Network Working Group Daniele Ceccarelli
Internet Draft Ericsson
Intended status: Informational Luyuan Fang
Expires: August 2014 Microsoft
Young Lee
Huawei
Diego Lopez
Telefonica
February 14, 2014
Framework for Abstraction and Control of Transport Networks
draft-ceccarelli-actn-framework-01.txt
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Abstract
This draft provides a framework for abstraction and control of
transport networks.
Table of Contents
1. Terminology....................................................3
2. Introduction...................................................3
3. Business Model of ACTN.........................................5
3.1. Customers.................................................6
3.2. Service Providers.........................................7
3.3. Network Providers.........................................9
4. Computation Model of ACTN......................................9
4.1. Request Processing........................................9
4.2. Types of Network Resources...............................10
4.3. Accuracy of Network Resource Representation..............10
4.4. Resource Efficiency......................................10
4.5. Guarantee of Client Isolation............................10
4.6. Computing Time...........................................11
4.7. Admission Control........................................11
4.8. Path Constraints.........................................11
5. Control and Interface Model for ACTN..........................11
5.1. A High-level ACTN Control Architecture...................11
5.2. Customer Controller......................................14
5.3. Abstracted Topology......................................16
5.4. Workflows of ACTN Control Modules........................21
5.5. Programmability of the ACTN Interfaces...................23
6. Design Principles of ACTN.....................................23
6.1. Network Security.........................................23
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6.2. Privacy and Isolation....................................23
6.3. Scalability..............................................24
6.4. Manageability and Orchestration..........................24
6.5. Programmability..........................................24
6.6. Network Stability........................................24
7. References....................................................25
7.1. Informative References...................................25
8. Contributors..................................................25
Authors' Addresses...............................................26
Intellectual Property Statement..................................26
Disclaimer of Validity...........................................27
1. Terminology
This document uses the terminology defined in [RFC4655], and
[RFC5440].
CVI Customer-VNC Interface
PCA Path Computation Agent
PNC Physical Network Controller
VL Virtual Link
VN Virtual Network
VNM Virtual Network Mapping
VNC Virtual Network Controller
VNE Virtual Network Element
VNS Virtual Network Service
VPI VNC-PNC Interface
2. Introduction
Transport 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.
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Transport networks in this draft refer to a set of different type of
connection-oriented networks, primarily Connection-Oriented Circuit
Switched (CO-CS) networks and Connection-Oriented Packet Switched
(CO-PS) networks. This implies that at least the following transport
networks are in scope of the discussion of this draft: L1 optical
networks (e.g., OTN and WDM), MPLS-TP, MPLS-TE, as well as other
emerging connection-oriented networks such as Segment Routing (SR).
One of the characteristics of these network types is the ability of
dynamic provisioning and traffic engineering such that resource
guarantee can be provided to their clients.
One of the main drivers for Software Defined Networking (SDN) is a
physical separation 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
PCE [PCE] for TE-based transport networks. In fact, in transport
networks such separation of data and control plane was dictated at
the onset due to the very different natures of the data plane
(circuit switched TDM or WDM) and a packet switched control plane.
The physical separation of the control plane and the data plane is a
major step towards allowing operators to gain the full control for
optimized network design and operation. Moreover, another advantage
of SDN is its logically centralized control regime that allows a
global view of the underlying network under its control. Centralized
control in SDN helps improve network resources utilization from a
distributed network control. For TE-based transport network control,
PCE is essentially equivalent to a logically centralized control for
path computation function.
As transport networks evolve, the need to provide network
abstraction has emerged as a key requirement for operators; this
implies in effect the virtualization of network resources so that
the network is "sliced" for different uses, applications, services,
and customers each being given a different partial view of the total
topology and each considering that it is operating with or on a
single, stand-alone and consistent network.
Network virtualization, in general, refers to allowing the customers
to utilize a certain amount of network resources as if they own them
and thus control their allocated resources in a way most optimal
with higher layer or application processes. This empowerment of
customer control facilitates introduction of new services and
applications as the customers are permitted to create, modify, and
delete their virtual network services. The level of virtual control
given to the customers can vary from a tunnel connecting two end-
points to virtual network elements that consist of a set of virtual
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nodes and virtual links in a mesh network topology. 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 abstracted network
topology. Such a view may be specific to the set of consumed
services as well as to a particular customer. As the customer
controller is envisioned to support a plethora of distinct
applications, there would be another level of virtualization from
the customer to individual applications.
