Advantages Of A Linear Bus Topology Computer Science Essay


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Physical topology is a network configuration of the cables, computers and other peripherals. Physical topology should not be confused, logical topology; the approach is to pass information between workstations.

Topology can be divided into the following three types:

Linear bus topology consists of a main terminal at each end to run cables. All nodes (file server, workstations and peripherals) connected to the linear cable.


Design star topology with each node (file server, workstations and peripherals) connected directly to a central network hub, switch or concentrator. Data on the stars through a network hub, switch or hub, and then continue to its destination. Hub, switch, or centralized management and control of all functions of the network. It can also be used as repeater data stream. This configuration is common twisted-pair cable, but it can also use coaxial cable or fiber optic cable.

Figure 2

Tree or Expanded Star

Characteristics of the tree topology, combined with the linear bus and star topologies. It consists of groups of star configuration workstation connected to a linear bus backbone cable. Tree topology to allow expansion of existing networks, so that the school configure the network to meet their needs.

Advantages of a Linear Bus Topology

Easy to connect a computer or peripheral to a linear bus.

Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

Entire network shuts down if there is a break in the main cable.

Terminators are required at both ends of the backbone cable.

Difficult to identify the problem if the entire network shuts down.

Not meant to be used as a stand-alone solution in a large building

Advantages of a Star Topology

Easy to install and wire.

No disruptions to the network when connecting or removing devices.

Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

Requires more cable length than a linear topology.

If the hub, switch, or concentrator fails, nodes attached are disabled.

More expensive than linear bus topologies because of the cost of the hubs, etc

Advantages of a Tree Topology

Point-to-point wiring for individual segments.

Supported by several hardware and software venders.

Disadvantages of a Tree Topology

Overall length of each segment is limited by the type of cabling used.

If the backbone line breaks, the entire segment goes down.

More difficult to configure and wire than other topologies. [1]

I recommend using star topology, because it is easy to expand the network to another concentrator, cable easy to install, no network connection interruption, easy to check and delete a part of the fault, and lower costs.

In the choice of using the topology must have the following factors:

Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.

Length of cable needed. The linear bus network uses shorter lengths of cable.

Future growth. With a star topology, expanding a network is easily done by adding another concentrator.

Cable type. The most common cable in schools is unshielded twisted pair, which is most often used with star topologies.

Easy to install and wire.

No interruption of the network connection or remove equipment.

Easy to detect faults and deleted.

From the above conditions, I recommend using the star topology, because it is easy to expand the network to another concentrator, wire easy to install, and no network connection interruption, easy to check the fault and remove a part of the emergency demand for the service conditions are met, and lower costs.

The Internet is a collection with a large global network of many networks and collaborative form of work: each network servers, communications equipment and wiring, etc., and directing the flow of data. More than one hundred countries and millions of users have on their computer is connected to this global network, forming a community, to exchange data, the new open and messages.

Internet services provided by major suppliers are as follows:

• Dial-up Internet connection service

• Integrated Services Digital Network (ISDN) Internet Service

• DSL Internet access services (including ADSL, VDSL, etc.)

• Cable Modem Internet Services

• Fiber Internet Services (FTTx services)

• Line (Leased Line) Internet Services

• Hosting (Collocation) Service • E-mail (E-Mail) Services

• Web Hosting Service

Part of the ISP company also will provide the following services︰

• Internet broadcasting, such as iTV, online music, etc.

• Wireless communications, including Wi-Fi, satellite communications, etc.

• Mobile Internet, such as GPRS, WEP, EDGE, HSDPA, W-CDMA etc.

