This document provides a background to the relevance of standards concerning mixed vendor environments in the context of urban-ITS. It describes key mixed vendor environments interfaces. It identifies existing open specifications for sensor systems; traffic control; traffic information; public transport information; distributed C-ITS; central systems. It provides common specifications of sensor systems; traffic control; traffic information; public transport information; distributed C-ITS; central systems. It describes openly plied proprietary standards and extant communications protocols that can be used in mixed vendor environments in the context of U-ITS.