ISO 21806-8:2020
(Main)Road vehicles — Media Oriented Systems Transport (MOST) — Part 8: 150-Mbit/s optical physical layer
Road vehicles — Media Oriented Systems Transport (MOST) — Part 8: 150-Mbit/s optical physical layer
This document specifies the 150-Mbit/s optical physical layer for MOST (MOST150 oPHY), a synchronous time-division-multiplexing network. This document specifies the applicable constraints and defines interfaces and parameters, suitable for the development of products based on MOST150 oPHY. Such products include fibre optical links and connectors, fibre optic receivers, fibre optic transmitters, electrical to optical converters, and optical to electrical converters. This document also establishes basic measurement techniques and actual parameter values for MOST150 oPHY.
Véhicules routiers — Système de transport axé sur les médias — Partie 8: Couche optique physique à150-Mbit/s
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 21806-8
First edition
2020-10
Road vehicles — Media Oriented
Systems Transport (MOST) —
Part 8:
150-Mbit/s optical physical layer
Véhicules routiers — Système de transport axé sur les médias —
Partie 8: Couche optique physique à150-Mbit/s
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
4.1 Symbols . 2
4.2 Abbreviated terms . 3
5 Conventions . 4
6 Physical layer service interface to OSI data link layer . 4
6.1 Overview . 4
6.2 Data type definitions . 4
6.3 Event indications and action requests . 4
6.3.1 P_EVENT.INDICATE . 4
6.3.2 P_ACTION.REQUEST . 4
6.4 Parameters . 4
6.4.1 PHY_Event . 4
6.4.2 PHY_Request . . 5
7 Basic physical layer requirements . 5
7.1 Logic terminology . 5
7.1.1 Single-ended low-voltage digital signals . 5
7.1.2 Differential LVDS signals . 6
7.2 Specification points (SPs) . 6
7.3 Phase variation . 7
7.3.1 General. 7
7.3.2 Wander . 7
7.3.3 Jitter . 7
7.3.4 Clock recovery and reference clock . 8
7.3.5 Link quality . 9
7.3.6 MOST network quality .10
8 MOST150 oPHY requirements .14
8.1 General MOST network parameters .14
8.1.1 MOST network coding .14
8.1.2 Specification Point details.15
8.2 Models and measurement methods .16
8.2.1 Golden PLL .16
8.2.2 Jitter filter .17
8.2.3 Retimed bypass mode and stress pattern .18
8.2.4 Optical signal level detection .18
8.2.5 Region of optical signal level detection .18
9 Link specifications .19
9.1 General .19
9.2 Specification Point 1 (SP1) .19
9.3 Specification Point 2 (SP2) .21
9.3.1 Link quality parameters .21
9.3.2 Optical overshoot and undershoot .23
9.4 Specification Point 3 (SP3) .26
9.5 Specification Point 4 (SP4) .27
10 Power-on and power-off .28
10.1 Frequency reference and power supply .28
10.2 Power supply monitoring circuitry .29
10.3 Optical and electrical signal power state .29
10.3.1 General.29
10.3.2 EOC requirements .29
10.3.3 EOC power-on and power-off sequence .31
10.3.4 OEC requirements .32
10.3.5 OEC power-on and power-off sequence .34
11 MOST network requirements .35
11.1 SP4 receiver tolerance .35
11.2 TimingMaster delay tolerance .36
11.3 Optical fibre link length requirement .36
11.4 Environmental requirements and considerations .36
12 Electrical interfaces .36
12.1 LVDS .36
12.2 Bit rate and frequency tolerance .37
13 FOT packaging .37
13.1 SMD package .37
13.1.1 SMD FOT package reference drawings .37
13.1.2 SMD FOT pinout.37
13.1.3 SMD OEC signal definitions .38
13.1.4 SMD EOC signal definitions .39
13.2 Through-hole mount (THM) package .39
13.2.1 THM FOT package reference drawings .39
13.2.2 THM FOT pinout .40
13.2.3 THM OEC signal definitions .40
13.2.4 THM EOC signal definitions .40
13.3 Small form connector 2+0 SMD 7-Pin-package .41
13.3.1 2+0 Small form connector SMD 7-Pin-package reference drawings .41
13.3.2 Small form connector 2+0 SMD 7-Pin-package FOT pinout .41
13.3.3 7-Pin OEC signal definitions.42
13.3.4 7-Pin EOC signal definitions.42
13.4 MOST150 FO-Transceiver THM 180° .43
13.4.1 MOST150 FO-Transceiver THM 180° reference drawings .43
13.4.2 MOST150 FO-Transceiver THM 180° FOT pinout .43
13.4.3 MOST150 FO-Transceiver THM 180° OEC signal definitions .43
13.4.4 MOST150 FO-Transceiver THM 180° EOC signal definitions .43
13.5 MOST150 FO-Transceiver SMD 90° .43
13.5.1 MOST150 FO-Transceiver SMD 90° reference drawings .43
13.5.2 MOST150 FO-Transceiver SMD 90° FOT pinout .43
13.5.3 MOST150 FO-Transceiver SMD 90° OEC signal definitions .44
13.5.4 MOST150 FO-Transceiver SMD 90° EOC signal definitions .44
14 Device connectors .45
14.1 Connector interfaces .45
14.2 Connector interface loss .45
Bibliography .47
iv © ISO 2020 – All rights reserved
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 31,
Data communication.
