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Keywords: SDN, Orchestration
Internet Engineering Task Force (IETF) D. Ceccarelli, Ed.
Request for Comments: 8453 Ericsson
Category: Informational Y. Lee, Ed.
ISSN: 2070-1721 Huawei
August 2018
Framework for Abstraction and Control of TE Networks (ACTN)
Abstract
Traffic Engineered (TE) networks have a variety of mechanisms to
facilitate the separation of the data plane and control plane. They
also have a range of management and provisioning protocols to
configure and activate network resources. These mechanisms represent
key technologies for enabling flexible and dynamic networking. The
term "Traffic Engineered network" refers to a network that uses any
connection-oriented technology under the control of a distributed or
centralized control plane to support dynamic provisioning of end-to-
end connectivity.
Abstraction of network resources is a technique that can be applied
to a single network domain or across multiple domains to create a
single virtualized network that is under the control of a network
operator or the customer of the operator that actually owns the
network resources.
This document provides a framework for Abstraction and Control of TE
Networks (ACTN) to support virtual network services and connectivity
services.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8453.
Ceccarelli & Lee Informational [Page 1]
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. VNS Model of ACTN . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Customers . . . . . . . . . . . . . . . . . . . . . . 9
2.2.2. Service Providers . . . . . . . . . . . . . . . . . . 9
2.2.3. Network Operators . . . . . . . . . . . . . . . . . . 10
3. ACTN Base Architecture . . . . . . . . . . . . . . . . . . . 10
3.1. Customer Network Controller . . . . . . . . . . . . . . . 12
3.2. Multi-Domain Service Coordinator . . . . . . . . . . . . 13
3.3. Provisioning Network Controller . . . . . . . . . . . . . 13
3.4. ACTN Interfaces . . . . . . . . . . . . . . . . . . . . . 14
4. Advanced ACTN Architectures . . . . . . . . . . . . . . . . . 15
4.1. MDSC Hierarchy . . . . . . . . . . . . . . . . . . . . . 15
4.2. Functional Split of MDSC Functions in Orchestrators . . . 16
5. Topology Abstraction Methods . . . . . . . . . . . . . . . . 18
5.1. Abstraction Factors . . . . . . . . . . . . . . . . . . . 18
5.2. Abstraction Types . . . . . . . . . . . . . . . . . . . . 19
5.2.1. Native/White Topology . . . . . . . . . . . . . . . . 19
5.2.2. Black Topology . . . . . . . . . . . . . . . . . . . 19
5.2.3. Grey Topology . . . . . . . . . . . . . . . . . . . . 20
5.3. Methods of Building Grey Topologies . . . . . . . . . . . 21
5.3.1. Automatic Generation of Abstract Topology by
Configuration . . . . . . . . . . . . . . . . . . . . 22
5.3.2. On-Demand Generation of Supplementary Topology via
Path Compute Request/Reply . . . . . . . . . . . . . 22
5.4. Hierarchical Topology Abstraction Example . . . . . . . . 23
5.5. VN Recursion with Network Layers . . . . . . . . . . . . 25
6. Access Points and Virtual Network Access Points . . . . . . . 28
6.1. Dual-Homing Scenario . . . . . . . . . . . . . . . . . . 30
Ceccarelli & Lee Informational [Page 2]
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7. Advanced ACTN Application: Multi-Destination Service . . . . . 31
7.1. Preplanned Endpoint Migration . . . . . . . . . . . . . . 32
7.2. On-the-Fly Endpoint Migration . . . . . . . . . . . . . . 33
8. Manageability Considerations . . . . . . . . . . . . . . . . 33
8.1. Policy . . . . . . . . . . . . . . . . . . . . . . . . . 34
8.2. Policy Applied to the Customer Network Controller . . . . 34
8.3. Policy Applied to the Multi-Domain Service Coordinator . 35
8.4. Policy Applied to the Provisioning Network Controller . . 35
9. Security Considerations . . . . . . . . . . . . . . . . . . . 36
9.1. CNC-MDSC Interface (CMI) . . . . . . . . . . . . . . . . 37
9.2. MDSC-PNC Interface (MPI) . . . . . . . . . . . . . . . . 37
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
11. Informative References . . . . . . . . . . . . . . . . . . . 38
Appendix A. Example of MDSC and PNC Functions Integrated in a
Service/Network Orchestrator . . . . . . . . . . . . 40
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction
The term "Traffic Engineered network" refers to a network that uses
any connection-oriented technology under the control of a distributed
or centralized control plane to support dynamic provisioning of end-
to-end connectivity. TE networks have a variety of mechanisms to
facilitate the separation of data planes and control planes including
distributed signaling for path setup and protection, centralized path
computation for planning and traffic engineering, and a range of
management and provisioning protocols to configure and activate
network resources. These mechanisms represent key technologies for
enabling flexible and dynamic networking. Some examples of networks
that are in scope of this definition are optical, MPLS Transport
Profile (MPLS-TP) [RFC5654], and MPLS-TE networks [RFC2702].
One of the main drivers for Software-Defined Networking (SDN)
[RFC7149] is a decoupling of the network control plane from the data
plane. This separation has been achieved for TE networks with the
development of MPLS/GMPLS [RFC3945] and the Path Computation Element
(PCE) [RFC4655]. One of the advantages of SDN is its logically
centralized control regime that allows a global view of the
underlying networks. Centralized control in SDN helps improve
network resource utilization compared with distributed network
control. For TE-based networks, a PCE may serve as a logically
centralized path computation function.
This document describes a set of management and control functions
used to operate one or more TE networks to construct virtual networks
that can be presented to customers and that are built from
abstractions of the underlying TE networks. For example, a link in
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the customer's network is constructed from a path or collection of
paths in the underlying networks. We call this set of functions
"Abstraction and Control of TE Networks" or "ACTN".
2. Overview
Three key aspects that need to be solved by SDN are:
o Separation of service requests from service delivery so that the
configuration and operation of a network is transparent from the
point of view of the customer but it remains responsive to the
customer's services and business needs.
o Network abstraction: As described in [RFC7926], abstraction is the
process of applying policy to a set of information about a TE
network to produce selective information that represents the
potential ability to connect across the network. The process of
abstraction presents the connectivity graph in a way that is
independent of the underlying network technologies, capabilities,
and topology so that the graph can be used to plan and deliver
network services in a uniform way
o Coordination of resources across multiple independent networks and
multiple technology layers to provide end-to-end services
regardless of whether or not the networks use SDN.
As networks evolve, the need to provide support for distinct
services, separated service orchestration, and resource abstraction
have emerged as key requirements for operators. In order to support
multiple customers each with its own view of and control of the
server network, a network operator needs to partition (or "slice") or
manage sharing of the network resources. Network slices can be
assigned to each customer for guaranteed usage, which is a step
further than shared use of common network resources.
Furthermore, each network represented to a customer can be built from
virtualization of the underlying networks so that, for example, a
link in the customer's network is constructed from a path or
collection of paths in the underlying network.
ACTN can facilitate virtual network operation via the creation of a
single virtualized network or a seamless service. This supports
operators in viewing and controlling different domains (at any
dimension: applied technology, administrative zones, or vendor-
specific technology islands) and presenting virtualized networks to
their customers.
