The document explains transmission media as pathways for data transfer within networks, categorizing them into bound (e.g., twisted pair, coaxial, fiber optic cables) and unbound (e.g., radio waves, microwaves, infrared). It further discusses LAN topologies—bus, ring, and star—detailing their advantages and disadvantages. Additionally, it covers networking devices such as hubs, switches, bridges, routers, and modems, as well as various types of websites including portals, news sites, and blogs.

1. Transmission Media
What is transmission media?
Transmission media is a pathway through which data are transmitted in network. We use different types
of cables or waves to transmit data.
What are the types of transmission media?
There are two types of transmission media namely: bound transmission media and unbound
transmission media.
Describe bound transmission media.
Bound transmission media are the cables that are tangible or have physical existence and are limited by
the physical geography. Popular bound transmission media in use are twisted pair cable, co-axial cable
and fiber optical cable.
Describe unbound transmission media.
Unbound transmission media are the ways of transmitting data without using any cables. These media
are not bounded by physical geography. Microwave, Radio wave, Infra red are some of popular unbound
transmission media.
LAN Topologies
The term topology defines the geographic arrangement of networking devices. It describes the actual
layout of the network hardware. Given the location of workstations and peripherals, the goal of
topology is to find the most economical and efficient way to connect all the users to the network
resources while providing adequate capacity to handle user demands, maintain system reliability and
minimize delay.
Different LAN Topologies
The selection of a topology for a network can not be done in isolation as it affects the choice of media
and the access method used. Because it determines the strategy used in wiring a building for a network
and deserves some careful study.
What are the basic LAN topologies?
The three simple LAN topologies that are combined to form any practical topology are known as basic
LAN topologies. They are, Bus Topology, Ring Topology and Star Topology.
Explain Bus Topology.
The physical Bus topology is the simplest and most widely used of the network designs. It consists of one
continuous length of cable (trunk) and a terminating resistor (terminator) at each end. Data

2. communication message travels along the bus in both directions until it is picked up by a workstation or
server NIC. If the message is missed or not recognized, it reaches the end of the cabling and dissipates at
the terminator.
All nodes on the bus topology have equal access to the trunk. This is accomplished using short drop
cables or direct T-connectors. The number of devices and the length of the trunk can be easily
expanded.
What are the advantages of bus topology?
The advantages of physical bus topology are:
a. It uses established standards and it is relatively easy to install.
b. It requires less media than other topologies.
What are the disadvantages of bus topology?
The disadvantages of bus topology are:
a. The bus networks are difficult to reconfigure, especially when the acceptable number of
connections or maximum distances have been reached.
b. They are also difficult to troubleshoot because everything happens on a single media segment.
This can have dangerous consequences because any break in the cabling brings the network to its knee.
What is Ring Topology?
The physical ring topology is a circular loop of point-to-point links. Each device connects directly to the
ring or indirectly through and interface device or drop cable. Message travel around the ring from node
to node in a very organized manner. Each workstation checks the message for a matching destination
address. If the address doesn't match the node simply regenerates the message and sends it on its way.
If the address matches, the node accepts the message and sends a reply to the originating sender.
Point out the major advantages of Ring Topology.
The advantages of ring topologies are:

3. a. They are very easy to troubleshoot because each device incorporates a repeater.
b. A special internal feature called beaconing allows troubled workstations to identify themselves
quickly.
Point out the disadvantages of Ring Topology.
The disadvantages of ring topologies are:
a. It is considerably difficult to install and reconfigure ring topology
b. Media failure on unidirectional or single loop causes complete network failure.
Explain Star Topology.
The physical star topology uses a central controlling hub with dedicated legs pointing in all directions –
like points of a star. Each network device has a dedicated point-to-point link to the central hub. This
strategy prevents troublesome collisions and keeps the lines of communications open and free of traffic.
This topology, obviously, require a great deal of cabling. This design provides an excellent platform for
reconfiguration and trouble- shooting. Changes to the network are as simple as plugging another
segment into the hub and a break in the LAN is easy to isolate and doesn't affect the rest of the
network.
What are the benefits of Star Topology?
The benefits of star topology are:
a. Relatively easy to configure.
b. Easy to troubleshoot
c. Media faults are automatically isolated to the failed segment.
What are the disadvantages of Star Topology?
The disadvantages are considered as follows:
a. Requires more cable than most topologies.
b. Moderately difficult to install.
Wireless transmission Media