The virtualization framework described in this draft is named
Abstraction and Control of Transport Network (ACTN) and facilitates:
- Abstraction of the underlying network resources to higher-layer
applications and users (customers);
- Slicing infrastructure to connect multiple customers to meet
specific application and users requirements;
- A computation scheme, via an information model, to serve
various customers that request network connectivity and
properties associated with it;
- A virtual network controller that adapts customer requests to
the virtual resources (allocated to them) to the supporting
physical network control and performs the necessary mapping,
translation, isolation and security/policy enforcement, etc.;
- The coordination of the underlying transport topology,
presenting it as an abstracted topology to the customers via
open and programmable interfaces.
The organization of this draft is as follows. Section 3 provides a
discussion for a Business Model, Section 4 a Computation Model,
Section 5 a Control and Interface model and Section 6 Design
Principles.
3. Business Model of ACTN
The traditional Virtual Private Network (VPN) and Overlay Network
(ON) models are built on the premise that one single network
provider provides all virtual private or overlay networks to its
customers. This model is simple to operate but has some
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disadvantages in accommodating the increasing need for flexible and
dynamic network virtualization capabilities.
The ACTN model is built upon entities that reflect the current
landscape of network virtualization environments. There are three
key entities in the ACTN model [REF probl stat]:
- Customers
- Service Providers
- Network Providers
3.1. Customers
Within the ACTN framework, different types of customers may be taken
into account depending on the type of their resource needs, on their
number and type of access. As 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 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
service and internet access.
Advanced Customer: Advanced customers typically include enterprises,
governments and utilities. Such customers can ask for both point to
point and multipoint connectivity with high resource demand
significantly varying in time and from customer to customer. This is
one of reasons why a bundled services offer is not enough but it is
desirable to provide each of them with customized virtual network
services. As customers are geographically spread over multiple
network provider domains, the necessary control and data interfaces
to support such customer needs is no longer a single interface
between the customer and one single network provider. With this
premise, customers have to interface multiple providers to get their
end-to-end network connectivity service and the associated topology
information. Customers may have to support multiple virtual network
services with differing service objectives and QoS requirements. For
flexible and dynamic applications, customers may want to control
their allocated virtual network resources in a dynamic fashion. To
allow that, customers should be given an abstracted view of topology
on which they can perform the necessary control decisions and take
the corresponding actions.
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Customers of a given service provider can in turn offer a service to
other customers in a recursive way. An example of recursiveness with
2 service providers is shown below.
- Customer (of service B)
- Customer (of service A) & Service Provider (of service B)
- Service Provider (of service A)
- Network Provider
+-----------------------------------------------------------------------+ ---
| | ^
| Customer (of service B)| .
| +---------------------------------------------------------------+ | B
| | | | --- .
| | Customer (of service A) & Service Provider(of service B)| | ^ .
| | +--------------------------------------------------------+ | | . .
| | | | | | . .
| | | Service Provider (of service A)| | | A .
| | |+-----------------------------------------------+ | | | . .
| | || | | | | . .
| | || Network provider| | | | v v
| | |+-----------------------------------------------+ | | | ---------
| | +--------------------------------------------------------+ | |
| +---------------------------------------------------------------+ |
+-----------------------------------------------------------------------+
3.2. Service Providers
Service providers are the providers of virtual network services to
their customers. Service providers may or may not own physical
network resources. When a service provider is the same as the
network provider, this is similar to traditional VPN models. This
model works well when the customer maintains a single interface with
a single provider. When customer location spans across 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 service providers directly interface their
customers. In this case, service providers themselves are 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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Customer X -----------------------------------X
Service Provider A X -----------------------------------X
Network Provider B X-----------------X
Network Provider A X------------------X
The ACTN network model is predicated upon this three tier model and
is summarized in figure below:
+----------------------+
| customer |
+----------------------+
|
| /\ Service/Customer specific
| || Abstract Topology
| ||
+----------------------+
| VNC | E2E abstract
| Service Provider | topology creation
+----------------------+
/ | \
/ | \ Network Topology
/ | \ (raw or abstract)
/ | \
+------------------+ +------------------+ +------------------+
|Network Provider 1| |Network Provider 2| |Network Provider 3|
+------------------+ +------------------+ +------------------+
Figure 1: Three tier model.
There can be multiple types of service providers.
