Different Types Of Basic Topologies Computer Science Essay

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A network consists of multiple computers connected using some type of interface, each having one or more interface devices such as a Network Interface Card (NIC) and/or a serial device for PPP networking. Each computer is supported by network software that provides the server or client functionality. The hardware used to transmit data across the network is called the media. It may include copper cable, fiber optic, or wireless transmission. The standard cabling used for the purposes of this document is 10Base-T category 5 Ethernet cable. This is twisted copper cabling which appears at the surface to look similar to TV coaxial cable. It is terminated on each end by a connector that looks much like a phone connector. Its maximum segment length is 100 meters.

In this Topology the nodes are connected to a single common backbone. This common medium proves to be a shared communication path for the nodes that are connected to it. A device which wants to communicate to other device sends a broadcast message on to the communication path; this message is read by every node in the network. It checks for which node

it was intended and only the destination message actually accepts that message and interprets it. This topologies are easy to install as it doesn't require too much of cabling. It works best when number of PC are less in the network. Performance is the issue when the nodes grow and if the backbone fails the whole network fails.

In this mapping of network each device has two neighbors for communication purpose. The message travels through the ring in either clockwise or anti-clockwise direction. A failure in the cable can breakdown the whole network. To implement this kind of network FDDI or Token ring technology is used. Found in some offices and schools.

Switch or a HUB. All the devices are connected to the central Hub by unshielded Twisted Pair Ethernet. Compared to Bus it requires more cables, however the performance is better than bus and ring. The whole network fails when only the central Hub fails. and the failure in a cable will take down only one PC and not the entire network as in the bus or ring.

Tree Topology:

This topology integrates more than one star topologies onto a Bus. Only the Hub devices are connected to the tree Bus, each Hub functions as the Root of the tree. This hybrid approach supports expandability of the network. It is also called as Hierarchical topology

Mesh Topology:

Now, in this topology the concept of route is introduced. In this topology the data passed on to the network can take several paths to reach the destinations, unlike the other topologies. Here every device is connected to every other device called as Full Mesh.

we can summarize this topologies, we can build a home or a small business network without understanding of the topologies, however if we understand each topology in a better way it can definitely help us in building a good network. A misconfigured network can result in a waste of time and energy as well as a lot of troubleshooting methods to resolve the issue. So the basic understanding of the network topologies and network devices is a must to build a good network.

To create the in-house network for the fire Department I would recommend "Star topology";

Due to its centralized nature, the topology offers simplicity of operation.

It also achieves an isolation of each device in the network.


Quotation (Emtel)

One of the most demanding services is wireless high speed internet, which enables you to be completely mobile whether you are in Mauritius or abroad. This can be accessed through a HSDPA Card, which is connected through a USB cable towards any PC or laptop, as follows:



Cost Of PC Card - Rs. 5999 (Excl. VAT)



Monthly Fee (Rs)*

Price for extra 100 Kb (Rs)

Tariff 1 Gb



Tariff 2 Gb



Tariff 5 Gb



Tariff 10 Gb






Billing Pulse



0.3 cents / KByte equivalent to Rs 3 per MByte




Emtel Wimax Professional

Monthly Charges

Monthly Charges


On Purchase Equipment

On Rental of Equipment

128 Kbps



256 Kbps



512 Kbps



1 Mega



2 Mega





Emtel Wimax Business

Monthly Charges

Monthly Charges



On Purchase Equipment

On Rental of Equipment

128 Kbps

32 Kbps



128 Kbps

64 Kbps



128 Kbps

128 Kbps



256 Kbps

64 Kbps



256 Kbps

128 Kbps



256 Kbps

256 Kbps



512 Kbps

128 Kbps



512 Kbps

256 Kbps



512 Kbps

512 Kbps



1 Mega

128 Kbps



1 Mega

256 Kbps



1 Mega

512 Kbps



1 Mega

1 Mega



2 Mega

128 Kbps



2 Mega

256 Kbps



2 Mega

512 Kbps



2 Mega

1 Mega



2 Mega

2 Mega



Quotation for supply and installation of Nomad Office Internet Package

Following your request, please find below quotation for Nomad Office Internet Packages.

