flags, time stamp, change of value counter, protection events. Association objects to control ICCP sessions. Extended Data Set Condition Monitoring: Provides report by exception capability for the data types that block 1 is able to transfer periodically. Block Data Transfer: Provides a means transferring Block 1 and Block 2 data types as block transfers instead of point by point. In some situations this may reduce bandwidth requirements. Information Messages: Simple text and binary files. Device Control: Device control requests: on/off, trip/close, raise/lower etc. and digital setpoints. Includes mechanisms for interlocked controls and select-beforeoperate. Program Control: Allows an ICCP client to remote control programs executing on an ICCP server. Event Reporting: Extended reporting to a client of error conditions and device state changes at a server. Additional User Objects: Scheduling, accounting, outage and plant information. Time Series Data: Allows a client to request a report from a server of historical time series data between a start and end date. Protocol Architecture ICCP is based on client / server principles. Data transfers result from a request from a control centre (client) to another control centre (server). Control centres may be both clients and servers. ICCP operates at the application layer in the OSI model. As such any physical interfaces, transport and network services that fit this model are supported. TCP/IP over Ethernet (802.3) seems to be the most common. ICCP may operate over a single point-to-point link between two control centres; however, the more general case is for many control centres and a routed wide area network. The logical connections or “associations” between control centres are completely general. A client may establish associations with more than one server and a client may establish more than one association with the same server. Multiple associations with same server can be established at different levels of quality of service so that high priority real time data is not delayed by lower priority or non real time data transfers. Access Control ICCP does not provide authentication or encryption. These services are normally provided by lower protocol layers. ICCP uses “Bilateral Tables” to control access. A Bilateral Table represents the agreement between two control centres connected with an ICCP link. The agreement identifies data elements and objects that can be accessed via the link and the level of access permitted. Once an ICCP link is established, the contents of the Bilateral Tables in the server and client