IEEE 802.3 Standards
| The IEEE 802.3 standards define a range of networking systems that are based on the original Ethernet standard. The variations include speed, physical topology, and implementation considerations. The following sections describe these standards. 10 Mbps Networking StandardsThere is no specific designation called 'standard Ethernet,' but if there were, it would be assigned to the 10Mbps variants of the IEEE 802.3 standards. Although 10Mbps is now considered too slow for most new networks, there are a large number of existing networks operating at 10Mbps. A number of 10Mbps standards exist, with 10BaseT now being the most common. In the following sections, we discuss a number of the 10Mbps standards.
10Base210Base2, 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 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 might make the network unusable.
10BaseTThe 10BaseT standard is another 10Mbps standard using UTP cabling. 10BaseT networks have a maximum segment length of 100 meters, and up to a total of five physical segments per network. 10BaseT networks use a star topology with a point-to-point connection between the computer and the hub or switch. 10BaseT can use different categories of UTP cabling, including 3, 4, 5. It can also be used with category 5e and category 6 cabling, but that is a little like renting the Daytona speedway for the day and then cycling around it.
10BaseFL10BaseFL is an implementation of 10Mbps Ethernet over fiber-optic cabling. Its primary benefit, over 10BaseT, is that it can be used in distances up to 2km. However, given the availability of other faster networking standards, such as 100BaseFX (discussed next), you are unlikely to encounter a large number of 10BaseFL implementations. Table 2.3 summarizes the characteristics of the 10Mbps networking standards discussed in this section.
Fast EthernetMany of the applications used on modern networks demand more bandwidth than what's provided by the 10Mbps network standards. To address this need for faster networks, the IEEE has developed the IEEE 802.3u specifications, of which there are three variations:
Of the three, 100BaseT4 is not listed in the latest version of the CompTIA Network+ objectives. However, we have chosen to include information on it in this section to provide rounded coverage of this topic. 100BaseTX100BaseTX is the most widely implemented of the Fast Ethernet standards. 100BaseTX uses two pairs of wire in Category 5 UTP cabling and can also use STP cable when a more resistant cable is required. 100BaseTX uses 100Mbps transmission and a total segment length of 100 meters. 100BaseT4The advantage to 100BaseT4 is its capability to use older categories of UTP cable to perform 100Mbps transfer. In environments already wired with Category 3 or 4 cable, 100BaseT4 can be used instead of replacing the existing cable. 100BaseT4 uses all four pairs of wire of Category 3, 4, and 5 twisted pair and, as such, is prevented from using full-duplex transmissions. The other characteristics of standard 100BaseTX are in effect with 100BaseT4. 100BaseFXThe IEEE 100BaseFX standard specifies 100Mbps transmissions speeds over fiber-optic cable. 100BaseFX can use both multimode and single mode fiber. It has a maximum segment length of 412 meters when used over multimode fiber and 10,000 meters when used over single-mode fiber. Table 2.4 summarizes the characteristics of Fast Ethernet.
Gigabit EthernetGigabit Ethernet networking, which is becoming increasingly common as a backbone connection method and for a server to switch connectivity, is achieved using either copper-based media or fiber optic cabling. The two IEEE standards that specify Gigabit transfer are 802.3z and 802.3ab. 802.3zThree distinct standards are specified under the 802.3z standard; they are referred to collectively as 1000BaseX. The three standards are 1000BaseLX, 1000BaseSX, and 1000BaseCX. 1000BaseLX and 1000BaseSX use long wavelength laser and short wavelength laser, respectively. Both 1000BaseSX and 1000BaseLX can be supported over two types of multimode fiber62.5 and 50 micron-diameter fibers. Only long wave lasers support the use of single-mode fiber. The 1000BaseCX standard specifies Gigabit Ethernet over STP cabling. Segment length of 1000BaseCX is extremely limited, reaching a maximum of 25 meters. 1000BaseCX is not widely implemented. 802.3abThe 802.3ab standard specifies Gigabit Ethernet transfer over Category 5 UTP cable. To achieve the 1000Mbps speeds, each of the four pairs of wires in a twisted-pair cable can transmit 250Mbps. Table 2.5 summarizes the characteristics of the Gigabit standards.
10 Gigabit EthernetAs the name suggests, 10 Gigabit Ethernet, which is referred to as 10GbE, has the capability to provide data transmission rates of up to 10 Gigabits per second. 10 Gigabit Ethernet is defined in the IEEE 802.3ae standard. There are a number of 10GbE implementations, though CompTIA chooses to focus on 10GBaseSR, 10GBaseLR, and 10GBaseER in the objectives for the Network+ exam. Of these standards, 10BaseSR is designed for LAN or MAN implementations, with a maximum distance of 300 meters using 50 micron multimode fiber-optic cabling. 10BaseSR can also be implemented with 62.5 micron multimode fiber, but is limited to 33 meters in this configuration. 10GBaseLR and 10GBaseER are designed for use in MAN and WAN implementations, and are implemented using single mode fiber-optic cabling. 10GBaseLR has a maximum distance of 10km, whereas 10GBaseER has a maximum distance of 40km. Table 2.6 summarizes the characteristics of 10 Gigabit Ethernet standards relevant to the Network+ exam.
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