To know the connection speed, we must first understand the process of data transmission, transmission data flow can be divided into the following two types:

The private to the private

Simple process is as follows, given a certain Internet companies to quickly refer to know your computer Whether with the minimum requirements, if not the Internet can not be said is in compliance with the slow pace of the problem is ISP; if the case is in compliance, transmission speed is being affected by their ISP and the speed of the other ISP, can not send files because the Internet is slow to medium ISP is a slow given the company, it may be friends of the ISP because they can not slow high-speed transfer files. Own computer from sending a file to a friend's computer, which processes are:

Your computer's hard drive -> home CAT5-> Machine Building -> transmission lines (such as optical fiber, coaxial cable) -> your ISP-> transmission line -> other ISP-> transmission line -> Machine Building -> home CAT5-> friends computer's hard drive.

A private local business type

Similarly, the computer is in compliance with the minimum requirements do not need to consider their own computer equipment, by the following knowledge, the speed being affected by your ISP and web server processing speed and the impact of its broadband, is not considered the speed of their ISP, a low-end server, slow processing speed of course, who can deal with relatively high-end feel a lot of data flowing. Downloaded from the Internet open a file, the process is:

Your computer's hard drive -> home CAT5-> Machine Building -> transmission lines (such as optical fiber, coaxial cable) -> your ISP-> transmission line -> DNS-> server on the network -> transmission line -> your ISP-> transmission line -> Machine Building -> home CAT5-> own


ISP speed of the affected factors:

a) The target server's processing capacity

b) The target server to provide broadband

c) Whether during busy time, because the server is busy and slow server or a lot of people make broadband Internet access less than

d) Speed of the other ISP

e) The other computer is busy (such as other open drug, watching movies and then send the file to be slow)

f) Their own computer set

g) Whether shared broadband, wired or wireless ROUTER

h) May be virus and even less RAM the Internet slow (their computer problems)

ISP (Internet Service Provider) which provides Internet services company, also known as the network provider. Part of the telecommunications company will also provide communications and other Internet services.

Hong Kong's Major Internet providers are as follows:

Netvigator Broadband

Netvigator is Hong Kong first broadband Internet service, coverage up to 97% (by xDSL technology transfer). Netvigator provide a range of choices for customers of broadband services, currently has more than one million users, for customers in Hong Kong has the largest broadband company.

Hong Kong Broadband Network Limited

Hong Kong Broadband is one of Hong Kong ISP, established in 1999, positive self-built network infrastructure with advanced technology to provide customers with a wide range of fixed telecommunications network services. Currently, Hong Kong Broadband provides fiber optic services, but also offers broadband Internet, voice, digital TV and corporate data services.

i-CABLE Broadband

In January 2000, i-CABLE started to provide home to share broadband Internet access service, its price is lower than its competitors, four in Hong Kong one of the broadband network service providers, but the form of i-CABLE is to provide broadband sharing service, when the increase in the number of users, users will be able to share less and less bandwidth, Internet sharp decline in the quality and speed, resulting in unstable connections, often not even the case of foreign websites.

HGC (Hutchison Global Communications)

HGC main business is to provide voice and data communications services, medium-sized computer systems integration, software development and provision of related services, distribution of computer products. Broadband services, including "Residential Broadband" and "Union of broadband" Internet services.

Above four network services provided by suppliers are able to meet the requirements of the program. [3]

Select Internet Service Provider in the plan, requires four conditions:

Network connection speed

Network stability

Network coverage

Network service charges

The following are the four ISP connections to upload and download test speed comparison

The chart shows in Hong Kong Broadband Upload speed better than the other Providers

The chart shows in Hong Kong Broadband Download speed better than the other Providers

The chart shows Netvigator Broadband Providers in the coverage ratios of other advantages.

The chart shows Netvigator Broadband connection stability better than other Providers

The following is a list ISP service charge, but does not include installation and pre-paid fees:

Netvigator Broadband

Hong Kong Broadband


HGC (Hutchison Global Communications)

From the above analysis, the network connection speed the performance of Hong Kong Broadband is the best, and the price charged is not the highest, but it is not wide coverage, and the connection speed instability, and i-CABLE Broadband connection speeds, and HGC in and the price charged is not ideal, so I recommend using Netvigator Broadband, Though connection speed is not the best and the price charged is not the lowest, but its most wide coverage of 97%, the connection is stable and can meet the needs of emergency services.

