ccsds-sois fall meeting 2008, berlin, germany olivier notebaert – astrium satellites – asg74

Central Engineering / ASG 74Data Processing Advanced Studies

SOIS Standard Services for Communications over 1553 Implementation with ECSS-E-ST-50-13C defined services and protocols

CCSDS-SOIS Fall Meeting 2008, Berlin, Germany

Olivier Notebaert – Astrium Satellites – ASG74Convenor of the ECSS Working Group for standardization on 1553 MilBus

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ECSS-E-50-13WORKING GROUP

Summary

Context

The ECSS Working Group and the drafting process

ECSS-E-50-13 Draft-C Standard Overview

Conclusion

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ContextMil-Bus in Space Applications

a proven Standard Well defined physical and data link layers requirements

But does not provide any “sub-network service layer” (according to CCSDS SOIS model)

But does not provide any user level communication protocol

well adapted to spacecrafts Data-Handling Very good reliability characteristics

Allows deterministic and efficient real-time command/control

Lot of sensors, commercial products and test equipments

Large return on experience in space applications

used successfully for many space applications Launcher avionics on Ariane 5 and Vega

Spacecrafts control for many platforms and payloads

In-Orbit infrastructure and manned flight for ISS and ATV

still with good perspective Evolutions are foreseen to allow higher bandwidth and lower power consumptions

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Summary

Context



Conclusion

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ECSS 1553 Working GroupObjectives and Strategy

Physical layer and Data link layers are well defined by the Mil standard but there are several usage variants

Identify best practices for harmonization

Capitalize the acquired experience on 1553 based systems

Adapt requirements from existing projects and take into account existing communication devices

Several services and communication protocols exist with similar properties

Define a standard set of services and protocols suitable to most 1553 based systems taking into account applications needs

Take into account the sub-network services reference defined by CCSDS/SOIS

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ECSS 1553 Working GroupMembers and interfaces

The WG activity started in December 2005 with the initial objective for a Draft standard delivery at the end of 2007

It is ruled by ECSS standards productions procedures and by an agreed Term of Reference

8 members involved in on-board 1553 systems from European space agencies and industry

ECSS-E-50Engineering panel

CCSDS/SOIS(ESA: Chris Taylor)

ECSS secretariatECSS

Technical Authority

ECSS-E-50ESA/Industry

Working Group

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Standard verification activities

Standard engineering - elaboration and maturation

ECSS 1553 Working GroupDrafting Process

Technical review(Industry + ESA)

studyProjects needsand experience

Draft AApril 2007

CCSDS/SOIS

Working GroupAnalysis and Drafting

Public reviewEditorial review(ECSS Secretariat)

Verification(ESA)

Draft BNovember 2007

Draft CMay 2008

Publication(end 2008)

SOIS mapping& prototyping

Modeling

Mil 1553

Draft D September 2008

Edition

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Summary

Context


ECSS-E-50-13 Draft-D Standard Overview

Conclusion

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Draft-D OverviewTable of Content

1. Scope

2. Normative References

3. Terms, definition and Abbreviated terms

4. Overview

5. Physical layer requirements

6. Data Link layer requirements

7. Services definition

8. Protocol Specification

9. Test and Verification

Annexes

A Tailoring guidelines

B Unreferenced requirements inMil-Std-1553

C Bibliography

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Draft-D OverviewScope

A reference architecture for 1553 systems, a service model and a bus profiling concept are defined

gathering experience of 1553 based projects aiming at determinism of data bus exchanges thus allowing

bandwidth allocation on the bus to ensure: Guaranteed availability for critical data Flexibility for asynchronous and sporadic traffic

in Section 4 (Informative) Harmonisation rules, services and protocols are defined

mapping on SOIS architecture and service model re-using existing requirements and protocol elements from space

projects

in Section 5 to 9 (Normative)

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Draft-D OverviewReference Architecture

SendUser Data

Services W, X,Y,Z

BCApplication

ReceiveUser Data

Physical LayerFunctions: Retry, Error detection…

Elements of Protocol: Synch pattern, parity,...

