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What do you understand by network topology compare and contrast different network topologies used
in LAN?
Physical or Logical Network Topologies
With the brief introduction provided above, we simply understand what a basic computer network is all
about.
A network topology can either be the physical or logical arrangement of devices on a network.
These connected devices can be routers, switches, firewalls, network printers, wireless access points,
user computers etc [basically anything that can be assigned an IP address]. Note that end user devices
are also part of the network topology.
Logical topology deals with how data is transferred and flows on the network, while physical topology is
concerned with the physical layout of the devices on the network and how they are physically
connected.
Types of Network Topologies
Network topology goes beyond logical or physical arrangement of devices. This brings us to the various
types of network topologies available today. These topologies are Bus, Star, Ring, Tree, Hybrid and Mesh
network topologies. Let us take a closer look at each of these types mentioned.
Bus Topology – Advantages and Disadvantages
Bus topology has a network arrangement where nodes make use of a single communication line for data
transmission.
MORE READING: 10 Best Computer Networking Jobs with High Salaries in USA
Many networks at the beginning of computer networking era made use of this topology due to easy
implementation.
Advantages
Since there is a single communication line, means the same medium is shared. Therefore, the major
advantage of using this topology is its simplicity.
Easy to setup and extend.
Less costly. Less cabling needs.
Disadvantages
On the other hand, having a single communication line for data transmission makes it easier for collision
to occur, which is seen as a disadvantage of using this network topology.
If the single network cable has a problem or disconnection, the whole network breaks.
Difficult to identify a problem.
All devices receive all signals from every other host. This is not efficient.
What is network topology?
Network topology is the description of the arrangement of nodes [e.g. networking switches and routers]
and connections in a network, often represented as a graph.
No matter how identical two organizations are, no two networks are exactly alike. However, many
organizations are relying on well-established network topology models. Network topologies outline how
devices are connected together and how data is transmitted from one node to another.
A logical network topology is a conceptual representation of how devices operate at particular layers of
abstraction. A physical topology details how devices are physically connected.Logical and physical
topologies can both be represented as visual diagrams.
A network topology map is a map that allows an administrator to see the physical network layout of
connected devices. Having the map of a network’s topology on hand is very useful for understanding
how devices connect to each other and the best techniques for troubleshooting.
Types of Network Topology
The arrangement of a network that comprises nodes and connecting lines via sender and receiver is
referred to as network topology. The various network topologies are:
What is Topology?
Network topologies describe the methods in which all the elements of a network are mapped. The
topology term refers to both the physical and logical layout of a network.
In this network topology tutorial, we will explain:
What is Topology?
Type of Network Topology
Point to Point
Bus Topology
Ring Topology
Star Topology
Mesh Topology
Tree Topology
Hybrid Topology
How to select a Network Topology?
TopologiesEdit
Diagram of different network topologies.
Two basic categories of network topologies exist, physical topologies and logical topologies.[5]
The transmission medium layout used to link devices is the physical topology of the network. For
conductive or fiber optical mediums, this refers to the layout of cabling, the locations of nodes, and the
links 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 telecommunication circuits.
In contrast, logical topology is the way that the signals act on the network media,[6] 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.[7] 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
carried on a physical star topology. Token Ring is a logical ring topology, but is wired as a physical star
from the media access unit. Physically, AFDX can be a cascaded star topology of multiple dual redundant
Ethernet switches; however, the AFDX Virtual links are modeled as time-switched single-transmitter bus
connections, thus following the safety model of a single-transmitter bus topology previously used in
aircraft. Logical topologies are often closely associated with media access control methods and protocols.
Some networks are able to dynamically change their logical topology through configuration changes to
their routers and switches.
The transmission media [often referred to in the literature as the physical media] used to link devices to
form a computer network include electrical cables [Ethernet, HomePNA, power line communication,
G.hn], optical fiber [fiber-optic communication], and radio waves [wireless networking]. In the OSI
model, these are defined at layers 1 and 2 — the physical layer and the data link layer.
