Five Types Of Physical Topology Computer Science Essay

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Topology of a network refers the logical and physical connection between hosts of a network. Logical Topology explains how the data transfer is going to take place while the Physical Topology is concerned with how the nodes are going to be connected by means of wires, cables or other physical medium.

The bus topology exists when each of the systems is connected in a shared medium and line. In this topology, all the systems are chained to each other and terminated on each end. This topology is inexpensive to use and relatively easy to set up.

Ring

The ring topology exists when each of the hosts are connected to its respective neighbor forming a circular ring. The systems are connected all together in a loop liek a circle, there is no beginning and thus, no end point as there is with the bus topology.

Star

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In the star topology, the host are connected to a central device e.g. Hub or Switch. One feature is that when one system goes down, it does not bring the rest of the network down with it as it does in the bus or ring topologies. Star topology is the most implemented physical topology.

Hybrid/Tree

Hybrid/Tree topology is nothing but a combination of other topologies. In the above figure, a combination of star topologies are given.

There are two types of logical topology:

Bus

Ring

Physical Topology of a network can be star or mesh or something else but its logical topology has to be anyone of Bus or Ring.

Bus Topology

Bus networks uses a common backbone to connect all devices. The backbone is used to connect all the host in the network and therefore, have a shared communication medium. Since, they are shared Logical Bus Topology is susceptible to an amount of traffic collision.

Ring Topology

In Ring Logical Topology, all communicate through the use of Token. When a device wants to send a message they attach their message to the token and sends to the recipient. Since, only users with Token can send message, collisions are prevented.

B) Suitable media types available for forming the network are:

Unshielded Twisted Pair(UTP) Cables

Category 5e

Category 6

Category 7

Optical Fibre Cable

Wireless Communication

Radio

Microwave

Infrared

Unshielded Twisted Pair(UTP) Cables

Advantages of UTP Cable:

Less expensive and comparably efficient

Available

Easy to install

Many categories to choose from

Disadvantages of UTP Cables:

High Cost maintainence

Susceptible to corrison quickly

High probability of theft

Vulnerable to crosstalk, noise and interference

Optical Fibre Cable

Advantages of Optical Fibres:

It provides a higher transmission capacity

It provides broad bandwidth range

It is easily transportable

Immune to electromagnetic interference, noise and crosstalk

Disadvantages of Optical Fibres:

Used only in particular circumstances and situations

Very expensive

Fragile than other kinds of cables

Wireless

Advantages of Wireless Transmission:

Workstations can be added easily

Workstations can be mobile

Installation less difficult

Environment remains neat and clean due to less wiring

Disadvantages of Wireless Transmission:

Lower bandwidth due to limitations of signals

Wireless devices costs more than wired devices

High probability of interference and attenuation occuring

Many security threat implications

C) For logical topology Bus Topology would be best suitable because then there would not be chance for latency between communications as there would be in Ring and for physical topology, Hybrid/Tree Topology of Star will be applicable because there will be multiple worstations connected from multiple sites to a server and it will also ensure reliablity in case of a node breakdown. The medium suited for the network would be a category of UTP Cable and it should be Category 7 because it is shielded and immune to crosstalk or noise. Optical Fibres will be overhead because the communication is in-house. Wireless transmission cannot be implemented because there will be many openings to information theft and protecting the signals will add more cost to the budget.

Task-2

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A) Types of Internet Services:

Dial-up

Cable

DSL

Wireless

Cable connection(e.g. T-1) will be required because compared to analogue connections(e.g. dial-up, DSL) Digital connectivity through cables would provide better bandwidth and security. Same goes for wireless connections. Since, wireless connection(WiFi) signals are attenuated and vary from site to site it would be very unreliable for official work and has great many chances of threats.

B)

Designation

Bandwidth

District

No. of workstation

Multiplier

Total(~)

District Commander

384 kbps

4

1

x4

1.5 mbps

Deputy Dst. Commander

384 kbps

4

1

x4

1.5 mbps

Seargent

256 kbps

4

1

x4

1 mbps

Constable

256 kbps

4

5

x20

5 mbps

Det. Chief Inspector

512 kbps

n/a

1

x1

0.5 mbps

Detectives

512 kbps

n/a

20

x20

10 mbps

Grand Total

19.5 mbps

According to the above calculation, suitable dedicated bandwidth taken from the ISP would be 20 Mbps.