A list of all parts in the ISO 21806 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
Introduction
The Media Oriented Systems Transport (MOST) communication technology was initially developed at
the end of the 1990s in order to support complex audio applications in cars. The MOST Cooperation was
founded in 1998 with the goal to develop and enable the technology for the automotive industry. Today,
1)
MOST enables the transport of high quality of service (QoS) audio and video together with packet data
and real-time control to support modern automotive multimedia and similar applications. MOST is a
function-oriented communication technology to network a variety of multimedia devices comprising
one or more MOST nodes.
Figure 1 shows a MOST network example.
Figure 1 — MOST network example
The MOST communication technology provides:
— synchronous and isochronous streaming,
— small overhead for administrative communication control,
— a functional and hierarchical system model,
— API standardization through a function block (FBlock) framework,
— free partitioning of functionality to real devices,
— service discovery and notification, and
[4]
— flexibly scalable automotive-ready Ethernet communication according to ISO/IEC/IEEE 8802-3 .
MOST is a synchronous time-division-multiplexing (TDM) network that transports different data types
on separate channels at low latency. MOST supports different bit rates and physical layers. The network
clock is provided with a continuous data signal.
1) MOST® is the registered trademark of Microchip Technology Inc. This information is given for the convenience
of users of this document and does not constitute an endorsement by ISO.
vi © ISO 2020 – All rights reserved
Within the synchronous base data signal, the content of multiple streaming connections and control
data is transported. For streaming data connections, bandwidth is reserved to avoid interruptions,
collisions, or delays in the transport of the data stream.
MOST specifies mechanisms for sending anisochronous, packet-based data in addition to control data
and streaming data. The transmission of packet-based data is separated from the transmission of
control data and streaming data. None of them interfere with each other.
A MOST network consists of devices that are connected to one common control channel and packet
channel.
In summary, MOST is a network that has mechanisms to transport the various signals and data streams
that occur in multimedia and infotainment systems.
The ISO standards maintenance portal (https:// standards .iso .org/ iso/ ) provides references to MOST
specifications implemented in today's road vehicles because easy access via hyperlinks to these
specifications is necessary. It references documents that are normative or informative for the MOST
versions 4V0, 3V1, 3V0, and 2V5.
The ISO 21806 series has been established in order to specify requirements and recommendations
for implementing the MOST communication technology into multimedia devices and to provide
conformance test plans for implementing related test tools and test procedures.
To achieve this, the ISO 21806 series is based on the open systems interconnection (OSI) basic reference
[2] [3]
model in accordance with ISO/IEC 7498-1 and ISO/IEC 10731 , which structures communication
systems into seven layers as shown in Figure 2. Stream transmission applications use a direct stream
data interface (transparent) to the data link layer.
Figure 2 — The ISO 21806 series reference according to the OSI model
The International Organization for Standardization (ISO) draws attention to the fact that it is claimed
that compliance with this document may involve the use of a patent.
