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Chapter 6. Ethernet Networking Standards > 802.3 Ethernet Standards

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.

Exam Alert: The 802.3 standards

Pay special attention to the 802.3 standards. You can expect a question regarding the characteristics of the various standards on the Network+ exam.


Note: 10Base2 coverage

Even though it is not specifically stated in the CompTIA Network+ objectives, we have included coverage on 10Base2 because there is still a chance that you will encounter it in the real world. Also, you never know when CompTIA might choose to include 10Base2 as a wrong answer for a question related to one of the other networking standards discussed in this section. When taking an exam, knowing what something isn’t can be as useful as knowing what it is!


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.

Note: What is base?

When discussing network standards, the word base, as in 10Base2, defines that the media can carry only one data signal per wire, or channel, at one time.


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.

Tip: Cable break

The coax cable used in 10Base2 networks is prone to cable breaks. A break anywhere in the cable makes the entire network inaccessible.


Note: Coaxial and the 5-4-3 rule

When working with ethernet networks that use coaxial media, the 5-4-3 rule applies. The rule specifies that the network is limited to a total of five cable segments. These five segments can be connected using no more than four repeaters, and only three segments on the network can be populated.


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.

Note: Cable types

For more information on the STP and other forms of cabling, refer to Chapter 2, “Media and Connectors.”


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.

Note: Crossover cable

You can link two 10BaseT computer systems directly, without the use of a hub, by using a specially constructed crossover cable. Crossover cables are also sometimes used to establish other same device connections, such as when connecting two hubs or two switches to create a larger network.


Table 6.2 summarizes the characteristics of the 10BaseT standard.

Table 6.2. Summary of 10BaseT Characteristics
CharacteristicDescription
Transmission methodBaseband
Speed10Mbps
Total distance/segment100 meters
Cable typeCategory 3, 4, or 5 UTP or STP
ConnectorRJ-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.

Note: Fast Ethernet lingo

Fast Ethernet is often referred to as 100BaseX, which also refers collectively to the 100BaseTX, 100BaseT4, and 100BaseFX standards.


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.

Note: Limited implementation

100BaseT4 is not a common implementation of Fast Ethernet. As a result, it is not included in the CompTIA objectives for the Network+ exam.


Note: Repeaters

Fast Ethernet repeaters are sometimes needed when you connect segments that use 100BaseTX, 100BaseT4, or 100BaseFX.


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.

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