Limit on DDS topic names

Question

I am currently using RTI DDS and am writing some specifications. However, I don't want any of the topic names in my specifications to over exceed the limit for the topic name in DDS. I tried searching and could not find if any such limit exist. Does anyone happen to know if DDS limits your topic name to a certain length of if it is just to not exceed the limit on the length of a String for whatever language you are programming in?

Answer 1

The OMG standard for DDS (rev 1.2) does not supply an arbitrary limit to Topic name length.

A Topic is identified by its name, which must be unique in the whole Domain.

According to the RTI documentation (5.1.0 Users Guide pdf, Section 5.1.1, page 170), RTI's implementation of the Standard implements an arbitrary limit:

topic_name | Name for the new Topic, must not exceed 255 characters

This appears to be the length max for any Entity (you can name entities in its QoS, so that tools can report human-readable names for which Entity they are reporting on).

Answer 2

While it is true that the DDS API specification does not mention a limit for Topic names. The complementary DDS Wire Protocol specification: Real-Time Publish Subscribe (RTPS) protocol (http://www.omg.org/spec/DDSI-RTPS/2.2), does state that Topic names shall not exceed 256 characters (see Table 9.12).

So the 256 character limit on Topic name lengths imposed by the RTI DDS implementation is not arbitrary. It is precisely what is required to be interoperable with other DDS implementations.

Gerardo