Ceccarelli & Lee Informational [Page 4]
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The ACTN framework described in this document facilitates:
o Abstraction of the underlying network resources to higher-layer
applications and customers [RFC7926].
o Virtualization of particular underlying resources, whose selection
criterion is the allocation of those resources to a particular
customer, application, or service [ONF-ARCH].
o TE Network slicing of infrastructure to meet specific customers'
service requirements.
o Creation of an abstract environment allowing operators to view and
control multi-domain networks as a single abstract network.
o The presentation to customers of networks as a virtual network via
open and programmable interfaces.
2.1. Terminology
The following terms are used in this document. Some of them are
newly defined, some others reference existing definitions:
Domain: A domain as defined by [RFC4655] is "any collection of
network elements within a common sphere of address management or
path computation responsibility". Specifically, within this
document we mean a part of an operator's network that is under
common management (i.e., under shared operational management using
the same instances of a tool and the same policies). Network
elements will often be grouped into domains based on technology
types, vendor profiles, and geographic proximity.
Abstraction: This process is defined in [RFC7926].
TE Network Slicing: In the context of ACTN, a TE network slice is a
collection of resources that is used to establish a logically
dedicated virtual network over one or more TE networks. TE
network slicing allows a network operator to provide dedicated
virtual networks for applications/customers over a common network
infrastructure. The logically dedicated resources are a part of
the larger common network infrastructures that are shared among
various TE network slice instances, which are the end-to-end
realization of TE network slicing, consisting of the combination
of physically or logically dedicated resources.
Ceccarelli & Lee Informational [Page 5]
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Node: A node is a vertex on the graph representation of a TE
topology. In a physical network topology, a node corresponds to a
physical network element (NE) such as a router. In an abstract
network topology, a node (sometimes called an "abstract node") is
a representation as a single vertex of one or more physical NEs
and their connecting physical connections. The concept of a node
represents the ability to connect from any access to the node (a
link end) to any other access to that node, although "limited
cross-connect capabilities" may also be defined to restrict this
functionality. Network abstraction may be applied recursively, so
a node in one topology may be created by applying abstraction to
the nodes in the underlying topology.
Link: A link is an edge on the graph representation of a TE
topology. Two nodes connected by a link are said to be "adjacent"
in the TE topology. In a physical network topology, a link
corresponds to a physical connection. In an abstract network
topology, a link (sometimes called an "abstract link") is a
representation of the potential to connect a pair of points with
certain TE parameters (see [RFC7926] for details). Network
abstraction may be applied recursively, so a link in one topology
may be created by applying abstraction to the links in the
underlying topology.
Abstract Topology: The topology of abstract nodes and abstract links
presented through the process of abstraction by a lower-layer
network for use by a higher-layer network.
Virtual Network (VN): A VN is a network provided by a service
provider to a customer for the customer to use in any way it wants
as though it was a physical network. There are two views of a VN
as follows:
o The VN can be abstracted as a set of edge-to-edge links (a Type
1 VN). Each link is referred as a "VN member" and is formed as
an end-to-end tunnel across the underlying networks. Such
tunnels may be constructed by recursive slicing or abstraction
of paths in the underlying networks and can encompass edge
points of the customer's network, access links, intra-domain
paths, and inter-domain links.
o The VN can also be abstracted as a topology of virtual nodes
and virtual links (a Type 2 VN). The operator needs to map the
VN to actual resource assignment, which is known as "virtual
network embedding". The nodes in this case include physical
endpoints, border nodes, and internal nodes as well as
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abstracted nodes. Similarly, the links include physical access
links, inter-domain links, and intra-domain links as well as
abstract links.
Clearly, a Type 1 VN is a special case of a Type 2 VN.
Access link: A link between a customer node and an operator node.
Inter-domain link: A link between domains under distinct management
administration.
Access Point (AP): An AP is a logical identifier shared between the
customer and the operator used to identify an access link. The AP
is used by the customer when requesting a Virtual Network Service
(VNS). Note that the term "TE Link Termination Point" defined in
[TE-TOPO] describes the endpoints of links, while an AP is a
common identifier for the link itself.
VN Access Point (VNAP): A VNAP is the binding between an AP and a
given VN.
Server Network: As defined in [RFC7926], a server network is a
network that provides connectivity for another network (the Client
Network) in a client-server relationship.
2.2. VNS Model of ACTN
A Virtual Network Service (VNS) is the service agreement between a
customer and operator to provide a VN. When a VN is a simple
connectivity between two points, the difference between VNS and
connectivity service becomes blurred. There are three types of VNSs
defined in this document.
o Type 1 VNS refers to a VNS in which the customer is allowed to
create and operate a Type 1 VN.
o Type 2a and 2b VNS refer to VNSs in which the customer is allowed
to create and operates a Type 2 VN. With a Type 2a VNS, the VN is
statically created at service configuration time, and the customer
is not allowed to change the topology (e.g., by adding or deleting
abstract nodes and links). A Type 2b VNS is the same as a Type 2a
VNS except that the customer is allowed to make dynamic changes to
the initial topology created at service configuration time.
Ceccarelli & Lee Informational [Page 7]
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VN Operations are functions that a customer can exercise on a VN
depending on the agreement between the customer and the operator.
o VN Creation allows a customer to request the instantiation of a
VN. This could be through offline preconfiguration or through
dynamic requests specifying attributes to a Service Level
Agreement (SLA) to satisfy the customer's objectives.
o Dynamic Operations allow a customer to modify or delete the VN.
The customer can further act upon the virtual network to
create/modify/delete virtual links and nodes. These changes will
result in subsequent tunnel management in the operator's networks.
There are three key entities in the ACTN VNS model:
o Customers
o Service Providers
o Network Operators
These entities are related in a three tier model as shown in
Figure 1.
+----------------------+
| Customer |
+----------------------+
|
VNS || | /\ VNS
Request || | || Reply
\/ | ||
+----------------------+
| Service Provider |
+----------------------+
/ | \
/ | \
/ | \
/ | \
+------------------+ +------------------+ +------------------+
|Network Operator 1| |Network Operator 2| |Network Operator 3|
+------------------+ +------------------+ +------------------+
Figure 1: The Three-Tier Model
The commercial roles of these entities are described in the following
sections.
Ceccarelli & Lee Informational [Page 8]
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2.2.1. Customers
Basic customers include fixed residential users, mobile users, and
small enterprises. Each requires a small amount of resources and is
characterized by steady requests (relatively time invariant). Basic
customers do not modify their services themselves: if a service
change is needed, it is performed by the provider as a proxy.
Advanced customers include enterprises and governments. Such
customers ask for both point-to point and multipoint connectivity
with high resource demands varying significantly in time. This is
one of the reasons why a bundled service offering is not enough, and
it is desirable to provide each advanced customer with a customized
VNS. Advanced customers may also have the ability to modify their
service parameters within the scope of their virtualized
environments. The primary focus of ACTN is Advanced Customers.
As customers are geographically spread over multiple network operator
domains, they have to interface to multiple operators and may have to
support multiple virtual network services with different underlying
objectives set by the network operators. To enable these customers
to support flexible and dynamic applications, they need to control
their allocated virtual network resources in a dynamic fashion; that
means that they need a view of the topology that spans all of the
network operators. Customers of a given service provider can, in
turn, offer a service to other customers in a recursive way.
