Understanding Networking Devices – A Brief Introduction | TechLinu.com

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Understanding Networking Devices – A Brief Introduction
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All but the most basic of networks require devices to provide connectivity and functionality.
Understanding how these networking devices operate and identifying the tasks they perform are
important skills for any network administrator and requirements for a Network+ candidate.
This brief guide introduces usually used networking devices that you may encounter in your career
as Network Administrator. This guide is also useful for BCS students and for passionate network
learners.
Network HUBS
At the bottom of the networking food chain, so to speak, are hubs. Hubs are used in networks that
use twisted-pair cabling to connect devices. Hubs can also be joined together to create larger
networks. Hubs are simple devices that direct data packets to all devices connected to the hub,
regardless of whether the data package is destined for the device. This makes them inefficient
devices and can create a performance bottleneck on busy networks.
In its most basic form, a hub does nothing except provide a pathway for the electrical signals to
travel along. Such a device is called a passive hub. Far more common nowadays is an active hub,
which, as well as providing a path for the data signals, regenerates the signal before it forwards it to
all of the connected devices. A hub does not perform any processing on the data that it forwards,
nor does it perform any fault checking.
Hubs come in a variety of forms and sizes. Small hubs with five or eight connection ports are usually
referred to as workgroup hubs. Others can accommodate larger numbers of devices (normally up to
32). These are referred to as high-density devices. Because hubs don’t perform any processing, they
do little except enable communication between connected devices. For today’s high-demand
network applications, something with a little more intelligence is required. That’s where switches

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come in.
Network Switches
Like hubs, switches are the connectivity points of an Ethernet network. Devices connect to switches
via twisted-pair cabling, one cable for each device. The difference between hubs and switches is in
how the devices deal with the data that they obtain. Whereas a hub forwards the data it receives to
all of the ports on the device, a switch forwards it only to the port that connects to the destination
device. It does this by learning the MAC address of the devices attached to it, and then by matching
the destination MAC address in the data it receives. The figure below shows how a switch works.
By forwarding data only to the connection that should receive it, the switch can improve network
performance in two ways. First, by creating a direct path between two devices and controlling their
communication, it can really reduce the number of collisions on the network. As you might know,
collisions occur on Ethernet networks when two devices attempt to transmit at exactly the same
time. In addition, the lack of collisions enables switches to communicate with devices in full-duplex
mode. In a full-duplex configuration, devices can send and receive data from the switch at the same
time. Contrast this with half-duplex communication, in which communication can occur in only one
direction at a time. Full-duplex transmissions speeds are double that of a standard, half-duplex,
connection. So, a 10Mbps connection becomes 20Mbps, and a 100Mbps connection becomes
200Mbps.
The net result of these measures is that switches can offer significant performance improvements

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over hub-based networks, particularly when network use is high.
Irrespective of whether a connection is at full or half duplex, the technique of switching dictates how
the switch deals with the data it receives. The following is a brief clarification of each method:
1. Cut-through — In a cut-through switching environment, the packet begins to be forwarded
as soon as it is received. This method is very rapid, but creates the possibility of errors being
propagated through the network, as there is no error checking.
2. Store-and-forward — Unlike cut-through, in a store-and-forward switching environment,
the entire packet is received and error checked before being forwarded. The upside of this
method is that errors are not propagated through the network. The downside is that the
error checking process takes a relatively long time, and store-and-forward switching is
considerably slower as a result.
3. FragmentFree — To take advantage of the error checking of store-and-forward switching,
but still offer performance levels nearing that of cut-through switching, FragmentFree
switching can be used. In a FragmentFree-switching environment, enough of the packet is
read so that the switch can define whether the packet has been involved in a collision. As
soon as the collision status has been defined, the packet is forwarded.
Network Bridges
Bridges are used to divide larger networks into smaller sections. They do this by sitting between two
physical network segments and managing the flow of data between the two. By looking at the MAC
address of the devices connected to each segment, bridges can elect to forward the data (if they
believe that the destination address is on another interface), or block it from crossing (if they can
verify that it is on the interface from which it came).

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The Figure below shows how a bridge functions.
Note: Bridges can also be used to connect two physical LANs into a larger logical LAN.
When bridges were introduced, the MAC addresses of the devices on the connected networks had
to be entered manually, a time-consuming process that had plenty of opportunity for error. Today,
almost all bridges can build a list of the MAC addresses on an interface by watching the traffic on the
network. Such devices are called learning bridges because of this functionality.
Kinds of Bridges
Three types of bridges are used in networks:
1. Transparent bridge — Derives its name from the fact that the devices on the network are
unaware of its existence. A transparent bridge does nothing except block or forward data
based on the MAC address.
2. Source route bridge — Used in Token Ring networks. The source route bridge derives its
name from the fact that the entire path that the packet is to take through the network is
embedded within the packet.
3. Translational bridge — Used to convert one networking data format to another; for
example, from Token Ring to Ethernet and vice versa.
Today, bridges are slowly but surely falling out of favor. Ethernet switches offer similar functionality;
they can provide logical divisions, or segments, in the network. In fact, switches are sometimes
referred to as multiport bridges because of the way they operate.