A widely adopted family of transmission media used in local area network [LAN] technology is
collectively known as Ethernet. The media and protocol standards that enable communication between
networked devices over Ethernet are defined by IEEE 802.3. Ethernet transmits data over both copper
and fiber cables. Wireless LAN standards [e.g. those defined by IEEE 802.11] use radio waves, or others
use infrared signals as a transmission medium. Power line communication uses a building's power
cabling to transmit data.
Wired technologiesEdit
The orders of the following wired technologies are, roughly, from slowest to fastest transmission speed.
Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local
area networks. The cables consist of copper or aluminum wire surrounded by an insulating layer
[typically a flexible material with a high dielectric constant], which itself is surrounded by a conductive
layer. The insulation between the conductors helps maintain the characteristic impedance of the cable
which can help improve its performance. Transmission speed ranges from 200 million bits per second to
more than 500 million bits per second.
ITU-T G.hn technology uses existing home wiring [coaxial cable, phone lines and power lines] to create a
high-speed [up to 1 Gigabit/s] local area network.
Signal traces on printed circuit boards are common for board-level serial communication, particularly
between certain types integrated circuits, a common example being SPI.
Ribbon cable [untwisted and possibly unshielded] has been a cost-effective media for serial protocols,
especially within metallic enclosures or rolled within copper braid or foil, over short distances, or at
lower data rates. Several serial network protocols can be deployed without shielded or twisted pair
cabling, that is, with "flat" or "ribbon" cable, or a hybrid flat/twisted ribbon cable, should EMC, length,
and bandwidth constraints permit: RS-232,[8] RS-422, RS-485,[9] CAN,[10] GPIB, SCSI,[11] etc.
Twisted pair wire is the most widely used medium for all telecommunication.[citation needed] Twistedpair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two
insulated copper wires twisted into pairs. Computer network cabling [wired Ethernet as defined by IEEE
802.3] consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The
use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The
transmission speed ranges from 2 million bits per second to 10 billion bits per second. Twisted pair
cabling comes in two forms: unshielded twisted pair [UTP] and shielded twisted-pair [STP]. Each form
comes in several category ratings, designed for use in various scenarios.
2007 map showing submarine optical fiber telecommunication cables around the world.
An optical fiber is a glass fiber. It carries pulses of light that represent data. Some advantages of optical
fibers over metal wires are very low transmission loss and immunity from electrical interference. Optical
fibers can simultaneously carry multiple wavelengths of light, which greatly increases the rate that data
can be sent, and helps enable data rates of up to trillions of bits per second. Optic fibers can be used for
long runs of cable carrying very high data rates, and are used for undersea cables to interconnect
continents.
Price is a main factor distinguishing wired- and wireless-technology options in a business. Wireless
options command a price premium that can make purchasing wired computers, printers and other
devices a financial benefit. Before making the decision to purchase hard-wired technology products, a
review of the restrictions and limitations of the selections is necessary. Business and employee needs
may override any cost considerations.[12]
Wireless technologiesEdit
Personal computers are very often connected to networks using wireless links
Terrestrial microwave– Terrestrial microwave communication uses Earth-based transmitters and
receivers resembling satellite dishes. Terrestrial microwaves are in the low gigahertz range, which limits
all communications to line-of-sight. Relay stations are spaced approximately 50km [30mi] apart.
Communications satellites– Satellites communicate via microwave radio waves, which are not deflected
by the Earth's atmosphere. The satellites are stationed in space, typically in geostationary orbit
35,786km [22,236mi] above the equator. These Earth-orbiting systems are capable of receiving and
relaying voice, data, and TV signals.
Cellular and PCS systems use several radio communications technologies. The systems divide the region
covered into multiple geographic areas. Each area has a low-power transmitter or radio relay antenna
device to relay calls from one area to the next area.
Radio and spread spectrum technologies– Wireless local area networks use a high-frequency radio
technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread
spectrum technology to enable communication between multiple devices in a limited area. IEEE 802.11
defines a common flavor of open-standards wireless radio-wave technology known as Wi-Fi.
Free-space optical communication uses visible or invisible light for communications. In most cases, lineof-sight propagation is used, which limits the physical positioning of communicating devices.
Exotic technologiesEdit
There have been various attempts at transporting data over exotic media:
Both cases have a large round-trip delay time, which gives slow two-way communication, but doesn't
prevent sending large amounts of information.
