Allied Telesis AT-x510-28GTX Installation Manual page 125

If you are using SFP+ slots 27 or 28 on a 28-port switch or slots 51

and 52 on a 52-port switch, check that the VCStack feature is
disabled on the switch. The VCStack feature has to be disabled
before you can use the slots with regular SFP or SFP+
transceivers. For instructions, refer to "Powering On the Switches
Simultaneously" on page 105
Verify that the operating specifications of the fiber optic ports on

the transceiver and remote network device are compatible.
Verify that the correct type of fiber optic cabling is being used.

Verify that the port is connected to the correct fiber optic cable.

This is to eliminate the possibility that the port is connected to the
wrong remote network device.
Try connecting another network device to the fiber optic port using

a different cable. If the port is able to establish a link, then the
problem is with the cable or other network device.
Use the switch's management software to verify that the port is

enabled.
If the remote network device is a managed device, use its

management firmware to determine whether its port is enabled.
Test the attenuation of both directions on the fiber optic cable with

a fiber optic tester to determine whether the optical signal is too
weak (sensitivity) or too strong (maximum input power).
Problem 6: Network performance between a twisted pair port on the
switch and a network device is slow.
Solution: There might be a duplex mode mismatch between the port and
the network device. This can occur when a twisted pair port using Auto-
Negotiation is connected to a remote device that has a fixed speed of 10
or 100 Mbps and a fixed duplex mode of full duplex. If this is the cause of
the problem, adjust the duplex mode of the port on the network device or
switch so that both ports are using the same duplex mode. You can use
either the LEDs or management software on the switch to determine the
duplex mode settings of the ports. The LEDs are described in Table 5 on
page 36.
Problem 7: The switch functions intermittently.
Solutions: Check the system hardware status through the management
software:
Use the SHOW SYSTEM ENVIRONMENT command in the

Privileged Exec mode to verify that the input voltage from the
power source to the switch is stable and within the approved
operating range. The unit will shut down if the input voltage
fluctuates above or below the approved operating range.
x510 Series Installation Guide for Stand-alone Switches
125