Bus Controller

Data Link Layer

ECSS ServicesFunctions: Segmentation,…

Elements of Protocol: Block data length, Address tables,…

1553Functions: Error detection, Delimiting and Synchronisation, …

Elements of Protocol: Message length, Start/end Marker, Status Word,…

ReceiveUser Data

RT XApplication

SendUser Data

Services W, X,Y, Z

Remote Terminal (with ECSS Services)

Data Link Layer

ECSS ServicesFunctions: Segmentation,…

Elements of Protocol: Block data length, Address tables,…




Elements of Protocol: Synch pattern, parity,…

ReceiveUser Data

RT YApplication

Services Y, Z

SendUser Data

Remote Terminal (Legacy)

Data Link Layer




Elements of Protocol: Synch pattern, parity,…

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Draft-D OverviewService Model and CCSDS/SOIS

Data Link

User Applications

Denotes service access point

Net

wor

k M

anag

emen

t

Network Protocol

Transport ProtocolTransferLayer

Plug

and

Pla

y Se

rvic

es

Packet Service

MemoryAccessService

SynchronisationService

DeviceDiscovery

Service

TestServiceSub-

NetworkLayer Data Link Convergence Functions

DeviceEnumeration

Service

ApplicationSupport Layer

TimeAccessService

FileServices

MessageTransferService

Cmd & DataAcquisition

Services

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Draft-D OverviewPhysical and Data Link Layer Harmonisation

The ECSS standard adds specific details for the Physical and Data Link Layers of MIL-STD-1553B

On the Physical layer: More precise definition of the bus cable impedance (using metric units) Selection of the transformer-coupled stub connection Application of bus cable and stub discharge resistances Definition of the connector interface between the terminals and the bus

On the Data Link Layer Rules on usage of mode codes RT to RT messages transfer not allowed 1553 Standard automatic retry not allowed Fixes the response timeout (14 µs to 22 µs without bus repeaters) Provides subaddress usage harmonisation rules and recommendations

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Draft-D OverviewPhysical and Data Link Layer Harmonisation

Retry function included in the 1553 standard It is not often used by space projects for several reasons such

as: In systems used cyclic scheduling (90%), an immediate retry modifies the

cyclic scheduling of the bus unless the retry transfer is systematically included within the frame which has a high bandwidth cost

The error rate on 1553 is very low – experience shows that retry’s are almost always application errors (and the retried message also fails)

It is often a system choice to handle errors and retries within the FDIR function (at application level) or within higher level services protocols

In most applications, the highest proportion of the traffic is periodic acquisition data and the system application is tolerant to one acquisition failure (even 2 or more). Retrying immediately is not necessary.

As a result, the ECSS standard does not use the built-in retry of the 1553 standard retry

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Draft-D OverviewStandard Services and protocols

Time Distribution and Synchronisation distribution of time information

Communication Synchronisation deterministic time multiplexing of

data bus messages Set Data and Get Data

Classical 1553 transfer oriented with additional built-in functions such as segmentation dedicated to direct RT memory access

Data Block Transfer Packet Transfer oriented service

supported by a handshake protocol providing different levels of QoS

Terminal management Rules and standard data structures

in support to the harmonisation of terminal configuration, test and bus management applications

TimeDistribution

and Synchronization

Communications synchronization

TerminalManagement

DataBlock

TransferGet / Set

TimeDistribution

and Synchronization

Communications synchronization

TerminalManagement

DataBlock

TransferGet / Set

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Standard Services and protocolsTime Distribution and Time Synchronisation (1/2)

The On Board Time Master is driving the 1553 Bus controller

Maintains a coherent time data for all users of the service

Remote terminal applications maintain local OBT synchronized through reception of broadcasted messages from OBT Master

The time format is normalized to CCSDS CUC

Time information is distributed at a fixed subaddress (29)

Accuracy is mission dependant (shall be better than 50 µs)

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Standard Services and protocolsTime Distribution and Time Synchronisation (2/2)

Table 1: Time Message data words, CCSDS CUC format Word N° Content 0 ‘0000 0000’ P-field 1 Time, values 231 - 216 s 2 Time, values 215 - 20 s 3 Time, values 2-1 - 2-16 s 4 Time, values 2-17 – 2-24 s ‘0000 0000’

