TEAS Working Group Daniele Ceccarelli (Ed)
Internet Draft Ericsson
Intended status: Informational Young Lee (Ed)
Expires: June 2017 Huawei
December 22, 2016
Framework for Abstraction and Control of Traffic Engineered Networks
draft-ietf-teas-actn-framework-02
Abstract
Traffic Engineered 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.
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
Traffic Engineered Networks (ACTN).
Status of this Memo
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reference material or to cite them other than as "work in progress."
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Table of Contents
1. Introduction...................................................3
1.1. Terminology...............................................6
2. Business Model of ACTN.........................................9
2.1. Customers.................................................9
2.2. Service Providers........................................10
2.3. Network Providers........................................12
3. ACTN Architecture.............................................12
3.1. Customer Network Controller..............................14
3.2. Multi Domain Service Coordinator.........................15
3.3. Physical Network Controller..............................16
3.4. ACTN Interfaces..........................................17
4. VN Creation Process...........................................19
5. Access Points and Virtual Network Access Points...............20
5.1. Dual homing scenario.....................................22
6. End Point Selection and Mobility..............................23
6.1. End Point Selection......................................23
6.2. Pre-Planned End Point Migration..........................24
6.3. On the Fly End Point Migration...........................25
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7. Manageability Considerations..................................25
7.1. Policy...................................................26
7.2. Policy applied to the Customer Network Controller........26
7.3. Policy applied to the Multi Domain Service Coordinator...27
7.4. Policy applied to the Physical Network Controller........27
8. Security Considerations.......................................28
8.1. Interface between the Application and Customer Network
Controller (CNC)..............................................29
8.2. Interface between the Customer Network Controller and Multi
Domain Service Coordinator (MDSC), CNC-MDSC Interface (CMI)...29
8.3. Interface between the Multi Domain Service Coordinator and
Physical Network Controller (PNC), MDSC-PNC Interface (MPI)...30
9. References....................................................30
9.1. Informative References...................................30
10. Contributors.................................................31
Authors' Addresses...............................................32
1. Introduction
Traffic Engineered networks have a variety of mechanisms to
facilitate separation of data plane and control plane 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.
The term Traffic Engineered network is used in this document to
refer 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. Some
examples of networks that are in scope of this definition are
optical networks, MPLS Transport Profile (MPLS-TP) networks
[RFC5654], and MPLS Traffic Engineering (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 of the control plane from the data plane has
been already achieved with the development of MPLS/GMPLS [GMPLS] and
the Path Computation Element (PCE) [RFC4655] for TE-based networks.
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, PCE is essentially equivalent to a logically centralized
path computation function.
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Three key aspects that need to be solved by SDN are:
. Separation of service requests from service delivery so that
the orchestration of a network is transparent from the point of
view of the customer but remains responsive to the customer's
services and business needs.
. 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 domain. The process of
abstraction presents the connectivity graph in a way that is
independent of the underlying network technologies,
capabilities, and topology so that it can be used to plan and
deliver network services in a uniform way
. Coordination of resources across multiple domains and multiple
layers to provide end-to-end services regardless of whether the
domains use SDN or not.
As networks evolve, the need to provide separated service
request/orchestration and resource abstraction has emerged as a key
requirement for operators. In order to support multiple clients each
with its own view of and control of the server network, a network
operator needs to partition (or "slice") the network resources. The
resulting slices can be assigned to each client for guaranteed usage
which is a step further than shared use of common network resources.
Furthermore, each network represented to a client can be built from
abstractions of the underlying networks so that, for example, a link
in the client's network is constructed from a path or collection of
paths in the underlying network.
We call the set of management and control functions used to provide
these features Abstraction and Control of Traffic Engineered
Networks (ACTN).
Particular attention needs to be paid to the multi-domain case, 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) as a single virtualized network.
Network virtualization refers to allowing the customers of network
operators (see Section 2.1) to utilize a certain amount of network
resources as if they own them and thus control their allocated
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resources with higher layer or application processes that enables
the resources to be used in the most optimal way. More flexible,
dynamic customer control capabilities are added to the traditional
VPN along with a customer-specific virtual network view. Customers
control a view of virtual network resources, specifically allocated
to each one of them. This view is called an virtual network
topology. Such a view may be specific to a service, the set of
consumed resources, or to a particular customer.
Network abstraction refers to presenting a customer with a view of
the operator's network in such a way that the links and nodes in
that view constitute an aggregation or abstraction of the real
resources in the operator's network in a way that is independent of
the underlying network technologies, capabilities, and topology.
The customer operates an abstract network as if it was their own
network, but the operational commands are mapped onto the underlying
network through orchestration.
The customer controller for a virtual or abstract network is
envisioned to support many distinct applications. This means that
there may be a further level of virtualization that provides a view
of resources in the customer's virtual network for use by an
individual application.