4. Unguided Transmission media : wireless, radio transmission
Unguided media transport electromagnetic waves without using a physical conductor. This type
of communication is often referred to as wireless communication.
The mediums used in wireless communications are air, vacuum and even water. Air is the
mostcommonly used medium.
Wireless Transmission
Wireless transmission can be categorized into three broad groups:
 Radio waves
 Microwaves
 Infrared
THE DIFFERENCE BETWEEN RADIO WAVES AND MICROWAVES
There is no clear difference between radio waves and microwaves.
 Electromagnetic waves ranging in frequencies between 3 KHz and 1 GHz are normally
called radiowaves.
 Waves ranging in frequencies between 1 and 300 GHz are normally called microwaves.
 Infrared signals have frequencies between 300 GHz to 400 THz.
It is actually the behavior of the waves rather than the frequencies that determines the
classification of wireless transmission.
Radio waves
Radio waves are normally omnidirectional. When an antenna transmits radio waves, they
arepropagated in all directions. This means that the sending and receiving antennas do not have
to be aligned. The omnidirectional characteristics of radio waves make them useful for

5. multicasting, in which there is one sender but many receivers. Our AM and FM radio stations,
cordless phones and televisions are examples of multicasting.
The Disadvantage of Radio waves
Radio waves transmitted by one antenna are susceptible to interference by another antenna that is
sending signals of the same frequency
MICROWAVES
Electronic waves with frequencies between 1 GHz to 300 GHz are normally called microwaves.
Unlike radio waves, microwaves are unidirectional, in which the sending and receiving antennas
need to be aligned. Microwaves propagation is line-of-sight therefore towers with mounted
antennas need to be in direct sight of each other. Due to the unidirectional property of
microwaves, a pair of antennas can be placed aligned together without interfering with another
pair of antennas using the same frequency.High-frequency microwaves cannot penetrate walls.
This is why receiving antennas cannot be placed inside buildings.
Infrared
Infrared is used in devices such as the mouse, wireless keyboard and printers. Some
manufacturers provide a special port called the IrDA port that allows a wireless keyboard to
communicate with a PC.
Infrared signals have frequencies between 300 GHz to 400 THz. They are used for short-range
communication.
Infrared signals have high frequencies and cannot penetrate walls. Due to its short-range
communication system, the use of an infrared communication system in one room will not be

6. affected by the use of another system in the next room.This is why using an infrared TV remote
control in our home will not interfere with the use of our neighbor’s infrared TV remote control.
THE DISADVANTAGES OF USING INFRARED
Infrared signals cannot be used for long distance communication. In addition, we cannot use
infrared waves outside a building because sun's rays contain infrared waves that can interfere
with communication.
Guided/ Wired Transmission Media
1. Twisted Pair Cable
2. Coaxial Cable
3. Fiber Optical Cable
1. Twisted Pair Cable
The least expensive and most widely used guided transmission medium is twisted pair
• If the pair of wires are not twisted, electromagnetic noises from, e.g., motors, will affect the
closer wire more than the further one, thereby causing errors
Twisted pair is the least expensive and most widely used guided transmission medium.
 Consists of two insulated copper wires arranged in a regular spiral pattern
 The cable is an electrical cable,can transmit both analog and digitalsignal but twisted pair
is also themost common medium used for digital signaling
 Least expensive and easy to install
 Most commonly used in the telephone network and for communications within buildings
 Requires amplifiers every 5-6 km for analog signals

7. Unshielded VS Shielded Twisted-Pair Cable
Unshielded Twisted-Pair (UTP) Shielded Twisted-Pair Cable (STP)
 Suffers from external
electromagnetic interference
 Ordinary telephone wire
 Cheapest
 Easiest to install
 Has metal braid or sheathing that
reducesinterference
 Has metal braid or sheathing that
reducesinterference
 More expensive
 Harder to handle (thick, heavy)
Connector