Network nodes are the points of connection of the transmission medium to transmitters and receivers
of the electrical, optical, or radio signals carried in the medium. Nodes may be associated with a
computer, but certain types may have only a microcontroller at a node or possibly no programmable
device at all. In the simplest of serial arrangements, one RS-232 transmitter can be connected by a pair
of wires to one receiver, forming two nodes on one link, or a Point-to-Point topology. Some protocols
permit a single node to only either transmit or receive [e.g., ARINC 429]. Other protocols have nodes
that can both transmit and receive into a single channel [e.g., CAN can have many transceivers
connected to a single bus]. While the conventional system building blocks of a computer network
include network interface controllers [NICs], repeaters, hubs, bridges, switches, routers, modems,
gateways, and firewalls, most address network concerns beyond the physical network topology and may
be represented as single nodes on a particular physical network topology.
Network interfacesEdit
An ATM network interface in the form of an accessory card. A lot of network interfaces are built-in.
A network interface controller [NIC] is computer hardware that provides a computer with the ability to
access the transmission media, and has the ability to process low-level network information. For
example, the NIC may have a connector for accepting a cable, or an aerial for wireless transmission and
reception, and the associated circuitry.
The NIC responds to traffic addressed to a network address for either the NIC or the computer as a
whole.
In Ethernet networks, each network interface controller has a unique Media Access Control [MAC]
address—usually stored in the controller's permanent memory. To avoid address conflicts between
network devices, the Institute of Electrical and Electronics Engineers [IEEE] maintains and administers
MAC address uniqueness. The size of an Ethernet MAC address is six octets. The three most significant
octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned
prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce.
Repeaters and hubsEdit
A repeater is an electronic device that receives a network signal, cleans it of unnecessary noise and
regenerates it. The signal may be reformed or retransmitted at a higher power level, to the other side of
an obstruction possibly using a different transmission medium, so that the signal can cover longer
distances without degradation. Commercial repeaters have extended RS-232 segments from 15 meters
to over a kilometer.[15] In most twisted pair Ethernet configurations, repeaters are required for cable
that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of
kilometers apart.
Repeaters work within the physical layer of the OSI model, that is, there is no end-to-end change in the
physical protocol across the repeater, or repeater pair, even if a different physical layer may be used
between the ends of the repeater, or repeater pair. Repeaters require a small amount of time to
regenerate the signal. This can cause a propagation delay that affects network performance and may
affect proper function. As a result, many network architectures limit the number of repeaters that can
be used in a row, e.g., the Ethernet 5-4-3 rule.
A repeater with multiple ports is known as hub, an Ethernet hub in Ethernet networks, a USB hub in USB
networks.
USB networks use hubs to form tiered-star topologies.
Ethernet hubs and repeaters in LANs have been mostly obsoleted by modern switches.
A network bridge connects and filters traffic between two network segments at the data link layer [layer
2] of the OSI model to form a single network. This breaks the network's collision domain but maintains a
unified broadcast domain. Network segmentation breaks down a large, congested network into an
aggregation of smaller, more efficient networks.
Bridges come in three basic types:
Local bridges: Directly connect LANs
Remote bridges: Can be used to create a wide area network [WAN] link between LANs. Remote bridges,
where the connecting link is slower than the end networks, largely have been replaced with routers.
Wireless bridges: Can be used to join LANs or connect remote devices to LANs.
A network switch is a device that forwards and filters OSI layer 2 datagrams [frames] between ports
based on the destination MAC address in each frame.[16] A switch is distinct from a hub in that it only
forwards the frames to the physical ports involved in the communication rather than all ports connected.
It can be thought of as a multi-port bridge.[17] It learns to associate physical ports to MAC addresses by
examining the source addresses of received frames. If an unknown destination is targeted, the switch
broadcasts to all ports but the source. Switches normally have numerous ports, facilitating a star
topology for devices, and cascading additional switches.
Multi-layer switches are capable of routing based on layer 3 addressing or additional logical levels. The
term switch is often used loosely to include devices such as routers and bridges, as well as devices that
may distribute traffic based on load or based on application content [e.g., a Web URL identifier].