The ACTN framework described in this document facilitates:
. Abstraction of the underlying network resources to higher-layer
applications and customers [RFC7926].
. Virtualization of particular underlying resources, whose
selection criterion is the allocation of those resources to a
particular customer, application or service [ONF-ARCH].
. Slicing of infrastructure to meet specific customers' service
requirements.
. Creation of a virtualized environment allowing operators to
view and control multi-domain networks as a single virtualized
network.
. The possibility of providing a customer with a virtualized
network.
. A virtualization/mapping network function that adapts the
customer's requests for control of the virtual resources that
have been allocated to the customer to control commands applied
to the underlying network resources. Such a function performs
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the necessary mapping, translation, isolation and
security/policy enforcement, etc. This function is often
referred to as orchestration.
. The presentation to customers of networks as a virtualized
topology via open and programmable interfaces. This allows for
the recursion of controllers in a customer-provider
relationship.
1.1. Terminology
The following terms are used in this document. Some of them are
newly defined, some others reference existing definition:
. Node: A node is a vertex on the graph representation of a TE
topology. In a physical network a node corresponds to a network
element (NE). In a sliced network, a node is some subset of the
capabilities of a physical network element. In an abstract
network, a node (sometimes called an abstract node) is a
representation as a single vertex in the topology of the
abstract network of one or more nodes and their connecting
links from the physical network. 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. Just as network slicing and
network abstraction may be applied recursively, so a node in a
topology may be created by applying slicing or abstraction on
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, a link
corresponds to a physical connection. In a sliced topology, a
link is some subset of the capabilities of a physical
connection. In an abstract network, a link (sometimes called an
abstract link) is a representation as an edge in the topology
of the abstract network of one or more links and the nodes they
connect from the physical network. Abstract links may be
realized by Label Switched Paths (LSPs) across the physical
network that may be pre-established or could be only
potentially achievable. Just as network slicing and network
abstraction may be applied recursively, so a link in a topology
may be created by applying slicing or abstraction on the links
in the underlying topology. While most links are point-to-
point, connecting just two nodes, the concept of a multi-access
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link exists where more than two nodes are collectively adjacent
and data sent on the link by one node will be equally delivered
to all other nodes connected by the link.
. PNC: A Physical Network Controller is a domain controller that
is responsible for controlling devices or NEs under its direct
control.
. PNC domain: 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 can be a link or a node.
_______ Border Link _______
_( )================( )_
_( )_ _( )_
( ) ---- ( )
( PNC )| |( PNC )
( Domain X )| |( Domain Y )
( )| |( )
(_ _) ---- (_ _)
(_ _) Border (_ _)
(_______) Node (_______)
Figure 1: PNC Domain Borders
. A Virtual Network (VN) is a customer view of the TE
network. It is presented by the provider as a set of physical
and/or abstracted resources. Depending on the agreement between
client and provider various VN operations and VN views are
possible as follows:
o VN Creation - VN could be pre-configured and created via
offline negotiation between customer and provider. In
other cases, the VN could also be created dynamically
based on a request from the customer with given SLA
attributes which satisfy the customer's objectives.
o Dynamic Operations - The VN could be further modified or
deleted based on a customer request to request. The
customer can further act upon the virtual network
resources to perform end-to-end tunnel management (set-
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up/release/modify). These changes will result in
subsequent LSP management at the operator's level.
o VN View:
a. The VN can be seen as set of end-to-end tunnels from a
customer point of view, where each tunnel is referred
as a VN member. Each VN member can then be formed by
recursive slicing or abstraction of paths in
underlying networks. Such end-to-end tunnels may
comprise of customer end points, access links, intra
domain paths, and inter-domain links. In this view VN
is thus a set of VN members.
b. The VN can also be seen as a topology comprising of
physical, sliced, and abstract nodes and links. The
nodes in this case include physical customer end
points, border nodes, and internal nodes as well as
abstracted nodes. Similarly the links include physical
access links, inter-domain links, and intra-domain
links as well as abstract links. The abstract nodes
and links in this view can be pre-negotiated or
created dynamically.
. Abstraction. This process is defined in [RFC7926].
. Abstract Link: The term "abstract link" is defined in
[RFC7926].
. 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.
. Access link: A link between a customer node and a provider
node.
. Inter-domain link: A link between domains managed by different
PNCs. The MDSC is in charge of managing inter-domain links.
. Access Point (AP): An access point is used to keep
confidentiality between the customer and the provider. It is a
logical identifier shared between the customer and the
provider, used to map the end points of the border node in both
the customer and the provider NW. The AP can be used by the
customer when requesting VN service to the provider.
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. VN Access Point (VNAP): A VNAP is defined as the binding
between an AP and a given VN and is used to identify the
portion of the access and/or inter-domain link dedicated to a
given VN.
