PNCs:
o the network topology, at both optical and IP layers, in terms of
nodes and links, including the access links, inter-domain IP links
as well as cross-layer links;
o the optical tunnels supporting multi-layer intra-domain IP links;
o both intra-domain and inter-domain L2/L3 VPN network services
deployed within the network;
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o the SR-TE paths supporting those L2/L3 VPN network services;
o the hardware inventory information of IP and optical equipment.
The O-PNC and P-PNC could discover and report the hardware network
inventory information of their equipment that is used by the
different management layers. In the context of POI, the inventory
information of IP and optical equipment can complement the topology
views and facilitate the packet/optical multi-layer view, e.g., by
providing a mapping between the lowest level LTPs in the topology
view and corresponding physical port in the network inventory view.
The MDSC could also discover the entire network inventory information
of both IP and optical equipment and correlate this information with
the links reported in the network topology.
Reporting the entire inventory and detailed topology information of
packet and optioncal networks to the MDSC may present, as a potential
drawback, scalability issues. The analysis of the scalability of this
approach and mechanisms to address potential issues is outside the
scope of this document.
Each PNC provides to the MDSC the topology view of the domain it
controls, as described in section 4.1 and 4.3. The MDSC uses this
information to discover the complete topology view of the multi-layer
multi-domain network it controls.
The MDSC should also maintain up-to-date inventory, service and
network topology databases of both IP and optical layers through the
use of IETF notifications through MPI with the PNCs when any network
inventory/topology/service change occurs.
It should be possible also to correlate information coming from IP
and optical layers (e.g., which port, lambda/OTSi, and direction, is
used by a specific IP service on the WDM equipment).
In particular, for the cross-layer links, it is key for MDSC to
automatically correlate the information from the PNC network
databases about the physical ports from the routers (single link or
bundle links for LAG) to client ports in the ROADM.
The analysis of multi-layer fault management is outside the scope of
this document. However, the discovered information should be
sufficient for the MDSC to easily correlate optical and IP layers
alarms to speed-up troubleshooting.
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Alarms and event notifications are required between MDSC and PNCs so
that any network changes are reported almost in real-time to the MDSC
(e.g., NE or link failure). As specified in [RFC7923], MDSC must
subscribe to specific objects from PNC YANG datastores for
notifications.
4.1. Optical topology discovery
The WSON Topology Model or, alternatively, the Flexi-grid Topology
model is used to report the DWDM network topology (e.g., ROADM nodes
and links), depending on whether the DWDM optical network is based on
fixed grid or flexible-grid.
The OTN Topology Model is used to report the OTN network topology
(e.g., OTN switching nodes and links), when the OTN switching layer
is deployed within the optical domain.
In order to allow the MDSC to discover the complete multi-layer and
multi-domain network topology and to correlate it with the hardware
inventory information, the O-PNCs report an abstract optical network
topology where:
o one TE node is reported for each optical NE deployed within the
optical network domain; and
o one TE link is reported for each OMS link and, optionally, for
each OTN link.
The Ethernet Topology Model is used to report the Ethernet client
LTPs that terminate the cross-layer links: one Ethernet client LTP is
reported for each Ethernet client interface on the optical NEs.
Since the MDSC delegates optical path computation to its underlay O-
PNCs, the following information can be abstracted and not reported at
the MPI:
o the optical parameters required for optical path computation, such
as those detailed in [OIA-TOPO];
o the underlay OTS links and ILAs of OMS links;
o the physical connectivity between the optical transponders and the
ROADMs.
The optical transponders and, optionally, the OTN access cards, are
abstracted at MPI by the O-PNC as Trail Termination Points (TTPs),
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defined in [RFC8795], within the optical network topology. This
abstraction is valid independently of the fact that optical
transponders are physically integrated within the same WDM node or
are physically located on a device external to the WDM node since it
both cases the optical transponders and the WDM node are under the
control of the same O-PNC.
The association between the Ethernet LTPs terminating the Ethernet
cross-layer links and the optical TTPs is reported using the Inter
Layer Lock (ILL) identifiers, defined in [RFC8795].
All the optical links are intra-domain and they are discovered by O-
PNCs, using mechanisms which are outside the scope of this document,
and reported at the MPIs within the optical network topology.
In case of a multi-layer DWDM/OTN network domain, multi-layer intra-
domain OTN links are supported by underlay DWDM tunnels, which can be
either WSON tunnels or, alternatively, Flexi-grid tunnels, depending
on whether the DWDM optical network is based on fixed grid or
flexible-grid. This relationship is reported by the mechanisms
described in section 4.2.
4.2. Optical path discovery
The WSON Tunnel Model or, alternatively, the Flexi-grid Tunnel model,
depending on whether the DWDM optical network is based on fixed grid
or flexible-grid, is used to report all the DWDM tunnels established
within the optical network.
When the OTN switching layer is deployed within the optical domain,
the OTN Tunnel Model is used to report all the OTN tunnels
established within the optical network.
The Ethernet client signal Model is used to report all the Ethernet
connectivity provided by the underlay optical tunnels between
Ethernet client LTPs. The underlay optical tunnels can be either DWDM
tunnels or, when the optional OTN switching layer is deployed, OTN
tunnels.
The DWDM tunnels can be used as underlay tunnels to support either
Ethernet client connectivity or multi-layer intra-domain OTN links.
In the latter case, the hierarchical-link container, defined in [TE-
TUNNEL], is used to reference which multi-layer intra-domain OTN
links are supported by the underlay DWDM tunnels.
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The O-PNCs report in their operational datastores all the Ethernet
client connectivities and all the optical tunnels deployed within
their optical domain regarless of the mechanisms being used to set
them up, such as the mechanisms described in section 5.2, as well as
other mechanism (e.g., static configuration), which are outside the
scope of this document.
4.3. Packet topology discovery
The L3 Topology Model, SR Topology Model, TE Topology Model and the
TE Packet Topology Model are used together to report the SR-TE
network topology, as described in figure 2 of [SR-TE-TOPO].