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Standard Services and protocolsCommunication Synchronisation

The standard defines Communication frames which embed all 1553 message sequences within time bounded and synchronized intervals

This supports messages time multiplexing in a deterministic way It allows to control user services latencies

A bus profile can be implemented for a given mission through:

Communication Frames programming in the Bus Controller at initialization time

Management of Communication Frames and real-time data at run-time

Real-time issues are guaranteed through resource reservation within the bus profile (bandwidth pre-allocation)

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Standard Services and protocolsCommunication synchronisation and bus profiling

1553 BC Message

Descriptor # 1

1553 BC Message

Descriptor # 2…

1553 BC Message

Descriptor # N……

…

CFSynchMsg

Pre-allocatedbandwidth, populated

content


content


content

Pre-allocatedbandwidth,

un-populatedcontent


un-populatedcontent


un-populatedcontent

1553 Message

# 1

1553 Message

# 2Spare

Time synchronisation Cycle(1Hz)

CommunicationCycle(8Hz)

Communication Frame #1








Sync Sync Sync Sync Sync Sync Sync Sync

1553 Message

# N

Spare

Delay1553 BC Message

Descriptor # 1

1553 BC Message

Descriptor # 2…

1553 BC Message

Descriptor # N……

…

CFSynchMsg


content


content


content


un-populatedcontent


un-populatedcontent


un-populatedcontent

1553 Message

# 1

1553 Message

# 2Spare












1553 Message

# N

Spare

…

CFSynchMsg


content


content


content


un-populatedcontent


un-populatedcontent


un-populatedcontent

1553 Message

# 1

1553 Message

# 2Spare































1553 Message

# N

Spare

Delay

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Standard Services and protocolsCommunication service and protocols

Two main use cases two services with adapted data transfer protocols:

Data transfer for real-time critical applications (Get/Set) Asymmetrical service provided on Bus controller only and dedicated to

command control of sensors by a central computer Typically sensor acquisition/distribution of unformatted data Segmentation included up to a configurable and limited maximum limit

(few Kbits) Easily mapped to SOIS Memory access service

Data transfer for on-board communications (Data Block Transfer) Symmetrical service provided between users on the Bus Controller and

users on Remote Terminals Asymmetrical protocol due to 1553 Master/slave characteristics Data bloc transmissions, including segmentation, sequence control, flow

control, confirmation, up to a maximum of 4 Kbytes Easily mapped to SOIS Packet service

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Standard Services and protocolsSet Data and Get Data

Classical 1553 data transfer with built-in functions Provided on the BC side only:

Set Data provides data transfer function from BC to one RT Get Data provides data transfer function from one RT to BC

Segmentation A single access to the service allows transmission of more than

32 words (maximum data size is application dependant)

Quality of Service and error detection The protocol requires that accesses are time-bounded

(maximum is one communication frame) The destination user application ensures timely retrieval of data

before it may be overwritten by new data Error report provided to the service user based on the 1553

status words of the transfers in support to user FDIR application

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Standard Services and protocolsExample: Invoked 1553 messages for a Set Data

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Standard Services and protocolsData Block Transfer

Capability to transfer data blocks on request of the sender, with completion by a confirmation

Adapted for RT’s that have the capability to handle, segmentre-assemble and store large data structures

Data transfer protocol control Handshake between sender and receiver Error controls Protocol Reset

Quality of Service Best Effort

No check for correctness of the transferred data Verified Length

Check that the correct number of bytes has been received Check for data bus transmission error

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Data Block TransferFlat and Deep sub-addressing modes

Flat sub-addressing

Different subaddresses are used to transfer different sections of the transmitted data block.