2.2.2. Service Providers
In the scope of ACTN, service providers deliver VNSs to their
customers. Service providers may or may not own physical network
resources (i.e., may or may not be network operators as described in
Section 2.2.3). When a service provider is the same as the network
operator, the case is similar to existing VPN models applied to a
single operator (although it may be hard to use this approach when
the customer spans multiple independent network operator domains).
When network operators supply only infrastructure, while distinct
service providers interface with the customers, the service providers
are themselves customers of the network infrastructure operators.
One service provider may need to keep multiple independent network
operators because its end users span geographically across multiple
network operator domains. In some cases, a service provider is also
a network operator when it owns network infrastructure on which
service is provided.
Ceccarelli & Lee Informational [Page 9]
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2.2.3. Network Operators
Network operators are the infrastructure operators that provision the
network resources and provide network resources to their customers.
The layered model described in this architecture separates the
concerns of network operators and customers, with service providers
acting as aggregators of customer requests.
3. ACTN Base Architecture
This section provides a high-level model of ACTN, showing the
interfaces and the flow of control between components.
The ACTN architecture is based on a three-tier reference model and
allows for hierarchy and recursion. The main functionalities within
an ACTN system are:
o Multi-domain coordination: This function oversees the specific
aspects of different domains and builds a single abstracted end-
to-end network topology in order to coordinate end-to-end path
computation and path/service provisioning. Domain sequence path
calculation/determination is also a part of this function.
o Abstraction: This function provides an abstracted view of the
underlying network resources for use by the customer -- a customer
may be the client or a higher-level controller entity. This
function includes network path computation based on customer-
service-connectivity request constraints, path computation based
on the global network-wide abstracted topology, and the creation
of an abstracted view of network resources allocated to each
customer. These operations depend on customer-specific network
objective functions and customer traffic profiles.
o Customer mapping/translation: This function is to map customer
requests/commands into network provisioning requests that can be
sent from the Multi-Domain Service Coordinator (MDSC) to the
Provisioning Network Controller (PNC) according to business
policies provisioned statically or dynamically at the Operations
Support System (OSS) / Network Management System (NMS).
Specifically, it provides mapping and translation of a customer's
service request into a set of parameters that are specific to a
network type and technology such that network configuration
process is made possible.
o Virtual service coordination: This function translates information
that is customer service related into virtual network service
operations in order to seamlessly operate virtual networks while
meeting a customer's service requirements. In the context of
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ACTN, service/virtual service coordination includes a number of
service orchestration functions such as multi-destination load-
balancing and guarantees of service quality. It also includes
notifications for service fault and performance degradation and so
forth.
The base ACTN architecture defines three controller types and the
corresponding interfaces between these controllers. The following
types of controller are shown in Figure 2:
o CNC - Customer Network Controller
o MDSC - Multi-Domain Service Coordinator
o PNC - Provisioning Network Controller
Figure 2 also shows the following interfaces
o CMI - CNC-MDSC Interface
o MPI - MDSC-PNC Interface
o SBI - Southbound Interface
Ceccarelli & Lee Informational [Page 11]
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+---------+ +---------+ +---------+
| CNC | | CNC | | CNC |
+---------+ +---------+ +---------+
\ | /
\ | /
Boundary ========\==================|=====================/=======
between \ | /
Customer & ----------- | CMI --------------
Network Operator \ | /
+---------------+
| MDSC |
+---------------+
/ | \
------------ | MPI -------------
/ | \
+-------+ +-------+ +-------+
| PNC | | PNC | | PNC |
+-------+ +-------+ +-------+
| SBI / | / \
| / | SBI SBI / \
--------- ----- | / \
( ) ( ) | / \
- Control - ( Phys. ) | / -----
( Plane ) ( Net ) | / ( )
( Physical ) ----- | / ( Phys. )
( Network ) ----- ----- ( Net )
- - ( ) ( ) -----
( ) ( Phys. ) ( Phys. )
--------- ( Net ) ( Net )
----- -----
Figure 2: ACTN Base Architecture
Note that this is a functional architecture: an implementation and
deployment might collocate one or more of the functional components.
Figure 2 shows a case where the service provider is also a network
operator.
3.1. Customer Network Controller
A Customer Network Controller (CNC) is responsible for communicating
a customer's VNS requirements to the network operator over the CNC-
MDSC Interface (CMI). It has knowledge of the endpoints associated
with the VNS (expressed as APs), the service policy, and other QoS
information related to the service.
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As the CNC directly interfaces with the applications, it understands
multiple application requirements and their service needs. The
capability of a CNC beyond its CMI role is outside the scope of ACTN
and may be implemented in different ways. For example, the CNC may,
in fact, be a controller or part of a controller in the customer's
domain, or the CNC functionality could also be implemented as part of
a service provider's portal.
3.2. Multi-Domain Service Coordinator
A Multi-Domain Service Coordinator (MDSC) is a functional block that
implements all of the ACTN functions listed in Section 3 and
described further in Section 4.2. Two functions of the MDSC, namely,
multi-domain coordination and virtualization/abstraction are referred
to as network-related functions; whereas the other two functions,
namely, customer mapping/translation and virtual service
coordination, are referred to as service-related functions. The MDSC
sits at the center of the ACTN model between the CNC that issues
connectivity requests and the Provisioning Network Controllers (PNCs)
that manage the network resources. The key point of the MDSC (and of
the whole ACTN framework) is detaching the network and service
control from underlying technology to help the customer express the
network as desired by business needs. The MDSC envelopes the
instantiation of the right technology and network control to meet
business criteria. In essence, it controls and manages the
primitives to achieve functionalities as desired by the CNC.
In order to allow for multi-domain coordination, a 1:N relationship
must be allowed between MDSCs and PNCs.
In addition to that, it could also be possible to have an M:1
relationship between MDSCs and PNCs to allow for network-resource
partitioning/sharing among different customers that are not
necessarily connected to the same MDSC (e.g., different service
providers) but that are all using the resources of a common network
infrastructure operator.
3.3. Provisioning Network Controller
The Provisioning Network Controller (PNC) oversees configuring the
network elements, monitoring the topology (physical or virtual) of
the network, and collecting information about the topology (either
raw or abstracted).
The PNC functions can be implemented as part of an SDN domain
controller, a Network Management System (NMS), an Element Management
System (EMS), an active PCE-based controller [RFC8283], or any other
means to dynamically control a set of nodes that implements a
Ceccarelli & Lee Informational [Page 13]
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northbound interface from the standpoint of the nodes (which is out
of the scope of this document). A PNC domain includes all the
resources under the control of a single PNC. It can be composed of
different routing domains and administrative domains, and the
resources may come from different layers. The interconnection
between PNC domains is illustrated in Figure 3.
_______ _______
_( )_ _( )_
_( )_ _( )_
( ) Border ( )
( PNC ------ Link ------ PNC )
( Domain X |Border|========|Border| Domain Y )
( | Node | | Node | )
( ------ ------ )
(_ _) (_ _)
(_ _) (_ _)
(_______) (_______)
Figure 3: PNC Domain Borders
3.4. ACTN Interfaces
Direct customer control of transport network elements and virtualized
services is not a viable proposition for network operators due to
security and policy concerns. Therefore, the network has to provide
open, programmable interfaces, through which customer applications
can create, replace, and modify virtual network resources and
services in an interactive, flexible, and dynamic fashion.
