History Of The Bus Topology

A bus topology is a network set up in which nodes are connected to a segment of cable in the logical shape of a line, with a terminator at each end. A bus topology connects each computer or nodes to a single segment trunk. All nodes on the network share a common bus and use a multi-drop transmission medium. Bus network allows only one device to transmit at a time. A distributed access protocol determines which station is to transmit. The signal goes from one end of the bus to another. A terminator is needed at each to cut down the signal so it does not reflect back across the bus. CSMA/CA, media access method, is used to control the collisions that take place when two signals placed on the wire at the same time.

There are two types of bus topology: Linear Bus Topology and Distributed Bus Topology. In Linear Bus Topology, all nodes of the network are connected to a common transmission medium which has exactly two endpoints. Distributed Bus in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium.

Bus networks do best with a limited number of devices. If more than limited computers are added to a bus, performance problems will be result. If the backbone cable fails, the entire network effectively becomes unusable.

Fig: Bus Topology

Ring Topology

Ring network topology has no central server and connects computers in a circle of point-to-point connections. Each node handles its own applications. And also shares resources over the entire network. If one node becomes break down, the others are still able to maintain contact with one another. Such a network is best for decentralized systems because no priorities are required.

The signal is transferred through a token for one station to the next. When a station needs to transmit, it grabs the token, attaches data and an address to it. And then routes it around the ring. The token travels along the ring till reaches the destination address. The receiving computer replies an acknowledgment to the sender source. The sender then releases the token for use by another computer. Each station on the ring has equal access but only one station can use token at a time. To allow an orderly access to the ring, a single electronic token passes from one computer to the next around the ring. A computer can only transmit data when it captures the token

Fig: Ring Topology

Star Topology

A star topology is one of the most use common network topology where each of the devices and computers on a network connect to a central hub or sometimes just a switch. On a star network, data passes though the hub to its destination. The hub manages and controls all functions of the network. It also performs as a repeater for the data flow. In a star network, the entire network is dependent on the hub so if there is a problem with the hub, the entire network is not working. This makes it easy to troubleshoot by offering a single point for error connection and at the same time the dependency is also very high on that single point. Every computer in the network is safe when the hub is safe. This type of network also offers more privacy than any other network.

The star network topology requires more cable than the usual Bus topology. A common cable that is used in star network is the UTP or the unshielded twisted pair cable. Another common cable that is used in star networks is the RJ45 or the Ethernet cables.

If one computer fails in the network, it does not affect any other computer in the network and the purposes of this computer can be easily changed to the next computer easily using the controls of hub. In a Star Network Topology it is possible to have all the important data backups on the hub in a private folder so if one computer fails, it can still use data using the next computer in the network and accessing the backup files on the hub.

New devices or nodes can easily be added to the Star Network by just extending a cable from the hub. Because of the hub controls everything, the addition or removal of devices are done using the hub. If the hub adds a device such as a printer or a fax machine, all the other computers on the network can access that new device by accessing the hub. The device is no need to be installed on all the computers in the entire network. The central function is cost effective and easier to maintain.

Fig: Star Topology

Mesh Topology

A type of network configuration where each of the computers and network devices are interconnected with one another allows for most transmissions to be distributed even if one of the connections goes down. This type of topology is not commonly used for most computer networks because it is difficult and expensive to have redundant connection to every computer.

In Mesh network, it can route data, voice and instructions between nodes. It allows for continuous connections and reconfiguration around broken or blocked paths by hopping from node to node until the destination is reached. A mesh network whose nodes are all connected to each other is a fully connected network. The network can still operate even when a node fails or a connection goes bad.

On a mesh network, messages can send via any of several possible paths from source to destination. It employs one of two connection arrangements, full mesh topology or partial mesh topology. In the full mesh topology, each node is connected directly to each of the others. In the partial mesh topology, some nodes are connected to all the others, but some of the nodes are connected only to those other nodes with which they exchange the most data.

Fig: Mesh Topology

Different types of cables

Different types of network cables are used depending on the kind of network. The type of cable used for a network depends on the network’s topology, protocol, and size. If a network has large number of network devices, it will need cables that provide high speed and error free connectivity.

