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 2023 January 11, 2023
Applicability of Abstraction and Control of Traffic Engineered
Networks (ACTN) to Packet Optical Integration (POI)
draft-ietf-teas-actn-poi-applicability-08
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 defined by the IETF to support this
deployment architecture and specific scenarios relevant to 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
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.................22
3.3. Path Computation Elment Protocol (PCEP)..................23
4. Inventory, Service and Network Topology Discovery.............24
4.1. Optical Topology Discovery...............................25
4.2. Optical Path Discovery...................................27
4.3. Packet Topology Discovery................................27
4.4. TE Path Discovery........................................28
4.5. Inter-domain Link Discovery..............................29
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4.5.1. Cross-layer Link Discovery..........................30
4.5.2. Inter-domain IP Link Discovery......................32
4.6. Multi-layer IP Link Discovery............................35
4.6.1. Single-layer Intra-domain IP Links..................37
4.7. LAG Discovery............................................39
4.8. L2/L3 VPN Network Services Discovery.....................41
4.9. Inventory Discovery......................................41
5. Establishment of L2/L3 VPN Services with TE Requirements......42
5.1. Optical Path Computation.................................44
5.2. Multi-layer IP Link Setup................................45
5.2.1. Multi-layer LAG Setup...............................47
5.2.2. Multi-layer LAG Update..............................47
5.2.3. Multi-layer SRLG Configuration......................48
5.3. TE Path Setup and Update.................................48
6. Conclusions...................................................49
7. Security Considerations.......................................50
8. Operational Considerations....................................50
9. IANA Considerations...........................................50
10. References...................................................50
10.1. Normative References....................................50
10.2. Informative References..................................52
Appendix A. OSS/Orchestration Layer...........................55
A.1. MDSC NBI................................................55
Appendix B. Multi-layer and Multi-domain Resiliency...........58
B.1. Maintenance Window......................................58
B.2. Router Port Failure.....................................58
Acknowledgments..................................................59
Contributors.....................................................59
Authors' Addresses...............................................61
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 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
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Internet Protocol (IP), and often Multiprotocol Label Switching
(MPLS) or Segment Routing (SR), 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 can be
different between a packet and an optical network, and it is not
uncommon to use other vendors in both domains. The operation of these
complex packet and optical networks is often siloed, as these
technology domains require specific skill sets.
The packet/optical network deployment and operation separation are
inefficient for many reasons. First, both capital expenditure (CAPEX)
and operational expenditure (OPEX) could be significantly reduced by
integrating the packet and the optical networks. Second, multi-layer
online topology insight can speed up troubleshooting (e.g., alarm
correlation) and network operation (e.g., coordination of maintenance
events), and multi-layer offline topology inventory can improve
service quality (e.g., detection of diversity constraint violations).
Third, 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
across layers (e.g., to achieve bandwidth-on-demand or to perform
activities during maintenance windows).
This document uses packet-based Traffic Engineered (TE) service
examples. These are described as "TE-path" in this document. Unless
otherwise stated, these TE services may be instantiated using RSVP-
TE-based or SR-TE-based, forwarding plane mechanisms.
The ACTN framework enables the complete multi-layer and multi-vendor
integration of packet and optical networks through a Multi-Domain
Service Coordinator (MDSC), and packet and optical Provisioning
Network Controllers (PNCs).
This document describes critical scenarios for POI from the packet
service layer perspective and identifies the required coordination
between packet and optical layers to improve POI deployment and
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operation. These scenarios focus on multi-domain packet networks
operated as a client of optical networks.
This document analyses the case where the packet networks support
multi-domain TE paths. The optical networks could be either a DWDM
network, an OTN network (without DWDM layer), or a multi-layer
OTN/DWDM network. Furthermore, DWDM networks could be either fixed-
grid or flexible-grid.
Multi-layer and multi-domain scenarios, based on the reference
network described in section 2 and very relevant for Service
Providers, are described in sections 4 and 5.
For each scenario, existing IETF protocols and data models,
identified in sections 3.1 and 3.2, are analysed with a 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.)
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Port:
the physical entity that transmits and receives physical signals
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.
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Intra-domain multi-layer Ethernet link:
an Ethernet link supported by two cross-layer links and an optical
tunnel in between
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
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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
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 a packet
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.
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o All the physical interfaces at inter-domain links are Ethernet
physical interfaces.
Although the new optical technologies (e.g., QSFP-DD ZR 400G) allow
the operators to provide DWDM pluggable interfaces on the routers,
the deployment of those pluggable optics is not yet widely adopted.
