 Network topologies

 Why is network topology important?

 Approaches to network topology
 Advantages and disadvantages
 Which topology to choose?
Network Topologies
A network topology describes how computers, printers, and other devices (i.e. nodes) are
connected to the network. The following topologies are most commonly used to build most
networks.
Our network cabling products - copper and fiber - provide the links between the nodes within
the topology.

 Regular networks– Grids, rings, etc.

 Real network- power law topologies
A scale-free network is a network whose degree distribution follows a power law, at least
asymptotically. There are two major components that explain the emergence of the scale-free
property in a complex networks:
1. Growth
2. Preferential attachment
By "growth" is called a growth process where, over an extended period of time, new nodes join
an already existing system, a network (like the World Wide Web which has grown by billions
of web pages over 10 years). Finally, by "preferential attachment" is called a new coming node
who prefers to connect to another node which has already a certain number of links with others.
Thus, there is a higher probability that more and more nodes will link themselves to that one
which has already many links, leading this node to a hub in-fine. Depending on the network,
the hubs might either be assortative or disassortative. Assortativity would be found in social
networks in which well-connected/famous people would tend to know better each other.
Disassortativity would be found in technological (Internet, World Wide Web) and biological
(protein interaction, metabolism) networks.

2
Why is network topology important?
The layout of the network is important for several reasons. Above all, it plays an essential role
in how and how well our network functions. Choosing the right topology for our company’s
operational model can increase performance while making it easier to locate faults,
troubleshoot errors, and more effectively allocate resources across the network to ensure
optimal network health. A streamlined and properly managed network topology can increase
energy and data efficiency, which can in turn help to reduce operational and maintenance costs.

The design and structure of a network are usually shown and manipulated in a software-created
network topology diagram. These diagrams are essential for a few reasons, but especially for
how they can provide visual representations of both physical and logical layout, allowing
administrators to see the connections between devices when troubleshooting.

Approaches to network topology

The way a network is arranged can make or break network functionality, connectivity, and
protection from downtime. The question of, “What is network topology?” can be answered
with an explanation of the two categories/approaches in the network topology.

1. Physical – The physical network topology refers to the actual physical connections and
interconnections between nodes and the network (wires, cables, etc.) and how the
network is arranged. Setup, maintenance, and provisioning tasks require insight into the
physical network.

Different types of Physical Topologies are:

 P2P Topology
 Bus Topology
 Ring Topology
 Star Topology
 Tree Topology
 Mesh Topology
 Hybrid Topology

2. Logical or Signal – The logical or signal topology is a higher-level idea of how the
network is set up, including which nodes connect to each other and in which ways, as
well as how data is transmitted through the network. Logical network topology includes
any virtual and cloud resources. It is a little more abstract and strategic, referring to the
conceptual understanding of how and why the network is arranged the way it is, and
how data moves through it.

Type of Logical Topologies is-

 Wireless network

Wireless network topology is a logical topology. It shows how the computers connect
and interact each other when there is no physical connection, no cables connecting the

3
 computers. The computers communicate each other directly, using the wireless devices.
Wireless networks can have infrastructure or ad hoc topology.

Effective network management and monitoring require a strong grasp of both the physical
and logical topology of a network to ensure our network is efficient and healthy.

Physical Topologies
Different types of Physical Topologies are:

 P2P Topology
 Bus Topology
 Ring Topology
 Star Topology
 Tree Topology
 Mesh Topology
 Hybrid Topology

Point to Point
Point-to-point topology is the easiest of all the network topologies. In this method, the
network consists of a direct link between two computers.

P2P Topology Diagram

4
Advantages:

 This is faster and highly reliable than other types of connections since there is a direct
connection.
 No need for a network operating system
 Does not need an expensive server as individual workstations are used to access the
files
 No need for any dedicated network technicians because each user sets their
permissions

Disadvantages:

 The biggest drawback is that it only be used for small areas where computers are in
close proximity.
 We can't back up files and folders centrally
 There is no security besides the permissions. Users often do not require to log onto
their workstations.

