Network Topology

Introduction

• This is also called LAN topology because of these are mostly and mainly implemented in a LAN network.

Definition

• Network topology is the study of geometric or graphical arrangement or mapping or layout of the network elements (may be devices, links, nodes etc.) in a computer network along with its interconnection among the elements.

Features

• Topology determines the strategy for physically expanding the network, in future.
• Topology gives the shape of the network.
• Topologies can be either physical or logical.
  • Physical Topology means the physical design/arrangement of a network with its required devices, location and cable installation.
  • Logical Topology is how data actually transfers/flows in a network as opposed to its design.

Types

• There are different types of topology in a computer network. These are –  [A] Cable/Wired Network Topology and [B] Wireless Topology.

[A] Cable/Wired Network Topology :

This topology uses cables or wires as transmission media/channel. These are of the following types –

(1) Mesh Topology (2) Star Topology (3) Ring Topology (4)Bus Topology (5) Tree Topology (6) Hybrid Topology.

(1.) Mesh Topology

Features/Characteristics

• • It is the topology widely used for wireless networks.
  • In this topology, there is no central connection point.
  • Each node in this topology is capable of sending messages to and receiving messages from other connected nodes.
  • In this topology, the nodes act/behaves like as relays and hence passing the message towards its final destination.
  • This topology has multiple connections thus, making it the most fault tolerant topology available.

Structure

• • It is a type of network setup or arrangement in which each computer/node or network device is interconnected with one another. In other words, every component of the network is connected directly to every other component.
  • Here, each node is connected directly, dynamically and non-hierarchically.
  •  Here, each node is connected to at least one/more other node directly. 

Advantages

• • Here, messages can be received more quickly due to direct connection of nodes.
  • This topology manages high amounts of traffic, because multiple devices can transmit/receive data simultaneously.
  • A failure of one device/node or adding new node,  does not disturb the transmission or structure of the network.

Disadvantages

• • Heavy power consumption.
  • Requires much cables to connect it.

(2.) Star Topology

Features/Characteristics

• • The name star is mainly due to its layout arrangement like a star.
  • A star topology is best suited for smaller networks and works efficiently when there is limited number of nodes.
  • This topology is considered as the most common and widely used LAN topology in small businesses and other organization.

Structure

• • In this topology, each computer/node on a network communicates with a central hub (also called as a concentrator) that re-sends the message either to all the computers/nodes or only to the destination computer.
  • Here, a hub expands one network connection with other. For example, a four-port hub connects up to four machines. A single hub is sufficient for a small network; however large networks require multiple hubs. But, it increases hardware and cabling costs.

Advantages

• • It is more reliable i.e. if one connection/node fails, it does not affect others during its removal. A new node can also be added easily without affecting others. In another words, It is easy to replace, install or remove hosts or other devices, problem can be easily detected-It is easier to modify or add a new computer without disturbing the rest of the network by simply running a new line from the computer to the central location and plugging it to the hub.
  • Hub detects the fault and isolates the faulty computer/node from the network.
  • Use of multiple cables types in a same network with a hub.
  • It has good performance

Disadvantages

• • It is expensive to install as it requires more cable, it costs more to cable a star network because all network cables must be pulled to one central point, requiring more cable length than other networking topologies.
  • Central hub dependency i.e. if central hub fails, the whole network fails to operate suddenly.
  • Many star networks require a device/hub/switch at the central point to re-broadcast or switch the network traffic.

(3.) Ring/Circular Topology

Features/Characteristics

• • In this topology, each node is connected to two and only two neighboring nodes.
  • The ring does not have an end.
  • It is made of short segments that connect one PC to the next PC and so on.
  • Here, data is accepted from one of the neighboring nodes and is transmitted onwards to another node .Therefore data travels in only direction from node to node around the rings.
  • Here, data transmission occurs either in clockwise or anti-clockwise direction.
  • Since, each computer re-transmits data what it receives, hence a ring topology is an active network and is not subject to the signal loss problems.
  • There is no termination end in this topology because there is no end to the ring.
  • This type of topology can be found in peer-to-peer networks, in which each machine manages both information processing and the distribution of data files.
  • Examples of ring topology: – IBM Token Ring, Fiber Distributed Data Interface (FDDI).

