The Interface Message Protocol (IMP) is a wrapper for link messages (llMessageLinked and link_message) that provides a header with message routing information and other metadata. The Mark 1 uses IMP to route requests, responses, and broadcasts to and from the interfaces available in the firmware and SCOPE.
IMP is documented and maintained by Buildtronics as part of the Xi LSL Library. IMP messages are sent using the xiIMP_Send(...) library function and received via the user-defined imp_message(...) function called by the optional link_message event handler.
The Technical Reference documents xiIMP_Send(...) syntax specifications for all IMP requests. Additionally, requests that have helper functions in the Mk1 Dev Library include the equivalent mk1*(...) function syntax specification.