OSI Layer: Foundations & Models

Definition

A computer network is a collection of autonomous devices (nodes) interconnected by transmission media, exchanging data under a common set of protocols.

Goals of Networking

• Resource sharing — hardware, software, data
• Reliability — redundant paths and replicated files
• Cost efficiency — shared servers instead of one mainframe
• Scalability — nodes added incrementally
• Communication — email, VoIP, video conferencing

Components

• End devices (hosts) — PCs, phones, servers
• Intermediary devices — hub, switch, router, gateway
• Transmission media — guided (copper, fibre) / unguided (radio, microwave)
• Protocols — rules of exchange
• NOS / network software — Windows Server, Linux

Performance Metrics

• Bandwidth — theoretical capacity of link (bps)
• Throughput — actual data rate achieved (always ≤ bandwidth)
• Latency — total delay = propagation + transmission + queuing + processing
• Jitter — variation in delay; critical for VoIP and live video