A typical home or small office router showing the ADSL telephone line and Ethernet network cable
connections
A router is an internetworking device that forwards packets between networks by processing the
routing information included in the packet or datagram [Internet protocol information from layer 3]. The
routing information is often processed in conjunction with the routing table [or forwarding table]. A
router uses its routing table to determine where to forward packets. A destination in a routing table can
include a "null" interface, also known as the "black hole" interface because data can go into it, however,
no further processing is done for said data, i.e. the packets are dropped.
Modems [MOdulator-DEModulator] are used to connect network nodes via wire not originally designed
for digital network traffic, or for wireless. To do this one or more carrier signals are modulated by the
digital signal to produce an analog signal that can be tailored to give the required properties for
transmission. Modems are commonly used for telephone lines, using a digital subscriber line technology.
FirewallsEdit
A firewall is a network device for controlling network security and access rules. Firewalls are typically
configured to reject access requests from unrecognized sources while allowing actions from recognized
ones. The vital role firewalls play in network security grows in parallel with the constant increase in
cyber attacks.
The study of network topology recognizes eight basic topologies: point-to-point, bus, star, ring or
circular, mesh, tree, hybrid, or daisy chain.[18]
Point-to-pointEdit
The simplest topology with a dedicated link between two endpoints. Easiest to understand, of the
variations of point-to-point topology, is a point-to-point communication 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.
Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up
dynamically and dropped when no longer needed. Switched point-to-point topologies are the basic
model of conventional telephony.
The value of a permanent point-to-point network is unimpeded communications between the two
endpoints. The value of an on-demand point-to-point connection is proportional to the number of
potential pairs of subscribers and has been expressed as Metcalfe's Law.
Daisy chainEdit
Daisy chaining is accomplished by connecting each computer in series to the next. If a message is
intended for a computer partway down the line, each system bounces it along in sequence until it
reaches the destination. A daisy-chained network can take two basic forms: linear and ring.
A linear topology puts a two-way link between one computer and the next. However, this was expensive
in the early days of computing, since each computer [except for the ones at each end] required two
receivers and two transmitters.
By connecting the computers at each end of the chain, a ring topology can be formed. When a node
sends a message, the message is processed by each computer in the ring. An advantage of the ring is
that the number of transmitters and receivers can be cut in half. Since a message will eventually loop all
of the way around, transmission does not need to go both directions. Alternatively, the ring can be used
to improve fault tolerance. If the ring breaks at a particular link then the transmission can be sent via the
reverse path thereby ensuring that all nodes are always connected in the case of a single failure.
In local area networks using bus topology, each node is connected by interface connectors to a single
central cable. This is the 'bus', also referred to as the backbone, or trunk– all data transmission 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]
A signal containing the address of the intended receiving machine travels from a source machine in both
directions to all machines connected to the bus until it finds the intended recipient, which then accepts
the data. If the machine address does not match the intended address for the data, the data portion of
the signal is ignored. Since the bus topology consists of only one wire it is less expensive to implement
than other topologies, but the savings are offset by the higher cost of managing the network.
Additionally, since the network is dependent on the single cable, it can be the single point of failure of
the network. In this topology data being transferred may be accessed by any node.
Linear busEdit
In a linear bus network, all of the nodes of the network are connected to a common transmission
medium which has just two endpoints. When the electrical signal reaches the end of the bus, the signal
is reflected back down the line, causing unwanted interference. To prevent this, the two endpoints of
the bus are normally terminated with a device called a terminator.
Distributed busEdit
In a distributed bus network, all of the nodes of the network are connected to a common transmission
medium with more than two endpoints, 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 because all nodes share a common transmission medium.
In star topology, every peripheral node [computer workstation or any other peripheral] is connected to
a central node called a hub or switch. The hub 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
peripheral nodes on the network must be connected to one central hub. All traffic that traverses the
network passes through the central hub, which acts as a signal repeater.
The star topology is considered the easiest topology to design and implement. One 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. Also, since all peripheral communication must flow
through the central hub, the aggregate central bandwidth forms a network bottleneck for large clusters.