A. Product Details & Features


Nomad Office 128k

Nomad Office 512k

Nomad Office 1 MB

Nomad Office 2 MB

Monthly Tariff

Rs 1100

Rs 2500

Rs 4500

Rs 8500

Modem Deposit (Refundable)

Rs 1000

Rs 1000

Rs 1000

Rs 1000

Registration Fees

RS 1000

RS 1000

RS 1000

RS 1000

B. Terms and Conditions

On subscription, you will be charged Rs. 1000/- as a security deposit (refundable) for the modem, Rs 1000/- as registration fee and one month in advance.

Quotations from Mauritius Telecom

Please find in attachment a typical layout of a wireless design for a campus. The main building will consist of an Access Point (together with its indoor unit). An omni antenna should be used and will radiate in the unlicensed frequency band; only a yearly apparatus fee is payable to the Information & Communication Technology Authority

All the computers are connected via Cat 5 cables to a 12 Port Switch.  



An approximate cost of an Access Point together with its IDU (indoor unit) = Rs 50,000

50, 0000

An approximate cost of an Subscriber Unit together with its IDU (indoor unit)


Include cabling costs

Cable CFD400

100 per meter

Omni Antenna


Features of the different equipment


Features of the equipment used


With tiny design and high speed, Huawei E220 USB Modem redefines mini fashion for the elite. The irresistible creation features the eye-catching sleek design and a great speed up to 3.6Mbps. Its USB cable can be used by both laptops and desktop computers. Put the chic near your hand and enjoy the charm of mini fashion. HSDPA packet data service with a maximum transmission rate of 3.6Mbps

UMTS packet data service with a maximum transmission rate of 384kbps

EDGE packet data service with a maximum transmission rate of 236.8kbps

SMS service

Auto installation, convenient for use

Windows 2000 and Windows XP Operating system

Technical standard HSDPA/UMTS: 3GPP R99, R5


Operating frequency HSDPA/UMTS 2100MHz

GSM/GPRS/EDGE 900/1800/1900MHz

External interface Mini USB interface: supporting USB 2.0 Full Speed

Antenna: Internal antenna

SIM/USIM card: standard 6 PIN SIM card interface

Dimension 89 mm (D) x 43 mm (W) x 14.5 mm (H)

Weight < 50g

Mauritius telecom

Access points provide a central base for your wireless network much the same as a switch / hub on a wired network. As with hubs / switches access points extend range, but there are also devices that only do range (no access point capability).Cisco Aironet 1250 Series wireless access points are the first business-class access points to be Wi-Fi 802.11n draft 2.0 certified. These modular wireless access points provide reliable and predictable WLAN coverage to improve the end user's experience with both existing 802.11a/b/g clients and new 802.11n clients. With these wireless access points you can:

Augment throughput for high-bandwidth wireless applications

Protect your investment in wireless networking

Increase network reliability for mission-critical application


Simple, Fast Deployment and Easy Installation.

No license required.

Cost effective alternative to wire/fiber connections.

Increased Security - per subscriber module authentication helps prevent unauthorized access.

10 Mbps connectivity.

Up to 5 mile point-to-point ranges (LOS).

Rugged outdoor design.

Seamless, Near Plug-and-Play Design and Installation.


Harel mallac

Ethernet Bridge

With the proliferation of unlicensed radio devices it can be a challenge to deploy and operate a reliable RF networks in the 2.4 GHz band. At Afar Communications we went to great extents to design a radio from the ground up that can provide dependable links under very adverse conditions. This includes the following features:

All the electronics are housed in an environmentally sealed enclosure rated for outdoor installation. You can mount the unit in close proximity to the antenna, which increases system performance by avoiding RF cable losses or expensive rigid coax cables.