Communication system consists of two major cable systems and wireless systems part. Cable system is mainly used as the backbone network contains the optical fiber, cable, ADSL, etc., which is very wide bandwidth, the transmission rate is also relatively large, so easy to cause communication delay. As the use of public spectrum wireless systems, each distribution system operators have limited bandwidth, limited by its data transmission rate easier, easier to become a communications bottleneck.

Wireless communication systems:

Mobile phone (two-way)

GSM (Global System for Mobile Communication) based. The digital-type (digital) systems and time division multiplexing (TDMA) technology. Including the 900 MHz (ie GSM900) and 1800 MHz (GSM1800 or the DCS1800) the two bands.

Mobile data communication (two-way)

Mobile data refers to the case of the mobile user can transmit data using radio communication channels for information, two-way data receiving and transmitting messages. 500MHz and 800MHz bands, does not provide voice communications services.

Paging system (double / single)

Simple wireless communication systems. Traditionally one-way paging, two-way paging services abroad in recent years.

Relay wireless telephone (two-way)

Trunked Radio System can be divided into traditional and multi-channel relay two types. Most of the traditional single-frequency analog systems only provide voice communication capabilities; multi-channel relay type is used to provide voice and non-voice communication services. Efficient multi-channel relay type, number of channels can be formed within a group can automatically search for free channels in the group of channels to users; and traditional only in its dedicated channel assigned only after waiting for their free use.

Dedicated Short Range Communication (two-way)

Regional communications side of the road system for communication with the vehicles or pedestrians range from 3 to 100 meters coverage support vehicles and communications workshop.

Subcarrier broadcasting system (one-way)

Subcarrier broadcasting system is accompanied by major sub-carrier signal; the use of the radio stations (mainly for the FM radio station) is assigned to the next unoccupied band to bring to pass. Subcarrier can be voice and data together with data transmitted through the same channel, but requires a special receiver to handle the reception of digital information channel section.

Digital broadcasting (one-way)

Digital broadcasting (DAB) using advanced digital signal processing (ie, frequency division multiplexing, OFDM), audio compression and channel coding technologies to provide CD-quality audio service and data services. DAB is the single frequency network system, do not like the FM transmitter signal to prevent overlap of the two regional interference, can not use the same frequency. DAB uses OFDM as modulation, which can effectively overcome the receiving device due to the Doppler Effect produced by movement and terrain factors caused by multipath interference. [8]


1. This licence shall not be construed as granting any exclusive rights to the licensee in the provision of the Service.

2. This licence replaces any licence, however described, which the Authority may have granted to the licensee for the Service.

3. The licensee shall at all times and from time to time during the continuance of this licence operate, maintain and provide the Service in a manner satisfactory to the Authority.

4. The licensee shall at all times perform and observe the requirements of the Constitution and Convention of the International Telecommunication Union and the regulations and recommendations annexed to or made under the Constitution and Convention as are applicable to the Hong Kong Special Administration Region except to the extent that the Authority may in writing expressly exempt the licensee from such compliance.

5. (1) Notwithstanding regulation 8(1) of the Telecommunications Regulations (Cap. 106 sub. leg.), the licensee may with the prior written consent of the Authority transfer this licence and any permission, right or benefit under this licence.

(2) The consent of the Authority shall be subject to such conditions as the Authority thinks fit.

(3) If the licensee transfers the licence or other right, the licensee shall give the Authority a true copy of the transfer document within 2 months of the date of the transfer.

6. (1) Each land station or land earth station shall be used only at the location and with emissions at the frequencies and of the classes and characteristics specified in Schedule 2, and with such power and aerial characteristics as are specified in Schedule 2 in relation to the class and characteristics of the emission in use.

(2) The apparatus comprised in each land station or land earth station shall at all times comply with the technical and performance standards as may be prescribed by the Authority and specified in Schedule 2.

