Network Topologies and the OSI Model: A Comprehensive Guide
Network Topologies
Mesh Topology
Definition: Each device has a dedicated point-to-point connection to every other device.
Advantages:
- High redundancy: If one device fails, the network continues to function.
- No data collisions.
- High security.
Disadvantages:
- Expensive and complex to deploy.
Bus Topology
Definition: All devices connect to a single cable (the bus).
Advantages:
- Easy installation and deployment.
Disadvantages:
- Data collisions can occur.
- Difficult error detection.
- Vulnerable to intrusion.
Ring Topology
Definition: Each device connects to two others, forming a closed loop.
Advantages:
- No collisions.
- Easy error detection.
- Can use optical fiber.
Disadvantages:
- Slower communication speed.
- If one device fails, the entire network can go down.
Star Topology
Definition: Each device connects to a central hub.
Advantages:
- Cost-effective.
- Easy deployment.
- Easy configuration.
Disadvantages:
- If the hub fails, the entire network goes down.
Tree Topology
Definition: A hierarchical structure with a central hub and branching connections.
Advantages:
- Cost-effective.
- Easy error detection.
- Easy deployment.
Disadvantages:
- Dependent on the central hub.
Network Cables
Coaxial Cable
Definition: A copper core surrounded by insulation, a braided metal layer, and an outer casing.
Advantages:
- Can transmit over long distances.
- Cost-effective.
Disadvantages:
- Difficult installation.
Twisted Pair Cable
Definition: Two insulated copper wires twisted together.
Types:
- Unshielded Twisted Pair (UTP)
- Shielded Twisted Pair (STP)
Characteristics:
- Maximum distance: 100 meters.
- Uses RJ45 connectors.
Fiber Optic Cable
Definition: Uses light to transmit data.
Advantages:
- High speed and capacity.
- High security.
Disadvantages:
- Expensive.
- Difficult installation.
Hub vs. Switch
A switch learns the MAC addresses of connected devices and forwards data only to the intended recipient. A hub broadcasts data to all connected devices.
OSI Model
The OSI model is a layered framework for network communication. Each layer provides services to the layer above it and receives services from the layer below it.
Key Concepts
- Entity: A specialized module within a layer that performs specific functions.
- PDU (Protocol Data Unit): The unit of information exchanged between peer entities.
- Service: What each layer provides to the layer above it.
- Protocol: Rules governing the exchange of PDUs.
- SAP (Service Access Point): The interface between two layers.
- Primitives: Commands sent between adjacent layers to access services.
Layers
- Physical Layer: Transmits raw bits over the physical medium. (e.g., Hub, Network Card)
- Data Link Layer: Handles data transfer between nodes on the same network. (e.g., Switch, MAC address)
- Network Layer: Provides end-to-end communication across different networks. (e.g., Router, IP address)
- Transport Layer: Ensures reliable data delivery end-to-end. (e.g., TCP, UDP, Ports)
- Session Layer: Manages communication sessions between applications.
- Presentation Layer: Handles data formatting and syntax conversion.
- Application Layer: Provides network services to applications. (e.g., HTTP, FTP, SMTP)