Sometime when you install a PTP820 link, you find that signal quality is great and the link is running at top modulation rate. but you cannot get the expected throughput when you try to pass data. One very important think to check is to make sure that you have good Ethernet connections on the data port. You may even see that the Ethernet interface is negotiated with correct speed (1000 Full). One thing worth looking into is the Ethernet interface statistics. You can go to Ethernet->PM & Statistics->RMON and look for any Tx/Rx frame errors, e.g. CRC error, FCS error, etc. If you see these errors increment when you send data over the link, it is highly likely that you have a physical problem with your ethernet cabling. Make sure that Ethernet ports are connected nicely and make sure that you have good Ethernet cable. It may just save your day.