In order to allow the MDSC to discover the complete multi-layer and
multi-domain network topology and to correlate it with the hardware
inventory information as well as to perform multi-domain SR-TE path
computation, the P-PNCs report the full SR-TE network, including all
the information that is required by the MDSC to perform SR-TE path
computation. In particular, one TE node is reported for each router
and one TE link is reported for each intra-domain IP link. The SR-TE
topology also reports the IP LTPs terminating the inter-domain IP
links.
All the intra-domain IP links are discovered by the P-PNCs, using
mechanisms, such as LLDP [IEEE 802.1AB], which are outside the scope
of this document, and reported at the MPIs within the SR-TE network
topology.
The Ethernet Topology Model is used to report the intra-domain
Ethernet links supporting the intra-domain IP links as well as the
Ethernet LTPs that might terminate cross-layer links, inter-domain
Ethernet links or access links, as described in detail in section 4.5
and in section 4.6.
4.4. SR-TE path discovery
This version of the draft assumes that discovery of existing SR-TE
paths, including their bandwidth, at the MPI is done using the
generic TE tunnel YANG data model, defined in [TE-TUNNEL], with SR-TE
specific augmentations, as outlined in section 1 of [TE-TUNNEL].
Note that technology-specific augmentations of the generic path TE
tunnel model for SR-TE path setup and discovery have been identified
as a gap.
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To enable MDSC to discover the full end-to-end SR-TE path
configuration, the SR-TE specific augmentation of the [TE-TUNNEL]
should allow the P-PNC to report the SID list assigned to an SR-TE
path within its domain.
For example, considering the L3VPN in Figure 2, the PE13-P16-PE14 SR-
TE path and the SR-TE path in the reverse direction (between PE14 and
PE13) could be reported by the P-PNC1 to the MDSC as TE paths of the
same TE tunnel instance. The bandwidth of these TE paths represents
the bandwidth allocated by P-PNC1 to the two SR-TE paths,which can be
symmetric or asymmetric in the two directions.
The P-PNCs use the TE tunnel model to report, at the MPI, all the SR-
TE paths established within their packet domain regardless of the
mechanism being used to set them up. In other words, the TE tunnel
data model reports within the operational datastore both the SR-TE
paths being setup by the MDSC at the MPI, using the mechanisms
described in section 5.3, as well as the SR-TE paths being setup by
other means, such as static configuration, which are outside the
scope of this document.
4.5. Inter-domain link discovery
In the reference network of Figure 1, there are three types of
inter-domain links:
o Inter-domain Ethernet links suppoting inter-domain IP links
between two adjancent IP domains;
o Cross-layer links between an an IP domain and an adjacent optical
domain;
o Access links between a CE device and a PE router.
All the three types of links are Ethernet links.
It is worth noting that the P-PNC may not be aware whether an
Ethernet interface terminates a cross-layer link, an inter-domain
Ethernet link or an access link.
It is not yet clarified which model can be used to report the access
links between CEs and PEs (e.g., by using the Ethernet Topology Model
defined in [CLIENT-TOPO] or by using the SAP Model defined in
[SAP]). This has been identified as a gap.
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The inter-domain Ethernet links and cross-layer links are discovered
by the MDSC using the plug-id attribute, as described in section 4.3
of [RFC8795].
More detailed description of how the plug-id can be used to discover
inter-domain links is also provided in section 5.1.4 of [TNBI].
This document considers the following two options for discovering
inter-domain links:
1. Static configuration
2. LLDP [IEEE 802.1AB] automatic discovery
Other options are possible but not described in this document.
As outlined in [TNBI], the encoding of the plug-id namespace and the
specific LLDP information reported within the plug-id value, such as
the Chassis ID and Port ID mandatory TLVs, is implementation specific
and needs to be consistent across all the PNCs within the network.
The static configuration requires an administrative burden to
configure network-wide unique identifiers: it is therefore more
viable for inter-domain Ethenet links. For the cross-layer links, the
automatic discovery solution based on LLDP snooping is preferable
when possible.
The routers exchange standard LLDP packets as defined in [IEEE
802.1AB] and the optical NEs snoop the LLDP packets received from the
local Ethernet interface and report to the O-PNCs the extracted
information, such as the Chassis ID, the Port ID, System Name TLVs.
Note that the optical NEs do not actively participate in the LLDP
packet exchange and does not send any LLDP packets.
4.5.1. Cross-layer link discovery
The MDSC can discover a cross-layer link by matching the plug-id
values of the two Ethernet LTPs reported by two adjacent O-PNC and P-
PNC: in case LLDP snooping is used, the P-PNC reports the LLDP
information sent by the corresponding Ethernet interface on the
router while the O-PNC reports the LLDP information received by the
corresponding Ethernet interface on the optical NE, e.g., between LTP
5-0 on PE13 and LTP 7-0 on NE11, as shown in Figure 4.
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+-----------------------------------------------------------+
/ Ethernet Topology (P-PNC) /
/ +-------------+ +-------------+ /
/ | PE13 | | BR11 | /
/ | (5-1)O O(6-1) | /
/ | (5-0) |\ /| (6-0) | /
/ +------O------+|(*) (*)|+------O------+ /
/ {PE13,5} ^\<-----+ +----->/^ {BR11,6} /
+-----------------:------------------------------:----------+
: :
: :
: :
: :
+--------:------------------------------:------------------+
/ : : /
/ {PE13,5} v v {BR11,6} /
/ +------O------+ +------O------+ /
/ | (7-0) | | (8-0) | /
/ | | | | /
/ | NE11 | | NE12 | /
/ +-------------+ +-------------+ /
/ Ethernet Topology (O-PNC) /
+----------------------------------------------------------+
Notes:
=====
(*) Supporting LTP
Legenda:
========
O LTP
----> Supporting LTP
<...> Link discovered by the MDSC
{ } LTP Plug-id reported by the PNC
Figure 4 - Cross-layer link discovery
It is worth noting that the discovery of cross-layer links is based
only on the LLDP information sent by the Ethernet interfaces of the
routers and received by the Ethernet interfaces of the opticl NEs,
Therefore the MDSC can discover these links also before overlay
multi-layer IP links are setup.