In this mode the maximum block length that can be transmitted is 1024 bytes

The subaddresses to be used are fixed and defined by the standard (11 to 26)

Deep sub-addressing A single subaddress is used to transfer different sections of the

transmitted data block Several subaddresses may be used resulting in several channels In this mode the maximum block length that can be transmitted is

4096 bytes The subaddress usage is determined by the RT design

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Data Block TransferData Transfer control

1. Data word (Distribution Data size) 2. Data word (Distribution Control)

( 4 Bit) (12 Bit) ( 1 Bit) ( 1 Bit) ( 1 Bit) ( 5 Bit) ( 8 Bit)

Reserved 0́000 ́

Number of bytes for the current data block (SIZE)

Error Reset Mode SA Distribution Block Count

(DBC)

Layout of the Distribution Transfer Confirmation (BC to RT, SA 27T)

1. Data word (Distribution Data size) 2. Data word (Distribution Control)

( 4 Bit) (12 Bit) ( 1 Bit) ( 1 Bit) ( 1 Bit) ( 5 Bit) ( 8 Bit)

Reserved 0́000 ́

Number of bytes for the current data block (SIZE)

QOS Reset Mode SA Distribution Block Count

(DBC)

Layout of the Distribution Transfer Descriptor (BC to RT, SA 27R)

Protocol data structures to be exchanged across the data bus

between BC and RT before and after the transfer of user-data

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Data Block TransferPerformance / QoS

Data Distribution timing withBest Effort QoS

Possible delay of one or more

complete Communication Frames

depending on the selected bus

profile and the RT application

timing. Maximum performance is one user

data block every second

Communication Frames

Data Distribution timing with Verified Length QoS

Maximum performance is one user

data block every fourth

Communication Frames

BC sendsDTD

BC sendsdata

Data to RT application and

DTC preparation

BC prepares

nexttransfer

BC sendsDTD

BC sendsdata


DTC preparation

BC prepares

nexttransfer

BC sendsDTD

BC sendsdata


DTC preparation

Indicates a possible time gap

BC sendsDTD

BC sendsdata


DTC preparation

BC prepares

nexttransfer

BC sendsDTD

BC sendsdata


DTC preparation

BC prepares

nexttransfer

BC sendsDTD

BC sendsdata


DTC preparation

Indicates a possible time gap

BC sendsDTD

BC sendsdata


DTC preparation

BC prepares

nexttransfer

BC sendsDTD

BC sendsdata


DTC preparation

BC reads DTC

BC sendsDTD

BC sendsdata


DTC preparation

BC prepares

nexttransfer

BC sendsDTD

BC sendsdata


DTC preparation

BC reads DTC

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Standard Services and protocolsTerminal Management

Provides data link layer harmonisation requirements for RT Health and Monitoring

Capability to receive information concerning health of Remote Terminals across the bus

Alarm Notification Allows a RT to signal events to the FDIR function of the bus management.

In the MIL-STD-1553B standard, this is covered by the status bits

Terminal Flag Bit concerning RT level problems;

Subsystem Flag Bit concerning RT subsystem, including SW for impact on the transferred data;

Terminal Configuration Allows the user on BC to be informed on and (re)configure the Remote Terminals

To be extended in support to the CCSDS/SOIS PnP service

The Data Wrap Around Service Provides support to requirement defined in section 30.7 of MIL-STD-1553B.

It can be used to test BC-to-RT bus connection in support of test services and FDIR

applications

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Summary

Context



Conclusion

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SOIS subnetwork 1553 services prototyping subnetwork services mapping to ECSS Standard

Packet transfer Mapped on Data Block

Transfer

Memory Access mapped on Get Data and Set

Data

Synchronisation mapped on the Time

Distribution and Time Synchronisation services

Test Relies on the Data Wrap-

Around function as defined in the Terminal management

Device Discovery Supported by Get Data and Set

Data using the Terminal management reserved sub addresses in order to exchange devices configuration data.

SOIS Subnetwork Services are all implemented and mapped on the ECSS-E-ST-50-13C defined services and protocols

19/02/2008

Thi

s do

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is t

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of A

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to

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with

out

prio

r w

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reem

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Its

con

tent

sha

ll no

t be

dis

clos

ed.


Conclusion

Using the ECSS-E-50-13 standard draft requirements, a SOIS subnetwork level communication services interface and protocols for 1553 Milbus systems has been defined and implemented

This Standard has completed verification activities and public review

provides feedback on the implementation and performance issues to CCSDS/SOIS and ECSS-E-50 WG

Publication awaited end 2008

Thank you for your attention !

ccsds-sois fall meeting 2008, berlin, germany olivier notebaert – astrium satellites – asg74

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