C) The ISPs providing best of services and reliable are as follows:

BDCOM Online Ltd.

One of the first and well-known ISP in Bangladesh and provides excellent service.

Link3 Technologies

New ISP in Bangladesh but has numerous network solutions to provide.

IS PROS Limited

Provides good services at affordable prices but bandwidths are mostly shared.

D) According to the ratio of price to service. BDCOM Online Ltd. has a very good reputation. Therefore, BDCOM Online Ltd. should be chosen. Their packages are as follows:

Monthly charge

128 kbps Dedicated Bandwidth Service

8,000 BDT

256 kbps Dedicated Bandwidth Service

12,500 BDT

512 kbps Dedicated Bandwidth Service

20,000 BDT

1 mbps Dedicated Bandwidth Service

38,000 BDT 

Total Expense: 38,000*20 = 7,60,000 BDT

Task-3

A) The method for Two-way voice communications available and suitable for the Police Department is PTMR(Private Trunked Mobile Radio).

Its characterstics are as follows:

Point to multi-point communications (as opposed to cell phones which are point to point communications)

Push to talk, release to listen - a single button press opens communication on a radio frequency channel

Large coverage areas

Closed user groups

Communication on a single channel(half duplex)

Use of VHF or UHF frequency bands

Requires license from govermental department

Bandwidth and channel availability limited

In general narrow band frequency modulation is the chosen form of modulation for PTMR. Typically a deviation of 25 kHz is used for FM and this enables a channel spacing of 12.5 kHz to be implemented. As the demands for PTMR are high, it is necessary to make effective use of the channels available. This is achieved by re-using the frequencies in different areas. Base stations must be located sufficiently far apart so that interference is not experienced (Professional Mobile Radio).

B) Licensing Gudelines:

1.01 The Licensee shall establish, operate and maintain the BWA Services as provided in the License.

1.02 In order to ensure proper competition among the BWA Services licensees, total 3 (three) licenses will be issued to provide nationwide BWA Services in 2.3 GHz and 2.5 GHz spectrum bands. An

additional BWA license (fourth license) may be issued to Bangladesh Telecommunications

Company Limited (BTCL) in the same terms and conditions including the License Acquisition

Fee (to be fixed by way of auction) as shall be applicable to the other BWA licensees.

1.03 Two licenses will be awarded to the prospective Applicant(s) to provide nationwide BWA

Services in 2.3 GHz and one license will be awarded in 2.5 GHz spectrum bands.

1.04 The duration of the Licenses, shall initially be for a term of 15 (fifteen) years. Upon expiry of the initial term, the License may be renewed for subsequent terms, each of 5 years in duration, subject to the approval from the Commission and to such conditions, including the payment of any fees, as may be specified herein and/or by the Commission under the Act.

Frequency Distribution:

2.01 Spectrum bands 2.3 GHz and 2.5 GHz have been considered for BWA Service License.

2.02 A contiguous 30 MHz of unpaired spectrum from 2.3 GHz band (23xx-23xx MHz and 23xx-23xx MHz) will be assigned to 2 licensees. (Licensing Guidelines)

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2.03 A contiguous 30 MHz of unpaired spectrum from 2.5 GHz band (25xx-26xx MHz) will be assigned to 1 licensee. 2615-2620 MHz is kept as guard block between TDD and future FDD assignment.

2.04 30MHz contiguous channel will be allocated to each operator to provide BWA services. Per channel bandwidth should be either 5 or 10 MHz.

2.05 The spectrum assignment will be inclusive of guard bands needed for the operation of the equipments to avoid causing harmful interference to adjacent equipments operating in adjacent bands. No separate spectrum shall be kept as guard band between two assignments in 2.3 GHz band. (Licensing Guidelines)

C) Fees and Charges

The spectrum charges shall be calculated using the following formula:

Spectrum Charges in Taka = STU x CF x BW x AF x BF

Where, STU=Spectrum Tariff Unit=Tk. 60.00 per MHz per Sq.km

CF=Contribution Factor

BW=Bandwidth Assigned for Access Frequency in MHz

AF=Area Factor for Access Frequency=147570 Sqkm

BF=Band Factor

(Licensing Guidelines)

1.

Application Fee

Taka 50,000.00 (Tk. Fifty thousand)

2.

