Transceivers
(Media Converters)
The term transceiver does describe a separate network device, but it can also be technology built and embedded in devices such as network cards and modems. In a network environment, a transceiver gets its name from being both a transmitter and a receiver of signals—thus the name transceivers. Technically, on a LAN, the transceiver is responsible for placing signals onto the network media and also detecting incoming signals traveling through the same wire. Given the description of the function of a transceiver, it makes sense that that technology would be found with network cards.
Although transceivers are found in network cards, they can be external devices as well. As far as networking is concerned, transceivers can ship as a module or chip type. Chip transceivers are small and are inserted into a system board or wired directly on a circuit board. Module transceivers are external to the network and are installed and function similarly to other computer peripherals, or they can function as standalone devices.
There are many types of transceivers—RF transceivers, fiber optic transceivers, Ethernet transceivers, wireless (WAP) transceivers, and more. Though each of these media types is different, the function of the transceiver remains the same. Each type of the transceiver used has different characteristics, such as the number of ports available to connect to the network and whether full-duplex communication is supported.
Listed
with transceivers in the CompTIA objectives are media converters. Media
converters are a technology that allows administrators to interconnect different
media types—for example, twisted pair, fiber, and Thin or thick coax—within an
existing network. Using a media converter, it is possible to connect newer
100Mbps, Gigabit Ethernet, or ATM equipment to existing networks such as
10BASE-T or 100BASE-T. They can also be used in pairs to insert a fiber segment
into copper networks to increase cabling distances and enhance immunity to
electromagnetic interference (EMI).
Network Cards
Network cards, also called Network Interface Cards, are devices that enable computers to connect to the network.
When specifying or installing a NIC, you must consider the following issues:
- System bus compatibility—If the network interface you are installing is an internal device, bus compatibility must be verified. The most common bus system in use is the Peripheral Component Interconnect (PCI) bus, but some older systems might still use Industry Standard Architecture (ISA) expansion cards.
- System resources—Network cards, like other devices, need IRQ and memory I/O addresses. If the network card does not operate correctly after installation, there might be a device conflict.
- Media compatibility—Today, the assumption is that networks use twisted-pair cabling, so if you need a card for coaxial or fiber-optic connections, you must specify this. Wireless network cards are also available.
Even more than the assumption you are using twisted-pair cabling is that the networking system being used is Ethernet. If you require a card for another networking system such as Token Ring, this must be specified when you order.
To install or configure a network interface, you will need drivers of the device, and might need to configure it, although many devices are now plug and play. Most network cards are now software configured. Many of these software configuration utilities also include testing capabilities. The drivers and software configuration utilities supplied with the cards are often not the latest available, so it is best practice to log on to the Internet and download the latest drivers and associated software.
Wireless
Access Points
Wireless access points (APs) are a transmitter and receiver (transceiver) device used to create a wireless LAN (WLAN). APs are typically a separate network device with a built-in antenna, transmitter, and adapter. APs use the wireless infrastructure network mode to provide a connection point between WLANs and a wired Ethernet LAN. APs also typically have several ports allowing a way to expand the network to support additional clients.
Depending on the size of the network, one or more APs might be required. Additional APs are used to allow access to more wireless clients and to expand the range of the wireless network. Each AP is limited by a transmissions range—the distance a client can be from a AP and still get a useable signal. The actual distance depends on the wireless standard being used and the obstructions and environmental conditions between the client and the AP. Saying that an AP is used to extend a wired LAN to wireless clients doesn’t give you the complete picture. A wireless AP today can provide different services in addition to just an access point. Today, the APs might provide many ports that can be used to easily increase the size of the network. Systems can be added and removed from the network with no affect on other systems on the network. Also, many APs provide firewall capabilities and DHCP service. When they are hooked up, they will provide client systems with a private IP address and then prevent Internet traffic from accessing client systems. So in effect, the AP is a switch, a DHCP Server, router, and a firewall.
APs
come in all different shapes and sizes. Many are cheaper and designed strictly
for home or small office use. Such APs have low powered antennas and limited
expansion ports. Higher end APs used for commercial purposes have very high
powered antennas enabling them to extend the range that the wireless signal can
travel.
Modems
A modem, short for
modulator/demodulator, is a device that converts the digital signals generated
by a computer into analog signals that can travel over conventional phone
lines. The modem at the receiving end converts the signal back into a format
the computer can understand. Modems can be used as a means to connect to an ISP or as a mechanism
for dialing up to a LAN.
Modems can be internal
add-in expansion cards, external devices that connect to the serial or USB port
of a system, PCMCIA cards designed for use in laptops, or proprietary devices
designed for use on other devices such as portables and handhelds.
The configuration of a
modem depends on whether it is an internal or external device. For internal
devices, the modem must be configured with an interrupt request (IRQ) and a
memory I/O address. It is common practice, when installing an internal modem,
to disable the built-in serial interfaces and assign the modem the resources of
one of those (typically COM2). Table 3.2 shows the resources associated with
serial (COM) port assignments.
For external modems,
you need not concern yourself directly with these port assignments, as the
modem connects to the serial port and uses the resources assigned to it. This
is a much more straightforward approach and one favored by those who work with
modems on a regular basis. For PCMCIA and USB modems, the plug-and-play nature
of these devices makes them simple to configure, and no manual resource
assignment is required. Once the modem is installed and recognized by the
system, drivers must be configured to enable use of the device.
Two factors directly
affect the speed of the modem connection—the speed of the modem itself and the
speed of the Universal Asynchronous Receiver/Transmitter (UART) chip in the
computer that is connected to the modem. The UART chip controls the serial
communication of a computer, and although modern systems have UART chips that
can accommodate far greater speeds than the modem is capable of, older systems
should be checked to make sure that the UART chip is of sufficient speed to
support the modem speed. The UART chip installed in the system can normally be
determined by looking at the documentation that comes with the system. Table
3.3 shows the maximum speed of the commonly used UART chip types.