Some of the cables being used today are Unshielded Twisted Pair (UTP) cables, coaxial cables and fiber optic cables. The UTP cable is the most popular variety, largely used for school networks as it transfers data at 100 mbps. Coaxial cables have a single copper conductor at their center. A plastic layer provides insulation between the center conductor and the braided metal shield. The outer metal shield blocks out outer interferences such as lights, motors and other computers. Fiber optic cables consist of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals and transfers signals over much longer distances than coaxial and twisted pair cables.

Network cables are the backbone of any network. However, today several networks are switching over to other mediums of data transfer such as high frequency radio signals, and infrared light beams to connect the workstations. These systems are not only fast and effective, but also do away with the problem of maintain several hundred feet of cables spreading across the workspace. With such technologies coming to the forefront, the future may well tilt in favor of wireless systems.

10Mbps Networking

Standard

Cable Type

Segment Length

Connector

10Base2

Thin Coaxial

185 meters

BNC

10BaseT

Category 3, 4, 5 twisted pair

100 meters

RJ-45

10BaseFL

Fiber-optic

2000 meters

SC/ST

b) Advantages and Disadvantages of medium.

Media Type

Maximum Segment Length

Speed

Cost

Advantages

Disadvantages

UTP

100 m

10 Mbps to 1000 Mbps

Least expensive

Easy to install; widely available and widely used

Susceptible to interference; can cover only a limited distance

STP

100 m

10 Mbps to 100 Mbps

More expensive than UTP

Reduced crosstalk; more resistant to EMI than Thinnet or UTP

Difficult to work with; can cover only a limited distance

Coaxial

500 m (Thicknet)

185 m (Thinnet)

10 Mbps to 100 Mbps

Relatively inexpensive, but more costly than UTP

Less susceptible to EMI interference than other types of copper media

Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network

Fiber-Optic

10 km and farther (single-mode)

2 km and farther (multimode)

100 Mbps to 100 Gbps (single mode)

100 Mbps to 9.92 Gbps (multimode)

Expensive

Cannot be tapped, so security is better; can be used over great distances; is not susceptible to EMI; has a higher data rate than coaxial and twisted-pair cable

Difficult to terminate

c) Recommendation.

Star topology would be the best way to use for renewing Townsville Police Department Network infrastructure because of in-house network (LAN) structure. Star topology should be also used for following reasons.

Easy to install and reconfigure.

No disruptions to the network when connecting or removing devices.

Easy to detect faults and to remove parts.

Less expensive.

Includes robustness, that is, if one link fails, only that link is affected, other links remain active.

It has been said that Townsville Police Department covers an area of 100 square kilometers and Townsville is divided into four districts (Northern, Eastern, Western and Southern). For that reason, the switch should be placed in the center of four districts. So, the network cable must cover 50 kilometer and the switch must be gigabit Ethernet. Therefore, UTP with cat6E is the most suitable network for such an area of network.

Category 6 UTP

Category 6 supports gigabit Ethernet and is recognized by standards bodies as supporting 10GBASE-T, however there are limitations that must be considered. The IEEE 802.3an standard cites a 55 meter distance limitation for standard category 6, which is not universally agreed upon within the TIA and ISO standards.TIA TSB 155 recently released a Technical Service Bulletin covering additional parameters for running 10GBASE-T on standard category 6. In this document a 37 meter distance limitation is referenced for 10GBASE-T on standards compliant category 6 systems. Between 37 meters and the IEEE referenced 55 meters, standard category 6 may support 10GBASE-T, but it is possible that the installer may have to use alien crosstalk mitigation techniques such as unbundling cables or replacing patch cords to improve the electrical parameters to allow 10GBASE-T to work properly. Above 55 meters, it is unlikely that category 6 UTP would work properly without a large amount of mitigation to reduce alien crosstalk. A key takeaway is that using category 6 UTP for 10GBASE-T should be focused on existing installations, not new installations. The choice for new installations designed to support 10GBASE-T should be augmented category 6 UTP, STP or optical fiber systems.

Category 6 Advantages

» Cost and size of media, relative to augmented category 6 and STP

» Installed base – currently the dominant UTP cabling standard

» Installation – widely accepted

Category 6 Disadvantages

» Limited distance for 10GBASE-T

» External noise suppression at 100 m, relative to shielded systems or augmented category 6

Task 2

Nowadays, there are several usages of Internet by means of so many ways. There are three basic Internet services:

Information (browsing, online-shopping, etc.)

Communications (mail, chat, Video conferencing, etc.)

