IEEE 802.3

• The reconciliation sublayer and the optional media-independent interface (MII in 10-Mbps and 100-Mbps Ethernet, GMII in Gigabit Ethernet) provide the logical connection between the MAC and the different sets of media-dependent layers. The MII and GMII are defined with separate transmit and receive data paths that are bit-serial for 10-Mbps implementations, nibble-serial (4 bits wide) for 100-Mbps implementations, and byte-serial (8 bits wide) for 1000-Mbps implementations. The media-independent interfaces and the reconciliation sublayer are common for their respective transmission rates and are configured for full-duplex operation in 10Base-T and all subsequent Ethernet versions.



• The media-dependent physical coding sublayer (PCS) provides the logic for encoding, multiplexing, and synchronization of the outgoing symbol streams as well symbol code alignment, demultiplexing, and decoding of the incoming data.



• The physical medium attachment (PMA) sublayer contains the signal transmitters and receivers (transceivers), as well as the clock recovery logic for the received data streams.



• The medium-dependent interface (MDI) is the cable connector between the signal transceivers and the link.



• The Auto-negotiation sublayer allows the NICs at each end of the link to exchange information about their individual capabilities, and then to negotiate and select.



• the most favorable operational mode that they both are capable of supporting. Auto-negotiation is optional in early Ethernet implementations and is mandatory in later versions.

• If the NIC at the other end of the link is also powered up, it responds with its own NLP.



• If the NIC at the other end of the link is not powered up, this NIC continues sending an NLP about once every 16 ms until it receives a response.

• The basic Ethernet frame format
  The IEEE 802.3 standard defines a basic data frame format that is required for all MAC implementations, plus several additional optional formats that are used to extend the protocol's basic capability.



Preamble	SFD	Destination	Source	Length Type	Data unit + pad	FCS
7 bytes	1 byte	6 bytes	6 bytes	2 bytes	46-1500 bytes	4 bytes



• Preamble (PRE)
  The PRE is an alternating pattern of ones and zeros that tells receiving stations that a frame is coming, and that provides a means to synchronize the frame-reception portions of receiving physical layers with the incoming bit stream.



• Start-of-frame delimiter (SOF)
  The SOF is an alternating pattern of ones and zeros, ending with two consecutive 1-bits indicating that the next bit is the left-most bit in the left-most byte of the destination address.



• Destination address (DA)
  The DA field identifies which station(s) should receive the frame.
  The address structure is as follows:
  

  I/G

  U/L

  Address bits

  
  

  I/G	Individual / group address may be:
  	0	Individual address.
  	1	Group address.
  U/L	Universal /local address may be:
  	0	Universally administered.
  	1	Locally administered.

  
  The left-most bit in the DA field indicates whether the address is an individual address (indicated by a 0) or a group address (indicated by a 1). The second bit from the left indicates whether the DA is globally administered (indicated by a 0) or locally administered (indicated by a 1). The remaining 46 bits are a uniquely assigned value that identifies a single station, a defined group of stations, or all stations on the network.



• Source addresses (SA)
  The SA field identifies the sending station. The address structure is as follows:
  

  0	The first bit is always 0.
  U/L	Universal/local address may be:
  	0	Universally administered.
  	1	Locally administered.




• Length/Type
  This field indicates either the number of MAC-client data bytes that are contained in the data field of the frame, or the frame type ID if the frame is assembled using an optional format. If the Length/Type field value is less than or equal to 1500, the number of LLC bytes in the Data field is equal to the Length/Type field value. If the Length/Type field value is greater than 1536, the frame is an optional type frame, and the Length/Type field value identifies the particular type of frame being sent or received.



• Data
  Is a sequence of n bytes of any value, where n is less than or equal to 1500. If the length of the Data field is less than 46, the Data field must be extended by adding a filler (a pad) sufficient to bring the Data field length to 46 bytes.



• Frame check sequence (FCS)
  This sequence contains a 32-bit cyclic redundancy check (CRC) value, which is created by the sending MAC and is recalculated by the receiving MAC to check for damaged frames. The FCS is generated over the DA, SA, Length/Type, and Data fields.



• IEEE 802.3 header



Destination Address	Source Address	Ethertype	Data
6 bytes	6 bytes	16 bytes	46-1500 bytes



• Destination Address
  MAC address of the destination node. This may be a unicast, multicast or broadcast address.



• Source Address
  The unicast MAC address of the source node.



• Ethertype
  The number of bytes encapsulated or the protocol type of the next higher protocol.

■ Parent layer
■ Child layer

MPLS VLAN

IEEE 802.3