​

WEEK-VI

​

Overview of Network Topologies

​

​

Basic Topologies

• The term physical topology refers to the way in which a network is laid out physically: I/O or more devices connect to a link; two or more links form a topology.
• There are four basic topologies possible: bus, ring, star, mesh and hybrid.

Bus Topology

​

• A bus topology, is multipoint. One long cable acts as a backbone to link all the devices in a network.
• As a signal travels along the backbone, some of its energy is transformed into heat.

• Therefore it becomes weaker and weaker as it travels farther and farther.

Advantages

• Bus topology includes ease of installation.
• A bus uses less cabling than mesh or star topologies.

​

Disadvantages

• Difficult reconnection and fault isolation.
• A fault or break in the bus cable stops all transmission, even between devices on the same side of the problem.

Ring topology

​

• Ring Topology In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it.
• A signal is passed along the ring in one direction, from device to device, until it reaches its destination.

Advantages

• A ring is relatively easy to install and reconfigure. Fault isolation is simplified.

​

Disadvantages

• Unidirectional traffic can be a disadvantage.
• In a simple ring, a break in the ring (such as a disabled station) can disable the entire network.

Star Topology

​

• In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub.
• The devices are not directly linked to one another.
• Unlike a mesh topology, a star topology does not allow direct traffic between devices.
• The controller acts as an exchange: If one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device.

Advantages

• A star topology is less expensive than a mesh topology.
• In a star, each device needs only one link and one I/O port to connect it to any number of others. This factor also makes it easy to install and reconfigure.
• Far less cabling needs to be housed, and additions, moves, and deletions involve only one connection: between that device and the hub.
• Star topology is robust, that is if one link fails, only that link is affected. All other links remain active.

Disadvantages

• The dependency of the whole topology on one single point, the hub. If the hub goes down, the whole system is dead.
• Although a star requires far less cable than a mesh, each node must be linked to a central hub.

​

Mesh Topology

• In a mesh topology, every device has a dedicated point-to-point link to every other device.
• The term dedicated means that the link carries traffic only between the two devices it connects.
• Node 1 must be connected to n – 1 nodes, node 2 must be connected to n – 1 nodes, and so on.We need n (n - 1) physical links.

• However, if each physical link allows communication in both directions, the no of links needed are n(n-1)/2.

Advantages

​

• The use of dedicated links guarantees that each connection can carry its own data load, thus eliminating the traffic problems that can occur when links must be shared by multiple devices.
• A mesh topology is robust. If one link becomes unusable, it does not incapacitate the entire system.
• There is the advantage of privacy or security. When every message travels along a dedicated line, only the intended recipient sees it.
• Point-to-point links make fault identification and fault isolation easy.

Disadvantages

​

• Related to amount of cabling and the number of I/O ports required.
• The sheer bulk of the wiring can be greater than the available space (in walls, ceilings, or floors) can accommodate.
• The hardware required to connect each link (I/O ports and cable) can be prohibitively expensive.

Hybrid Topology

​

• A network can be hybrid.
• For example, we can have a main star topology with each branch connecting several stations in a bus topology.

Advantages of Hybrid topology

• The topology can be chosen based on the requirement for example, scalability is our concern then we can use star topology instead of bus technology.
• Scalable – it is possible to connect other computer networks with the existing networks with different topologies.

Disadvantages of Hybrid topology

• Fault detection is difficult.
• Installation is difficult.
• Design is complex so maintenance is high thus expensive.

NETWORK SIMULATOR

• A network simulator is software that predicts the behavior of a computer network.
• As communication networks have become too complex for traditional analytical methods to provide an accurate understanding of system behavior, network simulators are used.
• In network simulation, a software replica of the network, or 'network model', is used to analyze how different components of the network (network devices such as routers and access points, smart phones, radios, satellites, wireless channels, etc.) .

• Network Simulation offers an efficient, cost-effective way to assess how the network will behave under different operating conditions.
• Simulation results can be analyzed to assess network performance, identity potential problems, understand root cause and resolve the issues prior to deployment.

​

Advantages of Network Simulation

• It provide practical feedback to the users while designing real-world systems.
• They allow the designers of the system to study trouble at numerous abstraction levels.

​

Disadvantages of Network Simulation

• Training required
• Interpretation of results required
• Time consuming /expensive
• Inappropriately used
• Simulation results are sometimes hard to interpret

​

PACKET TRACER

• Cisco Packet Tracer is Cisco's simulation software.
• It can be used to create complicated network topologies, to test and simulate abstract networking concepts.

• It acts as a playground for user to explore networking and the experience is very close to what user sees in computer networks.
• Packet Tracer enables students to create complicated and huge networks, which is frequently impossible with physical hardware due to cost considerations.
• iPacket Tracer is available for Linux, Windows, MacOS, Android, and iOS.
• Packet Tracer allows users to drag and drop routers, switches, and other network devices to create simulated network topologies.
• If user has a Netacad account, then it be downloaded for free.
• Packet Tracer is a cross-platform visual simulation tool designed by Cisco Systems that allows users to create network topologies and imitate modern computer networks.

​

​

​

• The software allows users to simulate the configuration of Cisco routers and switches using a simulated command line interface.

​

​

​