FEandGE接口及编码原理.ppt

Fast Ethernet The goal of the Fast Ethernet is to obtain an order of magnitude increase in speed over 10BaseT Ethernet (IEEE 802.3) while retaining the same wiring systems, MAC method, and frame formats. In IEEE 802.3, the longest distance between two stations is 2.5km, with a slot time of 51.2us (512 bits for 10Mbps). One way to increase the speed is to shorten the distance (Collision Window = 512 bit-time). In Hub architecture, the distance between station and Hub is at most 100m and the round-trip distance between two stations is 400m. A faster speed can be used to transmit frames under CSMA/CD protocol while keeping the minimum frame size as 512 bits. In the standard, the speed is 100Mbps and denoted as 100BaseT. Fast Ethernet Characteristics 100 Mbps IEEE 802.3 CSMA/CD frame format. Medium Twisted pair -- UTP, STP Fiber CSMA/CD Protocol, do not support priority scheme. Do not support guaranteed delay service Frames collision Bandwidth utilization is not guaranteed to be fair. Low bandwidth utilization under heavy load. Fast Ethernet Characteristics Suitable for multimedia communications under moderate load. Good fault tolerance Hub/Switch architecture 100Base4T Voice-grade Category 3 UTP. Use four pairs of twisted-pair wires. 100BaseX (100BaseTX, 100BaseFX, etc) Category 5 UTP, STP, or Fiber optic. Communication Architecture The Convergence Sublayer (CS) provides the interface between CSMA/CD MAC sublayer and PMD layer. MII Interface Signaling To support different transmission medium, a Media Independent Interface (MII) is defined between CS and PMD. The major functions of the CS Convert the transmit and receive serial data streams at the MAC sublayer interface into and from 4-bit nibbles for transfer across the MII. Relay the carrier sense and collision detection signals generated by the PMD sublayer to the MAC sublayer. MII Interface Signaling 100Base4T Category 3 UTP cable contains 4 separate twisted-pair wires. To reduce the bit rate used in each wire, al