Planet GST-702, User Manual

- 13 - 

4.2 Link Loss Return (LLR) 

The fiber ports of GST-70X have been designed with an LLR function for troubleshooting a remote connection. LLR works 
in conjunction with LLCF. 

When LLR is enabled*, the port’s transmitter shuts down when its receiver fails to detect a valid receive link. LLR should 
only be enabled on one end of the link and is typically enabled on either the unmanaged or remote device. 

The diagram below shows a typical network configuration with a good link status using GST-70X for remote connectivity. 
Note that LLR is enabled as indicated in the diagram. 

Management  Switch/Hub         Media                           Media               Switch/Hub   Management 

Station           w/SNMP          Converter               Converter            w/SNMP     Station 

●

 LED lit = established link    

○

 LED unlit = no link 

LLCF is ON 

LLCF is ON 

Fiber 

Cable 

If one of the optical conductors is bad (as shown in the diagram box below), the converter with LLR enabled will return a 
no-link condition to its link partner. With LLCF also default enabled, the no-link condition is carried forward to the switch/hub 
where a trap is generated to the management station, and the administrator can then determine the source of the loss. 

Management Switch/Hub    Media                        Media        Switch/Hub Management

Station           w/SNMP        Converter                  Converter         w/SNMP        Station

●

 LED lit = established link    

○

 LED unlit = no link 

LLCF is ON

LLCF is ON

Port 2 

Broken 

Fiber

Port 1 

Link Loss Carried Forward 

Link Loss Carried Forward 

Link Loss Returned 

#

Notice: 

1: LLR must NOT be active on both ends of a configuration. If it is, the link can never be established. 

2. Units are shipped with the LLR function disabled (DOWN).