Experimental discovery implementation using mDNS, DNS-SD and MongoDB

[tksuzuki0604]

I experimentally implemented discovery by combining existing technologies (mDNS, DNS-DS and MongDB).
The method is very similar to "Two-Phase Directory-Based Discovery".

Use-case

• Using appliances in smart home
• These appliances and a controller is located in the same network
  • The controller has a TD directory
  • All devices retrieve IP address from a DHCP server
    • Also the DHCP server is located in the network
• All TDs are registered to the directory
  • Implemented three ways to register TDs to the directory
    • a) The directory discovers Things and retrieves TDs from each device
    • b) Things discover the directory and register TDs by themselves
    • c) Human discover the directory and register TDs manually
• Users retrieve all TDs from the directory and select desired appliances in the local network

Requirements

• Needs to set each device's URL(ip address or resolvable hostname) in its TD (hrefs or base)
  • Things set URLs by themselves (case 'a' and 'b')
  • Human set URLs to TDs manually (case 'c')
• Needs to search Things and the directory in the same network
• The directory needs to know how to retrieve TD from Things for the case 'a'
• Human and Things needs to know how to register TD to the directory for case 'b' and 'c'
• Users need to know how to retrieve TDs from the directory
• Needs a TD directory implementation

Implementation

• Set unique hostnames to all devices (Things and the directory)
• Set <hostname>.local as a resolvable hostname in TDs for all cases
• Used mDNS and DNS-SD to discover things and directories
• Used DNS-SD to advertise the way to retrieve or register TDs
• Used mDNS to resolve hostname in TDs
• Used Mongo DB as a backend of directories
• Made a python script to cooperate mDNS+DNS-SD with MongoDB
  • The script aloso provides REST APIs to register and retrieve TDs from the directory

[k-toumura]

I created sequence diagrams for this implementation to better understanding.
Are all those figures correct?

[tksuzuki0604]

Thank you for writing diagrams.
Sequences are almost correct, but there are some implementation level differences from my experiment.

• Instead of using different types, I used sub-type to classify Things and directories
  Because, I thought both of them are WoT related services by mean of DNS-SD's service type. (But I don't know which way is better...)
• Instead of using well-known paths, Things and directories advertise their API information by DNS-SD
  Because, there are no standard way to retrieve and register TDs in the WoT

To be more specific, followings are examples of mDNS+DNS-SD settings.

• Thing

Service type: _wot._tcp
Sub type: _device._sub._wot._tcp
Port: 10080
Text record: "retrieve=/Things"

• Directory

Service type: _wot._tcp
Sub type: _directory._sub._wot._tcp
Port: 80
Text record: “retrieve=/Things“ “register=/Things/register”

[k-toumura]

I'd updated diagrams based on your information.
This concrete example of discovery mechanism may be helpful for discussion.
Also, it is useful for (virtual) plugfest because it makes easier to install devices on plugfest environment.

• SVG version
• PlantUML source

[mmccool]

Can this be captured and put into an MD file and submitted to the repo? That way we are sure what the current, "correct" description is.

[mmccool]

Already incorporated into an MD file, can consider this closed now