2. Business Model of ACTN
The Virtual Private Network (VPN) [RFC4026] and Overlay Network (ON)
models [RFC4208] are built on the premise that the network provider
provides all virtual private or overlay networks to its customers.
These models are simple to operate but have some disadvantages in
accommodating the increasing need for flexible and dynamic network
virtualization capabilities.
There are three key entities in the ACTN model:
- Customers
- Service Providers
- Network Providers
These are described in the following sections.
2.1. Customers
Within the ACTN framework, different types of customers may be taken
into account depending on the type of their resource needs, and on
their number and type of access. For example, it is possible to
group them into two main categories:
Basic Customer: Basic customers include fixed residential users,
mobile users and small enterprises. Usually, the number of basic
customers for a service provider is high: they require small amounts
of resources and are characterized by steady requests (relatively
time invariant). A typical request for a basic customer is for a
bundle of voice services and internet access. Moreover, basic
customers do not modify their services themselves: if a service
change is needed, it is performed by the provider as a proxy and the
services generally have very few dedicated resources (such as for
subscriber drop), with everything else shared on the basis of some
Service Level Agreement (LSA), which is usually best-efforts.
Advanced Customer: Advanced customers typically include enterprises,
governments and utilities. Such customers can ask for both point-to
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point and multipoint connectivity with high resource demands varying
significantly in time and from customer to customer. 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
virtual network service.
Advanced customers may own dedicated virtual resources, or share
resources. They 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
provider domains, they have to interface to multiple providers and
may have to support multiple virtual network services with different
underlying objectives set by the network providers. To enable these
customers to support flexible and dynamic applications they need to
control their allocated virtual network resources in a dynamic
fashion, and that means that they need a view of the
topology that spans all of the network providers.
Customers of a given service provider can in turn offer a service to
other customers in a recursive way.
2.2. Service Providers
Service providers are the providers of virtual network services to
their customers. Service providers may or may not own physical
network resources (i.e, may or may not be network providers as
described in Section 2.3). When a service provider is the same as
the network provider, this is similar to existing VPN models applied
to a single provider. This approach works well when the customer
maintains a single interface with a single provider. When customer
spans multiple independent network provider domains, then it becomes
hard to facilitate the creation of end-to-end virtual network
services with this model.
A more interesting case arises when network providers only provide
infrastructure, while distinct service providers interface to the
customers. In this case, service providers are, themselves customers
of the network infrastructure providers. One service provider may
need to keep multiple independent network providers as its end-users
span geographically across multiple network provider domains.
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The ACTN network model is predicated upon this three tier model and
is summarized in Figure 2:
+----------------------+
| customer |
+----------------------+
|
| /\ Service/Customer specific
| || Abstract Topology
| ||
+----------------------+ E2E abstract
| Service Provider | topology creation
+----------------------+
/ | \
/ | \ Network Topology
/ | \ (raw or abstract)
/ | \
+------------------+ +------------------+ +------------------+
|Network Provider 1| |Network Provider 2| |Network Provider 3|
+------------------+ +------------------+ +------------------+
Figure 2: Three tier model.
There can be multiple service providers to which a customer may
interface.
There are multiple types of service providers:
. Data Center providers can be viewed as a service provider type
as they own and operate data center resources for various WAN
customers, and they can lease physical network resources from
network providers.
. Internet Service Providers (ISP) are service providers of
internet services to their customers while leasing physical
network resources from network providers.
. Mobile Virtual Network Operators (MVNO) provide mobile services
to their end-users without owning the physical network
infrastructure.
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2.3. Network Providers
Network Providers are the infrastructure providers that own the
physical network resources and provide network resources to their
customers. The layered model described in this architecture
separates the concerns of network providers and customers, with
service providers acting as aggregators of customer requests.
3. ACTN Architecture
This section provides a high-level model of ACTN showing the
interfaces and the flow of control between components.
The ACTN architecture is aligned with the ONF SDN architecture [ONF-
ARCH] and presents a 3-tiers reference model. It allows for
hierarchy and recursiveness not only of SDN controllers but also of
traditionally controlled domains that use a control plane. It
defines three types of controllers depending on the functionalities
they implement. The main functionalities that are identified are:
. Multi-domain coordination function: This function oversees the
specific aspects of the 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.
. Virtualization/Abstraction function: 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 slices allocated to each customer. These operations
depend on customer-specific network objective functions and
customer traffic profiles.
. Customer mapping/translation function: This function is to map
customer requests/commands into network provisioning requests
that can be sent to the Physical Network Controller (PNC)
according to business policies provisioned statically or
dynamically at the OSS/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.
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. Virtual service coordination function: This function translates
customer service-related information into virtual network
service operations in order to seamlessly operate virtual
networks while meeting a customer's service requirements. In
the context of ACTN, service/virtual service coordination
includes a number of service orchestration functions such as
multi-destination load balancing, guarantees of service
quality, bandwidth and throughput. It also includes
notifications for service fault and performance degradation and
so forth.
