Applications can subscribe to specific data items they need, by using standards-based YANG data models over NETCONF, RESTCONF, or gRPC Network Management Interface (gNMI) protocols. Subscriptions can also be created by using CLIs if it is a configured subscription. Structured data is published at a defined cadence, or on-change, based upon the subscription criteria and data type. Telemetry Roles In systems that use telemetry, different roles are involved. In this document the following telemetry roles are described: • Publisher: Network element that sends the telemetry data. • Receiver: Receives the telemetry data. This is also called the collector. • Controller:
Network element that creates subscriptions but does not receive the telemetry data. The telemetry data associated with the subscriptions, it creates goes to receivers. This is also called the management agent or management entity. • Subscriber: Network element that creates subscriptions. Technically, while this does not have to be the receiver too, in this document, both are the same. Subscription Overview Subscriptions are items that create associations between telemetry roles, and define the data that is sent between them.
Specifically, a subscription is used to define the set of data that is requested as part of the telemetry data; when the data is required, how the data is to be formatted, and, when not implicit, who (which receivers) should receive the data. Even though the maximum number of supported subscriptions is platform-dependent, currently 100 subscriptions are supported. The subscriptions can be either configured or dynamic, and use any combination of transport protocols.
If too many subscriptions are operating at the same time to allow all the valid configured subscriptions to be active, the removal of an active subscription will cause one of the inactive but valid configured subscriptions to be attempted. Periodic triggered subscriptions (100 centiseconds is the default minimum) and on-change triggered subscriptions are supported. NETCONF and other northbound programmable interfaces (such as RESTCONF or gNMI) are supported to configure subscriptions. Two types of subscriptions are used in telemetry on Cisco IOS XE systems: dynamic and configured subscriptions.
Because dynamic subscriptions are created by clients (the subscriber) that connect into the publisher, they are considered dial-in. Configured subscriptions cause the publisher to initiate connections to receivers, and as a result, they are considered dial-out. Dial-In and Dial-Out Model-Driven Telemetry The two flavors of model-driven telemetry are, dial-in and dial-out. Model-Driven Telemetry Telemetry Roles Model-Driven Telemetry 6