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: July 2022 January 17, 2022
Applicability of Abstraction and Control of Traffic Engineered
Networks (ACTN) to Packet Optical Integration (POI)
draft-ietf-teas-actn-poi-applicability-04
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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Table of Contents
1. Introduction...................................................3
2. Reference architecture and network scenario....................4
2.1. L2/L3VPN Service Request North Bound of MDSC..............9
2.2. Service and Network Orchestration........................10
2.2.1. Hard Isolation......................................13
2.2.2. Shared Tunnel Selection.............................13
2.3. IP/MPLS Domain Controller and NE Functions...............14
2.4. Optical Domain Controller and NE Functions...............16
3. Interface protocols and YANG data models for the MPIs.........16
3.1. RESTCONF protocol at the MPIs............................16
3.2. YANG data models at the MPIs.............................17
3.2.1. Common YANG data models at the MPIs.................17
3.2.2. YANG models at the Optical MPIs.....................18
3.2.3. YANG data models at the Packet MPIs.................19
3.3. PCEP.....................................................20
4. Multi-layer and multi-domain services scenarios...............21
4.1. Scenario 1: inventory, service and network topology
discovery.....................................................21
4.1.1. Inter-domain link discovery.........................23
4.1.2. Multi-layer IP link discovery.......................24
4.1.3. Inventory discovery.................................24
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4.1.4. SR-TE paths discovery...............................25
4.2. Establishment of L2VPN/L3VPN with TE requirements........25
4.2.1. Optical Path Computation............................30
4.2.2. Multi-layer IP link Setup and Update................30
4.2.3. SR-TE Path Setup and Update.........................31
5. Security Considerations.......................................31
6. Operational Considerations....................................32
7. IANA Considerations...........................................32
8. References....................................................32
8.1. Normative References.....................................32
8.2. Informative References...................................34
Appendix A. Multi-layer and multi-domain resiliency...........36
A.1. Maintenance Window......................................36
A.2. Router port failure.....................................36
Acknowledgments..................................................37
Contributors.....................................................37
Authors' Addresses...............................................39
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. Thus allowing a wide range of transport connectivity
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), is typically realized on top of an 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
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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 network. 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 maintenance events).
ACTN framework enables this complete multi-layer and multi-vendor
integration of packet and optical networks through MDSC and packet
and optical PNCs.
In this document, critical scenarios for POI are described from the
packet service layer perspective and identify 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 IP/MPLS networks operated as a client
of optical DWDM networks. The scenarios are ordered by increasing
the level of integration and complexity. For each multi-layer
scenario, the document analyzes how to use the interfaces and data
models of the ACTN architecture.
Understanding the level of standardization and the possible gaps
will help assess the feasibility of integration between IP and
Optical DWDM domain (and optionally OTN layer) in an end-to-end
multi-vendor service provisioning perspective.
2. Reference architecture and network scenario
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:
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+----------+
| 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 Scenario
The ACTN architecture, defined in [RFC8453], is used to control this
multi-domain network where each Packet PNC (P-PNC) is responsible
for controlling its IP domain, which can be either an Autonomous
System (AS), [RFC1930], or an IGP area within the same operator
network. Each Optical PNC (O-PNC) in the above topology is
responsible for controlling its Optical Domain.
The routers between IP 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 a
ABR.
The MDSC is responsible for coordinating the whole multi-domain
multi-layer (Packet and Optical) network. A specific standard
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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 MPLS-TE
network).
In the network scenario of Figure 1, it is assumed that:
o The domain boundaries between the IP and Optical domains are
congruent. In other words, one Optical domain supports
connectivity between Routers in one and only one Packet Domain;
o Inter-domain links exist only between Packet domains (i.e.,
between BR routers) and between Packet and Optical domains (i.e.,
between routers and Optical NEs). In other words, there are no
inter-domain links between Optical domains;
o The interfaces between the Routers and the Optical NEs are
"Ethernet" physical interfaces;
o The interfaces between the Border Routers (BRs) are "Ethernet"
physical interfaces.
This version of the document assumes that the IP link supported by
the Optical network are always intra-AS (PE-BR, intra-domain BR-BR,
PE-P, BR-P, or P-P) and that the BRs are co-located and connected by
an IP link supported by an Ethernet physical link.
