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Ethernet header fields -
Preamble (DIX)
Provides synchronization and signal transitions to allow proper clocking of the transmitted signa.  Consists of 62 alternating 1s and 0s and ends with a pair of 1's.
Ethernet header fields -
Preamble and start of Frame Delimiter (802.3)
Same purpose and binary value as DIX preamble; 802.3 simply renames the 8-byte DIX preamble as a 7-byte preamble and a 1-byte Start of Frame Delimiter (SFD).
Ethernet Header Fields -
Type (or Protocol Type) (DIX)
2-byte field that identifies the type of protocol header that follows the header.  Allows the receiver of the frame to know how to process a received frame.
Ethernet Header Fields -
Length (802.3)
Describes the length, in bytes, of the data following the Length field, up to the Ethernet trailer.  Allows an Ethernet receiver to predict the end of the received frame.
Ethernet Header Fields -
Destination Service Access Point (DSAP) (802.3)
DSAP; 1-byte protocol type field.  The size limitations, along with other uses of the low-order bits, required the later addition of SNAP headers.
Ethernet Header Fields -
Source Service Access Point (802.3)
SSAP; 1-byte protocol type field that describes the upper-layer protocol that created the frame.
Ethernet Header Fields -
Control (802.2)
1- or 2-byte field that provides mechanisms for both connectionless and connection-oriented operation.  Generally used only for connectionless operation by modern protocols, with a 1-byte value of 0x03.
Ethernet Header Fields -
Organizationally Unique Identifier (SNAP)
OUI; 3 byte field, generally unused today, providing a place for the sender of the frame to code the OUI representing the manufacturer of the Ethernet NIC.
Ethernet Header Fields -
Type (SNAP)
2-byte Type field, using same values as the DIX Type field, overcoming deficiencies with size and use of the DSAP field.
Three types of Ethernet/MAC Addresses -
Unicast
Fancy term for an address that reprsents a single LAN interface.  The I/G bit, the most significant bit in the most significant byte, is set to 0.
Three types of Ethernet/MAC Addresses -
Broadcast
An address that means "all devices that reside on this LAN right now."  Always a value of hex FFFF.FFFF.FFFF.
Three types of Ethernet/MAC Addresses -
Multicast
A MAC address that implies some subnet of all devices currently on the LAN.  By definition, the I/G bit is set to 1.
I/G and U/L Bits -
I/G
Binary 0 means the address is a unicast; Binary 1 means the address is a multicast or broadcast.
I/G and U/L Bits -
U/L
Binary 0 means the address is vendor assigned; Binary 1 means the address has been administratively assigned, overriding the vendor-assigned address.
Ethernet Type Fields - 
Protocol Type
DIX V2 Type field; 2 bytes; registered values now administered by the IEEE.
Ethernet Type Fields -
DSAP
802.2 LLC; 1 byte, with a 2 high-order bits reserved for other purposes; registered values now administered by the IEEE.
Ethernet Type Fields -
SNAP
SNAP header, 2 bytes; uses same values as Ethernet Protocol Type; signified by 802.2 DSAP of 0xAA
Ethernet Standards -
10Base5
Commonly called "thick-net"; uses coaxial cabling.
Ethernet Standards -
10Base2
Commonly called "thin-net"; uses coaxial cabling.
Ethernet Standards -
10Base-T
First type of Ethernet to use twisted-pair cabling.
Ethernet Standards -
DIX Ethernet Version 2
Layer 1 and Layer 2 specifications for original Ethernet, from Digital/Intel/Xerox; typically called DIX V2
Ethernet Standards -
IEEE 802.3
Called MAC due to the name of the IEEE committee (Media Access Control); original Layer 1 and 2 specifications, standardized using DIX V2 as a basis.
Ethernet Standards -
IEEE 802.2
Called LLC due to the name of the IEEE committee (Logical Link Control); Layer 2  specification for header common to multiple IEEE LAN specifications.
Ethernet Standards - 
IEEE 802.3u
IEEE Standard for fast Ethernet (100 Mbps) over copper and optical cabling; typically called FastE.
Ethernet Standards -
IEEE 802.3z
Gigabit Ethernet over optical cabling; typcially called GigE.
Ethernet Standards -
IEEE 802.3ab
Gigabit Ethernet over copper cabling.
Switch Internal Processing -
Store and Forward
The switch fully receives all bits in the frame (store) before forwarding the frame (forward).  This allows the switch to check the FCS before forwarding the frame, thus ensuring that errored frames are not forwarded.
Switch Internal Processing -
Cut-Through
The switch performs the address table lookup as soon as the Destination Address field in the header is received.  The first bits in the frame can be sent out the outbound port before the final bits in the incoming frame are received.  This does not allow the switch to discard frames that fail the FCS check, but the forwrding action is faster, resulting in lower latency.
Switch Internal Processing -
Fragment-free
This performs like cut-through switching, but the switch waits for 64 bytes to be received before forwarding the first bytes of the outgoing frame.  According to the Ethernet specifications, collisions should be detected during the first 64 bytes of the frame, so frames that are in error because of a collision will not be forwarded.
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