IT Fundamentals – Network Topology Explained

9.1 # STATEMENT AND EXPLAINED THE TOPOLOGY IN COMPUTER NETWORK

Network topology is a physical layout of the computer network and it defines how the computers, devices, cables, etc are connected to each other. The topology description of a network can also include or imply the nature of the data flow through the network.

Different network topologies are used in different environments depending on network size, reliability, cost, and performance requirements. Below is where the major topologies are commonly used. The topologies can be either physical (Physical topologies describe how the cables are run) or logical (Logical topologies describe how the network messages travel).

BUS TOPOLOGY
Common Use: Small or temporary networks
Reason: Bus topology is low-cost and simple, but it is rarely used today because it has low reliability and scalability.
Example: Small office networks, Temporary LAN setups, Laboratory testing networks, Legacy Ethernet networks.

STAR TOPOLOGY
Common Use: Office LAN and home networks
Reason: All devices connect to a central switch, making it easy to manage, expand and troubleshoot.
Example: Office LAN networks, Schools and universities, Corporate networks, Home networks, Computer labs.

RING TOPOLOGY
Common Use: Telecom and fiber networks
Reason: Provides organized data flow and predictable network performance.
Example: Optical fiber networks, Metro networks, Telecom infrastructure include Fiber Distributed Data Interface and Token Ring.

MESH TOPOLOGY
Common Use: Internet backbone and data centers
Reason: Mesh topology provides high reliability and redundancy because devices have multiple paths for data transmission.
Example: Internet backbone networks, Data centers, Military communication networks, Wireless mesh networks.

TREE TOPOLOGY
Common Use: Enterprise and campus networks
Reason: Tree topology supports hierarchical network design with core, distribution, and access layers.
Example: Enterprise networks, Campus networks, Smart city infrastructure, Large corporate offices.

HYBRID TOPOLOGY
Common Use: Large complex infrastructures
Reason: Hybrid topology combines multiple topologies (star + mesh + tree) to improve performance and reliability.
Example: Large organizations, Data centers, Smart city command centers, Cloud infrastructure.

TIER-2 TOPOLOGY
Common Use: Small Data Centers / Small Government offices
Reason: Tier-2 topology usually refers to the two-tier architecture, which includes: Core Layer & Access Layer. Access switches connect directly to a core switch, and end devices such as PCs, printers, and IP phones connect to the access switches.
Example: Simple design , Lower cost, Easy deployment, Limited scalability.

TIER-3 TOPOLOGY
Common Use: Big one Data Centers / University campuses
Reason: Tier-3 topology refers to the three-tier architecture, which includes: Core Layer, Distribution Layer, Access Layer. This is the most common architecture in large enterprise networks.
Example: High scalability, Better network segmentation, Improved security, Higher redundancy.

Network Type	Oversubscription
Small LAN	1:1
Enterprise Access Layer	4:1
Campus Network	8:1
Data Center	1:1 or 3.1
CCTV Network	20.1

BANDWIDTH USAGE
🔹 If users are working only on a browser, the expected bandwidth usage is about 1–2 Mbps per user.
🔹 If users are working only on a Email/ERP, the expected bandwidth usage is about 2–5 Mbps per user.
🔹 If users are working only on a video meeting, the expected bandwidth usage is about 3–5 Mbps per user.
🔹 If users are working only on a downloading, the expected bandwidth usage is about 5-10 Mbps per user.

Organization	Concurrent Ratio
Call Center	80% to 90%
Data Centers	70% to 80%
Depaartmental Office	60% to 70%
School / University	50% to 60%
Industrail Factory	40% to 50%

Topology	Advantages	Disadvantages
Bus Topology	Uses minimal cable and is simple to install for small networks.	If the main backbone cable fails, the entire network goes down.
Star Topology	Easy to manage and isolate faults because all devices connect to a central switch or hub.	Failure of the central device stops the whole network.
Tree Topology	Scalable structure that allows easy network expansion with hierarchical control.	Failure of the root or backbone link can affect large parts of the network.
Ring Topology	Data travels in a predictable path which reduces packet collision.	A single device or link failure can break the entire ring network.
Mesh Topology	Provides very high reliability because multiple paths exist between devices.	Requires a large number of cables and ports, making it expensive.
Hybrid Topology	Combines multiple topologies to provide flexibility and optimized performance.	Design and troubleshooting become complex due to mixed structures.
Tier-2 Topology	Simpler design with fewer layers, reducing latency and deployment cost.	Limited scalability compared to multi-tier architectures.
Tier-3	Highly scalable and provides better traffic management with core, distribution, and access layers.	More expensive and complex to design and maintain.

