23-09-2016, 09:05 AM
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Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network.
[1][2] Essentially, it is the topological
[3]
structure
of a network and may be depicted physically or logically. Physical topology is the placement of the various components of a network, including device
location and cable installation, while logical topology illustrates how data flows within a network, regardless of its physical design. Distances between
nodes, physical interconnections, transmission rates, or signal types may differ between two networks, yet their topologies may be identical.
An example is a local area network (LAN): Any given node in the LAN has one or more physical links to other devices in the network; graphically
mapping these links results in a geometric shape that can be used to describe the physical topology of the network. Conversely, mapping the data flow
between the components determines the logical topology of the network.
Topology
There are two basic categories of network topologies:
[4] physical topologies and logical topologies.
The cabling layout used to link devices is the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the
interconnections between the nodes and the cabling.
[1] The physical topology of a network is determined by the capabilities of the network access
devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.
The logical topology in contrast, is the way that the signals act on the network media, or the way that the data passes 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 twisted pair Ethernet using repeater hubs was a logical bus topology with a physical star topology layout. Token
Ring is a logical ring topology, but is wired as a physical star from the Media Access Unit.
The logical classification of network topologies generally follows the same classifications as those in the physical classifications of network topologies
but describes the path that the data takes between nodes being used as opposed to the actual physical connections between nodes. The logical topologies
are generally determined by network protocols as opposed to being determined by the physical layout of cables, wires, and network devices or by the
flow of the electrical signals, although in many cases the paths that the electrical signals take between nodes may closely match the logical flow of data,
hence the convention of using the terms logical topology and signal topology interchangeably.
Logical topologies are often closely associated with Media Access Control methods and protocols. Logical topologies are able to be dynamically
reconfigured by special types of equipment such as routers and switches.
The study of network topology recognizes eight basic topologies:
[5] pointtopoint, bus, star, ring or circular, mesh, tree, hybrid, or daisy chain.
Pointtopoint
The simplest topology with a dedicated link between two endpoints. Switched pointtopoint
topologies are the basic model of conventional telephony. The value of a permanent pointtopoint
network is unimpeded communications between the two endpoints. The value of an ondemand
pointtopoint connection is proportional to the number of potential pairs of subscribers and has been
expressed as Metcalfe's Law.
Permanent (dedicated)
Easiest to understand, of the variations of pointtopoint topology, is a pointtopoint
communications channel that appears, to the user, to be permanently associated with the two endpoints. A child's tin can telephone is one
example of a physical dedicated channel.
Within many switched telecommunications systems, it is possible to establish a permanent circuit. One example might be a telephone in the
lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. "Nailing down" a switched connection
saves the cost of running a physical circuit between the two points. The resources in such a connection can be released when no longer
needed, for example, a television circuit from a parade route back to the studio.
Switched:
Using circuitswitching or packetswitching technologies, a pointtopoint circuit can be set up dynamically and dropped when no longer
needed. This is the basic mode of conventional telephony.
Bus
In local area networks where bus topology is used, each node is connected to a single cable, by the help of interface connectors.This central cable
is the backbone of the network and is known as the bus (thus the name). A signal from the source travels in both directions to all machines
connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the
machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Because the bus topology consists of only
one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is
offset by the high cost of managing the network. Additionally, because only one cable is utilized, it can be the single point of failure.
Linear bus
The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly
two endpoints (this is the 'bus', which is also commonly referred to as the backbone, or trunk) – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all
nodes in the network simultaneously.
[1]
Note: When the electrical signal reaches the end of the bus, the signal is reflected back down the
line, causing unwanted interference. As a solution, the two endpoints of the bus are normally
terminated with a device called a terminator that prevents this reflection.
Distributed bus
The type of network topology in which all of the nodes of the network are connected to a common
transmission medium which has more than two endpoints that are created by adding branches to the
main section of the transmission medium – the physical distributed bus topology functions in exactly
the same fashion as the physical linear bus topology (i.e., all nodes share a common transmission
medium).
