DDS-XRCE (Extremely Resource Constrained Environments)
2 likes1,478 views
The document outlines the DDS-XRCE (Data Distribution Service for Extremely Resource-Constrained Environments) specifications presented at an OMG meeting in June 2017, emphasizing its agent-based deployment model and interoperability for constrained networks. It details the architecture, message structure, and object model that supports efficient communication in low-bandwidth scenarios while maintaining compatibility with existing DDS systems. Additionally, it discusses security measures, transport requirements, and the potential for merging ongoing submissions from different contributors in the future.
![Example: DATA Message
©2017 Real-Time Innova?ons, Inc.
0 8 16 24 31
+---------------+---------------+---------------+---------------+
| clientKey |
+---------------+---------------+---------------+---------------+
| sessionId | streamId | sequenceNr |
+---------------+---------------+---------------+---------------+
| DATA | flags | submessageLength |
+-------+-------+---------------+---------------+---------------+
| dataWriterResourceId | count |
+-------+-------+---------------+---------------+---------------+
~ <payload – data [0] ~
~ <payload – data [1] ~
~ <payload – data [count -1] ~
+---------------+-------+-------+---------------+---------------+
Payload format
Depends on flags
Serializa?on uses DDS-
XTYPES format](https://image.slidesharecdn.com/ddsxrcedraftspecification-170623094954/85/DDS-XRCE-Extremely-Resource-Constrained-Environments-24-320.jpg)
![Example: DATA with Timestamp Message
©2017 Real-Time Innova?ons, Inc.
0 8 16 24 31
+---------------+---------------+---------------+---------------+
| clientKey |
+---------------+---------------+---------------+---------------+
| sessionId | streamId | sequenceNr |
+---------------+---------------+---------------+---------------+
| DATA | flags | submessageLength |
+-------+-------+---------------+---------------+---------------+
| dataWriterResourceId | count |
+-------+-------+---------------+---------------+---------------+
~ <payload – common timestamp> ~
~ <payload – data [0] ~
~ <payload – data [1] ~
~ <payload – data [count -1] ~
+---------------+-------+-------+---------------+---------------+](https://image.slidesharecdn.com/ddsxrcedraftspecification-170623094954/85/DDS-XRCE-Extremely-Resource-Constrained-Environments-25-320.jpg)
![Example: DATA with Timestamp Message
©2017 Real-Time Innova?ons, Inc.
0 8 16 24 31
+---------------+---------------+---------------+---------------+
| clientKey |
+---------------+---------------+---------------+---------------+
| sessionId | streamId | sequenceNr |
+---------------+---------------+---------------+---------------+
| DATA | flags | submessageLength |
+-------+-------+---------------+---------------+---------------+
| dataWriterResourceId | count |
+-------+-------+---------------+---------------+---------------+
~ <payload – timestamp_base> ~
~ <payload – timestamp_offset[0] ~
~ <payload – data [0] ~
~ <payload – timestamp_offset[1] ~
~ <payload – data [1] ~
~ <payload – timestamp_offset[count -1] ~
~ <payload – data [count -1] ~
+---------------+-------+-------+---------------+---------------+](https://image.slidesharecdn.com/ddsxrcedraftspecification-170623094954/85/DDS-XRCE-Extremely-Resource-Constrained-Environments-26-320.jpg)
DDS-XRCE (Extremely Resource Constrained Environments)
- 1. DDS-XRCE DDS for Extremely Resource Contained Networks Dra< specifica?on presented at OMG Brussels, June 2017 mars/17-06-11 Joint Submission: RTI, TwinOaks, eProsima Contact: Gerardo Pardo-Castellote, Ph.D.
- 3. Outline • Background • High Level Overview • Key Concepts and Features • An example • Status ©2017 Real-Time Innova?ons, Inc.
- 4. Backgrond • Two ini?al submissions in Chicago, 9/2016 – Joint Submission RTI, TwinOaks, eProsima – Submission by PrismTech • Presenta?ons in Reston focused on differences – Goal was explore joining submissions • Joining Submission stalled – Technical details and documents a moving target ©2017 Real-Time Innova?ons, Inc.
