Objective Domain 1: Media and Topologies continued
Objective 1.3 Specify the characteristics (e.g., speed, length, topology, cable type, etc.) of the following: 802.3 (Ethernet) standards, 10BASE-T, 100BASE-TX, 10BASE2, 10BASE5, 100BASE-FX, Gigabit Ethernet.The IEEE 802.3 protocol (commonly known as Ethernet) is the oldest of the data-link layer protocols still used. In its 25-year history, the protocol has evolved and now there are many different variations on it running at different speeds and using different types of media. These variations have two primary elements in common: the CSMA/CD MAC mechanism and the Ethernet frame format. The most common Ethernet variants are listed in the following table.
The various types of Ethernet are often referred to by their generic names, such as standard Ethernet, Fast Ethernet, and Gigabit Ethernet, but there are also abbreviations for the various physical layer specifications that Ethernet supports, which are more precise and commonly used. The format for these abbreviations consists of three parts, which specify network speed, the type of signaling, and either the maximum cable segment length or the type of cable used.
10Base5, the abbreviation used for Thick Ethernet, indicates that this type of network runs at 10 Mbps, uses baseband signaling, and supports a maximum cable segment length of 500 meters. Thick Ethernet networks use a type of coaxial cable called RG-8, which is relatively thick (0.405 inches), installed in a bus topology. The coaxial cable trunk can be up to 500 meters long. Each computer is connected to the trunk using a separate cable called an Attachment Unit Interface (AUI) cable, which can be up to 50 meters long.
10Base2, also known as Thin Ethernet, uses a different type of coaxial cable called RG-58, which is also installed in a bus topology. Because it's thinner (0.195 inches), RG-58 is more flexible and easier to install than RG-8. As a result, there is no need for AUI cables on this type of network, and the trunk cable runs right up to each computer's network interface adapter. Thin Ethernet also runs at 10 Mbps and uses baseband signaling (as do all of the Ethernet variants discussed here). The number 2 in the abbreviation 10Base2 suggests that the maximum allowable cable segment for a Thin Ethernet network is 200 meters. However, the specification actually limits the segment length to 185 meters.
10Base-T is the first Ethernet version to use UTP cable, which is installed in a star topology instead of a bus. 10Base-T runs at 10 Mbps, just like the coaxial standards, and uses baseband signaling. The letter T in 10Base-T signifies the twisted pair cable. A 10Base-T network can use any UTP cable that is Category 3 or higher, and each cable segment connecting a computer (or other device) to the hub can be up to 100 meters long. All three of the 10 Mbps Ethernet specifications listed here are defined in the IEEE 802.3 standard.
100Base-TX is the most popular of the Fast Ethernet physical layer specifications, all of which are defined in the IEEE 802.3u standard and are known collectively as 100Base-T. Running at 100 Mbps, a 100Base-TX network uses Category 5 UTP cable installed in a star topology with cable segments up to 100 meters long. Like 10Base-T, 100Base-TX uses only two of the four wire pairs in the UTP cable and provides greater speed because of the higher quality of Category 5 cable.
100Base-T4 is a Fast Ethernet specification intended to be an upgrade path for 10Base-T networks using Category 3 UTP cable. Like 100Base-TX, 100Base-T4 runs at 100 Mbps and is installed in a star topology with segments up to 100 meters long. To run at higher speeds on Category 3 cable, 100Base-T4 uses all four of the wire pairs in the cable. Two are dedicated transmit and receive pairs, as in 10Base-T and 100Base-TX. The other two pairs are bidirectional, carrying traffic in either direc- tion as needed.
100Base-FX is a Fast Ethernet specification that uses fiber optic cable instead of UTP. The network runs at the same speed as 100Base-TX and 100Base-T4100 Mbpsand uses the same star topology. But the 62.5/ 125-micron multimode fiber optic cable can have segments as long as 412 meters because of its resistance to attenuation. When running in full duplex mode, 100Base-FX cable segments can be up to 2 kilometers (2,000 meters) long.
Gigabit Ethernet is the latest form of Ethernet. It increases a network's transfer speed to 1,000 Mbps. Although most of the physical layer specifications for Gigabit Ethernet call for fiber optic cable, there is one standard, IEEE 802.3ab, that calls for Category 5 UTP cable installed in a star topology with a maximum segment length of 100 meters. This standard is referred to as 1000Base-T. To achieve this speed using standard Category 5 cable, 1000Base-T uses all four pairs of wires bidirectionally.