ISO takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured ISO that he/she is willing to negotiate licences under
reasonable and non-discriminatory terms and conditions with applicants throughout the world. In
this respect, the statement of the holder of this patent right is registered with ISO. Information may be
obtained from the patent database available at www .iso .org/ patents.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights other than those in the patent database. ISO shall not be held responsible for identifying
any or all such patent rights.
viii © ISO 2020 – All rights reserved
INTERNATIONAL STANDARD ISO 21806-8:2020(E)
Road vehicles — Media Oriented Systems Transport
(MOST) —
Part 8:
150-Mbit/s optical physical layer
1 Scope
This document specifies the 150-Mbit/s optical physical layer for MOST (MOST150 oPHY), a
synchronous time-division-multiplexing network.
This document specifies the applicable constraints and defines interfaces and parameters, suitable for
the development of products based on MOST150 oPHY. Such products include fibre optical links and
connectors, fibre optic receivers, fibre optic transmitters, electrical to optical converters, and optical to
electrical converters.
This document also establishes basic measurement techniques and actual parameter values for
MOST150 oPHY.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 21806-1, Road vehicles — Media Oriented Systems Transport (MOST) — Part 1: General information
and definitions
IEC 60825-2, Safety of laser products — Part 2: Safety of optical fibre communication systems (OFCS)
2)
JEDEC MS-013E , Standard — Very Thick Profile, Plastic Small Outline (SO) Family, 1,27 mm pitch, 7,50 mm
(.300 inch) Body Width. B1R-PDSO/SOP/SOIC
3)
JEDEC No. JESD8C.01 , Interface Standard for Nominal 3 V/3,3 V Supply Digital Integrated Circuits
4)
TIA/EIA-644-A , Electrical Characteristics of Low Voltage Differential Signaling (LVDS) Interface Circuits
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21806-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
2) Available at https:// www .jedec .org/ .
3) Available at https:// www .jedec .org/ .
4) Available at https:// www .tiaonline .org/ standards/ .
3.1
electrical to optical converter
EOC
MOST component that converts an electrical signal into an optical signal
3.2
MOST150 oPHY
150-Mbit/s optical physical layer
3.3
numerical aperture
NA
sine of the vertex angle of the largest cone of meridional rays that can enter or leave an optical system
or element, multiplied by the refractive index of the medium in which the vertex of the cone is located
[SOURCE: IEC Electropedia, 731-03-85]
3.4
optical to electrical converter
OEC
MOST component that converts an optical signal into an electrical signal
3.5
pigtail
short length of optical fibre, permanently attached to a component and intended to facilitate jointing
between that component and another optical fibre or component
[SOURCE: IEC Electropedia, 731-05-08, modified — The term was originally "optical fibre pigtail" and
the Note 1 to entry has been deleted.]
4 Symbols and abbreviated terms
4.1 Symbols
--- empty cell/undefined
b the optical signal level when a logic 0 is transmitted
b the optical signal level when a logic 1 is transmitted
N bits per frame
BPF
ρ network frame rate
Fs
ρ bit rate
BR
T ambient temperature
A
t TimingMaster delay tolerance
MDT
t unit interval
UI
V output high voltage
OH
V output low voltage
OL
2 © ISO 2020 – All rights reserved
4.2 Abbreviated terms
BER bit error rate
BPF bits per frame
Cd[n] condition
DC direct current
DCA DC adaptive
DDJ data-dependant jitter
DLL data link layer
DSV digital sum value
ECU electronic control unit
EOC electrical to optical converter
EMC electromagnetic compatibility
EMI electromagnetic interference
FOR fibre optic receiver
FOT fibre optic transceiver
FOX fibre optic transmitter
LS low sensitivity
LVDS Low Voltage Differential Signaling
NA numerical aperture
N/A not applicable
MNC MOST network controller
OEC optical to electrical converter
oPHY optical physical layer
PCB printed circuit board
PDF probability density function
PHY physical layer
PLL phase locked loop
POF polymer (plastic) optical fibre
RMS root mean square
Rx data MOST150 oPHY automotive encoded digital bit stream being received
SDA serial data analyser
SP[n] Specification Point
TDM time-division-multiplexing
Tx data MOST150 oPHY automotive encoded digital bit stream being transmitted
UI unit interval
5 Conventions
[3]
This document is based on OSI service conventions as specified in ISO/IEC 10731 .
6 Physical layer service interface to OSI data link layer
6.1 Overview
The physical layer (PHY) service interface specifies the abstract interface to the OSI data link layer
[1]
(DLL), see ISO 21806-6 .
