An SFP module provides either a 1000Base-X or SGMII interface protocol to
a host and provides a 1000Base-T media dependent interface (MDI). If the
SFP module is coupled a host that only implements the 1000Base-X protocol
then the SFP module translates the 1000Base-X protocol to the 1000Base-T
protocol so that the host MAC sees the 1000Base-T SFP module as if it
were an optical transceiver. If the host implements SGMII then the SFP
performs auto-negotiation of speed and communicates with the host
implement data transfer at a selected rate, e.g., 10, 100, or 1000 Mbps.