Advantage Of Star Topology

Star Topology: In a typical star topology, all computers/ stations are connected to a central device, usually a switch. They are connected to this central device via cable segments. Such cable segments are Unshielded Twisted Pair (UTP) and Shielded Twisted Pair, as well as, fibre optic cabling.

http://www.inetdaemon.com/img/topology_star.gif

Advantage of star topology: With the star topology, if one cable of device goes down, the rest of the network is not affected (fault tolerance).

Disadvantage of star topology: However, because management of communication is centralized, if the main switch or hub goes down the whole network goes down.

Extended Star Topology: As the name implies, it is a bit more advanced than the typical star topology. In this topology, there is also a central device, usually a switch, in the middle of the network. However, instead of computers being directly connected to this central switch, other switches or hubs are connected to its’ ports. Computers and other peripherals are then connected to these switches or hubs, forming other stars; hence an extended star is the final result.

http://t0.gstatic.com/images?q=tbn:O2WYXsb8K_NPNM:http://upload.wikimedia.org/wikipedia/ro/b/b5/Extended_star_topology.png

Advantage of extended star topology: As a result of there being a central switch, it is easy to locate and troubleshoot any problematic areas.

Disadvantage of extended star topology: Again, because of the use of the centralized switch, once the switch goes down it creates problems for the entire network.

Ring Topology: In this particular network topology, each computer/ station is directly connected to the next one in line and ends at the very first computer/ station, resulting in a circular formation/ arrangement of the cables. Each computer has the responsibility of retransmitting communication messages. The communication messages all travel in one direction and as a result of having no end in the circular formation, there is no real need for termination.

http://www.inetdaemon.com/img/topology_ring.gif

Advantage of ring topology: Due to the topology’s structure, there is no need for terminators.

Disadvantage of ring topology: Any break or fault in the cable can disrupt communications.

Bus/ Linear-Bus Topology: This structure utilizes a single cable segment which connects all the computers in a single straight line. All computers in this topology share this single cable segment and as a result a terminator is needed. This is due to the fact that the signals need to be absorbed as they reach the end of the bus in order to free the network for fresh and newer communications.

http://www.inetdaemon.com/img/topology_bus.png

Advantage of bus topology: This is an inexpensive topology to install.

Disadvantage of bus topology: With all the devices sharing the same “backbone” cable, communication speeds are lowered.

Tree Topology: Logically, this is an extension to the less complex bus topology. www.networkdictionary.com states that “The transmission medium is a branching cable with no closed loops. The tree layout begins at a point called the head-end, where one or more cables start, and each of these may have branches. The branches in turn may have additional branches to allow quite complex layouts.” It is often referred to as the star- bus topology.

Available from: www.networkdictionary.com/networking/lanat.php [Date accessed: October 24th 2009]

graphics/04fig11.gif

Advantage of tree topology: This topology allows point to point wiring for individual sectors.

Disadvantage of tree topology: A break in the main “backbone” cable will affect the entire network.

Mesh Topology: In the mesh topology, each device in a network is connected to every other device in the particular network. The mesh topology is typically used to connect several LANs together to create a WAN (it is more WAN based technology) e.g. the internet is a perfect example of a mesh topology.

http://www.google.tt/images?q=tbn:MKaJ7Z8cc3BUJM::www.erealmedia.com/cms102/uploads/NetworkingPrinciples/Chapter1/1_23_MeshTopology.jpg&t=1&h=196&w=176&usg=__QGrcgQACaPCnhXDPW-hE9X5a-Rw=

Advantage of mesh topology: Due to the fact that all devices are interconnected to each other, there are various alternate routes, which improve fault tolerance.

Disadvantage of mesh topology: Managing and troubleshooting this architecture is very difficult, complex and expensive.

1.2.0 Advantages and Disadvantages of LAN media

The media used in a typical LAN (Local Area Network) are Coaxial cables, Twisted-pair cables (Unshielded and shielded twisted pair) and Fibre Optic cables.

1.2.1 Advantages of Coaxial cables:

Appropriate for Broadband system: Coaxial cables possess adequate ranges of frequency that can support several network channels and as a result of such capability, allows for much greater throughput.

Better bandwidth: Compared to twisted pair cables, coaxial offers a better bandwidth system wide, as well as, better bandwidth for each network channel. As a result of this, there is support for a diverse range of service. Network functionalities such as data, voice, video and even multimedia can profit from the improved capacity.

An even better spacing between amplifiers: Due to the cable shielding possessed by coaxial, there is a reduction in noise and crosstalk, thereby allowing amplifiers to be spaced farther apart.

Lower error rate: Noise resistance is enhanced because the inner conductor is in a wire mesh and coaxial has lesser error rates.

Better channel capacity: Extensive capacity is offered from each of the several channels.

Disadvantages of Coaxial cables:

Installation can be expensive

Prone to damage from lightning strikes: People residing in areas, in which lightning strikes frequently occur, must be cautious. If the lightning is conducted by a coaxial, chances are that the equipment connected to the end of that particular coaxial, may be fried.

Noise: The path of return has noise exertion and the end apparatus requires additional aptitude to deal with error control.

Deployment architecture problems: The bus topology in which the coaxial is set up is vulnerable to noise, clogging and security can be jeopardized.

Bidirectional (two-way) upgrade is required: In countries where there is a history of cable television, these systems are designed and built for broadcasting, not interactive communications. For a service provider to offer a subscriber any form of two-way communication services, the current network system needs to be upgraded to a Bidirectional system.

