Phil,
You would use one of the AS-EC-XXE Ethernet Connection Cables. They come in 2, 10, 15, 20 and 30-foot lengths and the cable length is part of the part number. Just replace the “XX” with the cable length, so a 15-foot Ethernet Connection Cable is an AS-ETH-15E, while a 20-footer would be an AS-ETH-20E.