A Comparison of Management Request Encodings

Noack[1] has compared two compact XML encodings, namely Fast Infoset (FI) and Efficient XML Interchange (EXI), with the STRING encoded XML specified in Subclause 6.3 of the IEC 61499 Compliance Profile for Feasibility Demonstrations. Noack's results indicate that EXI is the most efficient, both in terms of message size and parsing time, than either of the other two encoding methods.

The table below presents a comparison of the STRING encoded XML as implemented in both the FBRT and FORTE runtimes, versus the EXI and MGT_REQ encodings. The length of the MGT_REQ encodings is always within 4 octets of the EXI encoding, and represents a compression factor of approximately 4:1 vs. the STRING encoded XML.

The slightly greater length of the MGT_REQ encodings should be weighed against the memory and execution speed advantages of using the built-in runtime parsing of IEC 61499 structured data types instead of an additional EXI or XML parser.

ID Encoded Command Length, Octets
1 78 88 19 22
2 102 112 26 29
3 92 88 20 22
4 33 38 5 9
5 90 86 20 22
6 90 100 21 22
7 55 96 18 19
Test Cases
<Request ID="1" Action="CREATE" >
  <FB Name="FBName" Type="FBType" />

<Request ID="2" Action="CREATE" >
  <Connection Source="FBName.Out" Destination="FBName.In" />

<Request ID="3" Action="DELETE" >
  <FB Name="FBName" Type="FBType" />

<Request ID="4" Action="START" />

<Request ID="5" Action="KILL" >
  <FB Name="FBName" Type="FBType" />

<Request ID="6" Action="WRITE" >
  <Parameter Reference="Location" Value="Data" />

<Request ID="7" Action="READ" >
  <Parameter Reference="Location" Value="*" />

[1] F.Noack, "Evaluation of Binary XML for Configuring Industrial Control Systems," Bachelor’s Thesis in Informatics, Technische Universität München, 2016-02-15.