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4.5.2. Inter-domain IP link discovery
The MDSC can discover an inter-domain Ethernet link which supports an
inter-domain IP link, by matching the plug-id values of the two
Ethernet LTPs reported by the two adjacent P-PNCs: the two P-PNCs
report the LLDP information being sent and being received from the
corresponding Ethernet interfaces, e.g., between the Ethernet LTP 3-1
on BR11 and the Ethernet LTP 4-1 on BR21 shown in Figure 5.
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+--------------------------+ +-------------------------+
/ IP Topology (P-PNC 1) / / IP Topology (P-PNC 2) /
/ +-------------+ / / +-------------+ /
/ | BR11 | / / | BR21 | /
/ | (3-2)O<................>O(4-2) | /
/ | |\ / / /| | /
/ +-------------+| / / |+-------------+ /
/ | / / | /
+------------------------|-+ +-------------------------+
| |
Supporting LTP | | Supporting LTP
| |
| |
+--------------|----------+ +|------------------------+
/ V / / V /
/ +-------------+/ / / \+-------------+ /
/ | {1}(3-1)O.................>O(4-1){1} | /
/ | |\ / / /| | /
/ | BR11 |V(*) / / (*)V| BR21 | /
/ | |/ / / \| | /
/ | {2}(3-0)O<~~~~~~~~~~~~~~~~>O(4-0){2} | /
/ +-------------+ / / +-------------+ /
/ Eth. Topology (P-PNC 1) / / Eth. Topology (P-PNC 2) /
+-------------------------+ +-------------------------+
Notes:
=====
(*) Supporting LTP
{1} {BR11,3,BR21,4}
{2} {BR11,3}
Legenda:
========
O LTP
----> Supporting LTP
<...> Link discovered by the MDSC
<~~~> Link inferred by the MDSC
{ } LTP Plug-id reported by the PNC
Figure 5 - Inter-domain Ethernet and IP link discovery
Different information is required to be encoded within the plug-id
attribute of the Etherent LTPs to discover cross-layer links and
inter-domain Ethernet links.
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If the P-PNC does not know a priori whether an Ethernet interface on
a router terminates a cross-layer link or an inter-domain Ethernet
link, it has to report at the MPI two Ethernet LTPs representing the
same Ethernet interface, e.g., both the Ethernet LTP 3-0 and the
Ethenet LTP 3-1, supported by LTP 3-0, shown in Figure 5:
o The physical Ethernet LTP is used to represent the physical
adjacency between the router Ethernet interface and either the
adjacent router Ethernet interface (in case of a single-layer
Ethernet link) or the optical NE Ethernet interface (in case of a
multi-layer Ethernet link). Therefore, this LTP reports, within
the plug-id attribute, the LLDP information sent by the
corresponding router Ethernet interface;
o The logical Ethernet LTP, supported by a physical Ethernet LTP, is
used to discover the logical adjancecy between router Ethernet
interfaces, which can be either single-layer or multi-layer.
Therefore, this LTP reports, within the plug-id attribute, the
LLDP information sent and received by the corresponding router
Ethernet interface.
It is worth noting that in case of an inter-domain single-layer
Ethernet link, the physical adjacency between the two router Ethernet
interfaces cannot be discovered by the MDSC, using the LLDP
information reported in the plug-id attributes, as shown in Figure 5.
However, the MDSC may infer these links if it knows a priori, using
mechanisms which are outside the scope of this document, that inter-
domain Ethernet links are always single-layer, e.g., as shown in
Figure 5.
The P-PNC can omit reporting the physical Ethernet LTPs when it
knows, by mechanisms which are outside the scope of this document,
that the corresponding router Ethernet interfaces terminate single-
layer inter-domain Ethernet links.
The MDSC can then discover an inter-domain IP link between the two IP
LTPs that are supported by the two Ethernet LTPs terminating an
inter-domain Ethernet link, discovered as described in section 4.5.2,
e.g., between the IP LTP 3-2 on BR21 and the IP LTP 4-2 on BR22,
supported respectively by the Ethernet LTP 3-1 on BR11 and by the
Ethernet LTP 4-1 on BR21, as shown in Figure 5.
4.6. Multi-layer IP link discovery
A multi-layer intra-domain IP link and its supporting multi-layer
intra-domain Ethernet link are discovered by the P-PNC like any other
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intra-domain IP and Ethernet links, as described in section 4.3, and
reported at the MPI within the SR-TE and Ethernet network topologies,
e.g., as shown in Figure 6.
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+-----------------------------------------------------------+
/ IP Topology (P-PNC 1) /
/ +---------+ +---------+ /
/ | PE13 | | BR11 | /
/ | (5-2)O<======================>O(6-2) | /
/ | | | | | /
/ +---------+ | +---------+ /
/ | /
+-----------------------------------|-----------------------+
|
| Supporting Link
|
+---------------------------|-------------------------------+
/ Ethernet Topology (P-PNC1) | /
/ +-------------+ | +-------------+ /
/ | PE13 | V | BR11 | /
/ | (5-1)O<==============>O(6-1) | /
/ | (5-0) |\ /| (6-0) | /
/ +------O------+|(*) (*)|+------O------+ /
/ ^ \<----+ +----->/^ /
+-----------------:------------------------------:----------+
: :
: :
: :
+---------:------------------------------:------------------+
/ V Ethernet Topology (O-PNC 1) V /
/ +------O------+ +------O------+ /
/ | (7-0) |Eth. client sig.| (8-0) | /
/ | X----------+-------------------X | /
/ | NE11 | | | NE12 | /
/ +-------------+ | +-------------+ /
/ | /
+----------------------------|------------------------------+
| Underlay
| tunnel
|
+-----------------------------------------------------------+
/ __ | __ /
/ +-----\/------+ v +------\/-----+ /
/ | X======|================|======X | /
/ | NE11 | Opt. Tunnel | NE12 | /
/ | | | | /
/ +-------------+ +-------------+ /
/ Optical Topology (O-PNC 1) /
+-----------------------------------------------------------+
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Notes:
=====
(*) Supporting LTP
Legenda:
========
O LTP
----> Supporting LTP or Supporting Link or Underlay tunnel
<===> Link discovered by the PNC and reported at the MPI
<...> Link discovered by the MDSC
<~~~> Link inferred by the MDSC
x---x Ethernet client signal
X===X Optical tunnel
Figure 6 - Multi-layer intra-domain Ethernet and IP link discovery
The P-PNC does not report any plug-id information on the Ethernet
LTPs terminating intra-domain Ethernet links since these links are
discovered by the PNC.
