Tài liệu Control net

What is ControlNet? ControlNet, like other CIP Networks, follows the Open Systems Interconnection (OSI) model, which defines a framework for implementing network protocols in seven layers: physical, data link, network, transport, session, presentation and application. Networks that follow this model define a complete suite of network functionality from the physical implementation through the application or user interface layer. As with all CIP Networks, ControlNet implements CIP at the Session layer and above while adapting CIP to the specific ControlNet technology at the Transport layer and below. This network architecture is shown in Figure 1. ControlNet is a digital network that provides high-speed transport of time-critical I/O and messaging data—including upload/download of programming and configuration data and peer-to-peer messaging—on a single physical media link. Each device and/or controller is a node on the network. The ControlNet network infrastructure is passive, making node functionality independent of physical location and the network itself inherently tolerant to individual lost node connections. Figure 1 ControlNet as Part of the CIP OSI Model To further decrease complexity, ControlNet systems require only a single point of connection for both configuration and control. This is because ControlNet supports both I/O (or implicit) messages—those that typically contain time-critical control data—and explicit messages— those in which the data field carries both protocol information and specific service requests. And, as a producer-consumer network that supports multiple communication hierarchies and message prioritization, ControlNet provides more efficient use of bandwidth than a device network based on a source-destination model. ControlNet systems can be configured to operate either in a centralized or distributed control architecture using peer-to-peer communication. ControlNet’s time-based message scheduling mechanism provides network devices with deterministic and predictable access to the network while preventing network collisions. This scheduling mechanism allows time-critical data, which is required on a periodic, repeatable and predictable basis, to be produced on a predefined schedule without the loss of efficiency associated with continuously requesting, or “polling,” for the required data. The Physical Layer ControlNet offers users a choice of network topologies and physical media. The possible variants in topology are shown in Figure 2. Multiple topologies and media types can be mixed within one system. End-to-end network length varies based on the number of nodes, type of media and use of repeaters, as shown in Table 1. The CIP Advantage: Technology Overview Series PUB00200R0 ©2008 ODVA, Inc. Figure 2 ControlNet Topology Options ControlNet - CIP on CTDMA Technology www.odva.org Page 2 When a coax cable media is chosen, ControlNet uses RG-6 quad shield coax cable, the same standard cable that is used in the cable TV industry. This coax cable is inexpensive, readily available and has high noise immunity. Several types of outer jackets are available (plenum, high flex, armor) to meet any application or environmental requirement. Media Coax Fiber Coax or Fiber with Repeater Maximum Drop Length 2 32 48 49-99 Nodes Nodes Nodes Nodes 1000 m 500 m 250 m requires (3280 ft) (1520 ft) (820 ft) repeaters Depends on repeater capability, fiber and termination quality Depends on number of repeaters, repeater capability, fiber and termination quality 1m (3.3 ft) 1m (3.3 ft) 1m (3.3 ft) 1m (3.3 ft) Table 1 End-to-end network distance based on cable media Connectors are standard BNC-type for IP20 applications and TNC-type for IP67 applications where dust, dirt and/or liquids are present. Two 75-W termination resistors are required: one on each end of the cable to limit the reflections from transmitted signals on the trunkline. A passive tap is required for every permanent node on the network. Custom taps for ControlNet can be rail-mounted and easily connected to the ControlNet trunk cable. Taps are available in different styles, including straight, right angle and “Y.” Although the taps must be installed while the network is powered-down, they allow devices to be added or removed while the network is powered. Taps may be installed anywhere along the ControlNet trunk cable, with no minimum separation distance. A 1m drop line from the tap to the device is standard. Transformer coupling is utilized in each node to provide electrical isolation. When a fiber optic media is chosen, ControlNet incorporates a full-duplex, point-to-point fiber link using a transmitter and receiver at each end of a pair of fibers. The fiber characteristics are shown in Table 2. Specification Fiber Technology Core/Cladding Numerical Aperture Short Range (300 m) Step index, hard clad silica (HCS) 200/230 um 0.5 Medium Range (3000 m) Graded index, multi-mode 62.5/125 um 0.275 Table 2 Fiber characteristics Redundant cable media is a ControlNet option that allows all messages to be transmitted simultaneously on both cable paths. Each node evaluates signal quality, and the best quality signal is chosen dynamically. The CIP Advantage: