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Description / Abstract:
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
a) Provides a general description of the token ring local area
network (LAN) architecture (clause 2); b) Defines the frame format,
including the delimiters, address fields, information field, and
framecheck sequence (FCS). Defines the Medium Access Control (MAC)
frames, timers, and error counters (clause 3);
c) Defines the MAC protocols including finite state machines and
state tables (clause 4);
d) Defines the system level Physical layer (PHY) signaling
specifications that are specific to a ring station (clause 5);
e) 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);
f) 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);
g) Defines the concentrator, incorporating multiple trunk
coupling units (TCUs), for the attachment of a group of stations to
the ring (clause 8);
h) 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);
i) Includes channel design examples and formulas for calculating
cabling and concentrator system configurations (annex B);
j) Describes jitter components and provides an example of jitter
buildup using a phase lock loop recovery circuit (annex C);
k) Provides informative transmitter filter design example (annex
D);
l) Provides recommended guidelines for safety and operating
environments (annex E);
m) Illustrates the MAC finite state machines in a notation
similar to that used in ISO/IEC 8802- 5 : 1992 (annex F);
n) Describes major improvements made after the first edition of
the standard (annex G);
o) Provides a sample algorithm for the parsing of MAC frames
(annex H);
p) Provides recommendations for the use of token ring access
priorities to support multimedia traffic (annex I);
q) 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:
a) Controlled bit altering by any device except a station.
b) Methodology to assure handling of joining of multiple rings
as may be used by managed concentrators to assure normal insertion
process protection mechanisms (such as duplicate address test or
ring parameter server notification).
c) Ring data rate determination to allow managed data rate
adaptation between stations.
d) 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.
e) Converters that allow the interconnection of stations on
different media types.
f) Methodologies to provide enhanced transmission reliability
over the trunk cable.
g) Definition of concentrator managed objects.
1Information on references can be found in 1.2.