Bus Topology

Bus Topology Diagram

A bus topology exists when all of the nodes on the network are connected to a single cable.
This single cable is commonly referred to as a backbone. Bus topology was used for early
10Base-2, ThinNet, and 10Base-5, ThickNet, coaxial cable Ethernet networks. In this topology
messages sent from a node are broadcast to all nodes on the network. Only the intended
recipient node accepts and processes the message. This type of network topology is relatively
easy to install and inexpensive.

Network using a bus topology are limited to only a few dozen computers. If the network
exceeds this size performance, problems will likely result. If there is a failure in the backbone
cable connecting all of the nodes, then the entire network will become unstable and potentially
cease to function. This topology is not typically used in modern networks.

5
Smaller networks with this type of topology use a coaxial or RJ45 cable to link devices
together. However, the bus topology layout is outdated and we unlikely to encounter a company
using a bus topology today.

It is a Passive topology. This means that computers on the bus only listen for data being sent,
they are not responsible for moving the data from one computer to the next. When one
computer sends a signal using the cable, all the computers on the network receive the
information, but only one (Addressee) accepts it. The rest disregard the message.

Advantages:

Here are pros/benefits of using a bus topology:

 Cost of the cable is very less as compared to other topology, so it is widely used to
build small networks.
 Famous for LAN network because they are inexpensive and easy to install.
 It is widely used when a network installation is small, simple, or temporary.
 It is one of the passive topologies. So computers on the bus only listen for data being
sent, that are not responsible for moving the data from one computer to others.
 If N devices are connected to each other in bus topology, then the number of cables
required to connect them is 1 which is known as backbone cable and N drop lines are
required.
 Cost of the cable is less as compared to other topology, but it is used to built small
networks.
 If the network traffic is heavy, it increases collisions in the network. To avoid this,
various protocols are used in MAC layer known as Pure Aloha, Slotted Aloha,
CSMA/CD etc.

Disadvantages:

Here are the cons/drawbacks of bus topology:

 In case if the common cable fails, then the entire system will crash down.
 When network traffic is heavy, it develops collisions in the network.
 Whenever network traffic is heavy, or nodes are too many, the performance time of
the network significantly decreases.
 Cables are always of a limited length.

Devices:

6
Terminator: A device attached to the end-points of a bus network or daisy-chain. The purpose
of the terminator is to absorb signals so that they do not reflect back down the line. If the
backbone is not terminated, then signal is likely to bounce back from the end of the cable
causing data collisions and noise that may disrupt the network. One of the computers in the
network acts as the computer server. When it has two endpoints, it is known as a linear bus
topology. Ethernet networks require a terminator at both ends of the bus, and SCSI (Small
Computer System Interface) chains require a single terminator at the end of the chain.

The bus computer network topology uses coaxial cable. Each end of each segment of the
network has a special cable terminator on it. If this terminator is not present then the network
will not function.

7
Ring Topology

Ring Topology Diagram

Years ago, ring topologies were common in LANs, as two popular networking technologies
used rings:

1. ARCNET
2. Token Ring.

ARCNET is still used for certain applications such as factory automation, but is rarely used in
business networks. Token Ring is still a popular network technology for IBM midrange
computers. Although plenty of Token Ring networks are still in existence, not many new
networks use Token Ring any more.

Ring topology was also used by FDDI, one of the first types of fiber-optic network connections.
FDDI has given way to more efficient fiber-optic techniques, however. So ring networks have
all but vanished from business networks.

8
A ring topology exists when all of the nodes on the network are connected in a circle. Each
node in the network acts as a repeater keeping the signal strong as it travels through the
network. A node will generate a signal that is addressed to a specific computer on the network,
and then the signal will be sent through the network in either a clockwise or counterclockwise
direction. It is important to note that all signals on a network using this type of topology must
travel in the same direction. This reduces the amount of data collision and noise on the network.
The signal will continue through each node until it reaches the intended destination node.
Typically this type of network will use a Token Ring protocol, which allows only one computer
to transmit a signal at any given time. The main drawback of this type of topology is that if
there is a failure of any of the nodes or cables connecting the nodes, then the network will
become unstable and potentially cease to function. The solution to this drawback is a double
ring topology. The double ring adds a secondary cable for redundancy in the case of a failure.
In a ring network, every device has exactly two neighboring devices for communication
purpose.