Files sharing (downloading, uploading, etc.)

The connecting suitable for above severs are as follows:

For Information service:

It can cover only 100 Kbits/s usually prove adequate.

For Communication:

For video conferencing, bandwidths of no more than 384 Kbits/s usually prove adequate. As for chatting communication, especially for yahoo chat, 28 Kbits/s should be enough.

For File Sharing:

As for file sharing, bandwidths of more than 1 Mbit/s are most suitable.

c) The Internet Service Provider in Myanmar

Myanmar Posts and Telecommunications

The Myanmar Posts and Telecommunications (MPT), is the sole provider of telecommunication services in Myanmar. It is a Government Agency, operating under the Ministry of Communications, Posts and Telegraphs. It was founded in 1884 as a small Department of Posts and Telegraphs and has grown into the present day Myanma Posts and Telecommunications with approximately 13800 employees of which about 380 are managerial level staff. The present organization is headed by the Managing Director and a General Manager as his deputy. There are nine major departments operating under respective deputy general managers/chief engineers in the fields of administration, works and inspection, planning, training, finance, stores, automatic telephones, overseas communications and long distance communications. The three main categories of services rendered by MPT are the postal services, telegraph services and telephone services, for both domestic and international communications.

Since, there is only one ISP in our country (Myanmar); we have to use MPT (Myanmar Posts and Telecommunication) as an ISP for our country.

Task 3

a)

Methods of Two-Way Voice communications

Two-way voice communications (radios) are essentially available in three types:

Hand-held portable,

Vehicle-mounted mobile, and

Desktop-base station

There are also unique two-way radio devices such as indoor and outdoor call boxes and one-way radio receivers for wireless paging.

Hand-held portable two-way radios are the walkie talkie type of radios. As ruled by the FCC (Federal Communications Commission), hand-held radios may not have more than 5 watts of power.

Vehicle-mounted mobile two-way radios mount in a car or truck and they use the vehicle’s battery for power. They may have their own antenna, but better range is achieved by using an externally-mounted antenna.

Desktop base station radios use wall AC power and they too may have a built-in antenna, but this antenna may be disconnected and then connected to cable that leads to an external-mounted antenna. The higher the antenna is mounted, the better the range.

The vehicle-mounted mobile radios are usually used as base stations by just adding an AC to DC power converter.

Mobile and Base station radios are usually more powerful than hand-held radios and may have as much as 100 watts of power.

Frequencies

There are two major frequency formats for two-way radios. They are Ultra High Frequency (UHF) radio and Very High Frequency (VHF) radio. Neither frequency band is inherently better than the other. They each have their pluses and minuses. Both formats are effective ways to communicate with another person.

UHF radio

The UHF radio band for commercial radios is between 400 – 512 MHz. Until recently, it wasn’t widely used. Now, the UHF radio frequency is used for two-way radios, GPS, Blue-tooth, cordless phones, and WiFi.

VHF radio

The VHF radio band for commercial radios is between 130 – 174 MHz. FM radio, two-way radios, and television broadcasts operate in this range.

Both UHF and VHF radios are prone to line of sight factors, but VHF a little more so. The waves make it through trees and rugged landscapes, but not as well as UHF frequencies do. However, if a VHF wave and a UHF wave were transmitted over an area without barriers, the VHF wave would travel almost twice as far. This makes VHF easier to broadcast over a long range.

Two-way radios, hand-held portable, vehicle-mounted mobile and desktop base station are full duplex.

Legal requirement for operation system

Two -way radio devices

Two-way radio power

Antennas

Channel usages

FCC Licensing

Audio Accessories

Cases, Holsters, and Belt Clips

Batteries

Repeaters

Drop-in Charger

Multi-charging Units

Selectable Power

Operators

Administrators

Control station

Additional and optional knowledge of two-way voice communication technology

Overall knowledge of how to use a selected two-way voice communication device

Costs of setting up and operating the system in my country

As for hand-held two way voice communication device, according to amazon.com, the costs are as follows:

For Cobra CTX400 GMRS/FRS 2-Way Rechargeable Radio with Hands-Free Operation (Pair)

$36.88

For Townsville Police Department, total cost for using hand-held two way voice communication device is up to $2065.28.

d) Limitations of each method (interference, range, etc.).

