ISO/IEC 9314-8:1998

INTERNATIONAL
ISO/IEC
STANDARD
9314-8
First edition
1998-08
Information technology –
Fibre Distributed Data Interface (FDDI) –
Part 8:
Media Access Control-2 (MAC-2)
Reference number
INTERNATIONAL
ISO/IEC
STANDARD
9314-8
First edition
1998-08
Information technology –
Fibre Distributed Data Interface (FDDI) –
Part 8:
Media Access Control-2 (MAC-2)
 ISO/IEC 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any
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– ii – 9314-8 © ISO/IEC:1998(E)
CONTENTS
Page
FOREWORD . v
INTRODUCTION . vi
Clause
1 Scope. 1
2 Normative references . 3
3 Definitions. 4
4 Conventions and abbreviations .7
4.1 Conventions . 7
4.1.1 Addressing. 7
4.1.2 Timing values and timers. 7
4.2 Abbreviations . 8
5 General description . 10
6 Services. 11
6.1 MAC-to-LLC services.12
6.1.1 MA_UNITDATA.request . 12
6.1.2 MA_UNITDATA.indication . 14
6.1.3 MA_UNITDATA_STATUS.indication. 16
6.1.4 MA_TOKEN.request. 16
6.2 MAC-to-PHY services. 17
6.2.1 PH_UNITDATA.request. 18
6.2.2 PH_UNITDATA.indication . 18
6.2.3 PH_INVALID.indication. 18
6.3 MAC-to-H-MUX Services. 19
6.3.1 HM_MODE.indication . 19
6.3.2 HP_UNITDATA.request. 20
6.3.3 HP_UNITDATA.indication . 20
6.3.4 HP_INVALID.indication. 21
6.3.5 HP_MODE.request. 21
6.4 MAC-to-SMT services. 22
6.4.1 SM_MA_INITIALIZE_PROTOCOL.request. 22
6.4.2 SM_MA_CONTROL.request . 24
6.4.3 SM_MA_STATUS.indication . 26
6.4.4 SM_MA_UNITDATA.request. 28
6.4.5 SM_MA_UNITDATA.indication. 29
6.4.6 SM_MA_UNITDATA_STATUS.indication . 31
6.4.7 SM_MA_TOKEN.request . 31
7 Facilities. 32
7.1 Symbol set . 32
7.1.1 Line state symbols. 32
7.1.2 Control symbols. 33
7.1.3 Data Quartets (0-F) . 34
7.1.4 Violation symbol (V). 34

9314-8 © ISO/IEC:1998(E) – iii –
7.2 Protocol Data Units. 34
7.2.1 Token. 35
7.2.2 Frame . 35
7.3 Fields . 36
7.3.1 Preamble (PA) . 36
7.3.2 Starting Delimiter (SD). 36
7.3.3 Frame Control (FC) . 36
7.3.4 Destination and source addresses . 39
7.3.5 Routing Information (RI) field. 42
7.3.6 Information (INFO) field. 42
7.3.7 Frame Check Sequence (FCS) . 43
7.3.8 Ending Delimiter (ED). 44
7.3.9 Frame Status (FS). 45
7.4 Timers. 46
7.4.1 Token-Holding Timer (THT) . 46
7.4.2 Valid-Transmission Timer (TVX) . 46
7.4.3 Token-Rotation Timer (TRT) . 47
7.4.4 Late Counter (Late_ct). 48
7.4.5 Token Counter (Token_ct) . 48
7.5 Frame counts. 48
7.5.1 Frame_ct . 48
7.5.2 Error_ct. 48
7.5.3 Lost_ct . 48
7.5.4 Copied_ct.49
7.5.5 Transmit_ct. 49
7.5.6 Not_Copied_ct. 49
8 Operation. 49
8.1 Overview . 49
8.1.1 Frame transmission. 50
8.1.2 Token transmission . 50
8.1.3 Frame stripping. 50
8.1.4 Ring scheduling . 51
8.1.5 Ring monitoring . 53
8.2 Structure . 55
8.3 Receiver. 56
8.3.1 Token and frame validity criteria. 57
8.3.2 State R0: LISTEN . 58
8.3.3 State R1: AWAIT_SD (Await Starting Delimiter) . 58
8.3.4 State R2: RC_FR_CTRL (Receive Frame Control Field). 59
8.3.5 State R3: RC_FR_BODY (Receive Frame Body) . 60
8.3.6 State R4: RC_FR_STATUS (Receive Frame Status) . 62
8.3.7 State R5: CHECK_TK (Check Token). 64
8.4 Transmitter. 65
8.4.1 State T0: TX_IDLE (Transmitter Idle). 65
8.4.2 State T1: REPEAT (Repeat). 67
8.4.3 State T2: TX_DATA (Transmit data) . 69
8.4.4 State T3: ISSUE_TK (Issue Token) . 71
8.4.5 State T4: CLAIM_TK (Claim Token). 72
8.4.6 State T5: TX_BEACON (Transmit Beacon) . 73

– iv – 9314-8 © ISO/IEC:1998(E)
Annex A (informative) Addressing . 83
A.1 General structure. 83