8. 2. Coaxial Cable
BNC connectors
Coaxial cable is widely used as a means of distributing TV signals to individual homes—cable
TVused for long distance telephone transmission and LANs
 Used to transmit both analog and digital signals
 Superior frequency characteristics compared to twisted pair
 Can support higher frequencies and data rates
 Requires amplifiers every few kilometers for long distance transmission
 Requires repeaters every few kilometers for digital transmission

9. 3. Fiber Optical Cable
Fiber-optic cable connectors
Fiber optic cable is the transmission medium used to transmit data in the form of light.
 Various glasses and plastics can be used to make optical fibers
 Widely used in long distance telecommunications
 Higher bandwidth
 No noise
 Performance, price and advantages have made it popular to use
 Need Installation requires specialist because hard to install, easily broken and expensive

10. Guided transmission media summary
Type Advantage Disadvantage
Twisted Pair cable  Very inexpensive
 Easy to install
 Already installed in
many locations
Doesn’t pass high frequencies
well
Coaxial cable  Shielded
 Fairly inexpensive
 Moderately high
bandwidth
Bulky and somewhat inflexible
Fiber optic cable  Transmission unaffected
by noise
 Very high bandwidth
 Great repeater spacing
Expensive to install
Networking Devices
Network devices are components used to connect computers or other electronic devices together
so that they can share files or resources like printers or fax machines. Devices used to setup a
Local Area Network (LAN) are the most common types of network devices used by the public.
A LAN requires a hub, router, cabling or radio technology, network cards, and if online access is
desired, a high-speed modem.
1. Hub
A hub is a device that connects a number of computers together to make a LAN. The typical use
of a hub is at the center of a star network (or as part of a hybrid network) - the hub has cables
plugged into it from each computer.The basic form of concentrator is the hub.
Diagram Image

11. Comparison and properties of a Hub
 A Hub is the simplest of these devices out of the five compared.
 Hubs cannot filter data so data packets are sent to all connected devices/computers. The
device has to make decision if it needs the packet. This can slow down the network
overall.
 Hubs do not have intelligence to find out best path for data packets. This leads to
inefficiencies and wastage.
 Hubs are used on small networks where data transmission is not very high.
2. Switch
Switch are a special type of hub that offers an additional layer of intelligence to basic, physical-
layer repeater hubs. A switch must be able to read the MAC address of each frame it receives.
This information allows switches to repeat incoming data frames only to the computer or
computers to which a frame is addressed. This speeds up the network and reduces congestion.
Diagram
Image
Switch operate at both the physical layer and the data link layer of the OSI Model.
Comparison and properties of a Switch
 A switch when compared to bridge has multiple ports.
 Switches can perform error checking before forwarding data.

12.  Switches are very efficient by not forwarding packets that error-ed out or forwarding
good packets selectively to correct devices only.
 Switches can support both layer 2 (based on MAC Address) and layer 3 (Based on IP
address) depending on the type of switch.
 Usually large networks use switches instead of hubs to connect computers within the
same subnet.
3. Bridges
A bridge is used to join two network segments together, it allows computers on either segment to
access resources on the other. They can also be used to divide large networks into smaller
segments. Bridges have all the features of repeaters, but can have more nodes, and since the
network is divided, there is fewer computers competing for resources on each segment thus
improving network performance.
Diagram
Image
Bridges can also connect networks that run at different speeds, different topologies, or different
protocols. But they cannot, join an Ethernet segment with a Token Ring segment, because these
use different networking standards. Bridges operate at both the Physical Layer and the MAC
sub-layer of the Data Link layer.
Comparison and properties of a Bridge
 A bridge is more complex than hub.
 A bridge maintains a MAC address table for both LAN segments it is connected to.
 Bridge has a single incoming and outgoing port.
 Bridge filters traffic on the LAN by looking at the MAC address.

