esp-protocols-skill

Use the esp_modem component: create a PPP netif with ESP_NETIF_DEFAULT_PPP, then create the DCE with esp_modem_new_dev(ESP_MODEM_DCE_SIM7600, ...), and switch to ESP_MODEM_MODE_DATA. The IP address arrives via the IP_EVENT_PPP_GOT_IP event, so register IP_EVENT and NETIF_PPP_STATUS handlers first.

Use CMUX mode (ESP_MODEM_MODE_CMUX), which creates separate virtual channels for data and commands, or call esp_modem_pause_net to temporarily suspend the network. Note that SIM7000 does not support CMUX, and A76xx modules require disabling CONFIG_ESP_MODEM_CMUX_DEFRAGMENT_PAYLOAD.

Yes, esp_websocket_client supports wss connections using cert_pem, use_global_ca_store, or crt_bundle_attach with esp_crt_bundle_attach for server verification. Never call stop, destroy, or close inside the event handler because those APIs self-deadlock; signal an external task instead.

mDNS requires calling mdns_init() and mdns_hostname_set() before mdns_service_add(), otherwise publishing fails. Also confirm both devices are on the same multicast domain with UDP port 5353 allowed, and free query results with mdns_query_results_free to avoid memory leaks.

Yes, the ap_to_pppos example creates a WiFi soft-AP and forwards client traffic to the modem's PPP interface using lwIP NAPT. You must enable CONFIG_LWIP_IP_FORWARD and CONFIG_LWIP_IPV4_NAPT, then call ip_napt_enable on the AP interface IP and push the PPP DNS to DHCP clients.

mosq_broker_run blocks the calling thread rather than spawning its own task, so the calling task needs at least 5 kB of stack. Each connected client consumes about 4 kB of heap, and you must call mosq_broker_stop to unblock the run loop.