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Center-to-Field (C2F) Communications Profiles
Published: August 2007
C2F Standards Framework
The full list of C2F communications standards and their status at the time of this advisory publication are listed in the C2F Communications Standards section of the advisory. These standards are described in more detail in this section according to their level in the NTCIP communications stack.
Information-Level Standards
Information-Level standards define messages and data, Informational Level dialogues, type of message encoding and naming rules, and object definitions. Informational-level dialogues define the format of commands, responses, and information to be transferred, including the sequence of data exchanges. Object definitions unambiguously define the content, terminology, and units. Object definitions standards are outside the scope of this advisory. The Information-Level standards follow the NTCIP numbering convention of "12XX," but other ITS standards, such as the Transit Communications Interface Profiles (TCIP), might also be used in conjunction with the underlying communications profiles.
Applications-Level Standards
Applications-Level standards define the rules and procedures for exchanging data. Encoding rules define the methodology for formatting and preparing data for transmission between two entities (e.g., between field devices and centers). In the OSI model, these standards roughly equate to the Session, Presentation, and Applications levels. In the NTCIP C2F standards family, Applications-Level standards include Simple Network Management Protocol (SNMP) with Basic Encoding Rules (BER), Simple Transportation Management Protocol (STMP) with Octet Encoding Rules (OER), Simple Fixed Message Protocol (SFMP) with OER, Trivial File Transfer Protocol (TFTP), and File Transfer Protocol (FTP). These standards use the same base data elements as defined in the NTCIP 1200 series of publications. Applications-Level profile standards follow the NTCIP numbering convention "23XX," while NTCIP-specific base standards follow the NTCIP numbering convention "11XX"; however, profiles do reference other non-NTCIP-specific standards such as the IETF standard SNMP.
Transport-Level Standards
Transport-Level standards define rules and procedures for exchanging Applications-Level data between two or more points on a network, including routing and switching. In the OSI model, these standards roughly equate to the Transport and Network Layers. In the NTCIP C2F standards family, Transport-Level standards include the User Datagram Protocol (UDP) over Internet Protocol (UDP/IP) for the connectionless transport services standard and the Transmission Control Protocol (TCP) over Internet Protocol (TCP/IP) for the connection-oriented transport services standard. Another very important standard, the Transportation Transport (T2) Profile, was developed specifically for use in low-bandwidth/throughput environments encountered often in transportation environments. These standards may be used with any of the above Applications-Level standards and follow the NTCIP numbering convention of "22XX."
Subnetwork-Level Standards
Subnetwork-Level standards define rules and procedures for encoding and decoding information at the bit level to be transmitted and received between two points in a network. In the OSI model, these standards roughly equate to the data link and physical layers. In the NTCIP C2F standards family, Subnetwork-Level standards include the Ethernet, Point-to-Point Over RS-232 Protocol, and Point-to-Multi-Point using RS-232 or frequency-shift keying (FSK) modem standards. These Subnetwork-Level standards follow the NTCIP numbering convention of "21XX."
C2F Standards Framework Summary
For each C2F interface, deployers must select a protocol or profile (a combination of protocols and base standards) from each level of the NTCIP framework. While it is theoretically possible to mix any Applications Profile with any Transport Profile and any Subnetwork Profile standard, in reality this is not practical; in fact, very few combinations are used. For more detailed information, please see the NTCIP 9001 — NTCIP Guide.
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