The Open Control Architecture (OCA) is a communications protocol architecture for control, monitoring, and connection management of networked audio and video devices. Such networks are referred to as "media networks".

The official specification of OCA is the Audio Engineering Society (AES) standard known as AES70-2015, or just AES70.

AES70 is an open standard that may be used freely, without licenses, fees, or organization memberships.

Applicability

AES70 is intended to support media networks that combine devices from diverse manufacturers. Targeted for professional applications, AES70 is suitable for media networks of 2 to 10,000 devices, including networks with mission-critical and/or life-safety roles.

AES70 is for device control, monitoring, and connection management only. It does not provide transport of media program material. However, AES70 is designed to work with virtually any media transport scheme, as the application requires.

AES70's parts are separable and may be used independently. For example, a device may implement AES70 connection management, but use other means for operational control and monitoring.

AES70 is termed an "architecture" because it provides the basis for definition of multiple control protocols. These protocols all share a common programming model, but vary in signalling detail, depending on the form of the underlying data transport mechanism. An AES70 application will use whichever AES70 protocol is appropriate for the communications method available.

Background

OCA, the architecture of AES70, was developed by the OCA Alliance,The Open Control Architecture Alliance, http://ocaalliance.com/ trade association, beginning in 2011. OCA was based on an existing control protocol named OCP, which had been created by Bosch Communications Systems in 2009 and 2010. OCP was in turn based on an embryonic control protocol standard named AES-24 AES24-1-1999 (w2004): AES standard for sound system control - Application protocol for controlling and monitoring audio devices via digital data networks - Part 1: Principles, formats, and basic procedures. 2004: Audio Engineering Society, New York. AES24-2-tu (w2004): PROPOSED DRAFT AES standard for sound system control - application protocol for controlling and monitoring audio devices via digital data networks - Part 2, data types, constants, and class structure (for Trial Use). 2004: Audio Engineering Society, New York. developed by the AES in the early 1990s.

From the outset, it was the intention of all involved to have OCA rendered into an open public standard. The Alliance completed OCA development in the Fall of 2014, and transferred the specification to the AES for rendering into a formal standard. AES70, the formal standard, was published on January 4, 2016.

Today, the OCA Alliance works to develop and enhance the functionality of AES70 and to promote AES70's adoption throughout the professional media systems industry. The Alliance promotes understanding and adoption of AES70, facilitates the creation of AES70 implementations and related tools and technologies, and develops future functional enhancements of the AES70 standard.

Structural Overview

Scope

AES70 defines the control interface that a media device presents to a network to which it is connected. Thus, AES70 is concerned with the representation of device functions in a systematic way, and with the control and monitoring of those functions via a well-defined family of protocols.

Media networks normally include one or more devices called "controllers" with user interfaces that allow humans to control and monitor the audio and/or video functioning of the networked devices. In AES70-compliant networks, controllers use AES70 protocols to communicate with the devices they control.

AES70 defines the control protocol used between controllers and devices; its scope does not extend to cover the design or construction of controllers or their user interfaces.

AES70 is intended to be used for professional applications. Technical requirements for such applications have been detailed elsewhere .Jeffrey Berryman, "Technical Criteria for Professional Media Networks," in Proceedings of AES 44th Conference on Networking, San Diego, 2011. OCA's scope excludes applications in homes, automobiles, and other consumer areas.

Device Model

The AES70 Device Model is the canonical description of the control interface that an AES70-compliant device presents to the network. The AES70 Device Model is object-oriented. It defines a required and an optional set of objects ("OCA objects") that the device's control interface implements. Using an AES70 protocol, controllers may access the properties of these objects to perform control, monitoring, and connection management operations.

OCA objects are abstractions that represent device control and monitoring points and media connections. They may or may not correspond to actual programming objects or hardware components inside the device. If a device correctly implements an AES70 protocol, it is AES70-compliant. AES70 does not define how that may or should be accomplished.

Generally speaking, the AES70 device model tends to differ from device models in other control architectures.American National Standards Institute. "E1-17: Architecture for Control Networks" . Definition of ACN. Package of 17 documents plus supporting files. At http://webstore.ansi.org.Richard Foss and Andrew Eales, "Towards a Standard Model for Networked Audio Devices," in Proceedings of the AES 44th International Conference - Audio Networking, San Diego, 2011 . Includes a helpful overview of current media system control protocols. in several ways:

AES70 does not presume a hierarchical device structure. AES70 does not predefine specific processing configurations, signal processing modules, device types, or device families. AES70 does not define controller user interfaces or user interface elements. AES70 has strong support for dynamically reconfigurable devices. AES70 offers a strong and transport-agnostic model for connection management. AES70's repertoire of management and housekeeping functions is relatively rich.

