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For the purpose of compatible interconnection of data processing equipment via a local area network (LAN) using the token ring access method, this part of ISO/IEC 8802

• Provides a general description of the token ring local area network (LAN) architecture (clause 2);
• Defines the frame format, including the delimiters, address fields, information field, and frame-check sequence (FCS). Defines the Medium Access Control (MAC) frames, timers, and error counters (clause 3);
• Defines the MAC protocols including finite state machines and state tables (clause 4);
• Defines the system level Physical layer (PHY) signaling specifications that are specific to a ring station (clause 5);
• Defines the managed objects necessary to manage the service and protocol elements that are involved in the management of a token ring station (clause 6);
• Defines the PHY station attachment specification for 4 and 16 Mbit/s operation. This includes the transmitter, receiver, medium interface connector, and transmission channel for both shielded twisted pair (STP) and unshielded twisted pair (UTP) media (clause 7);
• Defines the concentrator, incorporating multiple trunk coupling units (TCUs), for the attachment of a group of stations to the ring (clause 8);
• Includes the protocol implementation conformance statement (PICS) proforma in compliance with the relevant requirements, and in accordance with the relevant guidance, given in ISO/IEC 9646-2 : 1994¹ (annex A);
• Includes channel design examples and formulas for calculating cabling and concentrator system configurations (annex B);
• Describes jitter components and provides an example of jitter buildup using a phase lock loop recovery circuit (annex C);
• Provides informative transmitter filter design example (annex D);
• Provides recommended guidelines for safety and operating environments (annex E);
• Illustrates the MAC finite state machines in a notation similar to that used in lSO/IEC 8802-5 : 1992 (annex F);
• Describes major improvements made after the first edition of the standard (annex G);
• Provides a sample algorithm for the parsing of MAC frames (annex H);
• Provides recommendations for the use of token ring access priorities to support multimedia traffic (annex I);
• Provides bit error rate (BER) criteria for lobe media testing (annex P).

A particular emphasis of this standard is to specify the externally visible characteristics needed for interconnection compatibility, while avoiding unnecessary constraints upon and changes to internal design and implementation of the heterogeneous processing equipment to be interconnected.

The applications environment for the LAN is intended to be commercial and light industrial. The use of token ring LANs in home and heavy industrial environments, while not precluded, has not been considered in the development of this standard.

This standard, the Third Edition of this part of ISO/IEC 8802, provides enhancements and corrections to the Second Edition. The Second Edition provided greater specificity and improved clarity to the First Edition (1992-06-12) to ensure interoperability of the various components in the token ring network. The intent of this edition is to maintain interoperability with stations designed to this specification and stations designed to prior editions of the standard. However, interoperability with prior implementations (particularly in regard to clause 7) cannot be guaranteed due to nonspecificity within the 1992 edition. Annex G lists the specific differences between the second edition and the first edition.

The following items are subjects for future study:

• Controlled bit altering by any device except a station.
• Methodology to assure handling of joining of multiple rings as may be used by managed concen-trators to assure normal insertion process protection mechanisms (such as duplicate address test or ring parameter server notification).
• Ring data rate determination to allow managed data rate adaptation between stations.
• Alternative active concentrators or repeaters that provide increased cabling distances and/or enhanced operation of rings containing devices built to the first edition of this standard, ISO/IEC 8802-5 : 1992.
• Converters that allow the interconnection of stations on different media types.
• Methodologies to provide enhanced transmission reliability over the trunk cable.
• Definition of concentrator managed objects.

¹ Information on references can be found in 1.2.