The paper “Comparison of the Communication Protocols DLMS/COSEM, SML and IEC 61850 for Smart Metering Applications” analyzes these protocols … especially to figure out the message lengths. The application the authors have in mind is for metering application. Independent of the application it is interesting what they figured out.
The major result is summarized as “In this paper the most significant qualitative features of a smart metering application layer protocol have been identified. The comparison of DLMS/COSEM, SML, and IEC 61850 has shown that no single protocol is superior in all aspects. The analysis and comparison of the message size has shown that DLMS and the MMS IEC 61850 clearly outperform the rest. …”
The message length of the protocols is one aspect. The more crucial impact on the needed resources is determined by the system behavior:
- Is TLS used? TLS adds a lot of bytes ... especially for the hand-shake for opening a secure connection. By the way, IEC 61850 has security measures: defined in IEC 62351-4. Encryption eats a lot of the computing resources!
- Is cyclic sending of the payload supported issued by the server (cyclic reports in IEC 61850 do not need a request message)?
- Frequency to exchange the metered values. How often are the metered values read? Will the TCP connection closed/resumed between two transmissions? In case of permanent TCP connections, there may be more bandwidth consumed for TCP keep-alive than for the payload.
The paper can be downloaded [PDF, 200 KB].
It is recommended to focus on the system – message encoding should have a lower priority when building future power automation systems!
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1 comment:
Karlheinz, TCP comes with another drawback. It is not a good choice in Meshed Network topologies like 802.15.4 where UDP is used. The costs (in terms of resources) would be much too high, especially in networks with a high number of endpoints (meter). Such a solution does not scale. Only one use case to illustrate this: Having a firmware/software update for all meters in the network. With TCP+TLS, it brings the AMI network down. MGSeewald
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