![]() The sending adaptor attaches the preamble and CRC before transmitting, and the receiving adaptor removes them. Note that from the host's perspective, an Ethernet frame has a 14-byte header: two 6-byte addresses and a 2-byte type field. Like the HDLC protocol described in Section 2.3.2, the Ethernet is a bit-oriented framing protocol. Finally, each frame includes a 32-bit CRC. ![]() The reason for this minimum frame size is that the frame must be long enough to detect a collision we discuss this more below. Minimally, a frame must contain at least 46 bytes of data, even if this means the host has to pad the frame before transmitting it. Each frame contains up to 1500 bytes of data. ![]() The packet type field serves as the demultiplexing key it identifies to which of possibly many higher-level protocols this frame should be delivered. Both the source and destination hosts are identified with a 48-bit address. ![]() 6 The 64-bit preamble allows the receiver to synchronize with the signal it is a sequence of alternating 0s and 1s. Each Ethernet frame is defined by the format given in Figure 2.25. ![]()
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