1.2.2 Advantages of Twisted pair cables:

The cost of installing twisted pair on site is low

High availability: Billions telephone subscriber lines established on twisted-pair have been set up and because it is already in the ground, the telecommunication companies will use it.

Low cost for local moves, additions and changes in places: Individuals can swap twisted-pair terminating in a modular plug with another jack. This can be done without a service technician, given that the wiring is already in place.

Disadvantages of Twisted pair cables:

Frequency spectrum is limited: The total serviceable frequency spectrum of is about 1MHz.

High error rates: It is extremely susceptible to interferences in signal communications, caused by EMI (Electromagnetic Interference) or RFI (Radio Frequency Interference).

Data rates are limited: The longer the distance the signal travels over cable, the lower the data rate will be. At 30 feet (100m), twisted-pair is capable of carrying 100Mbps. At 3.5 miles (5.5km), the data rate can drop to 2Mbps or possibly less.

Short distances are required between repeaters.

1.2.3 Advantages of Fibre Optic cables:

Fibre optic cables have higher bandwidth compared to other mediums.

It is impossible to tap into fibre optic cables. This makes them much more secure compared to other mediums.

One can add equipment to provide extra capability over a fibre without having to change it.

No electricity passes through the cables what so ever, and as a result they do not conduct lightning strikes

They are light weight

Disadvantages of Fibre Optic cables:

They are more fragile compared to other mediums.

Installation of the cables is quite expensive.

Termination of fibre optic cables is quite complex and requires special tools

1.3.0 Recommendation

After much investigation of the various LAN topologies and media, I have gathered comprehensive information and have come to a conclusion which topology and media type should be used. With respects to the LAN topology, I strongly recommend that the extended star topology be implemented. The extended star offers fault tolerance in that, if failure in one cable or device occurs, it doesn’t pose as a threat to the rest of the network. If at all there are problems with particular cables or devices, the task of locating them is quite easy. Management is centralized due to the use of the centralized switch and it is easy to add devices as the network expands. Also, it can be upgraded for faster speeds and better performance, not to mention that it is the most widely used, so much support is available. Such a LAN topology proves to be quite costly but with all its benefits it is worth the expense.

With regards to network media, if the extended star LAN topology is to be in use, the unshielded twisted-pair cables are a suitable medium. The installation costs are low and in addition, any changes or additions are cheaper compared to other media types. Furthermore, telecommunication companies will use subscriber lines that already exist, so there is no need for additional costs of running lines.

Bibliography

K. Wilson Jarrett and L. Goleniewski, (Oct. 12th, 2007), Traditional Transmission Media for Networking and Telecommunications. (Coaxial Cable)

www.informit.com/articles/article.aspx?p=683070&seqNum=2#

[Date accessed: October 24th 2009]

K. Wilson Jarrett and L. Goleniewski, (Oct. 12th, 2007), Traditional Transmission Media for Networking and Telecommunications. (Twisted-Pair)

http://www.informit.com/articles/article.aspx?p=683070

[Date accessed: October 24th 2009]

K. Wilson Jarrett and L. Goleniewski, (Oct. 12th, 2007), Traditional Transmission Media for Networking and Telecommunications. (Fibre Optics)

http://www.informit.com/articles/article.aspx?p=683070&seqNum=5

[Date accessed: October 24th 2009]

Network Dictionary, (2004-2010), LAN Architectures and Topologies: Bus, Star, Ring and Tree.

www.networkdictionary.com/networking/lanat.php

[Date accessed: October 24th 2009]

Task 2

a) 2.1.0 Internet services required

2.1.1 E mail: The abbreviation for electronic mail; this is a system of exchanging information/ messages digitally via the internet.

2.1.2 Voice/VoIP: The abbreviation for Voice Over internet Protocol; this is a system used in telecommunications for the transmission of voice traffic/phone calls over any network based on IP (Internet Protocol) e.g. the internet.

2.1.3 FTP: The abbreviation for File Transfer Protocol; this is the TCP/IP standard used for the transferring of files from one computer to another.

2.1.4 TELNET: This is the TCP/IP standard used for remote terminal services. It allows users at one site to transparently interact with a remote system or network at another site, whilst appearing as a local terminal.

2.1.5 Video communication: J. Wilcox Pg.3 states, “Video communication is real-time exchange of digitized video images and sounds between conference participants at two or more separate sites.”

2.2.0 Required connection speeds

2.3.1 With regards to Audio and Data communication, 64 Kbits/s is sufficient enough for use of this service. In the case of Video communication, bandwidth of 2Mbits/s or more may be required for proper transmission. Furthermore, www.whichvoip.com states “VoIP requires anywhere from about 24Kbits/s to about 90Kbits/s”. Overall, once serviced with an appropriate broadband package, these requirements will be addressed.

Available from: http://www.whichvoip.com/voip/speed_test/ppspeed.html [Date accessed: October 27th 2009]

2.3.0 Internet Service Providers (ISPs)

In Trinidad, there are various internet service providers from which one can subscribe for broadband services. Blink, Flow, and Lisa Communications are such ISPs.

2.3.1 Blink Packages

2.3.2 Flow Packages

2.3.3 Lisa communications

2.4.0 Recommendation

After investigations on ISPs in Trinidad regarding their services and prices offered, I have seen favourable packages with one particular ISP, Flow. Flow offers its customers bandwidth speeds ranging from 512k/1Mbps to 3Mbps/9Mbps. Also they provide free static IP addresses and email addresses, and the number of IP email addresses one receives depends on the package one chooses. The packages are as follows: