💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc7491.txt captured on 2024-06-16 at 15:33:11.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Internet Engineering Task Force (IETF) D. King
Request for Comments: 7491 Old Dog Consulting
Category: Informational A. Farrel
ISSN: 2070-1721 Juniper Networks
March 2015
A PCE-Based Architecture for Application-Based Network Operations
Abstract
Services such as content distribution, distributed databases, or
inter-data center connectivity place a set of new requirements on the
operation of networks. They need on-demand and application-specific
reservation of network connectivity, reliability, and resources (such
as bandwidth) in a variety of network applications (such as point-to-
point connectivity, network virtualization, or mobile back-haul) and
in a range of network technologies from packet (IP/MPLS) down to
optical. An environment that operates to meet these types of
requirements is said to have Application-Based Network Operations
(ABNO). ABNO brings together many existing technologies and may be
seen as the use of a toolbox of existing components enhanced with a
few new elements.
This document describes an architecture and framework for ABNO,
showing how these components fit together. It provides a cookbook of
existing technologies to satisfy the architecture and meet the needs
of the applications.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7491.
King & Farrel Informational [Page 1]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
King & Farrel Informational [Page 2]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Table of Contents
1. Introduction ....................................................4
1.1. Scope ......................................................5
2. Application-Based Network Operations (ABNO) .....................6
2.1. Assumptions ................................................6
2.2. Implementation of the Architecture .........................6
2.3. Generic ABNO Architecture ..................................7
2.3.1. ABNO Components .....................................8
2.3.2. Functional Interfaces ..............................15
3. ABNO Use Cases .................................................24
3.1. Inter-AS Connectivity .....................................24
3.2. Multi-Layer Networking ....................................30
3.2.1. Data Center Interconnection across
Multi-Layer Networks ...............................34
3.3. Make-before-Break .........................................37
3.3.1. Make-before-Break for Reoptimization ...............37
3.3.2. Make-before-Break for Restoration ..................38
3.3.3. Make-before-Break for Path Test and Selection ......40
3.4. Global Concurrent Optimization ............................42
3.4.1. Use Case: GCO with MPLS LSPs .......................43
3.5. Adaptive Network Management (ANM) .........................45
3.5.1. ANM Trigger ........................................46
3.5.2. Processing Request and GCO Computation .............46
3.5.3. Automated Provisioning Process .....................47
3.6. Pseudowire Operations and Management ......................48
3.6.1. Multi-Segment Pseudowires ..........................48
3.6.2. Path-Diverse Pseudowires ...........................50
3.6.3. Path-Diverse Multi-Segment Pseudowires .............51
3.6.4. Pseudowire Segment Protection ......................52
3.6.5. Applicability of ABNO to Pseudowires ...............52
3.7. Cross-Stratum Optimization (CSO) ..........................53
3.7.1. Data Center Network Operation ......................53
3.7.2. Application of the ABNO Architecture ...............56
3.8. ALTO Server ...............................................58
3.9. Other Potential Use Cases .................................61
3.9.1. Traffic Grooming and Regrooming ....................61
3.9.2. Bandwidth Scheduling ...............................62
4. Survivability and Redundancy within the ABNO Architecture ......62
5. Security Considerations ........................................63
6. Manageability Considerations ...................................63
7. Informative References .........................................64
Appendix A. Undefined Interfaces ..................................69
Acknowledgements ..................................................70
Contributors ......................................................71
Authors' Addresses ................................................71
King & Farrel Informational [Page 3]
RFC 7491 PCE-Based Architecture for ABNO March 2015
1. Introduction
Networks today integrate multiple technologies allowing network
infrastructure to deliver a variety of services to support the
different characteristics and demands of applications. There is an
increasing demand to make the network responsive to service requests
issued directly from the application layer. This differs from the
established model where services in the network are delivered in
response to management commands driven by a human user.
These application-driven requests and the services they establish
place a set of new requirements on the operation of networks. They
need on-demand and application-specific reservation of network
connectivity, reliability, and resources (such as bandwidth) in a
variety of network applications (such as point-to-point connectivity,
network virtualization, or mobile back-haul) and in a range of
network technologies from packet (IP/MPLS) down to optical. An
environment that operates to meet this type of application-aware
requirement is said to have Application-Based Network Operations
(ABNO).
The Path Computation Element (PCE) [RFC4655] was developed to provide
path computation services for GMPLS- and MPLS-controlled networks.
The applicability of PCEs can be extended to provide path computation
and policy enforcement capabilities for ABNO platforms and services.
ABNO can provide the following types of service to applications by
coordinating the components that operate and manage the network:
- Optimization of traffic flows between applications to create an
overlay network for communication in use cases such as file
sharing, data caching or mirroring, media streaming, or real-time
communications described as Application-Layer Traffic Optimization
(ALTO) [RFC5693].
- Remote control of network components allowing coordinated
programming of network resources through such techniques as
Forwarding and Control Element Separation (ForCES) [RFC3746],
OpenFlow [ONF], and the Interface to the Routing System (I2RS)
[I2RS-Arch], or through the control plane coordinated through the
PCE Communication Protocol (PCEP) [PCE-Init-LSP].
- Interconnection of Content Delivery Networks (CDNi) [RFC6707]
through the establishment and resizing of connections between
content distribution networks. Similarly, ABNO can coordinate
inter-data center connections.
King & Farrel Informational [Page 4]
RFC 7491 PCE-Based Architecture for ABNO March 2015
- Network resource coordination to automate provisioning, and to
facilitate traffic grooming and regrooming, bandwidth scheduling,
and Global Concurrent Optimization using PCEP [RFC5557].
- Virtual Private Network (VPN) planning in support of deployment of
new VPN customers and to facilitate inter-data center connectivity.
This document outlines the architecture and use cases for ABNO, and
shows how the ABNO architecture can be used for coordinating control
system and application requests to compute paths, enforce policies,
and manage network resources for the benefit of the applications that
use the network. The examination of the use cases shows the ABNO
architecture as a toolkit comprising many existing components and
protocols, and so this document looks like a cookbook. ABNO is
compatible with pre-existing Network Management System (NMS) and
Operations Support System (OSS) deployments as well as with more
recent developments in programmatic networks such as Software-Defined
Networking (SDN).
1.1. Scope
This document describes a toolkit. It shows how existing functional
components described in a large number of separate documents can be
brought together within a single architecture to provide the function
necessary for ABNO.
In many cases, existing protocols are known to be good enough or
almost good enough to satisfy the requirements of interfaces between
the components. In these cases, the protocols are called out as
suitable candidates for use within an implementation of ABNO.
In other cases, it is clear that further work will be required, and
in those cases a pointer to ongoing work that may be of use is
provided. Where there is no current work that can be identified by
the authors, a short description of the missing interface protocol is
given in Appendix A.
Thus, this document may be seen as providing an applicability
statement for existing protocols, and guidance for developers of new
protocols or protocol extensions.
King & Farrel Informational [Page 5]
RFC 7491 PCE-Based Architecture for ABNO March 2015
2. Application-Based Network Operations (ABNO)
2.1. Assumptions
The principal assumption underlying this document is that existing
technologies should be used where they are adequate for the task.
Furthermore, when an existing technology is almost sufficient, it is
assumed to be preferable to make minor extensions rather than to
invent a whole new technology.
Note that this document describes an architecture. Functional
components are architectural concepts and have distinct and clear
responsibilities. Pairs of functional components interact over
functional interfaces that are, themselves, architectural concepts.
2.2. Implementation of the Architecture
It needs to be strongly emphasized that this document describes a
functional architecture. It is not a software design. Thus, it is
not intended that this architecture constrain implementations.
However, the separation of the ABNO functions into separate
functional components with clear interfaces between them enables
implementations to choose which features to include and allows
different functions to be distributed across distinct processes or
even processors.
An implementation of this architecture may make several important
decisions about the functional components:
- Multiple functional components may be grouped together into one
software component such that all of the functions are bundled and
only the external interfaces are exposed. This may have distinct
advantages for fast paths within the software and can reduce
interprocess communication overhead.
For example, an Active, Stateful PCE could be implemented as a
single server combining the ABNO components of the PCE, the Traffic
Engineering Database, the Label Switched Path Database, and the
Provisioning Manager (see Section 2.3).
- The functional components could be distributed across separate
processes, processors, or servers so that the interfaces are
exposed as external protocols.
King & Farrel Informational [Page 6]
RFC 7491 PCE-Based Architecture for ABNO March 2015
For example, the Operations, Administration, and Maintenance (OAM)
Handler (see Section 2.3.1.6) could be presented on a dedicated
server in the network that consumes all status reports from the
network, aggregates them, correlates them, and then dispatches
notifications to other servers that need to understand what has
happened.
- There could be multiple instances of any or each of the components.
That is, the function of a functional component could be
partitioned across multiple software components with each
responsible for handling a specific feature or a partition of the
network.
For example, there may be multiple Traffic Engineering Databases
(see Section 2.3.1.8) in an implementation, with each holding the
topology information of a separate network domain (such as a
network layer or an Autonomous System). Similarly, there could be
multiple PCE instances, each processing a different Traffic
Engineering Database, and potentially distributed on different
servers under different management control. As a final example,
there could be multiple ABNO Controllers, each with capability to
support different classes of application or application service.
The purpose of the description of this architecture is to facilitate
different implementations while offering interoperability between
implementations of key components, and easy interaction with the
applications and with the network devices.
2.3. Generic ABNO Architecture
Figure 1 illustrates the ABNO architecture. The components and
functional interfaces are discussed in Sections 2.3.1 and 2.3.2,
respectively. The use cases described in Section 3 show how
different components are used selectively to provide different
services. It is important to understand that the relationships and
interfaces shown between components in this figure are illustrative
of some of the common or likely interactions; however, this figure
does not preclude other interfaces and relationships as necessary to
realize specific functionality.
King & Farrel Informational [Page 7]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+----------------------------------------------------------------+
| OSS / NMS / Application Service Coordinator |
+-+---+---+----+-----------+---------------------------------+---+
| | | | | |
...|...|...|....|...........|.................................|......
: | | | | +----+----------------------+ | :
: | | | +--+---+ | | +---+---+ :
: | | | |Policy+--+ ABNO Controller +------+ | :
: | | | |Agent | | +--+ | OAM | :
: | | | +-+--+-+ +-+------------+----------+-+ | |Handler| :
: | | | | | | | | | | | :
: | | +-+---++ | +----+-+ +-------+-------+ | | +---+---+ :
: | | |ALTO | +-+ VNTM |--+ | | | | :
: | | |Server| +--+-+-+ | | | +--+---+ | :
: | | +--+---+ | | | PCE | | | I2RS | | :
: | | | +-------+ | | | | |Client| | :
: | | | | | | | | +-+--+-+ | :
: | +-+----+--+-+ | | | | | | | :
: | | Databases +-------:----+ | | | | | :
: | | TED | | +-+---+----+----+ | | | | :
: | | LSP-DB | | | | | | | | | :
: | +-----+--+--+ +-+---------------+-------+-+ | | | :
: | | | | Provisioning Manager | | | | :
: | | | +-----------------+---+-----+ | | | :
...|.......|..|.................|...|....|...|.......|..|.....|......
| | | | | | | | | |
| +-+--+-----------------+--------+-----------+----+ |
+----/ Client Network Layer \--+
| +----------------------------------------------------+ |
| | | | | |
++------+-------------------------+--------+----------+-----+-+
/ Server Network Layers \
+-----------------------------------------------------------------+
Figure 1: Generic ABNO Architecture
2.3.1. ABNO Components
This section describes the functional components shown as boxes in
Figure 1. The interactions between those components, the functional
interfaces, are described in Section 2.3.2.
King & Farrel Informational [Page 8]
RFC 7491 PCE-Based Architecture for ABNO March 2015
2.3.1.1. NMS and OSS
A Network Management System (NMS) or an Operations Support System
(OSS) can be used to control, operate, and manage a network. Within
the ABNO architecture, an NMS or OSS may issue high-level service
requests to the ABNO Controller. It may also establish policies for
the activities of the components within the architecture.
The NMS and OSS can be consumers of network events reported through
the OAM Handler and can act on these reports as well as displaying
them to users and raising alarms. The NMS and OSS can also access
the Traffic Engineering Database (TED) and Label Switched Path
Database (LSP-DB) to show the users the current state of the network.
Lastly, the NMS and OSS may utilize a direct programmatic or
configuration interface to interact with the network elements within
the network.
2.3.1.2. Application Service Coordinator
In addition to the NMS and OSS, services in the ABNO architecture may
be requested by or on behalf of applications. In this context, the
term "application" is very broad. An application may be a program
that runs on a host or server and that provides services to a user,
such as a video conferencing application. Alternatively, an
application may be a software tool that a user uses to make requests
to the network to set up specific services such as end-to-end
connections or scheduled bandwidth reservations. Finally, an
application may be a sophisticated control system that is responsible
for arranging the provision of a more complex network service such as
a virtual private network.
For the sake of this architecture, all of these concepts of an
application are grouped together and are shown as the Application
Service Coordinator, since they are all in some way responsible for
coordinating the activity of the network to provide services for use
by applications. In practice, the function of the Application
Service Coordinator may be distributed across multiple applications
or servers.
The Application Service Coordinator communicates with the ABNO
Controller to request operations on the network.
King & Farrel Informational [Page 9]
RFC 7491 PCE-Based Architecture for ABNO March 2015
2.3.1.3. ABNO Controller
The ABNO Controller is the main gateway to the network for the NMS,
OSS, and Application Service Coordinator for the provision of
advanced network coordination and functions. The ABNO Controller
governs the behavior of the network in response to changing network
conditions and in accordance with application network requirements
and policies. It is the point of attachment, and it invokes the
right components in the right order.
The use cases in Section 3 provide a clearer picture of how the ABNO
Controller interacts with the other components in the ABNO
architecture.
2.3.1.4. Policy Agent
Policy plays a very important role in the control and management of
the network. It is, therefore, significant in influencing how the
key components of the ABNO architecture operate.
