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Standards Compliance
Standards are designed to facilitate the integration of system components by providing a predefined and public (open) interface that vendors/developers can design and build their products around. Ideally, when standards are implemented by different developers (software or hardware), their products will work together seamlessly. Some simple but ubiquitous examples of standards in action are the 120V electrical plug, RJ-45 cable connector, and CD-ROM. It is just assumed that you can take one of these items to the appropriate device/receptacle and it will work.
The USDOT’s Joint Program Office is supporting the development and maintenance of a number of transportation-related standards as part of the National Intelligent Transportation Systems Architecture framework. These standards are being developed by a number of organizations and are in a various stages of development and acceptance. Even so, use of standards can greatly assist in the decision-making process by reducing the ever-present question of component interoperability (“Will this new device from Vendor X work with that one from Vendor Y?”).
An important goal of the LA County IEN system design is adherence to open industry standards. The following standards are used in the IEN:
Component Model
The IEN is designed using a component-based methodology. Each “component” is a software object that communicates with other components using a standard interface framework. In general, each component corresponds to an application program or a dynamic link library. The IEN’s use of the CORBA (Common Object Request Broker Architecture) and COM (Component Object Model) component model standards is described below.
CORBA
CORBA is an open standard for implementing distributed object-oriented systems. For more information, visit www.omg.org. Most inter-process communications between IEN software components running on different machines is accomplished using CORBA-compliant interfaces. The standard CORBA Naming Service is used by components to locate other components on the network. The standard CORBA Event Service is used to distribute dynamic data updates throughout the IEN.
COM
Microsoft’s Component Object Model (COM) is used by several workstation components that run under the Windows operating system. COM is used for communications between components running on the same workstation.
TCP/IP
All communications protocols used by the IEN are based upon the standard Transmission Control Protocol/Internet Protocol (TCP/IP) family of internetworking protocols. TCP/IP-based protocols used within the IEN include SNMP, SMTP, HTTP, and IIOP.
TMDD
Many IEN data elements are based upon elements defined in the standardized Traffic Management Data Dictionary (TMDD) jointly developed by ITE, FHWA, and AASHTO. The TMDD definitions do not map directly to any programming language, and are not intended for object-oriented programming. Therefore, its concepts have been adapted as appropriate for the IEN system design.
The following TMDD-derived conventions are used throughout the design of IEN data elements:
- Most objects have a unique “identifier” attribute (text string of up to 32 alphanumeric characters) and a “name” attribute (text string of up to 128 alphanumeric characters). The “identifier” is used internally by the IEN system to keep track of objects, whereas the “name” is something meaningful to system operators.
- Geographic coordinates are specified in microdegrees of latitude and longitude.
- Textual data elements have a maximum length specified that matches that of the corresponding TMDD element.
SAE LRMS
Location-referencing data elements are based upon the message profiles specified in the Society of Automotive Engineers (SAE) Location Referencing Message Specification. The data elements have been adapted as necessary for use in a CORBA-based design.
Southern California Priority Corridor Interfaces
The IEN uses the following CORBA Interface Definition Language (IDL) files developed for the Southern California Priority Corridor Showcase projects:
- date_time.idl
- location.idl
- scbridge.idl
- sckernel.idl
- sclog.idl
- sctypes.idl
- security_service.idl
Database Connectivity
The system also allows smaller agencies to share limited control of their traffic control system to another agency for off-hours support. Thus, a single agency can serve as the after hours coordination center for neighboring agencies.
Several IEN components make use of a central relational database to store persistent data. All database access is performed using the industry-standard ODBC (Open Database Connectivity) and OLE (Object Linking and Embedding) DB interface standards. Proprietary database protocols are not used by any applications.