Three interfaces exist in the ACTN architecture as shown in Figure 2.
o CMI: The CNC-MDSC Interface (CMI) is an interface between a CNC
and an MDSC. The CMI is a business boundary between customer and
network operator. It is used to request a VNS for an application.
All service-related information is conveyed over this interface
(such as the VNS type, topology, bandwidth, and service
constraints). Most of the information over this interface is
agnostic of the technology used by network operators, but there
are some cases (e.g., access link configuration) where it is
necessary to specify technology-specific details.
o MPI: The MDSC-PNC Interface (MPI) is an interface between an MDSC
and a PNC. It communicates requests for new connectivity or for
bandwidth changes in the physical network. In multi-domain
environments, the MDSC needs to communicate with multiple PNCs,
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each responsible for control of a domain. The MPI presents an
abstracted topology to the MDSC hiding technology-specific aspects
of the network and hiding topology according to policy.
o SBI: The Southbound Interface (SBI) is out of scope of ACTN. Many
different SBIs have been defined for different environments,
technologies, standards organizations, and vendors. It is shown
in Figure 3 for reference reason only.
4. Advanced ACTN Architectures
This section describes advanced configurations of the ACTN
architecture.
4.1. MDSC Hierarchy
A hierarchy of MDSCs can be foreseen for many reasons, among which
are scalability, administrative choices, or putting together
different layers and technologies in the network. In the case where
there is a hierarchy of MDSCs, we introduce the terms "higher-level
MDSC" (MDSC-H) and "lower-level MDSC" (MDSC-L). The interface
between them is a recursion of the MPI. An implementation of an
MDSC-H makes provisioning requests as normal using the MPI, but an
MDSC-L must be able to receive requests as normal at the CMI and also
at the MPI. The hierarchy of MDSCs can be seen in Figure 4.
Another implementation choice could foresee the usage of an MDSC-L
for all the PNCs related to a given technology (e.g., Internet
Protocol (IP) / Multiprotocol Label Switching (MPLS)) and a different
MDSC-L for the PNCs related to another technology (e.g., Optical
Transport Network (OTN) / Wavelength Division Multiplexing (WDM)) and
an MDSC-H to coordinate them.
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+--------+
| CNC |
+--------+
| +-----+
| CMI | CNC |
+----------+ +-----+
-------| MDSC-H |---- |
| +----------+ | | CMI
MPI | MPI | |
| | |
+---------+ +---------+
| MDSC-L | | MDSC-L |
+---------+ +---------+
MPI | | | |
| | | |
----- ----- ----- -----
| PNC | | PNC | | PNC | | PNC |
----- ----- ----- -----
Figure 4: MDSC Hierarchy
The hierarchy of MDSC can be recursive, where an MDSC-H is, in turn,
an MDSC-L to a higher-level MDSC-H.
4.2. Functional Split of MDSC Functions in Orchestrators
An implementation choice could separate the MDSC functions into two
groups: one group for service-related functions and the other for
network-related functions. This enables the implementation of a
service orchestrator that provides the service-related functions of
the MDSC and a network orchestrator that provides the network-related
functions of the MDSC. This split is consistent with the YANG
service model architecture described in [RFC8309]. Figure 5 depicts
this and shows how the ACTN interfaces may map to YANG data models.
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+--------------------+
| Customer |
| +-----+ |
| | CNC | |
| +-----+ |
+--------------------+
CMI | Customer Service Model
|
+---------------------------------------+
| Service |
********|*********************** Orchestrator |
* MDSC | +-----------------+ * |
* | | Service-related | * |
* | | Functions | * |
* | +-----------------+ * |
* +----------------------*----------------+
* * | Service Delivery
* * | Model
* +----------------------*----------------+
* | * Network |
* | +-----------------+ * Orchestrator |
* | | Network-related | * |
* | | Functions | * |
* | +-----------------+ * |
********|*********************** |
+---------------------------------------+
MPI | Network Configuration
| Model
+------------------------+
| Domain |
| +------+ Controller |
| | PNC | |
| +------+ |
+------------------------+
SBI | Device Configuration
| Model
+--------+
| Device |
+--------+
Figure 5: ACTN Architecture in the Context of the YANG Service Models
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5. Topology Abstraction Methods
Topology abstraction is described in [RFC7926]. This section
discusses topology abstraction factors, types, and their context in
the ACTN architecture.
Abstraction in ACTN is performed by the PNC when presenting available
topology to the MDSC, or by an MDSC-L when presenting topology to an
MDSC-H. This function is different from the creation of a VN (and
particularly a Type 2 VN) that is not abstraction but construction of
virtual resources.
5.1. Abstraction Factors
As discussed in [RFC7926], abstraction is tied with the policy of the
networks. For instance, per an operational policy, the PNC would not
provide any technology-specific details (e.g., optical parameters for
Wavelength Switched Optical Network (WSON) in the abstract topology
it provides to the MDSC. Similarly, the policy of the networks may
determine the abstraction type as described in Section 5.2.
There are many factors that may impact the choice of abstraction:
o Abstraction depends on the nature of the underlying domain
networks. For instance, packet networks may be abstracted with
fine granularity while abstraction of optical networks depends on
the switching units (such as wavelengths) and the end-to-end
continuity and cross-connect limitations within the network.
o Abstraction also depends on the capability of the PNCs. As
abstraction requires hiding details of the underlying network
resources, the PNC's capability to run algorithms impacts the
feasibility of abstraction. Some PNCs may not have the ability to
abstract native topology while other PNCs may have the ability to
use sophisticated algorithms.
o Abstraction is a tool that can improve scalability. Where the
native network resource information is of a large size, there is a
specific scaling benefit to abstraction.
o The proper abstraction level may depend on the frequency of
topology updates and vice versa.
o The nature of the MDSC's support for technology-specific
parameters impacts the degree/level of abstraction. If the MDSC
is not capable of handling such parameters, then a higher level of
abstraction is needed.
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o In some cases, the PNC is required to hide key internal
topological data from the MDSC. Such confidentiality can be
achieved through abstraction.
5.2. Abstraction Types
This section defines the following three types of topology
abstraction:
o Native/White Topology (Section 5.2.1)
o Black Topology (Section 5.2.2)
o Grey Topology (Section 5.2.3)
5.2.1. Native/White Topology
This is a case where the PNC provides the actual network topology to
the MDSC without any hiding or filtering of information, i.e., no
abstraction is performed. In this case, the MDSC has the full
knowledge of the underlying network topology and can operate on it
directly.
5.2.2. Black Topology
A black topology replaces a full network with a minimal
representation of the edge-to-edge topology without disclosing any
node internal connectivity information. The entire domain network
may be abstracted as a single abstract node with the network's
access/egress links appearing as the ports to the abstract node and
the implication that any port can be "cross-connected" to any other.
Figure 6 depicts a native topology with the corresponding black
topology with one virtual node and inter-domain links. In this case,
the MDSC has to make a provisioning request to the PNCs to establish
the port-to-port connection. If there is a large number of
interconnected domains, this abstraction method may impose a heavy
coordination load at the MDSC level in order to find an optimal end-
to-end path since the abstraction hides so much information that it
is not possible to determine whether an end-to-end path is feasible
without asking each PNC to set up each path fragment. For this
reason, the MPI might need to be enhanced to allow the PNCs to be
queried for the practicality and characteristics of paths across the
abstract node.