. Data Center providers: can be viewed as a service provider type
as they own and operate data center resources to various WAN
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clients, they can lease physical network resources from network
providers.
. Internet Service Providers (ISP): can be a service provider 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.
3.3. Network Providers
Network Providers are the infrastructure providers that own the
physical network resources and provide network resources to their
customers. The layered model proposed by this draft separates the
concerns of network providers and customers, with service providers
acting as aggregators of customer requests.
4. Computation Model of ACTN
This section discusses ACTN framework from a computational point of
view. As multiple customers run their virtualized network on a
shared infrastructure, making efficient use of the underlying
resources requires effective computational models and algorithms.
This general problem space is known as Virtual Network Mapping or
Embedding (VNM or VNE). [Editors's note(Put some reference)].
As VNM/VNE issues impose some additional compute models and
algorithms for virtual network path computation, this section
discusses key issues and constraints for virtual network path
computation.
4.1. Request Processing
This is concerned about whether a set of customer requests for VN
creation can be dealt with in real-time or off line, and in the
latter case, simultaneously or not. This depends on the nature of
applications the customer support. There are applications and use
cases, like e.g. management of catastrophic events or real time SLA
negotiation, that require a real-time VN creation. If the customer
does not require real-time instantiation of VN creation, the
computation engine can process a set of VN creation requests
simultaneously to improve network efficiency.
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4.2. Types of Network Resources
When a customer makes a VN creation request to the substrate
network, what kind of network resources is consumed is of concern of
both the customer and service/network providers. The customer needs
to put constraints (e.g. TE parameters, resiliency) for the
provisioning of the VN, while the service and network providers need
to choose which resources meet such constraints and possibly have
fewest impact on the capability of serving other customers. For
transport network virtualization, the network resource consumed is
primarily network bandwidth that the required paths would occupy on
the physical link(s). However, there may be other resource types
such as CPU and memory that need to be considered for certain
applications. These resource types shall be part of the VN request
made by the customer.
4.3. Accuracy of Network Resource Representation
As the underlying transport network in itself may consist of a
layered structure, it is a challenge how to represent these
underlying physical network resources and topology into a form that
can be reliably used by the computation engine that assigns customer
requests into the physical network resource and topology.
4.4. Resource Sharing and Efficiency
Related to the accuracy of network resource representation is
resource efficiency. As a set of independent customer VN is created
and mapped onto physical network resources, the overall network
resource utilization is the primary concern of the network provider.
In order to provide an efficient utilization of the resources of the
provider network, it should be possible to share given physical
resources among a number of different VNs. Whether a virtual
resource is sharable among a set of VNs (and hence of customers) is
something the service provider needs to agree with each customer.
Preemption and priority management are tools that could help provide
an efficient sharing of physical resources among different VNs.
4.5. Guarantee of Client Isolation
While network resource sharing across a set of customers for
efficient utilization is an important aspect of network
virtualization, customer isolation has to be guaranteed. Admissions
of new customer requests or any changes of other existing customer
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VNs must not affect any particular customer in terms of resource
guarantee, security constraints, and other performance constraints.
4.6. Computing Time
Depending on the nature of applications, how quickly a VN is
instantiated from the time of request is an important factor. For
dynamic applications that require instantaneous VN creation or VN
changes from the existing one, the computation model/algorithm
should support this constraint.
4.7. Admission Control
To coordinate the request process of multiple customers, an
admission control will help maximize an overall efficiency.
4.8. Path Constraints
There may be some factors of path constraints that can affect the
overall efficiency. Path Split can lower VN request blocking if the
underlying network can support such capability. A packet-based TE
network can support path split while circuit-based transport may
have limitations.
Path migration is a technique that allows changes of nodes or link
assignments of the established paths in an effort to accommodate new
requests that would not be accepted without such path migration(s).
This can improve overall efficiency, yet additional care needs to be
applied to avoid any adverse impacts associated with changing the
existing paths.
Re-optimization is a global process to re-shuffle all existing path
assignments to minimize network resource fragmentation. Again, an
extra care needs to be applied for re-optimization.
5. Control and Interface Model for ACTN
This section provides a high-level control and interface model of
ACTN.
5.1. A High-level ACTN Control Architecture
To allow virtualization, the network has to provide open,
programmable interfaces, in which customer applications can create,
replace and modify virtual network resources in an interactive,
flexible and dynamic fashion while having no impact on other
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customers. Direct customer control of transport network elements
over existing interfaces (control or management plane) 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 the previous section, the network control
plane for transport networks has been separated from data plane and
as such it is not viable for the customer to directly interface with
transport network elements.