- 11. XRCE Agent Object Model class DDS-Mapping DdsXrce:: DomainParticipant DdsXrce::Publisher DdsXrce::Subscriber DdsXrce:: DataWriter DdsXrce::DataReader DdsXrce::Topic DDS::DomainParticipantFactory DDS::DomainParticipant DDS::Publisher DDS::Subscriber DDS::TopicDescription DDS::Topic DDS::ContentFilteredTopic DDS::DataReader DDS::DataWriter «value» DdsXrce::Qos «value» DdsXrce:: QosProfile Qos + DataReaderQos + DataWriterQos + DomainParticipantQos + PublisherQos + SubscriberQos + TopicQos (from DDS) DdsXrce::Application «use» «use» «use» «use» «use» «use» «use» «use» 0..* «use» «use» «use»
- 12. XRCE Object Model highlights • Uses UML to model Agent behavior • XRCE Objects modeled as “resources” – Addressable by their “name” – CRUD opera?ons: • Create/Read/Update(Write)/Delete ©2017 Real-Time Innova?ons, Inc.
- 13. ©2017 Real-Time Innova?ons, Inc. class Application DdsXrce::Application + create_participant(): ReturnStatus + update_participant(): ReturnStatus + delete_participant(): ReturnStatus + create_waitset(): ReturnStatus + update_waitset(): ReturnStatus + delete_waitset(): ReturnStatus DdsXrce::DomainParticipant DDS::DomainParticipant DDS:: DomainParticipantFactory DdsXrce::AccessController + check_permissions(): ReturnStatus DdsXrce::WaitSet «value» DdsXrce::Type «value» DdsXrce:: QosProfile DdsXrce::QosLibrary «use» «use» «use» «use» «use» 0..* «use»
- 14. ©2017 Real-Time Innova?ons, Inc. class Participant DdsXrce::Application DdsXrce::DomainParticipant + register_type(): ReturnStatus + unregister_type(): ReturnStatus + create_topic(): ReturnStatus + update_topic(): ReturnStatus + delete_topic(): ReturnStatus + create_publisher(): ReturnStatus + update_publisher(): ReturnStatus + delete_publisher(): ReturnStatus + create_subscriber(): ReturnStatus + update_subscriber(): ReturnStatus + delete_subscriber(): ReturnStatus + get_topics(): ReturnStatus + get_publishers(): ReturnStatus + get_subscribers(): ReturnStatus DDS::DomainParticipant DDS:: DomainParticipantFactory DdsXrce::AccessController + check_permissions(): ReturnStatus DdsXrce::Topic DdsXrce:: Publisher DdsXrce:: Subscriber «value» DdsXrce::Type DdsXrce:: RegisteredType «interface» DdsXrce::Entity + name: string «use» «use» 0..* «use» «use» «use» «use» «use» typeName registeredTypeName
- 15. ©2017 Real-Time Innova?ons, Inc. class DataWriter DdsXrce::DataWriter + create_instance(): ReturnStatus + update_instance(): ReturnStatus + delete_instance(): ReturnStatus + write(): ReturnStatus DDS::DataWriter DdsXrce:: Publisher DdsXrce::Topic DDS::Publisher TopicDescription DDS::Topic «interface» DdsXrce::Entity + name: string «use» «use» «use»
- 16. ©2017 Real-Time Innova?ons, Inc. class DataReader DdsXrce:: Subscriber DdsXrce::DataReader + get(): ReturnStatus DdsXrce::Topic - registeredTypeName: string - topicName: string DDS:: TopicDescription DDS::Topic DDS::DataReader DDS::Subscriber «interface» DdsXrce::Entity + name: string «use» «use» «use» «use»
- 17. ©2017 Real-Time Innova?ons, Inc. class AccessController DdsXrce::AccessController + check_permissions(): ReturnStatus «singleton» DdsXrce::Root DdsXrce::Application DdsXrce:: Publisher DdsXrce:: Subscriber DdsXrce:: DomainParticipant DdsXrce::Client - clientAPIKey: string 0..* «use» «use» «use» «use» 0..* 0..* 1 0..*
- 18. Resource Names, Representa?on, and ID • Each resource has: – A name (addresses it within the Agent) and Context • Example the type “ShapeType” – A representa?on. Describes the resource • Declara?ve way to configure Agent resources • Not expected to go on the wire in most cases • Example: <struct name="ShapeStruct"> <member name="color" type="string"/> <member name="x" type="int32"/> <member name="y" type="int32"/> <member name="shapesize" type="int32"/> </struct> – An ID. Provides (integer) shortcurt for Client to reference XRCE object/resource • Note: Mul?ple representa?ons possible – Currently leverages exis?ng XML formats • As defined in various exis?ng DDS specifica?ons – JSON and Binary are possible alterna?ves, if required ©2017 Real-Time Innova?ons, Inc.