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.....................................
: PNC Domain :
: +--+ +--+ +--+ +--+ :
------+ +-----+ +-----+ +-----+ +------
: ++-+ ++-+ +-++ +-++ :
: | | | | :
: | | | | :
: | | | | :
: | | | | :
: ++-+ ++-+ +-++ +-++ :
------+ +-----+ +-----+ +-----+ +------
: +--+ +--+ +--+ +--+ :
:....................................
+----------+
---+ +---
| Abstract |
| Node |
---+ +---
+----------+
Figure 6: Native Topology with Corresponding
Black Topology Expressed as an Abstract Node
5.2.3. Grey Topology
A grey topology represents a compromise between black and white
topologies from a granularity point of view. In this case, the PNC
exposes an abstract topology containing all PNC domain border nodes
and an abstraction of the connectivity between those border nodes.
This abstraction may contain either physical or abstract nodes/links.
Two types of grey topology are identified:
o In a type A grey topology, border nodes are connected by a full
mesh of TE links (see Figure 7).
o In a type B grey topology, border nodes are connected over a more-
detailed network comprising internal abstract nodes and abstracted
links. This mode of abstraction supplies the MDSC with more
information about the internals of the PNC domain and allows it to
make more informed choices about how to route connectivity over
the underlying network.
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.....................................
: PNC Domain :
: +--+ +--+ +--+ +--+ :
------+ +-----+ +-----+ +-----+ +------
: ++-+ ++-+ +-++ +-++ :
: | | | | :
: | | | | :
: | | | | :
: | | | | :
: ++-+ ++-+ +-++ +-++ :
------+ +-----+ +-----+ +-----+ +------
: +--+ +--+ +--+ +--+ :
:....................................
....................
: Abstract Network :
: :
: +--+ +--+ :
-------+ +----+ +-------
: ++-+ +-++ :
: | \ / | :
: | \/ | :
: | /\ | :
: | / \ | :
: ++-+ +-++ :
-------+ +----+ +-------
: +--+ +--+ :
:..................:
Figure 7: Native Topology with Corresponding Grey Topology
5.3. Methods of Building Grey Topologies
This section discusses two different methods of building a grey
topology:
o Automatic generation of abstract topology by configuration
(Section 5.3.1)
o On-demand generation of supplementary topology via path
computation request/reply (Section 5.3.2)
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5.3.1. Automatic Generation of Abstract Topology by Configuration
Automatic generation is based on the abstraction/summarization of the
whole domain by the PNC and its advertisement on the MPI. The level
of abstraction can be decided based on PNC configuration parameters
(e.g., "provide the potential connectivity between any PE and any
ASBR in an MPLS-TE network").
Note that the configuration parameters for this abstract topology can
include available bandwidth, latency, or any combination of defined
parameters. How to generate such information is beyond the scope of
this document.
This abstract topology may need to be periodically or incrementally
updated when there is a change in the underlying network or the use
of the network resources that make connectivity more or less
available.
5.3.2. On-Demand Generation of Supplementary Topology via Path Compute
Request/Reply
While abstract topology is generated and updated automatically by
configuration as explained in Section 5.3.1, additional supplementary
topology may be obtained by the MDSC via a path compute request/reply
mechanism.
The abstract topology advertisements from PNCs give the MDSC the
border node/link information for each domain. Under this scenario,
when the MDSC needs to create a new VN, the MDSC can issue path
computation requests to PNCs with constraints matching the VN request
as described in [ACTN-YANG]. An example is provided in Figure 8,
where the MDSC is creating a P2P VN between AP1 and AP2. The MDSC
could use two different inter-domain links to get from domain X to
domain Y, but in order to choose the best end-to-end path, it needs
to know what domain X and Y can offer in terms of connectivity and
constraints between the PE nodes and the border nodes.
------- --------
( ) ( )
- BrdrX.1------- BrdrY.1 -
(+---+ ) ( +---+)
-+---( |PE1| Dom.X ) ( Dom.Y |PE2| )---+-
| (+---+ ) ( +---+) |
AP1 - BrdrX.2------- BrdrY.2 - AP2
( ) ( )
------- --------
Figure 8: A Multi-Domain Example
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The MDSC issues a path computation request to PNC.X asking for
potential connectivity between PE1 and border node BrdrX.1 and
between PE1 and BrdrX.2 with related objective functions and TE
metric constraints. A similar request for connectivity from the
border nodes in domain Y to PE2 will be issued to PNC.Y. The MDSC
merges the results to compute the optimal end-to-end path including
the inter-domain links. The MDSC can use the result of this
computation to request the PNCs to provision the underlying networks,
and the MDSC can then use the end-to-end path as a virtual link in
the VN it delivers to the customer.
5.4. Hierarchical Topology Abstraction Example
This section illustrates how topology abstraction operates in
different levels of a hierarchy of MDSCs as shown in Figure 9.
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+-----+
| CNC | CNC wants to create a VN
+-----+ between CE A and CE B
|
|
+-----------------------+
| MDSC-H |
+-----------------------+
/ \
/ \
+---------+ +---------+
| MDSC-L1 | | MDSC-L2 |
+---------+ +---------+
/ \ / \
/ \ / \
+----+ +----+ +----+ +----+
CE A o----|PNC1| |PNC2| |PNC3| |PNC4|----o CE B
+----+ +----+ +----+ +----+
Virtual Network Delivered to CNC
CE A o==============o CE B
Topology operated on by MDSC-H
CE A o----o==o==o===o----o CE B
Topology operated on by MDSC-L1 Topology operated on by MDSC-L2
_ _ _ _
( ) ( ) ( ) ( )
( ) ( ) ( ) ( )
CE A o--(o---o)==(o---o)==Dom.3 Dom.2==(o---o)==(o---o)--o CE B
( ) ( ) ( ) ( )
(_) (_) (_) (_)
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Actual Topology
___ ___ ___ ___
( ) ( ) ( ) ( )
( o ) ( o ) ( o--o) ( o )
( / \ ) ( |\ ) ( | | ) ( / \ )
CE A o---(o-o---o-o)==(o-o-o-o-o)==(o--o--o-o)==(o-o-o-o-o)---o CE B
( \ / ) ( | |/ ) ( | | ) ( \ / )
( o ) (o-o ) ( o--o) ( o )
(___) (___) (___) (___)
Domain 1 Domain 2 Domain 3 Domain 4
Where
o is a node
--- is a link
=== is a border link
Figure 9: Illustration of Hierarchical Topology Abstraction
In the example depicted in Figure 9, there are four domains under
control of PNCs: PNC1, PNC2, PNC3, and PNC4. MDSC-L1 controls PNC1
and PNC2, while MDSC-L2 controls PNC3 and PNC4. Each of the PNCs
provides a grey topology abstraction that presents only border nodes
and links across and outside the domain. The abstract topology
MDSC-L1 that operates is a combination of the two topologies from
PNC1 and PNC2. Likewise, the abstract topology that MDSC-L2 operates
is shown in Figure 9. Both MDSC-L1 and MDSC-L2 provide a black
topology abstraction to MDSC-H in which each PNC domain is presented
as a single virtual node. MDSC-H combines these two topologies to
create the abstraction topology on which it operates. MDSC-H sees
the whole four domain networks as four virtual nodes connected via
virtual links.
