Controllers
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Introduction
A Controller is Client software that interacts with the NMOS APIs to discover, connect and manage resources (Nodes, Devices, Senders and Receivers) within a networked media system.
- This document includes normative references to be followed when implementing a Controller.
- This document covers how the Controller interacts with the NMOS APIs only. It does not cover other features of the Controller software, such as presentation.
- This document does not cover any requirements relating to where a Controller is additionally acting as a Node (e.g. receiving monitoring information via IS-07).
Where this document refers to a User, this can include both human operators who drive a Controller manually and automation systems that drive a Controller programmatically.
General
HTTP APIs
Trailing Slashes
Controllers appending paths to href type attributes MUST support URLs both with and without a trailing slash, to avoid doubled or missing slashes.
Controllers performing requests other than GET or HEAD (i.e PUT, POST, DELETE, OPTIONS etc.) MUST use URLs with no trailing slash present.
API Versions
The versioning format is v<MAJOR>.<MINOR>
MINORincrements will be performed for non-breaking changes (such as the addition of attributes in a response)MAJORincrements will be performed for breaking changes (such as the renaming of a resource or attribute)
Versions MUST be represented as complete strings. Parsing MUST proceed as follows: separate into two strings, using the point (.) as a delimiter. Compare integer representations of MAJOR, MINOR version (such that v1.12 is greater than v1.5).
Implementers of Controllers are RECOMMENDED to support multiple versions of the NMOS APIs simultaneously in order to ease the upgrade process in live facilities.
Error Codes & Responses
The NMOS APIs use HTTP status codes to indicate success, failure and other cases to Controllers as per RFC 7231 and related standards.
As explicit handling of every possible HTTP response code is not expected, Controllers MUST implement generic handling for ranges of response codes (1xx, 2xx, 3xx, 4xx and 5xx).
However, where the API specifies explicit response codes the Controller SHOULD handle these cases explicitly.
When a Controller performs GET and HEAD requests, it MUST correctly handle a 301 (Moved Permanently) redirect to accommodate the API implementations permitted in the APIs: URLs: Approach to Trailing Slashes section of this specification.
If a Controller receives an HTTP 5xx or 4xx response code from the API, a failure has occurred.
The Controller SHOULD display the content of the response’s error field to the User if possible.
Connection Management
The Controller MUST implement connection management according to the APIs section of this specification.
The Controller MUST be able to perform immediate activations of Senders and Receivers to configure connections between them via the IS-05 Connection API.
The Controller MUST be able to perform an immediate activation to disable an active connection via the IS-05 Connection API.
The Controller tracks the connection status of IS-05 Senders and Receivers being controlled. The Version Timestamp section describes a mechanism to enable this.
- The Controller MUST identify that a connection to a Receiver has been activated.
- The Controller MUST be able to identify that an NMOS Sender is connected to that Receiver.
- The Controller MUST identify when the Receiver connection has been deactivated.
Where making requests to a large number of Senders and/or Receivers on the same Device, Controllers SHOULD make use of the /bulk endpoint to bundle them into a single request.
When altering the transport parameters in the /staged endpoint, the Controller SHOULD check the /constraints endpoint for the available choices for parameters accepted by the particular Sender or Receiver.
When PATCHing the transport parameters, parameters could possibly have changed since the last GET.
Therefore the Controller SHOULD set parameters that are important for a connection (e.g. master_enable and rtp_enable) in the PATCH request, even if the Controller believes they are already set as required.
The Connection API includes a sender_id parameter in each Receiver’s /active and /staged endpoints.
Similarly, it includes a receiver_id parameter in each Sender’s /active and /staged endpoints.
When modifying transport_params or transport_file to configure a Receiver to connect with a specific NMOS Sender, for example, via unicast RTP or source-specific multicast, the Controller MUST set the sender_id parameter.
Similarly, when modifying transport_params to configure a Sender to connect with a specific NMOS Receiver, for example, via unicast RTP, the Controller MUST set the receiver_id parameter.
Otherwise, when modifying transport_params or transport_file, the Controller MUST set the sender_id or receiver_id parameter to null.
Client Side Implementation Notes
Controllers MUST adhere to the APIs: Client Side Implementation Notes described in this specification, such as the sections on Conformance to Schemas, RTP Operating Point, and Failure Modes.
Interoperability
Interoperability with IS-04
API Common Keys
Controllers MUST follow the requirements for common API keys specified in the IS-04 APIs: Common Keys document including the requirements regarding use of URNs.
Interacting with Non-NMOS Devices
Controllers MUST follow the requirements for a Client interacting with non-NMOS Devices, as described in the Interoperability: Non-NMOS Devices section of this Specification.
Behaviour
Operation with SMPTE 2022-7
When the Controller is interacting with Receivers that support SMPTE 2022-7 it MUST follow the requirements for Clients described in the Behaviour: RTP Transport Type: Operation with SMPTE 2022-7 section of this specification.
Version Timestamp
In IS-04, a version timestamp increment indicates that the properties of a resource have changed, for example by the action of another Controller, and as such any information cached by the Controller could possibly be stale.
In Registered Operation, to avoid polling of the HTTP API the Controller SHOULD use an IS-04 Query API WebSocket connection to monitor version timestamp increments on Senders and Receivers being controlled.
Sender Multicast Address
The Controller MUST allow the User to configure the multicast transmit information (using IS-05 transport_params) before or in the same transaction as enabling the transmitter (setting master_enable to true).
This allows avoiding conflicts with other senders’ configurations, in particular when a Sender is added to a new system.
TCP Sessions
The Controller SHOULD use persistent TCP connections wherever possible, to allow multiple operations to be performed without repeatedly closing and reopening connections for each operation.
If the Controller uses HTTP pipelining, the guidelines set out in RFC 7230 section 6.3.2 apply.
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