Navigating the Open Systems Interconnection Model for Seamless Communication

Why do we need a communication model?

• Agnostic applications

  • Without a standard model, your application must know the underlying network medium

  • Imagine if you have to author different version of your apps so that it works on wifi vs ethernet vs LTE vs fibre

• Network Equipment Management

  • Without a standard model, upgrading network equipment becomes difficult

• Decoupled Innovation

  • Innovations can be done in each layer separately without affecting the rest of the models

The OSI Layers (Sender)

• 7 Layers each describe a specific networking component

• Layer 7 - Application - HTTP/FTP/gRPC

  • Post request with JSON data to HTTPS server

• Layer 6 - Presentation - Encoding, Serialization

  • Serialize JSON to flat byte strings

• Layer 5 - Session - Connection establishment, TLS

  • Request to establish TCP connection/TLS

• Layer 4 - Transport - UDP/TCP

  • Sends SYN request target port 443

• Layer 3 - Network - IP

  • SYN is placed an IP packet(s) and adds the source/dest IPs

• Layer 2 - Data link - Frames, Mac address Ethernet

  • Each packet goes into a single frame and adds the source/dest MAC addresses

• Layer 1 - Physical - Electric signals, fibre or radio wave

  • Each frame becomes a string of bits which converted into either a radio signal(wifi), electric signal(ethernet) or light(fibre)

The OSI Layers (Receiver)

Layer 1 - Physical

• • Radio, electric or light is received and converted into digital bits

• Layer 2 - Datalink

  • The bits from Layer 1 are assembled into frames

• Layer 3 - Network

  • The frames from layer 2 are assembled into the IP packet

• Layer 4 - Transport

  • The IP packets from layer 3 are assembled into the TCP segment

  • Deals with congestion control/ flow control/transmission in case of TCP

  • If Segment is SYN we don’t need to go further into more layers as we are still processing the connection request

• Layer 5 - Session

  • The connection session is established or identified

  • We only arrive at the layer when necessary (a three-way handshake is done)

• Layer 6 - Presentation

  • Deserialize flat byte strings back to JSON for the app to consume

• Layer 7 - Application

  • The application understands the JSON POST request and your express JSON or Apache request receive event is triggered