5.5. VN Recursion with Network Layers
In some cases, the VN supplied to a customer may be built using
resources from different technology layers operated by different
operators. For example, one operator may run a packet TE network and
use optical connectivity provided by another operator.
As shown in Figure 10, a customer asks for end-to-end connectivity
between CE A and CE B, a virtual network. The customer's CNC makes a
request to Operator 1's MDSC. The MDSC works out which network
resources need to be configured and sends instructions to the
appropriate PNCs. However, the link between Q and R is a virtual
link supplied by Operator 2: Operator 1 is a customer of Operator 2.
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To support this, Operator 1 has a CNC that communicates with Operator
2's MDSC. Note that Operator 1's CNC in Figure 10 is a functional
component that does not dictate implementation: it may be embedded in
a PNC.
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Virtual CE A o===============================o CE B
Network
----- CNC wants to create a VN
Customer | CNC | between CE A and CE B
-----
:
***********************************************
:
Operator 1 ---------------------------
| MDSC |
---------------------------
: : :
: : :
----- ------------- -----
| PNC | | PNC | | PNC |
----- ------------- -----
: : : : :
Higher v v : v v
Layer CE A o---P-----Q===========R-----S---o CE B
Network | : |
| : |
| ----- |
| | CNC | |
| ----- |
| : |
***********************************************
| : |
Operator 2 | ------ |
| | MDSC | |
| ------ |
| : |
| ------- |
| | PNC | |
| ------- |
\ : : : /
Lower \v v v/
Layer X--Y--Z
Network
Where
--- is a link
=== is a virtual link
Figure 10: VN Recursion with Network Layers
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6. Access Points and Virtual Network Access Points
In order to map identification of connections between the customer's
sites and the TE networks and to scope the connectivity requested in
the VNS, the CNC and the MDSC refer to the connections using the
Access Point (AP) construct as shown in Figure 11.
-------------
( )
- -
+---+ X ( ) Z +---+
|CE1|---+----( )---+---|CE2|
+---+ | ( ) | +---+
AP1 - - AP2
( )
-------------
Figure 11: Customer View of APs
Let's take as an example a scenario shown in Figure 11. CE1 is
connected to the network via a 10 Gbps link and CE2 via a 40 Gbps
link. Before the creation of any VN between AP1 and AP2, the
customer view can be summarized as shown in Figure 12.
+----------+------------------------+
| Endpoint | Access Link Bandwidth |
+-----+----------+----------+-------------+
|AP id| CE,port | MaxResBw | AvailableBw |
+-----+----------+----------+-------------+
| AP1 |CE1,portX | 10 Gbps | 10 Gbps |
+-----+----------+----------+-------------+
| AP2 |CE2,portZ | 40 Gbps | 40 Gbps |
+-----+----------+----------+-------------+
Figure 12: AP - Customer View
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On the other hand, what the operator sees is shown in Figure 13
------- -------
( ) ( )
- - - -
W (+---+ ) ( +---+) Y
-+---( |PE1| Dom.X )----( Dom.Y |PE2| )---+-
| (+---+ ) ( +---+) |
AP1 - - - - AP2
( ) ( )
------- -------
Figure 13: Operator View of the AP
which results in a summarization as shown in Figure 14.
+----------+------------------------+
| Endpoint | Access Link Bandwidth |
+-----+----------+----------+-------------+
|AP id| PE,port | MaxResBw | AvailableBw |
+-----+----------+----------+-------------+
| AP1 |PE1,portW | 10 Gbps | 10 Gbps |
+-----+----------+----------+-------------+
| AP2 |PE2,portY | 40 Gbps | 40 Gbps |
+-----+----------+----------+-------------+
Figure 14: AP - Operator View
A Virtual Network Access Point (VNAP) needs to be defined as binding
between an AP and a VN. It is used to allow different VNs to start
from the same AP. It also allows for traffic engineering on the
access and/or inter-domain links (e.g., keeping track of bandwidth
allocation). A different VNAP is created on an AP for each VN.
In this simple scenario, we suppose we want to create two virtual
networks: the first with VN identifier 9 between AP1 and AP2 with
bandwidth of 1 Gbps and the second with VN identifier 5, again
between AP1 and AP2 and with bandwidth 2 Gbps.
The operator view would evolve as shown in Figure 15.
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+----------+------------------------+
| Endpoint | Access Link/VNAP Bw |
+---------+----------+----------+-------------+
|AP/VNAPid| PE,port | MaxResBw | AvailableBw |
+---------+----------+----------+-------------+
|AP1 |PE1,portW | 10 Gbps | 7 Gbps |
| -VNAP1.9| | 1 Gbps | N.A. |
| -VNAP1.5| | 2 Gbps | N.A |
+---------+----------+----------+-------------+
|AP2 |PE2,portY | 4 0Gbps | 37 Gbps |
| -VNAP2.9| | 1 Gbps | N.A. |
| -VNAP2.5| | 2 Gbps | N.A |
+---------+----------+----------+-------------+
Figure 15: AP and VNAP - Operator View after VNS Creation
6.1. Dual-Homing Scenario
Often there is a dual-homing relationship between a CE and a pair of
PEs. This case needs to be supported by the definition of VN, APs,
and VNAPs. Suppose CE1 connected to two different PEs in the
operator domain via AP1 and AP2 and that the customer needs 5 Gbps of
bandwidth between CE1 and CE2. This is shown in Figure 16.
____________
AP1 ( ) AP3
-------(PE1) (PE3)-------
W / ( ) \ X
+---+/ ( ) \+---+
|CE1| ( ) |CE2|
+---+\ ( ) /+---+
Y \ ( ) / Z
-------(PE2) (PE4)-------
AP2 (____________)
Figure 16: Dual-Homing Scenario
In this case, the customer will request a VN between AP1, AP2, and
AP3 specifying a dual-homing relationship between AP1 and AP2. As a
consequence, no traffic will flow between AP1 and AP2. The dual-
homing relationship would then be mapped against the VNAPs (since
other independent VNs might have AP1 and AP2 as endpoints).
The customer view would be shown in Figure 17.
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+----------+------------------------+
| Endpoint | Access Link/VNAP Bw |
+---------+----------+----------+-------------+-----------+
|AP/VNAPid| CE,port | MaxResBw | AvailableBw |Dual Homing|
+---------+----------+----------+-------------+-----------+
|AP1 |CE1,portW | 10 Gbps | 5 Gbps | |
| -VNAP1.9| | 5 Gbps | N.A. | VNAP2.9 |
+---------+----------+----------+-------------+-----------+
|AP2 |CE1,portY | 40 Gbps | 35 Gbps | |
| -VNAP2.9| | 5 Gbps | N.A. | VNAP1.9 |
+---------+----------+----------+-------------+-----------+
|AP3 |CE2,portX | 50 Gbps | 45 Gbps | |
| -VNAP3.9| | 5 Gbps | N.A. | NONE |
+---------+----------+----------+-------------+-----------+
Figure 17: Dual-Homing -- Customer View after VN Creation
7. Advanced ACTN Application: Multi-Destination Service
A more-advanced application of ACTN is the case of data center (DC)
selection, where the customer requires the DC selection to be based
on the network status; this is referred to as "Multi-Destination
Service" in [ACTN-REQ]. In terms of ACTN, a CNC could request a VNS
between a set of source APs and destination APs and leave it up to
the network (MDSC) to decide which source and destination APs to be
used to set up the VNS. The candidate list of source and destination
APs is decided by a CNC (or an entity outside of ACTN) based on
certain factors that are outside the scope of ACTN.