A.2 Administration of addresses . 83
A.2.1 Locally administered addresses. 84
A.2.2 Universally administered addresses. 84
A.3 Transmission order. 85
A.3.1 Representation of addresses . 85
A.4 Group addresses. 86
A.4.1 Broadcast address . 86
A.4.2 Assignment of group addresses for use in standards. 87
A.4.3 Group addresses assigned for use in FDDI. 87
A.5 Source routing addressing. 87
A.6 References . 87
Annex B (informative) Frame Check Sequence . 88
B.1 Description. 88
B.2 Generation of the FCS. 88
B.3 Checking the FCS . 89
B.4 Implementation. 89
B.5 Related standards . 91
Annex C (informative) Bridging. 92
C.1 Bridge architectures. 92
C.2 Destination Address recognition. 93
C.3 Indicator setting . 93
C.4 Stripping.93
Annex D (informative) Elements of timer calculation. 95
Annex E (informative) Bibliography . 98
Tables
Table 1 – Interpretation of FC field . 59
Figures
Figure 1 – FDDI structure . 3
Figure 2 – Token ring logical configuration example. 11
Figure 3 – MAC Receiver state diagram. 75
Figure 4 – MAC Transmitter state diagram . 79
Figure B.1 – FCS implementation example. 90

9314-8 © ISO/IEC:1998(E) – v –
FOREWORD
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical activity.
ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work.
In the field of information technology, ISO and IEC have established a joint technical committee,
ISO/IEC JTC 1. Draft International Standards adopted by the joint technical committee are circulated to
national bodies for voting. Publication as an International Standard requires approval by at least 75 %
of the national bodies casting a vote.
International Standard ISO/IEC 9314-8 was prepared by Joint Technical Committee ISO/IEC JTC 1
Information technology, Subcommittee SC 25, Interconnection of information technology equipment.
ISO/IEC 9314 consists of the following parts, under the general title Information technology – Fibre
Distributed Data Interface (FDDI):
– Part 1: Token Ring Physical Layer Protocol (PHY) (1989)
– Part 2: Token Ring Media Access Control (MAC) (1989)
– Part 3: Physical Layer Medium Dependent (PMD) (1990)
1)
– Part 4: Single Mode Fibre Physical Layer Medium Dependent (SMF-PMD)
– Part 5: Hybrid Ring Control (HRC) (1995)
– Part 6: Station Management (SMT)
– Part 7: Physical Layer Protocol (PHY-2)
– Part 8: Media Access Control-2 (MAC-2)
– Part 9: Low-Cost Fibre – Physical Medium Dependent (LCF-PMD) (under consideration)
– Part 10: Token Ring Twisted Pair Physical layer Medium Dependent (TP-PMD) (under
consideration)
– Part 13: Conformance Test Protocol Implementation Conformance Statement Proforma (CT-PICS)
– Part 20: Physical Medium Dependent Conformance Testing (PMD-ATS) (under consideration)
– Part 21: Physical Layer Protocol Conformance Testing (PHY-ATS) (under consideration)
– Part 25: Abstract test suite for FDDI – Station Management Conformance Testing (SMT-ATS)
– Part 26: Media Access Control Conformance Testing (MAC-ATS) (under consideration)
–––––––––––
1)
To be published
– vi – 9314-8 © ISO/IEC:1998(E)
INTRODUCTION
The Fibre Distributed Data Interface (FDDI), ISO/IEC 9314, is intended for use in a high-performance
general purpose multi-node network and is designed for efficient operation with a peak data rate of
100 Mbit/s. It uses a Token Ring architecture with optical fibre as the transmission medium. FDDI
provides for hundreds of nodes operating over an extent of tens of kilometres.
