< Day Day Up > |
There are four major types of network cables:
Network cards are designed to interface with one or more types of network cables. Serial (RS-232) null modem and parallel (LPT) crossover cables can be used with direct cable connection, which is a special type of two-station network included in Windows that uses standard network protocols but does not use network cards. UTP and STP CablingUnshielded twisted pair ( UTP ) cabling is the most common of the major cabling types. The name refers to its physical construction:four twisted pairs of wire surrounded by a flexible jacket. UTP cable comes in various grades, of which Category 5 is the most common of the standard cabling grades. Category 5 cabling is suitable for use with both standard 10BaseT and Fast Ethernet networking, and can also be used for Gigabit Ethernet networks if tested for compliance. Shielded twisted pair ( STP ) cabling (Category 4) is designed for use on IBM Token-Ring Networks. STP uses the same RJ-45 connector as UTP, but includes wire mesh for electrical insulation between the wire pairs and the outer jacket. It's stiffer and more durable, but also more expensive and harder to loop through tight spaces than UTP. Type 1 STP cable used by older token-ring adapters has a 9-pin connector. Table 21.4 lists the various types of UTP and STP cabling in use and what they're best suited for. Table 21.4. Categories and Uses for UTP and STP Cabling
Figure 21.8 compares Ethernet cards using UTP, thin coaxial, and thick coaxial cables and connectors to each other. Figure 21.8. Combo UTP/BNC/AUI Ethernet network cards (left and right) compared with a UTP-only Ethernet card (center) and cables.
The connector used by Ethernet cards that use UTP is called an RJ-45 connector, and it resembles a larger version of the RJ-11 connector used for telephone cabling. UTP cabling runs between a computer on the network and the hub, which routes signals to other computers (servers or workstations) on the network. It can be purchased in prebuilt form or as bulk cable with connectors, so you can build the cable to the length you need.
To attach UTP cable to a network card or other device, plug it into the connector so that the plastic locking clip snaps into place; the cable and connector will fit together only one way. Squeeze the locking clip toward the RJ45 connector and pull the connector out of the RJ45 jack if you need to remove the cable. Some cables use a snagless connector; squeeze the guard over the locking clip to open the clip to remove the cable. UTP cable can be purchased in prebuilt assemblies or can be built from bulk cable and connectors. Fiber OpticFiber-optic cabling transmits signals with light rather than with electrical signals, which makes it immune to electrical interference. It is used primarily as a backbone between networks. Fiber-optic cable comes in two major types:
Fiber-optic cabling can be purchased prebuilt, but if you need a custom length, it should be built and installed by experienced cable installers because of the expense and risk of damage. Some network adapters built for servers are designed to use fiber-optic cable. Otherwise, media converters are used to interconnect fiber optic to conventional cables on networks. CoaxialCoaxial cabling is the oldest type of network cabling; its data wires are surrounded by a wire mesh for insulation. Coaxial cables, which resemble cable TV connections, are not popular for network use today because they must be run from one station directly to another rather than to or from a hub/switch. Coaxial cabling creates a bus topology; each end of the bus must be terminated , and if any part of the bus fails, the entire network fails. The oldest Ethernet standard, 10Base5, uses a very thick coaxial cable (RG-8) that is attached to a NIC through a transceiver that uses a so-called "vampire tap" to connect the transceiver to the cable. This type of coaxial cable is also referred to as Thick Ethernet or Thicknet. Thin Ethernet, also referred to as Thinnet, Cheapernet, or 10Base2 Ethernet was used for low-cost Ethernet networks before the advent of UTP cable. The coaxial cable used with 10Base2 is referred to as RG-58. This type of coaxial cable connects to network cards through a T-connector that bayonet-mounts to the rear of the network card using a BNC connector. The arms of the T are used to connect two cables, each running to another computer in the network. If the workstation is at the end of a network, a terminating resistor is connected to one arm of the T to indicate the end of the network (refer to Figure 21.8). If a resistor is removed, the network fails; if a station on the network fails, the network fails. Two other types of coaxial cable are common in cable Internet, satellite Internet, and fixed wireless Internet installations:
Plenum and PVCThe outer jacket of UTP, STP, and coaxial cable is usually made of PVC (polyvinyl chloride), a low-cost durable vinyl compound. Unfortunately, PVC creates dense poisonous smoke when burned. If you need to run network cable through suspended ceiling or air vents, you should use more-expensive plenum cable, which produces less smoke and a lower level of toxic chemicals when burned. Connector TypesMost coaxial cables, including RG-58, RG-59, and RG-6 use a BNC (Bayonet Neill-Concelman) connector. RG-58 uses a T-adapter to connect to a 10Base2 Ethernet adapter. RG-11 (Thicknet) cable is connected to an Ethernet card by means of an external transceiver, which attaches to the AUI port on the rear of older Ethernet network cards. The transceiver attaches to the cable with a so-called "vampire tap." 10BaseT, 100BaseT, and 1000BaseT Ethernet cards using copper wire all use the RJ-45 connector shown in Figure 21.8, as do newer token-ring and all ISDN and cable Internet devices. DSL devices often use the RJ-11 connector shown in Figure 21.3, as do dial-up modems. Older token-ring cards use the 9-pin DB-9 Type 1 STP cable; the cable has a male connector and the card has a female connector. |
< Day Day Up > |