ETSI - CPS Implementation Task Force UPER bit incompatibility of different ANS.1 Compilers

Abstract

As part of the Implementation Taskforce, a working group was set up with VW, Bosch and DLR to carry out initial tests. The first objective was to check whether a CPM message v2.1.1 can be read with different compilers. In short, can we understand each other fundamentally? We noticed that the UPER coded message from the generated decoder of one compiler decodes the message correctly and is not decoded correctly by the other compiler. These compilers are in widespread use in the ITS world. The CPM V2.1.1 employs an ASN.1 construct (further constraining a type defined with an extensible constraint)[3, p. 96] which has not been used yet in an ITS V2X message yet. This deviation of compilers for this construct poses an interoperability issue for V2X communication if the use of this construct is not avoided. Avoiding this or similar constructs does not represent a limitation of functionality.