Extended starEdit
The extended star network topology extends a physical star topology by one or more repeaters between
the central node and the peripheral [or 'spoke'] nodes. The repeaters are used to extend the maximum
transmission distance of the physical layer, the point-to-point distance between the central node and
the peripheral nodes. Repeaters allow greater transmission distance, further than would be possible
using just the transmitting power of the central node. The use of repeaters can also overcome
limitations from the standard upon which the physical layer is based.
A physical extended star topology in which repeaters are replaced with hubs or switches is a type of
hybrid network topology and is referred to as a physical hierarchical star topology, although some texts
make no distinction between the two topologies.
A physical hierarchical star topology can also be referred as a tier-star topology, this topology differs
from a tree topology in the way star networks are connected together. A tier-star topology uses a
central node, while a tree topology uses a central bus and can also be referred as a star-bus network.
Distributed starEdit
A distributed star is a network topology that is composed of individual networks that are based upon the
physical star topology connected in a linear fashion– i.e., 'daisy-chained'– with no central or top level
connection point [e.g., two or more 'stacked' hubs, along with their associated star connected nodes or
'spokes'].
A ring topology is a daisy chain in a closed loop. Data travels around the ring in one direction. When one
node sends data to another, the data passes through each intermediate node on the ring until it reaches
its destination. The intermediate nodes repeat [re transmit] the data to keep the signal strong.[5] Every
node is a peer; there is no hierarchical relationship of clients and servers. If one node is unable to re
transmit data, it severs communication between the nodes before and after it in the bus.
Advantages:
When the load on the network increases, its performance is better than bus topology.
There is no need of network server to control the connectivity between workstations.
Disadvantages:
Aggregate network bandwidth is bottlenecked by the weakest link between two nodes.
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 networkEdit
Fully connected mesh topology
In a fully connected network, all nodes are interconnected. [In graph theory this is called a complete
graph.] The simplest fully connected network is a two-node network. A fully connected network doesn't
need to use packet switching or broadcasting. However, since the number of connections grows
quadratically with the number of nodes:
c=n[n−1]2.{\displaystyle c={\frac {n[n-1]}{2}}.\,}
This makes it impractical for large networks. This kind of topology does not trip and affect other nodes in
the network.
Partially connected networkEdit
Partially connected mesh topology
In a partially connected network, certain nodes are connected to exactly one other node; but some
nodes are connected to two or more other nodes with a point-to-point link. This makes it possible to
make use of some of the redundancy of mesh topology that is physically fully connected, without the
expense and complexity required for a connection between every node in the network.
Hybrid topology is also known as hybrid network.[19] Hybrid networks combine two or more topologies
in such a way that the resulting network does not exhibit one of the standard topologies [e.g., bus, star,
ring, etc.]. For example, a tree network [or star-bus network] is a hybrid topology in which star networks
are interconnected via bus networks.[20][21] However, a tree network connected to another tree
network is still topologically a tree network, not a distinct network type. A hybrid topology is always
produced when two different basic network topologies are connected.
A star-ring network consists of two or more ring networks connected using a multistation access unit
[MAU] as a centralized hub.
Snowflake topology is a star network of star networks.[citation needed]
Two other hybrid network types are hybrid mesh and hierarchical star.[20]
Types of Network Topology
Network Topology is the schematic description of a network arrangement, connecting various
nodes[sender and receiver] through lines of connection.
LAN Network Topologies
Written by Administrator. Posted in Network Fundamentals
Network topologies can take a bit of time to understand when you're all new to this kind of cool stuff,
but it's very important to fully understand them as they are key elements to understanding and
troubleshooting networks and will help you decide what actions to take when you're faced with network
problems.
This article explains the different network topologies found in today's networks. We examine Bus
Topology, Ring Topology, Star Topology, Mesh Topology, Hybrid Topology and many more.
Physical and Logical Topologies
There are two types of topologies: Physical and Logical. The physical topology of a network refers to the
layout of cables, computers and other peripherals. Try to imagine yourself in a room with a small
network, you can see network cables coming out of every computer that is part of the network, then
those cables plug into a hub or switch. What you're looking at is the physical topology of that network !
Logical topology is the method used to pass the information between the computers. In other words,
looking at that same room, if you were to try to see how the network works with all the computers
talking [think of the computers generating traffic and packets of data going everywhere on the network]
you would be looking at the logical part of the network. The way the computers will be talking to each
other and the direction of the traffic is controlled by the various protocols [like Ethernet] or, if you like,
rules.
