Local Area Transport (LAT) Specification

This document defines the Local Area Transport (LAT) architecture, a communication protocol designed for Ethernet local area networks to facilitate data exchange between terminals connected to terminal servers and host operating system processes. LAT operates as a low-level service upon which higher-level services are layered, utilizing the Ethernet's broadcast and multicast capabilities.

Key elements of the LAT architecture include:

• Asymmetry: Communication is inherently asymmetric, establishing master/slave relationships between terminal servers (masters) and hosts (slaves) to simplify connection management and host implementation.
• Layering: The architecture is modular, consisting of a Slot Layer (for user session establishment and data transfer) and a Virtual Circuit Layer (for maintaining a reliable, error-free communication path over the unreliable Ethernet datagram service).
• Directory Service: A mechanism for nodes to advertise available services via multicast, allowing for dynamic discovery of hosts and services on the local area network.
• Connection Solicitation: A process introduced in version 5.1 that allows slave nodes to solicit connections from masters, enabling host-initiated connections to application terminals such as printers.
• Compatibility: The specification provides detailed information on maintaining compatibility between different versions (LAT 5.0 and 5.1) and implementation guidelines for various hardware and software configurations.

The document includes detailed message formats (Start, Run, Stop, Command, Status, and Solicit), architectural state tables for connection management, and algorithms for identifier assignment.