The Media Access Control (MAC) specifies the lower sublayer of the Data Link Layer for the FDDI. As
such, it presents the specifications and services provided for conforming FDDI attachment devices.
MAC specifies the access to the medium, including addressing, data checking, and data framing. MAC
also specifies the receiver and transmitter state machines.
When the set of basic FDDI standards, ISO/IEC 9314, is completed it will include the following
standards:
a) A Physical Layer Protocol (PHY), which specifies the upper sublayer of the Physical Layer of
ISO/IEC 9314.
b) A Physical Layer Media Dependent (PMD), which specifies the lower sublayer of the Physical
Layer of ISO/IEC 9314.
c) A Station Management (SMT), which specifies the local portion of the system management
application process of ISO/IEC 9314.
A number of extensions to ISO/IEC 9314 are completed or in process. One extension, ISO/IEC 9314-5,
for Hybrid Ring Control (HRC), commonly known as FDDI-II, extends the capability of FDDI to handle
isochronous data streams at a multiplicity of data rates. Another extension, ISO/IEC 9314-4, provides
for a single-mode optical fibre version of PMD (SMF-PMD) and will permit optical links of up to 60 km.
Other work, addressing alternate PMDs, is aimed at providing low-cost attachments for use in
concentrator-to-workstation environments. This work includes a Low-Cost Fibre PMD (LCF-PMD) and
a (copper) Twisted Pair PMD (TP-PMD).
This part of ISO/IEC 9314 for MAC-2 is an enhancement to the original FDDI standard on MAC (ISO
9314-2). It is referred to as MAC-2 when it is necessary to distinguish it from the original MAC.
Changes include those identified in footnotes to ISO 9314-2 as areas that the standards committee
intended to change as well as changes that were required for extensions to FDDI, such as FDDI-II and
MAC level bridging. MAC-2 also includes editorial corrections and clarifications.

9314-8 © ISO/IEC:1998(E) – 1 –
INFORMATION TECHNOLOGY —
FIBRE DISTRIBUTED DATA INTERFACE (FDDI) —
Part 8: Media Access Control-2 (MAC-2)
1 Scope
This part of ISO/IEC 9314 specifies the Media Access Control (MAC), the middle sublayer of
the Data Link Layer (DLL), for Fibre Distributed Data Interface (FDDI).
FDDI (ISO/IEC 9314) provides a high-bandwidth (100 Mbit/s), general-purpose
interconnection among information processing systems, subsystems and peripheral
equipment, using fibre optics or other transmission media. FDDI can be configured to
support a sustained data transfer rate of at least 80 Mbit/s (10 Mbyte/s). FDDI provides
connectivity for many nodes distributed over distances of many kilometres in extent. Certain
default parameter values for FDDI (e.g. timer settings) are calculated on the basis of up to
1 000 transmission links or up to 200 km total fibre path length (typically corresponding to
500 nodes and 100 km of dual fibre cable, respectively); however, the FDDI protocols can
support much larger networks by increasing these parameter values.