The reason is that most operators are not yet ready to manage packet
and optical networks in a single unified domain. Therefore, a unified
use case analysis is outside this draft's scope.
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 and provides
multi-layer/multi-domain L2/L3 VPN network services requested by an
OSS/Orchestration layer.
From an implementation perspective, the functions associated with
MDSC described in [RFC8453] may be grouped differently.
1. 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
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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 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.
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] described in
point 2 above. Therefore, the MDSC deals 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 outside this document's scope.
There are two prominent workflow cases when the MDSC multi-layer
coordination is initiated:
o Initiated by request from the OSS/Orchestration layer to setup
L2/L3 VPN network services that require multi-layer/multi-domain
coordination;
o The MDSC initiates them 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 fulfilment, these workflows are not related to a
network service provisioning request 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 and Figure 3 provide an example of a 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.
------
| CE13 | Packet Domain 1 Packet Domain 2
------ ____________________ __________________
( | ) ( )
( | PE13 P15 BR11 ) ( BR21 P24 )
( |____ ___ ____ ) ( ____ ___ )
( / \ _ _ _ / \ _ _ / \________/ \ / \ )
( \____/ \___/ \___ / \____/ \_ _/ )
( PE14 :\_ _ / ) ( / : : \__ )
( ____ : \__ P16 ___/ ) ( __/_ _\__ )
( / \ : / \- - -/ \__________/ \ :_ _ _ :_ / \ )
( \____/ \___/ \____/ ) ( \____/ \____/ )
( / : : : : BR12 ) ( : : : | )
(/ ) ( BR22 PE23| )
------ : : : : ) ( : : : | )
| CE14 | (__ ____ _________ _____) (_____ ___ _ ------
------ : : : : : : : | CE23 |
------
: : : : : : :
_ ___ ____ _________ ________ ______ ___ _______
( : : : : ) : : : )
( ____ : ____ ) ( ____ .. .. )
( : / \_ _ _ _/ \ NE12 ) ( : / \ _ : )
( NE11 \____/ : \____/ ) ( NE21 \____/ \ )
( : / \ _ _ / \ ) ( : / \ : )
( ___/ \:_| \____ ) ( .___/ _\__ )
( / \_ _ / \ _ _ _ / \ ) ( / \ _ _ _ / \ )
( \____/ \____/ \____/ ) ( \____/ \____/ )
( NE13 NE14 NE15 ) ( NE22 NE23 )
(_____________________________) (___________________)
Optical Domain 1 Optical Domain 2
_____ = Inter-domain links
.. .. = Cross-layer links
_ _ _ = Intra-domain links
Figure 2 - Multi-domain VPN topology example
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------
| CE13 | Packet Domain 1 Packet Domain 2
------ ____________________ _________________
( | ) ( )
( | PE13 P15 BR11 ) ( BR21 P24 )
( |____ ___ ____ ) ( ____ ___ )
( / H \ / \ / \________/.. \ / ..\ .. )
( \____/..... \___/ \___ / .. .. ..___:/ \___/ : )
( PE14 : : .. .. ) ( : )
( ____ : _:_ P16 ____ : ) ( ____ : __:_ )
( / S \ : / ..\ / ..__________/ \ : / S \ )
( \____/ \__:/ \____/ ) ( \____/ : \____/ )
( / : : : :BR12 ) ( : | )
(/ : : ) ( BR22 : PE23| )
------ : : : : ) ( : | )
| CE14 |:(__ _____:__________ ___) (__:______ __ ------
------ : : : : : | CE23 |
: : : ------
: : : : :
_:___________:________ ______ ___:______ _______
( : : : : ) ( : .. .. )
( : ____ : ____ ) ( :____ )
( : / .. \.. : ../ .. \ NE12 ) ( /.. \ : )
( NE11 \____/ : \____/ ) ( NE21 \__:_/ )
( : : ) ( : )
( _:__ ___: ____ ) ( ____ : .. ____ )
( / :..\..../...:\ / \ ) ( / \ /.. :\ )
( \____/ \____/ \____/ ) ( \____/ \____/ )
( NE13 NE14 NE15 ) ( NE22 NE23 )
(_____________________________) (__________________)
Optical Domain 1 Optical Domain 2
H / S = Hub VRF / Spoke VRF
..... = Intra-domain TE Path 1 {PE13, P16, NE14, NE13, PE14}
.. .. = Inter-domain TE Path 2 {PE13, NE11, NE12, BR12,
BR11, BR21, NE21, NE23, P24, PE23}
Figure 3 - Multi-domain VPN TE paths example
There are many options to implement multi-domain L2/L3 VPNs,
including:
1. BGP-LU ([RFC8277])
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2. Inter-domain RSVP-TE
3. Inter-domain SR-TE
This document analyses the inter-domain TE options for which the TE
tunnel model, defined in [TE-TUNNEL], could be used at the MPI for
intra-domain or inter-domain TE configuration. The analysis of other
options is outside the scope of this draft.
