Core Components of Model-driven Telemetry Streaming
The core components used in streaming model-driven telemetry data are:
A telemetry session can be initiated using:
In a dial-in mode,
an MDT receiver dials in to the router, and subscribes dynamically to one or
more sensor paths or subscriptions. The router acts as the server and the
receiver is the client. The router streams telemetry data through the same
session. The dial-in mode of subscriptions is dynamic. This dynamic
subscription terminates when the receiver cancels the subscription or when the
There are two
methods to request sensor-paths in a dynamic subscription:
subscribe RPC defined in the model is used to specify
sensor-paths and frequency. In this method, the subscription is not associated
with an existing configured subscription. A subsequent
cancel RPC defined in the model removes an existing
IOS XR MDT RPC:
IOS XR defines RPCs to subscribe and to cancel one or more configured
subscriptions. The sensor-paths and frequency are part of the telemetry
configuration on the router. A subscription is identified by its configured
subscription name in the RPCs.
In a dial-out mode,
the router dials out to the receiver. This is the default mode of operation.
The router acts as a client and receiver acts as a server. In this mode,
sensor-paths and destinations are configured and bound together into one or
more subscriptions. The router continually attempts to establish a session with
each destination in the subscription, and streams data to the receiver. The
dial-out mode of subscriptions is persistent. When a session terminates, the
router continually attempts to re-establish a new session with the receiver for
every 30 seconds.
The sensor path
describes a YANG path or a subset of data definitions in a YANG model with a
container. In a YANG model, the sensor path can be specified to end at any
level in the container hierarchy.
device, such as a router, associates the sensor path to the nearest container
path in the model. The router encodes and streams the container path within a
single telemetry message. A receiver receives data about all the containers and
leaf nodes at and below this container path.
The router streams telemetry data for one or more sensor-paths, at the configured frequency (cadence-based streaming) or when the sensor-path content changes (event-based streaming), to one or more receivers through subscribed sessions.
A subscription binds one or more sensor paths and destinations. An MDT-capable device streams data for each sensor path at the configured frequency (cadence-based streaming) or when the sensor-path content changes (event-based streaming) to the destination.
The router streams
telemetry data using a transport mechanism. The generated data is encapsulated
into the desired format using encoders.
Telemetry (MDT) data is streamed through
these supported transport
Google Protocol RPC
(gRPC): used for both dial-in and dial-out modes.
Transmission Control Protocol
(TCP): used for only dial-out mode.
User Datagram Protocol (UDP): used for only dial-out mode.
GPB encoding: configuring for GPB encoding requires metadata in the form of compiled .proto files. A .proto file describes the GPB message format, which is used to stream data. The .proto files are available at https://github.com/cisco/bigmuddy-network-telemetry-proto/tree/master/proto_archive.
Compact GPB encoding: data is streamed in compressed and non self-describing format. A .proto file corresponding to each sensor-path must be used by the receiver to decode the streamed data.
Key-value (KV-GPB) encoding: data of each sensor path streamed is in a self-describing formatted ASCII text. A single .proto file telemetry.proto is used by the receiver to decode any sensor path data. Because the key names are included in the streamed data, the data on the wire is much larger as compared to compact GPB encoding.