As shown in figure 1, ISO/IEC 9314 consists of
a) A Physical Layer (PL), which is divided into two sublayers:
1) A Physical Medium Dependent (PMD), which provides the digital baseband point-
to-point communication between nodes in the FDDI network. The PMD provides
all services necessary to transport a suitably coded digital bit stream from node to
node. The PMD defines and characterizes the fibre-optic drivers and receivers,
medium-dependent code requirements, cables, connectors, power budgets, optical
bypass provisions, and physical-hardware-related characteristics. It specifies the
point of interconnectability for conforming FDDI attachments. The initial PMD
standard, ISO/IEC 9314-3, defines attachment to multi-mode fibre. Additional
PMD sublayer standards are being developed for attachment to single-mode fibre
and SONET.
2) A Physical Layer Protocol (PHY), which provides connection between the PMD
and the Data Link Layer. PHY establishes clock synchronization with the upstream
code-bit data stream and decodes this incoming code-bit stream into an equivalent
symbol stream for use by the higher layers. PHY provides encoding and decoding
between data and control indicator symbols and code bits, medium conditioning
and initializing, the synchronization of incoming and outgoing code-bit clocks, and
the delineation of octet boundaries as required for the transmission of information
to or from higher layers. Information to be transmitted on the medium is encoded
by the PHY using a group transmission code.
b) A Data Link Layer (DLL), which is divided into two or more sublayers:
1) An optional Hybrid Ring Control (HRC), which provides multiplexing of packet and
circuit switched data on the shared FDDI medium. HRC comprises two internal
components, a Hybrid Multiplexer (H-MUX) and an isochronous MAC (I-MAC).
H-MUX maintains a synchronous 125 μs cycle structure and multiplexes the
packet and circuit switched data streams, and I-MAC provides access to circuit
switched channels.
– 2 – 9314-8 © ISO/IEC:1998(E)
2) A Media Access Control (MAC), which provides fair and deterministic access to the
medium, address recognition, and generation and verification of frame check
sequences. Its primary function is the delivery of packet data, including frame
generation, repetition, and removal. The definition of MAC is contained in this part
of ISO/IEC 9314.
3) An optional Logical Link Control (LLC), which provides a common protocol for any
required packet data adaptation services between MAC and the Network Layer.
LLC is not specified by FDDI.
4) An optional Circuit Switching Multiplexer (CS-MUX), which provides a common
protocol for any required circuit data adaptation services between I-MAC and the
Network Layer. CS-MUX is not specified by FDDI.
c) A Station Management (SMT), which provides the control necessary at the node level
to manage the processes under way in the various FDDI layers such that a node may
work cooperatively on a ring. SMT provides services such as control of configuration
management, fault isolation and recovery, and scheduling policies.
The MAC definition contained herein is designed to be as independent as possible from both
the physical medium and the speed of operation. Concepts employed in ISO/IEC 8802-5,
dealing with Token Ring MAC operation have been modified to accommodate the higher
FDDI speeds, while retaining a similar set of services and facilities.
ISO/IEC 9314 specifies the interfaces, functions, and operations necessary to ensure
interoperability between conforming FDDI implementations. This part of ISO/IEC 9314
provides a functional description. Conforming implementations may employ any design
technique that does not violate interoperability. Implementations that conform to this part of
ISO/IEC 9314 shall also be interoperable with implementations that conform to ISO 9314-2 if
the additional capability of hybrid mode operation (as defined in this document) is not being
used. Implementers are encouraged to consult ISO 9314-2 in addition to this part of
ISO/IEC 9314.