While the current network control plane is well suited for control
of physical network resources via dynamic provisioning, path
computation, etc., a virtual network controller needs to be built on
top of physical network controller to support network
virtualization. On a high-level, virtual network control refers to a
mediation layer that performs several functions:
- Computation of customer resource requests into virtual network
paths based on the global network-wide abstracted topology;
- Mapping and translation of customer virtual network slices into
physical network resources;
- Creation of an abstracted view of network slices allocated to each
customer, according to customer-specific objective functions, and
to the customer traffic profile.
In order to facilitate the above-mentioned virtual control
functions, the virtual network controller (aka., "virtualizer")
needs to maintain two interfaces:
- One interface with the physical network controller functions which
is termed as the VNC-PNC Interface (VPI).
- Another interface with the customer controller for the virtual
network, which is termed as Client-VNC Interface (CVI).
Figure 2 depicts a high-level control and interface architecture for
ACTN.
------------------------------------------
| Application Layer |
------------------------------------------
/|\ /|\ /|\
| | \|/ Northbound API
| | ---------------
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| \|/ | Customer |
| --------------- Controller |
\|/ | Customer |------------
-------------- Controller | /|\
| Customer |----------- |
| Controller | /|\ |
-------------- | |
/|\ | | Customer-VNC
| | | Interface (CVI)
\|/ \|/ \|/
-----------------------------------
| Virtual Network Controller (VNC) |
-----------------------------------
/|\
| VNC-PNC Interface (VPI)
\|/
-----------------------------------
| Physical Network Controller (PNC) |
-----------------------------------
/|\
| Control Interface to NEs
\|/
Physical Network Infrastructure
Figure 2: Control and Interface Architecture for ACTN.
Figure 2 shows that there are multiple customer controllers, which
are independent to one another, and that each customer supports
various business applications over its NB API. There are layered
client-server relationships in this architecture. As various
applications are clients to the customer controller, it also becomes
itself a client to the virtual network controller. Likewise, the
virtual network controller is also a client to the physical network
controller. This layered relationship is important in the protocol
definition work on the NB API, the CVI and VPI interfaces as this
allows third-party software developers to program client controllers
and virtual network controllers independently.
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There are several ways in which the Physical Network Controller
manages the network elements, e.g. via management protocols,
PCEP+GMPLS, or any other type of protocol. In other words the ACTN
architecture both applies to physical networks controlled by control
plane protocols (e.g. PCEP+GMPLS) or management plane protocols
(e.g. SNMP).
5.2. Customer Controller
A Virtual Network Service is instantiated by the customer controller
via the CVI. As the customer controller directly interfaces the
application stratum, it understands multiple application
requirements and their service needs. It is assumed that the
customer controller and the VNC have a common knowledge on the end-
point interfaces based on their business negotiation prior to
service instantiation. End-point interfaces refer to customer-
network physical interfaces that connect customer premise equipment
to network provider equipment. Figure 5 shows an example physical
network topology that supports multiple customers. In this example,
customer A has three end-points A.1, A.2 and A.3. The interfaces
between customers and transport networks are assumed to be 40G OTU
links. For simplicity's sake, all network interfaces are assumed to
be 40G OTU links and all network ports support ODU switching and
grooming on the level of ODU1 and ODU2. Customer controller for A
provides its traffic demand matrix that describes bandwidth
requirements and other optional QoS parameters (e.g., latency,
diversity requirement, etc.) for each pair of end-point connections.
5.3. Virtual Network Controller
The virtual network controller sits between the consumer controller
(the one issuing connectivity requests) and the physical network
controller (the one managing the resources). The Virtual Network
controller can be collocated with the physical network controller,
especially in those cases where the service provider and the network
provider are the same entity.
The virtual network controller is composed by the following
functional components:
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+------------------------------------------------------------------+
| |
| Virtual +-------------+ +------------------------+ |
| Network | VNS Proxy | | Abstract Topology DB | |
| Controller +-------------+ +------------------------+ |
| |
| +-------------------+ +-------------------+ +---------------+ |
| | Resource Manager | | vConnection Agent | |VNC OAM handler| |
| +-------------------+ +-------------------+ +---------------+ |
+------------------------------------------------------------------+
. VNS proxy: The VNS proxy is the functional module in charge of
performing policy management and AAA (Authentication,
authorization, and accounting) functions. It is the one that
receives that VN instantiation and resource allocation requests
from the Customer controllers.
