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Dated: Jun. 24, 2012
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Networking In General
Overview of Star Topology
Since over a decade, star topologies have been preferred over bus topologies by the administrators. In star topology, a central device (Hub or Switch) is used to connect multiple PCs in a local area network. Central devices that are used in star topologies have multiple LAN ports integrated in them and the PCs are connected to the central devices via patch cables. In most cases patch cables are twisted pair cables that have four twisted pairs (eight wires in all) which are crimped to the RJ-45 connectors. The reason why star topology is mostly preferred nowadays is that it does not provide a single point of failure and is highly scalable. This means that if something goes wrong with any one computer or patch cable, only the system or the segment with errors is not able to communicate with other computers, and the rest of the network remains intact. Moreover, if administrators plan to add additional PCs to the network, they just need to add a patch cable to the central devices and connect the other end of the cables to the PCs and they are done.
Types of Central Devices Used in Star Topology
As mentioned above, star topologies depend on central devices. It becomes quite important for the administrators to understand the behavior of central devices. This helps them select appropriate central devices according to the requirements of their network environments and the organizations. The different types of central devices are:
Hubs (Obsolete): These types of central devices were previously used, when the concept of star topology was new to the networking world. When Hubs were added to the network environments, their physical topologies were known star. However because of the logical structures of these central devices, which worked in the form of bus, network environments still worked on logical bus topologies.
Multi-Station Access Unit a.k.a. MAU or MSAU (Obsolete): These central devices looked exactly the way the Hubs did but logically they used to transfer data packets in the form of the ring. This was the reason that when these were used as central devices, the physical topologies were considered star whereas logically they worked as ring topologies.
LAN Switches (Widely Used): These central devices are widely used and are accepted by most organizations and administrators. Since these devices create virtual circuits between the source and destination ports, the data transfer efficiency enhances remarkably. Because of the virtual circuits that are created on one-to-one basis, both physical and logical topologies are star topologies while using LAN switches.
LAN switches are divided into two major categories. The categories are:
Non-Managed LAN Switches: These LAN switches work exactly as Hubs as far as the physical network architecture is concerned. Logically they form virtual circuits between the source and destination ports.
Managed LAN Switches: These LAN switches are a bit expensive as compared to the non-managed LAN switches. In most production environments managed LAN switches are used because they can be configured on per port basis. This means that security policies and other protection measures can be applied on these LAN switches as they provide their own CLI or GUI interfaces that administrators use to type commands while configuring them. Name of the vendors that manufacture managed LAN switches are Cisco, Juniper, 3Com, etc.
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