It is also assumed that:
o the bandwidth of each intra-domain TE path is managed by its
respective P-PNC;
o technology-specific mechanisms (in the case of inter-domain SR-TE,
the binding SID) are used for the inter-domain TE path stitching;
o each packet domain in Figure 2 uses technology-specific local
protection mechanisms (in the case of SR-TE, TI-LFA), with SRLG
awareness.
In the case of inter-domain TE-paths, it is also assumed that each
packet domain in Figure 2 and Figure 3 implements the same TE
technology, and the stitching between two domains is done using
inter-domain TE.
In this scenario, one of the key MDSC functions is to identify the
multi-domain/multi-layer 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 TE
paths.
The selection of the 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 to dynamically create
and bind tunnels to the service so that they are not shared by
other services (e.g. VPN).
The level of isolation can be different:
a) Hard isolation with deterministic latency means L2/L3 VPN
requires a set of dedicated TE Tunnels (neither sharing
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with other services nor competing for bandwidth with other
tunnels), providing deterministic latency performances
b) Hard isolation but without deterministic characteristics
c) Soft isolation 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 for isolation and could request a VPN
service where associated tunnels can be shared across multiple
VPNs.
For each TE path required to support the L2/L3 VPN network service,
it is possible that:
1. A TE path that meets the TE and binding requirements already
exists in the network.
2. An existing TE path could be modified (e.g., through bandwidth
increase) to meet the TE and binding requirements:
a. The 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 TE paths (multi-
layer coordination is required).
3. A new TE path needs to be setup to meet the TE and binding
requirements:
a. The new 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 TE path (multi-layer
coordination is required).
This document analyses scenarios where only one TE path is used to
carry the VPN traffic between PEs. Scenarios, where multiple parallel
TE paths are used in load-balancing to carry the VPN traffic between
PEs, are possible but their analysis is outside the scope of this
document.
2.1.2. Multi-domain and Multi-layer Path Computation
When a new TE path needs to be setup, the MDSC is also responsible
for coordinating the multi-layer/multi-domain path computation.
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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:
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.
Then, 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 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 abstract 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 complete
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. It uses
the information received by the O-PNCs and 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 a 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 different vendors provide them).
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
Each packet domain in Figure 1, 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 for setting up the TE paths between any two
PEs or BRs in their respective controlled domains, as requested by
MDSC, and providing topology information to the MDSC.
For example, for inter-domain SR-TE, the setup bidirectional SR-TE
path from PE13 in domain 1 to PE23 in domain 2, as shown in Figure 3,
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, including the Binding SID
associated with the SR-TE path in Domain 1 with PE13 as the target
destination (reverse direction).
With reference to Figure 4, P-PNCs are then responsible:
1. To expose to MDSC their respective detailed TE topology
2. To perform single-layer single-domain local TE path computation,
when requested by MDSC between two PEs (for single-domain end-to-
end TE path) or between PEs and BRs for an inter-domain TE path
selected by MDSC;
3. To configure the routers in their respective domain to setup a TE
path;
4. To configure 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.TE | 2.VPN | 1.TE | 2.VPN
| Path | Provisioning | Path | Provisioning
| Config | | Config |
V V V V
+---------------------+ +---------------------+
CE / PE TE path 1 BR\ / BR TE path 2 PE \ CE
o--/---o..................o--\-----/--o..................o---\--o
\ / \ /
\ Domain 1 / \ Domain 2 /
+---------------------+ +---------------------+
End-to-end TE path
<------------------------------------------------->
Figure 4 Domain Controller & NE Functions
When requesting the setup of a new 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 complete list of
nodes involved in the path (strict mode). In this case, the P-PNC is
just responsible to set up that explicit TE path. For example:
o with SR-TE, the P-PNC pushes to headend PE or BR the list of SIDs
to create the explicit SR-TE path, provided by the MDSC;
o with RSVP-TE, the P-PNC requests the headend PE or BR to start
signaling the explicit RSVP-TE path, provided by the MDSC.