6.2 Data type definitions
The data type Enum is defined as an 8-bit enumeration.
6.3 Event indications and action requests
6.3.1 P_EVENT.INDICATE
The PHY shall use P_EVENT.INDICATE to indicate the occurrence of an event to the DLL.
P_EVENT.INDICATE{
PHY_Event
}
6.3.2 P_ACTION.REQUEST
P_ACTION.REQUEST shall trigger the execution of a request.
P_ACTION.REQUEST {
PHY_Request
}
6.4 Parameters
6.4.1 PHY_Event
Table 1 specifies the PHY_Event parameter, which notifies the DLL about events.
4 © ISO 2020 – All rights reserved
Table 1 — Parameter passed from PHY to DLL
Parameter Data type Description
PHY_Event
Enum { An event that is reported to the DLL.
PHY_Output_Off,
PHY_Network_Activity
}
Table 2 specifies the parameter values for the PHY_Event Enum.
Table 2 — PHY_Event Enum values
Enum value Description
PHY_Output_Off
MNC transmit terminal switched off.
PHY_Network_Activity
Network activity detected at the MNC receive terminal.
6.4.2 PHY_Request
Table 3 specifies the PHY_Request parameter, which is passed from DLL to PHY.
Table 3 — Parameter passed from DLL to PHY
Parameter Data type Description
PHY_Request
Enum { A request from the DLL
cmd_Output_Off,
cmd_Output_On,
cmd_Open_Bypass,
}
Table 4 specifies the parameter values for the PHY_Request Enum.
Table 4 — PHY_Request Enum values
Enum value Description
cmd_Output_Off
Switching off the MNC transmit terminal requested. By default, it is off.
cmd_Output_On
Switching on the MNC transmit terminal requested. By default, it is off.
cmd_Open_Bypass
Opening the bypass requested. By default, the bypass is closed.
7 Basic physical layer requirements
7.1 Logic terminology
7.1.1 Single-ended low-voltage digital signals
For the parameters provided in JEDEC No. JESD8C.01, Table 5 defines the corresponding terms for
single-ended signals used in this document. These terms are used to describe the logic states of signals
/RST and STATUS.
Table 5 — Terms for single-ended signals
Term Corresponding JEDEC parameter
Low
V (output low voltage)
OL
Logic 0
High
V (output high voltage)
OH
Logic 1
7.1.2 Differential LVDS signals
TIA/EIA-644-A uses the labels A and B for the device output terminals; this document uses P and an N,
respectively. Table 6 specifies the terms for LVDS signals. The terms correspond to the TIA/EIA-644-A
specification.
Table 6 — Terms for LVDS signals
Term Corresponding JEDEC parameter
Low
The P terminal shall be negative with respect to the N terminal for a binary 0 state.
Logic 0
High
The P terminal shall be positive with respect to the N terminal for a binary 1 state.
Logic 1
Since some of the MOST devices specified in this document use a tri-state LVDS interface, Table 7
specifies the terms for LVDS bus states.
Table 7 — Terms for LVDS bus states
Term Corresponding TIA/EIA description
Disabled
The P and N terminals are in a high impedance state. If small leakage currents
exist, they might cause an indeterminate voltage on the line/load.
Off
Enabled
The P and the N terminals are driving the line/load. The outputs are at valid LVDS
logic levels provided the input data is valid.
On
Valid LVDS signal Data or LVDS 0, according to LVDS voltage levels.
7.2 Specification points (SPs)
A physical connection of two MOST devices is called a link. Measurements are taken at specific locations
along a link. These locations are called SPs. The location of the SPs is shown in Figure 3.
6 © ISO 2020 – All rights reserved
Key
1 specification point 1
2 specification point 2
3 specification point 3
4 specification point 4
Figure 3 — Location of SPs along a link
SPs define interfaces that are boundaries between a transmitting and a receiving MOST component.
For each of those interfaces, a set of requirements and properties is defined (e.g. signal timing, signal
amplitude, connector interface drawings). SP1 and SP4 are located between a MOST network controller
(MNC) and the corresponding transceiver. SP2 and SP3 are located between transceivers and a wiring
harness.
For MOST components that are located between two adjacent SPs, requirements and properties can
be derived. The definitions of the second SP of the pair specify the component's output performance to
be achieved, considering input conditions as defined in the first SP. For example, a transmit converter
component specification can be derived from SP1 and SP2. Receive converter component requirements
are covered by SP3 and SP4. Wiring harness requirements can be derived from SP2 and SP3.