In addition, the P-PNC also reports the physical Ethernet LTPs that
terminate the cross-layer links supporting the multi-layer intra-
domain Ethernet links, e.g., the Ethernet LTP 5-0 on PE13 and the
Ethernet LTP 6-0 on BR11, shown in Figure 6.
The MDSC discovers, using the mechanisms described in section 4.5,
which Ethernet cross-layer links support the multi-layer intra-domain
Ethernet links, e.g. as shown in Figure 6.
The MDSC also discovers, from the information provided by the O-PNC
and described in section 4.2, which optical tunnels support the
multi-layer intra-domain IP links and therefore the path within the
optical network that supports a multi-layer intra-domain IP link,
e.g., as shown in Figure 6.
4.6.1. Single-layer intra-domain IP links
It is worth noting that the P-PNC may not be aware of whether an
Ethernet interface on the router terminates a multi-layer or a
single-layer intra-domain Ethernet link.
In this case, the P-PNC, always reports two Ethernet LTPs for each
Ethernet interface on the router, e.g., the Ethernet LTP 1-0 and 1-1
on PE13, shown in Figure 7.
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+-----------------------------------------------------------+
/ IP Topology (P-PNC 1) /
/ +---------+ +---------+ /
/ | PE13 | | P16 | /
/ | (1-2)O<======================>O(2-2) | /
/ | | | | | /
/ +---------+ | +---------+ /
/ | /
+---------------------------------|-------------------------+
|
| Supporting Link
|
|
+------------------------|--------------------------------+
/ | /
/ +---------+ v +---------+ /
/ | (1-1)O<======================>O(2-1) | /
/ | |\ /| | /
/ | PE13 |V(*) (*)V| P16 | /
/ | |/ \| | /
/ | {1}(1-0)O<~~~~~~~~~~~~~~~~~~~~~~>O(2-0){2} | /
/ +---------+ +---------+ /
/ Ethernet Topology (P-PNC 1) /
+---------------------------------------------------------+
Notes:
=====
(*) Supporting LTP
{1} {PE13,1}
{2} {P16,2}
Legenda:
========
O LTP
----> Supporting LTP
<===> Link discovered by the PNC and reported at the MPI
<~~~> Link inferred by the MDSC
{ } LTP Plug-id reported by the PNC
Figure 7 - Single-layer intra-domain Ethernet and IP link discovery
In this case, the MDSC, using the plug-id information reported in the
physical Ethernet LTPs, does not discover any cross-layer link being
terminated by the corresponding Ethernet interface. The MDSC may
infer the physical intra-domain Ethernet link, e.g., between LTP 1-0
on PE13 and LTP 2-0 on P16, as shown in Figure 7, if it knows a
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priori, by mechanisms which are outside the scope of this document,
that all the Ethernet interfaces on the routers either terminates a
cross-layer link or a single-layer intra-domain Ethernet link.
The P-PNC can omit reporting the physical Ethernet LTP if it knows,
by mechanisms which are outside the scope of this document, that the
intra-domain Ethernet link is single-layer.
4.7. LAG discovery
TBA
4.8. L2/L3 VPN network services discovery
TBA
4.9. Inventory discovery
The are no YANG data models in IETF that could be used to report at
the MPI the whole inventory information discovered by a PNC.
[RFC8345] had foreseen some work for inventory as an augmentation of
the network model, but no YANG data model has been developed so far.
There are also no YANG data models in IETF that could be used to
correlate topology information, e.g., a link termination point (LTP),
with inventory information, e.g., the physical port supporting an
LTP, if any.
Inventory information through MPI and correlation with topology
information is identified as a gap requiring further work and outside
of the scope of this draft.
5. Establishment of L2/L3 VPN network services with TE requirements
In this scenario the MDSC needs to setup a multi-domain L2VPN or a
multi-domain L3VPN with some SLA requirements.
The MDSC receives the request to setup a L2/L3 VPN network service
from the OSS/Orchestration layer (see Appendix A).
The MDSC translates the L2/L3 VPN SLA requirements into TE
requirements (e.g., bandwidth, TE metric bounds, SRLG disjointness,
nodes/links/domains inclusion/exclusion) and find the SR-TE paths
that meet these TE requirements (see section 2.1.1).
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For example, considering the L3VPN in Figure 2, the MDSC finds that:
o a PE13-P16-PE14 SR-TE path already exists but have not enough
bandwidth to support the new L3VPN, as described in section 4.4;
o the IP link(s) between P16 and PE14 has not enough bandwidth to
support increasing the bandwidth of that SR-TE path, as described
in section 4.3;
o a new underlay optical tunnel could be setup to increase the
bandwidth IP link(s) between P16 and PE14 to support increasing
the bandwidth of that overlay SR-TE path, as described in section
5.2. The dimensioning of the underlay optical tunnel is decided by
the MDSC based on the bandwidth requested by the SR-TE path and on
its multi-layer optimization policy, which is an internal MDSC
implementation issue.
Considering for example the L3VPN in Figure 2, the MDSC can also
decide that a new multi-domain SR-TE path needs to be setup between
PE13 and PE23, e.g., either because existing SR-TE paths between PE13
and PE23 are not able to meet the TE and binding requirements of the
L2/L3 VPN service or because there is no SR-TE path between PE13 and
PE23.
