The only thing between the Ethernet cable and the Altera FPGA (with some Verilog inside) is a pair of transformers and a couple of resistors. The Verilog handles all the encoding and decoding.

New Native System Verilog Ethernet VIP Complements Synopsys' 112G High-Speed SerDes PHY IP to Enable High-Performance Cloud Computing Solutions MOUNTAIN VIEW, Calif. -- March 23, 2020-- Synopsys, Inc.