🔹 How do we calculate access switch requirement in Tier-3 topology ?
Calculate Access Switch Formula : -
Nuumber of Access Switches = Total End Devices / Ports per Switch
Where, Total End Devices = 1000 : These are all devices connected to the network, such as: Laptop, Desktop and etc. Ports per Switch = 48 : The number of Ethernet ports available on the switch such as: 24/48 ports. Total Access Switches = ? : These switches are located in the access Layer and connect multiple end point devices.
Apply the formula : -
Number of Access Switches = 1000 / 48 = 21
Number of Access Switches = 21 ✅

🔹 How do we calculate Distribution Switch requirement in Tier-3 topology ?
Calculate Distribution Switch Formula : -
Nuumber of Distribution Switches = Access Switches / Aggregation Ratio
Where, Total Access Switches = 24 : These switches are located in the access Layer and connect multiple end point devices. Aggregation Ratio = 4 (Common aggregation ratios used in network design) : The number of access switches connected to one distribution switch. Total Distribution Switches = ? : These switches are located in the Distribution Layer and connect multiple Access Switches.
Apply the formula : -
Number of Distribution Switches = 24 / 4 = 6
Number of Distribution Switches = 6 ✅

🔹 How do we calculate Core Switch requirement in Tier-3 topology ?
Calculate Core Switch Formula : -
Nuumber of Core Switches = Distribution Switches / 2
Where, Distribution Switches = 6 : These switches are located in the Distribution Layer and connect multiple Access Switches. /2 = So the network design may use 2 core switches : This is very common because two core switches provide redundancy. Total Core Switches = ? : Core switches form the high-speed backbone of the network.
Apply the formula : -
Core Switches = 6 / 2 = 3
Core Switches = 3 ✅
Note : (Typically 2 core switches are deployed for redundancy)

🔹 How do we calculate Core Switch requirement in Tier-2 topology ?
Calculate Core Switch Formula : -
Nuumber of Core Switches = Access Switches x 2 (Redundancy)
Where, Access Switches = 9 : These switches are located in the access Layer and connect multiple end point devices. 2 = Redundancy : Uplink per L2 switch should be redundancy. Total Core Switches = ? : Core switches form the high-speed backbone of the network.
Apply the formula : -
Core Switches = 9 x 2 = 18
Core Switches = 18 (Mean to say that eighteen port should be available on core switch
Should be twenty-four -> One core switch is enough
Total core switch = 1 ✅

🔹 How do we determine uplink bandwidth requirement ?
Access Bandwidth Formula : -
Total Access Bandwidth = Access Ports × Port Speed
Where, Access Ports = 48 ports : The total number of Ethernet ports available on the access switch that connect to end devices. Port Speed = 1 Gbps : The data transmission speed of each port. Total Access Bandwidth = ? : The maximum theoretical bandwidth that all ports together can generate.
Apply the formula : -
Total Access Bandwidth = 48 ports × 1Gbps = 48Gbps
Total Access Bandwidth = 48 Gbps ✅

🔹 How can network engineers estimate total network capacity in Tier-3 topology ?
Network Capacity Formula : -
Network Capacity = Core Bandwidth × Number of Core Links
Where, Core Bandwidth = 10 Gbps : The speed of each link connected to the core switch. Number of Core Links = 4 : The total number of uplink connections between core switches and distribution switches. Total Network Capacity = ? : The total data throughput that the core layer can handle.
Apply the formula : -
Network Capacity = 10 Gbps x 4 = 40 Gbps
Network Capacity = 40 Gbps ✅

🔹 What is the ideal uplink ratio in Tier-3 design ?
Typical oversubscription ratio : 20:1 or 10:1
20:1 (Oversubscription) Access Layer = 200 ports × 1 Gbps = 200 Gbps Distribution Uplink = 10 Gbps Oversubscription = 200 / 10 = 20 : 1
10:1 (Oversubscription) Access Layer = 100 ports × 1 Gbps = 100 Gbps Distribution Uplink = 10 Gbps Oversubscription = 100 / 10 = 10 : 1
Traffic flow : - End Devices │ Access Switch │ (Oversubscription occurs here) Distribution Switch │ Core Switch

