Overview of OSI Model (Open System Interconnect) OSI PROTOCOL STACK MODEL Network design focus on the lower layers of the protocol stack Central goal of network design is to build reliable networks for application use Network designers are concerned with Layers 1 through 4 or 5 OSI PROTOCOL STACK MODEL Seven layers: Layer 7 – Application for user and application data Layer 6 – Presentation for data formatting, encryption and character encoding Layer 5 –Session which negotiates and maintains connections OSI PROTOCOL STACK MODEL Layer 4 – Transport for End to end packet sequencing and reliability Layer 3 – Network for routing, flow control, translations between different media types Layer 2 – Data link (MAC) basic framing of packets, error detection, transmission control Layer 1-Physical for electrical and optical media, cabling, signalling and properties OSI PROTOCOL STACK MODEL TOP-DOWN DESIGN PHILOSOPHY Design starts at top when designing the network - application layer Good network design should be flexible to support changes without wholesome redesign Network should be scalable, manageable and reliable END OF SESSION