In addition to the definitions of the SPs for a point-to-point link, this document defines requirements
covering the stability of the MOST network. Examples are requirements regarding jitter transfer
through MOST devices, jitter accumulation through the MOST network, and power state transitions.
The specified parameters in this document are minimum values to ensure functionality of the MOST
network in a wide range of environmental conditions.
7.3 Phase variation
7.3.1 General
Phase variation is caused by data stream timing noise and distortion.
7.3.2 Wander
Wander is made up of any phase variation from 0 Hz to 10 Hz. All active MOST components in the MOST
network create wander. Wander is a function of the temperature drift and propagates from node to
node. Typically, wander does not affect alignment jitter eye masks.
NOTE It is possible that the wander impacts the TimingMaster.
7.3.3 Jitter
Jitter is any phase variation of frequencies above 10 Hz. Every MOST component and the transmission
medium create jitter in the MOST network. Jitter is correlated or uncorrelated. The dominant jitter
sources in the MOST network consist of PLL noise, link-induced DDJ, sensitivity-induced OEC noise,
crosstalk, or phenomena such as power supply coupling. Data scrambling is used to eliminate DDJ
correlation between nodes.
There are two jitter categories as shown in Figure 4:
— Alignment jitter: jitter that affects the reception of data by degrading the receiver eye diagram
with horizontal closure (influences eye diagram measurement); it has impact only on a link as data
recovery is performed by the MNC.
— Transferred jitter: jitter that is accumulated over all links (does not influence eye diagram
measurement); the TimingMaster jitter tolerance shall be determined accordingly.
As the jitter on the measured signal increases, the eye closes more and more. A keep-out mask is
specified to detect possible error traces. If the eye does not hit the mask then data recovery is ensured.
Mask design depends on the required receiver margin and the characteristics of the channel.
Figure 4 shows the phase variation measurements.
Figure 4 — Phase variation measurements
7.3.4 Clock recovery and reference clock
7.3.4.1 General
Phase variation can be measured directly on a data stream. To view alignment jitter and transferred
jitter independently, special tools are required.
All MOST networks contain one device that implements the TimingMaster, which creates the reference
clock. This clock is embedded within the data stream. All other MOST devices contain TimingSlaves
that recover the clock from the data stream. Therefore, clock recovery is a basic functionality of an
MNC. MOST components add a phase variation to the data stream. This degrades the reference clock.
Receiver jitter tolerance and jitter transfer are basic operation properties of any MNC. Alignment jitter
is measured by means of an eye diagram formed with a Golden PLL. Transferred jitter is measured with
a jitter filter.
Figure 5 illustrates clock recovery and data recovery in an MNC. Therefore, there is a need for a Golden
PLL model and a jitter filter model. Together they reflect the required jitter behaviour of an MNC.
8 © ISO 2020 – All rights reserved
Figure 5 — Clock and data recovery example
7.3.4.2 Golden PLL
The Golden PLL is a simplified model which describes the behaviour of the MNC when jitter is applied to
its input. A Golden PLL can be constructed out of hardware or software but shall obtain data from the
SP and output a clock at the UI frequency for eye diagram formation.
7.3.4.3 Jitter filter
The jitter filter is a simplified model which describes the worst-case MNC jitter transfer function. A
jitter filter can be constructed out of hardware or software but shall obtain data from the SP and output
the RMS value of the transferred jitter at the SP.
7.3.5 Link quality
7.3.5.1 General
Link quality describes the minimum performance of MOST components along a single link.
7.3.5.2 Alignment jitter
Link quality eye diagrams are used to specify and measure link operation and MOST network level
performance. A jitter budget is created top down starting from SP4. The difference between the SPs
gives the tolerable contribution of alignment jitter for the respective MOST component or transmission
medium. As an example, link quality eyes can be required at every point along the link to allow each
MOST component’s alignment jitter contribution to be specified. Figure 6 shows an example of the eye
diagrams that correspond to the SPs in a link.