Figure 1 shows the Policy Agent as a component that is configured by
the NMS/OSS with the policies that it applies. The Policy Agent is
responsible for propagating those policies into the other components
of the system.
Simplicity in the figure necessitates leaving out many of the policy
interactions that will take place. Although the Policy Agent is only
shown interacting with the ABNO Controller, the ALTO Server, and the
Virtual Network Topology Manager (VNTM), it will also interact with a
number of other components and the network elements themselves. For
example, the Path Computation Element (PCE) will be a Policy
Enforcement Point (PEP) [RFC2753] as described in [RFC5394], and the
Interface to the Routing System (I2RS) Client will also be a PEP as
noted in [I2RS-Arch].
2.3.1.5. Interface to the Routing System (I2RS) Client
The Interface to the Routing System (I2RS) is described in
[I2RS-Arch]. The interface provides a programmatic way to access
(for read and write) the routing state and policy information on
routers in the network.
The I2RS Client is introduced in [I2RS-PS]. Its purpose is to manage
information requests across a number of routers (each of which runs
an I2RS Agent) and coordinate setting or gathering state to/from
those routers.
King & Farrel Informational [Page 10]
RFC 7491 PCE-Based Architecture for ABNO March 2015
2.3.1.6. OAM Handler
Operations, Administration, and Maintenance (OAM) plays a critical
role in understanding how a network is operating, detecting faults,
and taking the necessary action to react to problems in the network.
Within the ABNO architecture, the OAM Handler is responsible for
receiving notifications (often called alerts) from the network about
potential problems, for correlating them, and for triggering other
components of the system to take action to preserve or recover the
services that were established by the ABNO Controller. The OAM
Handler also reports network problems and, in particular, service-
affecting problems to the NMS, OSS, and Application Service
Coordinator.
Additionally, the OAM Handler interacts with the devices in the
network to initiate OAM actions within the data plane, such as
monitoring and testing.
2.3.1.7. Path Computation Element (PCE)
PCE is introduced in [RFC4655]. It is a functional component that
services requests to compute paths across a network graph. In
particular, it can generate traffic-engineered routes for MPLS-TE and
GMPLS Label Switched Paths (LSPs). The PCE may receive these
requests from the ABNO Controller, from the Virtual Network Topology
Manager, or from network elements themselves.
The PCE operates on a view of the network topology stored in the
Traffic Engineering Database (TED). A more sophisticated computation
may be provided by a Stateful PCE that enhances the TED with a
database (the LSP-DB -- see Section 2.3.1.8.2) containing information
about the LSPs that are provisioned and operational within the
network as described in [RFC4655] and [Stateful-PCE].
Additional functionality in an Active PCE allows a functional
component that includes a Stateful PCE to make provisioning requests
to set up new services or to modify in-place services as described in
[Stateful-PCE] and [PCE-Init-LSP]. This function may directly access
the network elements or may be channeled through the Provisioning
Manager.
Coordination between multiple PCEs operating on different TEDs can
prove useful for performing path computation in multi-domain or
multi-layer networks. A domain in this case might be an Autonomous
System (AS), thus enabling inter-AS path computation.
King & Farrel Informational [Page 11]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Since the PCE is a key component of the ABNO architecture, a better
view of its role can be gained by examining the use cases described
in Section 3.
2.3.1.8. Databases
The ABNO architecture includes a number of databases that contain
information stored for use by the system. The two main databases are
the TED and the LSP Database (LSP-DB), but there may be a number of
other databases used to contain information about topology (ALTO
Server), policy (Policy Agent), services (ABNO Controller), etc.
In the text that follows, specific key components that are consumers
of the databases are highlighted. It should be noted that the
databases are available for inspection by any of the ABNO components.
Updates to the databases should be handled with some care, since
allowing multiple components to write to a database can be the cause
of a number of contention and sequencing problems.
2.3.1.8.1. Traffic Engineering Database (TED)
The TED is a data store of topology information about a network that
may be enhanced with capability data (such as metrics or bandwidth
capacity) and active status information (such as up/down status or
residual unreserved bandwidth).
The TED may be built from information supplied by the network or from
data (such as inventory details) sourced through the NMS/OSS.
The principal use of the TED in the ABNO architecture is to provide
the raw data on which the Path Computation Element operates. But the
TED may also be inspected by users at the NMS/OSS to view the current
status of the network and may provide information to application
services such as Application-Layer Traffic Optimization (ALTO)
[RFC5693].
2.3.1.8.2. LSP Database
The LSP-DB is a data store of information about LSPs that have been
set up in the network or that could be established. The information
stored includes the paths and resource usage of the LSPs.
The LSP-DB may be built from information generated locally. For
example, when LSPs are provisioned, the LSP-DB can be updated. The
database can also be constructed from information gathered from the
network by polling or reading the state of LSPs that have already
been set up.
King & Farrel Informational [Page 12]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The main use of the LSP-DB within the ABNO architecture is to enhance
the planning and optimization of LSPs. New LSPs can be established
to be path-disjoint from other LSPs in order to offer protected
services; LSPs can be rerouted in order to put them on more optimal
paths or to make network resources available for other LSPs; LSPs can
be rapidly repaired when a network failure is reported; LSPs can be
moved onto other paths in order to avoid resources that have planned
maintenance outages. A Stateful PCE (see Section 2.3.1.7) is a
primary consumer of the LSP-DB.
2.3.1.8.3. Shared Risk Link Group (SRLG) Databases
The TED may, itself, be supplemented by SRLG information that assigns
to each network resource one or more identifiers that associate the
resource with other resources in the same TED that share the same
risk of failure.
While this information can be highly useful, it may be supplemented
by additional detailed information maintained in a separate database
and indexed using the SRLG identifier from the TED. Such a database
can interpret SRLG information provided by other networks (such as
server networks), can provide failure probabilities associated with
each SRLG, can offer prioritization when SRLG-disjoint paths cannot
be found, and can correlate SRLGs between different server networks
or between different peer networks.
2.3.1.8.4. Other Databases
There may be other databases that are built within the ABNO system
and that are referenced when operating the network. These databases
might include information about, for example, traffic flows and
demands, predicted or scheduled traffic demands, link and node
failure and repair history, network resources such as packet labels
and physical labels (i.e., MPLS and GMPLS labels), etc.
As mentioned in Section 2.3.1.8.1, the TED may be enhanced by
inventory information. It is quite likely in many networks that such
an inventory is held in a separate database (the Inventory Database)
that includes details of the manufacturer, model, installation date,
etc.
2.3.1.9. ALTO Server
The ALTO Server provides network information to the application layer
based on abstract maps of a network region. This information
provides a simplified view, but it is useful to steer application-
layer traffic. ALTO services enable service providers to share
information about network locations and the costs of paths between
King & Farrel Informational [Page 13]
RFC 7491 PCE-Based Architecture for ABNO March 2015
them. The selection criteria to choose between two locations may
depend on information such as maximum bandwidth, minimum cross-domain
traffic, lower cost to the user, etc.
The ALTO Server generates ALTO views to share information with the
Application Service Coordinator so that it can better select paths in
the network to carry application-layer traffic. The ALTO views are
computed based on information from the network databases, from
policies configured by the Policy Agent, and through the algorithms
used by the PCE.
Specifically, the base ALTO protocol [RFC7285] defines a single-node
abstract view of a network to the Application Service Coordinator.
Such a view consists of two maps: a network map and a cost map. A
network map defines multiple Provider-defined Identifiers (PIDs),
which represent entrance points to the network. Each node in the
application layer is known as an End Point (EP), and each EP is
assigned to a PID, because PIDs are the entry points of the
application in the network. As defined in [RFC7285], a PID can
denote a subnet, a set of subnets, a metropolitan area, a Point of
Presence (PoP), etc. Each such network region can be a single domain
or multiple networks; it is just the view that the ALTO Server is
exposing to the application layer. A cost map provides costs between
EPs and/or PIDs. The criteria that the Application Service
Coordinator uses to choose application routes between two locations
may depend on attributes such as maximum bandwidth, minimum cross-
domain traffic, lower cost to the user, etc.
2.3.1.10. Virtual Network Topology Manager (VNTM)
A Virtual Network Topology (VNT) is defined in [RFC5212] as a set of
one or more LSPs in one or more lower-layer networks that provides
information for efficient path handling in an upper-layer network.
For instance, a set of LSPs in a wavelength division multiplexed
(WDM) network can provide connectivity as virtual links in a higher-
layer packet-switched network.
The VNT enhances the physical/dedicated links that are available in
the upper-layer network and is configured by setting up or tearing
down the lower-layer LSPs and by advertising the changes into the
higher-layer network. The VNT can be adapted to traffic demands so
that capacity in the higher-layer network can be created or released
as needed. Releasing unwanted VNT resources makes them available in
the lower-layer network for other uses.
King & Farrel Informational [Page 14]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The creation of virtual topology for inclusion in a network is not a
simple task. Decisions must be made about which nodes in the upper
layer it is best to connect, in which lower-layer network to
provision LSPs to provide the connectivity, and how to route the LSPs
in the lower-layer network. Furthermore, some specific actions have
to be taken to cause the lower-layer LSPs to be provisioned and the
connectivity in the upper-layer network to be advertised.
[RFC5623] describes how the VNTM may instantiate connections in the
server layer in support of connectivity in the client layer. Within
the ABNO architecture, the creation of new connections may be
delegated to the Provisioning Manager as discussed in
Section 2.3.1.11.
All of these actions and decisions are heavily influenced by policy,
so the VNTM component that coordinates them takes input from the
Policy Agent. The VNTM is also closely associated with the PCE for
the upper-layer network and each of the PCEs for the lower-layer
networks.
2.3.1.11. 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].
See Section 2.3.2.6 for more details of the interactions between the
Provisioning Manager and the network.
2.3.1.12. Client and Server Network Layers
The client and server networks are shown in Figure 1 as illustrative
examples of the fact that the ABNO architecture may be used to
coordinate services across multiple networks where lower-layer
networks provide connectivity in upper-layer networks.
Section 3.2 describes a set of use cases for multi-layer networking.
2.3.2. Functional Interfaces
This section describes the interfaces between functional components
that might be externalized in an implementation allowing the
components to be distributed across platforms. Where existing
protocols might provide all or most of the necessary capabilities,
they are noted. Appendix A notes the interfaces where more protocol
specification may be needed.
King & Farrel Informational [Page 15]
RFC 7491 PCE-Based Architecture for ABNO March 2015
As noted at the top of Section 2.3, it is important to understand
that the relationships and interfaces shown between components in
Figure 1 are illustrative of some of the common or likely
interactions; however, this figure and the descriptions in the
subsections below do not preclude other interfaces and relationships
as necessary to realize specific functionality. Thus, some of the
interfaces described below might not be visible as specific
relationships in Figure 1, but they can nevertheless exist.
2.3.2.1. Configuration and Programmatic Interfaces
The network devices may be configured or programmed directly from the
NMS/OSS. Many protocols already exist to perform these functions,
including the following:
- SNMP [RFC3412]
- The Network Configuration Protocol (NETCONF) [RFC6241]
- RESTCONF [RESTCONF]
- The General Switch Management Protocol (GSMP) [RFC3292]
- ForCES [RFC5810]
- OpenFlow [ONF]
- PCEP [PCE-Init-LSP]
The TeleManagement Forum (TMF) Multi-Technology Operations Systems
Interface (MTOSI) standard [TMF-MTOSI] was developed to facilitate
application-to-application interworking and provides network-level
management capabilities to discover, configure, and activate
resources. Initially, the MTOSI information model was only capable
of representing connection-oriented networks and resources. In later
releases, support was added for connectionless networks. MTOSI is,
from the NMS perspective, a north-bound interface and is based on
SOAP web services.
From the ABNO perspective, network configuration is a pass-through
function. It can be seen represented on the left-hand side of
Figure 1.
2.3.2.2. TED Construction from the Networks
As described in Section 2.3.1.8, the TED provides details of the
capabilities and state of the network for use by the ABNO system and
the PCE in particular.
King & Farrel Informational [Page 16]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The TED can be constructed by participating in the IGP-TE protocols
run by the networks (for example, OSPF-TE [RFC3630] and IS-IS TE
[RFC5305]). Alternatively, the TED may be fed using link-state
distribution extensions to BGP [BGP-LS].
The ABNO system may maintain a single TED unified across multiple
networks or may retain a separate TED for each network.
Additionally, an ALTO Server [RFC5693] may provide an abstracted
topology from a network to build an application-level TED that can be
used by a PCE to compute paths between servers and application-layer
entities for the provision of application services.
2.3.2.3. TED Enhancement
The TED may be enhanced by inventory information supplied from the
NMS/OSS. This may supplement the data collected as described in
Section 2.3.2.2 with information that is not normally distributed
within the network, such as node types and capabilities, or the
characteristics of optical links.
No protocol is currently identified for this interface, but the
protocol developed or adopted to satisfy the requirements of the
Interface to the Routing System (I2RS) [I2RS-Arch] may be a suitable
candidate because it is required to be able to distribute bulk
routing state information in a well-defined encoding language.
Another candidate protocol may be NETCONF [RFC6241] passing data
encoded using YANG [RFC6020].
Note that, in general, any combination of protocol and encoding that
is suitable for presenting the TED as described in Section 2.3.2.4
will likely be suitable (or could be made suitable) for enabling
write-access to the TED as described in this section.
2.3.2.4. TED Presentation
The TED may be presented north-bound from the ABNO system for use by
an NMS/OSS or by the Application Service Coordinator. This allows
users and applications to get a view of the network topology and the
status of the network resources. It also allows planning and
provisioning of application services.
There are several protocols available for exporting the TED north-
bound:
- The ALTO protocol [RFC7285] is designed to distribute the
abstracted topology used by an ALTO Server and may prove useful for
exporting the TED. The ALTO Server provides the cost between EPs
King & Farrel Informational [Page 17]
RFC 7491 PCE-Based Architecture for ABNO March 2015
or between PIDs, so the application layer can select which is the
most appropriate connection for the information exchange between
its application end points.
