LwM2M Observe Notifications Not Sent

In this tutorial, you'll learn about LwM2M Observe Notifications Not Sent. We cover key concepts, practical examples, and best practices.

The Problem

LwM2M server observes a client resource but does not receive change notifications.

Quick Fix

Wrong

// Client does not send notifications on value change

Server observes the resource but never receives updates.

Right

# Anjay observation handling
#include <anjay/anjay.h>

static int temperature_read(
  anjay_t *anjay, const anjay_rid_t *rid,
  anjay_output_ctx_t *ctx) {
  
  anjay_ret_float(ctx, current_temp);
  return 0;
}

// Notify server when temperature changes
void temperature_changed(float new_temp) {
  current_temp = new_temp;
  
  // Notify all observers of /3303/0/5700
  anjay_notify_changed(anjay, ANJAY_DM_PATH(3303, 0, 5700));
}

// Server subscribes by sending Observe (GET with Observe:0)
// CoAP CoRE resource link must have 'obs' attribute
# '/3303/0/5700';rt='sensor';obs

Server receives notifications when temperature changes (Observe sequence increments).

Prevention

Call anjay_notify_changed() when the resource value changes. Observation is triggered by the server sending GET with Observe flag. Resources must have 'obs' attribute in CoRE Link Format. Set pmin/pmax attributes to control notification rate. Notifications include a sequence number — reset indicates re-registration.

DodaTech engineers apply these same patterns across Doda Browser, DodaZIP, and Durga Antivirus Pro for production IoT reliability.

FAQ