Product Features

22 Mile Range, 22 Channels & 121 Privacy Codes

10 Channel NOAA radio & Hands-free operation (VOX)

8 Rechargeable AAA batteries, and a 2 port desk charger included

Maximum range extender and belt clip included for maximum efficiency and carrying ease

Lead-Free, Eco-Friendly Packaging

e) As for following feature Highlights, tow way voice communication should be set up.

VOX

The Voice Activated Transmit (VOX) feature enables us to use our radio “hands free.” When VOX is turned on, the radio will automatically begin transmitting when we speak, without pressing the push-to-talk button. VOX works well for any application.

On most VOX-capable radios there is a slight delay between when we start speaking and when the microphone turns on so the first part of the conversation may be clipped. Most radio users overcome this by repeating the first word.

Military Specification Standards

In an effort to achieve standardization objectives for purchases of products used by the military and other government organizations, the U.S. Department of Defense created standards that these products must meet. We will see these standards called military standard, “MIL-STD”, or “MIL-SPEC.” These standards ensure products meet certain requirements, commonality, reliability, compatibility, and similar defense-related objectives.

According to Military Specification Standards, Townsville Police Department should be used Cobra CTX400 GMRS/FRS 2-Way Rechargeable Radio.

Task 4

a)

Since AVAYA IP Office 4.0 is only software for PBX telephone system, the main equipment that would be installed is only software. The procedure for the installation is as follows:

Installation

To establish and maintain an IP DECT installation, a network infrastructure is assumed, which comprises at least the following components:

IP Base Stations

IP DECT phone

IP Office

TFTP server (which can be the IP Office or 3rd Party)

Depending on the operational requirements the following services should be provided:

DHCP

SNTP

DNS

WML/HTTP

Syslog daemon

b) AVAYA IP Office 4.0 Telephone System (IP DECT)

Digital Enhanced Cordless Telecommunication

The standard (ETS 300 175) essentially specifies the air interface, known as the radio interface. Voice and data can both be transmitted via this interface.

DECT key technical characteristics are:

Frequency range: approximately 1,880 – 1,900 GHz (approximately 20 MHz bandwidth)

10 carrier frequencies (1,728 MHz spacing) with 12 time slots each

Doubling the number of time slots (to 24) using the TDMA process

Net data rate per channel of 32 kbit/s (for voice transmission using ADPCM)

Voice coding using the ADPCM method

Maximum transmission power of 10 mW

GAP Generic

About the IP DECT Base Stations

There are two types of IP Base Station. All IP Base Stations have the same hardware and software capabilities.

Indoor IP Base Station

The indoor IP Base Station is for indoor use only. It can be powered by a mains adapter or by 802.3af compliant power over Ethernet.

Note

For Australia and New Zealand the mains adaptor is not currently supported. Only 802.3af compliant power over Ethernet is supported.

Outdoor IP Base Station

The outdoor IP Base Station can be used outdoors or indoors. The outdoor IP Base Station can only be powered by 802.3af compliant power over Ethernet.

Note

Avaya Power over Ethernet adaptors are non 802.3af compliant, and therefore cannot power the ADMM.

One of the IP Base Station within an IP DECT installation must be chosen (at installation time) to operate as the ADMM. This ADMM mode is in addition to the normal IP Base Station functionality that all the other base stations retain.

c) Costs for installing AVAYA IP office

There are two models of phones: the 3701 and 3711 phones. Avaya Kirk DECT phones (WT9620 and DT20) function on the IP DECT solution, but the functionality is limited.

AVAYA Partner 18D- Digital phone

3 new from $95.00

Avaya 6408D+- Digital phone -multi-line operation

Avaya 5621SWP IP Phone (700385982)

Avaya IP400 Analog Trunk 4 card

Available at external website: Atlas Phones for $199.00

d) Costs for operating the system

Avaya IP Office Smart Card w/Voicemail Pro like new, available at external website: Atlas Phones for $1,095.00.

Premise-based IP PBX systems vary extremely widely in cost and even more so as we look at wide-scale deployments and future growth and additions to a system. A basic premise-based box for a relatively small number of users – say up to 20 in a single location – can cost less than $1,000 excluding the phones themselves. But expansion costs and other branch locations can change the cost equation dramatically. In addition, we will have ongoing costs related to connection to the regular phone system and whatever connection costs are imposed by our backbone supplier. These ongoing costs are nevertheless going to be considerably lower than any other form of phone system. They should be lower than hosted VoIP solutions, and they will be dramatically lower than any older PBX and telecommunications provider.