As described in section 2.1.2, with partial summarization, the MDSC
will use the TE topology information provided by the P-PNCs and the
results of the path computation requests sent to the O-PNCs, as
described in section 5.1, to compute the multi-layer/multi-domain
path between PE13 and PE23.
For example, the multi-layer/multi-domain performed by the MDSC could
require the setup of:
o a new underlay optical tunnel between PE13 and BR11, supporting a
new IP link, as described in section 5.2;
o a new underlay optical tunnel between BR21 and P24 to increase the
bandwidth of the IP link(s) between BR21 and P24, as described in
section 5.2.
When the setup of the L2/L3 VPN network service requires multi-domain
and multi-layer coordination, the MDSC is also responsible for
coordinating the network configuration required to realize the
request network service across the appropriate optical and packet
domains.
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The MDSC would therefore request:
o the O-PNC1 to setup a new optical tunnel between the ROADMs
connected to P16 and PE14, as described in section 5.2;
o the P-PNC1 to update the configuration of the existing IP link, in
case of LAG, or configure a new IP link, in case of ECMP, between
P16 and PE14, as described in section 5.2;
o the P-PNC1 to update the bandwidth of the selected SR-TE path
between PE13 and PE14, as described in section 5.3.
After that, the MDSC requests P-PNC2 to setup an SR-TE path between
BR21 and PE23, with an explicit path (BR21, P24, PE23) to constraint
this new SR-TE path to use the new underlay optical tunnel setup
between BR21 and P24, as described in section 5.3. The P-PNC2,
knowing the node and the adjacency SIDs assigned within its domain,
can install the proper SR policy, or hierarchical policies, within
BR21 and returns to the MDSC the binding SID it has assigned to this
policy in BR21.
Then the MDSC requests P-PNC1 to setup an SR-TE path between PE13 and
BR11, with an explicit path (PE13, BR11) to constraint this new SR-TE
path to use the new underlay optical tunnel setup between PE13 and
BR11, specifying also which inter-domain link should be used to send
traffic to BR21 and the binding SID that has been assigned by P-PNC2
to the corresponding SR policy in BR21, to be used for the end-to-end
SR-TE path stitching, as described in section 5.3. The P-PNC1,
knowing also the node and the adjacency SIDs assigned within its
domain and the EPE SID assigned by P-PNC1 to the inter-domain link
between BR11 and BR21, and the binding SID assigned by P-PNC2,
installs the proper policy, or policies, within PE13.
Once the SR-TE paths have been selected and, if needed,
setup/modified, the MDSC can request to both P-PNCs to configure the
L3VPN and its binding with the selected SR-TE paths using the
[RFC9182] and [TSM] YANG data models.
[Editor's Note] Further investigation is needed to understand how the
binding between a L3VPN and this new end-to-end SR-TE path can be
configured.
5.1. Optical Path Computation
As described in section 2.1.2, the optical path computation is
usually performed by the O-PNCs.
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When performing multi-layer/multi-domain path computation, the MDSC
can delegate the O-PNC for single-domain optical path computation.
As discussed in [PATH-COMPUTE], there are two options to request an
O-PNC to perform optical path computation: either via a "compute-
only" TE tunnel path, using the generic TE tunnel YANG data model
defined in [TE-TUNNEL] or via the path computation RPC defined in
[PATH-COMPUTE].
This draft assumes that the path computation RPC is used.
As described in sections 4.1 and 4.5, there is a one-to-one
relationship between the router ports, the cross-layer links and the
optical TTPs. Therefore, the properties of an optical path between
two optical TTPs, as computed by the O-PNC, can be used by the MDSC
to infer the properties of the multi-layer single-domain IP link
between the router ports associated with the two optical TTPs.
The are no YANG data models in IETF that could be used to augment the
generic path computation RPC with technology-specific attributes.
Optical technology-specific augmentation for the path computation RPC
is identified as a gap requiring further work outside of this draft's
scope.
5.2. Multi-layer IP link Setup
To setup a new multi-layer IP link between two router ports, the MDSC
requires the O-PNC to setup an optical tunnel (either a WSON Tunnel
or a Flexi-grid Tunnel or an OTN Tunnel) within the optical network
between the two TTPs associated, as described in section 5.1, with
these two router Ethernet interfaces.
The MDSC also requires the O-PNC to steer the Ethernet client traffic
between the two cross-layer links over the optical tunnel using the
Ethernet Client Signal Model.
After the optical tunnel has been setup and the client traffic
steering configured, the two IP routers can exchange Ethernet packets
between themselves, including LLDP messages.
If LLDP [IEEE 802.1AB] or any other discovery mechanisms, which are
outside the scope of this document, is used between the adjacency
between the two routers' ports, the P-PNC can automatically discover
the underlay multi-layer single-domain Ethernet link being set up by
the MDSC and report it to the P-PNC.
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Otherwise, if there are no automatic discovery mechanisms, the MDSC
can configure this multi-layer single-domain Ethernet link at the MPI
of the P-PNC.
The two Ethernet LTPs terminating this multi-layer single-domain
Ethernet link are supported by the two underlay Ethernet LTPs
terminating the two cross-layer links, e.g., as shown in Figure 6.
After the multi-layer single-domain Ethernet link has been
configured, the corresponding multi-lyaer single-domain IP link can
also be configured either by the MDSC or by the P-PNC.
This document assumes that this IP link is configured by the P-PNC,
when the underlying multi-layer single-domain Ethernet link is either
discovered by the P-PNC or configured by the MDSC at the MPI.
[Editor's Note] Add text for IP link update in case of LAG either
here or in a new section.
[Editor's Note] Add text about the configuration of multi-layer SRLG
information (issue #45).
It is worth noting that the list of SRLGs for a multi-layer IP link
can be quite long. Implementation-specific mechanisms can be
implemented by the MDSC or by the O-PNC to summarize the SRLGs of an
optical tunnel. These mechanisms are implementation-specific and have
no impact on the YANG models nor on the interoperability at the MPI,
but cares have to be taken to avoid missing information.
