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Topologies Comparison

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Topologies Comparison

Topologies are categorized into different virtual shapes or structures with the basic types being Mesh, Bus, Ring, and Star. “More complex networks can be built as hybrids of two or more of the above basic topologies.” (Mitchell, 2008) These basic topologies are structured in to networks as Ethernet, Token Ring, FDDI, and wireless networking. Any business or individual making a decision of which type of topology is best used for a specific environment or network should know and understand the advantages and disadvantages of each type of topology, in addition to the advantages and disadvantages of each network type.
MESH
MESH topology routes data sent through any of several possible avenues to the receiving node. MESH arrives at its name due to the amount of cabling and connections used to establish this type of topology. MESH topology is expensive to establish as it connects every node to all nodes on the network, however, MESH is considered the most reliable as it has the most redundancy. If one node fails the network can re-route traffic to another node. A MESH topology network can be straightforward to trouble shoot when a problem arises. “Full mesh is usually reserved for backbone networks.” (NetworkDictionary.com, 2008) This type of topology can be found in connection to a WAN or Wide Area Network and is frequently found in conjunction with other topologies to create a hybrid topology.

BUS
BUS topology uses a single cable, or common backbone to connect the nodes on the network. BUS arrives at its name as all nodes are linked by one linear bus or cable; all data sent onto the network transmits the length of the BUS. The node sending communication to the network broadcasts the data onto the wire, all devices linked to the network can see the data but only the intended receiving node will accept and process the data. BUS topology is simple to install as it does not require much cabling compared to other alternatives. BUS works best with a small number of nodes. If the single cable fails the entire network is unusable.
RING
RING topology connects each node to two neighboring nodes creating a RING. This topology connects each node on the network to a repeater. The data is sent to a sending device which then proceeds to the next device to retrieve or drop off information before continuing on. RING topology is considered to be inefficient as data can only travel in one route to reach its destination, and the data usually travels to several points prior to reaching its intended destination. A failure in one device or in one part of the cable can cause the entire network to fail. This topology can be found in some school campuses and in some office buildings.
STAR
STAR topology network connects all nodes to a central device such as a hub, switch, or router, creating a Star type configuration. All data sent from a node is sent to the central hub, switch, or router which then broadcasts or sends the data to all nodes on the network. The nodes may only communicate with the central device which then communicates to all the nodes on the network. If one node fails then the others will continue to function, however, if the central device fails the entire network fails.
NETWORKS
Each of the listed topologies is used to create a network which communicates between nodes on the network. A laptop computer can be linked to the network to communicate with a desktop computer or a printer linked to the same network. The most common protocol in use currently is Transmission Control Protocol/Internet Protocol more commonly known as TCP/IP. TCP functions at layer 4 of the OSI Model known as the Transport Layer. IP or Internet Protocol functions at layer 3 of the OSI Model known as the Network Layer. TCP/IP essentially means that TCP delivers or transports data across IP the Network Layer.
Ethernet
Ethernet was developed in the 1970s and with widespread use beginning in the 1980s. Ethernet is currently the most popular local area network or LAN in use throughout the world. Nodes are connected to each other in a STAR or BUS configuration. The hub or repeater connects all the nodes on the network and receives data from the sending node and re-transmits the data to all the nodes except the sending node. This data travels in units called Frames. Ethernet transmission is limited to 100 meters and is easily bridged to extend further for a network. All versions of Ethernet use Media Access Control (MAC) with a Carrier Sense Multiple Access / Collision Detection or CSMA/CD protocol which determines which nodes and send data and when they can send it. This helps to prevent collision of data being sent at the same time.
Token Ring
A Token Ring network can be beneficial for sending data that is time sensitive as the time between transmission of the data and receipt of the data by the receiving node can be calculated based upon the amount of time the Token takes to complete one trip around the network. Each node is allowed to keep the Token for a specified time and then the Token must pass to the next node. This type of network prevents data collisions and one or more Tokens can circulate the network to allow for faster transmission of data. The disadvantages are that the node that needs to send data must wait until the token is received by it to send the data and, “The complicated process of creating and passing the token requires more expensive equipment than that used by contention-based networks” (Tomsho, Tittel, & Johnson, 2004, p. 94).
FDDI
Fiber Distributed Data Interface or FDDI is a protocol for sending digital data over a fiber optic cable. This is similar to a Token Ring network protocol as a token is passed over the network. FDDI employs dual rings which counter rotate or flow in opposite directions. This is a fast and reliable network, but a disadvantage is the expense involved in establishing and maintaining this type of network as it requires sophisticated equipment. FDDI is a combination of four specifications: (NetworkDictionary.com, 2008)
• the Media Access Control or MAC which defines how the data is accessed,
• Physical Layer Protocol from the OSI Model which defines the data encoding and decoding as well as procedures and other functions,
• Physical-Medium Dependent or PMD which defines the power levels, the fiber optic links, connections, and other components,
• Station Management (SMT) specifications which define the station and ring configuration along with the ring control features.
Wireless
Wireless networks can be established in areas where cabling is not possible, such as outdoor areas and historical buildings. Wireless or Wi-Fi will allow for network expansion without the additional costs involved for cabling purchase and installation. “Widely available in more than 250,000 public hot spots and tens of millions of homes and corporate and university campuses worldwide, as of 2007, Wi-Fi has become the preferred method of network connectivity” (Mikialov, 2008)

Conclusion
Understanding the different topologies and networks available will allow any business or individual to determine the network that will best suit the business or individual needs and will help to establish the correct expectations. Knowing what budget constraints exist for the business or individual as well as what the physical constraints of where the network is to be located will help the stakeholders make the correct decisions on which topology and network would be most beneficial to them.

References:
NetworkDicitionary.com (2008), FDDI Fiber Distributed Data Interface. Retrieved June
June 28, 2009 from http://www.networkdictionary.com/protocols/fddi.php
NetworkDictionary.com. (2008). Mesh Network Topology and Architecture. Retrieved
June 28, 2009 from http://www.networkdicitionary.com/networking/mesh.php
Mikailov, PhD, M., April 28, 2008, BrainMass.com, OTA ID#: 105277, Retrieved
June 29, 2008, from http://www.brainmass.com/instant/?id
Mitchell, B. (2008) Your Guide to Wireless/Networking, About.com. Retrieved
June 28, 2008 at http://compnetworking.about.com/od/networkdesign/a/topologies.htm
Tomsho, G., Tittel, E., & Johnson, D. (2004). Guide to Networking Essentials. , Ch 6,
pg 94, Retrieved from UOP Library June 29, 2008 at
https://ecampus.phoenix.edu/content/eBookLibrary/content/eReader.h

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