Phones are an additional cost, but when buying a premise-based IP PBX system, we often have greater flexibility than in any other arrangement. We can choose to go with very low-cost, no-name or bottom-of-the-line phones (which are still perfectly capable) all the way up to top-notch phones from manufacturers such as Polycom and Siemens that provide usability benefits (although often at a price premium).

For Townsville Police Department, AVAYA Partner 18D- Digital phone should be used up to 6 base stations as for details, one Headquarter Reception Area, four Districts, and one serious crime squad.

e) Recommendation for AVAYA

The IP DECT solution delivers all the benefits of IP-based converged communications with the convenience of “in-building” wireless communications. Designed to support a large number of users, the IP DECT system enables users to carry a wireless phone and get full access to all the features they are accustomed to using at their desk phone. The IP DECT solution, which connects to the IP Office using a variant of the H.323 protocol, can support users in different offices that are connected via a WAN. An IP DECT cordless handset can travel from one office to another, making and taking calls.

The DECT over IP system comprises the following components:

At least one IP Base Station connected over an IP network and offering IP DECT as a wireless interface.

A maximum of 32 IP Base Stations are supported.

IP Office Small Office Edition, IP Office 406v2, 403, 406v1 or 412 with available VCM resources.

IP DECT phone: Avaya 3701 and Avaya 3711 wireless phones.

A maximum of 120 IP DECT phones are supported.

Avaya IP DECT Mobility Manager (ADMM): management interface for IP DECT Wireless

Solution, which runs on either one of the IP DECT Base Stations.

The picture displayed next page gives a graphical overview of the architecture of the IP DECT Wireless solution. The IP Office, ADMM and the IP Base Stations communicate through the IP infrastructure. The IP Base Stations and the IP DECT phones communicate over air.

Graphical overview of the architecture of the IP DECT Wireless solution

Task 5

Task (5)

This is the detail report for the overall tasks sorting from Task 1 to Task 4.In Task 1, the Townsville Police Department should be used Category 6 UTP by the following reasons:

» Cost and size of media, relative to augmented category 6 and STP

» Installed base – currently the dominant UTP cabling standard

» Installation – widely accepted

And it is suitable for Townsville Police Department.

Townsville Police Department has been restructured within an area of 100 square kilometers. But Townsville PD could not over more than 500 square kilometers because the head departments are divided into four districts (Northern, Eastern, Western and southern). Cat 6 UTP could support that area.

For Task 2, the services for internet connections are as follows:

Information (browsing, online-shopping, etc.)

Communications (mail, chat, Video conferencing, etc.)

Files sharing (downloading, uploading, etc.)

These services are the most common used for internet.

And recommended connection speeds are as follows:

For Information service:

It can cover only 100 Kbits/s usually prove adequate.

For Communication:

For video conferencing, bandwidths of no more than 384 Kbits/s usually prove adequate. As for chatting communication, especially for most chatting communications, 28 Kbits/s should be enough.

For File Sharing:

As for file sharing, bandwidths of more than 1 Mbit/s are most suitable.

There is only one Internet Service Provider in our country, Myanmar Ports and Communications.

In Task 3, there are too many options for two -way voice communication devices. Two-way voice communications (radios) are essentially available in three types:

Hand-held portable,

Vehicle-mounted mobile, and

Desktop-base station

These are most common used for two-way voice communication. And I provided the recommendation the device as follows:

Military Specification Standards

According to Military Specification Standards, Townsville Police Department should be used two way voice communication technology.

For Task 4, the main equipments that would be installed are just only the software. There are so many options and vendors that provide telephone known as PBX. Among those vendors, I chose AVAYA IP Office 4.0 Telephone System (IP DECT). As for Townsville Police Department, like military office, it is important to choose the right products. The IP DECT solution delivers all the benefits of IP-based converged communications with the convenience of “in-building” wireless communications. Designed to support a large number of users, the IP DECT system enables users to carry a wireless phone and get full access to all the features they are accustomed to using at their desk phone. The IP DECT solution, which connects to the IP Office using a variant of the H.323 protocol, can support users in different offices that are connected via a WAN. An IP DECT cordless handset can travel from one office to another, making and taking calls.

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