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Repeater
A repeater is an electronic device that amplifies the signal it receives. In other terms, you can think
of repeater as a device which receives a signal and retransmits it at a higher level or higher power so
that the signal can cover longer distances.
For example, inside a college campus, the hostels might be far away from the main college where
the ISP line comes in. If the college authority wants to pull a wire in between the hostels and main
campus, they will have to use repeaters if the distance is much because different types of cables
have limitations in terms of the distances they can carry the data for.
When these network devices take a particular configurational shape on a network, their
configuration gets a particular name and the whole formation is called Network topology. In certain
circumstances when we add some more network devices to a network topology, it’s called Daisy
chaining.
Network Routers

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In a common configuration, routers are used to create larger networks by joining two network
segments. Such as a SOHO router used to connect a user to the Internet. A router can be a dedicated
hardware device or a computer system with more than one network interface and the right routing
software. All modern network operating systems include the functionality to act as a router.
Routers will normally create, add, or divide on the Network Layer as they are normally IP-based
devices.
A router derives its name from the fact that it can route data it receives from one network onto
another. When a router receives a packet of data, it reads the header of the packet to define the
destination address. Once it has defined the address, it looks in its routing table to determine
whether it knows how to reach the destination and, if it does, it forwards the packet to the next hop
on the route. The next hop might be the final destination, or it might be another router. The Figure
below shows, in basic terms, how a router works.
As you can see from this example, routing tables play a very important role in the routing process.
They are the means by which the router makes its decisions. For this reason, a routing table needs to
be two things. It must be up-to-date, and it must be complete. There are two ways that the router
can get the information for the routing table—through static routing or dynamic routing.
Network Gateways

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Any device that translates one data format to another is called a gateway. Some examples of
gateways include a router that translates data from one network protocol to another, a bridge that
converts between two networking systems, and a software application that converts between two
different formats. The key point about a gateway is that only the data format is translated, not the
data itself. In many cases, the gateway functionality is incorporated into another device.
CSU/DSU
A Channel Service Unit/Digital Service Unit (CSU/DSU), sometimes called Data Service Unit, is a
device that converts the digital signal format used on LANs into one used on WANs. Such translation
is necessary because the networking technologies used on WANs are different from those used on
LANs.
The CSU/DSU sits between the LAN and the access point provided by the telecommunications
company. Many router manufacturers are now incorporating CSU/DSU functionality into their
products.
Network Cards (NICs)

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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:
1. 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.
2. 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.
3. 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.
Note: When working on a Token Ring network, you have to ensure that all network cards are set to
transmit at the same speeds. NICs on an Ethernet network can operate at various speeds.
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.
ISDN Adapters
Integrated Services Digital Network (ISDN) is a remote access and WAN technology that can be used

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in place of a Plain Old Telephone Service (POTS) dial-up link if it is available. The availability of ISDN
depends on whether your local telecommunications service provider offers the service, the quality
of the line to your premises, and your proximity to the provider’s location. ISDN offers greater
speeds than a modem and can also pick up and drop the line considerably faster.
If ISDN is available and you do elect to use it, a special device called an ISDN terminal adapter is
needed to connect to the line. ISDN terminal adapters can be add-in expansion cards, external
devices that connect to the serial port of the system, or specialized interfaces built in to routers or
other networking equipment. The ISDN terminal adapter is necessary because, although it uses
digital signals, the signals are formatted differently from those used on a LAN. In addition, ISDN can
create multiple communication channels on a single line. Today, ISDN is not widely deployed and has
been replaced by faster and often cheaper technologies.
Wireless Access Points (APs)
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.
A WAP can operate as a bridge connecting a standard wired network to wireless devices or as a

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router passing data transmissions from one access point to another.
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 effect 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.
APs are used to create a wireless LAN and to extend a wired network. APs are used in the
infrastructure wireless topology.
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).

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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 are
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).

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Firewalls
A firewall is a networking device, either hardware or software based, that controls access to your
organization’s network. This controlled access is designed to protect data and resources from an
outside threat. To do this, firewalls are typically placed at entry/exit points of a network—for
example, placing a firewall between an internal network and the Internet. Once there, it can control
access in and out of that point.
Although firewalls typically protect internal networks from public networks, they are also used to
control access between specific network segments within a network—for example, placing a firewall
between the Accounts and the Sales departments.
As mentioned, firewalls can be implemented through software or through a dedicated hardware
device. Organizations implement software firewalls through network operating systems (NOS) such
as Linux/UNIX, Windows servers, and Mac OS servers. The firewall is configured on the server to
allow or permit certain types of network traffic. In small offices and for regular home use, a firewall
is commonly installed on the local system and configured to control traffic. Many third-party
firewalls are available.
Hardware firewalls are used in networks of all sizes today. Hardware firewalls are often dedicated
network devices that can be implemented with very little configuration and protect all systems
behind the firewall from outside sources. Hardware firewalls are readily available and often
combined with other devices today. For example, many broadband routers and wireless access
points have firewall functionality built in. In such case, the router or WAP might have a number of
ports available to plug systems in to.
Conclusion
Different networking devices have different roles to play in a computer network. These network
devices also work at different segments of a computer network performing different works.

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