The virtual services that are coordinated under ACTN can be split
into two categories:
. Service-aware Connectivity Services: This category includes all
the network service operations used to provide connectivity
between customer end-points while meeting policies and service
related constraints. The data model for this category would
include topology entities such as virtual nodes, virtual links,
adaptation and termination points and service-related entities
such as policies and service related constraints. (See Section
4.2.2)
. Network Function Virtualization (NFV) Services: These kinds of
service are usually set up in NFV (e.g. cloud) providers and
require connectivity between a customer site and the NFV
provider site (e.g., a data center). These NFV services may
include a security function like a firewall, a traffic
optimizer, and the provisioning of storage or computation
capacity. In these cases the customer does not care whether the
service is implemented in one data center or another. This
allows the network provider divert customer requests to the
most suitable data center. This is also known as the "end
points mobility" case (see Section 4.2.3).
The types of controller defined in the ACTN architecture are shown
in Figure 3 below and are as follows:
. CNC - Customer Network Controller
. MDSC - Multi Domain Service Coordinator
. PNC - Physical Network Controller
Figure 3 also shows the following interfaces:
. CMI - CNC-MPI Interface
. MPI - MDSC-PNC Interface
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VPN customer NW Mobile Customer ISP NW service Customer
| | |
+-------+ +-------+ +-------+
| CNC-A | | CNC-B | | CNC-C |
+-------+ +-------+ +-------+
\ | /
----------- |CMI I/F --------------
\ | /
+-----------------------+
| MDSC |
+-----------------------+
/ | \
------------- |MPI I/F -------------
/ | \
+-------+ +-------+ +-------+
| PNC | | PNC | | PNC |
+-------+ +-------+ +-------+
| GMPLS / | / \
| trigger / | / \
-------- ---- +-----+ +-----+ \
( ) ( ) | PNC | | PCE | \
- - ( Phys ) +-----+ +-----+ -----
( GMPLS ) (Netw) | / ( )
( Physical ) ---- | / ( Phys. )
( Network ) ----- ----- ( Net )
- - ( ) ( ) -----
( ) ( Phys. ) ( Phys )
-------- ( Net ) ( Net )
----- -----
Figure 3: ACTN Control Hierarchy
3.1. Customer Network Controller
A Virtual Network Service is instantiated by the Customer Network
Controller via the CNC-MDSC Interface (CMI). As the Customer Network
Controller directly interfaces to the applications, it understands
multiple application requirements and their service needs. It is
assumed that the Customer Network Controller and the MDSC have a
common knowledge of the end-point interfaces based on their business
negotiations prior to service instantiation. End-point interfaces
refer to customer-network physical interfaces that connect customer
premise equipment to network provider equipment.
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3.2. Multi Domain Service Coordinator
The Multi Domain Service Coordinator (MDSC) sits between the CNC
that issues connectivity requests and the Physical Network
Controllers (PNCs) that manage the physical network resources. The
MDSC can be collocated with the PNC, especially in those cases where
the service provider and the network provider are the same entity.
The internal system architecture and building blocks of the MDSC are
out of the scope of ACTN. Some examples can be found in the
Application Based Network Operations (ABNO) architecture [RFC7491]
and the ONF SDN architecture [ONF-ARCH].
The MDSC is the only building block of the architecture that is able
to implement all four ACTN main functions, i.e., multi domain
coordination, virtualization/abstraction, customer
mapping/translation, and virtual service coordination. The first two
functions of the MDSC, namely, multi domain coordination and
virtualization/abstraction are referred to as network
control/orchestration functions while the last two functions,
namely, customer mapping/translation and virtual service
coordination are referred to as service control/orchestration
functions.
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 CNC
A hierarchy of MDSCs can be foreseen for scalability and
administrative choices as shown in Figure 4.
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+-------+ +-------+ +-------+
| CNC-A | | CNC-B | | CNC-C |
+-------+ +-------+ +-------+
\ | /
---------- | ----------
\ | /
+-----------------------+
| MDSC |
+-----------------------+
/ | \
---------- | -----------
/ | \
+----------+ +----------+ +--------+
| MDSC | | MDSC | | MDSC |
+----------+ +----------+ +--------+
| / | / \
| / | / \
+-----+ +-----+ +-----+ +-----+ +-----+
| PNC | | PNC | | PNC | | PNC | | PNC |
+-----+ +-----+ +-----+ +-----+ +-----+
Figure 4: Controller recursiveness
In order to allow for multi-domain coordination a 1:N relationship
must be allowed between MDSCs and between MDSCs and PNCs (i.e. 1
parent MDSC and N child MDSC or 1 MDSC and N PNCs). In the case
where there is a hierarchy of MDSCs, the interface above the top
MDSC (i.e., CMI) and the interface below the bottom MDSCs (i.e.,
SBI) remain the same. The recursion of MDSCs in the middle layers
within this hierarchy of MDSCs may take place.
