This document describes the Automatic Laser Shutdown (ALS) mechanism of the Cisco Metro 1500. For reasons of laser safety, the Wavelength Channel Module (WCM) is equipped with an ALS mechanism, which reduces the optical output power of the remote transmitter whenever a remote link is broken.
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This document is not restricted to specific software and hardware versions.
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Let's look at a brief overview of the optical handshake:
The application (Cient_A) has to be connected to Local Receiver (L/R) of Site_A.
Every ten seconds, Site_A sends a defined burst in milliseconds (ms) duration.
Site_B receives the burst and answers with a predefined answer burst.
Site_A detects the answer pulse and switches the application on the fiber.
If the application (modulated light) is lost for a defined time, for example if the fiber is broken or the application is shut down and there is a Loss of Signal (LOS), then the remote laser (R/T) shuts down.
Let's look at how ALS works using some examples. In the following example, we assume that the fibers are okay and there are two applications on both ends of the Cisco Metro 1500 link.
Client_A starts to send the light to the connector of the WCM labeled L/R, which is called Site_A. As a result, the green LED of the L/R of the WCM is switched on.
The ALS starts working on Site_A. Every ten seconds, the R/T sends a defined burst lasting several ms, and the R/T LED blinks briefly.
If the fiber is okay between Site_A and Site_B, then the Remote Receiver (R/R) on Site_B receives the burst from Site_A and switches the R/R LED on.
When the R/R of Site_B detects the incoming signal, it switches the Local Transmitter (L/T) on.
At this point, Client_B receives the light signal from the Cisco Metro 1500 and starts its laser (Tx).
Should the L/R of Site_B receive any incoming light from Client_B, it sends an answer burst back to Site_A.
When the R/R of Site_A receives the answer burst from Site_B, it switches the L/T on and switches the application on fiber.
In the next example, we assume that the fibers are okay and there is only one application on Site_A of the Cisco Metro 1500 link.
Client_A starts to send the light to the L/R connector of the WCM Site_A.
On Site_A, the ALS starts working. Every ten seconds, the R/T sends a defined burst during a period of several ms, and the R/T LED blinks shortly. When the R/R of Site_B detects the incoming signal it switches the L/T on. There is no application or loopback connected to Site_B, so the L/R and R/T of Site_B stay off. The R/R of Site_A waits for the answer burst during a period of several ms from Site_B.
If the R/R of Site_A doesn't receive any answer from Site_B during the predefined ms time, it shuts off the R/T. This causes the local laser on Site_B to be switched off.
After ten seconds, the remote laser of Site_A sends the defined burst again during a period of several milliseconds. It repeats this until the remote receiver detects the incoming signal from Site_B. If the remote receiver of Site_A detects the light from Site_B, it switches the application on the fibers (as described in steps 6 and 7 above).
The WCM LEDs provide information about its operating status.
|On/Err||Green||Power is on. No software or hardware errors are detected.|
|Red||A hardware or software error was detected or the initialization is in progress (during system startup only).|
|Red blinking||WCM is in manual setting mode (not shown in case of error).|
|Loop||Orange||A remote or a local loop is established.|
|L/R||Green||Data is received from the local port.|
|L/T||Green||Data is transmitted to the local port.|
|R/R||Green||Data is received from the remote end of the link.|
|R/T||Green||Data is transmitted to the remote end of the link.|
|Green blinking||WCM is in ALS mode; LED blinks once every ten seconds.|
* Any state other than the ones listed indicates a possible failure in the local system.
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