To scale in large SR-TE packet domains, the MDSC can provide P-PNC a
loose path, together with per-domain TE constraints. The P-PNC can
then select the complete path within its domain.
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.
From the Figure 3 example, the TE path requested by the MDSC touches
PE13 - P16 - BR12 - BR21 - PE23. P-PNC2 is aware of two paths with
the same topology metric, e.g. BR21 - P24 - PE23 and BR21 - BR22 -
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PE23, but with different loads. It may prefer to steer the traffic on
the latter because it is less loaded.
For the purposes of this document it is assumed that the MDSC always
provides the explicit list of all the hops to the P-PNCs to setup or
modify the TE path.
2.3. Optical Domain Controller and NE Functions
The optical network provides 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 to 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
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Architecture (NMDA) defined in [RFC8342], are assumed to be used as
well at these MPI interfaces and also at MDSC NBI 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
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.
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];
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o Subscription to YANG Notifications for Datastores updates as
defined in [RFC8641].
PNCs and MDSCs comply 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].
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3.2.3. YANG data models at the Packet MPIs
The Packet PNC also at least the following technology-specific
topology YANG data models:
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];
[Editors note - 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 also uses at least one of the following technology-
specific topology YANG data models:
o The MPLS-TE Topology Model, defined in the "ietf-te-mpls-topology"
YANG module of [MPLS-TE-TOPO], which augments the TE Packet
Topology Model;
o the SR Topology Model, defined in the "ietf-sr-mpls-topology" YANG
module of [SR-TE-TOPO].
The Packet PNC uses at least one of the following technology-specific
tunnel YANG data models, which augments the generic TE Tunnel Model:
o The MPLS-TE Tunnel Model, defined in the "ietf-te-mpls" YANG
modules of [MPLS-TE-TUNNEL];
o the SR-TE Tunnel Model which is to be defined as described in
section 6.
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];
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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. Path Computation Elment Protocol (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 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,
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
lists the PCEP extension for the 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
perform full multi-layer path computation or delegate path
computation to the underneath PNCs.
This approach is desirable for operators from a multi-vendor
integration perspective as it is simple. We need only one type of
interface (RESTCONF) and use the relevant YANG data models
depending on the operator use case considered. The benefits of
having only one protocol for the MPI between MDSC and PNC have
already been highlighted in [PATH-COMPUTE].
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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;
o the 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 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 optical networks to the MDSC may present scalability
issues as a potential drawback. The analysis of the scalability of
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this approach and mechanisms to address potential issues is outside
the scope of this document.
Each PNC provides 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 networks it controls.
The MDSC should also maintain up-to-date inventory, service and
network topology databases of IP and optical layers through IETF
notifications through MPI with the PNCs when any network
inventory/topology/service change occurs.
It should also be possible to correlate information from IP and
optical layers (e.g., which port, lambda/OTSi, and direction are 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 correlate optical and IP layers alarms to
speed-up troubleshooting easily.
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.
To allow the MDSC to discover the complete multi-layer and multi-
domain network topology and to correlate it with the hardware
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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 reports 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),
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.
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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 signal or multi-layer intra-domain OTN links. In the
latter case, the hierarchical-link container, defined in [TE-TUNNEL],
associates the underlay DWDM tunnel with the supported multi-layer
intra-domain OTN link.
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].
The L3 Topology Model, TE Topology Model, TE Packet Topology Model
and MPLS-TE Topology Model are used together to report the MPLS-TE
network topology, as described in [MPLS-TE-TOPO].
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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 TE path
computation, the P-PNCs report the full packet network, including all
the information that the MDSC requires to perform 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 packet
topology also reports the IP LTPs terminating the inter-domain IP
links.
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.
All the intra-domain Ethernet and 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 Ethernet or the packet network topology.
4.4. TE Path Discovery
We assume that the discovery of existing TE paths, including their
bandwidth, at the MPI is done using the generic TE tunnel YANG data
model, defined in [TE-TUNNEL], with packet technology-specific (e.g.,
MPLS-TE or SR-TE) augmentations.
Note that technology-specific augmentations of the generic path TE
tunnel model for SR-TE path setup and discovery is outlined in
section 1 of [TE-TUNNEL] but are currently identified as a gap in
section 6.
To enable MDSC to discover the full end-to-end TE path configuration,
the technology-specific augmentation of the [TE-TUNNEL] should allow
the P-PNC to report the TE path within its domain (e.g., the SID list
assigned to an SR-TE path).