In addition to that, it could also be possible to have an M:1
relationship between MDSCs and PNC to allow for network resource
partitioning/sharing among different customers not necessarily
connected to the same MDSC (e.g., different service providers).
3.3. Physical Network Controller
The Physical Network Controller (PNC) is in charge of configuring
the network elements, monitoring the physical topology of the
network, and passing information about the topology (either raw or
abstracted) to the MDSC.
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The internal architecture of the PNC, its building blocks, and the
way it controls its domain are out of the scope of ACTN. Some
examples can be found in the Application Based Network Operations
(ABNO) architecture [RFC7491] and the ONF SDN architecture [ONF-
ARCH]
The PNC, in addition to being in charge of controlling the physical
network, is able to implement two of the four main ACTN main
functions: multi domain coordination and virtualization/abstraction
function.
A hierarchy of PNCs can be foreseen for scalability and
administrative choices.
3.4. ACTN Interfaces
To allow virtualization and multi domain coordination, 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 while having no impact on other customers. Direct customer
control of transport network elements and virtualized services is
not perceived as a viable proposition for transport network
providers due to security and policy concerns among other reasons.
In addition, as discussed in Section 3.3, the network control plane
for transport networks has been separated from the data plane and as
such it is not viable for the customer to directly interface with
transport network elements.
Figure 5 depicts a high-level control and interface architecture for
ACTN. A number of key ACTN interfaces exist for deployment and
operation of ACTN-based networks. These are highlighted in Figure 5
(ACTN Interfaces).
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.--------------
------------- |
| Application |--
-------------
^
| I/F A --------
v ( )
-------------- - -
| Customer | ( Customer )
| Network |--------->( Network )
| Controller | ( )
-------------- - -
^ ( )
| I/F B --------
v
--------------
| MultiDomain |
| Service |
| Coordinator| --------
-------------- ( )
^ - -
| I/F C ( Physical )
v ( Network )
--------------- ( ) --------
| |<----> - - ( )
-------------- | ( ) - -
| Physical |-- -------- ( Physical )
| Network |<---------------------->( Network )
| Controller | I/F D ( )
-------------- - -
( )
--------
Figure 5: ACTN Interfaces
The interfaces and functions are described below:
. Interface A: A north-bound interface (NBI) that communicates
the service request or application demand. A request includes
specific service properties, including service type, topology,
bandwidth, and constraint information.
. Interface B: The CNC-MDSC Interface (CMI) is an interface
between a CNC and an MDSC. It is used to request the creation
of network resources, topology or services for the
applications. Note that all service related information
conveyed via Interface A (i.e., specific service properties,
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including service type, topology, bandwidth, and constraint
information) needs to be transparently carried over this
interface. The MDSC may also report potential network topology
availability if queried for current capability from the CNC.
. Interface C: The MDSC-PNC Interface (MPI) is an interface
between an MDSC and a PNC. It communicates the creation
requests for new connectivity or for bandwidth changes in the
physical network. In multi-domain environments, the MDSC needs
to establish multiple MPIs, one for each PNC, as there is one
PNC responsible for control of each domain.
. Interface D: The provisioning interface for creating forwarding
state in the physical network, requested via the Physical
Network Controller.
The interfaces within the ACTN scope are B and C.
4. VN Creation Process
The provider can present different level of network abstraction to
the customer, spanning from one extreme (say "black") where nothing
except the Access Points (APs) is shown to the other extreme (say
"white") where an actual network topology is shown to the customer.
There are shades of "gray" in between where a number of abstract
links and nodes can be shown.
VN creation is composed of two phases: Negotiation and
Implementation.
Negotiation: In the case of gray/white topology abstraction, there
is an initial phase in which the customer agrees with the provider
on the type of topology to be shown (e.g., 10 virtual links and 5
virtual nodes) with a given interconnectivity. This is something
that is assumed to be preconfigured by the operator off-line. What
is on-line is the capability to modify/delete something (e.g., a
virtual link). In the case of "black" abstraction this negotiation
phase does not happen because there is nothing to negotiate: the
customer can only see the APs of the network.
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Implementation: In the case of black topology abstraction, the
customers can ask for connectivity with given constraints/SLA
between the APs and LSPs/tunnels created by the provider to satisfy
the request. What the customer sees is only that his CEs are
connected with a given SLA. In the case of grey/white topology the
customer creates his own LSPs accordingly to the topology that was
presented to him.
5. Access Points and Virtual Network Access Points
In order not to share unwanted topological information between the
customer domain and provider domain, a new entity is defined which
is referred to as the Access Point (AP). See the definition of AP in
Section 1.1.
A customer node will use APs as the end points for the request of
VNs as shown in Figure 6.
