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Interoperability: IS-04

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The Connection API shares a data model with the IS-04 specification, and as a result it is designed to be used alongside it. The following sub-sections identify correct behaviour for doing this.

When this API is used alongside IS-04 in a deployment, the IS-04 APIs SHOULD be operating at version 1.2 or greater in order to ensure full interoperability.

Discovery

The Connection API SHOULD be advertised as a control endpoint when publishing a compliant NMOS Device. Control interfaces can identify all Devices which implement the Connection API by a type Uniform Resource Name (URN) having the base urn:x-nmos:control:sr-ctrl followed by a / character and the API version. The associated href is the URL of the Connection API base resource.

Example: The controls attribute of a single NMOS Device

...
"controls": [
  {
    "type": "urn:x-nmos:control:sr-ctrl/v1.1",
    "href": "http://192.168.10.3/x-nmos/connection/v1.1/"
  }
]
...

As shown above the API version is included in the type, and in the href. Further control endpoints for the Connection API MAY be advertised for Devices which support multiple versions simultaneously, or have multiple network interfaces.

More details about multi-version support can be found in Upgrade Path.

A given instance of the Connection API MAY offer control of multiple Devices in a Node from a single URI. Alternatively there MAY be multiple instances of the API on one Node, each corresponding to one Device. A separate endpoint for each Device’s Connection Management instance MUST be advertised in the Device’s controls, even if the URI is the same.

API implementations MAY list an href with or without a trailing slash, provided that the trailing slash policy in APIs is adhered to. Implementers of clients need to avoid double or missing slashes when appending paths onto hrefs.

Sender & Receiver IDs

The UUIDs used to advertise Senders and Receivers in the Connection API MUST match those used in a corresponding IS-04 implementation.

Version Increments

In order to prevent unnecessary polling of the Connection API, changes to active connection parameters are signalled via the IS-04 versioning mechanism. When the active parameters of a Sender or Receiver are modified, or when a re-activation of the same parameters is performed, the version attribute of the relevant IS-04 Sender or Receiver MUST be incremented.

Identifying Active Connections

In order to populate the subscription attribute of IS-04 Senders and Receivers, the Connection API includes keys for sender_id and receiver_id in its staged parameters. These SHOULD be used to signal that a Sender or Receiver is being connected to another NMOS compatible Sender or Receiver. It is the client’s responsibility to set and unset (using null) the sender_id or receiver_id parameters when modifying the transport_params or transport_file.

Support For Legacy IS-04 Connection Management

The Connection API supersedes the now deprecated method of updating the /target resource on Node API Receivers in order to establish connections. The two methods of operation are likely to co-exist until Version 2.0 of IS-04. As such the following best practice SHOULD be followed when both are in use:

If staged modifications are present when a legacy activation is performed, these parameters MUST be discarded in favour of those provided via the Node API interface.

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