Common Network Topologies
Overview
network topology: The specific physical, i.e., real, or logical, i.e., virtual, arrangement of the elements of a network.: Two networks have the same topology if the connection configuration is the same, although the networks may differ in physical interconnections, distances between nodes, transmission rates, and/or signal types.
The common types of network topology are defined in alphabetical order below:
· bus topology: A network topology in which all nodes, i.e., stations, are connected together by a single bus.
· fully connected topology: A network topology in which there is a direct path (branch) between any two nodes.
· hybrid topology: A combination of any two or more network topologies.
Instances can occur where two basic network topologies, when connected together, can still retain the basic network character, and therefore not be a hybrid network.
For example, a tree network connected to a tree network is still a tree network. Therefore, a hybrid network accrues only when two basic networks are connected and the resulting network topology fails to meet one of the basic topology definitions. For example, two star networks connected together exhibit hybrid network topologies. A hybrid topology always accrues when two different basic network topologies are connected.
· mesh topology: A network topology in which there are at least two nodes with two or more paths between them.
· ring topology: A network topology in which every node has exactly two branches connected to it.
· star topology: A network topology in which peripheral nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node.
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All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. The failure of a transmission line, i.e., channel, linking any peripheral node to the central node will result in the isolation of that peripheral node from all others. If the star central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time, i.e., to and from the central node, plus any delay generated in the central node. An active star network has an active central node that usually has the means to prevent echo-related problems.
· tree topology: A network topology that, from a purely topologic viewpoint, resembles an interconnection of star networks in that individual peripheral nodes are required to transmit to and receive from one other node only, toward a central node, and are not required to act as repeaters or regenerators. The function of the central node may be distributed. As in the conventional star network, individual nodes may thus still be isolated from the network by a single-point failure of a transmission path to the node. A single-point failure of a transmission path within a distributed node will result in partitioning two or more stations from the rest of the network.
Ring Topology
Each workstation on the network is connected to two other workstations, forming a loop or ring as illustrated in the diagram below. Data is sent around the loop in one direction. 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.
Ring topology provides stable networking for over 10 users. Like bus topologies, rings are easy and relatively inexpensive to install. The number of workstations on the ring determines response time on a ring. Even if one connection fails, the rest of the network will function.
The ring topology is an older technology with a few limitations. The ring is difficult to troubleshoot, because when one connection fails, it is hard to determine where that problem is. Reconfiguring a ring will shut down the network.
Star Topology
Usually connected by Ethernet cables or Unshielded Twisted Pair (UTP), the star is configured around a central wiring device or switching element, usually an intelligent hub, as shown in the diagram below. The hub or collapsed backbone is a high-speed, efficient device that extends the capabilities of a simple cable. 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.
When it is important that your network have increased stability and speed, the star topology should be considered. When you use a hub, you get centralized administration and security control, low configuration costs and easy troubleshooting. When one node or workstation goes down, the rest of your network will still be functional.
Limitations include possible network failures due to a hub cable breaking or the hub itself failing. The number of ports on the hub limits the number of users you may connect. To expand a star topology network, you'll need to add another hub and go to a "star of stars" topology.
Tree Topology
Each device is connected to its own port on a hub, just like the star topology. A tree or "star of stars" topology interconnects hubs in a hierarchy, so one hub at the top of the hierarchy will connect to more hubs, which will break off to clients and even more hubs. The diagram below shows a simple tree topology.
The highly flexible tree topology lets you add users by simply adding a hub. Centralized monitoring and administration makes it easier to control a large network or reconfigure it. Isolating problems is easy, and if one node goes down, the rest of the network stays online.
An extensive tree topology will be more expensive to administer than any of the previous topologies due to its size and complexity. If a hub cable or a hub fails, a portion of the network will go down.
Mesh Topology
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. The diagram below shows four sites connected to each other in a mesh network.
Mesh topologies offer stability for single application servers. The redundant connections make the mesh network very reliable, even in high volume traffic situations. There are few troubleshooting problems in this WAN topology.
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.
Different topologies achieve different results under different circumstances. As you can see, these are just a few of the most common network topologies in use today. Choosing the proper topology to work with your business is half the battle.
Sources Used
Works Cited
www.sterlinginfo.com/ring.html
www.its.bldrdoc.gov
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