-------------
( )
- -
+---+ X ( ) Z +---+
|CE1|---+----( )---+---|CE2|
+---+ | ( ) | +---+
AP1 - - AP2
( )
-------------
Figure 6: APs definition customer view
Let's take as an example a scenario shown in Figure 6. CE1 is
connected to the network via a 10Gb link and CE2 via a 40Gb link.
Before the creation of any VN between AP1 and AP2 the customer view
can be summarized as shown in Table 1:
+----------+------------------------+
|End Point | Access Link Bandwidth |
+-----+----------+----------+-------------+
|AP id| CE,port | MaxResBw | AvailableBw |
+-----+----------+----------+-------------+
| AP1 |CE1,portX | 10Gb | 10Gb |
+-----+----------+----------+-------------+
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| AP2 |CE2,portZ | 40Gb | 40Gb |
+-----+----------+----------+-------------+
Table 1: AP - customer view
On the other hand, what the provider sees is shown in Figure 7.
------- -------
( ) ( )
- - - -
W (+---+ ) ( +---+) Y
-+---( |PE1| Dom.X )----( Dom.Y |PE2| )---+-
| (+---+ ) ( +---+) |
AP1 - - - - AP2
( ) ( )
------- -------
Figure 7: Provider view of the AP
Which results in a summarization as shown in Table 2.
+----------+------------------------+
|End Point | Access Link Bandwidth |
+-----+----------+----------+-------------+
|AP id| PE,port | MaxResBw | AvailableBw |
+-----+----------+----------+-------------+
| AP1 |PE1,portW | 10Gb | 10Gb |
+-----+----------+----------+-------------+
| AP2 |PE2,portY | 40Gb | 40Gb |
+-----+----------+----------+-------------+
Table 2: AP - provider view
A Virtual Network Access Point (VNAP) needs to be defined as binding
between the AP that is linked to a VN and that is used to allow for
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.
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In the simple scenario depicted above we suppose we want to create
two virtual networks. The first with VN identifier 9 between AP1 and
AP2 with bandwidth of 1Gbps, while the second with VN id 5, again
between AP1 and AP2 and with bandwidth 2Gbps.
The provider view would evolve as shown in Table 3.
+----------+------------------------+
|End Point | Access Link/VNAP Bw |
+---------+----------+----------+-------------+
|AP/VNAPid| PE,port | MaxResBw | AvailableBw |
+---------+----------+----------+-------------+
|AP1 |PE1,portW | 10Gbps | 7Gbps |
| -VNAP1.9| | 1Gbps | N.A. |
| -VNAP1.5| | 2Gbps | N.A |
+---------+----------+----------+-------------+
|AP2 |PE2,portY | 40Gbps | 37Gbps |
| -VNAP2.9| | 1Gbps | N.A. |
| -VNAP2.5| | 2Gbps | N.A |
+---------+----------+----------+-------------+
Table 3: AP and VNAP - provider view after VN creation
5.1. 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 5Gbps of
bandwidth between CE1 and CE2. This is shown in Figure 8.
____________
AP1 ( ) AP3
-------(PE1) (PE3)-------
W/ ( ) \X
+---+/ ( ) \+---+
|CE1| ( ) |CE2|
+---+\ ( ) /+---+
Y\ ( ) /Z
-------(PE2) (PE4)-------
AP2 (____________)
Figure 8: Dual homing scenario
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In this case, the customer will request for 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 end points).
The customer view would be shown in Table 4.
+----------+------------------------+
|End Point | Access Link/VNAP Bw |
+---------+----------+----------+-------------+-----------+
|AP/VNAPid| CE,port | MaxResBw | AvailableBw |Dual Homing|
+---------+----------+----------+-------------+-----------+
|AP1 |CE1,portW | 10Gbps | 5Gbps | |
| -VNAP1.9| | 5Gbps | N.A. | VNAP2.9 |
+---------+----------+----------+-------------+-----------+
|AP2 |CE1,portY | 40Gbps | 35Gbps | |
| -VNAP2.9| | 5Gbps | N.A. | VNAP1.9 |
+---------+----------+----------+-------------+-----------+
|AP3 |CE2,portX | 40Gbps | 35Gbps | |
| -VNAP3.9| | 5Gbps | N.A. | NONE |
+---------+----------+----------+-------------+-----------+
Table 4: Dual homing - customer view after VN creation
6. End Point Selection and Mobility
Virtual networks could be used as the infrastructure to connect a
number of sites belonging to a customer or to provide connectivity
between customer sites and Virtualized Network Functions (VNF) such
as virtualized firewalls, virtual Broadband Network Gateway (vBNG),
storage, or computational functions.
6.1. End Point Selection
A VNF could be deployed in different places (e.g., data centers A,
B, or C in Figure 9), but the VNF provider (that is, the ACTN
customer) doesn't know which is the best site in which to install
the VNF from a network point of view (e.g., to optimize for low
latency). For example, it is possible to compute a path minimizing
the delay between AP1 and AP2, but the customer doesn't know if the
path with minimum delay is towards DC-A, DC-B, or DC-C.