The possibility to setup inter-AS/inter-area IP links (e.g.,
inter-domain BR-BR or PE-PE), supported by optical network, is for
further study.
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 NEs within the optical domains can be ROADMs or OTN
switches, with or without a ROADM.
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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 L2/L3VPN services.
Although the new optical technologies (e.g. QSFP-DD ZR 400G)
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 Transport networks in a single unified domain. As
a consequence, this draft is not addressing the unified scenario.
Instead, the unified use case will be described in a different
draft.
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].
3. Another implementation can choose to split the MDSC functions
between an "higher-level MDSC" (MDSC-H) responsible for
packet-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.
Please note that 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. In this case, the MDSC is
dealing with the network services requests received from the
OSS/Orchestration layer.
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[Editors'note:] Check for a better term to define the network
services. It may be worthwhile defining what are the customer and
network services.
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.
The functionality of the OSS/Orchestration layer and the interface
toward the MDSC are usually operator-specific and outside the scope
of this draft. For example, this document assumes that the
OSS/Orchestrator requests MDSC to set up L2VPN/L3VPN services
through mechanisms that are outside the scope of this document.
There are two prominent cases when MDSC coordination of underlying
PNCs for POI networking is initiated:
o Initiated by a request from the OSS/Orchestration layer to setup
L2VPN/L3VPN 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
service provisioning request being received from
the OSS/Orchestration layer.
The two aforemetioned MDSC workflow cases are in the scope of this
draft. The workflow initiation is transparent at the MPI.
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2.1. L2/L3VPN Service Request North Bound of MDSC
As explained in section 2, the OSS/Orchestration layer can request
the MDSC to setup L2/L3VPN 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 2 shows an example of possible control flow between the
OSS/Orchestration layer and the MDSC to instantiate L2/L3VPN
services, using the YANG models under the definition in [VN],
[L2NM], [L3NM] and [TSM].
+-------------------------------------------+
| |
| OSS/Orchestration layer |
| |
+-----------------------+-------------------+
|
1.VN 2. L2/L3NM & | ^
| TSM | |
| | | |
| | | |
v v | 3. Update VN
|
+-----------------------+-------------------+
| |
| MDSC |
| |
+-------------------------------------------+
Figure 2 Service Request Process
o The VN YANG model [VN], whose primary focus is the CMI, can also
provide VN Service configuration from an orchestrated
connectivity service point of view when the L2/L3VPN service has
TE requirements. However, this model is not used to setup
L2/L3VPN service with no TE requirements.
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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 YANG model [L2NM], whose primary focus is the MPI, can
also be used to provide L2VPN service configuration and site
information, from a orchestrated connectivity service point of
view.
o The L3NM YANG model [L3NM], whose primary focus is the MPI, can
also be used to provide all L3VPN service configuration and site
information, from a orchestrated connectivity service point of
view.
o The TE & Service Mapping YANG model [TSM] provides TE-service
mapping as well as site mapping.
o TE-service mapping provides the mapping between a L2/L3VPN
instance and the corresponding VN instances.
o The TE-service mapping also provides the service mapping
requirement type as to how each L2/L3VPN/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). See Section 2.2 for a detailed discussion on the
mapping requirement types.
o Site mapping provides the site reference information across
L2/L3VPN Site ID, VN Access Point ID, and the LTP of the
access link.
2.2. Service and Network Orchestration
From a functional standpoint, MDSC represented in Figure 2
interfaces with the OSS/Orchestration layer and decoupled L2/L3VPN
service configuration functions from network configuration
functions. Therefore in this document, the MDSC performs the
functions of the Network Orchestrator, as defined in [RFC8309].
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One of the important MDSC functions is to identify which TE Tunnels
should carry the L2/L3VPN traffic (e.g., from TE & Service Mapping
configuration) and to relay this information to the P-PNCs, to
ensure the PEs' forwarding tables (e.g., VRF) are properly
populated, according to the TE binding requirement for the L2/L3VPN.