- The same protocol used to export topology information from the
network can be used to export the topology from the TED [BGP-LS].
- The I2RS [I2RS-Arch] will require a protocol that is capable of
handling bulk routing information exchanges that would be suitable
for exporting the TED. In this case, it would make sense to have a
standardized representation of the TED in a formal data modeling
language such as YANG [RFC6020] so that an existing protocol such
as NETCONF [RFC6241] or the Extensible Messaging and Presence
Protocol (XMPP) [RFC6120] could be used.
Note that export from the TED can be a full dump of the content
(expressed in a suitable abstraction language) as described above, or
it could be an aggregated or filtered set of data based on policies
or specific requirements. Thus, the relationships shown in Figure 1
may be a little simplistic in that the ABNO Controller may also be
involved in preparing and presenting the TED information over a
north-bound interface.
2.3.2.5. Path Computation Requests from the Network
As originally specified in the PCE architecture [RFC4655], network
elements can make path computation requests to a PCE using PCEP
[RFC5440]. This facilitates the network setting up LSPs in response
to simple connectivity requests, and it allows the network to
reoptimize or repair LSPs.
2.3.2.6. Provisioning Manager Control of Networks
As described in Section 2.3.1.11, the Provisioning Manager makes or
channels requests to provision resources in the network. These
operations can take place at two levels: there can be requests to
program/configure specific resources in the data or forwarding
planes, and there can be requests to trigger a set of actions to be
programmed with the assistance of a control plane.
King & Farrel Informational [Page 18]
RFC 7491 PCE-Based Architecture for ABNO March 2015
A number of protocols already exist to provision network resources,
as follows:
o Program/configure specific network resources
- ForCES [RFC5810] defines a protocol for separation of the
control element (the Provisioning Manager) from the forwarding
elements in each node in the network.
- The General Switch Management Protocol (GSMP) [RFC3292] is an
asymmetric protocol that allows one or more external switch
controllers (such as the Provisioning Manager) to establish and
maintain the state of a label switch such as an MPLS switch.
- OpenFlow [ONF] is a communications protocol that gives an
OpenFlow Controller (such as the Provisioning Manager) access to
the forwarding plane of a network switch or router in the
network.
- Historically, other configuration-based mechanisms have been
used to set up the forwarding/switching state at individual
nodes within networks. Such mechanisms have ranged from
non-standard command line interfaces (CLIs) to various
standards-based options such as Transaction Language 1 (TL1)
[TL1] and SNMP [RFC3412]. These mechanisms are not designed for
rapid operation of a network and are not easily programmatic.
They are not proposed for use by the Provisioning Manager as
part of the ABNO architecture.
- NETCONF [RFC6241] provides a more active configuration protocol
that may be suitable for bulk programming of network resources.
Its use in this way is dependent on suitable YANG modules being
defined for the necessary options. Early work in the IETF's
NETMOD working group is focused on a higher level of routing
function more comparable with the function discussed in
Section 2.3.2.8; see [YANG-Rtg].
- The [TMF-MTOSI] specification provides provisioning, activation,
deactivation, and release of resources via the Service
Activation Interface (SAI). The Common Communication Vehicle
(CCV) is the middleware required to implement MTOSI. The CCV is
then used to provide middleware abstraction in combination with
the Web Services Description Language (WSDL) to allow MTOSIs to
be bound to different middleware technologies as needed.
King & Farrel Informational [Page 19]
RFC 7491 PCE-Based Architecture for ABNO March 2015
o Trigger actions through the control plane
- LSPs can be requested using a management system interface to the
head end of the LSP using tools such as CLIs, TL1 [TL1], or SNMP
[RFC3412]. Configuration at this granularity is not as time-
critical as when individual network resources are programmed,
because the main task of programming end-to-end connectivity is
devolved to the control plane. Nevertheless, these mechanisms
remain unsuitable for programmatic control of the network and
are not proposed for use by the Provisioning Manager as part of
the ABNO architecture.
- As noted above, NETCONF [RFC6241] provides a more active
configuration protocol. This may be particularly suitable for
requesting the establishment of LSPs. Work would be needed to
complete a suitable YANG module.
- The PCE Communication Protocol (PCEP) [RFC5440] has been
proposed as a suitable protocol for requesting the establishment
of LSPs [PCE-Init-LSP]. This works well, because the protocol
elements necessary are exactly the same as those used to respond
to a path computation request.
The functional element that issues PCEP requests to establish
LSPs is known as an "Active PCE"; however, it should be noted
that the ABNO functional component responsible for requesting
LSPs is the Provisioning Manager. Other controllers like the
VNTM and the ABNO Controller use the services of the
Provisioning Manager to isolate the twin functions of computing
and requesting paths from the provisioning mechanisms in place
with any given network.
Note that I2RS does not provide a mechanism for control of network
resources at this level, as it is designed to provide control of
routing state in routers, not forwarding state in the data plane.
King & Farrel Informational [Page 20]
RFC 7491 PCE-Based Architecture for ABNO March 2015
2.3.2.7. Auditing the Network
Once resources have been provisioned or connections established in
the network, it is important that the ABNO system can determine the
state of the network. Similarly, when provisioned resources are
modified or taken out of service, the changes in the network need to
be understood by the ABNO system. This function falls into four
categories:
- Updates to the TED are gathered as described in Section 2.3.2.2.
- Explicit notification of the successful establishment and the
subsequent state of the LSP can be provided through extensions to
PCEP as described in [Stateful-PCE] and [PCE-Init-LSP].
- OAM can be commissioned and the results inspected by the OAM
Handler as described in Section 2.3.2.14.
- A number of ABNO components may make inquiries and inspect network
state through a variety of techniques, including I2RS, NETCONF, or
SNMP.
2.3.2.8. Controlling the Routing System
As discussed in Section 2.3.1.5, the Interface to the Routing System
(I2RS) provides a programmatic way to access (for read and write) the
routing state and policy information on routers in the network. The
I2RS Client issues requests to routers in the network to establish or
retrieve routing state. Those requests utilize the I2RS protocol,
which will be based on a combination of NETCONF [RFC6241] and
RESTCONF [RESTCONF] with some additional features.
2.3.2.9. ABNO Controller Interface to PCE
The ABNO Controller needs to be able to consult the PCE to determine
what services can be provisioned in the network. There is no reason
why this interface cannot be based on standard PCEP as defined in
[RFC5440].
2.3.2.10. VNTM Interface to and from PCE
There are two interactions between the Virtual Network Topology
Manager and the PCE:
The first interaction is used when VNTM wants to determine what LSPs
can be set up in a network: in this case, it uses the standard PCEP
interface [RFC5440] to make path computation requests.
King & Farrel Informational [Page 21]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The second interaction arises when a PCE determines that it cannot
compute a requested path or notices that (according to some
configured policy) a network is low on resources (for example, the
capacity on some key link is nearly exhausted). In this case, the
PCE may notify the VNTM, which may (again according to policy) act to
construct more virtual topology. This second interface is not
currently specified, although it may be that the protocol selected or
designed to satisfy I2RS will provide suitable features (see
Section 2.3.2.8); alternatively, an extension to the PCEP Notify
message (PCNtf) [RFC5440] could be made.
2.3.2.11. ABNO Control Interfaces
The north-bound interface from the ABNO Controller is used by the
NMS, OSS, and Application Service Coordinator to request services in
the network in support of applications. The interface will also need
to be able to report the asynchronous completion of service requests
and convey changes in the status of services.
This interface will also need strong capabilities for security,
authentication, and policy.
This interface is not currently specified. It needs to be a
transactional interface that supports the specification of abstract
services with adequate flexibility to facilitate easy extension and
yet be concise and easily parsable.
It is possible that the protocol designed to satisfy I2RS will
provide suitable features (see Section 2.3.2.8).
2.3.2.12. ABNO Provisioning Requests
Under some circumstances, the ABNO Controller may make requests
directly to the Provisioning Manager. For example, if the
Provisioning Manager is acting as an SDN Controller, then the ABNO
Controller may use one of the APIs defined to allow requests to be
made to the SDN Controller (such as the Floodlight REST API [Flood]).
Alternatively, since the Provisioning Manager may also receive
instructions from a Stateful PCE, the use of PCEP extensions might be
appropriate in some cases [PCE-Init-LSP].
King & Farrel Informational [Page 22]
RFC 7491 PCE-Based Architecture for ABNO March 2015
2.3.2.13. Policy Interfaces
As described in Section 2.3.1.4 and throughout this document, policy
forms a critical component of the ABNO architecture. The role of
policy will include enforcing the following rules and requirements:
- Adding resources on demand should be gated by the authorized
capability.
- Client microflows should not trigger server-layer setup or
allocation.
- Accounting capabilities should be supported.
- Security mechanisms for authorization of requests and capabilities
are required.
Other policy-related functionality in the system might include the
policy behavior of the routing and forwarding system, such as:
- ECMP behavior
- Classification of packets onto LSPs or QoS categories.
Various policy-capable architectures have been defined, including a
framework for using policy with a PCE-enabled system [RFC5394].
However, the take-up of the IETF's Common Open Policy Service
protocol (COPS) [RFC2748] has been poor.
New work will be needed to define all of the policy interfaces within
the ABNO architecture. Work will also be needed to determine which
are internal interfaces and which may be external and so in need of a
protocol specification. There is some discussion that the I2RS
protocol may support the configuration and manipulation of policies.
2.3.2.14. OAM and Reporting
The OAM Handler must interact with the network to perform several
actions:
- Enabling OAM function within the network.
- Performing proactive OAM operations in the network.
- Receiving notifications of network events.
King & Farrel Informational [Page 23]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Any of the configuration and programmatic interfaces described in
Section 2.3.2.1 may serve this purpose. NETCONF notifications are
described in [RFC5277], and OpenFlow supports a number of
asynchronous event notifications [ONF]. Additionally, Syslog
[RFC5424] is a protocol for reporting events from the network, and IP
Flow Information Export (IPFIX) [RFC7011] is designed to allow
network statistics to be aggregated and reported.
The OAM Handler also correlates events reported from the network and
reports them onward to the ABNO Controller (which can apply the
information to the recovery of services that it has provisioned) and
to the NMS, OSS, and Application Service Coordinator. The reporting
mechanism used here can be essentially the same as the mechanism used
when events are reported from the network; no new protocol is needed,
although new data models may be required for technology-independent
OAM reporting.
3. ABNO Use Cases
This section provides a number of examples of how the ABNO
architecture can be applied to provide application-driven and
NMS/OSS-driven network operations. The purpose of these examples is
to give some concrete material to demonstrate the architecture so
that it may be more easily comprehended, and to illustrate that the
application of the architecture is achieved by "profiling" and by
selecting only the relevant components and interfaces.
Similarly, it is not the intention that this section contain a
complete list of all possible applications of ABNO. The examples are
intended to broadly cover a number of applications that are commonly
discussed, but this does not preclude other use cases.
The descriptions in this section are not fully detailed applicability
statements for ABNO. It is anticipated that such applicability
statements, for the use cases described and for other use cases,
could be suitable material for separate documents.
3.1. Inter-AS Connectivity
The following use case describes how the ABNO framework can be used
to set up an end-to-end MPLS service across multiple Autonomous
Systems (ASes). Consider the simple network topology shown in
Figure 2. The three ASes (ASa, ASb, and ASc) are connected at AS
Border Routers (ASBRs) a1, a2, b1 through b4, c1, and c2. A source
node (s) located in ASa is to be connected to a destination node (d)
located in ASc. The optimal path for the LSP from s to d must be
computed, and then the network must be triggered to set up the LSP.
King & Farrel Informational [Page 24]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+--------------+ +-----------------+ +--------------+
|ASa | | ASb | | ASc |
| +--+ | | +--+ +--+ | | +--+ |
| |a1|-|-|-|b1| |b3|-|-|-|c1| |
| +-+ +--+ | | +--+ +--+ | | +--+ +-+ |
| |s| | | | | |d| |
| +-+ +--+ | | +--+ +--+ | | +--+ +-+ |
| |a2|-|-|-|b2| |b4|-|-|-|c2| |
| +--+ | | +--+ +--+ | | +--+ |
| | | | | |
+--------------+ +-----------------+ +--------------+
Figure 2: Inter-AS Domain Topology with Hierarchical PCE (Parent PCE)
The following steps are performed to deliver the service within the
ABNO architecture:
1. Request Management
As shown in Figure 3, the NMS/OSS issues a request to the ABNO
Controller for a path between s and d. The ABNO Controller
verifies that the NMS/OSS has sufficient rights to make the
service request.
+---------------------+
| NMS/OSS |
+----------+----------+
|
V
+--------+ +-----------+-------------+
| Policy +-->-+ ABNO Controller |
| Agent | | |
+--------+ +-------------------------+
Figure 3: ABNO Request Management
2. Service Path Computation with Hierarchical PCE
The ABNO Controller needs to determine an end-to-end path for the
LSP. Since the ASes will want to maintain a degree of
confidentiality about their internal resources and topology, they
will not share a TED and each will have its own PCE. In such a
situation, the Hierarchical PCE (H-PCE) architecture described in
[RFC6805] is applicable.
As shown in Figure 4, the ABNO Controller sends a request to the
parent PCE for an end-to-end path. As described in [RFC6805], the
parent PCE consults its TED, which shows the connectivity between
King & Farrel Informational [Page 25]
RFC 7491 PCE-Based Architecture for ABNO March 2015
ASes. This helps it understand that the end-to-end path must
cross each of ASa, ASb, and ASc, so it sends individual path
computation requests to each of PCEs a, b, and c to determine the
best options for crossing the ASes.
Each child PCE applies policy to the requests it receives to
determine whether the request is to be allowed and to select the
types of network resources that can be used in the computation
result. For confidentiality reasons, each child PCE may supply
its computation responses using a path key [RFC5520] to hide the
details of the path segment it has computed.
