RFC 7491
A PCE-Based Architecture for Application-Based Network Operations
Pages: 71
Informational
Informational
Part 1 of 4 – Pages 1 to 24
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 OperationsAbstract
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.
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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
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.
- 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.
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.
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.
+----------------------------------------------------------------+ | 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 Architecture2.3.1. 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.
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.
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.
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.
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.
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
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.
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.
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.
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
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.
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.
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.
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.
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].
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.
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.
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