Figure 6 — Illustration of eye diagrams at SPs in a link
7.3.5.3 Transferred jitter
A portion of every jitter source in the MOST network has some spectral content below the jitter filter
bandwidth. Jitter passed by the filter accumulates in the following nodes. Transferred jitter from all
sources combines to form accumulated jitter. Accumulated jitter starts small with the first TimingSlave
and gets larger towards the end of the ring. Therefore, the total jitter at the last SP4 point in the MOST
network has two components, one being the total jitter generated in the final link, and the second being
the accumulated jitter from all the links before. Each node shall limit its contribution to the accumulated
jitter to prevent end-of-ring eye closure and receiver failure. The TimingMaster shall be able to tolerate
the peak-to-peak swing of this accumulated jitter. Transferred jitter is critical to MOST network
performance. Transferred jitter is measured by filtering the phase variation at any SPn with a jitter
filter. The RMS (standard deviation) of the output of this jitter filter is the amount of jitter contributed
to accumulated jitter. Transferred jitter specifications are placed at every SP as shown in Figure 7.
Figure 7 — Illustration of transferred jitter accumulation at various SPs in a link
7.3.6 MOST network quality
7.3.6.1 Receiver tolerance
Receiver tolerance describes the minimum alignment jitter tolerance of an MNC and the maximum
tolerable alignment jitter that may occur at any place in the MOST network.
The minimum and maximum limits of the eye mask define the receiver tolerance. The closure of the eye
mask originates from accumulated jitter in the MOST network. An MNC recovers all signals that fit into
the SP4 receiver tolerance mask. A MOST device recovers all signals that satisfy the SP3 link quality
requirements. Figure 8 shows the typical SPs in a ring where the SP4 receiver tolerance limits can be
applied as a test of MOST network performance.
10 © ISO 2020 – All rights reserved
Figure 8 — Locations where receiver tolerance eye mask can be applied
7.3.6.2 TimingMaster delay tolerance
The MOST network stability is determined by the ability of the TimingMaster node to tolerate the
accumulated delay present at the end of the ring. TimingMaster delay tolerance is the maximum amount
of accumulated delay for an MNC that is configured as TimingMaster.
TimingMaster delay tolerance is tied to the delay, transferred jitter, transferred wander and maximum
node count.
Formula (1) defines the minimum for the TimingMaster delay tolerance (t ). The relevance of the
MDT
different types of phase variation for the accumulated delay is shown in Table 8.
The requirements for the MOST network design are combined in the Formula (1) — TimingMaster delay
tolerance t .
MDT
m−1 m−1 m−1
tt≥ ()Mt+ ()nt+ ()nt++α× tn() (1)
∑∑ ∑
MDTD DW DMediumTJ
n=1 n=0 n=0
where
t is the TimingMaster delay tolerance;
MDT
M is the position of the TimingMaster;
m is the number of nodes in the network;
n is the position of the node in the network;
t (M) is the delay of the TimingMaster node caused by Rx and Tx converter;
D
t is the total delay caused by the medium;
D Medium
α is a scaling factor that depends on the BER, see Table 8;
t (n) is the delay of a TimingSlave node, see Table 8;
D
t (n) is the wander (phase drift) of the node and link (peak-to-peak);
W
t (n) is the transferred jitter of the node (RMS) (i.e. α = 12, derived from ±6 σ for
TJ
−9
BER = 10 ).
Assumption
t is correlated from node to node;
W
t is uncorrelated from node to node.
TJ
Table 8 shows the purpose of the MOST network delay and jitter parameters that are combined in
Formula (1).
Table 8 — MOST network delay and jitter parameters
Delay Formula Description
Delay of (2) t (M) is the delay caused by Rx and Tx converter of the TimingMaster node.
D
TimingMaster
node
Delay of a (3) A MOST network operates properly if the TimingMaster complies with this
TimingSlave node Formula.
Accumulation of (4) t is the delay caused by the (m − 1) TimingSlave nodes. The delay per node
DS
delay of is determined by the contribution of Rx converter, MNC and Tx converter.
TimingSlave nodes
Delay of the t Total delay caused by the medium (e.g. depending on the length of the
D Medium
medium medium in use).
Accumulation (5) t is the accumulated wander of all nodes. Due to the low-frequency
W_SUM
of wander characteristic of wander, either most or all of this phase variation is
transferred by a PLL. Wander is generated by all active MOST components of
the link and by the MNC chip. Wander is most commonly caused by
variations in temperature. It shall be specified in the data sheet
...
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