Ethernet Frame II

Preamble- Preamble is of 8 bytes. It contains bit pattern 10101010, and is used by the receiver to allow it to establish bit synchronization (there is no clocking information on the ether when nothing is being sent)

Start frame delimiter- is a single byte, 10101011, which is a frame flag, indicating the start of a frame.

 Mac Address- When a message is sent between host on a network or the same switch, the switch check its mac address table for the destination address. A switch mac address table contains a list of all active ports, host or PCs mac addresses that are attached to it. If the destination Mac address is not found in the table, the switch will not have the necessary information to forward the message. When the switch cannot determine where the destination host is located, it will flood or forward the message out to all attached host. Each host compares the destination mac address in the message to its own mac address, but only the host with the correct destination address processes the message and responds.

Frame Type- Numbering generally start from 0x0800. In modern implementations of Ethernet, the field within the Ethernet frame used to describe the Ether Type also can be used it represent the size of the payload of the Ethernet frame. Historically, depending on the type of Ethernet framing that was in use on an Ethernet segment, both interpretations were simultaneously valid, leading to ambiguity. Ethernet framing considered these octets to represent ether type while the original IEEE 802.3 framing considered these octets to represent the size of the payload in bytes.

Data In Frame- Or payload the minimum payload is 42 octets when an 802.1q tag is present and 46 octets when absent. The maximum payload is 1500 octets. Non-standard jumbo frame allow for larger maximum payload size.

Cyclic Redundancy Check (CRC)- is an error detecting code commonly used in digital network and storage devices to detect accidental changes to raw data. Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents, on retrieval the calculation is repeated, and  corrective action can be taken against presumed data corruption if the check values do not match.