Star
In local area networks with a star topology, each network host is connected to a central hub with a pointtopoint
connection. So it can be said that every computer is indirectly connected to every other node with the
help of the hub. In Star topology every node (computer workstation or any other peripheral) is connected to
a central node called hub, router or switch. The switch is the server and the peripherals are the clients. The
network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes
on the network must be connected to one central device. All traffic that traverses the network passes
through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest
topology to design and implement. An advantage of the star topology is the simplicity of adding additional
nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.
Extended star
A type of network topology in which a network that is based upon the physical star topology has one
or more repeaters between the central node and the peripheral or 'spoke' nodes, the repeaters being
used to extend the maximum transmission distance of the pointtopoint links between the central
node and the peripheral nodes beyond that which is supported by the transmitter power of the central
node or beyond that which is supported by the standard upon which the physical layer of the physical star network is based.
If the repeaters in a network that is based upon the physical extended star topology are replaced with hubs or switches, then a hybrid
network topology is created that is referred to as a physical hierarchical star topology, although some texts make no distinction between the Distributed Star
A type of network topology that is composed of individual networks that are based upon the physical star topology connected in a linear
fashion – i.e., 'daisychained' – with no central or top level connection point (e.g., two or more 'stacked' hubs, along with their associated
star connected nodes or 'spokes').
Ring
A network topology is set up in a circular fashion in such a way that they make a closed loop. This way
data travels around the ring in one direction and each device on the ring acts as a repeater to keep the signal
strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send
the data on to the next device in the ring. The network is dependent on the ability of the signal to travel
around the ring. When a device sends data, it must travel through each device on the ring until it reaches its
destination. Every node is a critical link.
[4]
In a ring topology, there is no server computer present; all
nodes work as a server and repeat the signal. The disadvantage of this topology is that if one node stops
working, the entire network is affected or stops working.
Mesh
The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that
communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's
Law.
Fully connected network
A fully connected network is a communication network in which each of the nodes is connected to each other. In graph theory it known as
a complete graph. A fully connected network doesn't need to use switching or broadcasting. However, its major disadvantage is that the
number of connections grows quadratically with the number of nodes, as per the formula
Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network.
[1][2] Essentially, it is the topological
[3]
structure
of a network and may be depicted physically or logically. Physical topology is the placement of the various components of a network, including device
location and cable installation, while logical topology illustrates how data flows within a network, regardless of its physical design. Distances between
nodes, physical interconnections, transmission rates, or signal types may differ between two networks, yet their topologies may be identical.
An example is a local area network (LAN): Any given node in the LAN has one or more physical links to other devices in the network; graphically
mapping these links results in a geometric shape that can be used to describe the physical topology of the network. Conversely, mapping the data flow
between the components determines the logical topology of the network.
Topology
There are two basic categories of network topologies:
[4] physical topologies and logical topologies.
The cabling layout used to link devices is the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the
interconnections between the nodes and the cabling.
[1] The physical topology of a network is determined by the capabilities of the network access
devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.
The logical topology in contrast, is the way that the signals act on the network media, or the way that the data passes 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 twisted pair Ethernet using repeater hubs was a logical bus topology with a physical star topology layout. Token
Ring is a logical ring topology, but is wired as a physical star from the Media Access Unit.
The logical classification of network topologies generally follows the same classifications as those in the physical classifications of network topologies
but describes the path that the data takes between nodes being used as opposed to the actual physical connections between nodes. The logical topologies
are generally determined by network protocols as opposed to being determined by the physical layout of cables, wires, and network devices or by the
flow of the electrical signals, although in many cases the paths that the electrical signals take between nodes may closely match the logical flow of data,
hence the convention of using the terms logical topology and signal topology interchangeably.
Logical topologies are often closely associated with Media Access Control methods and protocols. Logical topologies are able to be dynamically
reconfigured by special types of equipment such as routers and switches.
The study of network topology recognizes eight basic topologies:
[5] pointtopoint, bus, star, ring or circular, mesh, tree, hybrid, or daisy chain.
