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Physical topology is used to explain the wide layout of the network cables and workstations and the location of all network components. It is also informative of how the information and data flows within the network. I like to explain here in most common five topologies
Bus topology refers to one cable that connects all the workstations, servers, printers and other devices on the network. The cable runs from device to device by using T connectors that plug into the network adapter cards. Each end device has a terminator on one end of the T connector and a cable going out to the next device on the other end while all devices in the middle have one cable coming in and one going out. The terminators on each end device simply stop the network signal from reflecting back into the cable and running over with other transmissions. RG-58 thin net is the most common type of network cable used for a bus topology. There are network size limitations. We may have a maximum of twenty network devices on a segment and the segment cannot go over 185 meters in total length. By using a repeater that boosts up the signal we can have up to five segments on a network. But only three of these segments can have devices attached to them. The other two segments are used to connect the three populated segments giving a maximum number of sixty devices with a total network length of 925 meters. This topology works similarly well for either peer to peer or client server.
Easy to connect a workstation or peripheral to a linear bus.
Less cable length is required.
If there is a break in the backbone cable, entire network shuts down.
Terminators are required at both ends of the main cable.
If the entire network shuts down it's difficult to identify the problem.
Each network device has a home run of cabling back to a network hub giving every device a separate connection to the network. If there is a problem with a cable it will commonly not affect the rest of the network. The most common cable media in use for star topology is unshielded twisted pair cabling. Category 3 is still found regularly in older installations. It's capable of 10 megabits per second data transfer rate making it appropriate for only 10 BASE T Ethernet. Category 5 cabling is used in most new installations. It is capable of data transfer rates of 100 megabits per second enabling it to use 100 BASE T Ethernet also known as Fast Ethernet. More importantly, brand new 1000 BASE T Ethernet standard will be able to run over most existing Category 5. Finally fiber optic cable can be used to transmit also 10 BASE T or 100 BASE T Ethernet frames.
Two differences of the star topology used by larger Ethernet networks today are the Star bus and Star tree topologies. Essentially the star bus topology has multiple data closets interconnected by bus trunk lines of thin net while the star tree topology connects multiple data closets with twisted pair or fiber optic. These types of network topologies allow a network to cover up a much larger physical area.
The maximum number of network devices is 1024 and the highest number of data closets is 4. When using Category 3 or Category 5 twisted pair cabling, individual cables can't exceed 100 meters. In regard to whole network length, the maximum when linking data closets with twisted pair is 500 meters between the farthest two devices. If multi mode fiber optic is used to link closets and then the distance between closets can be up to 2000 meters.
It's easy to install and wire.
No disturbances to the network when connecting or removing devices.
Easy to notice faults and to remove parts.
Requires more cable length than a bus topology.
If the hub, switch or concentrator fails then nodes attached will be disabled.
More expensive than creating a bus topology.
A tree topology combines features of Bus topology and Star topology. It contains of groups of star configured workstations connected to a bus backbone cable. Tree topologies allow for the expansion of a standing network.
Point to point wiring for individual sections.
Supported by several software and hardware venders.
On the whole length of each segment is limited by the cabling type of used.
If the backbone cable breaks down, the entire segment goes down.
More complicated to configure and wire.
On token ring networks are used ring topologies. Every device processes and retransmits the signal and so it is capable of supporting many devices in a somewhat slow but very orderly fashion. A token or small data packet is always passed around the network. When a device needs to transmit, it reserves the token for the next trip around and then connects its data packet to it. The receiving device sends back the packet with an acknowledgment of receipt and then the sending device puts the token back out on the network. The majority token ring networks have the physical cabling of a star topology. The logical function of a ring through has use of Multi Access Units (MAU). The network signal is passed through each network card of each device and passed on to the next device in a ring topology. All devices have a cable home run back to the Multi Access Units. The MAU makes a logical ring connection between the devices on the inside. When each device signs on or off, it sends an electrical signal which trips mechanical switches inside the MAU to also connect the device to the ring or drop it off the ring. The most common type of cabling used for token ring network is twisted pair and although there are nine different types that can be used. With IBM Type 1 Shielded cable we can have up to 33 network segments with 260 devices on each. Transmission rates are 4 or 16 megabits per second.
Very arranged network where every device has access to the token and the chance to transmit
Act upon better than a star topology under heavy network load
Using Token Ring can be created much larger network
One faulty workstation or bad port in the MAU can create problems for the entire network
Moves, changes and adds of devices can affect the network
Network adapter cards and MAU's are much more expensive.
Under normal load much slower than an Ethernet network
Mesh network is a network where all the nodes are attached to each other and is a complete network. Every node is connected to other nodes on the network through hops in a mesh network. Some are connected through single hops and some may be bonded with more than one hope. It is possible to transmit data from one node to many other nodes at the same time with the arrangement of the network nodes. The arrangement where every network node is attached to every other node of the network, many of the connections serve no major purpose. It is leads to the redundancy of many of the network connections.
5.2. How I chose Appropriate Topology
Consideration When Choosing a Topology………
Money: - A bus network topology may be the least expensive way to install a network.
Cable length: - The bus network topology uses shorter lengths of cable.
Future growth: - With a star topology expanding a network can be easily done.
Type of the cable: - The most common cable is unshielded twisted pair which is most frequently used with star topology.
After considering these points I selected STAR TOPOLOGY for every branches of my network. BlueStar is a brand new company in Sri Lanka and it will be larger day by day in future. Therefore the networking system will be expanded. It is easier to expand the network in future by using star topology.
If any trouble in the network it can be easily detect faults and to remove parts and repair it in quickly. No disruptions to the network when we connecting or removing devices (easy to repair). Therefore the maintaining cost will minimum.