- 19. Qos Representa?on • Expect pre-defined profiles in Agent – Just send QosPofile name • Allow sending Qos using XML (or JSON format) – JSON could be added • Can configure complete set of DDS Qos policies ©2017 Real-Time Innova?ons, Inc.
- 21. Message Header + Submessages ©2017 Real-Time Innova?ons, Inc. XRCE Header Submessage Submessage Submessage 0 8 16 24 31 +---------------+---------------+---------------+---------------+ | clientKey | +---------------+---------------+---------------+---------------+ | sessionId | streamId | sequenceNr | +---------------+-------+-------+---------------+---------------+ 0 4 8 16 24 31 +---------------+---------------+---------------+---------------+ | smId | flags | resourceType | submessageLength | +-------+-------+---------------+---------------+---------------+ | resourceId | count | +-------+-------+---------------+---------------+---------------+ ~ <payload – depends on smId & resourceType > ~ +-------+-------+---------------+---------------+---------------+ XRCE Header Submessage
- 22. 12 kind of Sub Messages ©2017 Real-Time Innova?ons, Inc. class Submessages DdsXrce::Submessage DdsXrce:: Submessage:: CREATE DdsXrce:: Submessage:: GET_INFO DdsXrce:: Submessage:: DELETE DdsXrce:: Submessage:: INFO DdsXrce:: Submessage:: STATUS DdsXrce:: Submessage:: ACKNACK DdsXrce:: Submessage:: HEARTBEAT DdsXrce::Submessage:: SubmessageHeader - submessageId: byte - flags: byte - submessageLength: short DdsXrce:: Submessage:: DATA DdsXrce:: Submessage:: FRAGMENT DdsXrce:: Submessage:: READ_DATA DdsXrce:: Submessage:: WRITE_DATA DdsXrce:: Submessage:: RESET 1
- 23. Submessage kinds ©2017 Real-Time Innova?ons, Inc. SubmessageId Value Note CREATE 1 Client to Agent. Specifies resource Name or Representation GET_INFO 2 Client to Agent. DELETE 3 Client to Agent. STATUS 4 Response to CREATE, UPDATE or DELETE. INFO 5 Response to a GET_INFO. Contains information about an Xrce: Object. WRITE_DATA 6 Client to Agent. Used to write data using a Xrce::DataWriter. READ_DATA 7 Client to Agent. Used to read data using a Xrce::DataReader. DATA 8 Agent to Client in response to a READ_DATA ACKNACK 9 Bi-directional. HEARTBEAT 10 Bi-directional. RESET 11 Agent to Client. FRAGMENT 12 Bi-directional
- 24. Example: DATA Message ©2017 Real-Time Innova?ons, Inc. 0 8 16 24 31 +---------------+---------------+---------------+---------------+ | clientKey | +---------------+---------------+---------------+---------------+ | sessionId | streamId | sequenceNr | +---------------+---------------+---------------+---------------+ | DATA | flags | submessageLength | +-------+-------+---------------+---------------+---------------+ | dataWriterResourceId | count | +-------+-------+---------------+---------------+---------------+ ~ <payload – data [0] ~ ~ <payload – data [1] ~ ~ <payload – data [count -1] ~ +---------------+-------+-------+---------------+---------------+ Payload format Depends on flags Serializa?on uses DDS- XTYPES format
