Mesh, Bus, Ring and Star Topologies

Mesh, Bus, Ring and Star topologies

Mesh

A mesh topology typically refers to a Wide Area Network where there are multiple paths connecting multiple sites. A router is used to search multiple paths and determine the best path for the data. Routes are determined by least cost, time of day and performance. A three or four site mesh network is relatively easy to create, whereas it is impractical to set up a mesh network of 100 sites or nodes. Mesh networks are used in Wide Area Networks (WANs) where reliability is important and the number of sites being connected together is fairly small.

A mesh network is costly to reconfigure, replace and administer. A mesh is best suited for situations where it will not need to be moved or expanded beyond five sites or nodes. If one site fails, an entire application can fail. (Bloom, 1998).

Bus

An Ethernet cable usually connects Bus topologies. A bus topology connects your workstations along an open cable length or backbone. If a problem occurs on the backbone, the entire network will go down. Troubleshooting can be difficult, and because data is sent one packet at a time, adding users to the network will slow it down. (Bloom, 1998). Bus topologies are relatively easy to install.

Star

Ethernet cables or Unshielded Twisted Pair (UTP) cables usually connects Star topologies. The star is configured around a central wiring device or switching element, usually an intelligent hub. The hub interprets and routes electrical signals using a high-speed backplane or bus. Each device (workstation, server, etc.) is connected singly to a port on the hub. (Bloom, 1998). Star topologies can be expensive to install, however, quickly identified nodes on the network through the switches, or hubs, will drastically decrease downtime.

Ring

Each workstation on the network is connected to two other workstations, forming a loop or ring. Conflicts in the transmission of data are avoided with token ring technology, which grants messages a "token" or permission to send. Each workstation receives, regenerates and retransmits a token signal until it reaches its destination. (Bloom, 1998).

The variations in connection methods by topology bring about their differences in layout and functionality. A Mesh connects multiple sites unlike any of the other mentioned topologies. A Star topology connects at a central point using an intelligent hub or switch, whereas none of the others utilize a central connection point. The Bus and Ring topologies are most similar in that the nodes on the network are responsible for receiving, regenerating, and retransmitting messages. However, Bus and Ring differ in that a bus connects workstations in a straight line without connecting end points.

Ethernet, Token Ring, FDDI and Wireless

Ethernet

Ethernet is a large, diverse family of frame-based computer networking technologies that operates at many speeds for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format.

Ethernet has been standardized as IEEE 802.3. The combination of the twisted pair versions of ethernet for connecting end systems to the network with the fiber optic versions for site backbones become the most widespread wired LAN technology in use from the 1990s to the present, largely replacing competing LAN standards such as coaxial cable Ethernet, token ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN standardized by IEEE 802.11, has been used instead of Ethernet for many home and small office networks and in addition to Ethernet in larger installations. (Wikipedia, 2007).

Token Ring

Stations on a token ring LAN are logically organized in a ring topology with data being transmitted sequentially from one ring station to the next with a control token circulating around the ring controlling access. This token passing mechanism is shared by ARCNET, token bus, and FDDI, and has theoretical advantages over the stochastic CSMA/CD of Ethernet.

Each station passes or repeats the special token frame around the ring to its nearest downstream neighbor. This token-passing process is used to arbitrate access to the shared ring media. Stations that have data frames to transmit must first acquire the token before they can transmit them. (Wikipedia, 2007).

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