🔹 How can we determine uplink ports requirement in Tier-3 topology ?
Total uplink Formula : -
Number of Uplink Ports = Access Switches × 2 (for redundancy)
Where, Access Switches = 10 : Access switches connect end devices. Uplink Ports = 2 : Uplink ports are high-speed ports used to connect access switches to distribution switches.
Apply the formula : -
Uplink Ports = 10 x 2 = 20
Total Uplink Ports = 20 ✅

🔹 How do engineers determine VLAN requirements ?
Number of VLAN Formula : -
VLAN Count = Number of Departments + Services
Suppose an organization has the following departments (HR, IT and Sales) and services (CCTV Network, VoIP and Wi-Fi Users) : Total Departments = 5 & Total Services = 4
Apply the formula : -
VLAN Count = 5 + 4 = 9
Total VLAN Count = 9 ✅

🔹 How do engineers estimate network growth capacity ?
Network Growth Formula : -
Growth Capacity = current devices × Expected growth %
Where, Current Devices = 500 : The number of devices currently connected to the network, such as: Desktop computers, Laptops, IP phones, CCTV cameras, Wi-Fi access points, Printers and IoT devices Example: 500 devices currently in the network. Expected Growth % = 25% : The anticipated percentage increase in devices over a certain period (often 3–5 years) Typical planning values: 1. 20% growth → slow expansion 2. 30% growth → moderate expansion 3. 50% growth → fast expansion Growth Capacity = ? : The number of additional devices the network should be designed to support.
Apply the formula : -
Growth Capacity = 500 × 25% = 125
Growth Capacity = 125 Devices ✅

🔹 How do we determine ISP bandwidth requirement ?
ISP Bandwidth Formula : -
Bandwidth = Users × Usage per user × Concurrent ratio
Where, Users = 500 : Total number of users or devices in the network. Example: 100 users in an office. Usage per users : Average bandwidth consumed by one user. Typical planning values: 1. Web browsing → ~ 1 – 2 Mbps 2. Video streaming → ~ 3 – 5 Mbps 3. Video conferencing → ~ 2 – 4 Mbps 👉 You choose this value based on application type. Cocurrent ratio = ? : Not all users use the network at the same time. This factor represents simultaneous active users. 1. 1.0 = 100% users active 2. 0.5 = 50% users active 3.0.3 = 30% users active
Apply the formula : -
If 100% users active (Concurrent = 1) Bandwidth = 420 × 20 × 1 = 8400 Mbps = 8.4 Gbps ✅
Apply the formula : -
If 50% users active (Concurrent = 0.5) Bandwidth = 420 × 20 × 0.5 = 4200 Mbps = 4.2 Gbps ✅
Apply the formula : -
If 30% users active (Concurrent = 0.3) Bandwidth = 420 × 20 × 0.3 = 2520 Mbps = 2.52 Gbps ✅

📌 Practical Example (All-in-One)
Assume:
- Devices = 1000
- Switch Ports = 48
- Aggregation Ratio = 4:1
- Port Speed = 1 Gbps
- Uplink = 10 Gbps
- Growth = 30%
Step-by-step: -
1. Access Switches = 1000 / 48 ≈ 21
2. Distribution = 21 / 4 ≈ 6
3. Core Switches = 6 / 2 = 3 (or typically 2)

4. Access Bandwidth = 48 × 1G = 48 Gbps
5. Oversubscription = 48 / 10 = 4.8 : 1

6. Growth = 1000 × 30% = 300 devices
Future Devices = 1300

7. VLANs = Departments + Services

Formula Name	Formula	Purpose
Access Switch Calculation	= No. of Devices / Port per Switch	Calculate required access switches
Distribution Switch Calculation	= Access Switch / Aggregation Ratio	Estimate distribution switches
Core Switch Calculation	= Distribution Switch / 2	Plan core layer (redundancy)
Total Access Bandwidth	= No. of Ports x Ports speed	Calculate traffic generated at access layer
Uplink Ports Requirement	= Access Switch x 2	Ensure redundancy (dual uplinks)
Oversubscription Ratio	= Access Bandwidth / Uplink Bandwidth	Measure bandwidth sharing
Network Core Capacity	= Core Bandwidth × Core Links	Estimate backbone capacity
VLAN Planning	= Departments + Services	Plan network segmentation
Growth Capacity	= Current Devices × Growth %	Plan future expansion

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IT Fundamentals – Network Topology Explained

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IT Fundamentals – Network Topology Explained

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