Token: Rings are an active topology. The information travels around the ring until it either
reaches its destination or returns to the sender. Token can circle a ring 200 meters in diameter
at about 10,000 times a second.

Within this topology, one node is chosen to configure the network and monitor other devices.
Ring topologies are half-duplex but can also be made full-duplex. To make ring topologies full-
duplex we would need to have two connections between network nodes to form a Dual Ring
Topology.

As mentioned above, if ring topologies are configured to be bidirectional then they are referred
to as dual ring topologies. Dual ring topologies provide each node with two connections, one
in each direction. Thus, data can flow in a clockwise or counterclockwise direction. When
there is interference, Token Ring goes into a lengthy recovery mode.

Dual-Ring Topology

A network with ring topology is half-duplex, meaning data can only move in one direction at
a time. Ring topologies can be made full-duplex by adding a second connection between
network nodes, creating a dual ring topology.

9
Advantages of Dual-Ring Topology

The primary advantage of dual ring topology is its efficiency: because each node has two
connections on either side, information can be sent both clockwise and counterclockwise along
the network. The secondary ring included in a dual-ring topology setup can act as a redundant
layer and backup, which helps solve for many of the disadvantages of traditional ring topology.
Dual ring topologies offer a little extra security, too: if one ring fails within a node, the other
ring is still able to send data.

Advantages:

Here are pros/benefits of ring topology:

 Easy to install and reconfigure.

 Adding or deleting a device in-ring topology needs to move only two connections.
 The troubleshooting process is difficult in a ring topology.
 Failure of one computer can disturb the whole network.
 Offers equal access to all the computers of the networks
 Faster error checking and acknowledgment.

Disadvantages:

Here are drawbacks/cons of ring topology:

 Unidirectional traffic.
 Break in a single ring can risk the breaking of the entire network
 Modern days high-speed LANs made this topology less popular.
 In the ring, topology signals are circulating at all times, which develops unwanted
power consumption.
 It is very difficult to troubleshoot the ring network.
 Adding or removing the computers can disturb the network activity.

Device:

A multistation access unit (MSAU), also called a media access unit (MAU), is a central device
that acts as Ethernet transceivers in local area networks. It is used to connect network stations
or nodes in LANs and operates according to the principle of token ring. The multiple stations
are connected in a star topology physically but are internally wired into a logical ring.

10
The following figure shows a MSAU having 8 ports shown in black squares and numbered
from 1 to 8, each of which can be connected to a device. Additionally, it has two ports ring-out
(RO) and ring-in (RI) for connecting to other MSAUs. The physical connection between the
computers is shown by bold blue lines while the logical ring is shown using dashed lines.

The logical configuration forms a ring topology where each message passes through every
device one by one. Each device passes the message on to the next station in a continuous circle.
However, an advantage of MSAU over conventional ring topology is that if one device in the
ring fails, the MSAU can bypass it and forward the message to the next device in the ring, thus
keeping the connection intact.

The ring-in ring-out ports allow multiple MSAUs to be connected in a ring, thus extending the
size of the LAN in multiples of 8. For example, if we have four MSAUs, the total number of
computers that can be connected will be 4 × 8 = 32. The MSAUs are connected so that RI of
one MSAU is connected to the RO of the next MSAU.

This is shown in the following diagram −

11
12
Star Topology

Star Topology Diagram

The star and extended star are the most popular topologies for Ethernet networks. This type
network is easy to setup, relatively inexpensive, and provides more redundancy than other
topologies, i.e. bus topology. The star topology is configured by connecting all of the nodes on
the network to central device. The central connection allows the network to continue
functioning even if a single node or cable fails. The major drawback to this topology is that if
the central device fails, then the network will become unstable or cease to function. The star
topology is most suitable for small, centralized networks. The extended star topology adds sub-
central devices that are connect to the central device. This type of topology is advantageous for
large networks and provides functionality for the organization and subnetting of the IP address
allocation within the network. The extended star topology is most suitable for large networks
that may span an entire building.

