Controller Protection Through Link Fault Indication (Lfi) - Siemens RUGGEDCOM ROS User Manual

RUGGEDCOM ROS
User Guide
• Section 3.6.6, "Managing SFP Transceivers"
• Section 3.6.7, "Configuring an Ethernet Port"
• Section 3.6.8, "Configuring Port Rate Limiting"
• Section 3.6.9, "Configuring Port Mirroring"
• Section 3.6.10, "Configuring Link Detection"
• Section 3.6.11, "Detecting Cable Faults"
• Section 3.6.12, "Resetting Ethernet Ports"
Section 3.6.1

Controller Protection Through Link Fault Indication (LFI)

Modern industrial controllers often feature backup Ethernet ports used in the event of a link failure. When these
interfaces are supported by media (such as fiber) that employ separate transmit and receive paths, the interface
can be vulnerable to failures that occur in only one of the two paths.
Consider for instance two switches (A and B) connected to a controller. Switch A is connected to the main port on
the controller, while Switch B is connected to the backup port, which is shut down by the controller while the link
with Switch A is active. Switch B must forward frames to the controller through Switch A.
Figure 20: Example
1. Switch A 2. Switch B
If the transmit path from the controller to Switch A fails, Switch A still generates a link signal to the controller
through the receive path. The controller still detects the link with Switch A and does not failover to the backup
port.
This situation illustrates the need for a notification method that tells a link partner when the link integrity signal
has stopped. Such a method natively exists in some link media, but not all.
100Base-TX, 1000Base-T, 1000Base-X
100Base-FX Links
10Base-FL LInks
Controller Protection Through Link Fault Indication (LFI)
1
3
5
3. Main Transmit Path 4. Backup Transmit Path
Includes a built-in auto-negotiation feature (i.e. a special flag called Remote Fault Indication
is set in the transmitted auto-negotation signal).
Includes a standard Far-End-Fault-Indication (FEFI) feature defined by the IEEE 802.3
standard for this link type. This feature includes:
• Transmitting FEFI
Transmits a modified link integrity signal in case a link failure is detected (i.e. no link
signal is received from the link partner)
• Detecting FEFI
Indicates link loss in case an FEFI signal is received from the link partner
No standard support.
2
4
5. Controller
Chapter 3
Device Management
57