Technology Overview Series PUB00200R0 ©2008 ODVA, Inc. ControlNet - CIP on CTDMA Technology www.odva.org Page 3 In addition to its ControlNet port for control and information, each ControlNet node has a network access port that makes it possible for a computer or other support tool to plug into the network and communicate with any other device on the network. The network access port uses a standard 8-pin, RJ-45 connector. Repeaters may be used to increase end-to-end network lengths and the number of nodes per segment. They may also be used to connect coax to fiber cables for increased noise immunity or greater distance. For a given system, the maximum number of repeaters will be limited by the propagation delay introduced by the repeater. When determining the maximum number of repeaters and/or the maximum distance capabilities of the system, the individual propagation delays (media, taps and repeaters) must total less than 120 microseconds between the two furthest points on the network. Intrinsically safe options are available through vendor implementations of ControlNet products that meet various EU, CENELEC, UL and FM certifications for use in potentially explosive atmospheres. The Data Link Layer ControlNet uses a Concurrent Time Domain, Multiple Access (CTDMA) algorithm to ensure the precise time for message delivery. This protocol is based on a fixed, repetitive time cycle called a Network Update Time (NUT), as shown in Figure 4. The NUT can be configured for a duration ranging from 2 to 100 milliseconds. Each node contains its own timer synchronized to the NUT for the local link. Media access is determined by local subdivision of the NUT into access slots based on node number. Each NUT is divided into three major parts: scheduled, unscheduled and guardband, and this sequence is repeated in every NUT. Figure 4 The CTDMA algorithm’s NUT ensures precise time for message delivery Users select NUT parameters with a network configuration tool. These parameters are distributed to all nodes via the moderator, which is the node with the lowest MAC ID on the link. The network parameters are broadcast during the guardband portion of the bandwidth. ControlNet’s network synchronization method assures that no node will transmit on the medium with parameters that do not agree with those currently in use. Different links (joined by bridges) may have different NUT durations and network parameters, and will have their own moderators. The Network and Transport Layers ControlNet uses two forms of messaging: Unconnected messaging is used in the connection establishment process and for infrequent, low-priority messages. Unconnected messages always use the unscheduled bandwidth, and the unconnected resources in a device are referred to as the Unconnected Message Manager, or UCMM. To receive a Declaration of Conformity, ControlNet products are required to implement a UCMM to receive requests from other devices. The CIP Advantage: Technology Overview Series PUB00200R0 ©2008 ODVA, Inc. ControlNet - CIP on CTDMA Technology www.odva.org Page 4 Connected messaging on ControlNet utilizes resources within each node that are dedicated in advance to a particular purpose, such as frequent explicit message transactions or real-time I/O data transfers. Connection resources are reserved and configured using communications services available via the UCMM. The process of opening a connection is called Connection Origination, and the node that initiates the connection establishment request is called a Connection Originator, or just an Originator. Conversely, the node that responds to the establishment request is called a Connection Target, or a Target. ControlNet has two types of messaging connections: explicit and implicit (I/O data). Explicit messaging connections are point-to-point relationships that are established to facilitate request-response transactions between two nodes. These connections are general purpose in nature and can be used to reach any network-accessible items within a device. Explicit messaging connections utilize unscheduled services on ControlNet. Implicit connections, on the other hand, are established to move application-specific I/O data at regular intervals. These connections are multicast in nature, and often are set up as one-to-many relationships in order to take full advantage of the producer/consumer model. Implicit connections utilize scheduled services on ControlNet, providing highly deterministic transfer of data. ControlNet supports three device classes based on network communication capabilities: Messaging Class, Adapter Class and Scanner Class. Each class supports a basic set of communications services, but may provide other optional services too. Messaging Class products support unscheduled explicit messaging (connected or unconnected) that is sent or received from all other classes of products. Messaging Class products are the targets of explicit message connection requests, and may also be an originator of these requests, but they cannot send or receive scheduled, real-time I/O data. Examples of products in this class include: Computer interface cards for program upload and download to HMI products, robots and PLCs; Computer