– 4 – 9314-8 © ISO/IEC:1998(E)
ISO 9314-1: 1989,
Information processing systems - Fibre Distributed Data Interface (FDDI)
- Part 1: Token Ring Physical Layer Protocol (PHY)
ISO 9314-2: 1989,
Information processing systems - Fibre Distributed Data Interface (FDDI)
- Part 2: Token Ring Media Access Control (MAC)
ISO/IEC 9314-3: 1990,
Information processing systems – Fibre Distributed Data Interface
(FDDI) – Part 3: Physical Layer Medium Dependent (PMD)
ISO/IEC 9314-4,
Information technology – Fibre Distributed Data Interface (FDDI) – Part 4:
1)
Single Mode Fibre Physical Layer Medium Dependent (SMF-PMD)
ISO/IEC 9314-5:1995,
Information technology - Fibre Distributed Data Interface (FDDI) -
Part 5: Hybrid Ring Control (HRC)
ISO/IEC 9314-6:
Information technology - Fibre Distributed Data Interface (FDDI) - Part 6:
Station Management (SMT)
ISO/IEC 9314-7:
Information technology - Fibre Distributed Data Interface (FDDI) - Part 7:
Physical Layer Protocol (PHY-2)
ISO/IEC 10038: 1993,
Information technology - Telecommunications and information
exchange between systems - Local area networks - Media access control (MAC) bridges
3 Definitions
For the purposes of this part of ISO/IEC 9314, the following definitions apply. In some cases
these definitions may duplicate those contained in other parts of ISO/IEC 9314. Such
definitions are included for completeness and to improve readability. In certain cases,
definitions herein may slightly update those contained in the earlier published parts of
ISO/IEC 9314 to improve their clarity.
3.1 asynchronous: A class of data transmission service whereby all requests for service
contend for a pool of dynamically allocated ring bandwidth and response time.
3.2 Basic mode: The mode of ring operation where MAC PDUs (frames and tokens) are
directly transmitted by PHY.
3.3 bypass: The ability of a node to optically isolate itself from the FDDI network while
maintaining the continuity of the cable plant.
The act of removing a token from the ring for the purpose of Frame
3.4 capture:
transmission.
A process whereby one or more MACs bid for the right to initialize the
3.5 claim token:
ring.
An arrangement whereby two signal paths in opposite directions
3.6 counter-rotating:
exist in a ring topology.
A Protocol Data Unit transmitted between cooperating HRC entities on a ring,
3.7 cycle:
consisting of a fixed number of octets in each 125 μs interval.
–––––––––––
1)
To be published.
9314-8 © ISO/IEC:1998(E) – 5 –
3.8 entity: An active service or management element within an Open System
Interconnection (OSI) layer, or sublayer.
3.9 fibre optics: A technology whereby signals are transmitted over an optical waveguide
medium through the use of light-generating transmitters and light-detecting receivers.
3.10 frame: A Protocol Data Unit transmitted between cooperating MAC entities on a logical
ring, consisting of a variable number of octets and control symbols.
The mode of ring operation where HRC PDUs (cycles) are transmitted
3.11 Hybrid mode:
by PHY.
The Data Link Layer entity responsible for multiplexing of
3.12 Hybrid Ring Control (HRC):
packet and circuit switched data, and providing access to circuit switched channels, in an
FDDI logical ring.
A class of data transmission service whereby requests for service from
3.13 immediate:
SMT when the ring is non-operational are performed immediately without capture of a token.
The set of FDDI Data Link Layer entities (HRC or MAC) serially
3.14 logical ring:
connected to form a single ring. The FDDI network topology can form two counter-rotating
logical rings; however, some subsets of this topology only form a single logical ring.
The Data Link Layer entity responsible for scheduling
3.15 Media Access Control (MAC):
and routing packet data transmissions in an FDDI logical ring.
The 48-bit Individual Address of this MAC.
3.16 my long address (MLA):
3.17 my short address (MSA): The 16-bit Individual Address of this MAC.
3.18 network (FDDI network): A collection of FDDI nodes interconnected to form a trunk,
or a tree, or a trunk with multiple trees. This topology is sometimes called a dual ring of
trees.
3.19 node: A collection of Physical Layer (e.g. PMD and PHY) and optional Data Link Layer
(e.g. MAC and HRC) entities within an FDDI network, capable of repeating information and
optionally of transmitting and receiving information, and managed by one SMT entity.
3.20 non-restricted token: A token denoting the normal mode of asynchronous bandwidth
allocation, wherein the available bandwidth is shared among requesters.
