IEC 61158-3-21:2010 pdf download – Industrial communication networks – Fieldbus specifications – Part 3-21: Data-link layer service definition – Type 21 elements
In the diagrams illustrating these interfaces,dashed lines indicate cause and effect or timesequence relationships,and wavy lines indicate that events occur at approximately the sametime.
3.5.2Additional conventions
ln the diagrams illustrating the DLS and DLM interfaces,dashed lines indicate cause andeffect or time sequence relationships between actions at different stations，while solid lineswith arrows indicate cause and effect time sequence relationships that occur within the DLEprovider at a single station.
The following notation,a shortened form of the primitive classes defined in 3.5.1, is used inthe figures and tables.
req: request primitive
ind : indication primitive
cnf: confirmation primitive (confirmation)
rsp: response primitive
4Data-link layer services and concepts
4.1General
4.1.1overview
This standard specifies the Type 21 data link services for an ISO/IEC 8802-3:2000 basedtime-deterministic control network，which is one of the communication networks for RTE.Thecommunication services support timing demands typical of high-performance automationapplications.They do not change the basic principles of lSonIEC 8802-3:2000, but extend ittoward RTE.Thus, it is possible to continue to use standard Ethernet hardware,infrastructurecomponents, or test and measurement equipment, such as network analyzers.
The Type 21 DLL provides reliable and transparent data communication between two Type 21end devices. The Type 21 DLL also guarantees abstract transparent data transfer betweenDL-users so that DLL provides flexible and convenient network connectivity to network users.
4.1.2overview of full duplex flow control
A Type 21 device is based on an integrated switch with two ports (ring ports) connected to thering. Therefore, a Type 21 network system is made up of full-duplex,collision-free switchingdevices configured as a ring or a line network. Figure 1 shows the full-duplex flow controlprocedure in a Type 21 network system.Type 21 guarantees collision-free data transmissionbetween two devices linked by a full-duplex Ethernet connection so that the Type 21 DLLprovides reliable,transparent, and collision-free data transmission to the DLS-users.
4.1.3Types and classes of DL-layer service4.1.3.1overview
The DLs provides transparent and reliable data transmission between DLS-users overType 21. The DLS is based onservicesprovided by the physical layer ofISO/IEC 8802-3:2000 to the conceptual interface between the physical and data link layers.Three types of data transmission services are provided.
Data service (DL-DATA)
Data service is used to transmit a Type 21 frame to a destination device or devices using thepriority option.DL-DATA service is a queued service using the RT-queue.
Sporadic data service (DL-SPDATA)
Sporadic data service is used to transmit a common protocol frame,such as TCP/IP or UDP.Type 21 data link layer transmits without modification any received DLSDUs generated by aDLS-user. In this case,DLSDU is assumed to include ‘DLPDU. DL-SPDATA is a queuedservice using the NRT-queue.
Network control message
Network-control-message service is used by the DL-management entity to share network-related information with the other devices in a Type 21 network segment.
4.1.3.2 Primitives of the data service
The sequence of primitives for the data service is shown in Figure 2.
DL-DATA request and DL-DATA indication correspond to the MA-DATA request and MA-DATA indication defined by ISO/IEC 8802-3:2000, respectively.
The sender DLS-user prepares a DLSDU for a single receiver-side DLS-user, or for multiple DLS-users. The DLSDU is passed to the local DLE via the DLS interface by means of a DL-DATA request primitive. The DLE queues the service request, and the queued service request is transmitted by the DLPM to the receiver DLE or to multiple DLEs. The receiving DLE(s) attempt to deliver the received DLSDU to the specified DLS-user(s). There is no confirmation of correct receipt at the remote DLEs or of delivery to the intended DLS-user(s); acknowledgements do not occur. When the DLSDU is transmitted, it reaches all receiver-side DLEs at about the same time, ignoring signal propagation delays. Each DLE addressed by the DLSDU that has received the data error-free, passes the DLSDU and associated addressing information to the local DLS-user by means of a DL-DATA indication primitive.
4.1 .3.3 Primitives of the sporadic data service The sequence of primitives for the sporadic data service is shown in Figure 3. DL-SPDATA request and DL-SPDATA indication correspond to the MA-DATA request and MA-DATA indication defined by ISO/IEC 8802-3:2000, respectively.