TE binding requirement types [TSM] are:
1. Hard Isolation with deterministic latency: The L2/L3VPN service
requires a set of dedicated TE Tunnels providing deterministic
latency performances and that cannot be not shared with other
services, nor compete for bandwidth with other Tunnels.
2. Hard Isolation: This is similar to the above case without
deterministic latency requirements.
3. Soft Isolation: The L2/L3VPN service requires a set of dedicated
MPLS-TE tunnels that cannot be shared with other services, but
which could compete for bandwidth with other Tunnels.
4. Sharing: The L2/L3VPN service allows sharing the MPLS-TE Tunnels
supporting it with other services.
There could be additional TE binding requirements for the first
three types with respect to different VN members of the same VN (on
how different VN members, belonging to the same VN, can share or not
network resources). For the first two cases, VN members can be
hard-isolated, soft-isolated, or shared. For the third case, VN
members can be soft-isolated or shared.
In order to fulfil the L2/L3VPN end-to-end TE requirements,
including the TE binding requirements, the MDSC needs to perform
multi-layer/multi-domain path computation to select the BRs, the
intra-domain MPLS-TE Tunnels and the intra-domain Optical Tunnels.
Depending on the knowledge that MDSC has of the topology and
configuration of the underlying network domains, three models for
performing path computation are possible:
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1. Summarization: MDSC has an abstracted TE topology view of all of
the underlying domains, both packet and optical. MDSC does not
have enough TE topology information to perform
multi-layer/multi-domain path computation. Therefore MDSC
delegates the P-PNCs and O-PNCs to perform a local path
computation within their 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 model presents an issue to P-PNC, which does not have the
capability of performing a single-domain/multi-layer path
computation (that is, P-PNC does not have any possibility to
retrieve the topology/configuration information from the Optical
controller). A possible solution could be to include a CNC
function in the P-PNC to request the MDSC multi-domain Optical
path computation, as shown in Figure 10 of [RFC8453].
Another possible 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.
2. Partial summarization: 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.
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 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.
The role of P-PNC is minimized, i.e. is limited to management.
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3. Full knowledge: 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 model 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).
The current version of this draft assumes that MDSC supports at
least model #2 (Partial summarization).
[Note: check with opeerators for some references on real deployment]
2.2.1. Hard Isolation
For example, when "Hard Isolation with, or without, deterministic
latency" TE binding requirement is applied for a L2/L3VPN, new
Optical Tunnels need to be setup to support dedicated IP links
between PEs and BRs.
The MDSC needs to identify the set of IP/MPLS domains and their BRs.
This requires the MDSC to request each O-PNC to compute the
intra-domain optical paths between each PEs/BRs pairs.
When requesting optical path computation to the O-PNC, the MDSC
needs to take into account the inter-layer peering points, such as
the interconnections between the PE/BR nodes and the edge Optical
nodes (e.g., using the inter-layer lock or the transitional link
information, defined in [RFC8795]).
When the optimal multi-layer/multi-domain path has been computed,
the MDSC requests each O-PNC to setup the selected Optical Tunnels
and P-PNC to setup the intra-domain MPLS-TE Tunnels, over the
selected Optical Tunnels. MDSC also properly configures its BGP
speakers and PE/BR forwarding tables to ensure that the VPN traffic
is properly forwarded.
2.2.2. Shared Tunnel Selection
In case of shared tunnel selection, the MDSC needs to check if there
is a multi-domain path which can support the L2/L3VPN end-to-end TE
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service requirements (e.g., bandwidth, latency, etc.) using existing
intra-domain MPLS-TE tunnels.
If such a path is found, the MDSC selects the optimal path from the
candidate pool and request each P-PNC to setup the L2/L3VPN service
using the selected intra-domain MPLS-TE tunnel, between PE/BR nodes.
Otherwise, the MDSC should detect if the multi-domain path can be
setup using existing intra-domain MPLS-TE tunnels with modifications
(e.g., increasing the tunnel bandwidth) or setting up new intra-
domain MPLS-TE tunnel(s).