For example, considering the L3VPN in Figure 2, the TE path 1 in one
direction (PE13-P16-PE14) and the TE path in the reverse direction
(between PE14 and PE13) should be reported by the P-PNC1 to the MDSC
as TE primary and primary-reverse paths of the same TE tunnel
instance. The bandwidth of these TE paths represents the bandwidth
allocated by P-PNC1 to the two TE paths, which can be symmetric or
asymmetric in the two directions.
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The P-PNCs use the TE tunnel model to report, at the MPI, all the TE
paths established within their packet domain regardless of the
mechanism being used to set them up; i.e., independently on whether
the mechanisms described in section 5.3 or other means, such as
static configuration, which are outside the scope of this document,
are used.
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.
There are two possible models to report the access links between CEs
and PEs: the Ethernet Topology Model, defined in [CLIENT-TOPO], or
the Service Attachment Points (SAP) Model, defined in [SAP].
Clarifying the relationship between these two models has been
identified as a gap.
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. The Ethernet Topology Model supports
the discovery for all these types of links with no need for the P-PNC
to know the type of inter-domain link.
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].
The plug-id attribute can also be used to discover the access-links,
but the analysis of the access-link discovery is outside the scope of
this document.
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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 5.
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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 5 - 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 optical NEs.
Therefore the MDSC can discover these links also before optical
paths, supporting 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 6.
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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){3} | /
/ +-------------+ / / +-------------+ /
/ Eth. Topology (P-PNC 1) / / Eth. Topology (P-PNC 2) /
+-------------------------+ +-------------------------+
Notes:
=====
(*) Supporting LTP
{1} {BR11,3,BR21,4}
{2} {BR11,3}
{3} {BR21,4}
Legenda:
========
O LTP
----> Supporting LTP
<...> Link discovered by the MDSC
<~~~> Link inferred by the MDSC
{ } LTP Plug-id reported by the PNC
Figure 6 - Inter-domain Ethernet and IP link discovery
Different information is required to be encoded by the P-PNC 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 6:
o The physical Ethernet LTP (e.g., LTP 3-0 in BR11, as shown in
Figure 6) 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, as described in section 4.5.1, the P-PNC reports,
within the plug-id attribute of this LTP, the LLDP information
sent by the corresponding router Ethernet interface; such as the
{BR11,3} and {BR21,4} plug-id values reported, respectively, by
the Ethernet LTP 3-0 on BR11 and by the Ethernet LTP 4-0 on BR21,
as shown in Figure 6;
o The logical Ethernet LTP (e.g., LTP 3-1 in BR11, as shown in
Figure 6), supported by a physical Ethernet LTP (e.g., LTP 3-0 in
BR11, as shown in Figure 6), is used to discover the logical
adjacency between router Ethernet interfaces, which can be either
single-layer or multi-layer. Therefore, the P-PNC reports, within
the plug-id attribute of this LTP, the LLDP information sent and
received by the corresponding router Ethernet interface; such as
the {BR11,3,BR21,4} plug-id values reported by the Ethernet LTP 3-
1 on BR11 and by the Ethernet LTP 4-1 on BR21, as shown in Figure
6.
It is worth noting that in case of an inter-domain single-layer
Ethernet links, the MDSC cannot discover, using the the LLDP
information reported in the plug-id attributes, the physical
adjacency between the two router Ethernet interfaces because these
two plug-id values do not match, such as the plug-id values {BR11,3}
and {BR21,4} shown in Figure 6. However, the MDSC may infer the
physical intra-domain Etherent links if it knows a priori, using
mechanisms which are outside the scope of this document, that the
Ethernet interfaces on the routers either terminates a cross-layer
link or a single-layer (intra-domain or inter-domain) Ethernet link,
e.g., as shown in Figure 6.
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.
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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 6.
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
intra-domain IP and Ethernet links, as described in section 4.3, and
reported at the MPI within the packet and the Ethernet network
topologies, e.g., as shown in Figure 7.
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+-----------------------------------------------------------+
/ IP Topology (P-PNC 1) /
/ +---------+ +---------+ /
/ | PE13 | | BR11 | /
/ | (5-2)O<======================>O(6-2) | /
/ | | | | | /
/ +---------+ | +---------+ /
/ | /
+-----------------------------------|-----------------------+
|
| Supporting Link
|
+---------------------------|-------------------------------+
/ Ethernet Topology (P-PNC 1)| /
/ +-------------+ | +-------------+ /
/ | 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
x---x Ethernet client signal
X===X Optical tunnel
Figure 7 - Multi-layer intra-domain Ethernet and IP link discovery
The P-PNC does not report any plug-id information on the logical
Ethernet LTPs terminating intra-domain Ethernet links, such as the
LTP 5-1 on PE13 and LTP 6-1 in BR11 shown in Figure 7, 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 7.