(3) The apparatus comprised in each land station or land earth station or mobile station or mobile earth station (being a mobile station or mobile earth station used by the customer of the licensee) shall be so designed, constructed, maintained and operated that its use does not cause any avoidable interference with any radio communications.

(4) Each land station or land earth station shall be operated only by the licensee or a person authorized by the licensee in that behalf. The licensee shall not permit or suffer any person not so authorized to have access to the apparatus comprised in each land station or land earth station. The licensee shall ensure that persons operating each land station or land earth station observe the conditions of the licence at all times.

(5) The licensee -

(a) Shall not make any change -

(i) In any land station or land earth station; or

(ii) In the address at which each land station or land earth station is installed, without the prior approval in writing of the Authority; and

(b) Shall return this licence to the Authority for amendment when a change referred to in sub-subparagraph (a) has been effected.

(6) If power for the working of any land station or land earth station is taken from a public electricity supply, no direct connection shall be made between the supply mains and the aerial.

(7) If any land station or land earth station aerial crosses above or may fall or be blown onto any overhead power wire (including electric lighting and tramway wires) or power apparatus it shall be guarded to the reasonable satisfaction of the owner of the power apparatus concerned.

(8) The licensee shall take all reasonable measures to ensure that customers of the Service do not cause interference to other users of radio communications and shall take all the necessary measures to stop such interference as may occur.

7. The apparatus operated by the licensee shall be operated only on such radio frequencies as the Authority may assign to the licensee and the Authority may refuse to assign further frequencies or require the licensee, by notice to him, to cease to operate the apparatus on any frequency previously assigned to him if in the opinion of the Authority the licensee is not making efficient use of that frequency.

8. The Authority may, by giving not less than 12 months' notice in writing to the licensee, require him upon such date as may be specified in the notice to cease using any frequency previously assigned to him by the Authority and to use such new frequency as the Authority may designate.

9. The licensee shall not enter into any agreement or arrangement whether legally enforceable or not which shall in any way prevents or restricts competition in relation to the operation of the Service or any other telecommunications service licensed by the Authority.

10. In this licence - "land earth station" means an earth station in a mobile-satellite service not intended to be used while in motion; "land station" means a station in a mobile service not intended to be used while in motion; "station", "earth station", "mobile service", "land mobile service" and "mobile-satellite service" have the same meanings as defined in the Radio Regulations annexed to the Constitution and Convention of the International Telecommunication Union. [10]

Allocation of radio frequencies

The TA manages all spectrum use in Hong Kong. Information on spectrum allocations in Hong Kong is made publicly available in the Hong Kong Table of Frequency Allocations (HKTFA). This contains information on the Region 3 allocation, the Hong Kong allocation and the mix of uses in the band and, in some cases, the frequencies allocated to each use.

Policy initiatives that will be undertaken by the CTB and OFTA for the period July 2005-June 2007 are published and these include spectrum related activities: specifically analogue to digital terrestrial TV migration, the framework for the deployment of BWA and the commissioning of this study. In addition, OFTA publishes an annual statement of the major tasks and projects it intends to undertake in the year ahead and these include numerous spectrum related activities. OFTA does not produce a statement of its plans for future release of spectrum. However, it often brings position papers on allocation and other issues to the Radio Spectrum Advisory Committee (RSAC) for discussion in advance of formal consultation. The papers submitted to the RSAC are published as are the agendas and meeting minutes. This gives a degree of transparency concerning OFTA's plans, however, industry participants would like to see more information on existing spectrum use, currently available spectrum and future spectrum releases in the public domain so that they can better plan their wireless investments and make better informed decisions concerning which spectrum they should bid/apply for. For example, OFTA may release a number of frequency bands at 2GHz that could be used to provide potentially competing mobile broadband services. The allocation and re-allocation of the use of spectrum is decided by the TA in consultation with industry, other interested parties and the RSAC. There is no requirement to undertake impact (or cost benefit) analysis for allocation decisions though we understand this is sometimes done informally by OFTA. The majority of allocations to licence exempt use are designated in an order issued under the TO. As a general rule the bands conform to internationally harmonized bands for licence exempt services in Region 3. [11]

c) Costs of setting up and operating the system, including licensing costs, equipment costs, etc. (6 marks)

Radio Relay Station Licence

It is to be issued a license valid until the year of the next year, until it has been issued in the next month until the first day of the month, the license may be renewed each year subject to the discretion of the Secretary of the restrictions. When the cost of the license is issued or renewed, they should pay $750.