3.21 null address: An address of all zeros, or an address that is either not implemented or
implemented but not enabled.
3.22 octet: A data unit composed of eight ordered binary bits. An octet is represented in
FDDI as a pair of data symbols.
The Physical Layer entity responsible for
3.23 Physical Layer Medium Dependent (PMD):
delivering a code bit stream produced by a PHY entity to the physically adjacent PHY entity,
attached via fibre optics, in an FDDI network.
The Physical Layer entity responsible for delivering a
3.24 Physical Layer Protocol (PHY):
symbol stream produced by an upstream DLL entity (MAC or HRC) to the logically adjacent
downstream DLL entity in an FDDI network.
An element of the services provided by one entity to another.
3.25 primitive:
The unit of information transfer between communicating
3.26 Protocol Data Unit (PDU):
peer layer entities. It may contain control information, address information, data (e.g. an
SDU from a higher layer entity), or any combination of the three. The FDDI MAC PDUs are
tokens and frames.
– 6 – 9314-8 © ISO/IEC:1998(E)
3.27 receive: The action of a node that consists of accepting an information stream (e.g.
frame, token, cycle or control sequence) from the medium. The node receiving the
information stream may examine it and selectively copy it as appropriate.
3.28 repeat: The action of a node that consists of receiving an information stream from an
upstream node and reproducing it on the medium to a downstream node. The node
repeating the information stream may examine it and selectively copy or modify it as
appropriate.
3.29 restricted token: A token denoting a special mode of asynchronous bandwidth
allocation, wherein the bandwidth available for the asynchronous class of service is
dedicated to a single extended dialogue between specific requesters.
3.30 ring: A closed loop consisting of one or more stations connected by a physical
medium wherein information is passed sequentially between active stations, each station in
turn examining or copying and repeating the information, finally returning it to the originating
station.
3.31 Service Data Unit (SDU): The unit of data transfer between a service user and a
service provider.
A set of functions provided by one OSI layer or sublayer entity, for use by a
3.32 services:
higher layer or sublayer entity or by management entities. Data services are provided to a
higher layer or sublayer entity; management services are provided to a management entity.
A method of routing frames through a bridged network in which the
3.33 source routing:
source station specifies within each frame the route it will traverse.
An addressable logical and physical node in an FDDI network, capable of
3.34 station:
transmitting, repeating and receiving information. An FDDI station has one or more PHY
and PMD entities, zero or more HRC entities, one or more MAC entities, and one SMT
entity.
The supervisory entity within an FDDI node that
3.35 Station Management (SMT):
monitors and controls the other FDDI entities in the node.
The smallest signalling element used by the Data Link Layer (DLL). The
3.36 symbol:
symbol set consists of 16 data symbols and 9 control symbols.
A class of data transmission service whereby each requester is
3.37 synchronous:
preallocated a maximum bandwidth and guaranteed a maximum access time.
An explicit indication of the right to transmit on a shared medium. On a token
3.38 token:
ring, the token circulates sequentially through the stations in the ring. At any time, it may be
held by zero or one station. MAC uses two classes of tokens: restricted and non-restricted.
3.39 transmit: The action of a node that consists of generating an information stream (e.g.
frame, token, cycle or control sequence) and placing it on the medium.
A method of routing frames through a bridged network in which
3.40 transparent bridging:
intermediate bridge stations determine the route that each frame will traverse without explicit
involvement of the end stations.

9314-8 © ISO/IEC:1998(E) – 7 –
4 Conventions and abbreviations
4.1 Conventions
The terms SMT, MAC, HRC, PHY and PMD, when used without modifiers, refer specifically
to the local FDDI entities within a node. The term LLC unless otherwise qualified refers to
any local user of MAC data services, other than SMT, including those conforming to ISO
8802-2.
Low lines (e.g. requested_service_class) are used as a convenience to mark the name of
signals, functions, etc., that might otherwise be misinterpreted as independent individual
words if they were to appear in text.
