network topology physical & logical topology bus topology ring topology star topology tree...
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Data Communications and Networking332 Hardware Components of Data Communications
• Network Topology• Physical & Logical Topology• Bus Topology• Ring Topology• Star Topology• Tree Topology• Mesh Topology• Combined Topologies
Network Topology• Network topologies may be physical or
logical with respect their functionality.• In general, physical topology relates to
a core network whereas logical topology relates to basic network.
• Physical topology refers to the physical design of a network including the devices, location and cable installation.
• The shape of the cabling layout used to link devices is called the physical topology of the network. This refers to:– The layout of cabling– The locations of nodes– The interconnections between the nodes and the
cabling• The physical topology of a network is determined
by:– The capabilities of the network access devices and
media– The level of control– Fault tolerance desired– The cost associated with cabling or
• Logical topology refers to how data is actually transferred in a network as opposed to its physical design.
• The logical topology is define:– is the way that the signal act on the network media– The way that the data passed through the network
from one device to the next without regard to the physical interconnection of the devices.
• A network’s logical topology is not necessarily the same as its physical topology. For example:– The original UTP Ethernet using hubs/switches, but
logically connected but topology layout.– Token ring is a logical ring topology, but is wired a
physical star from the MSAU (Media Station Access Unit)
• A bus network topology is a network architecture in which a set of clients are connected via a shared communications line / medium, called a BUS topology.
• The bus topology is often referred to as a linear bus because the computers are connected in a straight line.
• This is the simplest and most common method of networking computers.
• Advantages:– Easy to connect a computer or peripheral to
a linear bus.– Easy to implement and extend– Well suited for temporary networks (quick
setup)– Typically the cheapest topology to implement– Faster than a ring network– If any node on the bus network fails, the bus
itself is not effected.– Requires less cable length than a star
• Disadvantages:– Difficult to administer/troubleshoot– Limited cable length and number of stations– A cable break can disable the entire network– Maintenance costs may be higher in the long run– Performance degrades as additional computers are added
or on heavy traffic– Low security (all computers on the bus can see all data
transmissions)– One virus in the network will affect all of them (but not as
badly as a star or ring network)– Proper termination is required. (loop must be in closed
path)– Significant. Capacitive load (each bus transaction must be
able to stretch to most distant link).
• In Star topology, it uses a central component that allows other devices connected to it to communicate with each other, such devices are commonly called hubs or switches.
• A hub does not perform any type of filtering or routing of the data. It is simply a junction that joins all the different nodes together.
• If a device wants to communicate, it does so only through the central hub/switch. That switch then passes the data to its destination.
• Advantages:– Good performance– Easy to set up and to expand; any non-
centralised failure will have very little effect on the network
• Disadvantages:– Expensive to install– Extra hardware required
• In Ring topology, devices are connected circularly.
• Each one can communicate directly with either or both of its neighbors but nobody else.
• If it wants to communicate with a device farther away, it sends a message that passes through each device in between.
• A ring network may be either unidirectional or bidirectional.
• Unidirectional means that all transmissions travel in the same direction . Thus, each device can communicate directly with only one neighbor.
• Bidirectional means that data transmissions travel in either direction, and a device can communicate directly with both neighbors.
• An early ring topology was IBM’s Token Ring network, which connected PCs in a single office or department.
• In a token ring network, communications are coordinated by passing a token (a predefined sequence of bits) among all the devices in the ring.
• A device can send something only when it receives the token.
• Advantages:– Data is quickly transferred without a
‘bottle neck’. (very fast, all data traffic is in the same direction)
– The transmission of data is relatively simple as packets travel in one direction only.
– Adding additional nodes has very little impact on bandwidth.
– It prevents network collisions because of the media access method or architecture required.
• Disadvantages:– Data packets must pass through every
computer between the sender and receipient therefore this makes it slower.
– If any of the nodes fail then the ring is broken and data cannot be transmitted successfully.
– It is difficult to troubleshoot the ring.– Because all stations are wired together, to add
a station you must shut down the network temporarily.
– In order for all computer to communicate with each other, all computers must be turned on.
– Total dependence upon the one cable.
• Tree topology integrates multiple star topologies together onto a bus.
• In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the root of a tree of devices.
MESH Topology• Mesh topology involves the concept of routes.• Messages sent on a mesh network can take any of
several possible paths from source to destination.• A mesh network in which every device connects to
every other is called full mesh.• Partial mesh network also exist in which some
devices connect only indirectly to others.
Fully Connected Topology• The fully connected topology has a direct
connection between every pair of devices in the network. This is an extreme design. Communication becomes very simple because there is no competition for common lines.
• If two devices want to communicate, they do so directly without involving other devices.
Combined Topologies• Many computer networks use combinations of the various
topologies.• It has common bus, which connects many devices directly.