Mobile Radio System Fixed Station Licence

It is to be issued a license valid until the year of the next year, until it has been issued in the next month until the first day of the month, the license may be renewed each year subject to the discretion of the Secretary of the restrictions. When the cost of the license is issued or renewed, they should pay $750.

Mobile Radio System Mobile Station Licence

It is to be issued a license valid until the year of the next year, until it has been issued in the next month until the first day of the month, the license may be renewed each year subject to the discretion of the Secretary of the restrictions. When the cost of the license is issued or renewed, they should pay $270. [12]

Reasons for wireless communication interference

Today, wireless communication interference may cause radio interference because the reasons are increasing, some of the obvious easy to follow, some are very subtle, difficult to identify findings. Although carefully designed transceiver and base station can provide some protection, but in most cases only the interference signal at the transmitter at the source control.

Radio frequency interference signals will give the coverage area wireless communications base station within the mobile communications has brought many problems, such as dropped calls, connection emergence of the noise, channel leakage and receive voice quality is poor and so on.

Today, the complexity of the latest and most advanced telecommunications technology mus also be with the old communication system (such as dedicated wireless communications or paging, etc.) coexist in a complex environment, other wireless RF devices such as digital video broadcasting and wireless local area network, etc. will produce new may signal disruption of existing communications services. Increasing due to environmental constraints. With mobile phones we use more and more frequent contact and communication will become more crowded skies.

Interference can be classified according to their own characteristics, but also can be base stations and mobile communications of its influence to points, the frequency of conflict is the source of interference and interference results show the most commonly used indicator.

Cause-of-band interference

This is a major interference, including some close to the receiver without the same high frequency signal, large enough to affect the strength of the input. These signals are usually very close to the scheduled frequency, although the receiver input filter will filter out other signals a huge difference.

In-band interference causes

Second communication signal interference and the frequency of the same book (whether strong or weak), usually caused by the following conditions:

‧ Normal mobile phone signal power beyond the scope of its intended.

‧ Transmitter normal fault or incorrectly configured.

‧ Normal harmonic signal transmitter.

‧ Other electrical devices no intention of interfering signals radiated. [13]

Voice over Internet Protocol (IP Voice, VoIP) is a general term used for the family approach, communication protocols, and transmission technology, multimedia conferencing and voice communications to provide Internet Protocol (IP) networks, such as the Internet. Frequently encountered in other areas, often is a synonym for Internet telephony using IP telephony, Internet telephony, voice, broadband (broadband voice), broadband phone, and broadband phone. [14]


Integrated Services Digital Network (ISDN) is a set of communication standards for synchronous digital transmission of voice, video, data and other network services over traditional circuit-switched public telephone network. Prior to the ISDN, the telephone system is seen as a way to transmit voice, some special services, can be used for the data. The key features of ISDN are that it integrates voice and data in the same line, adding features, not available in the classic telephone system.

There are several types of access ISDN interface is defined as the Basic Rate Interface (BRI), Primary Rate Interface (PRI) and broadband ISDN (B-ISDN) in the. ISDN is a circuit switched telephone network system, the system also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in better voice quality than can analog phone can provide. It provides circuit-switched connection (either voice or data), and packet switched connection (data). [15]

Bearer Services

Bearer service is a telecommunications term refers to services that enable information transfer signals between the network interfaces. These services give users the ability required for the appropriate signal between the transmissions of certain access points, the user network interface.

