RouteMaster: Websocket Protocol for Router Control

Most control protocols for Broadcast routers come from the era of RS422 serial comms. Even those routers which support control via IP tend to use proprietary protocols that are not easily compatible with web-based control applications.

The RouteMaster Websocket protocol was designed to use web standards to enable router control from web applications running on any modern browser. This allows web pages to easily control routers and receive status from any router controlled via the RouteMaster system.

RouteMaster Web Panels use this protocol to control routers connected to the RouteMaster system. RouteMaster can also use the same protocol to control routers that support it, or downstream RouteMaster systems.

Client vs Server

The ‘client’ is typically any application that wants to make routes or receive router status, and the ‘server’ is typically the RouteMaster system (or any other router using this protocol).

The ‘server’ typically listens for connections on TCP/IP port 81, although other ports can be configured. Servers support multiple simultaneous client connections. RouteMaster limits the number of simultaneous clients according to the number of installed licenses.

WebSocket protocol

Messages are exchanged between client and server using the WebSocket protocol, described in overview here. https://en.wikipedia.org/wiki/WebSocket

Unlike HTTP it offers a persistent full-duplex connection. RouteMaster V2.3.7 and later support encrypted Websockets (‘wss://hostname:portnum’’). This can be enabled in the RouteMaster client configuration dialog.

Protocol URL

When controlling RouteMaster from other systems such as Helm, you may need to enter the URL of the connection. like an HTTP URL, this has the format <protocol>://<host>:<port>, where the protocol is ws (or wss for secure websockets)

In addition, optional query parameters can be appended which affect the operation of the protocol. currently the only one defined is the version parameter.

Examples:

• ws://localhost:81
• wss://192.168.0.222:84
• wss://webcentre.rascular.com:81?version=2

Protocol Version

The query parameter version specifies the version of protocol to be used. Version 1 is the default.

If Version 2, is specified, the multiple tallyCrosspoint messages sent on connection are replaced with a single bulkCrosspoints message.

JSON

WebSockets give a way of sending ‘messages’ between endpoints, but does not define the content and structure of those messages. Messages could be binary, XML or any proprietary format. RouteMaster uses JSON for the message structure, which fits well with JavaScript used in browser-side applications. http://json.org/

Message Flow

The protocol does not impose any restrictions on message flow. Messages can normally be sent by both client and server at any time, and in any order. However, when a new client connects to a server, it should be sent the entire router state including source and destination names, protect and crosspoint status.

The final message after the initial state has been sent will be the connectComplete message.

No Ack/Nak

Messages do not implicitly cause Ack or Nak replies to be sent. but the success of messages forcing a change of state can be determined by the tally messages returning when an operation completes.

No Query Commands

There are no query commands to request state from RouteMaster. This is because the full router state is automatically sent to all clients when they connect, and clients are then automatically notified whenever the state changes.

Use Persistent Connections

Each time a WebSocket connection is established, the full router state with names, etc is sent to the client. Client software should keep the connection open, rather than opening it every time a command must be sent.

Input/Output numbering

All sources, destinations and levels are numbered starting from ZERO.

JSON Message fields

Every JSON message has a mandatory string field “event” which is describes the message type. A structure ‘data’ then contains parameters and data regarding the event. Unknown incoming events will be ignored, and unknown fields in the JSON data are also ignored.

API on Postman

We’re switching to Postman to design, test and document our APIs. Postman support for WebSocket APIs is improving, and you’ll find the RouteMaster API with example messages here.

Messages from Server to Client

{
  "event": "tallyCrosspoint",
  "data": {
     "sources": [0,0],
  "destination":0
  }
}

{
  "event": "sourceName",
  "data": {
    "names": ["XXX A", "SRC 1", "SRC 2", "SRC 3"],
    "source":0
  }
}

{
  "event": "destName",
  "data": {
    "names":["MON", ”DST 1", ”DST 2", ”DST 3"], 
    "destination": 0 
  }
}

{
  "event": "levelName",
  "data": { 
    "names":["Video”, ”Audio”],
    "level": 0
  } 
}

{
  "event": "routerData",
  "data": 
  {
    "sources": 64, 
     "levels": 2, 
    "dests": 64, 
    "name": "DUMMY"
  }
}

{
  "event": "protectState",
  "data":
  {
    "state": [
      {"prot": "Unlocked"},
      {"prot":"Locked", “user”:”Joe”}],
    "dest": 0
  }
}

{
  "event": "connectComplete"
}

{
  "event":"salvoNames",
  "data": {
    "names": ["Salvo 1", "Salvo 2", "My Salvo"]
  }
}

{
  "event":"bulkCrosspoints",
  "data": {
    ...
  }
}

{
  "event": "sourceStatus",
  "data": {
    "source": 42,
    "state": [{...}, {...}]
  }
}

{
  "event": "destStatus",
  "data": {
    "dest": 42,
    "state": [{...}, {...}]
  }
}

Messages from Client to Server

{
  "event": "makeCrosspoint",
  "data": {
    "source":6,
    "destination":2,
    "levels":"L0"
  }
}

{
  "event": "lockOutput",  
  "data": {
    "destination": 2,
    "state":"Locked"
  } 
}

{
  "event": "fireSalvo",
  "data": {
    "id": "RESET"
  }
}

{
  "event": "freeTieline",
  "data": {
    "tieline": "Example"
  }
}

JavaScript implementation of WebSocket clients

For a good overview of how to handle JSON-based WebSockets from JavaScript, see this page:

https://www.new-bamboo.co.uk/blog/2010/02/10/json-event-based-convention-websockets/

Test Server

You can try out the  protocol using our online test server at wss://webcentre.rascular.com/routemaster . To easily view and test messages, just enter that URL at https://websocket.org/echo and ‘connect’.