COMPUTER NETWORK TOPOLOGY

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What is Computer Network Topology?

Topology refers to the configuration of a network, illustrating how all its components are interconnected. There are two main types of topology: physical topology, which shows the actual layout of the hardware connections, and logical topology, which describes the path data takes within the network.

Types of Computer Network Topology

Physical topology represents the geometric arrangement of all nodes within a network. There are six types of network topology: Bus Topology, Ring Topology, Tree Topology, Star Topology, Mesh Topology, and Hybrid Topology.

Bus Topology

• The bus topology connects all stations via a single backbone cable.
• Each node is linked to the backbone cable either directly or through a drop cable.
• Messages sent by a node are broadcast to all stations on the network.
• Commonly used in 802.3 (Ethernet) and 802.4 standard networks.
• Simpler configuration compared to other topologies.
• The backbone cable serves as a "single lane" for message transmission.
• CSMA (Carrier Sense Multiple Access) is the most common access method.

CSMA (Carrier Sense Multiple Access) is a media access control method used to regulate data flow and ensure data integrity, preventing packet loss. When two nodes send messages simultaneously, CSMA offers two alternative solutions to handle the resulting conflicts.

CSMA/CD: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is an access method that detects collisions on the network. When a collision is detected, the sender stops transmitting data, thus focusing on "recovery after the collision."

CSMA/CA: Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is an access method designed to prevent collisions by checking if the transmission medium is busy. If the medium is busy, the sender waits until it becomes idle. This technique effectively reduces the likelihood of collisions and does not rely on "recovery after the collision."

Advantage of Bus Topology

• Cost-effective installation: Nodes in a bus topology connect directly to a single cable, reducing the initial installation costs compared to more complex network layouts.
• Moderate data speeds: Typically using coaxial or twisted pair cables, bus networks can support moderate data speeds, generally up to 10 Mbps.
• Familiar technology: Bus topology is well-established, making it familiar to network administrators. Installation and troubleshooting techniques are widely known, and necessary hardware components are readily available.
• Isolated node failures: Unlike some network topologies, a failure in one node of a bus network does not impact the operation of other nodes, enhancing overall reliability.

Disadvantage of Bus Topology

• Extensive cabling: Implementing bus topology requires significant amounts of cabling, which can increase costs and complexity, especially in larger networks.
• Challenging troubleshooting: Identifying faults in the cable requires specialized testing equipment. If a fault occurs in the cable, it can disrupt communication for all nodes connected to that segment.
• Signal interference: Simultaneous transmissions from multiple nodes can result in signal collisions, leading to data loss or corruption. This can impact network performance and reliability.
• Difficult reconfiguration: Adding or removing devices on a bus network can be complex and may require network downtime, affecting overall network efficiency.
• Attenuation: Signal loss, known as attenuation, can occur over long cable lengths or due to environmental factors. Repeaters are necessary to regenerate signals and maintain communication quality.

Ring Topology

Ring topology is similar to bus topology but forms a closed loop. Data flows in one direction continuously. Each node passes data to the next in line. Token passing manages access, using a circulating token to control transmissions.

Work of Token Passing

• In ring topology, a token circulates among computers in the network.
• Each computer modifies the token by appending its address and data.
• The token travels from one device to the next until it reaches the intended destination address.
• Upon receiving the token, the destination device processes the data and sends an acknowledgment back to the sender.

Advantage of  Ring Topology

• Network Management: Faulty devices can be removed from the network without disrupting overall network operation.
• Product Availability: A wide array of hardware and software tools are readily accessible for network operation and monitoring.
• Cost-Effective: Twisted pair cabling is affordable and widely accessible, resulting in low installation costs.
• Reliability: The network is dependable as communication isn't reliant on a single host computer.

Disadvantage of Ring Topology

• Troubleshooting Challenges: Identifying cable faults in this topology demands specialized testing equipment. A single cable fault can disrupt communication across all connected nodes.
• Single Point of Failure: If one station malfunctions, it can bring down the entire network.
• Complex Reconfiguration: Integrating new devices into the network can significantly reduce its speed and efficiency.
• Increased Latency: As the number of nodes grows, so does the potential for communication delays. Adding more devices further exacerbates this issue.

Star Topology

• In a star topology, each node is connected to a central hub, switch, or computer.
• The central computer is called a server, while the connected peripheral devices are known as clients.
• Coaxial cables or RJ-45 cables are used for connecting the computers.
• Hubs or switches serve as the primary connection devices.
• Star topology is the most widely used topology in network implementation.

