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PacketId and MessageId

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Feng 2016-04-02 14:48:50 +08:00
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docs/source/design.rst
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@ -32,15 +32,19 @@ System Layers
-------------
1. Connection Layer:
Handle TCP and WebSocket connections, encode/decode MQTT packets.
2. Session Layer:
Process MQTT PUBLISH/SUBSCRIBE Packets received from client, and deliver MQTT messages to client.
3. PubSub Layer:
Dispatch MQTT messages to subscribers in a node.
4. Routing(Distributed) Layer:
Route MQTT messages between clustered nodes.
.. code::
@ -65,8 +69,8 @@ This layer is built on the `eSockd`_ library which is a general Non-blocking TCP
This layer is also responsible for encoding/decoding MQTT frames:
1. Parse MQTT frames received from client
2. Serialize MQTT frames sent to client
1. Parse MQTT frame received from client
2. Serialize MQTT frame sent to client
3. MQTT Connection Keepalive
Main modules of this layer:
@ -109,38 +113,37 @@ MQueue and Inflight Window
Concept of Message Queue and Inflight Window::
|<----------------- Max Len ----------------->|
-----------------------------------------------
IN -> | Messages Queue | Inflight Window | -> Out
-----------------------------------------------
|<--- Win Size --->|
|<----------------- Max Len ----------------->|
-----------------------------------------------
IN -> | Messages Queue | Inflight Window | -> Out
-----------------------------------------------
|<--- Win Size --->|
1. Inflight Window to store the messages delivered and awaiting for PUBACK.
2. Enqueue messages when the inflight window is full.
3. If the queue is full, dropped qos0 messages if store_qos0 is true,
otherwise dropped the oldest one.
3. If the queue is full, dropped qos0 messages if store_qos0 is true, otherwise dropped the oldest one.
The larger the inflight window size, the higher the throughput. The smaller the window size, the more strict the message order.
PacketId and MessageId
----------------------
The 16bits PacketId is defined by MQTT Protocol Specification, used by client/server to PUBLISH/PUBACK packets. A GUID(128bits global unique Id) will be generated by the broker and assigned to a MQTT message.
The 16bits PacketId is defined by MQTT Protocol Specification, used by client/server to PUBLISH/PUBACK packets. A GUID(128bits globally unique Id) will be generated by the broker and assigned to a MQTT message.
Format of the global unique message id::
Format of the globally unique message id:
+------------------------+----------------+------------+
| Timestamp | NodeID + PID | Sequence |
+------------------------+----------------+------------+
|<------- 64bits ------->|<--- 48bits --->|<- 16bits ->|
+------------------------+----------------+------------+
+------------------------+----------------+------------+
| Timestamp | NodeID + PID | Sequence |
+------------------------+----------------+------------+
| <-------64bits-------> | <---48bits---> | <-16bits-> |
+------------------------+----------------+------------+
1. Timestamp: erlang:system_time if Erlang >= R18, otherwise os:timestamp
2. NodeId: encode node() to 2 bytes integer
3. Pid: encode pid to 4 bytes integer
4. Sequence: 2 bytes sequence in one process
1. Timestamp: erlang:system_time if Erlang >= R18, otherwise os:timestamp
2. NodeId: encode node() to 2 bytes integer
3. Pid: encode pid to 4 bytes integer
4. Sequence: 2 bytes sequence in one process
The PacketId and MessageId in a End-to-End Message PubSub Sequence::