Structure

• • The layout of  this topology is similar to the linear bus topology, except that the nodes are connected in a circle.

Advantages

• • It is an orderly network where every device has access to the token (control signal) and the opportunity to transmit – because every computer is given equal access to the token, no computer can monopolize the network.
  • It performs better operation than a star topology under heavy network load situation.
  • We can create much larger network using this topology token ring concept.
  • It does not require network server/central point to manage the connectivity between the computers/nodes.

Disadvantages

• • Network adapter cards and Multi Access Units used in this topology are much more expensive than Ethernet cards and hubs used in bus topology.
  • It is much slower than an Ethernet network under normal load.
  • The problem finding is difficult to troubleshoot.
  • One malfunctioning node or bad port or adding new node or removal of node from this topology/Multi Access Units can create problems for the entire network.

(4.) Bus Topology

Definition

• • Bus topology has a single common communication line to which all the computers/nodes are connected.
  • The bus topology is the simplest and most widely used topology in local area network design.

Structure

• • It has a single length of cable with a terminator at each end.

Features/Characteristics

• • Working Mechanism:
    • It is a passive type of topology i.e. only one computer at a time can send a message. Hence, the number of computers attached to a bus network can significantly affect the speed of the network.
    • A computer in this topology, must wait until the bus medium or cable is free before it can transmit.
    • The computers/nodes attached on the bus cable keep on listening regularly. When they hear/match data that belongs to them, they receive.
    • When one device/node on the bus network wants to send a broadcast message to another device on the network, it first makes sure no one else on the bus cable is transmitting, and then it sends information out on the media/cable. All other devices attached on the network see it, but only the intended/genuine recipient accepts and processes it. This is accomplished by using data frames which contain source and destination addresses.
  • Each node of bus topology is connected to others nodes via a bus cable.
  • The network operating system keeps track of a unique address of each node and manages the flow of data between machines.

Advantages

• • It is simple, reliable, and easy to be used in a small sized local area network.
  • It requires least amount of cable to make/connect computers together and is therefore less expensive than other cabling arrangements.
  • It is easy to implement and extend using connectors when required.
  • If one computer/node on the bus topology fails, it does not affect the rest of the traffic on the bus, when removed affected one.
  • A new node can be added easily in this topology without affecting other one connected on the network.

Disadvantages

• • In this topology, no two/more computers can transmit data at the same time.
  • It does not operate well with heavy load which can slow down a bus considerably.
  • Performance degrades as more additional computers are added.
  • Terminators are required at both ends of the cable.

(5.) Tree Topology

Definition

• • This topology is extended form of Bus topology.

Features/Characteristics

• • A tree topology combines characteristics of (linear) bus and star topologies both.
  • It consists of groups of star-configured workstations/nodes connected to a linear bus backbone cable. 

Structure

• • This topology consists of many layers/branches of bus topology and appears like a tree, hence the name.

Advantages

• • It supports point-to-point connection for nodes.
  • It is highly flexible i.e. the other nodes in this network are not affected by others when one of their nodes get damaged or not working.
  • Tree topology has an easy maintenance and easy fault identification procedure.

Disadvantages

• • It is difficult to configure.
  • It contains a single point of failure.

Use

• • Tree topologies allow for the expansion of an existing network.

(6.) Hybrid Topology

Definition

• • A hybrid topology is a specific type of network topology that uses two or more different combination of network topologies as per need of the organisation.

Features/Characteristics

• • This topology can include a mix of any of these such as bus topology, mesh topology, ring topology, star topology, and tree topology.
  • Combination of Star-Ring and Star-Bus networks are the most common used examples of the hybrid network topology.

Advantages

• • This topology is highly flexible than others.
  • It has far better fault tolerance i.e. reliable.
  • It contains the best features of that topology.

Disadvantages

• • Since it uses more than one topology hence its design and installation process is more complex.
  • Since it has more complex structure hence its setup cost is high. 

Use

• • They are widely used in commercial and educational organisation.