ANSI INCITS 186

Abstract

This standard specifies a Hybrid Ring Control (HRC) protocol which provides a mode of operation in which both packet switched and isochronous data are transmitted within the same special frame structure, called a cycle. HRC is designed to operate with the existing Media Access Control (MAC), Physical Layer Protocol (PHY), and Physical Medium Dependent (PMD) layers of the FDDI protocol. The HRC is composed of the Hybrid Multiplexer (H-MUX) and the Isochronous Media Access Control (I-MAC) protocols. The H-MUX integrates packet and isochronous data into cycles which it transmits onto and receives from the medium using the services of the Physical Layer. The IMAC provides separate transmission channels for the transfer of user isochronous data streams. The format, clocking and synchronization of cycles, and the operation and interfaces of the HMUX and I-MAC are defined by this standard. These interfaces include the interface to the FDDI Station Management (SMT) protocol. The HRC is designed to support various transmission rates, scalable from 100 Mbps in increments of 6,144 Mbps. All transmission rate dependent parameters defined in this standard assume a transmission rate of 100 Mbps. Stations composed of FDDI and HRC entities are referred to as FDDI-II stations. The FDDI Packet MAC (P-MAC) and the HRC components, and their architectural relationship to LLC and a Circuit Switching Multiplexer (CS-MUX) are illustrated in figure 1. This figure does not imply an implementation configuration FDDI-II networks consist of FDDI-II stations. Interoperability between FDDI and FDDI-II stations on the same network is provided in HRC Basic Mode, which only supports packet transmission. The set of FDDI standards specifies the interfaces, functions, and operations necessary to ensure interoperability between conforming FDDI implementations. This FDDI standard specifies HRC. Conforming implementations may employ any design technique that does not violate interoperability.