The modification of an existing MPLS-TE Tunnel and the setup of a
new MPLS-TE Tunnel may also require multi-layer coordination e.g.,
in case the available bandwidth of underlying Optical Tunnels is not
sufficient. Based on multi-domain/multi-layer path computation, the
MDSC can decide for example to modify the bandwidth of an existing
Optical Tunnel (e.g., ODUflex bandwidth increase) or to setup new
Optical Tunnels to be used as additional LAG members of an existing
IP link or as new IP links to re-route the MPLS-TE Tunnel.
In all the cases, the labels used by the end-to-end tunnel are
distributed in the PE and BR nodes by BGP. The MDSC is responsible
to configure the BGP speakers in each P-PNC, if needed.
2.3. IP/MPLS Domain Controller and NE Functions
IP/MPLS networks are assumed to have multiple domains. Each domain,
corresponding to either an IGP area or an Autonomous System (AS)
within the same operator network, is controlled by an IP/MPLS domain
controller (P-PNC).
Among the functions of the P-PNC, there are the setup or
modification of the intra-domain MPLS-TE Tunnels, between PEs and
BRs, and the configuration of the VPN services, such as the VRF in
the PE nodes, as shown in Figure 3:
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+------------------+ +------------------+
| | | |
| P-PNC1 | | P-PNC2 |
| | | |
+--|-----------|---+ +--|-----------|---+
| 1.Tunnel | 2.VPN | 1.Tunnel | 2.VPN
| Config | Provisioning | Config | Provisioning
V V V V
+---------------------+ +---------------------+
CE / PE tunnel 1 BR\ / BR tunnel 2 PE \ CE
o--/---o..................o--\-----/--o..................o---\--o
\ / \ /
\ Domain 1 / \ Domain 2 /
+---------------------+ +---------------------+
End-to-end tunnel
<------------------------------------------------->
Figure 3 IP/MPLS Domain Controller & NE Functions
It is assumed that BGP is running in the inter-domain IP/MPLS
networks for L2/L3VPN. The P-PNC controller is also responsible for
configuring the BGP speakers within its control domain, if
necessary.
The BGP would be responsible for the end-to-end tunnel label
distribution on PE and BR nodes. The MDSC is responsible for
selecting the BRs and the intra-domain MPLS-TE Tunnels between PE/BR
nodes.
If new MPLS-TE Tunnels are needed or modifications (e.g., bandwidth
increase) to existing MPLS_TE Tunnels are needed, as outlined in
section 2.2, the MDSC would request their setup or modifications to
the P-PNCs (step 1 in Figure 3). Then the MDSC would request the
P-PNC to configure the VPN, including selecting the intra-domain TE
Tunnel (step 2 in Figure 3).
The P-PNC should configure, using mechanisms outside the scope of
this document, the ingress PE forwarding table, e.g., the VRF, to
forward the VPN traffic, received from the CE, with the following
three labels:
o VPN label: assigned by the egress PE and distributed by BGP;
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o end-to-end LSP label: assigned by the egress BR, selected by the
MDSC, and distributed by BGP;
o MPLS-TE tunnel label, assigned by the next hop P node of the
tunnel selected by the MDSC and distributed by mechanism internal
to the IP/MPLS domain (e.g., RSVP-TE).
2.4. Optical Domain Controller and NE Functions
The optical network provides the underlay connectivity services to
IP/MPLS networks. The coordination of Packet/Optical multi-layer 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, and
all 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
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Architecture (NMDA) defined in [RFC8342], are assumed to be used as
well at these MPI interfaces and also at CMI interfaces.
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
models at the MPI to report their abstract topologies:
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 with TE specific information.
These common YANG models are generic and augmented by technology-
specific YANG modules as described in the following sections.
Both Optical and Packet PNCs must use the following common
notifications YANG models at the MPI so that any network changes can
be reported almost in real-time to MDSC by the PNCs:
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].
PNCs and MDSCs must be compliant with subscription requirements as
stated in [RFC7923].
