ITWissen.info - Tech know how online

realtime Ethernet

Ethernet uses a stochastic access method that does not allow real-time capability. In addition, the frame length with up to 1,518 bytes hinders low- delay real-time behavior. However, since real-time applications play a decisive role in industry and automotive technology, there are various solutions based on Ethernet that use a deterministic access method.

These solutions, mainly developed for industrial and automotive applications, include Ethernet-Powerlink, EtherCAT, EtherNet/ IP, Profinet, Sercos, VARAN, TTEthernet, BroadR-Reach, Time-Sensitive Networking( TSN) and some other concepts.

One approach to real-time behavior is micro- segmentation, in which the Ethernet network is divided into the smallest LAN segments using Ethernet switching and only one station is assigned to each micro- segment. With simultaneous reduction of the Ethernet frame's payload, predictable timing behavior is achieved in this constellation.

Other methods override the CSMA/ CD access method by superimposing protocol layers and replace it with a time slot method or polling. In the Slot Communication Network Management( SCNM) isochronous time slot method, a central controller assigns access authority to stations connected to the network. A station can only access the network if it receives the corresponding time slot from the central unit. This method achieves guaranteed cycle times that depend on the number of stations connected. For example, the specifications of Ethernet Powerlink, which uses IEEE 802.3u as its basis, state a cycle time of about 2 ms for 100 connected stations, with a user data rate of 46 bytes.

Informations:
Englisch: realtime Ethernet
Updated at: 21.04.2015
#Words: 231
Links: Ethernet, method, indium (In), frame, delay (DEL)
Translations: DE
Sharing:    

All rights reserved DATACOM Buchverlag GmbH © 2024