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How do we connect to network resources? In this lesson, we’ll discuss physical and logical topologies, which are different ways of describing network connections. We’ll also look at characteristics of some commonly used topologies.

Physical & Logical Topologies

People often draw diagrams or pictures to help describe complicated things. Maps are pictures of routes to get from point A to point B.

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Instruction manuals use diagrams to help us figure out how to put things together.When we use the word topology in this lesson, we’re referring to how things in a network are connected, as in a configuration.

  • A physical topology describes how network devices are physically connected – in other words, how devices are actually plugged into each other.

    We’re talking about cables, wireless connectivity, and more.

  • A logical topology describes how network devices appear to be connected to each other.

For example, in a logical diagram of your office network, you may show a connection between city A and city B. But in the actual physical network, your data may go through switching points in several other cities as well. The logical path is a high-level representation; the physical path is the actual route.

Signal Topologies

Logical topology can also refer to the signal topology of the network, which is how the signals are passed across the physical network. How signals are set up and transmitted is governed by network protocols. The most common signal topologies are shared media access and token-based access.

  • In a shared media access network, all the devices on the network can transmit at any time, which sometimes results in collisions if two nodes transmit at once. Ethernet is based on shared media access.

  • In a token-based access network, nodes have to wait their turn with the network token before they can transmit.

Common Types of Physical Topologies

The common types of physical topologies for networks are star, bus, ring, and mesh.The most widely used physical topology in businesses today is the star topology, in which all network devices are connected back to a central hub or switch. In a bus topology, network devices are connected to a central cable in a linear direction, like stops on a bus route.In most offices and many home networks, the underlying network technology used is Ethernet. Ethernet (or shared media access) is based on a family of standards that has been around for almost 50 years and is not brand-specific to any one manufacturer. Devices can connect to Ethernet through wired or wireless connections.

Ethernet networks are logically a bus topology and physically a star topology.A ring topology means that the devices in the network are connected in a circular fashion, and every piece of data is sent around the ring until it finds the intended recipient. IBM had a version of a ring topology called Token Ring that was a popular choice for office networks for a while, but the network electronics were more expensive than Ethernet, and as Ethernet speeds grew, Token Ring fell out of favor.

IBM Token Ring was a token-based access network, just as the name implies.In a mesh network each node talks to the others, and they work together to distribute data. A common use for mesh networks is in wireless connectivity. For example – you’re walking through a large airport using your tablet to access the wireless Internet service it offers.

As you move along, you’re being passed from wireless access point to wireless access point, the one behind you setting up your conversation with the one in front of you as you go. A wireless access point’s coverage area only goes so far, so the points are positioned in a way that you’re never too far from one to get the best signal.

Lesson Summary

When we’re talking about the physical topology of a network, we’re talking about the nitty-gritty details of how things are actually connected – for example, what kinds of cables are used and what devices they’re plugged into. The logical topology is how the network connections appear to the end user or how the network signals are being passed along.

The most common signal topologies are:

  • Shared media access networks where all devices on the network can transmit at any time, which sometimes results in collisions. Ethernet uses this type of signal topology. And,
  • Token-based access networks where nodes have to wait their turn with the network token before they can transmit.

The most common types of physical topologies for networks are:

  • Star topology – where network devices are connected back to a central hub or switch.
  • Bus topology – where network devices are connected to a central cable in a linear direction, like stops on a bus route.
  • Ring topology – where network devices are connected in a circular fashion, and every piece of data is sent around the ring until it finds the intended recipient. And,
  • Mesh networks – where each node talks to the others and they work together to distribute data.

    A common use for mesh networks is in wireless connectivity.

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