+-----------------+
| ABNO Controller |
+----+-------+----+
| A
V |
+--+-------+--+ +--------+
+--------+ | | | |
| Policy +-->-+ Parent PCE +---+ AS TED |
| Agent | | | | |
+--------+ +-+----+----+-+ +--------+
/ | \
/ | \
+-----+-+ +---+---+ +-+-----+
| | | | | |
| PCE a | | PCE b | | PCE c |
| | | | | |
+---+---+ +---+---+ +---+---+
| | |
+--+--+ +--+--+ +--+--+
| TEDa| | TEDb| | TEDc|
+-----+ +-----+ +-----+
Figure 4: Path Computation Request with Hierarchical PCE
The parent PCE collates the responses from the children and
applies its own policy to stitch them together into the best
end-to-end path, which it returns as a response to the ABNO
Controller.
King & Farrel Informational [Page 26]
RFC 7491 PCE-Based Architecture for ABNO March 2015
3. Provisioning the End-to-End LSP
There are several options for how the end-to-end LSP gets
provisioned in the ABNO architecture. Some of these are described
below.
3a. Provisioning from the ABNO Controller with a Control Plane
Figure 5 shows how the ABNO Controller makes a request through
the Provisioning Manager to establish the end-to-end LSP. As
described in Section 2.3.2.6, these interactions can use the
NETCONF protocol [RFC6241] or the extensions to PCEP described
in [PCE-Init-LSP]. In either case, the provisioning request
is sent to the head-end Label Switching Router (LSR), and that
LSR signals in the control plane (using a protocol such as
RSVP-TE [RFC3209]) to cause the LSP to be established.
+-----------------+
| ABNO Controller |
+--------+--------+
|
V
+------+-------+
| Provisioning |
| Manager |
+------+-------+
|
V
+--------------------+------------------------+
/ Network \
+-------------------------------------------------+
Figure 5: Provisioning the End-to-End LSP
3b. Provisioning through Programming Network Resources
Another option is that the LSP is provisioned hop by hop from
the Provisioning Manager using a mechanism such as ForCES
[RFC5810] or OpenFlow [ONF] as described in Section 2.3.2.6.
In this case, the picture is the same as that shown in
Figure 5. The interaction between the ABNO Controller and the
Provisioning Manager will be PCEP or NETCONF as described in
option 3a, and the Provisioning Manager will be responsible
for fanning out the requests to the individual network
elements.
King & Farrel Informational [Page 27]
RFC 7491 PCE-Based Architecture for ABNO March 2015
3c. Provisioning with an Active Parent PCE
The Active PCE is described in Section 2.3.1.7, based on the
concepts expressed in [PCE-Init-LSP]. In this approach, the
process described in option 3a is modified such that the PCE
issues a direct PCEP command to the network, without a
response being first returned to the ABNO Controller.
This situation is shown in Figure 6 and could be modified so
that the Provisioning Manager still programs the individual
network elements as described in option 3b.
+-----------------+
| ABNO Controller |
+----+------------+
|
V
+--+----------+ +--------------+
+--------+ | | | Provisioning |
| Policy +-->-+ Parent PCE +---->----+ Manager |
| Agent | | | | |
+--------+ +-+----+----+-+ +-----+--------+
/ | \ |
/ | \ |
+-----+-+ +---+---+ +-+-----+ V
| | | | | | |
| PCE a | | PCE b | | PCE c | |
| | | | | | |
+-------+ +-------+ +-------+ |
|
+--------------------------------+------------+
/ Network \
+-------------------------------------------------+
Figure 6: LSP Provisioning with an Active PCE
3d. Provisioning with Active Child PCEs and Segment Stitching
A mixture of the approaches described in options 3b and 3c can
result in a combination of mechanisms to program the network
to provide the end-to-end LSP. Figure 7 shows how each child
PCE can be an Active PCE responsible for setting up an edge-
to-edge LSP segment across one of the ASes. The ABNO
Controller then uses the Provisioning Manager to program the
inter-AS connections using ForCES or OpenFlow, and the LSP
segments are stitched together following the ideas described
in [RFC5150]. Philosophers may debate whether the parent PCE
King & Farrel Informational [Page 28]
RFC 7491 PCE-Based Architecture for ABNO March 2015
in this model is active (instructing the children to provision
LSP segments) or passive (requesting path segments that the
children provision).
+-----------------+
| ABNO Controller +-------->--------+
+----+-------+----+ |
| A |
V | |
+--+-------+--+ |
+--------+ | | |
| Policy +-->-+ Parent PCE | |
| Agent | | | |
+--------+ ++-----+-----++ |
/ | \ |
/ | \ |
+---+-+ +--+--+ +-+---+ |
| | | | | | |
|PCE a| |PCE b| |PCE c| |
| | | | | | V
+--+--+ +--+--+ +---+-+ |
| | | |
V V V |
+----------+-+ +------------+ +-+----------+ |
|Provisioning| |Provisioning| |Provisioning| |
|Manager | |Manager | |Manager | |
+-+----------+ +-----+------+ +-----+------+ |
| | | |
V V V |
+--+-----+ +----+---+ +--+-----+ |
/ AS a \=====/ AS b \=====/ AS c \ |
+------------+ A +------------+ A +------------+ |
| | |
+-----+----------------+-----+ |
| Provisioning Manager +----<-------+
+----------------------------+
Figure 7: LSP Provisioning with Active Child PCEs and Stitching
4. Verification of Service
The ABNO Controller will need to ascertain that the end-to-end LSP
has been set up as requested. In the case of a control plane
being used to establish the LSP, the head-end LSR may send a
notification (perhaps using PCEP) to report successful setup, but
to be sure that the LSP is up, the ABNO Controller will request
the OAM Handler to perform Continuity Check OAM in the data plane
and report back that the LSP is ready to carry traffic.
King & Farrel Informational [Page 29]
RFC 7491 PCE-Based Architecture for ABNO March 2015
5. Notification of Service Fulfillment
Finally, when the ABNO Controller is satisfied that the requested
service is ready to carry traffic, it will notify the NMS/OSS.
The delivery of the service may be further checked through
auditing the network, as described in Section 2.3.2.7.
3.2. Multi-Layer Networking
Networks are typically constructed using multiple layers. These
layers represent separations of administrative regions or of
technologies and may also represent a distinction between client and
server networking roles.
It is preferable to coordinate network resource control and
utilization (i.e., consideration and control of multiple layers),
rather than controlling and optimizing resources at each layer
independently. This facilitates network efficiency and network
automation and may be defined as inter-layer traffic engineering.
The PCE architecture supports inter-layer traffic engineering
[RFC5623] and, in combination with the ABNO architecture, provides a
suite of capabilities for network resource coordination across
multiple layers.
The following use case demonstrates ABNO used to coordinate
allocation of server-layer network resources to create virtual
topology in a client-layer network in order to satisfy a request for
end-to-end client-layer connectivity. Consider the simple multi-
layer network in Figure 8.
+--+ +--+ +--+ +--+ +--+ +--+
|P1|---|P2|---|P3| |P4|---|P5|---|P6|
+--+ +--+ +--+ +--+ +--+ +--+
\ /
\ /
+--+ +--+ +--+
|L1|--|L2|--|L3|
+--+ +--+ +--+
Figure 8: Multi-Layer Network
There are six packet-layer routers (P1 through P6) and three optical-
layer lambda switches (L1 through L3). There is connectivity in the
packet layer between routers P1, P2, and P3, and also between routers
P4, P5, and P6, but there is no packet-layer connectivity between
these two islands of routers, perhaps because of a network failure or
perhaps because all existing bandwidth between the islands has
King & Farrel Informational [Page 30]
RFC 7491 PCE-Based Architecture for ABNO March 2015
already been used up. However, there is connectivity in the optical
layer between switches L1, L2, and L3, and the optical network is
connected out to routers P3 and P4 (they have optical line cards).
In this example, a packet-layer connection (an MPLS LSP) is desired
between P1 and P6.
In the ABNO architecture, the following steps are performed to
deliver the service.
1. Request Management
As shown in Figure 9, the Application Service Coordinator issues a
request for connectivity from P1 to P6 in the packet-layer
network. That is, the Application Service Coordinator requests an
MPLS LSP with a specific bandwidth to carry traffic for its
application. The ABNO Controller verifies that the Application
Service Coordinator has sufficient rights to make the service
request.
+---------------------------+
| Application Service |
| Coordinator |
+-------------+-------------+
|
V
+------+ +------------+------------+
|Policy+->-+ ABNO Controller |
|Agent | | |
+------+ +-------------------------+
Figure 9: Application Service Coordinator Request Management
2. Service Path Computation in the Packet Layer
The ABNO Controller sends a path computation request to the
packet-layer PCE to compute a suitable path for the requested LSP,
as shown in Figure 10. The PCE uses the appropriate policy for
the request and consults the TED for the packet layer. It
determines that no path is immediately available.
King & Farrel Informational [Page 31]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+-----------------+
| ABNO Controller |
+----+------------+
|
V
+--------+ +--+-----------+ +--------+
| Policy +-->--+ Packet-Layer +---+ Packet |
| Agent | | PCE | | TED |
+--------+ +--------------+ +--------+
Figure 10: Path Computation Request
3. Invocation of VNTM and Path Computation in the Optical Layer
After the path computation failure in step 2, instead of notifying
the ABNO Controller of the failure, the PCE invokes the VNTM to
see whether it can create the necessary link in the virtual
network topology to bridge the gap.
As shown in Figure 11, the packet-layer PCE reports the
connectivity problem to the VNTM, and the VNTM consults policy to
determine what it is allowed to do. Assuming that the policy
allows it, the VNTM asks the optical-layer PCE to find a path
across the optical network that could be provisioned to provide a
virtual link for the packet layer. In addressing this request,
the optical-layer PCE consults a TED for the optical-layer
network.
+------+
+--------+ | | +--------------+
| Policy +-->--+ VNTM +--<--+ Packet-Layer |
| Agent | | | | PCE |
+--------+ +---+--+ +--------------+
|
V
+---------------+ +---------+
| Optical-Layer +---+ Optical |
| PCE | | TED |
+---------------+ +---------+
Figure 11: Invocation of VNTM and Optical-Layer Path Computation
4. Provisioning in the Optical Layer
Once a path has been found across the optical-layer network, it
needs to be provisioned. The options follow those in step 3 of
Section 3.1. That is, provisioning can be initiated by the
optical-layer PCE or by its user, the VNTM. The command can be
King & Farrel Informational [Page 32]
RFC 7491 PCE-Based Architecture for ABNO March 2015
sent to the head end of the optical LSP (P3) so that the control
plane (for example, GMPLS RSVP-TE [RFC3473]) can be used to
provision the LSP. Alternatively, the network resources can be
provisioned directly, using any of the mechanisms described in
Section 2.3.2.6.
5. Creation of Virtual Topology in the Packet Layer
Once the LSP has been set up in the optical layer, it can be made
available in the packet layer as a virtual link. If the GMPLS
signaling used the mechanisms described in [RFC6107], this process
can be automated within the control plane; otherwise, it may
require a specific instruction to the head-end router of the
optical LSP (for example, through I2RS).
Once the virtual link is created as shown in Figure 12, it is
advertised in the IGP for the packet-layer network, and the link
will appear in the TED for the packet-layer network.
+--------+
| Packet |
| TED |
+------+-+
A
|
+--+ +--+
|P3|....................|P4|
+--+ +--+
\ /
\ /
+--+ +--+ +--+
|L1|--|L2|--|L3|
+--+ +--+ +--+
Figure 12: Advertisement of a New Virtual Link
6. Path Computation Completion and Provisioning in the Packet Layer
Now there are sufficient resources in the packet-layer network.
The PCE for the packet layer can complete its work, and the MPLS
LSP can be provisioned as described in Section 3.1.
7. Verification and Notification of Service Fulfillment
As discussed in Section 3.1, the ABNO Controller will need to
verify that the end-to-end LSP has been correctly established
before reporting service fulfillment to the Application Service
Coordinator.
King & Farrel Informational [Page 33]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Furthermore, it is highly likely that service verification will be
necessary before the optical-layer LSP can be put into service as
a virtual link. Thus, the VNTM will need to coordinate with the
OAM Handler to ensure that the LSP is ready for use.
3.2.1. Data Center Interconnection across Multi-Layer Networks
In order to support new and emerging cloud-based applications, such
as real-time data backup, virtual machine migration, server
clustering, or load reorganization, the dynamic provisioning and
allocation of IT resources and the interconnection of multiple,
remote Data Centers (DCs) is a growing requirement.
These operations require traffic being delivered between data
centers, and, typically, the connections providing such inter-DC
connectivity are provisioned using static circuits or dedicated
leased lines, leading to an inefficiency in terms of resource
utilization. Moreover, a basic requirement is that such a group of
remote DCs can be operated logically as one.
In such environments, the data plane technology is operator and
provider dependent. Their customers may rent lambda switch capable
(LSC), packet switch capable (PSC), or time division multiplexing
(TDM) services, and the application and usage of the ABNO
architecture and Controller enable the required dynamic end-to-end
network service provisioning, regardless of underlying service and
transport layers.
Consequently, the interconnection of DCs may involve the operation,
control, and management of heterogeneous environments: each DC site
and the metro-core network segment used to interconnect them, with
regard to not only the underlying data plane technology but also the
control plane. For example, each DC site or domain could be
controlled locally in a centralized way (e.g., via OpenFlow [ONF]),
whereas the metro-core transport infrastructure is controlled by
GMPLS. Although OpenFlow is specially adapted to single-domain
intra-DC networks (packet-level control, lots of routing exceptions),
a standardized GMPLS-based architecture would enable dynamic optical
resource allocation and restoration in multi-domain (e.g., multi-
vendor) core networks interconnecting distributed data centers.
