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As OPC UA works on top of TCP/IP, so the data packets format would be the same as that of TCP/IP or it will have different? I am interested in studying the data packets of OPC UA and its format and compare with MQTT data packets. If somebody has information about both, kindly share. Also the Overhead added to the data packet by OPC UA/MQTT to the original data.

Laurent LA RIZZA
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Azaksai
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  • OPC UA can work on top of TCP, or can use other transports. When used over TCP, asking whether the data packets are "the same" makes little sense - the framing is of TCP but the contents is UA. Quite similarly, MQTT work over TCP as well. OPC UA is defined in terms of services (request/response messages), and their encoding "on the wire". That's what the parts of the OPC specs are describing, and they are quite thick. If you just want to peek at the OPC UA message flow, then Wireshark has a free plugin (decoder) for that. – ZbynekZ Apr 28 '15 at 15:53
  • Thanks @ZbynekZ. I am trying to compare the Overhead/data rate/etc of the two protocols, and get sample data and show the data by using some graphs that which one is better/faster. kindly guide me for this. – Azaksai Apr 28 '15 at 16:01
  • I do not have experience with MQTT. If you want to make measurements with OPC UA, you can download the sample software (clients + servers) from OPC Foundation site for free (https://opcfoundation.org/developer-tools/developer-kits-unified-architecture/sample-applications/ ), set up some subscriptions, and measure performance (and possibly view the data being exchanged, using Wireshark). – ZbynekZ Apr 29 '15 at 17:40
  • I think you are comparing apples to oranges. MQTT is much simpler and therefore more efficient in general. OPC UA defines a session based communication, which enables full security on the wire. It also defines a lot of capabilities in defining information models, which can be exchanged between the applications. So in general it provides a much higher level interface. In future MQTT may be one of the transport protocols supported by OPC UA, which makes then the comparison even more "wrong". You will need to study the features of these protocols and then decide which is better for your case. – Jouni Aro May 26 '15 at 15:49

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You should see part 6 of the IEC 62541 series (publ. 2015), it deals with the concrete mapping of

  • abstract services (part 4),
  • data structures (part 5) and
  • the security model (part 2)

to 'physical' protocols and contains all information you need.

Section 5 contains the data encoding for OPC UA binary (5.2) and XML (5.3). Section 6 describes the implementation of security protocols and section 7 contains the mappings to concrete transport protocols:

  • sect. 7.1: OPC UA TCP
  • sect. 7.2: SOAP/HTTP
  • sect. 7.3: HTTPS
Martijn Pieters
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hecke
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