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., the link between LTP 5-0 on PE13 and LTP 7-0 on
NE11, shown in Figure 7.
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 7.
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 8.
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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 8 - Single-layer intra-domain Ethernet and IP link discovery
It is worth noting that in case of an intra-domain single-layer
Ethernet links, the MDSC cannot discover, using the LLDP information
reported in the plug-id attributes, the physical adjacency between
the two router Ethernet interfaces because the two plug-id values do
not match, such as the plug-id values {PE13,1} and {P16,2} shown in
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Figure 8. However, the MDSC may infer the physical intra-domain
Ethernet links, e.g., between LTP 1-0 on PE13 and LTP 2-0 on P16, as
shown in Figure 8, if it knows a priori, using 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 or inter-domain) Ethernet link, e.g., as shown in
Figure 8.
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
The P-PNCs can discover the configuration of the LAG groups within
its domain and report each intra-domain LAG as an Ethernet bundle
link, within the Ethernet topology exposed at the MPI.
This is done bundling multiple single-domain Ethernet links, as shown
in Figure 9. For example, the Ethernet bundled link between the
Ethernet LTP 5-1 on BR21 and the Ethernet LTP 6-1 on P24, is built
from the Ethernet links setup respectively:
o between the Ethernet LTP 1-1 on BR21 and the Ethernet LTP 2-1 on
P24; and
o between the Ethernet LTP 3-1 on BR21 and the Ethernet LTP 4-1 on
P24.
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+-----------------------------------------------------------+
/ IP Topology (P-PNC 2) /
/ +---------+ +---------+ /
/ | BR21 | | P24 | /
/ | (5-2)O<======================>O(6-2) | /
/ | | | | | /
/ +---------+ | +---------+ /
/ | /
+---------------------------------|-------------------------+
|
| Supporting Link
|
|
+-----------------------|---------------------------------+
/ | /
/ +---------+ v +---------+ /
/ | (5-1)O<======================>O(6-1) | /
/ | BR21 | Bundled Link | P24 | /
/ | | | | /
/ | (3-1)O<======================>O(4-1) | /
/ | (1-1)O<======================>O(2-1) | /
/ +---------+ +---------+ /
/ Ethernet Topology (P-PNC 2) /
+---------------------------------------------------------+
Legenda:
========
O LTP
<===> Link discovered by the PNC and reported at the MPI
Figure 9 - LAG
The mechanisms used by the MDSC to discover single-layer and multi-
layer intra-domain LAG link is the same (the only difference being
whether the bundled links are single-layer or multi-layer).
Instead, the mechanisms used by the MDSC to discover single-layer
inter-domain LAG links between two BRs are different and outside the
scope of this document since they do not imply any cross-layer
coordination between packet and optical domains.
As described in section 4.3, the mechanisms used by the P-PNC to
discover the configuration of the LAG groups within its domain, such
as LLDP [IEEE 802.1AB], are outside the scope of this document.
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However, it is worth noting that according to [IEEE 802.1AB], LLDP
can be configured on a LAG group (Aggregated Port) and/or on any
number of its LAG members (Aggregation Ports).
If LLDP is enabled on both LAG members and groups, two types of LLDP
packets are transmitted by the routers and received by the optical
NEs on some cross-layer links: one sent for the LLDP session
configured at LAG member (Aggregation Port)level and another one for
the LLDP session configured at LAG group (Aggregated Port)level. This
could cause some issues when LLDP snooping is used to discover the
cross-layer links, as defined in section 4.5.1.
The cross-layer link discovery is based only on the LLDP session
configured on the LAG members (Aggregation Ports) to allow discovery
of these links independently from the configuration of the underlay
optical tunnel or from the LAG group.
To avoid any ambiguity on how the optical NEs can identify which LLDP
packets belong to which LLDP session, the P-PNC can disable the LLDP
sessions on the LAG groups configured by the MDSC (e.g., the multi-
layer single-domain LAG groups configured using the mechanisms
described in section 5.2.1), keeping the LLDP sessions on the LAG
members enabled.
Another option is to rely on other mechanisms (e.g., the Port type
field in the Link Aggregation TLV defined in Annex F of [IEEE
802.1AX]) that allow the optical NE to identify which LLDP packets
belong to which LLDP session: the O-PNC can then use only the LLDP
information from the LLDP sessions configured on the LAG members to
support the cross-layer link discovery mechanisms defined in section
4.5.1.