B, C, D, and E
You are designing a single LAN that consists of 25 computers scattered around a building. The two most distant computers are 200 meters away from each other. Which of the following Ethernet physical layer specifications can you be certain will operate successfully? (Choose four.)
A. A 10Base2 (Thin Ethernet) network has a maximum cable segment length of 185 meters, despite the implication of the number 2 in its abbreviation. A 200-meter-long segment connecting the most distant computers would be too long and may not function properly.
B. A 10Base5 (Thick Ethernet) network can have a cable segment up to 500 meters long, which is easily enough to connect the two most distant computers.
C. The 10Base-T specification calls for cable segments up to 100 meters long, but when you use the star topology on an Ethernet network, the hub functions as a multiport repeater. Because the hub repeats the signals passing through it, each cable connecting a computer to the hub can be the maximum length of 100 meters. This enables you to connect two computers that are 200 meters apart.
D. The 100Base-FX specification permits the fiber optic cables to be as long as 412 meters, more than sufficient to connect the two distant computers.
E. Although a 100Base-TX network runs at 10 times the speed of 10Base-T, the fact that the protocol specification calls for Category 5 UTP cable enables the segments to be 100 meters long. Because 100Base-TX uses a star topology like 10Base-T does, the repeating hub enables the maximum distance between two computers to be 200 meters.
B and D
Which of the following Ethernet physical layer specifications are designed to run on Category 3 UTP cable? (Choose two.)
A. 10Base2, otherwise known as Thin Ethernet, runs on coaxial cable only.
B. The 10Base-T physical layer standard was developed at a time when most of the UTP cable being installed conformed to the Category 3 specification. This means that you can run 10Base-T on almost any UTP cable network you find today.
C. The 100Base-TX standard uses the same star topology and cable segment lengths as 10Base-T, as well as the same two wire pairs inside the cable, but it transmits data 10 times faster. As a result, 100Base-TX will not function properly on a Category 3 UTP network.
D. The 100Base-T4 standard was specifically developed to be an upgrade path for existing 10Base-T networks running on Category 3 UTP cable. Like 100Base-TX, 100Base-T4 runs at 100 Mbps and supports 100 meter segments. What makes it possible for a Category 3 UTP network to run at 100 Mbps is that 100Base-T4 uses all four pairs of wires in the cable.
E. Gigabit Ethernet networks run at 1,000 Mbps. Although the 1000Base-T standard uses UTP cable with a maximum segment length of 100 meters, like 10Base-T and 100Base-TX, the faster protocol stretches the limits of the UTP cable's capabilities. Category 5 is the minimum for a 1000Base-T network; Category 3 will not function properly with this protocol.
What distinguishes the 100Base-FX physical layer specification from the other Fast Ethernet specifications?
A. 100Base-FX transmits data at higher speeds than the other Fast Ethernet specifications.
A. All of the Fast Ethernet physical layer specifications, including 100Base-FX, transmit data at 100 Mbps.
B. 100Base-FX uses a different topology from the other Fast Ethernet specifications.
B. All of the Fast Ethernet physical layer specifications, including 100Base-FX, use the star topology.
C. 100Base-FX has a greater maximum segment length than the other Fast Ethernet specifications.
C. The 100Base-FX specification calls for 62.5/125-multimode fiber optic cable, which supports segment lengths of up to 412 meters, more than five times that of the copper-based Fast Ethernet specifications.
D. 100Base-FX is defined in a different standard document than the other Fast Ethernet specifications.
D. All of the Fast Ethernet physical layer specifications, including 100Base-FX, are defined in the IEEE 802.3u document.
A new tenant is moving into office space that is already wired with Category 5 UTP cable in a star topology with no segments longer than 100 meters. Which of the following Ethernet physical layer specifications can the tenant use to build the fastest possible network without installing new cable?
A. It is possible to install a 10Base-T network using existing Category 5 UTP cable, but Fast Ethernet and Gigabit Ethernet specifications would run faster.
B. The 100Base-T4 specification is designed for use with Category 3 UTP cable, but it would run perfectly well on Category 5. However, 100Base-TX runs more efficiently on Category 5 and 100Base-T runs on Category 5 cable at 1,000 Mbps10 times the speed of 100Base-T4.
C. The 100Base-TX specification calls for Category 5 UTP cable, as does the 1000Base-T specification, which runs 10 times faster.
D. The 1000Base-T specification is designed to run at 1 Gbps on the same type of cable installation as 100Base-TX, Category 5 UTP, using a star topology, and 100 meter maximum segments.