In This Issue
Fast Ethernet: Pg 1-2
Frame Relay -- A Perspective: Pg 3-4
Kent's Korner Pg 4
Fast Ethernet Seminar: Pg 4
Fast Ethernet: An Introduction
Driven by recent advances in computing technology, today's networking
applications have grown in speed, power and information processing.
However, these new applications are placing so much demand on the
underlying network that it is running out of capacity. This is the
driving need for greater bandwidth and improved response time. Based
on the same CSMA/CD protocols familiar to Ethernet users, 100BASE-T
Fast Ethernet offers a natural migration path from traditional Ethernet.
With many manufacturers shipping selectable 10/100 Mbps products,
you can protect your investment in existing 10 Mbps Ethernet LAN
equipment. Also, Fast Ethernet allows you to preserve investments
in existing cabling, since the technology is capable of running on
Category 3, 4, or 5 cabling.
Fast Ethernet Technology
The 100BASE-T standard consists of five different component
specifications. These include the Media Access Control (MAC)
layer, the Media Independent Interface (MII), and the three physical
layers, (100 BASE-TX, 100BASET4, and 100BASE-FX).
Media Access Control (MAC) Layer
The MAC layer is based on the same CSMA/CD protocol as 10Mbps Ethernet.
The only difference is that it runs ten times faster.
Fast Ethernet retains all of the robustness of the traditional
protocol. Rather than having to learn an entirely different
technology, the customer can rely on all the experience gathered
over the years while retaining a considerable investment in training,
management, and analysis tools.
Media Independent Interface (MII) Layer
The MII is a new specification that defines a standard interface
between the MAC layer and any of the three physical layers
(100BASE-TX, 100BASE-T4, and 100BASE-FX). It is capable of
supporting both 10 Mbps and 100Mbps data rates.
The MII can be implemented internally in a network device to connect
the MAC layer directly to the physical layer. This is often the case
with adapters (network interface cards or NICs).
The MII can be implemented externally in a network device via a 40-pin
connector. Some class I repeaters may be equipped with this connector
(Class I and Class II repeaters explained on page 2). With the MII
and the proper transceiver, a Class I repeater can be connected to any
STP, UTP, or fiber cable device; analagous to the AUI connector in 10
Mbps Ethernet networks.
100BASE-TX Physical Layer
This physical layer defines the specifications for 100BASE-T Ethernet
over two pairs of Category 5 UTP (unshielded twisted pair) wire, or
two pairs of Type I STP (shielded twisted-pair) wire. With one pair
for transmit and the other for receive, the wiring scheme is identical
to that used for 10BASE-T Ethernet.
100BASE-T4 Physical Layer
This physical layer defines the specification for 100BASE-T Ethernet
over four pairs of either Category 3, 4, or 5 UTP wire. With this
signaling method, three wire pairs are used for transmit and receive,
while the fourth pair listens for collisions.
100BASE-FX Physical Layer
This physical layer defines the specification for 100BASE-T Ethernet
over two strands of 62.5/125 micron fiber cable. One strand is used
for transmit, while the other is used for receive.
See Fast Ethernet on page 2.