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),
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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 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 TE paths that
meet these TE requirements (see section 2.1.1).
For example, considering the L3VPN in Figure 2 and Figure 3, the MDSC
finds that:
o PE13-P16-PE14 TE path already exists but have not enough bandwidth
to support the new L3VPN, as described in section 4.4;, and that:
o the IP link(s) between PE13 and P16 has not enough bandwidth
to support increasing the bandwidth of that TE path, as
described in section 4.3;
o a new underlay optical tunnel could be setup to increase the
bandwidth of the IP link(s) between PE13 and P16 to support
increasing the bandwidth of that overlay TE path, as described
in section 5.1. The dimensioning of the underlay optical
tunnel is decided by the MDSC based on the TE requirements
(e.g., the bandwidth) requested by the TE path and on its
multi-layer optimization policy, which is an internal MDSC
implementation issue;
o a new multi-domain TE path needs to be setup between PE13 and
PE23, e.g., either because existing 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 TE path between
PE13 and PE23.
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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.
The MDSC would therefore request:
o the O-PNC1 to setup a new optical tunnel between the ROADMs
connected to PE13 and P16, 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
PE13 and P16, as described in section 5.2;
o the P-PNC1 to update the bandwidth of the selected TE path between
PE13 and PE14, as described in section 5.3.
After that, the MDSC requests P-PNC2 to setup a TE path between BR21
and PE23, with an explicit path (BR21, P24, PE23) to constrainthis
new TE path to use the new underlay optical tunnel setup between BR21
and P24, as described in section 5.3. The P-PNC2 properly configures
the routers within its domain to setup the requested path and returns
to the MDSC the information which is needed for multi-domain TE path
stitching. For example, in case of inter-domain SR-TE, 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.
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Then the MDSC requests P-PNC1 to setup a TE path between PE13 and
BR11, with an explicit path (PE13, BR11) to constrain this new 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 information to be used for the multi-domain
TE path stitching, as described in section 4.4 (e.g., in case of
inter-domain SR-TE, the binding SID that has been assigned by P-PNC2
to the corresponding SR policy in BR21). The P-PNC1 properly
configures the routers within its domain to setup the requested path
and the multi-domain TE path stitching. For example, in case of
inter-domain SR-TE, 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 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 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.
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
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to infer the properties of the multi-layer single-domain IP link
between the router ports associated with the two optical TTPs.
There 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.
For example, with a reference to Figure 7, the MDSC can request the
O-PNC1 to setup an optical tunnel between the TTPs within NE11 and
NE14 to steer over this tunnel the Ethernet traffic between LTP (7-0)
on NE11 and LTP (8-0) on NE14.
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, as described in section 4.6.
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., the LTP 5-1 on PE13 and
6-1 on BR11 shown in Figure 7.
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After the multi-layer single-domain Ethernet link has been configured
by the MDSC or discovered by the P-PNC, the corresponding multi-layer
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.
It is worth noting that if LAG is not supported within the domain
controlled by the P-PNC, the P-PNC can configure the multi-layer
single-domain IP link as soon as the underlay multi-layer single-
domain Ethernet link is either discovered by the P-PNC or configured
by the MDSC at the MPI. However, if LAG is supported the P-PNC has
not enough information to know whether the discovered/configured
multi-layer single-domain Ethernet link would be:
1. Used to support a multi-layer single-domain IP link;
2. Used to create a new LAG group;
3. Added to an existing LAG group.
Therefore the P-PNC does not take any further action after a multi-
layer single-domain Ethernet link is discovered or configured by the
MDSC at the MPI.
The MDSC can request the P-PNC to configure a new multi-layer single-
domain IP link, supported by the the just discovered or configured
multi-layer single-domain Ethernet link, by creating an IP link
within the running datastore of the P-PNC MPI. Only the IP link, IP
LTPs and the reference to the supporting multi-layer single-domain
Ethernt link are configured by the MDSC. All the other configuration
is provided by the P-PNC.
For example, with a reference to Figure 7, the MDSC can request the
P-PNC1 to setup a multi-layer single-domain IP Link between IP LTP 5-
2 on PE13 and IP LTP 6-2 on BR11 supported by the multi-layer single-
domain Ethernet link between ETH LTP 5-1 on PE13 and ETH LTP 6-1 on
BR11.
The P-PNC configures the requested multi-layer single-domain IP link
and, once finished, reports it to the MDSC within the IP topology
exposed at its MPI.