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------- -------
( ) ( )
- - - -
+---+ ( ) ( ) +----+
|CE1|---+----( Domain X )----( Domain Y )---+---|DC-A|
+---+ | ( ) ( ) | +----+
AP1 - - - - AP2
( ) ( )
---+--- ---+---
AP3 | AP4 |
+----+ +----+
|DC-B| |DC-C|
+----+ +----+
Figure 9: End point selection
In this case the VNF provider (that is, the ACTN customer) should be
allowed to ask for a VN between AP1 and a set of end points. The
list of end points is supplied by the VNF provider. When the end
point is identified the connectivity can be instantiated and a
notification can be sent to the VNF provider for the instantiation
of the VNF.
6.2. Pre-Planned End Point Migration
A premium SLA for VNF service provisioning consists of offering of a
protected VNF instantiated on two or more sites and with a hot
stand-by protection mechanism. In this case the VN should be
provided so as to switch from one end point to another upon a
trigger from the VNF provider or from an automatic failure detection
mechanism. An example is provided in Figure 10 where the request
from the VNF provider is for connectivity with resiliency between
CE1 and a VNF with primary instantiation in DC-A and a protection
instance in DC-C.
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------- -------
( ) ( )
- - __ - -
+---+ ( ) ( ) +----+
|CE1|---+----( Domain X )----( Domain Y )---+---|DC-A|
+---+ | ( ) ( ) | +----+
AP1 - - - - AP2 |
( ) ( ) |
---+--- ---+--- |
AP3 | AP4 | HOT STANDBY
+----+ |
|DC-C|<-------------
+----+
Figure 10: Preplanned endpoint migration
6.3. On the Fly End Point Migration
On the fly end point migration concept is similar to the end point
selection one. The idea is to give the provider not only the list of
sites where the VNF can be installed, but also a mechanism to notify
changes in the network that have impacts on the SLA. After an
handshake with the customer controller/applications, the bandwidth
in network would be moved accordingly with the moving of the VNFs.
7. Manageability Considerations
The objective of ACTN is to manage traffic engineered resources, and
provide a set of mechanism to allow clients to request virtual
connectivity across server network resources. ACTN will support
multiple clients each with its own view of and control of the server
network, the network operator will need to partition (or "slice")
their network resources, and manage them 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
traffic engineered resources. The management requirements may be
categorized as follows:
. Management of external ACTN protocols
. Management of internal ACTN protocols
. Management and monitoring of ACTN components
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. Configuration of policy to be applied across the ACTN system
7.1. Policy
It is expected that a policy will be an important aspect of ACTN
control and management. Typically, policies are used via the
components and interfaces, during deployment of the service, to
ensure that the service is compliant with agreed policy factors
(often described in Service Level Agreements - SLAs), these include,
but are not limited to: connectivity, bandwidth, geographical
transit, technology selection, security, resilience, and economic
cost.
Depending on the deployment the ACTN deployment 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:
. 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.
. A global policy might constrain certain customer types (or
specific customer applications) to only use certain MDSCs, and
be restricted to physical network types managed by the PNCs. A
global policy agent would govern these types of policies.
This 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.
7.2. Policy applied to the Customer Network Controller
A virtual network service for a customer application will be
requested from the CNC. It will reflect the application requirements
and specific service policy 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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7.3. Policy applied to the Multi Domain Service Coordinator
A key objective of the MDSC is to help the customer express the
application connectivity request via its CNC as set of desired
business needs, therefore policy will play an important role.
Once authorised, 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
connectivity end-points, use of these end-points should be defined
as a policy expression when setting up or augmenting virtual network
services. Ensuring that permissible end-points are defined for CNCs
and applications will require the MDSC to maintain a registry of
permissible connection points for CNCs and application types.
It may also be necessary for the MDSC to resolve policy conflicts,
or at least flag any issues to administrator of the MDSC itself.
Conflicts may occur when virtual network service optimisation
criterion 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 specific type of end-to-end
service. This type of situation may be resolved using hard and soft
policy constraints.
7.4. Policy applied to the Physical Network Controller
The PNC is responsible for configuring the network elements,
monitoring physical network resources, and exposing connectivity
(direct or abstracted) to the MDSC. It is therefore expected that
policy will dictate what connectivity information will be exported
between the PNC, via the MDSC-PNC Interface (MPI), and MDSC.
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 become 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 virtual network service performance,
security and resilience guarantees. This will likely be implemented
via a local policy agent and subsequent protocol methods.
8. Security Considerations
The ACTN framework described in this document defines key components
and interfaces for managed traffic engineered networks. Securing the
request and control of resources, confidentially 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 as
a rule implementations should consider encrypting data that flow
between components, especially when they are implemented at remote
nodes, regardless if these are external or internal network
interfaces.
