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concept#Architecture#Software Engineering#Integration#Platform

Open Systems Interconnection Model (OSI)

A seven-layer logical reference model describing network functions. Serves as a communication and analysis tool between design, implementation, and operations.

The OSI model is a conceptual reference framework that divides network functions into seven distinct layers.
Established
Medium

Classification

  • Medium
  • Technical
  • Architectural
  • Intermediate

Technical context

Network monitoring tools (e.g., Wireshark, NetFlow)Security tools for TLS/PKI managementConfiguration management and orchestration systems

Principles & goals

Layering principle: clear separation of responsibilities per layer.Abstraction: implementation details should not cross layer boundaries.Interface clarity: defined protocols and interfaces between layers.
Discovery
Enterprise, Domain, Team

Use cases & scenarios

Compromises

  • Overly dogmatic use can block technical decisions.
  • Failure to map modern stacks may lead to incorrect assumptions.
  • Neglecting cross-layer non-functional requirements.
  • Use the model pragmatically, not dogmatically: document reasons for deviations.
  • Use layer boundaries as guidance for tests and responsibilities.
  • Explicitly address cross-layer requirements (security, performance).

I/O & resources

  • Protocol and system documentation
  • Network topology and configuration data
  • Application requirements and non-functional requirements
  • Layer mapping of components and interfaces
  • Recommendations for protocol and security selection
  • Testing and monitoring strategies per layer

Description

The OSI model is a conceptual reference framework that divides network functions into seven distinct layers. It facilitates communication, troubleshooting and architectural decisions by defining responsibilities and interfaces between layers. Primarily a didactic and structural tool, it helps classify protocols and services across networking stacks.

✔

  • Improved team communication via a shared vocabulary.
  • Facilitates troubleshooting by systematic layer isolation.
  • Supports modular architecture and incremental modernization.

✖

  • Not all real-world protocols fit strictly into seven layers.
  • May lead to misleading simplifications for modern protocols (e.g., QUIC).
  • Does not provide detailed implementation guidance.

  • Layer-specific latency

    Measurement of time packets or messages require per layer.

  • Mean time to isolate fault

    Average time to identify the affected layer.

  • Number of cross-layer security incidents

    Counts incidents where security concerns span multiple layers.

TCP/IP in the OSI context

A comparison showing how the TCP/IP stack maps to OSI layers and where deviations occur.

TLS as transport-layer security

Explanation of how TLS integrates at the transport layer and above, and which services it protects.

Network segmentation using VLANs

Practical case: VLANs and switch configuration to separate broadcast domains on layer 2/3.

1

Introduce the OSI model as a shared terminology within the team.

2

Map existing protocols and components to the layers.

3

Derive testing and monitoring strategies per layer.

4

Regular reviews to adapt to modern protocols and requirements.

⚠️ Technical debt & bottlenecks

  • Legacy protocol implementations that violate layer boundaries.
  • Unclear interface definitions between middleware components.
  • Incomplete documentation of layer mapping for existing services.
Throughput limits in transport and network layersLatency from repeated protocol handlingComplexity in cross-layer optimizations
  • Assuming QUIC fully resides on layer 4 without regard to implementation details.
  • Implementing security only at one layer while neglecting others.
  • Optimizing solely within one layer without system-level perspective.
  • Incorrect parallelization of layers and real protocol functions.
  • Overestimating the model's precision for architectural decisions.
  • Neglecting performance or security impacts across layers.
Fundamentals of networking and protocol analysisKnowledge of TCP/IP, routing and switchingAbility to interpret packet captures and logs
Interoperability between heterogeneous systemsTraceability of communication pathsSeparation of responsibilities for modularization
  • • Legacy protocols and dependencies in existing infrastructure
  • • Hardware and device constraints at the link layer
  • • Regulatory requirements for security and data flow