Bearer services include the following:

1) The interest rate adjustment sub-rate information, such as circuit switched data, synchronous and asynchronous duplex 300-9600.

2) Voice and data exchange in the call, the alternate voice and data.

3) The choice of modem, choose 310 kHz audio services, as between work and ISDN. [16]


When they turned to the remote service calls forwarded to volunteer their homes (or sometimes to the phone.) Cell phones are not encouraged, but acceptable, as long as the good, the reception is almost no background noise. Many call the remote service requested information about the meetings and activities. [17]

Supplementary services

Supplementary services is a set of network layer protocol functions, providing call independent functions for mobile phones. These include: call forwarding, follow me, consulting fees, reverse charging, etc. [18]

ISDN installation costs vary widely, from carrier to carrier, and sometimes may be abandoned. After customers buy equipment and pay installation, the following monthly recurring costs for both types of ISDN: line charges, local telephone (such as measurement services) and long distance telephone charges. Monthly line charges for the ISDN BRI are $ 50 and 150. The ISDN PRI lines typically cost 300 yuan and 1,000 yuan. Local telephone and long distance telephone charges are the same as standard voice telephone call rates. [19]

Telephone Company will install all necessary in their end, but you must have a different ISDN devices connected to the computer work. You can use an ISDN modem or ISDN router. If you want to connect multiple computers share a network connection, you also need to install network cards and cables. [20]

To select a Cisco router with the appropriate ISDN interface, do the following:

Determine whether the router supports ISDN BRI. Look on the back of the router for a BRI connector or a BRI WAN Interface Card (WIC).

Determine the provider of the NT1. An NT1 terminates the local loop to the central office (CO) of the ISDN service provider. In North America, the NT1 is part of the Customer Premise Equipment (CPE). This means that the customer must supply an NT1 device or a device with integrated NT1 functionality. In North America, ISDN routers are typically equipped with ISDN BRI-U interface cards to provide NT1 functionality. In Europe, the service provider supplies a separate NT1 device. Therefore, the customer supplies an ISDN capable device to connect to the NT1, such as a router with an ISDN BRI-ST interface.

If the NT1 is built into the CPE, the router should have a U interface. If the router has an S/T interface, then it will need an external NT1 to connect to the ISDN provider.

If the router has a connector labeled BRI then it is already ISDN-enabled. With a native ISDN interface already built in, the router is a TE1 and will need to connect to an NT1. If the router has a U interface, it also has a built-in NT1.

If the router does not have a connector labeled BRI, and it is a fixed-configuration, or non-modular router, then it must use an existing serial interface. With non-native ISDN interfaces such as serial interfaces, an external TA device must be attached to the serial interface to provide BRI connectivity. If the router is modular it may be possible to upgrade to a native ISDN interface, providing it has an available slot. [21]

If a major terrorist attack or war, no fixed power and telephone lines were broken, we can use the following equipment:

Mobile data communication (two-way)

Mobile data refers to the case of the mobile user can transmit data using radio communication channels for information, two-way data receiving and transmitting messages.

Dedicated Short Range Communication (two-way)

Regional communications side of the road system for communication with the vehicles or pedestrians range from 3 to 100 meters coverage support vehicles and communications workshop.

In emergency cases, is still able to maintain limited communications, and issue a message supported.

I propose the establishment of fire departments within the network (LAN) technology using the star topology, because it is easy to extend the network and check for errors, and ISDN telephone systems should be used because of its multi-function, and in line with computer network and broadcast systems.

In the computer network provider selection, I recommend using Netvigator Broadband, though connection speed is not the best and the price charged is not the lowest, but its most wide coverage of 97%, the connection is stable and can meet the needs of emergency services.

I recommend using the communications system, including imitation of the four communications: Mobile phone (two-way); Mobile data communication (two-way); Dedicated Short Range Communication (two-way); Digital broadcasting (one-way).

They have different functions in different environmental conditions can communicate, adapt to any emergency situation.

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