The ACTN security discussion is further split into three specific
categories described in the following sub-sections:
. Interface between the Application and Customer Network
Controller (CNC)
. Interface between the Customer Network Controller and Multi
Domain Service Coordinator (MDSC), CNC-MDSC Interface (CMI)
. Interface between the Multi Domain Service Coordinator and
Physical 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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8.1. Interface between the Application and Customer Network Controller
(CNC)
This is the external interface between the application and CNC. The
application request for virtual network service connectivity may
also contain data about the application, requested network
connectivity and the service that is eventually delivered to the
customer. It is likely to use external protocols and must be
appropriately secured using session encryption.
As highlighted in the policy section (see Section 7), it may be
necessary to enable different policies based on identity, and to
manage the application requests of virtual network services. Since
access will be largely be through external protocols, and
potentially across the public Internet, AAA-based controls should
also be used.
Several additional challenges face the CNC, as the Application to
CNC interface will be used by multiple applications. These include:
. A need to verify the credibility of customer applications.
. Malicious applications may tamper with or perform unauthorized
operations, such as obtaining sensitive information, obtaining
higher rights, or request changes to existing virtual network
services.
. The ability to recognize and respond to spoofing attacks or
buffer overflow attacks will also need to be considered.
8.2. Interface between the Customer Network Controller and Multi Domain
Service Coordinator (MDSC), CNC-MDSC Interface (CMI)
The role of the MDSC is to detach the network and service control
from underlying technology to help the customer express the network
as desired by business needs. It should be noted that data stored by
the MDSC will reveal details of the virtual network services, and
which CNC and application is consuming the resource. The data stored
must therefore be considered as a candidate for encryption.
CNC Access rights to an MDSC must be managed. MDSC resources must be
properly allocated, and methods to prevent policy conflicts,
resource wastage and denial of service attacks on the MDSC by rogue
CNCs, should also be considered.
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A CNC-MDSC protocol interface will likely be an external protocol
interface. Again, suitable authentication and authorization of each
CNC connecting to the MDSC will be required, especially, as these
are likely to be implemented by different organisations 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.
8.3. Interface between the Multi Domain Service Coordinator and
Physical Network Controller (PNC), MDSC-PNC Interface (MPI)
The function of the Physical Network Controller (PNC) is to
configure network elements, provide performance and monitoring
functions of the physical elements, and export physical topology
(full, partial, or abstracted) to the MDSC.
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.
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.
9. References
9.1. Informative References
[RFC2702] Awduche, D., et. al., "Requirements for Traffic
Engineering Over MPLS", RFC 2702, September 1999.
[RFC4026] L. Andersson, T. Madsen, "Provider Provisioned Virtual
Private Network (VPN) Terminology", RFC 4026, March 2005.
[RFC4208] G. Swallow, J. Drake, H.Ishimatsu, Y. Rekhter,
"Generalized Multiprotocol Label Switching (GMPLS) User-
Network Interface (UNI): Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, October 2005.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", IETF RFC
4655, August 2006.
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[RFC5654] Niven-Jenkins, B. (Ed.), D. Brungard (Ed.), and M. Betts
(Ed.), "Requirements of an MPLS Transport Profile", RFC
5654, September 2009.
[RFC7149] Boucadair, M. and Jacquenet, C., "Software-Defined
Networking: A Perspective from within a Service Provider
Environment", RFC 7149, March 2014.
[RFC7926] A. Farrel (Ed.), "Problem Statement and Architecture for
Information Exchange between Interconnected Traffic-
Engineered Networks", RFC 7926, July 2016.
[GMPLS] Manning, E., et al., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[ONF-ARCH] Open Networking Foundation, "OpenFlow Switch
Specification Version 1.4.0 (Wire Protocol 0x05)", October
2013.
[RFC7491] King, D., and Farrel, A., "A PCE-based Architecture for
Application-based Network Operations", RFC 7491, March
2015.
10. Contributors
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Italo Bush
Huawei
Email: Italo.Busi@huawei.com
Khuzema Pithewan
Infinera
Email: kpithewan@infinera.com
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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, USA
Phone: (469)277-5838
Email: leeyoung@huawei.com
Luyuan Fang
Microsoft
Email: luyuanf@gmail.com
Diego Lopez
Telefonica I+D
Don Ramon de la Cruz, 82
28006 Madrid, Spain
Email: diego@tid.es
Sergio Belotti
Alcatel Lucent
Via Trento, 30
Vimercate, Italy
Email: sergio.belotti@nokia.com
Daniel King
Lancaster University
Email: d.king@lancaster.ac.uk
Dhruv Dhoddy
Huawei Technologies
dhruv.ietf@gmail.com
Gert Grammel
Juniper Networks
ggrammel@juniper.net
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