King & Farrel Informational [Page 34]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The application of an ABNO architecture and related procedures would
involve the following aspects:
1. Request from the Application Service Coordinator or NMS
As shown in Figure 13, the ABNO Controller receives a request from
the Application Service Coordinator or from the NMS, in order to
create a new end-to-end connection between two end points. The
actual addressing of these end points is discussed in the next
section. The ABNO Controller asks the PCE for a path between
these two end points, after considering any applicable policy as
defined by the Policy Agent (see Figure 1).
+---------------------------+
| Application Service |
| Coordinator or NMS |
+-------------+-------------+
|
V
+------+ +------------+------------+
|Policy+->-+ ABNO Controller |
|Agent | | |
+------+ +-------------------------+
Figure 13: Application Service Coordinator Request Management
2. Address Mapping
In order to compute an end-to-end path, the PCE needs to have a
unified view of the overall topology, which means that it has to
consider and identify the actual end points with regard to the
client network addresses. The ABNO Controller and/or the PCE may
need to translate or map addresses from different address spaces.
Depending on how the topology information is disseminated and
gathered, there are two possible scenarios:
2a. The Application Layer Knows the Client Network Layer
Entities belonging to the application layer may have an
interface with the TED or with an ALTO Server allowing those
entities to map the high-level end points to network
addresses. The mechanism used to enable this address
correlation is out of scope for this document but relies on
direct interfaces to other ABNO components in addition to the
interface to the ABNO Controller.
King & Farrel Informational [Page 35]
RFC 7491 PCE-Based Architecture for ABNO March 2015
In this scenario, the request from the NMS or Application
Service Coordinator contains addresses in the client-layer
network. Therefore, when the ABNO Controller requests the PCE
to compute a path between two end points, the PCE is able to
use the supplied addresses, compute the path, and continue the
workflow in communication with the Provisioning Manager.
2b. The Application Layer Does Not Know the Client Network Layer
In this case, when the ABNO Controller receives a request from
the NMS or Application Service Coordinator, the request
contains only identifiers from the application-layer address
space. In order for the PCE to compute an end-to-end path,
these identifiers must be converted to addresses in the
client-layer network. This translation can be performed by
the ABNO Controller, which can access the TED and ALTO
databases allowing the path computation request that it sends
to the PCE to simply be contained within one network and TED.
Alternatively, the computation request could use the
application-layer identifiers, leaving the job of address
mapping to the PCE.
Note that in order to avoid any confusion both approaches in
this scenario require clear identification of the address
spaces that are in use.
3. Provisioning Process
Once the path has been obtained, the Provisioning Manager receives
a high-level provisioning request to provision the service.
Since, in the considered use case, the network elements are not
necessarily configured using the same protocol, the end-to-end
path is split into segments, and the ABNO Controller coordinates
or orchestrates the establishment by adapting and/or translating
the abstract provisioning request to concrete segment requests by
means of a VNTM or PCE that issues the corresponding commands or
instructions. The provisioning may involve configuring the data
plane elements directly or delegating the establishment of the
underlying connection to a dedicated control plane instance
responsible for that segment.
King & Farrel Informational [Page 36]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The Provisioning Manager could use a number of mechanisms to
program the network elements, as shown in Figure 14. It learns
which technology is used for the actual provisioning at each
segment by either manual configuration or discovery.
+-----------------+
| ABNO Controller |
+-------+---------+
|
|
V
+------+ +------+-------+
| VNTM +--<--+ PCE |
+---+--+ +------+-------+
| |
V V
+-----+---------------+------------+
| Provisioning Manager |
+----------------------------------+
| | | | |
V | V | V
OpenFlow V ForCES V PCEP
NETCONF SNMP
Figure 14: Provisioning Process
4. Verification and Notification of Service Fulfillment
Once the end-to-end connectivity service has been provisioned, and
after the verification of the correct operation of the service,
the ABNO Controller needs to notify the Application Service
Coordinator or NMS.
3.3. Make-before-Break
A number of different services depend on the establishment of a new
LSP so that traffic supported by an existing LSP can be switched with
little or no disruption. This section describes those use cases,
presents a generic model for make-before-break within the ABNO
architecture, and shows how each use case can be supported by using
elements of the generic model.
3.3.1. Make-before-Break for Reoptimization
Make-before-break is a mechanism supported in RSVP-TE signaling where
a new LSP is set up before the LSP it replaces is torn down
[RFC3209]. This process has several benefits in situations such as
reoptimization of in-service LSPs.
King & Farrel Informational [Page 37]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The process is simple, and the example shown in Figure 15 utilizes a
Stateful PCE [Stateful-PCE] to monitor the network and take
reoptimization actions when necessary. In this process, a service
request is made to the ABNO Controller by a requester such as the
OSS. The service request indicates that the LSP should be
reoptimized under specific conditions according to policy. This
allows the ABNO Controller to manage the sequence and prioritization
of reoptimizing multiple LSPs using elements of Global Concurrent
Optimization (GCO) as described in Section 3.4, and applying policies
across the network so that, for instance, LSPs for delay-sensitive
services are reoptimized first.
The ABNO Controller commissions the PCE to compute and set up the
initial path.
Over time, the PCE monitors the changes in the network as reflected
in the TED, and according to the configured policy may compute and
set up a replacement path, using make-before-break within the
network.
Once the new path has been set up and the network reports that it is
being used correctly, the PCE tears down the old path and may report
the reoptimization event to the ABNO Controller.
+---------------------------------------------+
| OSS / NMS / Application Service Coordinator |
+----------------------+----------------------+
|
+------------+------------+
| ABNO Controller |
+------------+------------+
|
+------+ +-------+-------+ +-----+
|Policy+-----+ PCE +-----+ TED |
|Agent | +-------+-------+ +-----+
+------+ |
|
+----------------------+----------------------+
/ Network \
+-------------------------------------------------+
Figure 15: The Make-before-Break Process
3.3.2. Make-before-Break for Restoration
Make-before-break may also be used to repair a failed LSP where there
is a desire to retain resources along some of the path, and where
there is the potential for other LSPs to "steal" the resources if the
King & Farrel Informational [Page 38]
RFC 7491 PCE-Based Architecture for ABNO March 2015
failed LSP is torn down first. Unlike the example in Section 3.3.1,
this case addresses a situation where the service is interrupted, but
this interruption arises from the break in service introduced by the
network failure. Obviously, in the case of a point-to-multipoint
LSP, the failure might only affect part of the tree and the
disruption will only be to a subset of the destination leaves so that
a make-before-break restoration approach will not cause disruption to
the leaves that were not affected by the original failure.
Figure 16 shows the components that interact for this use case. A
service request is made to the ABNO Controller by a requester such as
the OSS. The service request indicates that the LSP may be restored
after failure and should attempt to reuse as much of the original
path as possible.
The ABNO Controller commissions the PCE to compute and set up the
initial path. The ABNO Controller also requests the OAM Handler to
initiate OAM on the LSP and to monitor the results.
At some point, the network reports a fault to the OAM Handler, which
notifies the ABNO Controller.
The ABNO Controller commissions the PCE to compute a new path,
reusing as much of the original path as possible, and the PCE sets up
the new LSP.
Once the new path has been set up and the network reports that it is
being used correctly, the ABNO Controller instructs the PCE to tear
down the old path.
+---------------------------------------------+
| OSS / NMS / Application Service Coordinator |
+----------------------+----------------------+
|
+------------+------------+ +-------+
| ABNO Controller +---+ OAM |
+------------+------------+ |Handler|
| +---+---+
+-------+-------+ |
| PCE | |
+-------+-------+ |
| |
+----------------------+--------------------+-+
/ Network \
+-------------------------------------------------+
Figure 16: The Make-before-Break Restoration Process
King & Farrel Informational [Page 39]
RFC 7491 PCE-Based Architecture for ABNO March 2015
3.3.3. Make-before-Break for Path Test and Selection
In a more complicated use case, an LSP may be monitored for a number
of attributes, such as delay and jitter. When the LSP falls below a
threshold, the traffic may be moved to another LSP that offers the
desired (or at least a better) quality of service. To achieve this,
it is necessary to establish the new LSP and test it, and because the
traffic must not be interrupted, make-before-break must be used.
Moreover, it may be the case that no new LSP can provide the desired
attributes and that a number of LSPs need to be tested so that the
best can be selected. Furthermore, even when the original LSP is set
up, it could be desirable to test a number of LSPs before deciding
which should be used to carry the traffic.
Figure 17 shows the components that interact for this use case.
Because multiple LSPs might exist at once, a distinct action is
needed to coordinate which one carries the traffic, and this is the
job of the I2RS Client acting under the control of the ABNO
Controller.
The OAM Handler is responsible for initiating tests on the LSPs and
for reporting the results back to the ABNO Controller. The OAM
Handler can also check end-to-end connectivity test results across a
multi-domain network even when each domain runs a different
technology. For example, an end-to-end path might be achieved by
stitching together an MPLS segment, an Ethernet/VLAN segment, another
IP segment, etc.
Otherwise, the process is similar to that for reoptimization as
discussed in Section 3.3.1.
King & Farrel Informational [Page 40]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+---------------------------------------------+
| OSS / NMS / Application Service Coordinator |
+----------------------+----------------------+
|
+------+ +------------+------------+ +-------+
|Policy+---+ ABNO Controller +----+ OAM |
|Agent | | +--+ |Handler|
+------+ +------------+------------+ | +---+---+
| | |
+-------+-------+ +--+---+ |
| PCE | | I2RS | |
+-------+-------+ |Client| |
| +--+---+ |
| | |
+-----------------------+---------------+-----+-+
/ Network \
+---------------------------------------------------+
Figure 17: The Make-before-Break Path Test and Selection Process
The pseudocode that follows gives an indication of the interactions
between ABNO components.
OSS requests quality-assured service
:Label1
DoWhile not enough LSPs (ABNO Controller)
Instruct PCE to compute and provision the LSP (ABNO Controller)
Create the LSP (PCE)
EndDo
:Label2
DoFor each LSP (ABNO Controller)
Test LSP (OAM Handler)
Report results to ABNO Controller (OAM Handler)
EndDo
Evaluate results of all tests (ABNO Controller)
Select preferred LSP and instruct I2RS Client (ABNO Controller)
Put traffic on preferred LSP (I2RS Client)
DoWhile too many LSPs (ABNO Controller)
Instruct PCE to tear down unwanted LSP (ABNO Controller)
Tear down unwanted LSP (PCE)
EndDo
King & Farrel Informational [Page 41]
RFC 7491 PCE-Based Architecture for ABNO March 2015
DoUntil trigger (OAM Handler, ABNO Controller, Policy Agent)
keep sending traffic (Network)
Test LSP (OAM Handler)
EndDo
If there is already a suitable LSP (ABNO Controller)
GoTo Label2
Else
GoTo Label1
EndIf
3.4. Global Concurrent Optimization
Global Concurrent Optimization (GCO) is defined in [RFC5557] and
represents a key technology for maximizing network efficiency by
computing a set of traffic-engineered paths concurrently. A GCO path
computation request will simultaneously consider the entire topology
of the network, and the complete set of new LSPs together with their
respective constraints. Similarly, GCO may be applied to recompute
the paths of a set of existing LSPs.
GCO may be requested in a number of scenarios. These include:
o Routing of new services where the PCE should consider other
services or network topology.
o A reoptimization of existing services due to fragmented network
resources or suboptimized placement of sequentially computed
services.
o Recovery of connectivity for bulk services in the event of a
catastrophic network failure.
A service provider may also want to compute and deploy new bulk
services based on a predicted traffic matrix. The GCO functionality
and capability to perform concurrent computation provide a
significant network optimization advantage, thus utilizing network
resources optimally and avoiding blocking.
The following use case shows how the ABNO architecture and components
are used to achieve concurrent optimization across a set of services.
King & Farrel Informational [Page 42]
RFC 7491 PCE-Based Architecture for ABNO March 2015
3.4.1. Use Case: GCO with MPLS LSPs
When considering the GCO path computation problem, we can split the
GCO objective functions into three optimization categories:
o Minimize aggregate Bandwidth Consumption (MBC).
o Minimize the load of the Most Loaded Link (MLL).
o Minimize Cumulative Cost of a set of paths (MCC).
This use case assumes that the GCO request will be offline and be
initiated from an NMS/OSS; that is, it may take significant time to
compute the service, and the paths reported in the response may want
to be verified by the user before being provisioned within the
network.
1. Request Management
The NMS/OSS issues a request for new service connectivity for bulk
services. The ABNO Controller verifies that the NMS/OSS has
sufficient rights to make the service request and apply a GCO
attribute with a request to Minimize aggregate Bandwidth
Consumption (MBC), as shown in Figure 18.
+---------------------+
| NMS/OSS |
+----------+----------+
|
V
+--------+ +-----------+-------------+
| Policy +-->-+ ABNO Controller |
| Agent | | |
+--------+ +-------------------------+
Figure 18: NMS Request to ABNO Controller
1a. Each service request has a source, destination, and bandwidth
request. These service requests are sent to the ABNO
Controller and categorized as GCO requests. The PCE uses the
appropriate policy for each request and consults the TED for
the packet layer.
King & Farrel Informational [Page 43]
RFC 7491 PCE-Based Architecture for ABNO March 2015
2. Service Path Computation in the Packet Layer
To compute a set of services for the GCO application, PCEP
supports synchronization vector (SVEC) lists for synchronized
dependent path computations as defined in [RFC5440] and described
in [RFC6007].
2a. The ABNO Controller sends the bulk service request to the
GCO-capable packet-layer PCE using PCEP messaging. The PCE
uses the appropriate policy for the request and consults the
TED for the packet layer, as shown in Figure 19.
+-----------------+
| ABNO Controller |
+----+------------+
|
V
+--------+ +--+-----------+ +--------+
| | | | | |
| Policy +-->--+ GCO-Capable +---+ Packet |
| Agent | | Packet-Layer | | TED |
| | | PCE | | |
+--------+ +--------------+ +--------+
Figure 19: Path Computation Request from GCO-Capable PCE
2b. Upon receipt of the bulk (GCO) service requests, the PCE
applies the MBC objective function and computes the services
concurrently.