5.3. SR-TE Path Setup and Update
This version of the draft assumes that SR-TE path setup and update at
the MPI could be done using the generic TE tunnel YANG data model,
defined in [TE-TUNNEL], with SR-TE specific augmentations, as also
outlined in section 1 of [TE-TUNNEL].
When a new SR-TE path needs to be setup, the MDSC can use the [TE-
TUNNEL] model to request the P-PNC to setup TE paths, properly
specifying the path constraints, such as the explicit path, to force
the P-PNC to setup an SR-TE path that meets the end-to-end TE and
biding constraints and uses the optical tunnels setup by the MDSC for
the purpose of supporting this new SR-TE path.
The [TE-TUNNEL] model supports requesting the setup of both end-
to-end as well as segment TE tunnels (within one domain).
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In the latter case, SR-TE specific augmentations of the [TE-TUNNEL]
model should be defined to allow the MDSC to configure the binding
SIDs to be used for the end to-end SR-TE path stitching and to allow
the P-PNC to report the binding SID assigned to the segment TE paths.
The assigned binding SID should be persistent in case router or P-PNC
rebooting.
The MDSC can also use the [TE-TUNNEL] model to request the P-PNC to
increase the bandwidth allocated to an existing TE path, and, if
needed, also on its reverse TE path. The [TE-TUNNEL] model supports
both symmetric and asymmetric bandwidth configuration in the two
directions.
[Editor's Note:] Add some text about the protection options (to
further discuss whether to put this text here or in section 4.2.2).
The MDSC also request the P-PNC to configure TI-LFA local protection:
the mechanisms to request the configuration TI-LFA local protection
for SR-TE paths using the [TE-TUNNEL] are a gap in the current YANG
models.
The TI-LFA local protection within the P-PNC domain is configured by
the P-PNC through implementation specific mechanisms which are
outside the scope of this document. The P-PNC takes into account the
multi-layer SRLG information, configured by the MDSC as described in
section 5.2, when computing the TI-LFA post-convergence path for
multi-layer single-domain IP links.
SR-TE path setup and update (e.g., bandwidth increase) through MPI is
identified as a gap requiring further work, which is outside of the
scope of this draft.
6. Conclusions
The analysis provided in this document has shown that the IETF YANG
models described in 3.2 provides useful support for Packet Optical
Integration (POI) scenarios for resource discovery (network topology,
service, tunnels and network inventory discovery) as well as for
supporting multi-layer/multi-domain L2/L3 VPN network services.
Few gaps have been identified to be addressed by the relevant IETF
Working Groups:
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o network inventory model: this gap has been identified in section
4.9 and the solution in [NETWORK-INVENTORY] has been proposed to
resolve it;
o technology-specific augmentations of the path computation RPC,
defined in [PATH-COMPUTE] for optical networks: this gap has been
identified in section 5.1 and the solution in [OPTICAL-PATH-
COMPUTE] has been proposed to resolve it;
o relationship between a common discovery mechanisms applicable to
access links, inter-domain IP links and cross-layer links and the
UNI topology discover mechanism defined in [SAP]: this gap has
been identified in section 4.3;
o a mechanism applicable to the P-PNC NBI to configure the SR-TE
paths. Technology-specific augmentations of TE Tunnel model,
defined in [TE-TUNNEL], are foreseen in section 1 of [TE-TUNNEL]
but not yet defined: this gap has been identified in section 5.3.
7. Security Considerations
Several security considerations have been identified and will be
discussed in future versions of this document.
8. Operational Considerations
Telemetry data, such as collecting lower-layer networking health and
consideration of network and service performance from POI domain
controllers, may be required. These requirements and capabilities
will be discussed in future versions of this document.
9. IANA Considerations
This document requires no IANA actions.
10. References
10.1. Normative References
[RFC7923] Voit, E. et al., "Requirements for Subscription to YANG
Datastores", RFC 7923, June 2016.
[RFC7950] Bjorklund, M. et al., "The YANG 1.1 Data Modeling
Language", RFC 7950, August 2016.
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[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC
7951, August 2016.
[RFC8040] Bierman, A. et al., "RESTCONF Protocol", RFC 8040, January
2017.
[RFC8342] Bjorklund, M. et al., "Network Management Datastore
Architecture (NMDA)", RFC 8342, March 2018.
[RFC8345] Clemm, A., Medved, J. et al., "A Yang Data Model for
Network Topologies", RFC8345, March 2018.
[RFC8346] Clemm, A. et al., "A YANG Data Model for Layer 3
Topologies", RFC8346, March 2018.
[RFC8453] Ceccarelli, D., Lee, Y. et al., "Framework for Abstraction
and Control of TE Networks (ACTN)", RFC8453, August 2018.
[RFC8525] Bierman, A. et al., "YANG Library", RFC 8525, March 2019.
[RFC8527] Bjorklund, M. et al., "RESTCONF Extensions to Support the
Network Management Datastore Architecture", RFC 8527, March
2019.
[RFC8641] Clemm, A. and E. Voit, "Subscription to YANG Notifications
for Datastore Updates", RFC 8641, September 2019.
[RFC8650] Voit, E. et al., "Dynamic Subscription to YANG Events and
Datastores over RESTCONF", RFC 8650, November 2019.
[RFC8795] Liu, X. et al., "YANG Data Model for Traffic Engineering
(TE) Topologies", RFC8795, August 2020.
[RFC9094] Zheng H., Lee, Y. et al., "A YANG Data Model for Wavelength
Switched Optical Networks (WSONs)", RFC 9094, August 2021.
[IEEE 802.1AB] IEEE 802.1AB-2016, "IEEE Standard for Local and
metropolitan area networks - Station and Media Access
Control Connectivity Discovery", March 2016.
[Flexi-TOPO] Lopez de Vergara, J. E. et al., "YANG data model for
Flexi-Grid Optical Networks", draft-ietf-ccamp-flexigrid-
yang, work in progress.
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[OTN-TOPO] Zheng, H. et al., "A YANG Data Model for Optical Transport
Network Topology", draft-ietf-ccamp-otn-topo-yang, work in
progress.