The radio RF bandwidth is much narrower than other unlicensed devices in the 2.4 GHz band. This has several advantages, namely (i) the radio sensitivity is greatly improved allowing very long range wireless links, (ii) there is a much larger number of non-overlapping channels to choose from, and (iii) it is much easier to find an unused gap in a crowded spectrum.

In a long range wireless link under heavy interference, clear channels at each end of the link are often different. In the Afar radio the transmit and receive frequencies can be selected independently of each other, allowing you to select the two optimal frequencies to avoid local interferers.

The radio incorporates spectrum analysis and timing analysis tools, which allow the operator to quickly perform a survey of the RF environment without the need for expensive or heavy spectrum analyzers.

Unique antenna alignment aid provides audio feedback proportional to the RSSI, freeing the installer's hands to adjust and tighten the antenna without having to hold or look at other instrumentation.

PulsAR-24027 - Long Range Wireless Ethernet Bridge



RF Band

2.400 to 2.483 GHz

2.400 to 2.500 GHz option


RF Bandwidth:

4.6 MHz


RF Channels:

34 in steps of 2MHz

12 non-overlapping channels

Independent tx and rx channels


Transmit Power:

0 to 23 dBm (FCC)

0 to 20 dBm (CE)


Modulation Type:

Direct sequence spread spectrum


RF Data Rates:

0.25, 0.50, 1.375. 2.75 Mbps


Receiver Sensitivity (10-6 BER):

-98 dBm (at 0.25 Mbps)

-95 dBm (at 0.50 Mbps)

-93 dBm (at 1.375 Mbps)

-90 dBm (at 2.75 Mbps)

Ethernet Port



10/100 MHz, full/half duplex, auto-negotiate



8 pin circular (Lumberg 0321-08)

(RJ45 at the power inserter)

Console Port



RS-232 / V.24


Baud Rate:

9600 to 115.2 Kbaud



3 pin circular (Lumberg 0321-03)



Input Voltage:

8 to 28 Volts DC

110 to 220 VAC (external supply)



5 Watt



Operating Temperature:

-40 to +70 deg C

-40 to +158 deg F



up to 95% non-condensing




12.0 x 22.0 x 5.6 cm

4.72" (W) x 8.66"(H) x 2.20" (D)



1.5 Kg

3.4 lb

Polarized Antenna

Our circular polarized antenna is constructed of an aluminum allow back plate with a UV protected plastic random. Circular polarization is effective in minimizing multipath and has also been proven effective at improving signal through obstructions such as trees.


Adjustable tilt stainless steel bracket, for mounting on pole 1" to 2" outside diameter

Female N-type connector (connects to our radio with included CBL-0201-002 cable)

DC grounded for lightning protection

Rugged, lightweight and waterproof


Frequency Range

2400 to 2483 MHz


12 dBi


Circular (RHCP)


1.5 : 1

3 dB beamwidth 

37 deg


50 Ohm


8.5" L x 8" D

206 x 203 mm


1.1 lbs

0.5 Kg

Wind Loading:

  100 MPH (160 Km/h)

  125 MPH (200 Km/h)

14 lbs (6.5 Kg)

22 lbs (10 Kg)

CBL-0503-XXX:  This cable connects between the indoor power inserter and the outdoor Wireless Ethernet Bridge . It carries both your Ethernet data and the DC power to the radio.  At the radio end it is terminated in a metal cylindrical waterproof connector. You can order in standard lengths of 5, 50, 100, 200 or 300 ft (1.5, 15, 30, 60 or 90 meters).  The last three digitis of the part number specify the length in feet.

CBL-0403-003:  3 ft cable (1 meter) to convert from the three pin cylindrical connector on the PulsAR-24027 radio to a DB9 female connector.  You use this cable to connect the radio to a terminal over RS-232 as an optional way of configuring the radio on the bench.

