What is the COMM_TYPE in the simple message protocol?

edit

Sorry I missed this one.

The values for comm_type are actually documented in the simple_message.h file in the simple_message package of the industrial_core stack (from here) :

enum CommType
{
  INVALID = 0,
  TOPIC = 1,
  SERVICE_REQUEST = 2,
  SERVICE_REPLY = 3
};

You can also find the defined values for the other parts of the header there.

Additionally, the simple_message package has been documented using Doxygen, which is automatically generated by the ROS buildfarm. You can access that documentation here, which is also accessible from the simple_message wiki page (top-right, Package Links, Code API). You'll want to open the page for the SimpleMessage class, which contains references to the StandardMsgTypes, CommTypes and the ReplyTypes used in the header.

Finally, defined values for the msg_type field are documented in REP-I0004.

Edit: you might also be interested in the simple_message Wireshark dissector.