Media Connectors

• Recognize the following media connectors and describe their uses:

  • RJ-11

  • RJ-45

  • AUI

  • BNC

  • ST

  • SC

All forms of network media need to be physically attached to the networked devices in some way. Media connectors provide the interface between the cables and the devices to which they attach (similar to the way an electrical cord connects a television and an electrical outlet). This section explores the common connectors and adapters you are likely to encounter in your work and, perhaps more importantly, on the Network+ exam.

D-shell Connectors

D-shell connectors, which physically resemble a capital letter D, are perhaps the most common of all connector types. D-shell connectors use pins and sockets to connect devices; the number of pins used in a D-shell connector is reflected in the name of the specific connector. For example, a DB-15 uses 15 pins. D-shell connectors are used in everything from parallel ports to serial ports, joysticks, and video adapters.

Attachment Unit Interface Connectors

Attachment unit interface (AUI) ports are network interface ports that are often associated with thick coax (that is, 10Base5) networks. The AUI port is a 15-pin socket to which a transceiver is connected.

AUI ports also commonly appear on hubs and routers, and they are used for a variety of reasons. You are not likely to see AUI ports today, as 10Base5 networks are rarely used. You can expect to see AUI when you work with hubs. Figure 2.4 shows the AUI ports on the back of a network router; Figure 2.5 shows an AUI port and a BNC connector on the front of a network hub.

External SCSI Connectors

Some external SCSI connectors use D-shell connectors. The original SCSI standard, SCSI-1, used a 50-pin D-shell connector. That connector is no longer used, and you are unlikely to see 50-pin D-shell connectors in real-world environments. The newer external SCSI connectors use an improved version of D-shell connectors known as high-density external D-shell connectors. The spacing between the pins has been reduced in these connectors, making the cable less expensive and easier to use. High-density external SCSI cables come in 50-pin and 68-pin varieties and are in common use today.

Another external SCSI connector you might encounter is the very high-density cable interconnect (VHDCI) connector. VHDCI connectors are available in a 68-pin variety only. Figure 2.6 shows an external VHCDI SCSI connector.

Serial (RS-232) Connectors

Serial ports are familiar to those who have spent time around computers and have connected peripheral devices. Serial connectors, most commonly DB-9 or DB-25 pin varieties, are used for connecting devices such as mouse pointers, modems, handhelds, and scanners. In the network world, serial connectors are sometimes used to connect two computers together, although the transmission speed between those two computers is very slow compared to the speed you would get by using normal networking methods.

In addition, some managed network devices, such as hubs, switches, and routers, have serial ports that can be used to connect to the devices and manage them.

Parallel Connectors

Parallel ports are most often associated with printing and use a standard DB-25 connector. Sometimes, as with the serial port, the parallel port can be used to network two computer systems together. The short transfer distance of the parallel cable and the slow data transmission speeds make this a very impractical solution. But in some fairly unique environments you might encounter this configuration.

RJ Connectors

The connector you are most likely to encounter on modern networks is the RJ-45 (registered jack) connector. RJ-45 connectors bear a passing resemblance to the familiar RJ-11 connectors used with common phone connections. The difference between the two connectors is that the standard phone connector uses four wires, whereas the RJ-45 network connector uses eight. RJ-45 connectors are associated with twisted-pair cable. Figure 2.7 shows RJ-45 connectors.

BNCs

BNCs are commonly associated with Ethernet networks—more specifically, with Thinnet (that is, 10Base2) networks. BNCs are rarely used anymore; RJ-45 connectors are more prevalent because twisted-pair cable has almost completely replaced coaxial cable. However, if you find yourself working on an existing network or with legacy network cards, you might encounter BNCs. Many older 10Mbps network cards accommodate both BNCs and RJ-45 connectors, and some really old network cards even have BNC, RJ-45, and AUI connectors. These cards—or any other cards with more than one type of connector—are often referred to as combo cards. Figure 2.8 shows a network card with (from left to right) a BNC connector, an AUI connector, and an RJ-45 connector.

Fiber Connectors

Several types of connectors are associated with fiber-optic cable. Which one is used is determined by the fiber implementation. Figure 2.9 shows some of the different fiber connectors you might encounter when working with fiber networks.

Centronic Connectors

Unlike other connector types that often use rows of pins, a Centronic connector uses two rows of flat contacts. The most common place to see Centronic connectors is with standard printers, where the data cable plugs into the printer.

External SCSI Centronic connectors use the same design as connectors used with printers, but they use a wider row of contacts, typically 50 pins. Centronic connectors have latches on either side of the cable to help hold it in place. Figure 2.10 shows an external SCSI Centronic connector.