. Abstract Topology DB: This is the database where the abstract
topology, generated by the VNC or received from the PNC, is
stored. A different VN instance is kept for every different
customer.
. Resource Manager: The resource manager is in charge of
receiving VNS instantiation requests from the customer
controller and, as a consequence, triggering a concurrent path
computation request to the PCE in the PNC based on the traffic
matrix. The Resource manager is also in charge of generating
the abstract topology for the customer.
. vConnection Agent: This module is in charge of mapping VN setup
commands into network provisioning requests to the PNC.
. VNC OAM handler: The VNC OAM handler is the module that is in
charge of understanding how the network is operating, detecting
faults and reacting to problems related to the abstract
topology.
5.4. Physical Network Controller
The physical network controller is the one in charge of configuring
the network elements, monitoring the physical topology of the
network and passing it, either raw or abstracted, to the VNC.
It is composed by the following functional components:
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+------------------------------------------------------------------+
| |
| Physical +-----------+ +-----+ +------------------------+ |
| Network | VNC Proxy | | PCE | | Abstract Topology Gen. | |
| Controller +-----------+ +-----+ +------------------------+ |
| |
| +---------------+ +--------------------+ +--------------------+ |
| |PNC OAM Handler| |Provisioning Manager| |Physical Topology DB| |
| +---------------+ +--------------------+ +--------------------+ |
+------------------------------------------------------------------+
. VNC proxy: The VNC proxy is the functional module in charge of
performing policy management and AAA (Authentication,
authorization, and accounting) functions on requests coming
from the VNC.
. PCE: This is the stateful PCE performing the path computation
over the physical topology and that provides the vConnection
agent with the network topology.
. Abstract topology generator: the network topology can be passed
to the VNC as raw or abstract. In case the topology is passed
as abstract topology, this module is in charge of generating it
from the physical topology DB. The module is optional.
. ONC OAM handler: it verifies that connections exists,
implements monitoring functions to see if failures occurs. It
is the proxy to an OSS/NMS system but does not duplicate any of
OSS/NMS functionalities.
. Physical topology database: The physical topology database is
mainly composed by two databases: the Traffic Engineering
Database (TED) and the LSP Database (LSP-DB).
. Provisioning manager: The Provisioning Manager is responsible
for making or channeling requests for the establishment of
LSPs. This may be instructions to the control plane running in
the networks, or may involve the programming of individual
network devices. In the latter case, the Provisioning Manager
may act as an OpenFlow Controller [ONF].
5.5. Abstracted Topology
There are two levels of abstracted topology that needs to be
maintained and supported for ACTN. Customer-specific Abstracted
Topology refers to the abstracted view of network resources
allocated (shared or dedicated) to the customer. The granularity of
this abstraction varies depending on the nature of customer
applications. Figure 3 illustrates this.
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Figure 2 shows how three independent customers A, B and C provide
its respective traffic demand matrix to the VNC. The physical
network topology shown in Figure 2 is the provider's network
topology generated by the PNC topology creation engine such as the
link state database (LSDB) and Traffic Engineering DB (TEDB) based
on control plane discovery function. This topology is internal to
PNC and not available to customers. What is available to them is an
abstracted network topology (a virtual network topology) based on
the negotiated level of abstraction. This is a part of VNS
instantiation between a client control and VNC.
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+------+ +------+ +------+
A.1 ------o o-----------o o----------o o------- A.2
B.1 ------o 1 | | 2 | | 3 |
C.1 ------o o-----------o o----------o o------- B.2
+-o--o-+ +-o--o-+ +-o--o-+
| | | | | |
| | | | | |
| | | | | |
| | +-o--o-+ +-o--o-+
| `-------------o o----------o o------- B.3
| | 4 | | 5 |
`----------------o o----------o o------- C.3
+-o--o-+ +------+
| |
| |
C.2 A.3
Traffic Matrix Traffic Matrix Traffic Matrix
for Customer A for Customer B for Customer C
A.1 A.2 A.3 B.1 B.2 B.3 C.1 C.2 C.3
------------------- ------------------ -----------------
A.1 - 20G 20G B.1 - 40G 40G C.1 - 20G 20G
A.2 20G - 10G B.2 40G - 20G C.2 20G - 10G
A.3 20G 10G - B.3 40G 20G - C.3 20G 10G -
Figure 3: Physical network topology shared with multiple customers
Figure 4 depicts illustrative examples of different level of
topology abstractions that can be provided by the VNC topology
abstraction engine based on the physical topology base maintained by
the PNC. The level of topology abstraction is expressed in terms of
the number of virtual network elements (VNEs) and virtual links
(VLs). For example, the abstracted topology for customer A shows
there are 5 VNEs and 10 VLs. This is by far the most detailed
topology abstraction with a minimal link hiding compared to other
abstracted topologies in Figure 4.