CBL-0301-XXX:   Male to male RF coaxial cable of various lengths.  You may need an RF cable to connect between the antenna and the radio.  Our 24 dBi grid antenna comes with a short pigtail that connects directly to the radio.  The Flat Panels, and omni-directional antennas require a short coaxial cable to connect to the radio.  When you order the radio and antennas together we provide a 2 ft coaxial cable at no additional cost.

Suppressors: Provides surge protection for the antenna port of the PulsAR-24027 Wireless Ethernet Bridges . It uses quarter wave stub technology which shunts to ground surges that fall outside the 2.4 GHz operating band of the radio.  It is equipped with N-type connectors to be installed right at the antenna port of the radio.

Use this device if you have a long outdoor CAT5e cable between the radio and the indoor power inserter.  This suppressor  protects all 8 lines: the data lines for differential and common mode surges, the power lines for common mode surges to Earth Ground. The very low shunt capacitance in the signal lines allows operation in both 10Base-T and 100Base-T Networks.

The PulsAR-24027 Wireless Ethernet Bridge gets its power over the Cat5 Ethernet cable.  The Power Inserter Unit is a small indoor module that injects DC power into the unused lines of the Ethernet Cat5 cable .  There are two models (see figures), one for operation from an AC source (110-240 VAC), and the other for operation from a DC source (8 to 28 VDC).  If your DC supply is -48 VDC we also carry a DC/DC converter that you can use in conjunction with the DC Power inserter.

The Standard AC Power Inserter Unit (PWI-103) includes a power supply for connection to an AC outlet (110-240 VAC), two RJ45 connectors and a bi-color LED.  The two RJ-45 connectors are labeled "To LAN" and "To Radio". 


From the above table you can find out the features of the different equipment that can be used to implement the network. First of all we must determine the different needs of the site. In fact each department's need required the following capabilities:

High speed network availability on every floor of each building.

High speed connectivity between stories to maintain exchange of information.

Broadband access to the internet.

The Mauritius Telecom project seems much more feasible for the implementation of the network. In fact it proposes the installation of a wired and wireless network.


Two way voice communication

Effective communication has always been an important component of successful fire ground operation. However modern fire services depend heavily upon radio communication system, so much that efficient operation as well as fire fighter's safety depend to a great extent on how well the radio communication system function.

Two-way radio has been a successful analogue communication solution for generation and proves itself but in today's technologically advanced environment, new platform is possible-digital platform that break through to new levels of performance and productivity.

In the GFS "Government Fire Services" the radio system is an UHF analogue half duplex.

When talking about fire department communications systems usually we are talking about what are traditionally called land mobile radio systems.

It is important for firefighters and fire officers to have a basic knowledge of radio system technologies to help them during the design, procurement, or use of the radio system. By having this basic understanding, you will be able to participate effectively in critical discussions with technical staff, consultants, and manufacturers to get the safest, most effective voice communications system for your firefighters, Command Staff, and community.

Most radio system users do not need a detailed understanding of the technology behind the systems they use. However, such knowledge is important for those involved in procuring the systems, in developing procedures for the use of the systems, and in training field users to have a more comprehensive understanding of their operation. All technologies have strengths and weaknesses, and understanding those characteristics is important in making decisions related to the technologies. No matter what a salesperson will tell you during the procurement process, no system is without risk and all have had users who were not satisfied with some aspect of the system. The key is in understanding the technology enough to ask questions, understand the answers, and make a successful evaluation.

Radio Spectrum

Radio communications are possible because of electromagnetic waves. There are many types of electromagnetic waves, such as heat, light, and radio energy waves. The difference between these types of waves is their frequency and their wavelength. The frequency of the wave is its rate of oscillation. One oscillation cycle per second is called one hertz (Hz). The types of electromagnetic energy can be described by a diagram showing the types as the frequency of the waves increase.

Figure 1 - The Electromagnetic Spectrum.

When describing the frequencies used by common radio systems, we use the metric system to quantify the magnitude of the frequency. A typical frequency used in fire department radio systems is 154,280,000 Hz. This is a frequency designated by the FCC as a mutual-aid radio channel. Dividing the frequency by the metric system prefix mega, equal to 1,000,000, this becomes 154.280 megahertz or MHz.