If we used token ring, then the physical topology would have to change to meet the requirements of the
way the token ring protocol works [logically].
If it's all still confusing, consider this: The physical topology describes the layout of the network, just like
a map shows the layout of various roads, and the logical topology describes how the data is sent accross
the network or how the cars are able to travel [the direction and speed] at every road on the map.
The most common types of physical topologies, which we are going to analyse, are: Bus, Hub/Star and
Ring
The Physical Bus Topology
Bus topology is fairly old news and you probably won't be seeing much of these around in any modern
office or home.
With the Bus topology, all workstations are connect directly to the main backbone that carries the data.
Traffic generated by any computer will travel across the backbone and be received by all workstations.
This works well in a small network of 2-5 computers, but as the number of computers increases so will
the network traffic and this can greatly decrease the performance and available bandwidth of your
network.
As you can see in the above example, all computers are attached to a continuous cable which connects
them in a straight line. The arrows clearly indicate that the packet generated by Node 1 is transmitted to
all computers on the network, regardless the destination of this packet.
Also, because of the way the electrical signals are transmitted over this cable, its ends must be
terminated by special terminators that work as "shock absorbers", absorbing the signal so it won't
reflect back to where it came from. The value of 50Ohms has been selected after carefully taking in
consideration all the electrical characteristics of the cable used, the voltage that the signal which runs
through the cables, the maximum and minimum length of the bus and a few more.
If the bus [the long yellow cable] is damaged anywhere in its path, then it will most certainly cause the
network to stop working or, at the very least, cause big communication problems between the
workstations.
Thinnet - 10 Base2, also known as coax cable [Black in colour] and Thicknet - 10 Base 5 [Yellow in colour]
is used in these type of topologies.
The Physical HUB or STAR Topology
The Star or Hub topology is one of the most common network topologies found in most offices and
home networks. It has become very popular in contrast to the bus type [which we just spoke about],
because of the cost and the ease of troubleshooting.
The advantage of the star topology is that if one computer on the star topology fails, then only the failed
computer is unable to send or receive data. The remainder of the network functions normally.
The disadvantage of using this topology is that because each computer is connected to a central hub or
switch, if this device fails, the entire network fails!
A classic example of this type of topology is the UTP [10 base T], which normaly has a blue colour.
Personally I find it boring, so I decided to go out and get myself green, red and yellow colours :]
The Physical Ring Topology
In the ring topology, computers are connected on a single circle of cable. Unlike the bus topology, there
are no terminated ends. The signals travel around the loop in one direction and pass through each
computer, which acts as a repeater to boost the signal and send it to the next computer. On a larger
scale, multiple LANs can be connected to each other in a ring topology by using Thicknet coaxial or fiberoptic cable.
The method by which the data is transmitted around the ring is called token passing. IBM's token ring
uses this method. A token is a special series of bits that contains control information. Possession of the
token allows a network device to transmit data to the network. Each network has only one token.
The Physical Mesh Topology
In a mesh topology, each computer is connected to every other computer by a separate cable. This
configuration provides redundant paths through the new work, so if one computer blows up, you don't
lose the network :] On a large scale, you can connect multiple LANs using mesh topology with leased
telephone lines, Thicknet coaxial cable or fiber optic cable.
Again, the big advantage of this topology is its backup capabilities by providing multiple paths through
the network.
The Physical Hybrid Topology
With the hybrid topology, two or more topologies are combined to form a complete network. For
example, a hybrid topology could be the combination of a star and bus topology. These are also the
most common in use.
Star-Bus
In a star-bus topology, several star topology networks are linked to a bus connection. In this topology, if
a computer fails, it will not affect the rest of the network. However, if the central component, or hub,
that attaches all computers in a star, fails, then you have big problems since no computer will be able to
communicate.
Star-Ring
In the Star-Ring topology, the computers are connected to a central component as in a star network.
These components, however, are wired to form a ring network.
Like the star-bus topology, if a single computer fails, it will not affect the rest of the network. By using
token passing, each computer in a star-ring topology has an equal chance of communicating. This allows
for greater network traffic between segments than in a star-bus topology.