License acquisition fee

To be fixed by auction

3.

Annual License Fee

Taka 3 (three) crore

4.

Gross Revenue Sharing

4% for first two years

and 5% for the subsequent years

5.

Annual Spectrum Charge

As per the Spectrum formula

6.

Performance Bank Guarantee.

Taka 15 (fifteen) crore

7.

Radio Communication Vendor License

Taka 10,000

8.

Two-way communication devices

9,750

D) Limitations:

The operators, within 1 year of issuance of license, shall have to install minimum 5 full fledged Base Station Transceiver (BTS) radio sites in areas covering each Divisional Headquarters and 3 BTS covering each District.

Frequency Range: 2.3 Ghz - 2.5Ghz

Frequency Limitaion: 25 Km radius

Signalling: 5-Tone Advanced Signalling

Channel Spacing: 12.5 Khz

Interference: Co-channel Interference, Adjacent Channel Interference and Intermodulation (Operating frequency range explained, 2008).

E) To implement PTMR a network of stations are set up. These stations are linked generally using land lines, although optical fibers and point to point radio are also used. In this way the different base stations are able to communicate with each other. PTMR also allows number of users to share a set of frequency which is done by Radio Trunking. A Trunked radio system makes use of several radio channels centrally managed by a Trunked Controller to provide communication between radio users. When a user makes a call, the Trunked Controller automatically allocates a free channel and sends a message to the radio units involved in the call instructing them to change to the free channel. This means that a conversation can be made if any channel is available. Since the communication between the radios going on will be sensetive, Encryption is required to protect information being leaked by the use of Scanners. Encryption modifies a voice signal using a coding algorithm. An encryption key controls this algorithm. The encryption key is used by the transmiter and receiver radio to enable the voice signal to be coded and decoded for both radio. Therefore, all radios communicating must have matching encryption keys, or encryption will not work (PMR - Private Mobile Radio FAQ's).

If more range is to covered than the frequency coverage can be increased by the use of repeaters. A repeater can be a useful tool to increase the operating range of a radio system. With its relatively high transmitting power & external antenna, a well-sited repeater will provide an excellent platform to boost signals beyond the range of non-repeater networks. Whether it is sited at the centre of operating network or at a location prone to weak coverage, the repeater will instantaneously re-transmit received audio without any noticeable delay (Repeater applications explained!).

The above recommendation has been given due to many advantages explained in other Tasks but as an overview will be briefed below as the advantages of implementing the

PTMR communications system:

Improved communication and liaison between users

Increased intelligence exchange

Increased safety and confidence for users

A more effective early warning system enabling the users to provide a more pro-active approach

Support and backup

Crime deterrence, public safety and improved confidence for them

Greater knowledge of criminals, especially for retail operative

Quicker responses

Task-4

A) The organization investigated was a Computer Sales Plaza called IDB. The Adminstration department of IDB has a Hosted PBX(Private Branch Exchange) installed from BRTC. Every shop in IDB is connected through the Adsminstration office so that calls can be routed to specific shops. Since it is a hosted PBX, all the equipments are in BRTC's premises. So the following names of equipments are based on assumptions and references.

The equipments more or less required are:

The PBX's internal switching network.

Microcontroller or microcomputer for arbitrary data processing, control and logic.

Logic cards, switching and control cards, power cards and related devices that facilitate PBX operation.

Stations or telephone sets.

Outside Telco trunks that deliver signals to (and carry them from) the PBX.

Console or switchboard allows the operator to control incoming calls.

Uninterruptible Power Supply (UPS) consisting of sensors, power switches and batteries.

Interconnecting wiring.

B) The PBX features the following features from main to optional ones:

Main

Establishing connection between two telephone sets of two users

Maintaining connections as long as user requires

Dial outside lines

To make an extension query while connected to and on hold another external call.

Transfer an external call to the extension that has been enquired.

Additional

Auto-attendant 

Calls are answered automatically by a pre-recorded message or a menu system.

Automated directory services

Where callers can be routed to a given employee by keying or speaking the letters of the employee's name.

Call Diversion

Calls will be diverted to an extension when a given condition will be fulfilled.

Saved Number Dialled

Allows to save an incoming number and re-dial it at a later time.

Call park

 A feature of some telephone systems that allows a person to put a call on hold at one telephone set and continue the conversation from any other telephone set.