Land mobile radio systems are allowed to operate in portions of the radio spectrum under rules prescribed by the FCC. These portions of the spectrum are called bands, and land mobile radio systems typically operate with frequencies in the 30 MHz (VHF low), 150 MHz (VHF high), 450 MHz (UHF), 700 MHz, and 800 MHz bands.

The wavelength is the distance between two crests of the wave. The frequency and wavelength are inversely related so that, as the frequency of the wave increases, the wavelength decreases. The length of a radio antenna is related to the wavelength with which the antenna is designed to operate. In general, the higher the frequency of the waves used by the radio, the shorter the antenna on the radio.

Channel Bandwidth

The radio spectrum is divided into channels. Each radio channel is designated by a frequency number that designates the center of the channel, with half of the bandwidth located on each side of the center.

Radio channel bandwidth is the amount of radio spectrum used by the signal transmitted by a radio. The greater the bandwidth, the more information can be carried by the signal in the channel. Minimum channel bandwidth typically is limited by the state of technology, and the bandwidth required to carry a given amount of information has decreased by several times over the past 50 years. However, there is a theoretical limit below which the bandwidth cannot be decreased. In addition, the actual width of a channel often is slightly greater than the minimum width, to provide some space on each side of the signal for interference protection from adjacent channels. For the purposes of radio licensing, the FCC sets the maximum and minimum bandwidth for channels in each frequency band.

The bandwidth of channels typically used in land mobile radio is measured in thousands of hertz, or kilohertz, abbreviated kHz. In an effort to place more communications activity within a limited radio spectrum, permitted bandwidth has been decreasing. Under older licensing rules, some of which are still in effect, typical channel bandwidths were 25 kHz. Newer rules require bandwidths of 12.5 kHz


Radio frequency interference can be either natural or manmade. Interference from internal noise occurs naturally in all electronic equipment due to the nature of the electronic circuit itself. Manufacturers take this into account during equipment design, and obtaining a low-noise design is not particularly difficult. In addition, natural noise is produced by sunspot activity, cosmic activity, and lightning storms. This noise usually is of small magnitude and not significant for most land mobile radio communications. However, the VHF low band is affected significantly by severe sunspot activity, sometimes to the point of completely prohibiting communications.

More significant to radio communications systems is the interference produced by manmade sources. Vehicle ignitions, electric motors, high-voltage transmission lines, computers, and other equipment with microprocessors also emit radio signals that can interfere with public safety radios.

In general, manmade interference decreases with an increase in frequency. The UHF band and, initially, the 800 MHz band are much less susceptible to manmade interference than the VHF low and high bands. When systems are not subject to significant interference, they are said to be "noise limited," in contrast to "interference limited." The large number of transmitters used by cellular telephone companies has created intense interference in the 800 MHz band.

Although the separation of the channels allocated to cellular companies has reduced this interference, communications problems still can occur when a user is operating close to a cellular transmission facility. This type of interference is particularly a problem when the user is located near a cellular facility and the user's radio system site is located much further away. This creates a situation called near-far interference. The user's system signal strength is low, and the cellular signal is high, keeping the user's radio from receiving the desired signal. The 800 MHz band always was regarded as the "cleanest" band with respect to manmade interference, and systems initially were noise limited. However all systems in the band now must be designed for maximum interference from nearby transmitters, requiring more transmitter locations and higher power creating more costly systems.

Interference from cellular transmitters is illustrated. The blue area in the center is the public safety transmitter and in the center of the grey areas are the cellular transmitters.

Intermodulation interference is caused directly by the mixing of two or more radio signals. The mixing most commonly occurs inside the receiver or transmitter of a radio. This mixing can create a third signal that is radiated from the antenna out to other radios. The mixing also can occur outside a radio in the transmission line or through rusty tower bolts or guy wires. Intermodulation can be difficult to identify, due to the large number of frequencies that may be present at large communications sites.

