MQTT

RSMP 4 is build on top of MQTT. MQTT is based on a publish-subscribe model with a broker in the middle and topic paths as a flexible way to route and filter message.

Broker

With MQTT, all clients connect to a central broker, which routes messages basd on topics paths:

 graph LR;
      A[Client]---Broker;
      B[Client]---Broker;
      Broker---C[Client];
      Broker---D[Client];

The architecture makes it possible for clients to communicate with all other clients, via the broker. However, you can setup access control on the broker when needed.

There is no inherent idea of a site vs. supervisor side in MQTT, it’s all just clients connecting to the broker. In RSMP 4 clients are known as nodes.

Topic Paths

MQTT uses topic paths as a fundemental concept. A topic path is string using forward slashes as delimiters.

RSMP 4 uses a Device-Centric topic layout:

<../../node>/type/code[/<component>]

Sections

Section	Description	Format	Example
Node ID	Unique Device Identifier including optional hierarchy prefix.	[../../]node	tlc-001
Type	Protocol Keyword / Parsing Anchor.	Fixed Enum	command, status, alarm, presence
Code	Message Code (from SXL). Flattened to avoid ambiguity.	Dotted String	tlc.plan.set (derived from tlc/plan/set)
Component	Logic resource path.	Slashed String	sg/1

The node id can consist of 1 or more levels, e.g. af5g, zone1/tlc-001 or dk/cph/tlc-001. Using the same number of levels for all devices in a setup is recommended, but not required.

Examples

45fe/command/tlc.plan.set 45fe/status/tlc.plan.status

Wildcards

”#” (hash sign) is used to match multiple levels in the hierarchy.

This layout allows easy subscription to all messages for a specific device or area:

• All messages for a specific device: 45fe/#
• All messages for a region: dk/#

”\+” (plus sign) is used to match a single level in the hierarchy.

• All status messages for a device: 45fe/status/#