Back to Network Fundamentals
Types of Topology
There are five types of topology in computer networks:
1. Mesh Topology
2. Star Topology
3. Bus Topology
4. Ring Topology
5. Hybrid Topology
What is network topology and types of network topology?
Topology is derived from two Greek words topo and logy, where topo means 'place' and logy means
'study'. In computer networks, a topology is used to explain how a network is physically connected and
the logical flow of information in the network. A topology mainly describes how devices are connected
and interact with each other using communication links.
In computer networks, there are mainly two types of topologies, they are:
Physical Topology: A physical topology describes the way in which the computers or nodes are
connected with each other in a computer network. It is the arrangement of various elements[link, nodes,
etc.], including the device location and code installation of a computer network. In other words, we can
say that it is the physical layout of nodes, workstations, and cables in the network.
Logical Topology: A logical topology describes the way, data flow from one computer to another. It is
bound to a network protocol and defines how data is moved throughout the network and which path it
takes. In other words, it is the way in which the devices communicate internally.
Network topology defines the layout, virtual shape, or structure of the network, not only physically but
also logically. A network can have one physical topology and multiple logical topologies at the same time.
In this blog, we will mainly concentrate on physical topologies. We'll learn about different types of
physical topologies, their advantages, and disadvantages.
In a computer network, there are mainly six types of physical topology, they are:
Bus Topology
Ring Topology
Star Topology
Mesh Topology
Tree Topology
Hybrid Topology
Now let us learn these topologies one by one:
Bus Topology
Bus topology is the simplest kind of topology in which a common bus or channel is used for
communication in the network. The bus is connected to various taps and droplines. Taps are the
connectors, while droplines are the cables connecting the bus with the computer. In other words, there
is only a single transmission line for all nodes.
When a sender sends a message, all other computers can hear it, but only the receiver accepts
it[verifying the mac address attached with the data frame] and others reject it. Bus technology is mainly
suited for small networks like LAN, etc.
In this topology, the bus acts as the backbone of the network, which joins every computer and
peripherals in the network. Both ends of the shared channel have line terminators. The data is sent only
in one direction and as soon as it reaches the end, the terminator removes the data from the
communication line[to prevent signal bounce and data flow disruption].
In a bus topology, each computer communicates to another computer on the network independently.
Every computer can share the network's total bus capabilities. The devices share the responsibility for
the flow of data from one point to the other in the network.
For Example Ethernet cable, etc.
Following are the advantages of Bus topology:
Simple to use and install.
If a node fails, it will not affect other nodes.
Less cabling is required.
Cost-efficient to implement.
Following are the disadvantages of Bus topology:
Efficiency is less when nodes are more[strength of signal decreases].
If the bus fails, the network will fail.
A limited number of nodes can connect to the bus due to limited bus length.
Security issues and risks are more as messages are broadcasted to all nodes.
Congestion and traffic on the bus as it is the only source of communication.
Ring Topology
Ring topology is a topology in which each computer is connected to exactly two other computers to
form the ring. The message passing is unidirectional and circular in nature.
This network topology is deterministic in nature, i.e., each computer is given access for transmission at a
fixed time interval. All the nodes are connected in a closed-loop. This topology mainly works on a tokenbased system and the token travels in a loop in one specific direction.
In a ring topology, if a token is free then the node can capture the token and attach the data and
destination address to the token, and then leaves the token for communication. When this token
reaches the destination node, the data is removed by the receiver and the token is made free to carry
the next data.
For Example, Token Ring, etc.
Following are the advantages of Ring topology:
Easy Installation.
Less Cabling Required.
Reduces chances of data collision[unidirectional].
Easy to troubleshoot[the faulty node does not pass the token].
Each node gets the same access time.
Following are the disadvantages of Ring topology:
If a node fails, the whole network will fail.
Slow data transmission speed[each message has to go through the ring path].
Difficult to reconfigure[we have to break the ring].
Star Topology
Star topology is a computer network topology in which all the nodes are connected to a centralized hub.
The hub or switch acts as a middleware between the nodes. Any node requesting for service or
providing service, first contact the hub for communication.