2c. Once the requested GCO service path computation completes, the
PCE sends the resulting paths back to the ABNO Controller.
The response includes a fully computed explicit path for each
service (TE LSP).
King & Farrel Informational [Page 44]
RFC 7491 PCE-Based Architecture for ABNO March 2015
3. The concurrently computed solution received from the PCE is sent
back to the NMS/OSS by the ABNO Controller as a PCEP response, as
shown in Figure 20. The NMS/OSS user can then check the candidate
paths and either provision the new services or save the solution
for deployment in the future.
+---------------------+
| NMS/OSS |
+----------+----------+
^
|
+----------+----------+
| ABNO Controller |
| |
+---------------------+
Figure 20: ABNO Sends Solution to the NMS/OSS
3.5. Adaptive Network Management (ANM)
The ABNO architecture provides the capability for reactive network
control of resources relying on classification, profiling, and
prediction based on current demands and resource utilization.
Server-layer transport network resources, such as Optical Transport
Network (OTN) time-slicing [G.709], or the fine granularity grid of
wavelengths with variable spectral bandwidth (flexi-grid) [G.694.1],
can be manipulated to meet current and projected demands in a model
called Elastic Optical Networks (EON) [EON].
EON provides spectrum-efficient and scalable transport by introducing
flexible granular traffic grooming in the optical frequency domain.
This is achieved using arbitrary contiguous concatenation of the
optical spectrum that allows the creation of custom-sized bandwidth.
This bandwidth is defined in slots of 12.5 GHz.
Adaptive Network Management (ANM) with EON allows appropriately sized
optical bandwidth to be allocated to an end-to-end optical path. In
flexi-grid, the allocation is performed according to the traffic
volume, optical modulation format, and associated reach, or following
user requests, and can be achieved in a highly spectrum-efficient and
scalable manner. Similarly, OTN provides for flexible and granular
provisioning of bandwidth on top of Wavelength Switched Optical
Networks (WSONs).
To efficiently use optical resources, a system is required that can
monitor network resources and decide the optimal network
configuration based on the status, bandwidth availability, and user
service. We call this ANM.
King & Farrel Informational [Page 45]
RFC 7491 PCE-Based Architecture for ABNO March 2015
3.5.1. ANM Trigger
There are different reasons to trigger an adaptive network management
process; these include:
o Measurement: Traffic measurements can be used in order to cause
spectrum allocations that fit the traffic needs as efficiently as
possible. This function may be influenced by measuring the IP
router traffic flows, by examining traffic engineering or link
state databases, by usage thresholds for critical links in the
network, or by requests from external entities. Nowadays, network
operators have active monitoring probes in the network that store
their results in the OSS. The OSS or OAM Handler components
activate this measurement-based trigger, so the ABNO Controller
would not be directly involved in this case.
o Human: Operators may request ABNO to run an adaptive network
planning process via an NMS.
o Periodic: An adaptive network planning process can be run
periodically to find an optimum configuration.
An ABNO Controller would receive a request from an OSS or NMS to run
an adaptive network manager process.
3.5.2. Processing Request and GCO Computation
Based on the human or periodic trigger requests described in the
previous section, the OSS or NMS will send a request to the ABNO
Controller to perform EON-based GCO. The ABNO Controller will select
a set of services to be reoptimized and choose an objective function
that will deliver the best use of network resources. In making these
choices, the ABNO Controller is guided by network-wide policy on the
use of resources, the definition of optimization, and the level of
perturbation to existing services that is tolerable.
This request for GCO is passed to the PCE, along the lines of the
description in Section 3.4. The PCE can then consider the end-to-end
paths and every channel's optimal spectrum assignment in order to
satisfy traffic demands and optimize the optical spectrum consumption
within the network.
The PCE will operate on the TED but is likely to also be stateful so
that it knows which LSPs correspond to which waveband allocations on
which links in the network. Once the PCE arrives at an answer, it
returns a set of potential paths to the ABNO Controller, which passes
them on to the NMS or OSS to supervise/select the subsequent path
setup/modification process.
King & Farrel Informational [Page 46]
RFC 7491 PCE-Based Architecture for ABNO March 2015
This exchange is shown in Figure 21. Note that the figure does not
show the interactions used by the OSS/NMS for establishing or
modifying LSPs in the network.
+---------------------------+
| OSS or NMS |
+-----------+---+-----------+
| ^
V |
+------+ +----------+---+----------+
|Policy+->-+ ABNO Controller |
|Agent | | |
+------+ +----------+---+----------+
| ^
V |
+-----+---+----+
+ PCE |
+--------------+
Figure 21: Adaptive Network Management with Human Intervention
3.5.3. Automated Provisioning Process
Although most network operations are supervised by the operator,
there are some actions that may not require supervision, like a
simple modification of a modulation format in a Bit-rate Variable
Transponder (BVT) (to increase the optical spectrum efficiency or
reduce energy consumption). In this process, where human
intervention is not required, the PCE sends the Provisioning Manager
a new configuration to configure the network elements, as shown in
Figure 22.
King & Farrel Informational [Page 47]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+------------------------+
| OSS or NMS |
+-----------+------------+
|
V
+------+ +----------+------------+
|Policy+->-+ ABNO Controller |
|Agent | | |
+------+ +----------+------------+
|
V
+------+------+
+ PCE |
+------+------+
|
V
+----------------------------------+
| Provisioning Manager |
+----------------------------------+
Figure 22: Adaptive Network Management without Human Intervention
3.6. Pseudowire Operations and Management
Pseudowires in an MPLS network [RFC3985] operate as a form of layered
network over the connectivity provided by the MPLS network. The
pseudowires are carried by LSPs operating as transport tunnels, and
planning is necessary to determine how those tunnels are placed in
the network and which tunnels are used by any pseudowire.
This section considers four use cases: multi-segment pseudowires,
path-diverse pseudowires, path-diverse multi-segment pseudowires, and
pseudowire segment protection. Section 3.6.5 describes the
applicability of the ABNO architecture to these four use cases.
3.6.1. Multi-Segment Pseudowires
[RFC5254] describes the architecture for multi-segment pseudowires.
An end-to-end service, as shown in Figure 23, can consist of a series
of stitched segments shown in the figure as AC, PW1, PW2, PW3, and
AC. Each pseudowire segment is stitched at a "stitching Provider
Edge" (S-PE): for example, PW1 is stitched to PW2 at S-PE1. Each
access circuit (AC) is stitched to a pseudowire segment at a
"terminating PE" (T-PE): for example, PW1 is stitched to the AC at
T-PE1.
King & Farrel Informational [Page 48]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Each pseudowire segment is carried across the MPLS network in an LSP
operating as a transport tunnel: for example, PW1 is carried in LSP1.
The LSPs between PE nodes may traverse different MPLS networks with
the PEs as border nodes, or the PEs may lie within the network such
that each LSP spans only part of the network.
----- ----- ----- -----
--- |T-PE1| LSP1 |S-PE1| LSP2 |S-PE3| LSP3 |T-PE2| +---+
| | AC | |=======| |=======| |=======| | AC | |
|CE1|----|........PW1........|..PW2........|..PW3........|----|CE2|
| | | |=======| |=======| |=======| | | |
--- | | | | | | | | +---+
----- ----- ----- -----
Figure 23: Multi-Segment Pseudowire
While the topology shown in Figure 23 is easy to navigate, the
reality of a deployed network can be considerably more complex. The
topology in Figure 24 shows a small mesh of PEs. The links between
the PEs are not physical links but represent the potential of MPLS
LSPs between the PEs.
When establishing the end-to-end service between Customer Edge nodes
(CEs) CE1 and CE2, some choice must be made about which PEs to use.
In other words, a path computation must be made to determine the
pseudowire segment "hops", and then the necessary LSP tunnels must be
established to carry the pseudowire segments that will be stitched
together.
Of course, each LSP may itself require a path computation decision to
route it through the MPLS network between PEs.
The choice of path for the multi-segment pseudowire will depend on
such issues as:
- MPLS connectivity
- MPLS bandwidth availability
- pseudowire stitching capability and capacity at PEs
- policy and confidentiality considerations for use of PEs
King & Farrel Informational [Page 49]
RFC 7491 PCE-Based Architecture for ABNO March 2015
-----
|S-PE5|
/-----\
--- ----- -----/ \----- ----- ---
|CE1|----|T-PE1|-------|S-PE1|-------|S-PE3|-------|T-PE2|----|CE2|
--- -----\ -----\ ----- /----- ---
\ | ------- | /
\ ----- \----- /
-----|S-PE2|-------|S-PE4|-----
----- -----
Figure 24: Multi-Segment Pseudowire Network Topology
3.6.2. Path-Diverse Pseudowires
The connectivity service provided by a pseudowire may need to be
resilient to failure. In many cases, this function is provided by
provisioning a pair of pseudowires carried by path-diverse LSPs
across the network, as shown in Figure 25 (the terminology is
inherited directly from [RFC3985]). Clearly, in this case, the
challenge is to keep the two LSPs (LSP1 and LSP2) disjoint within the
MPLS network. This problem is not different from the normal MPLS
path-diversity problem.
------- -------
| PE1 | LSP1 | PE2 |
AC | |=======================| | AC
----...................PW1...................----
--- - / | |=======================| | \ -----
| |/ | | | | \| |
| CE1 + | | MPLS Network | | + CE2 |
| |\ | | | | /| |
--- - \ | |=======================| | / -----
----...................PW2...................----
AC | |=======================| | AC
| | LSP2 | |
------- -------
Figure 25: Path-Diverse Pseudowires
The path-diverse pseudowire is developed in Figure 26 by the
"dual-homing" of each CE through more than one PE. The requirement
for LSP path diversity is exactly the same, but it is complicated by
the LSPs having distinct end points. In this case, the head-end
router (e.g., PE1) cannot be relied upon to maintain the path
diversity through the signaling protocol because it is aware of the
path of only one of the LSPs. Thus, some form of coordinated path
computation approach is needed.
King & Farrel Informational [Page 50]
RFC 7491 PCE-Based Architecture for ABNO March 2015
------- -------
| PE1 | LSP1 | PE2 |
AC | |=======================| | AC
---...................PW1...................---
/ | |=======================| | \
----- / | | | | \ -----
| |/ ------- ------- \| |
| CE1 + MPLS Network + CE2 |
| |\ ------- ------- /| |
----- \ | PE3 | | PE4 | / -----
\ | |=======================| | /
---...................PW2...................---
AC | |=======================| | AC
| | LSP2 | |
------- -------
Figure 26: Path-Diverse Pseudowires with Disjoint PEs
3.6.3. Path-Diverse Multi-Segment Pseudowires
Figure 27 shows how the services in the previous two sections may be
combined to offer end-to-end diverse paths in a multi-segment
environment. To offer end-to-end resilience to failure, two entirely
diverse, end-to-end multi-segment pseudowires may be needed.
----- -----
|S-PE5|--------------|T-PE4|
/-----\ ----- \
----- -----/ \----- ----- \ ---
|T-PE1|-------|S-PE1|-------|S-PE3|-------|T-PE2|--|CE2|
--- / -----\ -----\ ----- /----- ---
|CE1|< ------- | ------- | /
--- \ ----- \----- \----- /
|T-PE3|-------|S-PE2|-------|S-PE4|-----
----- ----- -----
Figure 27: Path-Diverse Multi-Segment Pseudowire Network Topology
Just as in any diverse-path computation, the selection of the first
path needs to be made with awareness of the fact that a second, fully
diverse path is also needed. If a sequential computation was applied
to the topology in Figure 27, the first path CE1,T-PE1,S-PE1,
S-PE3,T-PE2,CE2 would make it impossible to find a second path that
was fully diverse from the first.
King & Farrel Informational [Page 51]
RFC 7491 PCE-Based Architecture for ABNO March 2015
But the problem is complicated by the multi-layer nature of the
network. It is not enough that the PEs are chosen to be diverse
because the LSP tunnels between them might share links within the
MPLS network. Thus, a multi-layer planning solution is needed to
achieve the desired level of service.
3.6.4. Pseudowire Segment Protection
An alternative to the end-to-end pseudowire protection service
enabled by the mechanism described in Section 3.6.3 can be achieved
by protecting individual pseudowire segments or PEs. For example, in
Figure 27, the pseudowire between S-PE1 and S-PE5 may be protected by
a pair of stitched segments running between S-PE1 and S-PE5, and
between S-PE5 and S-PE3. This is shown in detail in Figure 28.
------- ------- -------
| S-PE1 | LSP1 | S-PE5 | LSP3 | S-PE3 |
| |============| |============| |
| .........PW1..................PW3.......... | Outgoing
Incoming | : |============| |============| : | Segment
Segment | : | ------- | :..........
...........: | | : |
| : | | : |
| : |=================================| : |
| .........PW2............................... |
| |=================================| |
| | LSP2 | |
------- -------
Figure 28: Fragment of a Segment-Protected Multi-Segment Pseudowire
The determination of pseudowire protection segments requires
coordination and planning, and just as in Section 3.6.5, this
planning must be cognizant of the paths taken by LSPs through the
underlying MPLS networks.
3.6.5. Applicability of ABNO to Pseudowires
The ABNO architecture lends itself well to the planning and control
of pseudowires in the use cases described above. The user or
application needs a single point at which it requests services: the
ABNO Controller. The ABNO Controller can ask a PCE to draw on the
topology of pseudowire stitching-capable PEs as well as additional
information regarding PE capabilities, such as load on PEs and
administrative policies, and the PCE can use a series of TEDs or
other PCEs for the underlying MPLS networks to determine the paths of
the LSP tunnels. At the time of this writing, PCEP does not support
King & Farrel Informational [Page 52]
RFC 7491 PCE-Based Architecture for ABNO March 2015
path computation requests and responses concerning pseudowires, but
the concepts are very similar to existing uses and the necessary
extensions would be very small.