Advantages:

Here are pros/benefits of start topology:

 Easy to troubleshoot, set up, and modify.

 Only those nodes are affected, that has failed. Other nodes still work.
 Fast performance with few nodes and very low network traffic.
 In Star topology, addition, deletion, and moving of the devices are easy.
 If N devices are connected to each other in star topology, then the number of cables
required to connect them is N. So, it is easy to set up.
 Each device require only 1 port i.e. to connect to the hub.

13
Disadvantages:

Here are cons/drawbacks of using Star:

 If the hub or concentrator fails, attached nodes are disabled.

 Cost of installation of star topology is costly.
 Heavy network traffic can sometimes slow the bus considerably.
 Performance depends on the hub's capacity
 A damaged cable or lack of proper termination may bring the network down.

Device:
1. Central Hub
2. Switch

Hub or Switch
These devices serve as the central device. In establishing a typical Star Network Topology you
can use Hub or Switch. These are the devices where the cables from individual nodes are
plugged in. Both of these serve as an intermediate device through which data passes. Each time
a sender wants to send data to the receiver, the data has to pass through the central device.
There are three types of Hub:

1. Passive Hub- A Passive Hub simply receives the data from sender and transmits it to
all the Network Nodes without any form of processing or amplification. It is used in
Passive Star Topology.
2. Active Hub- An Active Hub works as a repeater. It not only transmits the data to the all
other Network Nodes but also amplifies it. This is done so that signals may not loose
strength. It is the basic device in Active Star Topology.
3. Intelligent Hub or Switch- An Intelligent Hub / Switch also works as a repeater and is
used in Switch Star Topology. It transmits sender`s data to a single receiver rather than
all the Network Nodes.

Mesh Topology
Mesh networks aren’t very practical in a LAN setting. For example, to network eight computers
in a mesh topology, each computer would have to have seven network interface cards, and 28
cables would be required to connect each computer to the seven other computers in the network.
Obviously, this scheme isn’t very scalable.

However, mesh networks are common for metropolitan or wide area networks. These networks
use devices called routers to route packets from network to network. For reliability and
performance reasons, routers are usually arranged in a way that provides multiple paths
between any two nodes on the network in a meshlike arrangement.

14
This topology is divided into two different types; full-mesh and partial mesh. A full mesh
topology provides a connection from each node to every other node on the network. This
provides a fully redundant network and is the most reliable of all networks. If any link or node
in the network fails, then there will be another path that will allow network traffic to continue.
The major drawback to this type of network is the expense and complexity required to
configure this topology. This type of topology is only used in small networks with only a few
nodes. A partial mesh topology provides alternate routes from each node to some of the other
nodes on the network. This type of topology provides some redundancy and is commonly used
in backbone environments, networks where services are vital, and in wide area networks,
WANs. The most notable partial mesh network is the Internet.

Fully connected mesh network therefore has n(n-1)/2 physical channels to link n devices. To
accommodate that many links, every device on the network must have n-1 input/output ports

Types of Mesh Topology:

 Partial Mesh Topology: In this type of topology, most of the devices are connected
almost similarly as full topology. The only difference is that few devices are connected
with just two or three devices.

Partially Connected Mesh Topology

 Full Mesh Topology: In this topology, every nodes or device are directly connected
with each other.

15
 Fully Connected Mesh Topology

Advantages:

Here, are pros/benefits of Mesh topology

 The network can be expanded without disrupting current users.

 Need extra capable compared with other LAN topologies.
 Complicated implementation.
 No traffic problem as nodes has dedicated links.
 It has multiple links, so if any single route is blocked, then other routes should be used
for data communication.
 P2P links make the fault identification isolation process easy.
 It helps us to avoid the chances of network failure by connecting all the systems to a
central node.
 It is robust.
 Fault is diagnosed easily. Data is reliable because data is transferred among the
devices through dedicated channels or links.
 Provides security and privacy.

Disadvantages:

 Installation is complex because every node is connected to every node.

