62 CHAPTER 4 Industrial Network Protocols Because many custom and proprietary protocols are used by asset vendors, a common protocol was needed to allow for reliable and standardized data exchange between control centers--especially between control centers that are operated by different owners, produce different products, or perform different operations. Basically, standardization became necessary to support the unique business and operational requirements of industry, especially the electrical utilities that require careful load balancing within a bulk system operated by many disparate facilities. For example, in North America, the division of utilities among several responsible regional entities requires a means of sharing information between utilities as well as the regional entity. Similarly, national and global energy markets require real-time information exchange for load distribution and trading that spans the boundaries of individual utilities. A working group was formed in 1991 to develop and test a standardized pro- tocol and to submit the specification to the IEC. The initial protocol was called ELCOM-90, or Telecontrol Application Service Element-1 (TASE.1). TASE.1 evolved into TASE.2, which is the most commonly used form of ICCP. 3 What It Does ICCP is used to perform a number of communication functions between control centers, including the following: l l l l l l l Establishing a connection. Accessing information (read requests). Information transmission (such as e-mail messages or energy market information). Notifications of changes, alarms, or other exception conditions. Configuration of remote devices. Control of remote devices. Control of operating programs. How It Works The ICCP protocol defines communication between two control centers using a client/server model. One control center (the server) contains application data and defined functions. Another control center (the client) issues requests to read from the server, and the server responds. Communications over ICCP occur using a com- mon format in order to ensure interoperability. ICCP support is typically either integrated directly into a control system, pro- vided via a gateway product, or provided as software running on Windows or Unix that can then be installed to perform gateway functions. Although ICCP is primarily a unidirectional client/server protocol, most modern implementations support both functions, allowing a single ICCP device to function as both a client and a server, and thus supporting bidirectional communication (of a sort) over a single connection. Although ICCP can operate over essentially any network protocol, including TCP/IP, it is commonly implemented using ISO transport on top of TCP port 102, as