Local Area Transport (LAT) Network Concepts

This manual describes Digital's Local Area Transport (LAT) architecture and protocol, designed for communications on Ethernet Local Area Networks (LANs). It provides server, system, and network managers with a comprehensive introduction to LAT networks, covering their components, features, operations, and management.

A LAT network's primary goal is to provide efficient access to computing resources, composed of LAT nodes, their network interfaces, and the connecting Ethernet LAN.

• Services are named resources (hardware, software, or logical functions) offered by service nodes.
• Terminal servers are specialized Ethernet devices running server software, enabling users to access these services via logical, two-way connections called sessions.
• LAT nodes can be either terminal servers or service nodes, which include general-purpose multiuser computers or dual-purpose terminal servers (running both server and service-node software). Dual-purpose servers can offer devices like modems, personal computers, and non-LAT hosts as services.

The document details the LAT architecture's layered model (Service Class, Slot, and Virtual Circuit layers, built upon DNA Data Link and Physical Link layers) and various communication processes. These include service announcement, session establishment, session management (featuring multiplexing, load balancing, and automatic failover), virtual circuit maintenance, and host-initiated requests. LAT groups allow for logical partitioning of the network to control communication access, and LAT networks can also interface with other protocols like DECnet and SNA for broader network access.

Key benefits of LAT networks include off-loading CPU interrupts, efficient utilization of Ethernet bandwidth, support for multiple concurrent sessions with automatic failover, and simplified network management, often facilitated by tools like the Terminal Server Manager (TSM).