13.  Bridge looks at the destination of the packet before forwarding unlike a hub.It restricts
transmission on other LAN segment if destination is not found.
 Bridges are used to separate parts of a network that do not need to communicate
regularly, but need to be connected.
4. Router
Router Are networking devices used to extend or segment networks by forwarding packets from
one logical network to another. Router are most often used in large internetworks that use the
TCP/IP protocol suite and for connecting TCP/IP hosts and local area networks (LANs) to the
Internet using dedicated leased lines.
Diagram Image
Comparison and properties of a Router
 A router, like a switch forwards packets based on address.
 A router uses the IP address to forward packets. This allows the network to go across
different protocols.
 Routers forward packets based on software while a switch (Layer 3 for example)
forwards using hardware called ASIC (Application Specific Integrated Circuits)
 Routers support different WAN technologies but switches do not.
 Wireless Routers have Access Point built in.
 The most common home use for routers is to share a broadband internet connection. The
router has a public IP address and that address is shared with the network. When data
comes through the router it is forwarded to the correct computer.
6. NICs (Network Interface Card)
Network Interface Card, or NIC is a hardware card installed in a computer so it can communicate
on a network. The network adapter provides one or more ports for the network cable to connect
to, and it transmits and receives data onto the network cable.

14. Wireless Lan card Network card
Every networked computer must also have a network adapter driver, which controls the network
adapter. Each network adapter driver is configured to run with a certain type of network adapter.
Repeater
Repeaters are built into the hubs or switches. Repeaters clean, amplify and resend the signals that
have been weakened due to long cables traveling large distances.
Diagram Image

15. 9. Modem
Diagram Image
A modem is a device that makes it possible for computers to communicate over telephone lines.
The word modem comes from Modulate and Demodulate. Because standard telephone lines use
analog signals, and computers digital signals, a sending modem must modulate its digital signals
into analog signals. The computers modem on the receiving end must then demodulate the
analog signals into digital signals.
Modems can be external, connected to the computers serial port by an RS-232 cable or internal
in one of the computers expansion slots. Modems connect to the phone line using standard
telephone RJ-11 connectors.

16. Types of Web Sites
Thirteen types of Web sites are portal, news,
informational, business/ marketing, blog, wiki,
online social network, educational, entertainment,
advocacy, Web application, content
aggregator, and personal (Figure 2-15). Many Web
sites fall in more than one
of these categories.
Portal A portal is a Web site that offers
a variety of Internet services from a single,
convenient location (Figure 2-15a). Most
portals offer these free services: search
engine; news; sports and weather; Web
publishing; reference tools such as yellow
pages, stock quotes, and maps; shopping;
and e-mail and other communications
services.
Many portals have online communities.
An online community is a Web site that
joins a specific group of people with similar
interests or relationships. These communities
may offer online photo albums,
chat rooms, and other services to facilitate
communications among members.
Popular portals include AltaVista, AOL,
Excite, GO.com, iGoogle, Lycos, MSN, and
Yahoo!. A wireless portal is a portal designed
for Internet-enabled mobile devices.
News A news Web site contains newsworthy
material including stories and articles relating
to current events, life, money, sports, and
the weather (Figure 2-15b). Many
magazines and newspapers sponsor
Web sites that provide summaries
of printed articles, as well as articles
not included in the printed versions.
News papers and television and radio
stations are some of the media that
maintain news Web sites.
Informational An informational
Web site contains factual information
(Figure 2-15c). Many United
States government agencies have
informational Web sites providing
information such as census data,
tax codes, and the congressional
budget. Other organizations provide
information such as public transportation
schedules and published research findings.
Business/Marketing A business/marketing
Web site contains content that promotes or sells
products or services (Figure 2-15d). Nearly every
enterprise has a business/marketing Web site.
Allstate Insurance Company, Dell Inc., General
Motors Corporation, Kraft Foods Inc., and Walt
Disney Company all have business/marketing
Web sites. Many of these enterprises also allow
you to purchase their products or services online.
Blog A blog, short for Weblog, is an informal Web
site consisting of time-stamped articles, or posts, in a
diary or journal format, usually listed in reverse
chronological order (Figure 2-15e). A blog that
contains video clips is called a video blog, or vlog. A
microblog allows users to publish short messages,
usually between 100 and 200 characters, for others
to read. Twitter is a popular microblog. The term
blogosphere refers to the worldwide collection of
blogs,
and the vlogosphere refers to all vlogs worldwide.
Blogs reflect the interests, opinions, and
personalities of the author, called the blogger or
vlogger (for vlog author), and sometimes site
visitors. Blogs have become an important means of
worldwide communications. Busi nesses create blogs
to communicate with employees, customers, and
vendors. Teachers create blogs to collaborate with
other teachers and students. Home users create
blogs to share aspects of their personal life with
family, friends, and others.
Wiki A wiki is a collaborative Web site that allows
users to create, add to, modify, or delete the Web
site content via their Web browser. Many wikis are
open to modification by the general public. Wikis
usually collect recent edits on a Web page so that
someone can review them for accuracy. The
difference between a wiki and a blog is that users
cannot modify
original posts made by the blogger. A popular wiki is
Wikipedia, a free Web encyclopedia (Figure 2-15f).
Read Ethics & Issues 2-3 for a related discussion.
Online Social Network An online social
network, also called a social networking Web site,
is a Web site that encourages members in its online
community to share their interests, ideas, stories,
photos, music, and videos with other registered
users (Figure 2-15g). Most include chat rooms,
newsgroups, and other communications services.
Popular social networking Web sites include
MySpace
and Facebook, with Facebook alone boasting more
than 300 million active users. In some social
networking Web sites, such as Second Life, users