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3.2.2. YANG models at the Optical MPIs
The Optical PNC also uses at least the following technology-specific
topology YANG models, providing WDM and Ethernet technology-specific
augmentations of the generic TE Topology Model:
o The WSON Topology Model, defined in the "ietf-wson-topology" YANG
modules of [RFC9094], or the Flexi-grid Topology Model, defined
in the "ietf-flexi-grid-topology" YANG module of [Flexi-TOPO];
o Optionally, when the OTN layer is used, the OTN Topology Model,
as defined in the "ietf-otn-topology" YANG module of [OTN-TOPO];
o The Ethernet Topology Model, defined in the "ietf-eth-te-
topology" YANG module of [CLIENT-TOPO];
o Optionally, when the OTN layer is used, the network data model
for L1 OTN services (e.g. an Ethernet transparent service) as
defined in "ietf-trans-client-service" YANG module of draft-ietf-
ccamp-client-signal-yang [CLIENT-SIGNAL];
o The WSON Topology Model or, alternatively, the Flexi-grid
Topology model is used to report the DWDM network topology (e.g.,
ROADMs and links) depending on whether the DWDM optical network
is based on fixed grid or flexible-grid.
The Ethernet Topology is used to report the cross-layer links
between the IP routers and the edge ROADMs.
The optical PNC uses at least the following YANG models:
o The TE Tunnel Model, defined in the "ietf-te" YANG module of
[TE-TUNNEL];
o The WSON Tunnel Model, defined in the "ietf-wson-tunnel" YANG
modules of [WSON-TUNNEL], or the Flexi-grid Media Channel Model,
defined in the "ietf-flexi-grid-media-channel" YANG module of
[Flexi-TUNNEL];
o Optionally, when the OTN layer is used, the OTN Tunnel Model,
defined in the "ietf-otn-tunnel" YANG module of [OTN-TUNNEL];
o The Ethernet Client Signal Model, defined in the "ietf-eth-tran-
service" YANG module of [CLIENT-SIGNAL].
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The TE Tunnel model is generic and augmented by technology-specific
models such as the WSON Tunnel Model and the Flexi-grid Media
Channel Model.
The WSON Tunnel Model, or the Flexi-grid Media Channel Model, may be
used to setup connectivity within the DWDM network depending on
whether the DWDM optical network is based on fixed grid or flexible-
grid.
The Ethernet Client Signal Model is used to configure the steering
of the Ethernet client traffic between Ethernet access links and TE
Tunnels, which in this case could be either WSON Tunnels or
Flexi-Grid Media Channels. This model is generic and applies to any
technology-specific TE Tunnel: technology-specific attributes are
provided by the technology-specific models which augment the generic
TE-Tunnel Model.
3.2.3. YANG data models at the Packet MPIs
The Packet PNC also uses at least the following technology-specific
topology YANG models, providing IP and Ethernet technology-specific
augmentations of the generic Topology Models described in section
3.2.1:
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 When SR-TE is used, the SR Topology Model, defined in the "ietf-
sr-mpls-topology" YANG module of [SR-TE-TOPO]: this YANG module
is used together with other YANG modules to provide the SR-TE
topology view as described in figure 2 of [SR-TE-TOPO];
o The Ethernet Topology Model, defined in the "ietf-eth-te-
topology" YANG module of [CLIENT-TOPO], which augments the TE
Topology Model.
The Ethernet Topology Model is used to report the cross-layer links
between the IP routers and the edge ROADMs as well as the
inter-domain links between ASBRs, while the L3 Topology Model is
used to report the IP network topology (e.g., IP routers and links).
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o The User Network Interface (UNI) Topology Model, being defined in
the "ietf-uni-topology" module of the draft-ogondio-opsawg-uni-
topology [UNI-TOPO] which augment "ietf-network" module defined
in [RFC8345] adding service attachment points to the nodes to
which L2VPN/L3VPN IP/MPLS services can be attached.
o L3VPN network data model defined in "ietf-l3vpn-ntw" module of
draft-ietf-opsawg-l3sm-l3nm [L3NM] used for non-ACTN MPI for
L3VPN service provisioning
o L2VPN network data model defined in "ietf-l2vpn-ntw" module of
draft-ietf-barguil-opsawg-l2sm-l2nm [L2NM] used for non-ACTN MPI
for L2VPN service provisioning
[Editor's note:] Add YANG models used for tunnel and service
configuration.
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.
[RFC8637] lists various PCEP extensions that apply to ACTN. It also
list the PCEP extension for optical network and POI.