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(a) Abstracted Topology for Customer A (5 VNEs and 10 VLs)
+------+ +------+ +------+
A.1 ------o o-----------o o----------o o------- A.2
| 1 | | 2 | | 3 |
| | | | | |
+-o----+ +-o----+ +-o----+
| | |
| | |
| | |
| +-o----+ +-o--o-+
| | | | |
| | 4 | | 5 |
`----------------o o----------o |
+----o-+ +------+
|
|
A.3
(b) Abstracted Topology for Customer B (3 VNEs and 6 VLs)
+------+ +------+
B.1 ------o o-----------------------------o o------ B.2
| 1 | | 3 |
| | | |
+-o----+ +-o----+
\ |
\ |
\ |
`------------------- |
` +-o----+
\ | o------ B.3
\ | 5 |
`-------o |
+------+
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(c) Abstracted Topology for Customer C (1 VNE and 3 VLs)
+-------------------------------------------+
| |
| |
C.1 ------o |
| |
| |
| |
| o--------C.3
| |
+--------------------o----------------------+
|
|
|
|
C.2
Figure 4: Topology Abstraction Examples for Customers
As different customers have different control/application needs,
abstracted topologies for customers B and C, respectively show a
much higher degree of abstraction. The level of abstraction is
determined by the policy (e.g., the granularity level) placed for
the customer and/or the path computation results by the PCE operated
by the PNC. The more granular the abstraction topology is, the more
control is given to the customer controller. If the customer
controller has applications that require more granular control of
virtual network resources, then the abstracted topology shown for
customer A may be the right abstraction level for such controller.
For instance, if the customer is a third-party virtual service
broker/provider, then it would desire much more sophisticated
control of virtual network resources to support different
application needs. On the other hand, if the customer were only to
support simple tunnel services to its applications, then the
abstracted topology shown for customer C (one VNE and three VLs)
would suffice.
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5.6. Workflows of ACTN Control Modules
Figure 5 shows workflows across the customer controller, VNC and PNC
for the VNS instantiation, topology exchange, and VNS setup.
The customer controller "owns" a VNS and initiates it by providing
the instantiation identifier with a traffic demand matrix that
includes path selection constraints for that instance. This VNS
instantiation request from the Customer Controller triggers a path
computation request by the Resource Manager in the VNC after VNC's
proxy's interlay of this request to the Resource Manager. PCA sends
a concurrent path computation request that is converted according to
the traffic demand matrix as part of the VNS instantiation request
from the Customer Controller. Upon receipt of this path computation
request, the PCE in the PNC block computes paths and updates network
topology DB and informs the Resource Manager of the VNC of the paths
and topology updates.
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------------------------------------------------------------------
| Customer ----------------------------------------------- |
| Controller | VNS Control | |
| ----------------------------------------------- |
------------------------------------------------------------------
1.VNS | /|\ 4. Abstracted | /|\
Instantiation | | Topology | |
(instance id, | | | |
Traffic Matr.) | | | | 8. VNS
| | 5. VNS | | Set-up
\|/ | Set-up \|/ | Confirm
------------------------------------------------------------------
| Virtual ----------------------------------------------- |
| Network | VNS Proxy | |
| Controller ----------------------------------------------- |
| ----------------------- ----------------------- |
| |Path Computation Agent | | vConnection Agent | |
| ----------------------- ----------------------- |
------------------------------------------------------------------
2. Path | /|\ 3. PC Reply | /|\
Computation | | with updated | |
Request | | topology | |
| | 6. Network | |8.Network
| | Provisioning | |Provisioning
\|/ | Request \|/ |Confirm
------------------------------------------------------------------
| Physical ------------- -------------------------- |
| Network | PCE | | Network Provisioning ||
| Controller ------------- -------------------------- |
------------------------------------------------------------------
Figure 5. Workflows across Customer Controller, VNC and PNC
It is assumed that the PCE in PNC is a stateful PCE [PCE-S]. PCA
abstracts the physical network topology into an abstracted topology
for the customer based on the agreed-upon granularity level. The
abstracted topology is then passed to the VNS control of the
Customer Controller. This controller computes and assigns virtual
network resources for its applications based on the abstracted
topology and creates VNS setup command to the VNC. The VNC
vConnection module turns this VN setup command into network
provisioning requests over the network elements.