interface cards or other hardware that supports HMI applications that gather data from control systems (i.e., MIS); Software applications that do not require real-time I/O response; and Network configuration and diagnostic tools. Adapter Class products are the targets of scheduled I/O data connection requests from Scanner Class products. They cannot send or receive scheduled real-time I/O data unless they are requested to do so by a scanner, and they do not store or originate the data transmit schedule. Adapter Class products receive unscheduled explicit message requests (connected or unconnected) from all other classes of products. They may also exchange (peer) data using unscheduled messages with any class of device, but they cannot originate such relationships. Examples of products in this class include: I/O rack adapters producing and consuming scheduled real-time data; Weigh scales, welders, drives and robots sending and receiving real time scheduled data at the request of PLCs and other controllers; Weigh scales, welders, drives and robots sending and receiving unscheduled message data to and from computer interface cards, PLCs and each other; and The CIP Advantage: Technology Overview Series PUB00200R0 ©2008 ODVA, Inc. ControlNet - CIP on CTDMA Technology www.odva.org Page 5 HMI products sending and receiving scheduled and unscheduled data to PLCs. Scanner Class products are the originators of scheduled I/O data connection requests to Adapter Class products, as well as to other Scanner Class products (i.e., scheduled peer-topeer). These products may also be the originators or targets of unscheduled explicit connection requests to and from other classes of products, and they can also send or receive unscheduled messages to or from all other classes of products. Examples of products in this class include: PLCs, controllers and robots sending and receiving real time scheduled data to I/O rack adapters, PLCs, robots, weigh scales, welders and MMI products; PLCs, controllers and robots sending and receiving unscheduled message data to other PLCs, robots, weigh scales, computer cards, welders and MMI products; and Computer interface cards used for PC-based control. The Upper Layers ControlNet uses the Common Industrial Protocol (CIP), a strictly object-oriented protocol, at the upper layers. Each CIP object has attributes (data), services (commands) and behaviors (reactions to events). CIP''s producer-consumer communication model provides more efficient use of network resources than a source-destination model by allowing the exchange of application information between a sending device (e.g., the producer) and many receiving devices (e.g., the consumers) without requiring data to be transmitted multiple times by a single source to multiple destinations. In producer-consumer networks, a message is identified by its connection ID, not its destination address (as is the case with source-destination networks). CIP’s message structure makes it possible for multiple nodes to consume data produced by a single source based solely on the connection ID to which the message refers. Thus, the producer-consumer model provides a clear advantage for users of CIP Networks by making efficient use of network resources in the following ways: If a node wants to receive data, it only needs to ask for it once to consume the data each time it is produced. If a second (third, fourth, etc.) node wants the same data, all it needs to know is the connection ID to receive the same data simultaneously with all other nodes. CIP also includes "device types" for which there are "device profiles." For a given device type, the device profile will specify the set of CIP objects that must be implemented, configuration options and I/O data formats. This consistency in object implementation for a given device type provides another clear advantage for users of CIP Networks by promoting a common application interface for a given device type and interoperability in networks comprised of devices from multiple vendors. For applications where unique functionality is required, it is also possible for a ControlNet vendor to define additional vendor-specific objects in a ControlNet-compliant product in order to support the functional requirements of particular applications. Seamless bridging and routing is perhaps the most significant advantage for users of CIP Networks for it is this mechanism that most protects the user''s investment for the future. The ability to originate a message on one CIP Network, such as DeviceNet, and then pass it to another CIP Network, such as ControlNet, with no presentation at the Application Layer, means that users can incorporate incremental application improvements to existing installations and/or integrate automation systems with diagnostic, prognostic and/or IT applications. Seamless bridging and routing between both homogeneous and heterogeneous CIP Networks is enabled by a set of objects that defines routing mechanisms for a device to use when forwarding the contents of a message produced on one network port to another. The CIP Advantage: Technology Overview Series PUB00200R0 ©2008 ODVA, Inc. ControlNet - CIP on CTDMA Technology www.odva.org Page 6