Archive for November 9, 2008

Physical topologies of a network

Posted in Networks on November 9, 2008 by Xacker

following: Exploring the functions of a network

Physical topologies:

  • Bus topology: in a bus topology a cable proceeds from one computer to the next. The main cable segment must end with a terminator to absorb the signal when it reaches the end of the line or wire. If there is no terminator, the electrical signal representing the data bounces back at the end of the wire, causing errors in the network.
  • Star and Extended-Star topologies: the Star topology is the most common physical topology in Ethernet LANs. It is made up of a central connection point that is a device, such as a hub, switch, or router, where all the cabling segments actually meet. Each device on the network is connected to the central device with its own cable.
    Although a physical star topology costs more to implement than the physical bus topology, the advantages of a star topology make it worth the additional cost. Each device is connected to the central device with its own wire, so that if that cable has a problem, only that one device is affected, and the rest of the network remains operational. This benefit is extremely important and is the reason why almost every newly designed Ethernet LAN has a physical star topology.
    When a star network is expanded to include an additional network device that is connected to the main network devices, the topology is referred to as an extended-star topology. The problem with the pure extended-star topology is that if the central node point fails, large portions of the network can become isolated.
  • Ring and Dual-Ring topologies: unlike the physical bus topology, a ring type of topology has no beginning or end that needs to be terminated. Data is transmitted in a way that is very different from the logical bus topology. In one implementation, a “token” travels around the ring, stopping at each device. If a device wants to transmit data, it adds that data and the destination address to the token. The token then continues around the ring until it finds the destination device, which takes the data out of the token. The advantage of using this type of method is that there are no collisions of data packets, later I will explain what collisions in a network are.
    In a single ring topology, all the devices on the network share a single cable, and the data travels in one direction only. Each device waits its turn to send data over the network. The single ring, however, is susceptible to a single failure, stopping the entire ring from functioning.
    In a dual ring topology, two rings allow data to be sent in both directions. This setup creates redundancy (fault tolerance), meaning that if one ring fails, data can be transmitted on the other ring.
  • Mesh and Partial-Mesh topologies: another type of topologies that is similar to the bus topology is mesh topology (لو كانت مش طبولوجي تبقى ايه :P). The mesh topology connects all devices to one another for redundancy and fault tolerance. Implementing a full mesh topology is expensive and difficult. This method is the most resistant to failures, because any single link failing will not affect reach ability, why? You will understand that when I explain switching and interconnections.
    In a partial-mesh topology, at least one device maintains multiple connections to all other devices, without being fully meshed. This method reduces the cost of meshing all devices by allowing the network designer to choose which nodes are the most critical and appropriately interconnect them.

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No more Arabic text

Posted in General on November 9, 2008 by Xacker

Sorry guys but I have decided not to publish anything in Arabic unless it was some small text with no extensive formatting required, I have noticed that the look of my blog went buggy on both IE and FF not to mention that any edit to any arabic post will lead into aftermath disasters.

Thus I declare the Keylogger topic is suspended until revised again.

If you need a shoulder now I know just the right guy for that, Nour, go get him 😛