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5.2.1. Multi-layer LAG Setup
The P-PNC configures a new LAG group between two routers when the
MDSC creates at the MPI a new Ethernet bundled link (using the
bundled-link container defined in [RFC8795]) bundling the multi-layer
single-domain Ethernet link(s) being created, as described above.
It is worth noting that a new LAG group can be created to bundle one
or more multi-layer single-domain Ethernet link(s).
For example, with a reference to Figure 9, the MDSC can request the
P-PNC2 to setup an Ethernet bundled link between the Ethernet LTP 5-1
on BR21 and the Ethernet LTP 6-1 on P24, bundling the multi-layer
single-domain Ethernet link between the Etherent LTP 1-1 on BR21 and
the Ethernet LTP 2-1 on P24.
It is worth noting that the MDSC needs to create also the Ethernet
LTPs terminating the Ethernet bundled link.
The MDSC can request the P-PNC to configure a new multi-layer single-
domain IP link, supported by the the just configured Ethernet bundled
link, following the same procedure described in section 5.2 above.
For example, with a reference to Figure 9, the MDSC can request the
P-PNC2 to setup a multi-layer single-domain IP Link between IP LTP 5-
2 on BR21 and IP LTP 6-2 on P24 supported by the Ethernet bundle link
between ETH LTP 5-1 on BR21 and the Ethernet LTP 6-1 on P24.
5.2.2. Multi-layer LAG Update
The P-PNC adds new member(s) to an existing LAG group when the MDSC
updates at the MPI the configuration of an existing Ethernet bundled
link adding the multi-layer single-domain Ethernet link(s) being
created, as described above.
For example, with a reference to Figure 9, the MDSC can request the
P-PNC2 to add the multi-layer single-domain Ethernet link setup
between the Etherent LTP 3-1 on BR21 and the Ethernet LTP 4-1 on P24
to the existing Ethernet bundle link setup between the Ethernet LTP
5-1 on node BR21 and the Ethernet LTP 6-1 on node P24.
After the LAG configuration has been updated, the P-PNC can also
update the bandwidth information of the multi-layer single-domain IP
link supported by the updated Ethernet bundled link.
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5.2.3. Multi-layer SRLG Configuration
[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. TE Path Setup and Update
This version of the draft assumes that TE path setup and update at
the MPI could be done using the generic TE tunnel YANG data model,
defined in [TE-TUNNEL], with packet technology-specific
agumentations, described in section 3.2.3.
When a new TE path needs to be setup, the MDSC can use the [TE-
TUNNEL] model to request the P-PNC to set it up, properly specifying
the path constraints, such as the explicit path, to force the P-PNC
to setup an TE path that meets the end-to-end TE and binding
constraints and uses the optical tunnels setup by the MDSC for the
purpose of supporting this new TE path.
The [TE-TUNNEL] model supports requesting the setup of both end-
to-end as well as segment TE tunnels (within one domain).
In the latter case, the technology-specific augmentations should
allow the configuration of the information needed for multi-domain TE
path stiching.
For example, the 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 multi-domain SR-TE path stitching and to
allow the P-PNC to report the binding SID assigned to the segment TE
paths. Note that 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.
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[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 local protection
mechanisms. For example, in case of SR-TE domain, the 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 requested local protection mechanisms within the P-PNC domain are
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 protection configuration (e.g., in case of SR-TE domains, 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:
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;
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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.
Although not analysed in this document, it has been noted that the TE
Tunnel model, defined in [TE-TUNNEL], needs also to be enhanced to
support scenarios where multiple parallel TE paths are used in load-
balancing to carry the traffic between two end-points (e.g., VPN
traffic between two PEs).
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.
[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.
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[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.
[IEEE 802.1AX] IEEE 802.1AB-2014, "IEEE Standard for Local and
metropolitan area networks - Link Aggregation", December
2014.
[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.
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[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.
[MPLS-TE-TOPO] Busi, I. et al., "A YANG Data Model for MPLS-TE
Topology", draft-busizheng-teas-yang-te-mpls-topology, 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.
[MPLS-TE-TUNNEL] Saad, T. et al., "A YANG Data Model for MPLS
Traffic Engineering Tunnels", draft-ietf-teas-yang-te-mpls,
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.
[RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address
Prefixes", RFC 8277, October 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.
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[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.
[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 10 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 10 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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Oscar Gonzalez de Dios
Telefonica
Email: oscar.gonzalezdedios@telefonica.com
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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