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5.7. Programmability of the ACTN Interfaces
From Figures 2 and 5, we have identified several interfaces that are
of interest of the ACTN model. More precisely, ACTN concerns the
following interfaces:
- Customer-VNC Interface (CVI): an interface between a customer
controller and a virtual network controller.
- VNC-PNC Interface (VPI): an interface between a virtual network
controller and a physical network controller.
The NBI interfaces and direct control interfaces to NEs are outside
of the scope of ACTN.
The CVI interface should allow programmability, first of all, to the
customer so they can create, modify and delete virtual network
service instances. This interface should also support open standard
information and data models that can transport abstracted topology.
The VPI interface should allow programmability to service
provider(s) (through VNCs) in such ways that control functions such
as path computation, provisioning, and restoration can be
facilitated. Seamless mapping and translation between physical
resources and virtual resources should also be facilitated via this
interface.
6. Design Principles of ACTN
6.1. Network Security
Network security concerns are always one of the primary principles
of any network design. ACTN is no exception. Due to the nature of
heterogeneous VNs that are to be created, maintained and deleted
flexibly and dynamically and the anticipated interaction with
physical network control components, secure programming models and
interfaces have to be available beyond secured tunnels, encryption
and other network security tools.
6.2. Privacy and Isolation
As physical network resources are shared with and controlled by
multiple independent customers, isolation and privacy for each
customer has to be guaranteed.
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Policy should be applied per client.
6.3. Scalability
As multiple VNs need to be supported seamlessly, there are
potentially several scaling issues associated with ACTN. The VN
Controller system should be scalable in supporting multiple parallel
computation requests from multiple customers. New VN request should
not affect the control and maintenance of the existing VNs. Any VN
request should also be satisfied within a time-bound of the customer
application request.
Interfaces should also be scalable as a large amount of data needs
to be transported across customers to virtual network controllers
and across virtual network controllers and physical network
controllers.
6.4. Manageability and Orchestration
As there are multiple entities participating in network
virtualization, seamless manageability has to be provided across
every layer of network virtualization. Orchestration is an important
aspect of manageability as the ACTN design should allow
orchestration capability.
ACTN orchestration should encompass network provider multi-domains,
relationships between service provider(s) and network provider(s),
and relationships between customers and service/network providers.
Ease of deploying end-to-end virtual network services across
heterogeneous network environments is a challenge.
6.5. Programmability
As discussed earlier in Section 5.5, the ACTN interfaces should
support open standard interfaces to allow flexible and dynamic
virtual service creation environments.
6.6. Network Stability
As multiple VNs are envisioned to share the same physical network
resources, combining many resources into one should not cause any
network instability. Provider network oscillation can affect readily
both on virtual networks and the end-users.
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Part of network instability can be caused when virtual network
mapping is done on an inaccurate or unreliable resource data. Data
base synchronization is one of the key issues that need to be
ensured in ACTN design.
7. References
7.1. Informative References
[PCE] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", IETF RFC
4655, August 2006.
[PCE-S] Crabbe, E, et. al., "PCEP extension for stateful
PCE",draft-ietf-pce-stateful-pce, work in progress.
[GMPLS] Manning, E., et al., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.
[NFV-AF] "Network Functions Virtualization (NFV); Architectural
Framework", ETSI GS NFV 002 v1.1.1, October 2013.
8. Contributors
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Authors' Addresses
Daniele Ceccarelli
Ericsson
Via Melen, 77
Genova, Italy
Email: daniele.ceccarelli@ericsson.com
Luyuan Fang
Email: luyuanf@gmail.com
Young Lee
Huawei Technologies
5340 Legacy Drive
Plano, TX 75023, USA
Phone: (469)277-5838
Email: leeyoung@huawei.com
Diego Lopez
Telefonica I+D
Don Ramon de la Cruz, 82
28006 Madrid, Spain
Email: diego@tid.es
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