Based on the AP selection as determined and returned by the network
(MDSC), the CNC (or an entity outside of ACTN) should further take
care of any subsequent actions such as orchestration or service setup
requirements. These further actions are outside the scope of ACTN.
Consider a case as shown in Figure 18, where three DCs are available,
but the customer requires the DC selection to be based on the network
status and the connectivity service setup between the AP1 (CE1) and
one of the destination APs (AP2 (DC-A), AP3 (DC-B), and AP4 (DC-C)).
The MDSC (in coordination with PNCs) would select the best
destination AP based on the constraints, optimization criteria,
policies, etc., and set up the connectivity service (virtual
network).
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------- -------
( ) ( )
- - - -
+---+ ( ) ( ) +----+
|CE1|---+---( Domain X )----( Domain Y )---+---|DC-A|
+---+ | ( ) ( ) | +----+
AP1 - - - - AP2
( ) ( )
---+--- ---+---
| |
AP3-+ AP4-+
| |
+----+ +----+
|DC-B| |DC-C|
+----+ +----+
Figure 18: Endpoint Selection Based on Network Status
7.1. Preplanned Endpoint Migration
Furthermore, in the case of DC selection, a customer could request a
backup DC to be selected, such that in case of failure, another DC
site could provide hot stand-by protection. As shown in Figure 19,
DC-C is selected as a backup for DC-A. Thus, the VN should be set up
by the MDSC to include primary connectivity between AP1 (CE1) and AP2
(DC-A) as well as protection connectivity between AP1 (CE1) and AP4
(DC-C).
------- -------
( ) ( )
- - __ - -
+---+ ( ) ( ) +----+
|CE1|---+----( Domain X )----( Domain Y )---+---|DC-A|
+---+ | ( ) ( ) | +----+
AP1 - - - - AP2 |
( ) ( ) |
---+--- ---+--- |
| | |
AP3-| AP4-| HOT STANDBY
| | |
+----+ +----+ |
|DC-D| |DC-C|<-------------
+----+ +----+
Figure 19: Preplanned Endpoint Migration
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7.2. On-the-Fly Endpoint Migration
Compared to preplanned endpoint migration, on-the-fly endpoint
selection is dynamic in that the migration is not preplanned but
decided based on network condition. Under this scenario, the MDSC
would monitor the network (based on the VN SLA) and notify the CNC in
the case where some other destination AP would be a better choice
based on the network parameters. The CNC should instruct the MDSC
when it is suitable to update the VN with the new AP if it is
required.
8. Manageability Considerations
The objective of ACTN is to manage traffic engineered resources and
provide a set of mechanisms to allow customers to request virtual
connectivity across server-network resources. ACTN supports multiple
customers, each with its own view of and control of a virtual network
built on the server network; the network operator will need to
partition (or "slice") their network resources, and manage the
resources accordingly.
The ACTN platform will, itself, need to support the request,
response, and reservations of client- and network-layer connectivity.
It will also need to provide performance monitoring and control of TE
resources. The management requirements may be categorized as
follows:
o Management of external ACTN protocols
o Management of internal ACTN interfaces/protocols
o Management and monitoring of ACTN components
o Configuration of policy to be applied across the ACTN system
The ACTN framework and interfaces are defined to enable traffic
engineering for virtual network services and connectivity services.
Network operators may have other Operations, Administration, and
Maintenance (OAM) tasks for service fulfillment, optimization, and
assurance beyond traffic engineering. The realization of OAM beyond
abstraction and control of TE networks is not discussed in this
document.
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8.1. Policy
Policy is an important aspect of ACTN control and management.
Policies are used via the components and interfaces, during
deployment of the service, to ensure that the service is compliant
with agreed-upon policy factors and variations (often described in
SLAs); these include, but are not limited to connectivity, bandwidth,
geographical transit, technology selection, security, resilience, and
economic cost.
Depending on the deployment of the ACTN architecture, some policies
may have local or global significance. That is, certain policies may
be ACTN component specific in scope, while others may have broader
scope and interact with multiple ACTN components. Two examples are
provided below:
o A local policy might limit the number, type, size, and scheduling
of virtual network services a customer may request via its CNC.
This type of policy would be implemented locally on the MDSC.
o A global policy might constrain certain customer types (or
specific customer applications) only to use certain MDSCs and be
restricted to physical network types managed by the PNCs. A
global policy agent would govern these types of policies.
The objective of this section is to discuss the applicability of ACTN
policy: requirements, components, interfaces, and examples. This
section provides an analysis and does not mandate a specific method
for enforcing policy, or the type of policy agent that would be
responsible for propagating policies across the ACTN components. It
does highlight examples of how policy may be applied in the context
of ACTN, but it is expected further discussion in an applicability or
solution-specific document, will be required.
8.2. Policy Applied to the Customer Network Controller
A virtual network service for a customer application will be
requested by the CNC. The request will reflect the application
requirements and specific service needs, including bandwidth, traffic
type and survivability. Furthermore, application access and type of
virtual network service requested by the CNC, will be need adhere to
specific access control policies.
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8.3. Policy Applied to the Multi-Domain Service Coordinator
A key objective of the MDSC is to support the customer's expression
of the application connectivity request via its CNC as a set of
desired business needs; therefore, policy will play an important
role.
Once authorized, the virtual network service will be instantiated via
the CNC-MDSC Interface (CMI); it will reflect the customer
application and connectivity requirements and specific service-
transport needs. The CNC and the MDSC components will have agreed-
upon connectivity endpoints; use of these endpoints should be defined
as a policy expression when setting up or augmenting virtual network
services. Ensuring that permissible endpoints are defined for CNCs
and applications will require the MDSC to maintain a registry of
permissible connection points for CNCs and application types.
Conflicts may occur when virtual network service optimization
criteria are in competition. For example, to meet objectives for
service reachability, a request may require an interconnection point
between multiple physical networks; however, this might break a
confidentially policy requirement of a specific type of end-to-end
service. Thus, an MDSC may have to balance a number of the
constraints on a service request and between different requested
services. It may also have to balance requested services with
operational norms for the underlying physical networks. This
balancing may be resolved using configured policy and using hard and
soft policy constraints.
8.4. Policy Applied to the Provisioning Network Controller
The PNC is responsible for configuring the network elements,
monitoring physical network resources, and exposing connectivity
(direct or abstracted) to the MDSC. Therefore, it is expected that
policy will dictate what connectivity information will be exchanged
on the MPI.
Policy interactions may arise when a PNC determines that it cannot
compute a requested path from the MDSC, or notices that (per a
locally configured policy) the network is low on resources (for
example, the capacity on key links became exhausted). In either
case, the PNC will be required to notify the MDSC, which may (again
per policy) act to construct a virtual network service across another
physical network topology.
