The Ethernet A Local Area Network Data Link Layer and Physical Layer Specifications

This document, titled "The Ethernet" Version 2.0, published in November 1982, provides the Data Link Layer and Physical Layer specifications for the Ethernet Local Area Network. It was developed jointly by Digital Equipment Corporation, Intel Corporation, and Xerox Corporation.

Key aspects of the specification include:

1. Purpose: It serves as a design reference document detailing the lower two layers of the Ethernet architecture, akin to the ISO Model for Open Systems Interconnection.
2. Goals: The design aims for simplicity, low cost, compatibility (enabling data exchange between all implementations), addressing flexibility (single, group, or broadcast addressing), fairness, progress, high speed (10 Mbps), low delay, stability, maintainability, and a layered architecture.
3. Non-Goals: It explicitly states what is not covered, such as full-duplex operation, complete error control (relegated to higher layers), security mechanisms, speed flexibility (fixed 10 Mbps), priority support, or protection against malicious users at the data link level.
4. Key Characteristics:
   • Physical Layer: Operates at 10 Million bits/sec, supports up to 1024 stations with a maximum separation of 2.8 kilometers, uses shielded coaxial cable with baseband signaling, and a branching non-rooted tree topology.
   • Data Link Layer: Employs a fully distributed peer protocol with statistical contention resolution (CSMA/CD), and uses variable-size frames with "best-effort" delivery.
5. Structure: The document is organized into 8 sections detailing the overall description, architectural structure (Data Link and Physical Layers), inter-layer interfaces (described with Pascal procedural models for the Data Link Layer), detailed specifications for both layers, and a configuration testing protocol for network management.
6. Compatibility: Version 2.0 is upward compatible with Version 1.0 and substantially compatible with CSMA/CD local area network standards being developed by IEEE and ECMA.

In essence, the document provides the definitive technical blueprint for implementing Ethernet, focusing on ensuring interoperability at its fundamental communication layers.