Note that the PCEP can be used in conjunction with the YANG models
described in the rest of this document. Depending on whether ACTN is
deployed in a greenfield or brownfield, two options are possible:
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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].
2. 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 of this draft analyses the case where a single
RESTCONF/YANG interface is deployed at the MPI (i.e., option 1
above).
4. Multi-layer and multi-domain services scenarios
Multi-layer and multi-domain scenarios, based on reference network
described in section 2, and very relevant for Service Providers, are
described in the next sections. For each scenario, existing IETF
protocols and data models are identified with particular focus on
the MPI in the ACTN architecture. Non-ACTN IETF data models required
for L2/L3VPN service provisioning between MDSC and packet PNCs are
also identified.
4.1. Scenario 1: inventory, service and network topology discovery
In this scenario, the MSDC needs to discover through the underlying
PNCs, the network topology, at both WDM and IP layers, in terms of
nodes and links, including inter-AS domain links as well as cross-
layer links but also in terms of tunnels (MPLS or SR paths in IP
layer and OCh and optionally ODUk tunnels in optical layer).
In addition, the MDSC should discover the IP/MPLS transport services
(L2VPN/L3VPN) deployed, both intra-domain and inter-domain wise.
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The O-PNC and P-PNC could discover and report the inventory
information of their equipment that is used by the different
management layers. In the context of POI, the inventory information
of IP and WDM equipment can complement the topology views and
facilitate the IP-Optical multi-layer view.
The MDSC could also discover the whole inventory information of both
IP and WDM equipment and correlate this information with the links
reported in the network topology.
Each PNC provides to the MDSC an abstracted or full topology view of
the WDM or the IP topology of the domain it controls. This topology
can be abstracted in the sense that some detailed NE information is
hidden at the MPI. All or some of the NEs and related physical links
are exposed as abstract nodes and logical (virtual) links, depending
on the level of abstraction the user requires. This information is
key to understanding both the inter-AS domain links (seen by each
controller as UNI interfaces but as I-NNI interfaces by the MDSC)
and the cross-layer mapping between IP and WDM layer.
The MDSC should also maintain up-to-date inventory, service and
network topology databases of both IP and WDM layers (and optionally
OTN layer) through the use of IETF notifications through MPI with
the PNCs when any inventory/topology/service change occurs.
It should be possible also to correlate information coming from IP
and WDM 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.
It should be possible at MDSC level to easily correlate WDM and IP
layers alarms to speed-up troubleshooting
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, MPLS tunnel switched from primary to back-
up path etc.). As specified in [RFC7923], MDSC must subscribe to
specific objects from PNC YANG datastores for notifications.
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4.1.1. Inter-domain link discovery
In the reference network of Figure 1, there are two types of
inter-domain links:
o Inter-domain links between two IP domains (ASes)
o Cross-layer links between an IP router and a ROADM
Both types of links are Ethernet physical links.
The inter-domain link information is reported to the MDSC by the two
adjacent PNCs, controlling the two ends of the inter-domain link.
The MDSC needs to understand how to merge these inter-domain
Ethernet links together.
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.
The MDSC can understand how to merge these inter-domain links using
the plug-id attribute defined in the TE Topology Model [RFC8795], as
described in section 4.3 of [RFC8795].
A 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].
Both types of inter-domain links are discovered using the plug-id
attributes reported in the Ethernet Topologies exposed by the two
adjacent PNCs. In addition, the MDSC can also discover an
inter-domain IP link/adjacency between the two IP LTPs, reported in
the IP Topologies exposed by the two adjacent P-PNCs, supported by
the two ETH LTPs of an Ethernet link discovered between these two
P-PNCs.
The static configuration requires an administrative burden to
configure network-wide unique identifiers: it is therefore more
viable for inter-AS links. For the cross-layer links between the IP
routers and the Optical NEs, the automatic discovery solution based
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on LLDP snooping is preferable when LLDP snooping is supported by
the Optical NEs.
As outlined in [TNBI], the encoding of the plug-id namespace and the
LLDP information within the plug-id value is implementation specific
and needs to be consistent across all the PNCs.