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Furthermore, additional forms of policy-based resource management
will be required to provide VNS performance, security, and resilience
guarantees. This will likely be implemented via a local policy agent
and additional protocol methods.
9. Security Considerations
The ACTN framework described in this document defines key components
and interfaces for managed TE networks. Securing the request and
control of resources, confidentiality of the information, and
availability of function should all be critical security
considerations when deploying and operating ACTN platforms.
Several distributed ACTN functional components are required, and
implementations should consider encrypting data that flows between
components, especially when they are implemented at remote nodes,
regardless of whether these data flows are on external or internal
network interfaces.
The ACTN security discussion is further split into two specific
categories described in the following subsections:
o Interface between the Customer Network Controller and Multi-Domain
Service Coordinator (MDSC), CNC-MDSC Interface (CMI)
o Interface between the Multi-Domain Service Coordinator and
Provisioning Network Controller (PNC), MDSC-PNC Interface (MPI)
From a security and reliability perspective, ACTN may encounter many
risks such as malicious attack and rogue elements attempting to
connect to various ACTN components. Furthermore, some ACTN
components represent a single point of failure and threat vector and
must also manage policy conflicts and eavesdropping of communication
between different ACTN components.
The conclusion is that all protocols used to realize the ACTN
framework should have rich security features, and customer,
application and network data should be stored in encrypted data
stores. Additional security risks may still exist. Therefore,
discussion and applicability of specific security functions and
protocols will be better described in documents that are use case and
environment specific.
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9.1. CNC-MDSC Interface (CMI)
Data stored by the MDSC will reveal details of the virtual network
services and which CNC and customer/application is consuming the
resource. Therefore, the data stored must be considered a candidate
for encryption.
CNC Access rights to an MDSC must be managed. The MDSC must allocate
resources properly, and methods to prevent policy conflicts, resource
waste, and denial-of-service attacks on the MDSC by rogue CNCs should
also be considered.
The CMI will likely be an external protocol interface. Suitable
authentication and authorization of each CNC connecting to the MDSC
will be required; especially, as these are likely to be implemented
by different organizations and on separate functional nodes. Use of
the AAA-based mechanisms would also provide role-based authorization
methods so that only authorized CNC's may access the different
functions of the MDSC.
9.2. MDSC-PNC Interface (MPI)
Where the MDSC must interact with multiple (distributed) PNCs, a PKI-
based mechanism is suggested, such as building a TLS or HTTPS
connection between the MDSC and PNCs, to ensure trust between the
physical network layer control components and the MDSC. Trust
anchors for the PKI can be configured to use a smaller (and
potentially non-intersecting) set of trusted Certificate Authorities
(CAs) than in the Web PKI.
Which MDSC the PNC exports topology information to, and the level of
detail (full or abstracted), should also be authenticated, and
specific access restrictions and topology views should be
configurable and/or policy based.
10. IANA Considerations
This document has no IANA actions.
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11. Informative References
[ACTN-REQ]
Lee, Y., Ceccarelli, D., Miyasaka, T., Shin, J., and K.
Lee, "Requirements for Abstraction and Control of TE
Networks", Work in Progress,
draft-ietf-teas-actn-requirements-09, March 2018.
[ACTN-YANG]
Lee, Y., Dhody, D., Ceccarelli, D., Bryskin, I., Yoon, B.,
Wu, Q., and P. Park, "A Yang Data Model for ACTN VN
Operation", Work in Progress,
draft-ietf-teas-actn-vn-yang-01, June 2018.
[ONF-ARCH]
Open Networking Foundation, "SDN Architecture", Issue
1.1, ONF TR-521, June 2016.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, DOI 10.17487/RFC2702, September 1999,
<https://www.rfc-editor.org/info/rfc2702>.
[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945,
DOI 10.17487/RFC3945, October 2004,
<https://www.rfc-editor.org/info/rfc3945>.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/info/rfc5654>.
[RFC7149] Boucadair, M. and C. Jacquenet, "Software-Defined
Networking: A Perspective from within a Service Provider
Environment", RFC 7149, DOI 10.17487/RFC7149, March 2014,
<https://www.rfc-editor.org/info/rfc7149>.
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RFC 8453 ACTN Framework August 2018
[RFC7926] Farrel, A., Ed., Drake, J., Bitar, N., Swallow, G.,
Ceccarelli, D., and X. Zhang, "Problem Statement and
Architecture for Information Exchange between
Interconnected Traffic-Engineered Networks", BCP 206,
RFC 7926, DOI 10.17487/RFC7926, July 2016,
<https://www.rfc-editor.org/info/rfc7926>.
[RFC8283] Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
Architecture for Use of PCE and the PCE Communication
Protocol (PCEP) in a Network with Central Control",
RFC 8283, DOI 10.17487/RFC8283, December 2017,
<https://www.rfc-editor.org/info/rfc8283>.
[RFC8309] Wu, Q., Liu, W., and A. Farrel, "Service Models
Explained", RFC 8309, DOI 10.17487/RFC8309, January 2018,
<https://www.rfc-editor.org/info/rfc8309>.
[TE-TOPO] Liu, X., Bryskin, I., Beeram, V., Saad, T., Shah, H., and
O. Dios, "YANG Data Model for Traffic Engineering (TE)
Topologies", Work in Progress,
draft-ietf-teas-yang-te-topo-18, June 2018.
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Appendix A. Example of MDSC and PNC Functions Integrated in a Service/
Network Orchestrator
This section provides an example of a possible deployment scenario,
in which Service/Network Orchestrator can include the PNC
functionalities for domain 2 and the MDSC functionalities.
Customer
+-------------------------------+
| +-----+ |
| | CNC | |
| +-----+ |
+-------|-----------------------+
|
Service/Network | CMI
Orchestrator |
+-------|------------------------+
| +------+ MPI +------+ |
| | MDSC |---------| PNC2 | |
| +------+ +------+ |
+-------|------------------|-----+
| MPI |
Domain Controller | |
+-------|-----+ |
| +-----+ | | SBI
| |PNC1 | | |
| +-----+ | |
+-------|-----+ |
v SBI v
------- -------
( ) ( )
- - - -
( ) ( )
( Domain 1 )----( Domain 2 )
( ) ( )
- - - -
( ) ( )
------- -------
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Contributors
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Italo Busi
Huawei
Email: Italo.Busi@huawei.com
Khuzema Pithewan
Peloton Technology
Email: khuzemap@gmail.com
Michael Scharf
Nokia
Email: michael.scharf@nokia.com
Luyuan Fang
eBay
Email: luyuanf@gmail.com
Diego Lopez
Telefonica I+D
Don Ramon de la Cruz, 82
28006 Madrid
Spain
Email: diego@tid.es
Sergio Belotti
Nokia
Via Trento, 30
Vimercate
Italy
Email: sergio.belotti@nokia.com
Daniel King
Lancaster University
Email: d.king@lancaster.ac.uk
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
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Gert Grammel
Juniper Networks
Email: ggrammel@juniper.net
Authors' Addresses
Daniele Ceccarelli (editor)
Ericsson
Torshamnsgatan, 48
Stockholm
Sweden
Email: daniele.ceccarelli@ericsson.com
Young Lee (editor)
Huawei Technologies
5340 Legacy Drive
Plano, TX 75023
United States of America
Email: leeyoung@huawei.com
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