The use of a period (e.g. MA_UNITDATA.request) is equivalent to the use of a low line
except that a period is used as an aid to distinguish modifier words appended to an
antecedent expression.
Subscripts or other object selectors are denoted by square brackets in text (
e.g.
aggregate object[subscript] ).
Optional capabilities are distinguished from required capabilities by the use of dashed lines
in drawings or curved braces in text ( required capability { | optional capability } ).
e.g.
Subordinate clauses in state machine footnotes are denoted by indentation ( matching
e.g.
THEN and ELSE clauses are indented one level beneath their IF clause).
Comments in state machine footnotes are denoted by double brackets (
e.g.
condition « comment » ).
4.1.1 Addressing
MSA = the 16-bit Individual Address of this MAC, if implemented and enabled by SMT;
otherwise MSA = Null.
MLA = the 48-bit Individual Address of this MAC, if enabled by SMT; otherwise MLA = Null.
Short_Addresses is the set of 16-bit MAC addresses including MSA if enabled, the 16-bit
Broadcast Address (all ones), and any other 16-bit Group Addresses recognized by this
MAC.
Long_Addresses is the set of 48-bit MAC addresses including MLA if enabled, the 48-bit
Broadcast Address (all ones), and any other 48-bit Group Addresses recognized by this
MAC.
When claiming the token, if the MAC transmits with 16-bit addressing, then MLA = Null;
conversely, if the MAC transmits with 48-bit addressing, then MSA = Null.
A Null Address consists of all zeros in MAC PDUs. The representation of Null and/or
disabled addresses within a station is not specified; however, by convention such addresses
are represented as all zeros in this document.
Transparent_Bridge_Addresses is the set of 48-bit MAC addresses to be forwarded by
transparent bridges.
4.1.2 Timing values and timers
All timing values, when encoded in binary form, are expressed as the unsigned twos
complement of the target or remaining time in octets, i.e. the numerically greater magnitude
represents the shortest time remaining. This definition is for reference purposes only and

– 8 – 9314-8 © ISO/IEC:1998(E)
does not prescribe the implementation, except where these timing values appear in Protocol
Data Units on the ring. These timing values are not all used simultaneously in the state
machines; consequently, the implementation need not instantiate them when they are not
needed.
Timers are given a name of the form TXX where XX are two capital letters, an example is
the token rotation timer TRT. By convention, all timers are assumed to be initialized with the
unsigned twos complement of the target, or remaining, time in octets. Timers are further
assumed to count upward if enabled, expiring when an overflow occurs. All timer
comparisons are expressed on the basis of elapsed time. These conventions are for
reference purposes only and do not prescribe implementation.
4.2 Abbreviations
A Address Recognized Indicator in Frame Status field of a frame
A_Flag Indicates Destination Address match in last received frame
A_Max Maximum signal acquisition time
B_Flag Indicates new restricted dialog may Begin on this token rotation
C Frame Copied Indicator in Frame Status field of a frame
CMT Connection Management function of Station Management
Copied_ct Count of PDUs addressed to and copied by the MAC
C_Flag Indicates successful copying of last received frame
DA Destination Address field of a frame
DLL Data Link Layer
DM_Min Minimum duplicate MAC frame detection delay
D_Flag Indicates that the duplicate MAC frame detection delay has transpired
D_Max Maximum ring latency time
E Error Detected Indicator in Frame Status field of a frame
ED Ending Delimiter field of a MAC PDU
Error_ct Count of reportable frame errors
E_Flag Indicates error detected in last received frame
FC Frame Control field of a MAC PDU
FCS Frame Check Sequence field of a frame
FF Frame Format bits in Frame Control field of a MAC PDU
Frame_ct Count of all frames received
FS Frame Status field of a frame
F_Max Maximum frame time
HRC Hybrid Ring Control
H_Flag Indicates Higher Source Address received
IG Individual/Group bit in Destination Address field of a frame
INFO Information field of a frame

9314-8 © ISO/IEC:1998(E) – 9 –
I_Max Maximum node physical insertion time
Last_FC The Frame Control field of the last valid Frame or Token Received
