A continuation of the Data Communication and Networking module from S3.
Why a Communications Architecture?
Communications systems are complex to build and reason about. Technologies change rapidly, and components from different vendors must interoperate. Three strategies manage this complexity.
Modularization
Breaking a large system into smaller, self-contained pieces. Each piece has a clearly defined job and can be designed, implemented, and tested independently, provided it adheres to the agreed interfaces.
Layering
The system is divided into layers. Each layer:
- Performs a specific function
- Provides services to the layer above
- Is independent of the others
Layering is a specific approach to modularization: a hierarchical organization of modules. Modularization is the general principle; layering is one common implementation.
The number of layers in an implementation should be:
- small enough to be manageable
- large enough to avoid grouping unrelated functions together
Interface
Defines how adjacent layers in a system interact. Each layer has two interfaces: one to the layer above and one to the layer below.
Peer
Matching layers on 2 different systems.
Protocol
Defines how peers interact.
Standardization of Interfaces
Interfaces must be standardized to prevent incompatible implementations. By using same interfaces, different implementations can still co-operate.
Standards ensure large markets for equipment and software, enabling mass production and lower costs. They allow multi-vendor interoperability. Standards can be voluntary (e.g. ISO, CCITT) or regulatory.
Voluntary Standards
Developed by independent, non-governmental standards bodies through a consensus-based process involving industry stakeholders, academics, and technical experts.
Developed via open and documented processes. Published and accessible to all. Compliance is not legally required. Adaption driven by market forces.
Key bodies:
- CCITT (Consultative Committee for International Telephony and Telegraphy) — now ITU-T (ITU Telecommunication Standardization Sector). Responsible for standards in telecommunications, e.g., X.25, V-series modem standards, H.323.
- ISO (International Organization for Standardization) — responsible for broad international standards, including the OSI Reference Model (ISO 7498).
- IEEE (Institute of Electrical and Electronics Engineers) — produces the 802.x family of LAN/MAN standards (802.3 Ethernet, 802.11 Wi-Fi, etc.).
- IETF (Internet Engineering Task Force) — produces RFCs governing Internet protocols (TCP/IP, BGP, DNS, etc.).
Regulatory Standards
Mandated by governments or statutory authorities through legislation or regulation. Compliance is legally required within the jurisdiction. Non-compliance results in penalties, denial of market access or license revocation.
Typically cover areas where public interest, safety, spectrum management, or national security is involved. For example radio frequency emission limits, spectrum allocation, equipment type approval, lawful intercept obligations, data protection requirements.
Key bodies:
- FCC in the USA
- OFCOM in the UK
- TRCSL in Sri Lanka
Regulatory Use of Voluntary Standards
Governments often incorporate voluntary standards into regulation by reference. This is more economical than writing entirely new technical specifications because:
- Governments lack the technical depth to author detailed technical specifications
- Voluntary standards already represent broad expert consensus
Vendors must still comply with the standard technically, but now also face legal liability for non-compliance. Common in the EU.
Terminology
Node
A router or switch in a network.
Communication Link
A connection between 2 nodes.
Client-Server Model
Server
Listens on a fixed port; waits for client connections.
Client
Initiates a connection (or sends a datagram) to the server’s port.