The central device[hub or switch] has point to point communication link[the dedicated link between the
devices which can not be accessed by some other computer] with the devices. The central device then
broadcast or unicast the message based on the central device used. The hub broadcasts the message,
while the switch unicasts the messages by maintaining a switch table. Broadcasting increases
unnecessary data traffic in the network.
In a star topology, hub and switch act as a server, and the other connected devices act as clients. Only
one input-output port and one cable are required to connect a node to the central device. This topology
is better in terms of security because the data does not pass through every node.
For Example High-Speed LAN, etc.
Following are the advantages of Star topology:
Centralized control.
Less Expensive.
Easy to troubleshoot[the faulty node does not give response].
Good fault tolerance due to centralized control on nodes.
Easy to scale[nodes can be added or removed to the network easily].
If a node fails, it will not affect other nodes.
Easy to reconfigure and upgrade[configured using a central device].
Following are the disadvantages of Star topology:
If the central device fails, the network will fail.
The number of devices in the network is limited[due to limited input-output port in a central device].
Mesh Topology
Mesh topology is a computer network topology in which nodes are interconnected with each other. In
other words, direct communication takes place between the nodes in the network.
There are mainly two types of Mesh:
Full Mesh: In which each node is connected to every other node in the network.
Partial Mesh: In which, some nodes are not connected to every node in the network.
In a fully connected mesh topology, each device has a point to point link with every other device in the
network. If there are 'n' devices in the network, then each device has exactly '[n-1]' input-output ports
and communication links. These links are simplex links, i.e., the data moves only in one direction. A
duplex link[in which data can travel in both the directions simultaneously] can replace two simplex links.
If we are using simplex links, then the number of communication links will be 'n[n-1]' for 'n' devices,
while it is 'n[n-1]/2' if we are using duplex links in the mesh topology.
For Example, the Internet[WAN], etc.
Following are the advantages of Mesh topology:
Dedicated links facilitate direct communication.
No congestion or traffic problems on the channels.
Good Fault tolerance due to the dedicated path for each node.
Very fast communication.
Maintains privacy and security due to a separate channel for communication.
If a node fails, other alternatives are present in the network.
Following are the disadvantages of Mesh topology:
Very high cabling required.
Cost inefficient to implement.
Complex to implement and takes large space to install the network.
Installation and maintenance are very difficult.
5. Tree Topology:
Tree topology is a computer network topology in which all the nodes are directly or indirectly connected
to the main bus cable. Tree topology is a combination of Bus and Star topology.
In a tree topology, the whole network is divided into segments, which can be easily managed and
maintained. There is a main hub and all the other sub-hubs are connected to each other in this topology.
Following are the advantages of Tree topology:
Large distance network coverage.
Fault finding is easy by checking each hierarchy.
Least or no data loss.
A Large number of nodes can be connected directly or indirectly.
Other hierarchical networks are not affected if one of them fails.
Following are the disadvantages of Tree topology:
Cabling and hardware cost is high.
Complex to implement.
Hub cabling is also required.
A large network using tree topology is hard to manage.
It requires very high maintenance.
If the main bus fails, the network will fail.
Hybrid Topology:
A Hybrid topology is a computer topology which is a combination of two or more topologies. In practical
use, they are the most widely used.
In this topology, all topologies are interconnected according to the needs to form a hybrid. All the good
features of each topology can be used to make an efficient hybrid topology.
Following are the advantages of Hybrid topology:
It can handle a large volume of nodes.
It provides flexibility to modify the network according to our needs.
Very Reliable[if one node fails it will not affect the whole network].
Following are the disadvantages of Hybrid topology:
Complex design.
Expensive to implement.
Multi-Station Access Unit[MSAL] required.
Hence, after learning the various computer network topologies, we can conclude that some points need
to be considered when selecting a physical topology:
Ease of Installation.
Fault Tolerance.
Implementation Cost.
Cabling Required.
Maintenance Required.
Reliable Nature.
Ease of Reconfiguration and upgradation.
This is all about the topology and its types in a computer network. Hope you learned something new
today. That's it for this blog.
Do share this blog with your friends to spread the knowledge. Visit our YouTube channel for more
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