Advantage of  Star Topology

• Efficient Troubleshooting: Troubleshooting in star topology is more efficient compared to bus topology. In bus topology, locating issues requires inspecting extensive lengths of cable, whereas in star topology, each station connects directly to a central hub, simplifying problem isolation to individual stations.
• Network Control: Star topology allows for straightforward implementation of advanced network control features. Changes made to the network configuration are automatically accommodated due to the centralized hub structure.
• Limited Failure Impact: Each station in star topology connects independently to the central hub with its own cable. Therefore, a failure in one station's cable does not disrupt the entire network.
• Familiar Technology: Star topology is well-established and familiar, supported by cost-effective tools and infrastructure.
• Scalability: It is easily expandable as new stations can be effortlessly added to available ports on the central hub.
• Cost-Effectiveness: Star topology networks utilize inexpensive coaxial cables, contributing to overall cost efficiency.
• High Data Speeds: Star topology supports high bandwidths, often up to 100 Mbps or more, with Ethernet 100BaseT being a common implementation in star networks.

Disadvantage of Star Topology

• Central Point of Failure: In star topology, all nodes rely on the central hub or switch for communication. If the central device malfunctions or loses power, communication between connected nodes will cease.
• Cable Routing Challenges: Managing cable routes can become complex, particularly when extensive routing is necessary to connect multiple nodes to the central hub or switch.

Tree Topology

• Combines characteristics of bus and star topologies.
• Computers are connected in a hierarchical structure.
• The top-most node is called the root node, with all other nodes as its descendants.
• Only one path exists between any two nodes for data transmission.
• Forms a parent-child hierarchy.

Advantage of Tree Topology

• Expansion Capability: It facilitates easy addition of new devices to an existing network, making tree topology highly scalable.
• Manageability: The network is organized into segments resembling star topologies, simplifying management and maintenance tasks.
• Error Handling: Error detection and correction are straightforward in tree topology configurations.
• Fault Isolation: A failure in one station does not disrupt the entire network due to the segmented nature of tree topology.
• Point-to-Point Connectivity: Each segment in tree topology utilizes point-to-point wiring, enhancing reliability and minimizing potential points of failure.

Disadvantage of Tree Topology

• High Costs: Implementing devices for broadband transmission in tree topology networks can incur significant expenses.
• Single Point of Failure: Tree topology heavily depends on the main bus cable; a failure in this cable can disrupt the entire network.
• Complex Reconfiguration: Adding new devices to a tree topology network can complicate reconfiguration processes.

Mesh Topology

• Computers are interconnected with redundant connections in mesh topology.
• Multiple paths exist between any two computers.
• Absence of central communication point like switches or hubs.
• Example: The Internet.
• Commonly used for WAN implementations with critical communication failure concerns.
• Frequently utilized in wireless networks.
• Formation formula: Number of cables = (n*(n-1))/2.

Mesh topology is categorized into two types:

• Fully Connected Mesh Topology
• Partially Connected Mesh Topology

Advantage of Mesh Topology

• Reliable: Mesh topology networks are highly dependable because the breakdown of any single link does not impact communication between connected computers.
• Fast Communication: Nodes in mesh topology communicate swiftly with each other.
• Simplified Reconfiguration: Introducing new devices does not interfere with existing communication among other devices.

Disadvantage of Mesh Topology

• Cost: Mesh topology requires a significant investment due to its extensive use of devices like routers and transmission media compared to other topologies.
• Management Complexity: Managing large mesh topology networks is challenging and requires diligent monitoring to detect and address communication link failures promptly.
• Efficiency Concerns: The high redundancy in connections within mesh topology networks can decrease overall network efficiency.
  

Hybrid Topology

• A hybrid topology involves combining different links and nodes to facilitate data transfer.
• In a hybrid topology, when two or more different topologies are interconnected, it is termed as a hybrid topology. However, if similar topologies are connected, it does not result in a hybrid topology.
• For instance, if one branch of ICICI bank employs a ring topology while another branch uses a bus topology, connecting these two topologies would result in a hybrid topology.

Advantage of Hybrid Topology

• Reliable: Faults in one part of the network do not disrupt the operation of other network segments.
• Scalable: Expansion of the network is straightforward by adding new devices, preserving the functionality of the existing network.
• Flexible: Hybrid topology offers flexibility in design, accommodating organizational needs and preferences.
• Effective: Hybrid topology maximizes network strengths and minimizes weaknesses, making it highly efficient for varied network requirements.

Disadvantage of Hybrid Topology

• Complex Design: Hybrid topology poses a challenge in designing its network architecture due to its complexity.
• Expensive Hubs: Hubs utilized in hybrid topology are notably costly compared to those used in other topologies.
• High Infrastructure Costs: Implementing a hybrid network demands substantial investments in cabling, network devices, and infrastructure components.

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