diff --git a/src/sa/model/index.md b/src/sa/model/index.md
index b34ea25..9b6f222 100644
--- a/src/sa/model/index.md
+++ b/src/sa/model/index.md
@@ -779,7 +779,7 @@ Exceed: Redesign based on >3 reused components (1 Logical View, >1 Process View,
 
 Components TBD:
 - https://github.com/hap-java/HAP-Java
-- https://github.com/tlaukkan/zigbee4java
+- https://github.com/tlaukkan/MQTT4java
 - instances of the PostgreSQL 15 RDBMS ([sources here](https://github.com/postgres/postgres) and [specification here](https://www.postgresql.org/docs/15/index.html)), a _free as in beer_ and FOSS piece of software. 
 - https://spring.io/projects/spring-boot
 
@@ -803,8 +803,8 @@ component "IoT Devices" as IOT {
 
   [HomeKit smart device] as HD <<user provided>>
   [HomeKit smart sensor] as HS <<user provided>>
-  [Zigbee smart device] as ZD <<user provided>>
-  [Zigbee smart sensor] as ZS <<user provided>>
+  [MQTT smart device] as ZD <<user provided>>
+  [MQTT smart sensor] as ZS <<user provided>>
 
   HD--HDF
   HS--HSF
@@ -829,12 +829,12 @@ component "Users and Devices" as DEV {
   interface " " as WSSF
 
   [HAP-java] as HAP <<external>>
-  [zigbee4java] as ZIG <<external>>
+  [paho.mqtt.java] as ZIG <<external>>
   [Device Engine] as DI
 
   note left of DI: Already implemented using Spring Boot
 
-  [Spring WebSocket API] as WSS <<external>>
+  [javax.websocket API] as WSS <<external>>
   [User and Device DB <$database{scale=0.33}> (PostgreSQL)] <<external>> as DIDB
 
   HDF )-- HAP
@@ -898,8 +898,8 @@ title Process View: UI updates state of device
 box "IoT Devices"
   participant "HomeKit dev." as HD
   participant "HomeKit sens." as HS
-  participant "Zigbee dev." as ZD
-  participant "Zigbee sens." as ZS
+  participant "MQTT dev." as ZD
+  participant "MQTT sens." as ZS
 end box
 
 box "User Interface"
@@ -908,11 +908,11 @@ box "User Interface"
 end box
 
 box "Users and Devices"
+  participant "javax.websocket" as WSS
   participant "HAP-java" as HAP
-  participant "zigbee4java" as ZIG  
+  participant "paho.mqtt.java" as ZIG  
   participant "Engine" as DI
   participant "DB" as DIDB
-  participant "Spring WS API" as WSS
 end box
 
 box "Triggers and Automations"
@@ -925,11 +925,15 @@ box "Scenes"
   participant "DB" as SCDB
 end box
 
-UI -> DI: request state update
-DI -> ZD: apply new state
-ZD -> DI: report successful application
-DI -> DIDB: store new state
-DI -> UI: display new state
+UI -> DI: update state (HTTP PUT)
+DI -> ZIG: client.publish(\n TOPIC,\n new MqttMessage(...)\n);\n(request state update)
+ZIG -> ZD: PUBLISH\n(state update request)
+ZD -> ZIG: PUBLISH\n(new state)
+ZIG -> DI: subscriber.subscribe(...) observer called \n(successful application)
+DI -> DIDB: JDBC transaction (UPDATE)\n(store new state)
+DI -> WSS: s.getBasicRemote().sendText(...)\n(send new device state)
+WSS -> WSC: WebSocket protocol
+WSC -> UI: connection.onmessage called\n(new device state received, updates UI)
 DI -> T: report latest device state
 
 skinparam monochrome true