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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

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.

Review Break

Fast Ethernet Comparison

Table 6.3 summarizes the characteristics of the 802.3u Fast Ethernet specifications.

Table 6.3. Summary of 802.3u Fast Ethernet Characteristics

Characteristic

100BaseTX

100BaseT4

100BaseFX

Transmission method

Baseband

Baseband

Baseband

Speed

100Mbps

100Mbps

100Mbps

Distance

100 meters

100 meters

412 meters (multimode, half duplex); 2 kilometers (multimode, full duplex); 10,000 meters (single mode, full duplex)

Cable type

Category UTP, STP

Category 3, 4, 5

Fiber optic 5 or greater

Connector type

RJ-45

RJ-45

SC, ST

Gigabit Ethernet

Fast Ethernet and the Fast Ethernet standards are still used today. However, in many modern network environments, real-time applications and heavier network use means something faster than Fast Ethernet and 100Mbps networking is required. This has led to the development of Gigabit Ethernet.

Gigabit Ethernet describes the ethernet implementations that provide the potential for 1000Mbps (1 Gbps) bandwidth. Gigabit Ethernet standards are available that define the use of both fiber- and copper-based media. The Gigabit standards include 1000BaseX and 1000BaseT.

1000BaseX

1000BaseX refers collectively to three distinct standards: 1000BaseLX, 1000BaseSX, and 1000BaseCX.

Both 1000BaseSX and 1000BaseLX are laser standards used over fiber. LX refers to long wavelength laser, and SX refers to short wavelength laser. Both the SX and LX wave lasers can be supported over two types of multimode fiber-optic cable: fibers of 62.5 micron and 50 micron diameters. Only LX wave lasers support the use of single-mode fiber. Information on the difference between the types of fiber-optic cable is given in Chapter 2.

At the end of the day, the differences between 1000BaseLX and the 1000BaseSX have to do with cost and transmission distance. 1000BaseLX can transmit over 316 meters in half duplex for both multimode fiber and single-mode fiber, 550 meters for full-duplex multimode fiber, and 5,000 meters for full-duplex single-mode fiber. Although 1000BaseSX is less expensive than 1000BaseLX, it cannot match the distances achieved by 1000BaseLX.

1000BaseCX moves away from the fiber cable and uses shielded copper wire. Segment lengths in 1000BaseCX are severely restricted; the maximum cable distance is 25 meters. Because of the restricted cable lengths, 1000BaseCX networks are not widely implemented. Table 6.4 summarizes the characteristics of Gigabit Ethernet 802.3z standards.

Table 6.4. Summary of IEEE 802.3z Gigabit Ethernet Characteristics

Characteristic

1000BaseSX

1000BaseLX

1000BaseCX

Transmission method

Baseband

Baseband

Baseband

Transfer rate

1000Mbps

1000Mbps

1000Mbps

Distance

Half-duplex 275 meters (62.5 micron multimode fiber); half-duplex 316 meters (50 micron multimode fiber); full-duplex 275 meters (62.5 micron multimode fiber); full-duplex 550 meters (50 micron multimode fiber)

Half-duplex 316 meters (multimode and single-mode fiber); full-duplex 550 meters (mulitmode fiber); full-duplex 5000 (single-mode fiber)

25 meters for both full-duplex and half-duplex operations

Cable type

62.5/125 and 50/125 multimode fiber

62.5/125 and 50/125 multimode fiber; two 10-micron single-mode optical fibers

Shielded copper cable

Connector type

Fiber connectors

Fiber connectors

9-pin shielded connector

1000BaseT

1000BaseT, sometimes referred to as 1000BaseTX, is another Gigabit Ethernet standard, and it is given the IEEE 802.3ab designation. The 802.3ab standard specifies Gigabit Ethernet over Category 5 UTP cable. The standard allows for full-duplex transmission using the four pairs of twisted cable. To reach data transfer rates of 1000Mbps over copper, a data transmission speed of 250Mbps is achieved using Cat 5e or Cat6 cabling. Table 6.5 summarizes the characteristics of 1000BaseT.

