EPL protocol
The EPL protocol is a deterministic access method for Ethernet Powerlink (EPL). As Ethernet-Powerlink is used in automation, production and manufacturing environments, time-critical data accumulates that must be transmitted with defined predictability. For this purpose, Ethernet Powerlink works with a delimited real-time domain, a special network segment over which the time-critical data traffic is handled. Up to 240 Controlled Node( CN), the name for the stations, can be connected to such a realtime segment.
The EPL protocol is a cyclic access method that ensures that all Controlled Nodes are synchronized to each other with a time delay of less than one microsecond.
In the EPL protocol, the Managing Node sends a start cycle( SoC) as a broadcast over the real-time domain tocheck timing. This start cycle marks the beginning of the strictly deterministic cycle period, where the Managing Node sends a poll to all Controlled Nodes in unicast, which then document their readiness to transmit with a corresponding response message. Since the poll response is sent in multicast, all Controlled Nodes receive it and can reset their send request.
Time-critical data is transmitted isochronously in time windows. Each station is assigned a time window. During this period, the nodes can send IP telegrams, which are the datagrams known from data communication, in the time window assigned to the station. Individual time windows can be assigned to several stations in the multiplex. The isochronous transmission is followed by a time window for asynchronous data. These are time-uncritical diagnostic and measurement data. In a transmission cycle, only one time slot for asynchronous data is assigned to a single station at a time. The time slots are assigned by the Managing Node, which prioritizes the requests from the individual stations. The EPLsafety protocol version is available for safety-critical applications.