 A mesh topology is robust.
 Every system has its privacy and security
 It is expensive due to the use of more cables. No proper utilization of systems.
 It requires more space for dedicated links.
 Because of the amount of cabling and the number of input-outputs, it is expensive to
implement.
 It requires a large space to run the cables.

16
Tree Topology

Tree Topology

Tree topologies have a root node, and all other nodes are connected which form a hierarchy.
So it is also known as hierarchical topology. This topology integrates various star topologies
together in a single bus, so it is known as a Star Bus topology. Tree topology is a very common
network which is similar to a bus and star topology.

Advantages:

Here are pros/benefits of tree topology:

 Failure of one node never affects the rest of the network.

 Node expansion is fast and easy.
 Detection of error is an easy process
 It is easy to manage and maintain

Disadvantages:

Here are cons/drawback of tree topology:

 It is heavily cabled topology

 If more nodes are added, then its maintenance is difficult
 If the hub or concentrator fails, attached nodes are also disabled.

17
Hybrid Topology

Hybrid topology

Hybrid topology combines two or more topologies. We can see in the above architecture in
such a manner that the resulting network does not exhibit one of the standard topologies.

For example, as we can see in the above image that in an office in one department, Star and
P2P topology is used. A hybrid topology is always produced when two different basic network
topologies are connected.

Advantages:
Here, are advantages/pros using Hybrid topology:

 Offers the easiest method for error detecting and troubleshooting

 Highly effective and flexible networking topology
 It is scalable so we can increase our network size

Disadvantages:
 The design of hybrid topology is complex
 It is one of the costliest processes

Cable:

18
Which topology is the best for our network?
No network topology is perfect, or even inherently better than the others, so determining the
right structure for our business will depend on the needs and size of our network. Here are the
key elements to consider:

1. Length of cable needed

2. Cable type
3. Cost
4. Scalability

Cable Length

Generally, the more cable involved in network topology, the more work it’ll require to set up.
The bus and star topologies are on the simpler side of things, both being fairly lightweight,
while mesh networks are much more cable- and labor-intensive.

Cable Type

The second point to consider is the type of cable we’ll install. Coaxial and twisted-pair cables
both use insulated copper or copper-based wiring, while fiber-optic cables are made from thin
and pliable plastic or glass tubes. Twisted-pair cables are cost-effective but have less bandwidth
than coaxial cables. Fiber-optic cables are high performing and can transmit data far faster than
twisted-pair or coaxial cables, but they also tend to be far more expensive to install, because
they require additional components like optical receivers. So, as with our choice of network
topology, the wiring we select depends on the needs of our network, including which
applications we’ll be running, the transmission distance, and desired performance.

Cost

As I’ve mentioned, the installation cost is important to account for, as the more complex
network topologies will require more time and funding to set up. This can be compounded if
we’re combining different elements, such as connecting a more complex network structure via
more expensive cables (though using fiber-optic cables in a mesh network is overdoing it, if
we ask me, because of how interconnected the topology is). Determining the right topology for
our needs, then, is a matter of striking the right balance between installation and operating costs
and the level of performance we require from the network.

Scalability

The last element to consider is scalability. If we anticipate our company and network
expanding—or if we’d like it to be able to—it’ll save we time and hassle down the line to use
an easily modifiable network topology. Star topologies are so common because they allow we
to add, remove, and alter nodes with minimal disruption to the rest of the network. Ring
networks, on the other hand, have to be taken entirely offline for any changes to be made to
any of the nodes.

19
Network Topology Mapping Software

There are many different network topology mapping products out there but one of the most
widely-used is

1. Microsoft Visio.
2. SolarWinds Network Topology Mapper
3. Lucidchart
4. LibreOffice Draw

With Microsoft Visio, we can draw up our network by adding network elements to a canvas.
This program allows to design a topology diagram that details our network. Of course, drawing
up our own network isn’t always ideal particularly when we’re attempting to map a larger
computer network.

As a result, we might want to consider using another tool like SolarWinds Network Topology
Mapper which can auto discover devices connected to our network. Auto discovery comes in
handy because it means that we don’t have to draw up our network structure manually.

20