What is GPS Vehicle tracking and how can it help you?

GPS stands for 'Global Positioning System' , GPS vehicle tracking systems make use of the satellite network placed around the world to establish their own locations. They do this by sending and receiving signals at timed intervals - updating their position each time

Digital two way radios offer several advantages over analog solutions, and is based on Time Division Multiple Access (TDMA) technology meaning that a single digital frequency can carry multiple audio lines

(b) Legal requirements

To establish a radio communication system in Mauritius one should have clearance from the ICTA and will be allocated a channel with a specific frequency. Those frequencies are monitored only by ICTA

Task 4

The main emergency hotline is at the control room "115". There the calls are handled for emergency for all over the island. The control room then refers the emergency to the fire station nearest to the incident with regards to the topography by either telephone or radio depending on availability of communication.

The PABX system

A PBX (Private Branch Exchange) system (PABX/EPABX) is a basic requirement for any type of business whether large or small they are. Without a proper communication backbone being setup in an organization, day to day activities will be affected that can result to inaccurate information exchange up to huge potential loss of business or revenue.

Why choose to have this system instead of the traditional PBX?

TS-PBX has a lot of features not found on traditional PABX systems such as on demand conferencing, scheduled conference calls , least cost routing, VOIP for remote sites/users, DISA (direct inward dialing for access to various outside lines), group ring, line hunting, voicemail, call recording, etc.

TS-PBX can bridge two remote sites to act as one single local system. Each site can have their own outside access and remote sites can access them

TS-PBX can allow remote users to connect IP phones and soft phones to the system giving them local access

To give you an idea of how the TS-PBX System can help us enhance communication, We would like to list down some significant features:

Call conferencing - we can setup call conferences and can connect remote users. This means you can invite customers, prospects, suppliers on a conference and talk even if some attending people are remote or not in the office.

Three way calling/call forwarding - if somebody is looking for a person that is not in the office, you can forward the call to anywhere like cellphone, home telephone, etc. This will make sure that if there's an urgent call from a customer he can always reach the person he needs to talk to.

VOIP interface - since this is VOIP based, i.e. your Laguna office will not need to pay long distance charges to reach somebody.

Remote users - since we have a lot of remote users, we can enable them to use SIP Phones or soft phones (software phones installed in laptops) so that anywhere that they can access the Internet, they can be reached or can join conferences.

Call attendant (IVR) - this will be an automated attendant that will answer calls giving them options to call consulting, support, sales, etc.

Direct Inward Dialing.

A walkie talkie radio is simple to use. It is not a cellular phone where we are able to speak simultaneously with the receiver. Walkie talkie radio is a push to talk device where one is speaking while the other is listening. Just press the special button (usually placed near volume control) to make a PTT (Push to Talk) call and to transmit your voice to the listener. Your call could also be heard by a group of people. To make a group call, you have to set-up your radio or create a group member then select your created list and you will perform a group call.

Walkie talkie radio is made in a simple form to operate. First, you have to set the two walkie talkie radios in the same channel or frequency. Just press the button and say your message on a microphone of a walkie talkie while holding the button or let go of it when you're going to listen the voice. Frequency is essential for this kind of communication; it transmits your voice to your listener or group listener. Now we can enjoy the communication using walkie talkie radio.


Fixed-Site Antennas

Fixed-site antennas are mounted on towers or buildings to provide the dispatch or repeater coverage throughout the service area. The antennas used must be designed to operate in the system's frequency band and, for best power coupling, should have a center frequency as close as possible to the actual operating frequency.

The radiation pattern for the antenna should be selected to provide a signal in the desired sections of the coverage area, and have minimal coverage outside the desired coverage area. This will help ensure that the system is not interfering with other systems unnecessarily. The most basic practical antennas are omni-directional, and have approximately equal coverage for 360 degrees around the antenna.

The Department should be well equipped with latest power generators also.