AL211 Allayer Communications, AL211 Datasheet - Page 13

• Manufacturer Part Number: AL211
• Description: Fast Ethernet Fiber to TP Media Converter
• Manufacturer: Allayer Communications

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The 100Base-FX specification provides a way to detect transmit link-failure. Whenever a fiber
receiver experiences receive link-failure, it will transmit a far-end fault signal. The far-end fault
signal is indicated by the far-end fault IDLE signal (84 “ones” follow by a “zero”).
When the AL211 receives the far-end fault signal, it is notified by the far-end station that a transmit
fault has occurred. The device will go into a link-down state and will take the following actions:
The data transmission will be assumed by the backup AL211 and start sending copies of the signal.
Upon re-establishment of the primary fiber, Redun# will be de-asserted and the backup data link
will be turned off.
Figure 1-7
The key to this configuration is that the transceivers of the fiber switch must support far-end fault
signaling (although the IEEE far-end fault signaling is an option).
The operation of this link configuration is very similar to the AL211 redundant link as described
above. Instead of the far-end transceivers being switched, the ports are now switched. Whenever,
the far-end transceiver receives the far-end fault signal or no IDLE signal, it will enter the link-fail
state. Thus, redundancy is accomplished.
There is no limit on the number of redundant links for the AL211. Also the Redun# and Data_off
signals can be cascaded as many times as it needs to offer two or more redundant links.
One minor disadvantage of this scenario with a switch, is that the link will not be functional
(spanning tree will cut off the port) until the addresses stored in the switch are aged out. However,
many of the switches today automatically delete the old address when there is a change of address.
With that feature, the link will be immediately established.
2.9.2 Transmit Link Fault
2.9.3 Redundant Link with Switches or Repeater
shows a redundant link implemented by a pair of AL211’s and a fiber switch/repeater.
1. Put the TPO+ and TPO- pins in high impedance; and
2. Assert Redun# signal.
Reference Only / Allayer Confidential
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