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CoAP Device

CoAP Device Setup

CoAP (Constrained Application Protocol) is a specialized web transfer protocol designed for use with constrained nodes and networks in the Internet of Things (IoT). It is a standard internet protocol closely related to HTTP in behavior and operations, but with much more efficient communication optimized for resource-limited devices.

Overview

CoAP is designed for:

  • Constrained devices with limited processing power and memory
  • Lossy networks with high packet loss and low bandwidth
  • Battery-powered devices requiring energy-efficient communication
  • Machine-to-machine (M2M) communication in IoT ecosystems
  • Embedded control systems and sensor networks

Key CoAP features:

  • UDP-based for low overhead (default port: 5683)
  • RESTful architecture similar to HTTP but optimized for constraints
  • Built-in discovery mechanism via /.well-known/core
  • Observe pattern for real-time data subscription
  • Block-wise transfers for handling large payloads

Supported Transports

ossia score supports all standard CoAP transports:

UDP (Default)

  • Lightweight, connectionless communication
  • Best for battery-powered and resource-constrained devices
  • Port 5683 (5684 for DTLS secure connections)

TCP

  • Reliable, connection-oriented communication
  • Better for stable network connections
  • Useful when message ordering is critical

WebSocket

  • CoAP over WebSocket transport
  • Browser compatibility and firewall traversal
  • Integration with web-based systems

Device Setup & Discovery

Basic Configuration

  1. Add CoAP Device: Right-click Device Explorer → Add Device → CoAP
  2. Configure Connection:
    • Host: Target device IP address (e.g., 192.168.1.100)
    • Port: CoAP port (5683 for UDP, custom for others)
    • Transport: UDP, TCP, or WebSocket

CoAP’s discovery mechanism then automatically finds available resources which get exposed as ossia device explorer nodes.

Practical Examples

Public CoAP Testing

Try with the public CoAP server at coap.me:

  1. Add CoAP Device with host coap.me, port 5683, UDP transport
  2. Explore resources like /hello, /time, /separate
  3. Test OBSERVE on resources that support real-time updates

CoAP.me Example

Troubleshooting

Connection Issues

  • Verify port 5683 accessibility through firewalls
  • Check device IP address and network connectivity
  • Test with CoAP tools (coap-client, Copper browser plugin)
  • Monitor UDP packet loss on unreliable networks

Discovery Problems

  • Check /.well-known/core endpoint responds correctly
  • Validate link format syntax in discovery responses
  • Try manual resource addition if auto-discovery fails
  • Verify content-type headers in discovery responses