Network Typologies

Computer Network Topology

by Abhay Mishra.

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hello friends today we discuss about a new amazing topic the topic is network topology

and its types...

A Network Topology is the arrangement with which computer systems or network devices are connected to each
other. Topology may define both physical and logical aspect of the network. Both logical and physical Topology
could be same or different in a same network.

Point-to-Point

Point-to-point networks contains exactly two hosts such as computer, switches
or routers, servers connected back to back using a single piece of cable. Often,
the receiving end of one host is connected to sending end of the other and vice versa.

Bus Topology

In case of Bus topology, all devices share single communication line or cable.Bus
topology may have problem while multiple hosts sending data at the same time.
Therefore, Bus topology either uses CSMA/CD technology or recognises one host as
Bus Master to solve the issue. It is one of the simple forms of networking where a
failure of a device does not affect the other devices. But failure of the shared
communication line can make all other devices stop functioning.
Both ends of the shared channel have line terminator. The data is sent in only one
direction and as soon as it reaches the extreme end, the terminator removes the data
from the line.

Advantages

1. It is easy to set up, handle, and implement.
2. It is best-suited for small networks.
3. It costs very less.

Disadvantages

1. The cable length is limited. This limits the number of network nodes that can be connected.
2. This network topology can perform well only for a limited number of nodes. When the number of devices
connected to the bus increases, the efficiency decreases.
3. It is suitable for networks with low traffic. High traffic increases load on the bus, and the network efficiency
drops.
4. It is heavily dependent on the central bus. A fault in the bus leads to network failure.
5. It is not easy to isolate faults in the network nodes.
6. Each device on the network "sees" all the data being transmitted, thus posing a security risk.
Note:

CSMA/CD:

 Short for Carrier Sense Multiple Access / Collision Detection, a
set of rules determining how network devices respond when two devices attempt
to use a data channel simultaneously (called a collision). Standard Ethernet
networks use CSMA/CD to physically monitor the traffic on the line at
participating stations.

Star Topology:

All hosts in Star topology are connected to a central device, known as hub device,
using a point-to-point connection. That is, there exists a point to point connection
between hosts and hub. The hub device can be any of the following:
As in Bus topology, hub acts as single point of failure. If hub fails, connectivity of all hosts to all other hosts fails.
Every communication between hosts, takes place through only the hub.Star topology is not expensive as to connect
one more host, only one cable is required and configuration is simple.

Advantages

▸ Due to its centralised nature, the topology offers simplicity of operation.
▸ It also achieves isolation of each device in the network.
▸ Adding or removing network nodes is easy, and can be done without affecting the entire network.
▸ Due to the centralised nature, it is easy to detect faults in the network devices.
▸ As the analysis of traffic is easy, the topology poses lesser security risk.
▸ Data packets do not have to pass through many nodes, like in the case of a ring network. Thus, with the use of a
high-capacity central hub, traffic load can be handled at fairly decent speeds.

Disadvantages

▸ Network operation depends on the functioning of the central hub. Hence, central hub failure leads to failure of the
entire network.
▸ Also, the number of nodes that can be added, depends on the capacity of the central hub.
▸ The setup cost is quite high.

Ring Topology:

In ring topology, each host machine connects to exactly two other machines, creating a circular network structure.
When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all
intermediate hosts. To connect one more host in the existing structure, the administrator may need only one more
extra cable. Failure of any host results in failure of the whole ring.Thus, every connection in the ring is a point of
failure. There are methods which employ one more backup ring.

Advantages

▸The data being transmitted between two nodes passes through all the intermediate nodes. A central server is not
required for the management of this topology.
▸ The traffic is unidirectional and the data transmission is high-speed.
▸ In comparison to a bus, a ring is better at handling load.
▸ The adding or removing of network nodes is easy, as the process requires
changing only two connections.
▸ The configuration makes it easy to identify faults in network nodes.

▸ In this topology, each node has the opportunity to transmit data. Thus, it is
a very organised network topology.
▸ It is less costly than a star topology.

Disadvantages

▸ The failure of a single node in the network can cause the entire network to
fail.
▸ The movement or changes made to network nodes affect the entire network's performance.
▸ Data sent from one node to another has to pass through all the intermediate nodes. This makes the transmission
slower in comparison to that in a star topology. The transmission speed drops with an increase in the number of nodes.
▸ There is heavy dependency on the wire connecting the network nodes in the ring.

