This document describes the protocol architecture of the LAN Emulation Version of the ATM LAN Access Switch (ALAX). The main function of the ALAX is to provide an interface between legacy LAN and ATM world giving network managers the option of gradually integrating ATM technology into their existing networks. To provide this functionality to the ALAX system, we decided to implement two versions of the ALAX system. One is the LAN emulation version and the other is the Multi Protocol Over ATM version. The most important design characteristics of the ALAX is the adoption of the IEEE P1355 Standard for Heterogeneous Inter Connect (HIC)[1] as the data communication paths within the ALAX switching system. This makes it possible to design the PC- based parallel architectured high performance switching system in conformance with emerging open technologies and related standards. The protocols needed within the LAN Emulation version of the ALAX include LAN Emulation, Bridging Relay function, P1355, MAC Mapping Layer (MML), MAC, LAN Physical, AAL5, ATM and ATM Physical Layer. Some other protocols needed in the ALAX include the ATM signaling which is defined in ATM Forum UNI 3.0[2] , Network Management (SNMP or CMIP)[3], Graphic User Interface and some main control functions of the ALAX. The details of all these protocols, the relationship among these protocols and the implementations of these protocols are described in this document.