Understanding the network.pdf - Back to Home

[†] To accommodate for 1,000 Base Ethernet's increased transmission rate, an increased slot-time is required.
[*] One bit time equals the cycle rate for the transmission path bandwidth. For example, 10Mbps Ethernet
operates at 10MHz so the bit time is 100ns.
[**] The minimum 64 byte Ethernet frame consists of the frame header, data PDU, and a CRC checksum for the
frame. This value does not include the additional 8-byte Ethernet frame preamble that is discarded when the
packet is actually processed. For the practical purposes of measuring the actual time it takes to transmit an
Ethernet frame and measure the FPS transmission rate of the segment, however, the preamble must be
accounted for in the packet size calculation. Therefore, by including the Preamble/Start of Frame Delimiter
minimum, Ethernet packet size is actually 72 bytes.
[††] Under half-duplex operation, actual minimum frame size for Gigabit Ethernet is actually 512K. To maintain
backwards compatibility with the other Ethernet MAC implementations, Gigabit uses a bit-stuffing process called
Carrier Extension to pad frames so they meet the minimum frame requirements for the enlarged Gigabit MAC
slot-time.
[***] The addition of the 8-byte preamble must also be done when calculating transmission times for the
maximum Ethernet frame size. Adding the preamble increases the maximum frame size to 1,526/1,530 bytes.
Ethernet/IEEE 802.3 MAC Framing
There are four Ethernet/802.3 frame types: the original DIX/Ethernet II and three
variations of the 802.3 frame. The Ethernet II and 802.3 frame formats are
illustrated in Figure 4.7. All the variations on the 802.3 frame relate to the format of
the data field (also known as the protocol data unit). These variations are discussed
in the next section.
NOTE
Figure 4.7. Ethernet II and IEEE 802.3ac frames.