FC-AL的美国国家标准规定了ANSI X3、FC-PH-x的信令接口增强功能，以允许L_端口以仲裁环路拓扑运行。本标准定义了保留ANSI X3 FC-PH-x中规定的端口功能的L_端口。仲裁环路拓扑在环路中连接多个通信点，无需交换机。仲裁环路拓扑是一种分布式拓扑，其中每个L_端口包含建立环路所需的最小功能。连接到仲裁环路的单个FL_端口允许多个NL_端口连接到结构。当一个L_端口与至少一个其他L_端口在环路上运行时，L_端口使用本标准中规定的ANSI X3、FC-PH-x协议扩展。 当L_端口与N_端口或F_端口连接时，L_端口使用ANSI X3 FC-PH-x中定义的协议进行通信。每个L_端口可以使用自发现程序来查找正确的操作模式，而无需外部控制。

This American National Standard for FC-AL specifies signaling interface enhancements for ANSI X3, FC-PH-x to allow L_Ports to operate with an Arbitrated Loop topology. This standard defines L_Ports that retain the functionality of Ports as specified in ANSI X3, FC-PH-x. The Arbitrated Loop topology attaches multiple communicating points in a Loop without requiring switches.The Arbitrated Loop topology is a distributed topology where each L_Port includes the minimum necessary function to establish a Loop circuit. A single FL_Port connected to an Arbitrated Loop allows multiple NL_Ports to attach to a Fabric.When an L_Port is operating on a Loop with at least one other L_Port, the L_Port uses the protocol extensions to ANSI X3, FC-PH-x that are specified in this standard.When an L_Port is connected with an N_Port or an F_Port, the L_Port communicates using the protocol defined in ANSI X3, FC-PH-x.Each L_Port may use a self-discovering procedure to find the correct operating mode without the need for external controls.