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Fieldbus Systems: Embedded Networks for Automation
Published in Richard Zurawski, Networked Embedded Systems, 2017
Figure 20.5 shows in detail how data are exchanged between service user and service provider or between two peer layers. The interface between two neighboring layers is called service access point (SAP). The vertical and horizontal communication is made up of two important units: Service Data Unit (SDU). Communication of layer N + 1 with the underlying layer N occurs via its services, or more accurately via the interfaces of these services. For layer N, the transferred data represent pure user data that are passed on to the next lowest layer for further processing.Protocol Data Unit (PDU). Communication between two peer layers is implemented via so-called PDUs. These represent the core element of the rule set that can only be understood and correctly interpreted by the peer layers. A PDU consists of the transmitted user data supplemented with parameters of the interface (interface control information [ICI]) and unique control information (protocol control information [PCI]).
Analysis of Threats to WiMAX/802.16 Security
Published in Yan Zhang, Hsiao-Hwa Chen, Mobile Wimax, 2007
Michel Barbeau, Christine Laurendeau
The protocol architecture of WiMAX/802.16 is structured into two main layers: the MAC layer and the PHY layer, as depicted in Figure 15.1. The diagram also indicates interfacing points where service access points (SAPs) are formally defined by the standard. The central element of the layered architecture is the common part sublayer, which is tightly integrated with the security sublayer. In this layer, MAC protocol data units (PDUs) are constructed, connections are established, and bandwidth is managed. The common part exchanges MAC service data units (SDUs) with the convergence layer, which adapts units of data (e.g., IP packets or asynchronous transfer mode [ATM] cells) from higher level protocols to the MAC SDU format, and vice versa. The convergence layer also sorts the incoming MAC SDUs by the connection to which they belong. The security sublayer addresses authentication, establishment of keys and encryption, and exchanges MAC PDUs with the PHY layer. The PHY layer is a two-way mapping between MAC PDUs and the PHY layer frames received and transmitted through coding and modulation of radio frequency (RF) signals.
Open Systems Interconnection Reference Model
Published in Goff Hill, The Cable and Telecommunications Professionals' Reference, 2012
This transfer of information between the systems involves the construction and forwarding of control information and data units that convey the actions and substance of the communication. Figure 3.9 presents the basic data unit structure that passes layer by layer within a system. A service data unit (SDU) is the data passed to the (N)-layer from the (N + 1)-layer for forwarding to the peer (N + 1)-entity in the destination system. Therefore, the (N)-layer is responsible for transferring the SDU transparently, so that it is delivered to the destination (N + 1)-entity exactly as it was received by the (N)-entity in the source system.
Using the Information Harm Triangle to Identify Risk-Informed Cybersecurity Strategies for Instrumentation and Control Systems
Published in Nuclear Technology, 2023
Michael T. Rowland, Lee T. Maccarone, Andrew J. Clark
The difference between data and meaning is implicit within the OSI layers. A service data unit (SDU) is how layers in a single system communicate with one another. The SDU is data generated by the user of a service transmitted to a peer service user in a way that does not change the meaning of the data. However, communicating peer entities (i.e., systems in the same OSI layer) can interpret the data and derive meaning from these data. The protocol data unit is composed of protocol-specific information (i.e., context and metadata). It is this composition that allows the peer entity to derive the correct meaning of the data.