Once the paths have been computed, a number of different provisioning
systems can be used to instantiate the LSPs and provision the
pseudowires under the control of the Provisioning Manager. The ABNO
Controller will use the I2RS Client to instruct the network devices
about what traffic should be placed on which pseudowires and, in
conjunction with the OAM Handler, can ensure that failure events are
handled correctly, that service quality levels are appropriate, and
that service protection levels are maintained.
In many respects, the pseudowire network forms an overlay network
(with its own TED and provisioning mechanisms) carried by underlying
packet networks. Further client networks (the pseudowire payloads)
may be carried by the pseudowire network. Thus, the problem space
being addressed by ABNO in this case is a classic multi-layer
network.
3.7. Cross-Stratum Optimization (CSO)
Considering the term "stratum" to broadly differentiate the layers of
most concern to the application and to the network in general, the
need for Cross-Stratum Optimization (CSO) arises when the application
stratum and network stratum need to be coordinated to achieve
operational efficiency as well as resource optimization in both
application and network strata.
Data center-based applications can provide a wide variety of services
such as video gaming, cloud computing, and grid applications. High-
bandwidth video applications are also emerging, such as remote
medical surgery, live concerts, and sporting events.
This use case for the ABNO architecture is mainly concerned with data
center applications that make substantial bandwidth demands either in
aggregate or individually. In addition, these applications may need
specific bounds on QoS-related parameters such as latency and jitter.
3.7.1. Data Center Network Operation
Data centers come in a wide variety of sizes and configurations, but
all contain compute servers, storage, and application control. Data
centers offer application services to end-users, such as video
gaming, cloud computing, and others. Since the data centers used to
provide application services may be distributed around a network, the
decisions about the control and management of application services,
such as where to instantiate another service instance or to which
King & Farrel Informational [Page 53]
RFC 7491 PCE-Based Architecture for ABNO March 2015
data center a new client is assigned, can have a significant impact
on the state of the network. Conversely, the capabilities and state
of the network can have a major impact on application performance.
These decisions are typically made by applications with very little
or no information concerning the underlying network. Hence, such
decisions may be suboptimal from the application's point of view or
considering network resource utilization and quality of service.
Cross-Stratum Optimization is the process of optimizing both the
application experience and the network utilization by coordinating
decisions in the application stratum and the network stratum.
Application resources can be roughly categorized into computing
resources (i.e., servers of various types and granularities, such as
Virtual Machines (VMs), memory, and storage) and content (e.g.,
video, audio, databases, and large data sets). By "network stratum"
we mean the IP layer and below (e.g., MPLS, Synchronous Digital
Hierarchy (SDH), OTN, WDM). The network stratum has resources that
include routers, switches, and links. We are particularly interested
in further unleashing the potential presented by MPLS and GMPLS
control planes at the lower network layers in response to the high
aggregate or individual demands from the application layer.
This use case demonstrates that the ABNO architecture can allow
cross-stratum application/network optimization for the data center
use case. Other forms of Cross-Stratum Optimization (for example,
for peer-to-peer applications) are out of scope.
3.7.1.1. Virtual Machine Migration
A key enabler for data center cost savings, consolidation,
flexibility, and application scalability has been the technology of
compute virtualization provided through Virtual Machines (VMs). To
the software application, a VM looks like a dedicated processor with
dedicated memory and a dedicated operating system.
VMs not only offer a unit of compute power but also provide an
"application environment" that can be replicated, backed up, and
moved. Different VM configurations may be offered that are optimized
for different types of processing (e.g., memory intensive, throughput
intensive).
King & Farrel Informational [Page 54]
RFC 7491 PCE-Based Architecture for ABNO March 2015
VMs may be moved between compute resources in a data center and could
be moved between data centers. VM migration serves to balance load
across data center resources and has several modes:
(i) scheduled vs. dynamic;
(ii) bulk vs. sequential;
(iii) point-to-point vs. point-to-multipoint
While VM migration may solve problems of load or planned maintenance
within a data center, it can also be effective to reduce network load
around the data center. But the act of migrating VMs, especially
between data centers, can impact the network and other services that
are offered.
For certain applications such as disaster recovery, bulk migration is
required on the fly, which may necessitate concurrent computation and
path setup dynamically.
Thus, application stratum operations must also take into account the
situation in the network stratum, even as the application stratum
actions may be driven by the status of the network stratum.
3.7.1.2. Load Balancing
Application servers may be instantiated in many data centers located
in different parts of the network. When an end-user makes an
application request, a decision has to be made about which data
center should host the processing and storage required to meet the
request. One of the major drivers for operating multiple data
centers (rather than one very large data center) is so that the
application will run on a machine that is closer to the end-users and
thus improve the user experience by reducing network latency.
However, if the network is congested or the data center is
overloaded, this strategy can backfire.
Thus, the key factors to be considered in choosing the server on
which to instantiate a VM for an application include:
- The utilization of the servers in the data center
- The network load conditions within a data center
- The network load conditions between data centers
- The network conditions between the end-user and data center
King & Farrel Informational [Page 55]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Again, the choices made in the application stratum need to consider
the situation in the network stratum.
3.7.2. Application of the ABNO Architecture
This section shows how the ABNO architecture is applicable to the
cross-stratum data center issues described in Section 3.7.1.
Figure 29 shows a diagram of an example data center-based
application. A carrier network provides access for an end-user
through PE4. Three data centers (DC1, DC2, and DC3) are accessed
through different parts of the network via PE1, PE2, and PE3.
The Application Service Coordinator receives information from the
end-user about the desired services and converts this information to
service requests that it passes to the ABNO Controller. The
end-users may already know which data center they wish to use, or the
Application Service Coordinator may be able to make this
determination; otherwise, the task of selecting the data center must
be performed by the ABNO Controller, and this may utilize a further
database (see Section 2.3.1.8) to contain information about server
loads and other data center parameters.
The ABNO Controller examines the network resources using information
gathered from the other ABNO components and uses those components to
configure the network to support the end-user's needs.
King & Farrel Informational [Page 56]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+----------+ +---------------------------------+
| End-User |--->| Application Service Coordinator |
+----------+ +---------------------------------+
| |
| v
| +-----------------+
| | ABNO Controller |
| +-----------------+
| |
| v
| +---------------------+ +--------------+
| |Other ABNO Components| | o o o DC 1 |
| +---------------------+ | \|/ |
| | ------|---O |
| v | | |
| --------------------------|-- +--------------+
| / Carrier Network PE1 | \
| / .....................O \ +--------------+
| | . | | o o o DC 2 |
| | PE4 . PE2 | | \|/ |
---------|----O........................O---|--|---O |
| . | | |
| . PE3 | +--------------+
\ .....................O /
\ | / +--------------+
--------------------------|-- | o o o DC 3 |
| | \|/ |
------|---O |
| |
+--------------+
Figure 29: The ABNO Architecture in the Context of
Cross-Stratum Optimization for Data Centers
3.7.2.1. Deployed Applications, Services, and Products
The ABNO Controller will need to utilize a number of components to
realize the CSO functions described in Section 3.7.1.
The ALTO Server provides information about topological proximity and
appropriate geographical location to servers with respect to the
underlying networks. This information can be used to optimize the
selection of peer location, which will help reduce the path of IP
traffic or can contain it within specific service providers'
networks. ALTO in conjunction with the ABNO Controller and the
Application Service Coordinator can address general problems such as
the selection of application servers based on resource availability
and usage of the underlying networks.
King & Farrel Informational [Page 57]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The ABNO Controller can also formulate a view of current network load
from the TED and from the OAM Handler (for example, by running
diagnostic tools that measure latency, jitter, and packet loss).
This view obviously influences not just how paths from the end-user
to the data center are provisioned but can also guide the selection
of which data center should provide the service and possibly even the
points of attachment to be used by the end-user and to reach the
chosen data center. A view of how the PCE can fit in with CSO is
provided in [CSO-PCE], on which the content of Figure 29 is based.
As already discussed, the combination of the ABNO Controller and the
Application Service Coordinator will need to be able to select (and
possibly migrate) the location of the VM that provides the service
for the end-user. Since a common technique used to direct the
end-user to the correct VM/server is to employ DNS redirection, an
important capability of the ABNO Controller will be the ability to
program the DNS servers accordingly.
Furthermore, as already noted in other sections of this document, the
ABNO Controller can coordinate the placement of traffic within the
network to achieve load balancing and to provide resilience to
failures. These features can be used in conjunction with the
functions discussed above, to ensure that the placement of new VMs,
the traffic that they generate, and the load caused by VM migration
can be carried by the network and do not disrupt existing services.
3.8. ALTO Server
The ABNO architecture allows use cases with joint network and
application-layer optimization. In such a use case, an application
is presented with an abstract network topology containing only
information relevant to the application. The application computes
its application-layer routing according to its application objective.
The application may interact with the ABNO Controller to set up
explicit LSPs to support its application-layer routing.
The following steps are performed to illustrate such a use case.
1. Application Request of Application-Layer Topology
Consider the network shown in Figure 30. The network consists of
five nodes and six links.
The application, which has end points hosted at N0, N1, and N2,
requests network topology so that it can compute its application-
layer routing, for example, to maximize the throughput of content
replication among end points at the three sites.
King & Farrel Informational [Page 58]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+----+ L0 Wt=10 BW=50 +----+
| N0 |............................| N3 |
+----+ +----+
| \ L4 |
| \ Wt=7 |
| \ BW=40 |
| \ |
L1 | +----+ |
Wt=10 | | N4 | L2 |
BW=45 | +----+ Wt=12 |
| / BW=30 |
| / L5 |
| / Wt=10 |
| / BW=45 |
+----+ +----+
| N1 |............................| N2 |
+----+ L3 Wt=15 BW=35 +----+
Figure 30: Raw Network Topology
The request arrives at the ABNO Controller, which forwards the
request to the ALTO Server component. The ALTO Server consults
the Policy Agent, the TED, and the PCE to return an abstract,
application-layer topology.
For example, the policy may specify that the bandwidth exposed to
an application may not exceed 40 Mbps. The network has
precomputed that the route from N0 to N2 should use the path
N0->N3->N2, according to goals such as GCO (see Section 3.4). The
ALTO Server can then produce a reduced topology for the
application, such as the topology shown in Figure 31.
King & Farrel Informational [Page 59]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+----+
| N0 |............
+----+ \
| \ \
| \ \
| \ \
| | \ AL0M2
L1 | | AL4M5 \ Wt=22
Wt=10 | | Wt=17 \ BW=30
BW=40 | | BW=40 \
| | \
| / \
| / \
| / \
+----+ +----+
| N1 |........................| N2 |
+----+ L3 Wt=15 BW=35 +----+
Figure 31: Reduced Graph for a Particular Application
The ALTO Server uses the topology and existing routing to compute
an abstract network map consisting of three PIDs. The pair-wise
bandwidth as well as shared bottlenecks will be computed from the
internal network topology and reflected in cost maps.
2. Application Computes Application Overlay
Using the abstract topology, the application computes an
application-layer routing. For concreteness, the application may
compute a spanning tree to maximize the total bandwidth from N0 to
N2. Figure 32 shows an example of application-layer routing,
using a route of N0->N1->N2 for 35 Mbps and N0->N2 for 30 Mbps,
for a total of 65 Mbps.
King & Farrel Informational [Page 60]
RFC 7491 PCE-Based Architecture for ABNO March 2015
+----+
| N0 |----------------------------------+
+----+ AL0M2 BW=30 |
| |
| |
| |
| |
| L1 |
| |
| BW=35 |
| |
| |
| |
V V
+----+ L3 BW=35 +----+
| N1 |...............................>| N2 |
+----+ +----+
Figure 32: Application-Layer Spanning Tree
3. Application Path Set Up by the ABNO Controller
The application may submit its application routes to the ABNO
Controller to set up explicit LSPs to support its operation. The
ABNO Controller consults the ALTO maps to map the application-
layer routing back to internal network topology and then instructs
the Provisioning Manager to set up the paths. The ABNO Controller
may re-trigger GCO to reoptimize network traffic engineering.
3.9. Other Potential Use Cases
This section serves as a placeholder for other potential use cases
that might get documented in future documents.
3.9.1. Traffic Grooming and Regrooming
This use case could cover the following scenarios:
- Nested LSPs
- Packet Classification (IP flows into LSPs at edge routers)
- Bucket Stuffing
- IP Flows into ECMP Hash Bucket
King & Farrel Informational [Page 61]
RFC 7491 PCE-Based Architecture for ABNO March 2015
3.9.2. Bandwidth Scheduling
Bandwidth scheduling consists of configuring LSPs based on a given
time schedule. This can be used to support maintenance or
operational schedules or to adjust network capacity based on traffic
pattern detection.
The ABNO framework provides the components to enable bandwidth
scheduling solutions.
4. Survivability and Redundancy within the ABNO Architecture
The ABNO architecture described in this document is presented in
terms of functional units. Each unit could be implemented separately
or bundled with other units into single programs or products.
Furthermore, each implemented unit or bundle could be deployed on a
separate device (for example, a network server) or on a separate
virtual machine (for example, in a data center), or groups of
programs could be deployed on the same processor. From the point of
view of the architectural model, these implementation and deployment
choices are entirely unimportant.
Similarly, the realization of a functional component of the ABNO
architecture could be supported by more than one instance of an
implementation, or by different instances of different
implementations that provide the same or similar function. For
example, the PCE component might have multiple instantiations for
sharing the processing load of a large number of computation
requests, and different instances might have different algorithmic
capabilities so that one instance might serve parallel computation
requests for disjoint paths, while another instance might have the
capability to compute optimal point-to-multipoint paths.
This ability to have multiple instances of ABNO components also
enables resiliency within the model, since in the event of the
failure of one instance of one component (because of software
failure, hardware failure, or connectivity problems) other instances
can take over. In some circumstances, synchronization between
instances of components may be needed in order to facilitate seamless
resiliency.
How these features are achieved in an ABNO implementation or
deployment is outside the scope of this document.
