Foundation Fieldbus (FF) is a control system protocol used at both the device and controller level. The H1 protocol is more popular for controller to instrument communications, and the HSE protocol is typically used for control center to controller communications. While FF is a global protocol, it has a higher market share in North America and Asia. It is used in a variety of vertical markets including chemical, oil & gas, mining, water/wastewater, paper, and manufacturing. FF has the strongest market position in the petrochemical sector.
The Fieldbus FOUNDATION was formed in 1994 as a merger between the ISP and WorldFIP in an effort to create a single, international fieldbus standard for hazardous environments. This same effort was pursued by the PROFIBUS proponents, but the Fieldbus FOUNDATION was focused on the US and Asia while PROFIBUS was dominant in Europe.
The resulting protocols from the Fieldbus FOUNDATION are called FOUNDATION Fieldbus (FF). The first FF specification was H1, which was released in 1995, demonstrated in 1996 and had registered products in 1998. FF added an Ethernet data link version of the protocol in a specification released in 1999.
The Fieldbus FOUNDATION claims there are over 250 FF compliant products and over 700,000 FF devices have been shipped.
Basic Foundation Fieldbus
The FF protocols use function blocks to pass data. A function block includes the value of the point and the status (quality) of the value. FF places emphasis on the integration of status in the function blocks as they felt this was important and missing from many fieldbus protocols.
There are function blocks for the typical data types in control systems such as discrete inputs and outputs, analog inputs and outputs, PID and other controllers, calculations, as well as device management function blocks. Note that FF can be used to communicate with instruments or with more intelligent controllers that implement control loops. It is a rich set of function blocks with much more capability than a simple protocol like Modbus.
On top of the defined function blocks, FF has introduced “flexible function blocks” for multiple I/O and application specific use. FF specifies different device classes that indicate different levels of function block support.
The FF protocol supports scheduled communication, via publish or publish/subscribe, and unscheduled communication, via client/server or report distribution. A special type of FF device, known as a Linkmaster device, is responsible for setting up timeslots for FF devices to send scheduled information. The parameters of this scheduled communication can be configured to provide the required performance criteria on a reliable basis.
Unscheduled communication implements a token based scheme in unallocated time slots. The performance of the unscheduled communication is typically reduced by at least a factor of 10 and is not reliable. As shown in figure below, User Data is encapsulated with a Fieldbus Message Header in a Fieldbus Message Specification PDU. This PDU is further encapsulated with a Type byte into a Fieldbus Access Sublayer PDU. The Fieldbus Access Sublayer is then presented to the H1 or HSE protocol stack for transmission.
Foundation Fieldbus Message Format
The first and most popular data link protocol in FF is the H1 protocol. This is a traditional fieldbus that does not support or rely on Ethernet or IP. As with other traditional fieldbus protocols, it would be difficult for an attacker to reach this network except in the case of a direct connection.
The HSE specification adds on to the FF H1 specification in the following areas:
- System Architecture Addendum
- System Management Addendum
- Network Management Addendum
- Data Link (Bridging) Addendum
- Ethernet Presence
- Field Device Access Agent
- Additional Function Blocks
- Flexible Function Block (MIO)
- Flexible Function Block (61131)
- FFB Application Guide
- Multi-Variable Optimization
FF User and application layer requirements are incorporated in HSE.
FF HSE Protocol Stack
The FF HSE protocol primarily uses UDP communication to provide high performance. Some non-critical FF HSE communication will use TCP ports. The FF UDP/TCP ports are:
- TCP/UDP 1089 FF Annunciation
- TCP/UDP 1090 FF Fieldbus Message Specfication
- TCP/UDP 1091 FF System Management
FF uses the term Linking Device (Class 42a) for a gateway between FF H1 and FF HSE. Linking Devices often have the capability to bridge DeviceNet and PROFIBUS communication to FF HSE.
Foundation Fieldbus Security
There is no security in the FF protocols.
Many of the vendors that offer PROFINET software and hardware stacks also sell FF H1 and HSE stacks. SOFTing claims to have a 50% market share in FF protocol stacks which would make them the clear market leader.