Link Loss Forwarding

An Ethernet connection is a managed point-to-point connection between two intelligent end devices.

Fig.16: Point-to-point connection between two Ethernet devices

Both devices transmit the so-called idle pattern in their Ethernet connection. When they also receive a corresponding pattern, the connection and thus the so-called link has been established. Both devices then know that they can use this connection. If the connection is interrupted, a link no longer exists and both devices indicate this, for example, by the LEDs.

Fig.17: Interrupted point-to-point connection

If a media converter is placed between the two stations, it too becomes an intelligent transmitter/receiver. If connection C is interrupted, device A would not necessarily be informed and would continue to send data to the converter via the existing link B, and the data would "trickle away". The EP9521 therefore supports Link Loss Forwarding (LLF) in a direction that must be selected. The message direction is selected by means of the rotary selection switch setting. Therefore, if the converter shown in Fig. Inline media converter in Ethernet link detects an interruption in connection C, it also removes the link from connection B.

Fig.18: Interposed media converter in the Ethernet connection

In both IP settings the EP9521 operates as a store and forward network device with checksum function. Frames that are faulty (CRC error), too short (<64 bytes) or too long (>1536 bytes) are not passed on.