4.1.2. Multi-layer IP link discovery
All the intra-domain IP links are discovered by P-PNC, using LLDP
[IEEE 802.1AB] or any other mechanisms which are outside the scope
of this document, and reported at the MPI within the L3 Topology.
In case of a multi-layer IP link, the P-PNC also reports the two
inter-domain ETH LTPs that supports the two IP LTPs terminating the
multi-layer IP link.
The MDSC can therefore discover which Ethernet access link supports
the multi-layer IP link as described in section 4.1.1.
The Optical Transponders, or the OTN access cards, are reported by
the O-PNC as Trail Termination Points (TTPs), defined in [RFC8795],
within the Optical Topology. The association between the Ethernet
access link and the Optical TTP is reported using the Inter Layer
Lock (ILL) identifiers, defined in [RFC8795], within the Ethernet
Topology and Optical Topology, exposed by the O-PNC.
The MDSC can discover throught the MPI the Optical Tunnels being
setup by each O-PNC and in particular which Optical Tunnel has been
setup between the two TTPs associated with the two Ethernet access
links supporting an inter-domain IP link.
4.1.3. 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] has 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.
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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.
4.1.4. SR-TE paths 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 also outlined in section 1 of
[TE-TUNNEL].
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.
[Editors' note:] Need to check if SR-TE specific augmentation is
required for SR-TE path discovery
For example, considering the L3VPN in Figure 4, 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.
4.2. Establishment of L2VPN/L3VPN with TE requirements
In this scenario the MDSC needs to setup a multi-domain L2VPN or a
L3VPN with some SLA requirements.
Figure 4 provides an example of an hub&spoke L3VPN 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 |
------ ------
_____________________________ ___________________
( ) ( )
( ____ ____ ) ( ____ )
( / \ __ _ _ _ _ / \ ) ( / \ _ _ )
( \____/.. \____/ ) ( \____/ \ )
( | :..... ...: \ ) ( / \ )
( _|__ :__: \____ ) ( ___/ __\_ )
( / \_ _ / \ _ _ _ / \ ) ( / \ _ _ _ / \ )
( \____/ \____/ \____/ ) ( \____/ \____/ )
( ) ( )
(_____________________________) (___________________)
Optical Domain 1 Optical Domain 2
H / S = Hub VRF / Spoke VRF
____ = Inter-domain interconnections
..... = SR policy Path 1
_ _ _ = SR policy Path 2
Figure 4 Multi-domain L3VPN example
[Editors' note:] Update the SR policy paths to show the intra-domain
PE13-P16-P14 and inter-domain PE13-BR11-BR12-P24-PE23 paths. No need
to show the TI-LFA in this figure. Remove also the intra-domain TI-
LFA.
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There are many options to implement multi-domain L3VPN, including:
1. BGP-LU (seamless MPLS)
2. Inter-domain RSVP-TE
3. Inter-domain SR-TE
This version of the draft provides an analysis of the inter-domain
SR-TE option. A future update of this draft will provide a high-
level analysis of the BGP-LU option.
It is assumed that each packet domain in Figure 4 is implementing
SR-TE and the stitching between two domains is done using end-to-
end/multi-domain SR-TE. It is assumed that the bandwidth of each
intra-domain SR-TE path is managed by its respective P-PNC and that
binding SID is used for the end-to-end SR-TE path stitching. It is
assumed that each packet domain in Figure 4 is using TI-LFA, with
SRLG awareness, for local protection within each domain.
[Editor's note:] Analyze how TI-LFA can take into account multi-
layer SRLG disjointness, providing that SRLG information is provided
by the O-PNCs to the P-PNC throught the MDSC.
It is assumed that the MDSC adopts the partial summarization model,
described in section 2.2, having full visibility of the packet layer
TE topology and an abstract view of the underlay optical layer TE
topology.
The MDSC needs to translate the L3VPN SLA requirements to TE
requirements (e.g., bandwidth, TE metric bounds, SRLG disjointness,
nodes/links/domains inclusion/exclusion) and find the SR-TE paths
between PE13 (hub PE) and, respectively, PE23 and PE14 (spoke PEs)
that meet these TE requirements.