[CLIENT-TOPO] Zheng, H. et al., "A YANG Data Model for Client-layer
Topology", draft-zheng-ccamp-client-topo-yang, work in
progress.
[L3-TE-TOPO] Liu, X. et al., "YANG Data Model for Layer 3 TE
Topologies", draft-ietf-teas-yang-l3-te-topo, work in
progress.
[SR-TE-TOPO] Liu, X. et al., "YANG Data Model for SR and SR TE
Topologies on MPLS Data Plane", draft-ietf-teas-yang-sr-te-
topo, 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.
[WSON-TUNNEL] Lee, Y. et al., "A Yang Data Model for WSON Tunnel",
draft-ietf-ccamp-wson-tunnel-model, work in progress.
[Flexi-TUNNEL] Lopez de Vergara, J. E. et al., "A YANG Data Model for
Flexi-Grid Tunnels ", draft-ietf-ccamp-flexigrid-tunnel-
yang, work in progress.
[OTN-TUNNEL] Zheng, H. et al., "OTN Tunnel YANG Model", draft-ietf-
ccamp-otn-tunnel-model, work in progress.
[PATH-COMPUTE] Busi, I., Belotti, S. et al, "Yang model for
requesting Path Computation", draft-ietf-teas-yang-path-
computation, work in progress.
[CLIENT-SIGNAL] Zheng, H. et al., "A YANG Data Model for Transport
Network Client Signals", draft-ietf-ccamp-client-signal-
yang, work in progress.
10.2. Informative References
[RFC1930] J. Hawkinson, T. Bates, "Guideline for creation, selection,
and registration of an Autonomous System (AS)", RFC 1930,
March 1996.
[RFC5440] Vasseur, JP. et al., "Path Computation Element (PCE)
Communication Protocol (PCEP)", RFC 5440, March 2009.
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[RFC5623] Oki, E. et al., "Framework for PCE-Based Inter-Layer MPLS
and GMPLS Traffic Engineering", RFC 5623, September 2009.
[RFC8231] Crabbe, E. et al., "Path Computation Element Communication
Protocol (PCEP) Extensions for Stateful PCE", RFC 8231,
September 2017.
[RFC8281] Crabbe, E. et al., "Path Computation Element Communication
Protocol (PCEP) Extensions for PCE-Initiated LSP Setup in a
Stateful PCE Model", RFC 8281, December 2017.
[RFC8283] Farrel, A. et al., "An Architecture for Use of PCE and the
PCE Communication Protocol (PCEP) in a Network with Central
Control", RFC 8283, December 2017.
[RFC8309] Q. Wu, W. Liu, and A. Farrel, "Service Model Explained",
RFC 8309, January 2018.
[RFC8637] Dhody, D. et al., "Applicability of the Path Computation
Element (PCE) to the Abstraction and Control of TE Networks
(ACTN)", RFC 8637, July 2019.
[RFC8751] Dhody, D. et al., "Hierarchical Stateful Path Computation
Element (PCE)", RFC 8751, March 2020.
[RFC9182] S. Barguil, et al., "A YANG Network Data Model for Layer
3 VPNs", RFC 9182, February 2022.
[L2NM] S. Barguil, et al., "A Layer 2 VPN Network YANG Model",
draft-ietf-opsawg-l2nm, work in progress.
[TSM] Y. Lee, et al., "Traffic Engineering and Service Mapping
Yang Model", draft-ietf-teas-te-service-mapping-yang, work
in progress.
[TNBI] Busi, I., Daniel, K. et al., "Transport Northbound
Interface Applicability Statement", draft-ietf-ccamp-
transport-nbi-app-statement, work in progress.
[VN] Y. Lee, et al., "A Yang Data Model for ACTN VN Operation",
draft-ietf-teas-actn-vn-yang, work in progress.
[OIA-TOPO] Lee Y. et al., "A YANG Data Model for Optical Impairment-
aware Topology", draft-ietf-ccamp-optical-impairment-
topology-yang, work in progress.
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[SAP] Gonzalez de Dios O. et al., "A Network YANG Model for
Service Attachment Points (SAPs)", draft-ietf-opsawg-sap,
work in progress.
[NETWORK-INVENTORY] Yu C. et al., "A YANG Data Model for Optical
Network Inventory", draft-yg3bp-ccamp-optical-inventory-
yang, work in progress.
[OPTICAL-PATH-COMPUTE] Busi I. et al., "YANG Data Models for
requesting Path Computation in Optical Networks", draft-
gbb-ccamp-optical-path-computation-yang, work in progress.
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Appendix A. OSS/Orchestration Layer
The OSS/Orchestration layer is a vital part of the architecture
framework for a service provider:
o to abstract (through MDSC and PNCs) the underlying transport
network complexity to the Business Systems Support layer;
o to coordinate NFV, Transport (e.g. IP, optical and microwave
networks), Fixed Acess, Core and Radio domains enabling full
automation of end-to-end services to the end customers;
o to enable catalogue-driven service provisioning from external
applications (e.g. Customer Portal for Enterprise Business
services), orchestrating the design and lifecycle management of
these end-to-end transport connectivity services, consuming IP
and/or optical transport connectivity services upon request.
As discussed in section 2.1, in this document, the MDSC interfaces
with the OSS/Orchestration layer and, therefore, it performs the
functions of the Network Orchestrator, defined in [RFC8309].
The OSS/Orchestration layer requests the creation of a network
service to the MDSC specifying its end-points (PEs and the interfaces
towards the CEs) as well as the network service SLA and then proceeds
to configuring accordingly the end-to-end customer service between
the CEs in the case of an operator managed service.
A.1. MDSC NBI
As explained in section 2, the OSS/Orchestration layer can request
the MDSC to setup L2/L3VPN network services (with or without TE
requirements).
Although the OSS/Orchestration layer interface is usually operator-
specific, typically it would be using a RESTCONF/YANG interface with
a more abstracted version of the MPI YANG data models used for
network configuration (e.g. L3NM, L2NM).