Pointtopoint
The simplest topology with a dedicated link between two endpoints. Switched pointtopoint
topologies are the basic model of conventional telephony. The value of a permanent pointtopoint
network is unimpeded communications between the two endpoints. The value of an ondemand
pointtopoint connection is proportional to the number of potential pairs of subscribers and has been
expressed as Metcalfe's Law.
Permanent (dedicated)
Easiest to understand, of the variations of pointtopoint topology, is a pointtopoint
communications channel that appears, to the user, to be permanently associated with the two endpoints. A child's tin can telephone is one
example of a physical dedicated channel.
Within many switched telecommunications systems, it is possible to establish a permanent circuit. One example might be a telephone in the
lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. "Nailing down" a switched connection
saves the cost of running a physical circuit between the two points. The resources in such a connection can be released when no longer
needed, for example, a television circuit from a parade route back to the studio.
Switched:
Using circuitswitching or packetswitching technologies, a pointtopoint circuit can be set up dynamically and dropped when no longer
needed. This is the basic mode of conventional telephony.
Bus
In local area networks where bus topology is used, each node is connected to a single cable, by the help of interface connectors.This central cable
is the backbone of the network and is known as the bus (thus the name). A signal from the source travels in both directions to all machines
connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the
machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Because the bus topology consists of only
one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of implementing the technology is
offset by the high cost of managing the network. Additionally, because only one cable is utilized, it can be the single point of failure.
Linear bus
The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly
two endpoints (this is the 'bus', which is also commonly referred to as the backbone, or trunk) – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all
nodes in the network simultaneously.
[1]
Note: When the electrical signal reaches the end of the bus, the signal is reflected back down the
line, causing unwanted interference. As a solution, the two endpoints of the bus are normally
terminated with a device called a terminator that prevents this reflection.
Distributed bus
The type of network topology in which all of the nodes of the network are connected to a common
transmission medium which has more than two endpoints that are created by adding branches to the
main section of the transmission medium – the physical distributed bus topology functions in exactly
the same fashion as the physical linear bus topology (i.e., all nodes share a common transmission
medium).
Star
In local area networks with a star topology, each network host is connected to a central hub with a pointtopoint
connection. So it can be said that every computer is indirectly connected to every other node with the
help of the hub. In Star topology every node (computer workstation or any other peripheral) is connected to
a central node called hub, router or switch. The switch is the server and the peripherals are the clients. The
network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes
on the network must be connected to one central device. All traffic that traverses the network passes
through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest
topology to design and implement. An advantage of the star topology is the simplicity of adding additional
nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.
Extended star
A type of network topology in which a network that is based upon the physical star topology has one
or more repeaters between the central node and the peripheral or 'spoke' nodes, the repeaters being
used to extend the maximum transmission distance of the pointtopoint links between the central
node and the peripheral nodes beyond that which is supported by the transmitter power of the central
node or beyond that which is supported by the standard upon which the physical layer of the physical star network is based.
If the repeaters in a network that is based upon the physical extended star topology are replaced with hubs or switches, then a hybrid
network topology is created that is referred to as a physical hierarchical star topology, although some texts make no distinction between the Distributed Star
A type of network topology that is composed of individual networks that are based upon the physical star topology connected in a linear
fashion – i.e., 'daisychained' – with no central or top level connection point (e.g., two or more 'stacked' hubs, along with their associated
star connected nodes or 'spokes').
Ring
A network topology is set up in a circular fashion in such a way that they make a closed loop. This way
data travels around the ring in one direction and each device on the ring acts as a repeater to keep the signal
strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send
the data on to the next device in the ring. The network is dependent on the ability of the signal to travel
around the ring. When a device sends data, it must travel through each device on the ring until it reaches its
destination. Every node is a critical link.
[4]
In a ring topology, there is no server computer present; all
nodes work as a server and repeat the signal. The disadvantage of this topology is that if one node stops
working, the entire network is affected or stops working.
Mesh
The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that
communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's
Law.
Fully connected network
A fully connected network is a communication network in which each of the nodes is connected to each other. In graph theory it known as
a complete graph. A fully connected network doesn't need to use switching or broadcasting. However, its major disadvantage is that the
number of connections grows quadratically with the number of nodes, as per the formula