Hunt Groups

If one extension is busy then the call will be routed to the available extension in the Hunt Group number.

C) Since the organization is using a Hosted PBX. They have disclosed the individual costs.

The hardware and setup cost included = 1,30,000 BDT/Month

D) If something goes wrong with the telephone sets or wiring in the user premesis then the users has to confront the costs. Their monthly cost on PBX requires as follows:

Replacing damages sets= 2,850 BDT/Telephone set

Wiring Replacement= 25 BDT/Feet of wire

Any damage occuring at the provider premesis is maintained by them.

E) The Hosted PBX is the best solution for any organization can afford. Because most of the problems are handled by the provider including any necessary cost(varies with provider). Other advantages of PBX are detailed below:

1. It allows all employees to share phone system lines, thus reducing overall telecommunication expenses.

2. The PBX system is totally programmable and can support complex installation or integration requirements.

3. There are a wide variety of standard, as well as additional features with the PBX system.

4. The PBX system is easily expandable as the organization grows.

 5. The physical PBX hub is low profile and does not require a large amount of space.

6. Installing PBX may require investment of a big amount but on the long run, it is profitable.

7. Save money with no PBX hardware to purchase or lease and no labor or maintenance ever needed

8. PBX provides the best sounding telephone conversations with digitally optimized voice handling

Due to all the above advantages over other telecommunication alternatives. It is recommended that Hosted PBX be used and if possible better provider and more features be adhered to. PBX woule be most suitable for the a Police department because then all the communications will be under theier control and given sensetive data and communication will take place this telecommunication solution should be implemented.

Task-5

Executive Summary

This report will be consisted of the following:

Topology that will be suitable for the Police Department Networking

Which Physical and Logical Topolgy

Advantages and Disadvantages of the medium

Recommendation for a Topology and its associated medium

Internet Connection Requirements for the Police Department

Type of Internet Service

Bandwidth most suitable

Providing ISPs available and the associated costs

Recommendation of an ISP

A Two-way voice communication method that can be implemented

Possible voice communication methods

Legislation

Costs and charges

Limitations and coverage

Recommendation for Telephone Systems to be purchased

Equipments required with related system

Features available with system

Cost of equipment, installation and maintainence

Recommendation for a Telecommunication system

Introduction

The compilation of this tasks forms an output which will provide a whole network structure required to operate large single-site organizations such as The Police Department. Since, imlementing such big network gets governmental, legal requirements are also required which have also been mentioned.

Topology that will be suitable for the Police Department Networking

To suggest a topology for the Police department, information about the topologies are also required. But before that, What is a Topology? Topology of a network refers the logical and physical connection between nodes(workstations). Logical Topology explains how the data transfer is going to take place while the Physical Topology is concerned with how the nodes are going to be connected by means of wires, cables or other medium. Why a Topology is required for the network? A topology is required because it gives the network an architecture or a structure to follow which will house the communications between the nodes and on the web. After a through analysis, it has been recommended that a logical Bus implemented as a physical star(Hybrid/Tree) be adopted. Because Bus topology compared to Ring will have communication and data transfer latency but it will be more susceptible to collision which can be prevented through the use of devices like Terminators and CSMA/CD. Physical Star will be most suitable because there will be multiple sites connected to a server. If Star is adopted then multiple sites can be connected with the help of hub/switch to form a centralized structure to the server and also gives centralized control and better reliability.

Internet Connection Requirements for the Police Department

Internet is required by any official departments. So, The Police Departments requires one too. Now, it might get very confusing about what Internet Service will be most suitable for the department. To narrow the search, concentration be put into the requirements of bandwidth and consumers. Since there are great number of bandwidth consumers, whose list will be provided below:

Wrok stations in each office in each district(x4):

District Commander= 1

Deputy District Commander= 1

Seargents= 1

Constables= 5

Detective Squad=21

Total= (1+1+1+5)x(4)+21= 53 Workstations required

Therefore, 53 Workstations total in 4 Districts

Assuming that all of the wokstations more or less is going to be active, high bandwidth is required. Therefore, it is suggested that Cable Broadband Internet Services be implemeted with the high bandwidth package the ISPs has to offer. Calculation will be done to minimum because ISP providers vary from place to place and their related charges. According to the ratio of price to service provided. BDCOM has a very good reputation. Therefore, BDCOM should be chosen. Their package is as follows:

