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Using Ethernet Media in Your Internetwork

IEEE passed both methods in June 1995, but because 802.3 Ethernet had
such a strong name in the industry, 802.12, also called Demand Priority
Access Method (DPAM), has virtually disappeared from the market. As with
the Macintosh and NetWare operating systems, it doesn't mean anything if
you have a better product; it only matters how you market it.

The IEEE 802.3u committee can be summarized as follows:

Provide seamless integration with the installed base

Provide 100BaseT at only two times the cost (or less) of 10BaseT

Increase aggregate bandwidth

Provide multiple-vendor standardization and operability

Provide time-bounded delivery

Media Independent Interface (MII)

FastEthernet requires a different interface than 10BaseT Ethernet. 10Mbps
Ethernet used the Attachment Unit Interface (AUI) to connect Ethernet seg-
ments together. This provided a decoupling of the MAC layer from the dif-
ferent requirements of the various Physical layer topologies, which allowed
the MAC to remain constant but meant the Physical layer could support any
existing and new technologies. However, the AUI interface could not sup-
port 100Mbps Ethernet because of the high frequencies involved. 100BaseT
needed a new interface, and the MII provides it.

100BaseT actually created a new subinterface between the Physical layer

and the Data Link layer called the Reconciliation Sublayer (RS). The RS
maps the 1s and 0s to the MII interface. The MII uses a nibble, which is
defined as 4 bits. AUI used only 1 bit at a time. Data transfers across the MII
at one nibble per clock cycle, which is 25MHz. 10Mbps uses a 2.5MHz
clock.

Full-Duplex Ethernet and FastEthernet

Full-duplex Ethernet can both transmit and receive simultaneously and uses
point-to-point connections. It is typically referred to as collision free because

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