Cisco Systems PA-2FE-TX Fast Ethernet Overview, IEEE 802.3u 100BASE-T Specifications, Parameter

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 1-1provides 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 51 UTP2, 22 to 24	62.5/125 multimode optical fiber
				AWG
		Maximum segment length		100 m	412 m
		(half-duplex)3
		Maximum segment length		100 m	2000 m
		(full-duplex)3
	PA-2FE-TX and PA-2FE-FX Two-Port Fast Ethernet Port Adapter Installation and Configuration
1-2					OL-3474-07