Figure 8 shows an example of possible control flow between the
OSS/Orchestration layer and the MDSC to instantiate L2/L3 VPN network
services, using the YANG data models under the definition in [VN],
[L2NM], [RFC9182] and [TSM].
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+-------------------------------------------+
| |
| OSS/Orchestration layer |
| |
+-----------------------+-------------------+
|
1.VN 2. L2/L3NM & | ^
| TSM | |
| | | |
| | | |
v v | 3. Update VN
|
+-----------------------+-------------------+
| |
| MDSC |
| |
+-------------------------------------------+
Figure 8 Service Request Process
o The VN YANG data model, defined in [VN], whose primary focus is
the CMI, can also provide VN Service configuration from an
orchestrated network service point of view when the L2/L3 VPN
network service has TE requirements. However, this model is not
used to setup L2/L3 VPN service with no TE requirements.
o It provides the profile of VN in terms of VN members, each of
which corresponds to an edge-to-edge link between customer
end-points (VNAPs). It also provides the mappings between the
VNAPs with the LTPs and the connectivity matrix with the VN
member. The associated traffic matrix (e.g., bandwidth,
latency, protection level, etc.) of VN member is expressed
(i.e., via the TE-topology's connectivity matrix).
o The model also provides VN-level preference information (e.g.,
VN member diversity) and VN-level admin-status and
operational-status.
o The L2NM and L3NM YANG data models, defined in [L2NM] and
[RFC9182], whose primary focus is the MPI, can also be used to
provide L2VPN and L3VPN network service configuration from a
orchestrated connectivity service point of view.
o The TE & Service Mapping YANG data model [TSM] provides TE-service
mapping.
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o TE-service mapping provides the mapping between a L2/L3 VPN
instance and the corresponding VN instances.
o The TE-service mapping also provides the binding requirements
as to how each L2/L3 VPN/VN instance is created concerning the
underlay TE tunnels (e.g., whether they require a new and
isolated set of TE underlay tunnels or not).
o Site mapping provides the site reference information across
L2/L3 VPN Site ID, VN Access Point ID, and the LTP of the
access link.
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Appendix B. Multi-layer and multi-domain resiliency
B.1. Maintenance Window
Before planned maintenance operation on DWDM network takes place, IP
traffic should be moved hitless to another link.
MDSC must reroute IP traffic before the events takes place. It should
be possible to lock IP traffic to the protection route until the
maintenance event is finished, unless a fault occurs on such path.
B.2. Router port failure
The focus is on client-side protection scheme between IP router and
reconfigurable ROADM. Scenario here is to define only one port in the
routers and in the ROADM muxponder board at both ends as back-up
ports to recover any other port failure on client-side of the ROADM
(either on router port side or on muxponder side or on the link
between them). When client-side port failure occurs, alarms are
raised to MDSC by IP-PNC and O-PNC (port status down, LOS etc.). MDSC
checks with OP-PNC(s) that there is no optical failure in the optical
layer.
There can be two cases here:
a) LAG was defined between the two end routers. MDSC, after checking
that optical layer is fine between the two end ROADMs, triggers
the ROADM configuration so that the router back-up port with its
associated muxponder port can reuse the OCh that was already in
use previously by the failed router port and adds the new link to
the LAG on the failure side.
While the ROADM reconfiguration takes place, IP/MPLS traffic is
using the reduced bandwidth of the IP link bundle, discarding
lower priority traffic if required. Once back-up port has been
reconfigured to reuse the existing OCh and new link has been added
to the LAG then original Bandwidth is recovered between the end
routers.
Note: in this LAG scenario let assume that BFD is running at LAG
level so that there is nothing triggered at MPLS level when one of
the link member of the LAG fails.
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b) If there is no LAG then the scenario is not clear since a router
port failure would automatically trigger (through BFD failure)
first a sub-50ms protection at MPLS level :FRR (MPLS RSVP-TE case)
or TI-LFA (MPLS based SR-TE case) through a protection port. At
the same time MDSC, after checking that optical network connection
is still fine, would trigger the reconfiguration of the back-up
port of the router and of the ROADM muxponder to re-use the same
OCh as the one used originally for the failed router port. Once
everything has been correctly configured, MDSC Global PCE could
suggest to the operator to trigger a possible re-optimization of
the back-up MPLS path to go back to the MPLS primary path through
the back-up port of the router and the original OCh if overall
cost, latency etc. is improved. However, in this scenario, there
is a need for protection port PLUS back-up port in the router
which does not lead to clear port savings.
Acknowledgments
This document was prepared using 2-Word-v2.0.template.dot.
Some of this analysis work was supported in part by the European
Commission funded H2020-ICT-2016-2 METRO-HAUL project (G.A. 761727).
Contributors
Sergio Belotti
Nokia
Email: sergio.belotti@nokia.com
Gabriele Galimberti
Cisco
Email: ggalimbe@cisco.com
Zheng Yanlei
China Unicom
Email: zhengyanlei@chinaunicom.cn
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Anton Snitser
Sedona
Email: antons@sedonasys.com
Washington Costa Pereira Correia
TIM Brasil
Email: wcorreia@timbrasil.com.br
Michael Scharf
Hochschule Esslingen - University of Applied Sciences
Email: michael.scharf@hs-esslingen.de
Young Lee
Sung Kyun Kwan University
Email: younglee.tx@gmail.com
Jeff Tantsura
Apstra
Email: jefftant.ietf@gmail.com
Paolo Volpato
Huawei
Email: paolo.volpato@huawei.com
Brent Foster
Cisco
Email: brfoster@cisco.com
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Authors' Addresses
Fabio Peruzzini
TIM
Email: fabio.peruzzini@telecomitalia.it
Jean-Francois Bouquier
Vodafone
Email: jeff.bouquier@vodafone.com
Italo Busi
Huawei
Email: Italo.busi@huawei.com
Daniel King
Old Dog Consulting
Email: daniel@olddog.co.uk
Daniele Ceccarelli
Ericsson
Email: daniele.ceccarelli@ericsson.com
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