Mesh Topology

In this type of topology, a host is connected to one or multiple hosts.This topology has
hosts in point-to-point connection with every other host or may also have hosts which are
in point-to-point connection to few hosts only. Hosts in Mesh topology also work as relay
for other hosts which do not have direct point-to-point links.

 Mesh technology comes into two types:
 Full Mesh: All hosts have a point-to-point connection to every other host in the network. Thus for every new host n(n-1)/2 connections are required. It provides the most reliable network structure among all network topologies.
 Partially Mesh: Not all hosts have point-to-point connection to every other host. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some hosts out of all.

Advantages

▸The arrangement of the network nodes is such that it is possible to transmit data from one node to many other nodes
at the same time.
▸ The failure of a single node does not cause the entire network to fail as there are alternate paths for data
transmission.
▸ It can handle heavy traffic, as there are dedicated paths between any two network nodes.
▸ Point-to-point contact between every pair of nodes, makes it easy to identify faults.

Disadvantages

▸ The arrangement wherein every network node is connected to every other node of the network, many connections
serve no major purpose. This leads to redundancy of many network connections.
▸ A lot of cabling is required. Thus, the costs incurred in setup and maintenance are high.
▸ Owing to its complexity, the administration of a mesh network is difficult.

Tree Topology:

 Also known as Hierarchical Topology, this is the
most common form of network topology in use presently.This topology
imitates as extended Star topology and inherits properties of bus
topology.

Advantages:

 Scalable as leaf nodes can accommodate more nodes in the
hierarchical chain.
 A point to point wiring to the central hub as each intermediate
node of a tree topology represents a node in the bus topology
 Other hierarchical networks are not affected if one of them gets
damaged
 Easier maintenance and fault finding

Disadvantages

 Huge cabling is needed
 A lot of maintenance is needed
 backbone forms the point of failure.

Hybrid Topology:

 A network structure whose design contains
more than one topology is said to be hybrid topology. Hybrid
topology inherits merits and demerits of all the incorporating
topologies. The combining topologies may contain attributes of Star,
Ring, Bus, and Daisy-chain topologies.

Advantages

1) Reliable : Unlike other networks, fault detection and troubleshooting is easy in this type of topology. The part in
which fault is detected can be isolated from the rest of network and required corrective measures can be taken,
WITHOUT affecting the functioning of rest of the network.
2) Scalable: Its easy to increase the size of network by adding new components, without disturbing existing
architecture.
3) Flexible: Hybrid Network can be designed according to the requirements of the organisation and by optimising
the available resources. Special care can be given to nodes where traffic is high as well as where chances of fault are
high.
4) Effective: Hybrid topology is the combination of two or more topologies, so we can design it in such a way that
strengths of constituent topologies are maximised while there weaknesses are neutralised. For example we saw Ring Topology has good data reliability (achieved by use of tokens) and Star topology has high tolerance capability (as each node is not directly connected to other but through central device), so these two can be used effectively in hybrid star-ring topology.

Disadvantages

1) Complexity of Design: One of the biggest drawback of hybrid topology is its design. Its not easy to design this
type of architecture and its a tough job for designers. Configuration and installation process needs to be very efficient.
2) Costly Hub: The hubs used to connect two distinct networks, are very expensive. These hubs are different from
usual hubs as they need to be intelligent enough to work with different architectures and should be function even if a
part of network is down.
3) Costly Infrastructure: As hybrid architectures are usually larger in scale, they require a lot of cables, cooling
systems, sophisticate network devices, etc.

Cellular Topology

This is a wireless topology where geographical area is divided into cells
or regions. Cellular systems implements Space Division Multiplexing
Technique (SDM). Each transmitter is called a base station and can cover
a fixed area called a cell. This area can vary from few meters to few
kilometres. Mobile network providers install several thousands of base
stations each with a smaller cell instead of using power full transmitters
with large cells because, when the cell size is small.

Advantages:

1. Higher capacity
Smaller the size of the cell more the number of concurrent users i.e. huge cells do not allow for more concurrent users.
2. Less transmission power
Huge cells require a greater transmission power than small cells.
3. Local interference only
For huge cells there are a number of interfering signals, while for small cells there is limited interference only.
4. Robustness
As cellular systems are decentralised, they are more robust against the failure of single components.

Disadvantages

1. Infrastructure needed
Small cells require a complex infrastructure to connect all base station. The infrastructure required includes switches
for call forwarding, location registers etc.
2. Handover needed
The mobile station has to perform a handover when changing from one cell to another very frequently.
3. Frequency planning
To avoid interference, frequency spectrum should be distributed properly with a very less range of frequency
spectrum.



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