Class Structure

The AES70 Class Structure defines a set of classes ("OCA Classes") that devices may use to instantiate OCA objects. There are three kinds of classes:

Workers, which represent application functions of devices—gain controls, level meters, switches, equalizers, et cetera. Agents, which modify and assist control functions in various ways. Managers, which represent various global device states.

OCA classes may be broadly grouped into three functional sets: Management classes, which provide basic device management and housekeeping functions. Control and monitoring classes, which are concerned with device operation. Connection management classes, which are concerned with setup, supervision, and teardown of media stream connections, and with directory (aka "discovery") services for location and identification of network devices.

Protocols

As noted above, the AES70 architecture supports multiple protocols, depending on the nature of the network medium used. At present, AES70 defines one protocol, named OCP.1. OCP.1 is the AES70 protocol for TCP/IP networks. Future plans include OCP.2, a byte-serial version for USB networks, Bluetooth connections, and point-to-point links, and OCP.3, a text version in JSON.

Each AES70 protocol defines three kinds of messages, as follows:

Commands - directives from a controller to an object in a device, requesting some kind of action or retrieving some parameter value; Responses - replies from an object to a controller, indicating success or failure of a previous command, and returning parameter values, where requested; Notifications - automatically generated messages from an object in a device to a controller, indicating the occurrence of some condition or periodically reporting a parameter value such as signal amplitude.

Control Repertoire

The AES70 control repertoire covers control, monitoring, and connection management of audio devices. Future versions will expand the audio control repertoire, and may address video devices as well.

AES70 includes features that allow manufacturers to extend the OCA class structure to address functions not in the standard repertoire. Such extensions may be public or confidential, as the manufacturer chooses.

Table 1 summarizes the AES70-2015 control repertoire.

Table 1. AES70-2015 Control RepertoireMedia Connection ManagementSignal Processing - Connection control - Gain controls - Directory/discovery functions - MutesAdditional Functions - Switches (n-position) - Control grouping (~VCA groups) - Delays - Crossfading - Equalizers - Snapshot & preset management - Filters (IIR & FIR) - Reconfigurable DSP device setup - Limiters & compressors - Reliable firmware updating - Expanders & gatesSignal Monitoring - Levelers - Level sensors (meters) - Matrices - Frequency sensors - Signal generators - Time interval sensors - Arbitrary numeric parameters - Temperature sensors - Arbitrary string parameters - Arbitrary numeric parameters+ Proprietary extensions as needed

Notable Features

Connection Management

Although AES70 does not itself provide media transport functions, it is designed to interface with modern media transport standards to control signal routing and other connection setup functions, and to interface with network directory/discovery services. In this capacity, AES70 provides a useful level of abstraction for applications, allowing controllers and devices to use one common software model for managing stream connections of various transport architectures.

The OCA Alliance defines recommended practices for interfacing AES70 with various well-known media transport architectures. The specification for interfacing AES70 with a given media transport scheme is called an AES70 Adaptation.

Control Grouping

AES70 includes an architectural solution to the problems of control grouping, i.e. the use of a single control input to effect multiple operating parameters. An example of control grouping is a master gain control covering multiple device channels in one or more devices.

Control grouping poses difficult problems, especially in systems where a given operating parameter may be affected by multiple control groups. For example, in a stereophonic multiway sound system, the gain of the left-channel high-frequency amplifier may be affected by settings of master controls for (a) overall high-frequency level, (b) left-channel level, and (c) overall level of the entire system. In such systems, machine intelligence is required to manage cumulative settings effects that lead to overrange or underrange parameter values. The AES70 grouping mechanism provides a basis for such management, for one or many devices.

Snapshot and Preset Management

AES70 includes a powerful and general mechanism for applying, storing, recalling, uploading, and downloading sets of operating parameter values. Both partial and full snapshots are supported.

Reconfigurable DSP Device Setup

AES70 includes complete support for managing the configurations of reconfigurable DSP devices, i.e. software-based devices whose signal processing topologies can be defined and redefined at runtime by external controllers. For such devices, AES70 supports creation, configuration, and deletion of signal processing elements and the internal signal paths that connect them.

Proprietary Extensibility

AES70 is designed to support proprietary extensions with maximum compatibility. Manufacturers may define their own extensions to the control repertoire, and these will coexist peacefully with standard elements.

Upward / Downward Compatibility

AES70 devices and controllers will continue to interoperate as AES70 evolves over the years. Devices that use various versions of OCA will generally be intermixable in one media network without problems.