1.1 Interfaces specified by this Standard 1.1.1 Business Context Real-time information may be exchanged between a number of different organisations, or between different systems belonging to the same organisation. Key interfaces include the following: " Between public transport vehicle control centres generally, for fleet and network management. " Between a control centre and an information provision system generally, to provide operational information for presentation to the public. " Between information provision systems generally, sharing information to ensure that publicly available information is complete and comprehensive. " Between information provision systems and data aggregation systems that collect and integrate data from many different sources and different types of data supplier and then distribute it onwards. " Between information provision systems and passenger information devices such as mobile phones, web browsers, etc. Annex B describes the business context for SIRI in more detail. SIRI is intended for wide scale, distributed deployment by a wide variety of installations. In such circumstances it is often not practical to upgrade all the systems at the same time. SIRI therefore includes a formal versioning system that allows for the concurrent operation of different levels at the same time and a disciplined upgrade process. In this general framework, SIRI defines a specific set of concrete functional services. The services separate the communication protocols from the message content ( functional services ). This allows the same functional content to be exchanged using different transport mechanisms, and different patterns of exchange. Figure 1 below shows this diagrammatically.