For each SR-TE path required to support the L3VPN, it is possible
that:
1. A SR-TE path that meets the TE requirements already exist in the
network.
2. An existing SR-TE path could be modified (e.g., through bandwidth
increase) to meet the TE requirements:
a. The SR-TE path characteristics can be modified only in the
packet layer.
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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:
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).
For example, considering the L3VPN in Figure 4, the MDSC discovers
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
4.1.4;
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 4.1;
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
4.2.1. 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.
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 4.2.2;
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 4.2.2;
o the P-PNC1 to update the bandwidth of the selected SR-TE path
between PE13 and PE14, as described in section 4.2.3.
For example, considering the L3VPN in Figure 4, the MDSC can also
decide that a new multi-domain SR-TE path needs to be setup between
PE13 and PE23.
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As described in section 2.2, 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 4.2.1, 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 4.2.2;
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 4.2.2.
After that, the MDSC requests P-PNC2 to setup an SR-TE path between
BR21 and PE23, with an explicit path (BR21, P24, PE23) as described
in section 4.2.3. 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
assigned binding SID.
[Editor's Note] Further investigation is needed for the SR specific
extensions to the TE tunnel model.
MDSC request P-PNC1 to setup an SR-TE path between PE13 and BR11,
with an explicit path (PE13, BR11), specifying the inter-domain link
toward BR21 and the binding SID to be used for the end-to-end SR-TE
path stitching, as described in section 4.2.3. The P-PNC1, knowing
also the node and the adjacency SIDs assigned within its domain and
the EPE SID assigned by BR11 to the inter-domain link toward BR21,
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 [L3NM]
and [TSM] YANG 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.
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4.2.1. Optical Path Computation
As described in section 2.2, the optical path computation is usually
performed by the Optical PNC.
When performing multi-layer/multi-domain path computation, the MDSC
can delegate the Optical PNCs for single-domain optical path
computation.
As discussed in [PATH-COMPUTE], there are two options to request an
Optical 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.
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.
4.2.2. Multi-layer IP link Setup and Update
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 Optical Transponders (OTs), in case
of DWDM network, or the two OTN access cards, in case of OTN
networks, associated with the two access links.
The MDSC also requires the O-PNC to steer the Ethernet client
traffic between the two access Ethernet links over the Optical
Tunnel.
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] is used between the two routers, the P- PNC
can automatically discover the IP link being set up by the MDSC. The
IP LTPs terminating this IP link are supported by the ETH LTPs
terminating the two access links.
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Otherwise, the MDSC needs to require the P-PNC to configure an IP
link between the two routers: the MDSC also configures the two ETH
LTPs which support the two IP LTPs terminating this IP link.
[Editor's Note] Add text for IP link update and clarify that the IP
link bandwidth increase can be done either by LAG or by ECMP. Both
options are valid and widely deployed and more or less the same from
POI perspective.
4.2.3. 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].
The MDSC can use the [TE-TUNNEL] model to request the P-PNC to setup
TE paths specifying the explicit path to force the P-PNC to setup
the actual path being computed by MDSC.
The [TE-TUNNEL] model supports requesting the setup of both end-
to-end as well as segment TE paths (within one domain).
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.
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.
5. Security Considerations
Several security considerations have been identified and will be
discussed in future versions of this document.
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6. 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.
7. IANA Considerations
This document requires no IANA actions.
8. References
8.1. 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.
[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.
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[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", RFC 8795, 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.
[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.
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[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.
8.2. 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.
[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.
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[RFC8751] Dhody, D. et al., "Hierarchical Stateful Path Computation
Element (PCE)", RFC 8751, March 2020.
[L2NM] S. Barguil, et al., "A Layer 2 VPN Network YANG Model",
draft-ietf-opsawg-l2nm, work in progress.
[L3NM] S. Barguil, et al., "A Layer 3 VPN Network YANG Model",
draft-ietf-opsawg-l3sm-l3nm, 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.
[UNI-TOPO] Gonzalez de Dios O., et al., "A Network YANG Model for
Service Attachment Points", draft-dbwb-opsawg-sap, work in
progress.
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Appendix A. Multi-layer and multi-domain resiliency
A.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.
A.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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