17. assume an imaginary identity and interact with other
users in a role-playing type of environment.
A media sharing Web site is a specific type of
online social network that enables members to share
media such as photos, music, and videos. Flickr,
Fotki, and Web shots are popular photo sharing
communities; Pixel Fish and YouTube are popular
video sharing communities.
Educational An educational Web site offers
exciting, challenging avenues for formal and informal
teaching and learning (Figure 2-15h). On the Web,
you can learn how airplanes fly or how to cook a
meal. For a more structured learning experience,
companies provide online training to employees;
and colleges offer online classes and degrees.
Instructors often use the Web to enhance classroom
teaching by publishing course materials,
grades, and other pertinent class information.
Entertainment An entertainment Web site
offers an interactive and engaging environment
(Figure 2-15i). Popular entertainment Web sites
offer music, videos, sports, games, ongoing Web
episodes, sweepstakes, chat rooms, and more.
Sophisticated entertainment Web sites often partner
with other technologies. For example, you can cast
your vote about a topic on a tele vision show.
Advocacy An advocacy Web site contains content
that describes a cause, opinion, or idea (Figure 2-
15j).
These Web sites usually present views of a particular
group or association. Sponsors of advocacy Web
sites
include the Democratic National Committee, the
Republican National Committee, the Society
for the Prevention of Cruelty to Animals, and
the Society to Protect Human Rights.
Web Application A Web application, or Web
app, is a Web site that allows users to access and
interact with software through a Web browser on
any computer or device that is connected to the
Internet. Some Web applications provide free access
to their software (Figure 2-15k). Others offer part of
their software free and
charge for access to more comprehensive features
or when a particular action is requested.
Examples of Web applications include Google
Docs (word processing, spreadsheets,
presentations),
TurboTax Online (tax preparation), and
Windows Live Hotmail (e-mail).
Content Aggregator A content aggregator is a
business that gathers and organizes Web content
and then distributes, or feeds, the content to
subscribers
for free or a fee (Figure 2-15l). Examples
of distributed content include news, music, video,
and pictures. Subscribers select content in which
they are interested. Whenever the selected content
changes, it is downloaded automatically (pushed)
to the subscriber’s computer or mobile device.
RSS 2.0, which stands for Really Simple
Syndication, is a specification that some content
aggregators use to distribute content to
subscribers. Atom is another specification
sometimes used by content aggregators to distribute
content. Some current browsers include a feature,
such as Internet Explorer’s Web Slices, that enables
content aggregators to mark sections of their Web
pages as feeds to which users can subscribe.
Personal A private individual or family not
usually associated with any organization may
maintain a personal Web site or just a single
Web page (Figure 2-15m). People publish personal
Web pages for a variety of reasons. Some are job
hunting. Others simply want to share life
experiences with the world.