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Newtown Department is renewing all of its networks for the new headquarters including the computer network. When fire engines are required for an emergency, the control centre sends details to a printer in the fire engine bay to provide written details of the incident. This print-out is taken by the Watch Officer as the watch leaves the building to attend the incident.
Here some investigation about the possible network topologies and media that could be used to create the in-house network (LAN) for the Fire Department.
Network Topology: Topology means the network's layout. By the network's topology it is determined that how different nodes are connected to each other and how they communicate. Topologies are either physical or logical.
Basically we have two options to implement the computer network.
Topology depends on the technology. Here some LAN technologies.
Now a day for this purpose Ethernet is the most suitable technology for cable network and Wi-Fi for wireless network.
Some Topologies for these two technologies:
The bus topology is basically a wire that all devices connect to using a passive interface. There are terminators on both ends of the wire to remove the frame.
Since all computers are connected to the medium, they all get all the frames sent. The terminators are responsible for the removal of the frame.
Figure 1: Bus topology
In baseband setup, each computer sends frames in all directions. In broadband setup, the transmission is unidirectional.
In a stat topology, each station is connected to a central node or hub /switch. Each station only talks to the central node.
Each station generally has two connections to the hub; one to send data to the hub, and another to get data from the hub. Thus, each connection is unidirectional.
The Star topology can use either broadband or baseband transmissions. Baseband is used for guided media (like wire), while broadband is used for unguided (wireless).
Figure 2: Star topology
The central hub or switch can be either active or passive. A passive hub just links all workstations together. An active hub reads and then retransmits the frame to all workstations.
If the star uses a hub, then addressing works just like in the bus network. If the star uses a switch, then the destination is determined by the switch.
Ad-hoc topology is a way for wireless devices to directly communicate with one another. Without involving central access points ad-hoc allows all wireless devices (within range) to discover and communicate in peer-to-peer style.
Figure 3: Ad-hoc
An ad-hoc network tends to feature a small group of devices all in very close proximity to each other. It is difficult to manage a large ad-hoc network. Without installing a special-purpose gateway Ad-hoc networks cannot bridge to wired LANs or to the Internet.
It is good when needing to build quickly a small, all-wireless LAN and spend low quantity of money on equipment.
It is the more familiar type of topology that allows access to wired network is the infrastructure topology. Access Points are added to a switch, which provides connectivity to wireless stations.
Figure 4: Infrastructure
An access point lets us easily expand a wired network with wireless capability. Wirelessly networked and wired computers can communicate with one another. It is the main feature of an infrastructure topology.
We can extend our wireless networkâ€™s range by placing an AP in between two wireless network adapters.
This table shows the advantages and disadvantages of the various medium for the LAN Network.
Advantage and disadvantage of twisted pair cable:
Twisted pair is less expensive than dedicated coaxial or fiber.
Very low cost for installing twisted-pair.
Easy to install and reconfigure.
Unshielded Twisted-Pair (UTP) Structured Cabling permits many communication protocols as voice, data and CCTV video and control.
UTP is Color-coded cabling.
UTP gives better interference rejection than coaxial cable.
It is physically smaller than coax and many other cable types.
It is very easy to terminate.
1MHz is the total usable frequency spectrum of twisted-pair copper cable.
It is highly susceptibility to signal interference. (EMI and RFI)
Over long distances they provide signal distortion errors and the relatively low transmission rates.
Maximum cable run of 100 meters
Advantage and disadvantage of twisted fiber optic:
Good system performance.
More bandwidth and capacity.
Lower signal loss.
immune to noise
Component are expensive
fiber optic transmitters and receivers are still relatively expensive compared to electrical interfaces
Requires dedicated infrastructure.
IT skills required for installation and maintenance
Advantage and disadvantage of Wireless 801.11a:
This version produced in 1999.
It supports data transfer rates of 54 Mbps and uses the radio frequency on the 5 GHz band.
Itâ€™s equipments are more expensive than 802.11b
802.11a products range is 115 feet
Products based on the standard rarely perform at more than 25 Mbps.
Advantage and disadvantage of Wireless 801.11b:
It uses a radio frequency of 2.4 GHz and can support data transfer rates of 11 Mbps.
Long range (100 meters)
Inexpensive hardware (Relatively)
RF Band is shared
In perspective of the scenario star topology and twisted pair cables as the medium would be the best for the Newtown fire department.
I Choose Star topology because:
Failure of the medium does not seriously disrupt communication.
Malfunctioning of the station doesnâ€™t seriously affect the communication.
The network can use guided or unguided media.
Only failure of the hub disrupts the communication.
I chose twisted pair cables because:
Small local area network with a limited number of users, twisted pair is an ideal choice because it is both inexpensive and easy to install.
It is more secure than wireless medium.
Physical access can be monitored easily.
Cost effective and can fulfill our requirements.
For the Newtown fire department in-house network, possible topology and medium can be chose clearly from this task.