Late_ct Count of TRT expirations (token lateness)
LLC Local Link Control
Lost_ct Count of PDUs detected as lost
L_Flag Indicates Lower Source Address received
L_Max Maximum transmitter frame set-up time
MAC Media Access Control
MLA My Long Address
MSA My Short Address
M_Flag Indicates My Source Address received
M_Max Maximum number of MAC entities allowed on the ring
Not_Copied_ct Count of PDUs addressed to and not copied by the MAC
NSA Next Station Addressing frame
N_Flag Indicates No copy acknowledgment for this frame
PA Preamble between MAC PDUs
PDU Protocol Data Unit
PHY Physical Layer Protocol
PMD Physical Layer Medium Dependent
P_Flag Indicates Purge in process
RI Routing Information field of a frame
RII Routing Information Indicator bit in Source Address field of a frame
RMT Ring Management function of Station Management
R_Flag Indicates last valid token received was restricted
SA Source Address field of a frame
SD Starting Delimiter field of a MAC PDU
SDU Service Data Unit
SMT Station Management
S_Min Minimum safety timing allowance
THT Token-Holding Timer
Token_ct Count of tokens received by the MAC
Transmit_ct Count of PDUs transmitted by the MAC
TRT Token-Rotation Timer
TTRT Target Token Rotation Time
TVX Valid-Transmission Timer
TVX_value TVX timeout value
– 10 – 9314-8 © ISO/IEC:1998(E)
T_Bid_rc Bidding TTRT received by this MAC in Claim Frames
T_Bid_tx Bidding TTRT transmitted in this MAC's Claim Frames
T_Flag Indicates that the last captured token was early
T_Init Maximum allowed ring initialization time
T_Max Maximum TTRT to be supported by this MAC
T_Min Minimum TTRT to be requested by this MAC
T_Neg Negotiated TTRT during Claim process (in receiver)
T_Opr Operative TTRT for this MAC (in transmitter)
T_Pri Set of n priority Token Rotation Time thresholds
T_Pri[n] Element n of the set T_Pri
T_React Maximum allowed time to react to a major ring fault
T_Req Requested TTRT for this MAC's traffic
T_Resp Maximum allowed time to recover a token
5 General description
An FDDI network consists of a set of nodes ( stations) connected by optical transmission
e.g.
media into one or more logical rings. A logical ring consists of a set of stations connected as
an alternating series of nodes and transmission media to form a closed loop (see figure 2).
Information is transmitted sequentially, as a stream of suitably encoded symbols, from one
active node to the next. Each node generally regenerates and repeats each symbol and
serves as the means for attaching one or more devices to the ring for the purpose of
communicating with other devices on the ring.
Two kinds of data service can be provided in a logical ring: packet service and circuit
service. For packet service, a given station (the one that has access to the medium)
transmits information on to the ring as a series of data packets, where each packet circulates
from one station to the next. The addressed destination station(s) copies the packets as
they pass. Finally, the station that transmitted the packets effectively removes them from
the ring. For circuit service, some of the logical ring bandwidth is allocated to independent
channels. Two or more stations can simultaneously communicate via each channel. The
structure of the information stream within each channel is determined by the stations sharing
that channel.
FDDI provides packet service via a token ring, wherein a station gains the right to transmit its
information on to the medium when it detects a token passing on the medium. The token is
a control signal comprised of a unique symbol sequence that circulates on the medium
following each series of transmitted packets. Any station, upon detection of a token, may
capture the token by removing it from the ring. The station may then transmit one or more
data packets. After transmitting its packets, the station issues a new token, which provides
other stations the opportunity to gain access to the ring.
A Token-Holding Timer, or equivalent means, limits the length of time a station may use
(occupy) the medium before passing the token.
Multiple levels of priority are available for independent and dynamic assignment depending
upon the relative class of service required. The classes of service may be synchronous
(typically used for applications
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