803.3 100Mbps (Fast Ethernet) Layer 1 (PHY) Implementations
100Mbps operation of 802.3 Ethernet required that adjustments be made to the MAC (OSI Layer 2) and PHY (OSI Layer 1). Although the MAC (frame format) layer itself and its operational proprieties (slot-period, and so on) are identical to the 10Mbps standard, the 10Base PLS, AUI, and PMA interfaces were inadequate for the new higher transmission rate. To replace them, the developers of Fast Ethernet developed a new PHY interface for the 100Base-T4 implementation and utilized existing FDDI PHY interface standards for the 100Base-TX and 100Base-FX implementation. From an operational perspective, the 802.3u standard defines the following operational characteristics for 100Base-T:
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