King & Farrel Informational [Page 62]
RFC 7491 PCE-Based Architecture for ABNO March 2015
5. Security Considerations
The ABNO architecture describes a network system, and security must
play an important part.
The first consideration is that the external protocols (those shown
as entering or leaving the big box in Figure 1) must be appropriately
secured. This security will include authentication and authorization
to control access to the different functions that the ABNO system can
perform, to enable different policies based on identity, and to
manage the control of the network devices.
Secondly, the internal protocols that are used between ABNO
components must also have appropriate security, particularly when the
components are implemented on separate network nodes.
Considering that the ABNO system contains a lot of data about the
network, the services carried by the network, and the services
delivered to customers, access to information held in the system must
be carefully managed. Since such access will be largely through the
external protocols, the policy-based controls enabled by
authentication will be powerful. But it should also be noted that
any data sent from the databases in the ABNO system can reveal
details of the network and should, therefore, be considered as a
candidate for encryption. Furthermore, since ABNO components can
access the information stored in the database, care is required to
ensure that all such components are genuine and to consider
encrypting data that flows between components when they are
implemented at remote nodes.
The conclusion is that all protocols used to realize the ABNO
architecture should have rich security features.
6. Manageability Considerations
The whole of the ABNO architecture is essentially about managing the
network. In this respect, there is very little extra to say. ABNO
provides a mechanism to gather and collate information about the
network, reporting it to management applications, storing it for
future inspection, and triggering actions according to configured
policies.
King & Farrel Informational [Page 63]
RFC 7491 PCE-Based Architecture for ABNO March 2015
The ABNO system will, itself, need monitoring and management. This
can be seen as falling into several categories:
- Management of external protocols
- Management of internal protocols
- Management and monitoring of ABNO components
- Configuration of policy to be applied across the ABNO system
7. Informative References
[BGP-LS] Gredler, H., Medved, J., Previdi, S., Farrel, A., and S.
Ray, "North-Bound Distribution of Link-State and TE
Information using BGP", Work in Progress, draft-ietf-idr-
ls-distribution-10, January 2015.
[CSO-PCE] Dhody, D., Lee, Y., Contreras, LM., Gonzalez de Dios, O.,
and N. Ciulli, "Cross Stratum Optimization enabled Path
Computation", Work in Progress, draft-dhody-pce-cso-
enabled-path-computation-07, January 2015.
[EON] Gerstel, O., Jinno, M., Lord, A., and S.J.B. Yoo, "Elastic
optical networking: a new dawn for the optical layer?",
IEEE Communications Magazine, Volume 50, Issue 2,
ISSN 0163-6804, February 2012.
[Flood] Project Floodlight, "Floodlight REST API",
<http://www.projectfloodlight.org>.
[G.694.1] ITU-T Recommendation G.694.1, "Spectral grids for WDM
applications: DWDM frequency grid", February 2012.
[G.709] ITU-T Recommendation G.709, "Interface for the optical
transport network", February 2012.
[I2RS-Arch]
Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
Nadeau, "An Architecture for the Interface to the Routing
System", Work in Progress, draft-ietf-i2rs-
architecture-09, March 2015.
[I2RS-PS] Atlas, A., Ed., Nadeau, T., Ed., and D. Ward, "Interface
to the Routing System Problem Statement", Work in
Progress, draft-ietf-i2rs-problem-statement-06,
January 2015.
King & Farrel Informational [Page 64]
RFC 7491 PCE-Based Architecture for ABNO March 2015
[ONF] Open Networking Foundation, "OpenFlow Switch Specification
Version 1.4.0 (Wire Protocol 0x05)", October 2013.
[PCE-Init-LSP]
Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", Work in Progress, draft-ietf-pce-pce-initiated-
lsp-03, March 2015.
[RESTCONF] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", Work in Progress, draft-ietf-netconf-
restconf-04, January 2015.
[RFC2748] Durham, D., Ed., Boyle, J., Cohen, R., Herzog, S., Rajan,
R., and A. Sastry, "The COPS (Common Open Policy Service)
Protocol", RFC 2748, January 2000,
<http://www.rfc-editor.org/info/rfc2748>.
[RFC2753] Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework
for Policy-based Admission Control", RFC 2753,
January 2000, <http://www.rfc-editor.org/info/rfc2753>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001,
<http://www.rfc-editor.org/info/rfc3209>.
[RFC3292] Doria, A., Hellstrand, F., Sundell, K., and T. Worster,
"General Switch Management Protocol (GSMP) V3", RFC 3292,
June 2002, <http://www.rfc-editor.org/info/rfc3292>.
[RFC3412] Case, J., Harrington, D., Presuhn, R., and B. Wijnen,
"Message Processing and Dispatching for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3412,
December 2002, <http://www.rfc-editor.org/info/rfc3412>.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003, <http://www.rfc-editor.org/info/rfc3473>.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003, <http://www.rfc-editor.org/info/rfc3630>.
King & Farrel Informational [Page 65]
RFC 7491 PCE-Based Architecture for ABNO March 2015
[RFC3746] Yang, L., Dantu, R., Anderson, T., and R. Gopal,
"Forwarding and Control Element Separation (ForCES)
Framework", RFC 3746, April 2004,
<http://www.rfc-editor.org/info/rfc3746>.
[RFC3985] Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005,
<http://www.rfc-editor.org/info/rfc3985>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006, <http://www.rfc-editor.org/info/rfc4655>.
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008,
<http://www.rfc-editor.org/info/rfc5150>.
[RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
M., and D. Brungard, "Requirements for GMPLS-Based Multi-
Region and Multi-Layer Networks (MRN/MLN)", RFC 5212,
July 2008, <http://www.rfc-editor.org/info/rfc5212>.
[RFC5254] Bitar, N., Ed., Bocci, M., Ed., and L. Martini, Ed.,
"Requirements for Multi-Segment Pseudowire Emulation Edge-
to-Edge (PWE3)", RFC 5254, October 2008,
<http://www.rfc-editor.org/info/rfc5254>.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, July 2008,
<http://www.rfc-editor.org/info/rfc5277>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008,
<http://www.rfc-editor.org/info/rfc5305>.
[RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
"Policy-Enabled Path Computation Framework", RFC 5394,
December 2008, <http://www.rfc-editor.org/info/rfc5394>.
[RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, March 2009,
<http://www.rfc-editor.org/info/rfc5424>.
[RFC5440] Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009, <http://www.rfc-editor.org/info/rfc5440>.
King & Farrel Informational [Page 66]
RFC 7491 PCE-Based Architecture for ABNO March 2015
[RFC5520] Bradford, R., Ed., Vasseur, JP., and A. Farrel,
"Preserving Topology Confidentiality in Inter-Domain Path
Computation Using a Path-Key-Based Mechanism", RFC 5520,
April 2009, <http://www.rfc-editor.org/info/rfc5520>.
[RFC5557] Lee, Y., Le Roux, JL., King, D., and E. Oki, "Path
Computation Element Communication Protocol (PCEP)
Requirements and Protocol Extensions in Support of Global
Concurrent Optimization", RFC 5557, July 2009,
<http://www.rfc-editor.org/info/rfc5557>.
[RFC5623] Oki, E., Takeda, T., Le Roux, JL., and A. Farrel,
"Framework for PCE-Based Inter-Layer MPLS and GMPLS
Traffic Engineering", RFC 5623, September 2009,
<http://www.rfc-editor.org/info/rfc5623>.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009, <http://www.rfc-editor.org/info/rfc5693>.
[RFC5810] Doria, A., Ed., Hadi Salim, J., Ed., Haas, R., Ed.,
Khosravi, H., Ed., Wang, W., Ed., Dong, L., Gopal, R., and
J. Halpern, "Forwarding and Control Element Separation
(ForCES) Protocol Specification", RFC 5810, March 2010,
<http://www.rfc-editor.org/info/rfc5810>.
[RFC6007] Nishioka, I. and D. King, "Use of the Synchronization
VECtor (SVEC) List for Synchronized Dependent Path
Computations", RFC 6007, September 2010,
<http://www.rfc-editor.org/info/rfc6007>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
October 2010, <http://www.rfc-editor.org/info/rfc6020>.
[RFC6107] Shiomoto, K., Ed., and A. Farrel, Ed., "Procedures for
Dynamically Signaled Hierarchical Label Switched Paths",
RFC 6107, February 2011,
<http://www.rfc-editor.org/info/rfc6107>.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011,
<http://www.rfc-editor.org/info/rfc6120>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
King & Farrel Informational [Page 67]
RFC 7491 PCE-Based Architecture for ABNO March 2015
[RFC6707] Niven-Jenkins, B., Le Faucheur, F., and N. Bitar, "Content
Distribution Network Interconnection (CDNI) Problem
Statement", RFC 6707, September 2012,
<http://www.rfc-editor.org/info/rfc6707>.
[RFC6805] King, D., Ed., and A. Farrel, Ed., "The Application of the
Path Computation Element Architecture to the Determination
of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
November 2012, <http://www.rfc-editor.org/info/rfc6805>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, September 2013,
<http://www.rfc-editor.org/info/rfc7011>.
[RFC7285] Alimi, R., Ed., Penno, R., Ed., Yang, Y., Ed., Kiesel, S.,
Previdi, S., Roome, W., Shalunov, S., and R. Woundy,
"Application-Layer Traffic Optimization (ALTO) Protocol",
RFC 7285, September 2014,
<http://www.rfc-editor.org/info/rfc7285>.
[RFC7297] Boucadair, M., Jacquenet, C., and N. Wang, "IP
Connectivity Provisioning Profile (CPP)", RFC 7297,
July 2014, <http://www.rfc-editor.org/info/rfc7297>.
[Stateful-PCE]
Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
Extensions for Stateful PCE", Work in Progress,
draft-ietf-pce-stateful-pce-10, October 2014.
[TL1] Telcorida, "Operations Application Messages - Language For
Operations Application Messages", GR-831, November 1996.
[TMF-MTOSI]
TeleManagement Forum, "Multi-Technology Operations Systems
Interface (MTOSI)",
<https://www.tmforum.org/MTOSI/2319/home.html>.
[YANG-Rtg] Lhotka, L. and A. Lindem, "A YANG Data Model for Routing
Management", Work in Progress, draft-ietf-netmod-routing-
cfg-17, March 2015.
King & Farrel Informational [Page 68]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Appendix A. Undefined Interfaces
This appendix provides a brief list of interfaces that are not yet
defined at the time of this writing. Interfaces where there is a
choice of existing protocols are not listed.
o An interface for adding additional information to the Traffic
Engineering Database is described in Section 2.3.2.3. No protocol
is currently identified for this interface, but candidates
include:
- The protocol developed or adopted to satisfy the requirements of
I2RS [I2RS-Arch]
- NETCONF [RFC6241]
o The protocol to be used by the Interface to the Routing System is
described in Section 2.3.2.8. The I2RS working group has
determined that this protocol will be based on a combination of
NETCONF [RFC6241] and RESTCONF [RESTCONF] with further additions
and modifications as deemed necessary to deliver the desired
function. The details of the protocol are still to be determined.
o As described in Section 2.3.2.10, the Virtual Network Topology
Manager needs an interface that can be used by a PCE or the ABNO
Controller to inform it that a client layer needs more virtual
topology. It is possible that the protocol identified for use
with I2RS will satisfy this requirement, or this could be achieved
using extensions to the PCEP Notify message (PCNtf).
o The north-bound interface from the ABNO Controller is used by the
NMS, OSS, and Application Service Coordinator to request services
in the network in support of applications as described in
Section 2.3.2.11.
- It is possible that the protocol selected or designed to satisfy
I2RS will address the requirement.
- A potential approach for this type of interface is described in
[RFC7297] for a simple use case.
o As noted in Section 2.3.2.14, there may be layer-independent data
models for offering common interfaces to control, configure, and
report OAM.
King & Farrel Informational [Page 69]
RFC 7491 PCE-Based Architecture for ABNO March 2015
o As noted in Section 3.6, the ABNO model could be applied to
placing multi-segment pseudowires in a network topology made up of
S-PEs and MPLS tunnels. The current definition of PCEP [RFC5440]
and associated extensions that are works in progress do not
include all of the details to request such paths, so some work
might be necessary, although the general concepts will be easily
reusable. Indeed, such work may be necessary for the wider
applicability of PCEs in many networking scenarios.
Acknowledgements
Thanks for discussions and review are due to Ken Gray, Jan Medved,
Nitin Bahadur, Diego Caviglia, Joel Halpern, Brian Field, Ori
Gerstel, Daniele Ceccarelli, Cyril Margaria, Jonathan Hardwick, Nico
Wauters, Tom Taylor, Qin Wu, and Luis Contreras. Thanks to George
Swallow for suggesting the existence of the SRLG database. Tomonori
Takeda and Julien Meuric provided valuable comments as part of their
Routing Directorate reviews. Tina Tsou provided comments as part of
her Operational Directorate review.
This work received funding from the European Union's Seventh
Framework Programme for research, technological development, and
demonstration, through the PACE project under grant agreement
number 619712 and through the IDEALIST project under grant agreement
number 317999.
King & Farrel Informational [Page 70]
RFC 7491 PCE-Based Architecture for ABNO March 2015
Contributors
Quintin Zhao
Huawei Technologies
125 Nagog Technology Park
Acton, MA 01719
United States
EMail: qzhao@huawei.com
Victor Lopez
Telefonica I+D
EMail: vlopez@tid.es
Ramon Casellas
CTTC
EMail: ramon.casellas@cttc.es
Yuji Kamite
NTT Communications Corporation
EMail: y.kamite@ntt.com
Yosuke Tanaka
NTT Communications Corporation
EMail: yosuke.tanaka@ntt.com
Young Lee
Huawei Technologies
EMail: leeyoung@huawei.com
Y. Richard Yang
Yale University
EMail: yry@cs.yale.edu
Authors' Addresses
Daniel King
Old Dog Consulting
EMail: daniel@olddog.co.uk
Adrian Farrel
Juniper Networks
EMail: adrian@olddog.co.uk
King & Farrel Informational [Page 71]