Content Overview Even though each local-area network is unique, there are many design aspects that are common to all LANs. For example, most LANs follow the same standards and the same components. This module presents information on elements of Ethernet LANs and common LAN devices. There are several wide-area network (WAN) connections available today. They range from dial-up to broadband access, and differ in bandwidth, cost, and required equipment. This module presents information on the various types of WAN connections. Students completing this module should be able to:
Content 5.1 Cabling the LAN 5.1.1 LAN physical layer Various symbols are used to represent media types. Token Ring is represented by a circle. Fiber Distributed Data Interface (FDDI) is represented by two concentric circles and the Ethernet symbol is represented by a straight line. Serial connections are represented by a lightning bolt. Each computer network can be built with many different media types. The function of media is to carry a flow of information through a LAN. Wireless LANs use the atmosphere, or space, as the medium. Other networking media confine network signals to a wire, cable, or fiber. Networking media are considered Layer 1, or physical layer, components of LANs. Each media has advantages and disadvantages. Some of the advantage or disadvantage comparisons concern: Coaxial cable, optical fiber, and even free space can carry network signals. However, the principal medium that will be studied is Category 5 unshielded twisted-pair cable (Cat 5 UTP) which includes the Cat 5e family of cables. Many topologies support LANs, as well as many different physical media. Figure shows a subset of physical layer implementations that can be deployed to support Ethernet. Web Links Physical Layer http://www.erg.abdn.ac.uk/users/gorry/course/ phy-pages/ phy.html
Content 5.1 Cabling the LAN 5.1.2 Ethernet in the campus Ethernet is the most widely used LAN technology. Ethernet was first implemented by the Digital, Intel, and Xerox group, referred to as DIX. DIX created and implemented the first Ethernet LAN specification, which was used as the basis for the Institute of Electrical and Electronics Engineers (IEEE) 802.3 specification, released in 1980. Later, the IEEE extended 802.3 to three new committees known as 802.3u (Fast Ethernet), 802.3z (Gigabit Ethernet over Fiber), and 802.3ab (Gigabit Ethernet over UTP). Network requirements might dictate that an upgrade to one of the faster Ethernet topologies be used. Most Ethernet networks support speeds of 10 Mbps and 100 Mbps. The new generation of multimedia, imaging, and database products, can easily overwhelm a network running at traditional Ethernet speeds of 10 and 100 Mbps. Network administrators may consider providing Gigabit Ethernet from the backbone to the end user. Costs for installing new cabling and adapters can make this prohibitive. Gigabit Ethernet to the desktop is not a standard installation at this time. In general, Ethernet technologies can be used in a campus network in several different ways:
Content 5.1 Cabling the LAN 5.1.3 Ethernet media and connector requirements Before selecting an Ethernet implementation, consider the media and connector requirements for each implementation. Also, consider the level of performance needed by the network.The cables and connector specifications used to support Ethernet implementations are derived from the Electronic Industries Association and the Telecommunications Industry Association (EIA/TIA) standards body. The categories of cabling defined for Ethernet are derived from the EIA/TIA-568 (SP-2840) Commercial Building Telecommunications Wiring Standards. Figure compares the cable and connector specifications for the most popular Ethernet implementations. It is important to note the difference in the media used for 10-Mbps Ethernet versus 100-Mbps Ethernet. Networks with a combination of 10- and 100-Mbps traffic use UTP Category 5 to support Fast Ethernet. Web Links Ethernet Hardware http://www.kan.org/networking/ nethardware.html
Content 5.1 Cabling the LAN 5.1.4 Connection media Figure illustrates the different connection types used by each physical layer implementation. The registered jack (RJ-45) connector and jack are the most common. RJ-45 connectors are discussed in more detail in the next section. In some cases the type of connector on a network interface card (NIC) does not match the media that it needs to connect to. As shown in Figure , an interface may exist for the 15-pin attachment unit interface (AUI) connector. The AUI connector allows different media to connect when used with the appropriate transceiver. A transceiver is an adapter that converts one type of connection to another. Typically, a transceiver converts an AUI to RJ-45, coax, or fiber optic connector. On 10BASE5 Ethernet, or Thicknet, a short cable is used to connect the AUI with a transceiver on the main cable.
Content 5.1 Cabling the LAN 5.1.5 UTP implementation EIA/TIA specifies an RJ-45 connector for UTP cable. The letters RJ stand for registered jack, and the number 45 refers to a specific wiring sequence. The RJ-45 transparent end connector shows eight colored wires. Four of the wires carry the voltage and are considered “tip” (T1 through T4). The other four wires are grounded and are called “ring” (R1 through R4). Tip and ring are terms that originated in the early days of the telephone. Today, these terms refer to the positive and the negative wire in a pair. The wires in the first pair in a cable or a connector are designated as T1 and R1. The second pair is T2 and R2, and so on. The RJ-45 connector is the male component, crimped on the end of the cable. When looking at the male connector from the front, the pin locations are numbered 8 on the left down to 1 on the right as seen in Figure . The jack is the female component in a network device, wall outlet, or patch panel as seen in Figure . Figure shows the punch-down connections at the back of the jack where the Ethernet UTP cable connects. For electricity to run between the connector and the jack, the order of the wires must follow EIA/TIA-T568-A or T568-B standards, as shown in Figure . Identify the correct EIA/TIA category of cable to use for a connecting device by determining what standard is being used by the jack on the network device. In addition to identifying the correct EIA/TIA category of cable, determine whether to use a straight-through cable or a crossover cable. If the two RJ-45 connectors of a