802.3 Ethernet Standards

Now that you have learned about the characteristics defined by the IEEE standards, let’s examine the standards themselves. Make sure that you are completely familiar with the information provided in each of the following sections before you take the Network+ exam.

10Base2

10Base2, which is defined as part of the IEEE 802.3a standard, specifies data transmission speeds of 10Mbps and a total segment length of 185 meters using RG-58 coaxial cable. The 10Base2 standard specifies a physical bus topology and uses Bayonet Neill Concelman (BNC) connectors with 50-ohm terminators at each end of the cable. One of the physical ends of each segment must be grounded.

10Base2 networks allow a maximum of five segments with only three of those segments populated. Each of the three populated segments can have a maximum of 30 nodes attached. 10Base2 requires that there is a minimum of .5 meters between nodes. For the network to function properly, the segment must be complete. With this in mind, the addition or removal of systems on a 10Base2 network might make the entire network unusable.

10BaseT

The 10BaseT LAN standard specifies an ethernet network that commonly uses unshielded twisted-pair cable; however, in some implementations that require a greater resistance to interference and attenuation, shielded twisted pair (STP) can be used. STP has extra shielding to combat interference.

10BaseT uses baseband transmission and has a maximum physical segment length of 100 meters. As with the coaxial cabling standards, repeaters are sometimes used to extend the maximum segment length, although the repeating capability is now often built in to networking devices used in twisted-pair networks. 10BaseT specifies transmission speeds of 10Mbps and can use several categories of UTP cable, including Categories 3, 4, and 5 (all of which use RJ-45 connectors). 10BaseT takes advantage of the multiple wires inside twisted-pair cable to create independent transmit and receive paths, which means that a full-duplex mode can be optionally supported. The maximum number of computers supported on a 10BaseT network is 1,024.

All 10BaseT networks use a point-to-point network design, with one end of the connection attaching to the network card and the other to a hub or switch. These point-to-point connections result in a physical star topology. See Chapter 3, “Networking Components and Devices,” for information on the devices used in twisted-pair networks.

Table 6.2 summarizes the characteristics of the 10BaseT standard.

Table 6.2. Summary of 10BaseT Characteristics

Characteristic	Description
Transmission method	Baseband
Speed	10Mbps
Total distance/segment	100 meters
Cable type	Category 3, 4, or 5 UTP or STP
Connector	RJ-45

Make or Buy? During your networking career, you will most certainly encounter the debate about whether to crimp your own twisted-pair network cables or buy them. The arguments for making cables always seem to hinge on cost savings. The arguments against crimping cables are often much more solid. Purchasing cables from a reputable maker ensures that the cables you install will work every time. The same cannot be said of homemade cables. In addition, when you factor in the time it takes to make a cable or troubleshoot a poorly made one, the cost savings are lessened. However, in some instances you’ll have no choice but to make cables—for example, when specific cable length cables are desired.

10BaseFL

10BaseFL is an implementation of 10Mbps ethernet over fiber-optic cabling. 10BaseFL’s primary advantage over 10BaseT is that it can be used over distances up to 2 kilometers. However, given the availability of other faster networking standards, such as 100BaseFX (discussed later), you are unlikely to encounter many 10BaseFL implementations.

Fast Ethernet

There was a time when 10Mbps networks were considered fast enough, but those days are long gone. Today, companies and home users alike demand more data throughput than is available with 10Mbps network solutions. For such networks, Fast Ethernet is the most commonly used network design. Fast Ethernet standards are specified in the IEEE 802.3u standard. Three standards are defined by 802.3u: 100BaseTX, 100BaseT4, and 100BaseFX.

100BaseTX

100BaseTX is a Fast Ethernet networking design and is one of three 802.3u standards. As its name suggests, 100BaseTX transmits network data at speeds up to 100Mbps, the speeds at which most LANs operate today. 100BaseTX is most often implemented with UTP cable, but it can use STP; therefore, it suffers from the same 100-meter distance limitations as other UTP-based networks. 100BaseTX uses Category 5 UTP cable, and, like 10BaseT, it uses independent transmit and receive paths and can therefore support full-duplex operation. 100BaseTX is without question the most common Fast Ethernet standard.

100BaseT4

100BaseT4 is the second Fast Ethernet standard specified under 802.3u. It can use Category 3, 4, and 5 UTP cable, and it uses all four of the available pairs of wires within the cable, limiting full-duplex transfer. 100BaseT4 is similar in other respects to 100BaseTX: Its cable distance is limited to 100 meters, and its maximum transfer speed is 100Mbps. 100BaseT4 is not widely implemented, but it is sometimes used in environments where existing cable, such as Category 3 cable, exists. In such a situation, you can use 100BaseT4 instead of replacing the Category 3 cable with Category 5 UTP.

100BaseFX

100BaseFX is the IEEE standard for running Fast Ethernet over fiber-optic cable. Because of the expense of fiber implementations, 100BaseFX is largely limited to use as a network backbone. 100BaseFX can use two-strand multimode fiber or single-mode fiber media. The maximum segment length for half-duplex multimode fiber is 412 meters, but when used in full-duplex mode over multimode fiber, distances can reach 2 kilometers. Using full-duplex single-mode fiber, 100BaseFX can reach distances up to 10,000 meters. 100BaseFX often uses SC or ST fiber connectors.