Table 6.5. Summary of 1000BaseT Characteristics

Characteristic

Description

Transmission method

Baseband

Maximum transfer rate

1000Mbps

Total distance/segment

100 meters

Cable type

Category 5 or better

Connector type

RJ-45

10 Gigabit Ethernet

In the never-ending quest for faster data transmission rates, network standards are always being pushed to the next level. In today's networking environments, that level is 10 Gigabit Ethernet, also referred to as 10GbE. As the name suggests, 10GbE has the capability to provide data transmission rates of up to 10 gigabits per second. That's 10,000Mbps, or 100 times faster than most modern LAN implementations. There are a number of 10GbE implementations; this section explores the 10GBaseSR/SW, 10GBaseLR/LW, 10GBaseER/EW, and 10GBaseT standards highlighted in the Network+ objectives.

Designed primarily as a WAN and MAN connectivity medium, 10GbE was ratified as the IEEE 802.3ae standard in June 2002. Many networking hardware manufacturers now market 10GbE equipment. Although 10GbE network implementations are very expensive, companies such as ISPs that require extremely high-speed networks have been relatively quick to implement 10GbE.

10GBaseSR/SW

The IEEE 802.3ae 10 Gigabit Ethernet specification includes a serial interface referred to as 10GBaseS that is designed for transmission on multimode fiber. Two ethernet standards that fall under the S category include 10GBaseSR and 10GBaseSW. Both SR and SW are designed for deployment over short wavelength multimode fiber. The distance for both classifications ranges from as little as 2 meters to 300 meters. The difference between the two classifications is that SR is designed for use over dark fiber. In the networking world, dark fiber refers to "unlit" fiber, or fiber that is not in use and connected to any other equipment. The 10GBaseSW standard is designed for longer distance data communications and connects to Sonet equipment. Sonet stands for Synchronous Optical Network. It is a fiber-optic transmission system for high-speed digital traffic. Sonet is discussed in Chapter 8, "Wide Area Networking."

10GBaseLR/LW

The 10GBaseLR/LW ethernet standards offer greater distances by using single-mode fiber rather than multimode fiber. Refer to Chapter 2 for a discussion of the differences between single-mode and multimode fiber.

Both the LR and LW standards are designed to be used over long-wavelength single-mode fiber, giving it a potential transmission range of anywhere from 2 meters to 10 kilometers. This transmission range makes the standards available for LAN, MAN, and WAN deployments. As with the previous standards, the LR standard is used with dark fiber where the LW standard is designed to connect to Sonet equipment.

10GBaseER/EW

For wide area networks that require greater transmission distances, the ethernet 10GBaseER/EW standards come into play. Both the ER and EW Gigabit standards are deployed with extra long wavelength single mode fiber. This medium provides transmission distances ranging from 2 meters to 40 kilometers. As with the previous two standards, ER is deployed over dark fiber, whereas the EW standard is used primarily with Sonet equipment. Table 6.6 outlines the characteristics of the 10GbE standards.

Table 6.6. Summary of 802.3ae Characteristics

Fiber

62.5 micron MMF

50 micron MMF

SMF

SR/SW

up to 33 meters

300 meters

Not used

LR/LW

Not used

Not used

10 kilometers

ER/EW

Not used

Not used

40 kilometers

10GBaseT

The final standard outlined in the Network+ objectives is the 802.3an ethernet standard. The 802.3an standard brings 10-gigabit speed to regular copper cabling. Although transmission distances may not be that of fiber, it allows a potential upgrade from 1000-gigabit networking to 10-gigabit networking using the current wiring infrastructure.

The 10GBaseT standard specifies 10-gigabit transmissions over UTP or STP twisted-pair cables. The standard calls for a cable specification of Category 6 or Category 6a be used. With Category 6, the maximum transmission range is 55 meters, with the augmented Category 6a cable, transmission range increases to 100 meters. Category 6 and 6a cables are specifically designed to reduce attenuation and cross talk, making 10-gigabit speeds possible. 802.3an specifies RJ-45 networking connectors. Table 6.7 outlines the characteristics of the 802.3an standard.

Table 6.7. Summary of 802.3an Characteristics

Characteristic

Description

Transmission method

Baseband

Speed

10-gigabit

Total distance/segment

100 meters Category 6a cable

Total distance/segment

55 meters Category 6 cable

Cable type

Category 6, 6a UTP or STP

Connector

RJ-45

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