Package: Broadband (Dedicated)- 1mbps*20=20 mbps

Monthly Charge: 20 mbps*38,000 BDT= 7,60,000 BDT

A Two-way voice communication method that can be implemented

There are many methods through which two-way communication could be achieved. They are PTMR, cellular Radio, MPDN and etc. But the system that is popular and implementable is the PTMR(Private Trunked Mobile Radio). PTMR has been used and is still being used by many Police forces around the globe. Therefore, it is perfect for the Townsville Police Department also. This method consists of Radio Devices which can be used to do both talking and hearing though the communication is half-duplex that is why use of phrases such as 'over and out' is essential. Every police officer will be carrying one of the radio devices and base stations will be set up in the district offices and the headquarters. Use of repeaters can also be implemeted if signals are distorted. Repeaters can increase the radius of signals thus, covering more distance. Encryption is encouraged because Police conversation is very important and sensetive so, its leak can create havoc and increase crimes. Signals can be protected through Encryption and prevent from getting captured by Scanners.

There are many legislation requirements for implementing the PTMR. The legislation is directly not named the PTMR rather named BWA(Broadband Wireless Access) which when obtained can be used to register frequency and then the vendor equipment license. There are rules and regualtions to be followed for registration. The rules are as follows:

1.01 The Licensee shall establish, operate and maintain the BWA Services as provided in the License.

1.02 In order to ensure proper competition among the BWA Services licensees, total 3 (three) licenses will be issued to provide nationwide BWA Services in 2.3 GHz and 2.5 GHz spectrum bands. An

additional BWA license (fourth license) may be issued to Bangladesh Telecommunications

Company Limited (BTCL) in the same terms and conditions including the License Acquisition

Fee (to be fixed by way of auction) as shall be applicable to the other BWA licensees.

1.03 Two licenses will be awarded to the prospective Applicant(s) to provide nationwide BWA

Services in 2.3 GHz and one license will be awarded in 2.5 GHz spectrum bands.

1.04 The duration of the Licenses, shall initially be for a term of 15 (fifteen) years. Upon expiry of the initial term, the License may be renewed for subsequent terms, each of 5 years in duration, subject to the approval from the Commission and to such conditions, including the payment of any fees, as may be specified herein and/or by the Commission under the Act.

The operators, within 1 year of issuance of license, shall have to install minimum 5 full fledged Base Station Transceiver (BTS) radio sites in areas covering each Divisional Headquarters and 3 BTS covering each District.

Frequency Range: 2.3 Ghz - 2.5Ghz

Frequency Limitaion: 25 Km radius

Signalling: 5-Tone Advanced Signalling

Channel Spacing: 12.5 Khz

Interference: Co-channel Interference, Adjacent Channel Interference and Intermodulation (Operating frequency range explained, 2008).

Recommendation for Telephone Systems to be purchased

Now, what is left for the police department is a Telecommunication system. The best possible solution is the PBX(Private Branch Exchange). Housing personal machines and equipments to implement a PBX is a big hassle. Therefore, it is popular and advisable that Hosted PBX be implemented. As the name suggests, a provider of PBX will do all the necessary work to implement the PBX and most of the equipments will be in their premises which decreases the cost and problem of maintaining the equipments. And as of privacy and security, the providers can be signed with for a QoS(Quality of Service) which will include rules and regulations of security and privacy of the client's communications through PBX.

A Hosted PBX includes the following costs and charges:

The hardware and setup cost included = 1,30,000 BDT/Month

If something goes wrong with the telephone sets or wiring in the user premesis then the users has to confront the costs. Their monthly cost on PBX requires as follows:

Replacing damages sets= 2,850 BDT/Telephone set

Wiring Replacement= 25 BDT/Feet of wire

Any damage occuring at the provider premesis is maintained by the providers themselves.

Assumptions

BRTC provides license of PTMR through BWA licenses.

Investigation source has concealed right information.

ISP will fulfill the requirements at the claimed price.

PTMR is mostly used in Bangladesh for Two-way communication.

Equipments that are required for PBX are roughly the same as denoted above.

The features investifation source claimed they have for PBX are true and accurate.

Hosted PBX in Bangladesh is at the price claimed above.

PTMR can be implemented in Bangladesh as claimed above.

Legal Requirements obtained from the BTRC web site are accurate.