| 单词 | Ethernet |
| 释义 | Ethernet fiber. Relatively unchanged have been the frame format and the protocols for medium access control (MAC), which include carrier sense multiple access with collision detection (CSMA/CD) and carrier sense multiple access/collision avoidance (CSMA/CA).The Ethernet frame, as illustrated in Figure E-3, is formatted as follows: • Preamble: A field of seven octets in an alternating pattern of 1s and 0s that advises the receiving stations that a frame of data is arriving. • Start of Frame (SOF): A delimiter of one octet that ends with two consecutive 1 bits that serve to synchronize the receiving stations on the rate of transmission. If multiple stations start sending to an idle network at nearly the same time, the preamble is long enough to ensure that a collision occurs before user data is sent by either station. • Destination and Source Addresses: The addresses of the target station and the originating station, respectively. Each address comprises each six octets, the first three of which are specified by the by the IEEE on a vendor-dependent basis and the last three of which are assigned by the vendor. • Length: A field of two octets that indicates the number of octets in the data field. • Data: A minimum of 64 octets and a maximum of 1518 octets. In consideration of the fact that 18 octets are consumed with Layer 1 and Layer 2 processing, the Data field, or payload, must comprise 46–1500 octets. In the event that the payload is less than 46 octets, padding bytes are inserted. • Frame Check Sequence (FCS): A 32-bit Cyclic Redundancy Check (CRC) comprising the frame trailer for purposes of error control. S Destination Source Preamble O Length Data FCS Address Address F Octets 7 1 6 6 2 46-1500 4 |
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