1-2
PA-2FE-TX and PA-2FE-FX Two-Port Fast Ethernet Port Adapter Installation and Configuration
OL-3474-06
Chapter 1 Overview
Fast Ethernet Overview
Fast Ethernet Overview
The term
Ethernet
is commonly used for all carrier sense multiple access collision detect (CSMA/CD)
LANs that generally conform to Ethernet specifications, including Fast Ethernet under IEEE 802.3u.
Note
100BASE-TX is intended for Environment A, and 100BASE-FX is intended for Environment B. Both
are described in the IEEE 802.3u standard.
IEEE 802.3u is well suited to applications where a local communication medium must carry sporadic,
occasionally heavy traffic at peak data rates. Stations on a CSMA/CD LAN can access the network at
any time. Before sending data, the station
listens
to the network to see if it is already in use. If it is in
use, the station waits until the network is not in use, then transmits. This process is known as
half-duplex
operation
. A collision occurs when two stations listen for network traffic, hear none, and transmit almost
simultaneously. When simultaneous transmission occurs, both transmissions are damaged and the
stations must retransmit. The stations detect the collision and use backoff algorithms to determine when
they should retransmit.
Both Ethernet and IEEE 802.3u are broadcast networks, which means that all stations see all
transmissions. Each station must examine received frames to determine whether it is the intended
destination and, if it is, pass the frame to a higher protocol layer for processing.
IEEE 802.3u specifies the following different physical layers for 100BASE-T:
•
100BASE-TX—100BASE-T, half- and full-duplex over Category 5 UTP, EIA/TIA–568-compliant
cable
•
100BASE-FX—100BASE-T, half- and full-duplex over optical fiber
Each physical layer protocol has a name that summarizes its characteristics in the format speed/signaling
method/segment length, where speed is the LAN speed in megabits per second (Mbps), signaling method
is the signaling method used (either
baseband
or
broadband
), and segment length is the maximum length
between stations in hundreds of meters. Therefore, 100BASE-T specifies a 100-Mbps, baseband LAN
with maximum network segments.
IEEE 802.3u 100BASE-T Specifications
This section provides specifications for IEEE 802.3u 100BASE-T. Table 1-1 provides cabling
specifications for 100BASE-TX Fast Ethernet transmission over UTP and foil twisted-pair (FTP), and
100BASE-FX Fast Ethernet over fiber-optic cables. It also summarizes IEEE 802.3u 100BASE-TX and
100BASE-FX physical characteristics. (See
Figure 1-3
.)
Table 1-1
Cabling Specifications
Parameter
100BASE-TX
100BASE-FX (Multimode)
Cable specification
Category 5
1
UTP
2
, 22 to 24
AWG
62.5/125 multimode optical fiber
Maximum segment length
(half-duplex)
3
100 m
412 m
Maximum segment length
(full-duplex)
3
100 m
2000 m