- 25. Example: DATA with Timestamp Message ©2017 Real-Time Innova?ons, Inc. 0 8 16 24 31 +---------------+---------------+---------------+---------------+ | clientKey | +---------------+---------------+---------------+---------------+ | sessionId | streamId | sequenceNr | +---------------+---------------+---------------+---------------+ | DATA | flags | submessageLength | +-------+-------+---------------+---------------+---------------+ | dataWriterResourceId | count | +-------+-------+---------------+---------------+---------------+ ~ <payload – common timestamp> ~ ~ <payload – data [0] ~ ~ <payload – data [1] ~ ~ <payload – data [count -1] ~ +---------------+-------+-------+---------------+---------------+
- 26. Example: DATA with Timestamp Message ©2017 Real-Time Innova?ons, Inc. 0 8 16 24 31 +---------------+---------------+---------------+---------------+ | clientKey | +---------------+---------------+---------------+---------------+ | sessionId | streamId | sequenceNr | +---------------+---------------+---------------+---------------+ | DATA | flags | submessageLength | +-------+-------+---------------+---------------+---------------+ | dataWriterResourceId | count | +-------+-------+---------------+---------------+---------------+ ~ <payload – timestamp_base> ~ ~ <payload – timestamp_offset[0] ~ ~ <payload – data [0] ~ ~ <payload – timestamp_offset[1] ~ ~ <payload – data [1] ~ ~ <payload – timestamp_offset[count -1] ~ ~ <payload – data [count -1] ~ +---------------+-------+-------+---------------+---------------+
- 28. ©2017 Real-Time Innova?ons, Inc. sd Client Agent XRCE AgentXRCE Client RESOURCE_STATUS(DataWriter) RESOURCE_STATUS(Session) ASSERT_RESOURCE(Session) WRITE_DATA(DataWriter) WRITE_DATA(DataWriter) ASSERT_RESOURCE(DataWriter) DELETE_RESOURCE(DataWriter, Session) WRITE_DATA(DataWriter) ASSERT_RESOURCE iden?fies (preconfigured) resource by means its Name and retrieves resourceId Note: Using CREATE instead of ASSERT_RESOURCE can create the resource from its representa?on
- 29. ©2017 Real-Time Innova?ons, Inc. sd Minimal Publisher XRCE Client XRCE Agent DELETE_RESOURCE() WRITE_DATA() ASSERT_RESOURCE(Session) WRITE_DATA() RESOURCE_STATUS() WRITE_DATA() The resourceId for specific objects (e.g. a DataWriter) can also be pre-configured. This saves having to ASSERT it.
- 30. ©2017 Real-Time Innova?ons, Inc. sd Minimal Subscriber XRCE Client XRCE Agent DATA() DATA() ASSERT_RESOURCE(Session) DELETE_RESOURCE() DATA() CONFIG_READ()
- 32. Transport requirements • Packet-oriented or connec?on oriented • It does not need to provide reliability – Messages may be dropped • It does not need to provide ordering – Messages may arrive out of order • It does not need to provide no?fica?on of dropped messages • Must support transport-level security (e.g. TLS or DTLS) ©2017 Real-Time Innova?ons, Inc.
- 33. Reliability • Reliability per stream, mul?ple (256) streams – Buil?n streams 0-5 are present on every session – Even-numbered streamIds are best-efforts. – Reliable streams use HB/ ACKNACK protocol • Similar to DDS/RTPS • Mul?ple Writers can share same stream as configured by client • Mul?ple Readers can also share the same stream ©2017 Real-Time Innova?ons, Inc.
- 35. Security approach • Assumes transport-level security is in place • Message Header includes (4-Byte) secret ClientKey • Agent uses ClientKey to determine client permissions and Iden?ty – Leverages DDS-Security iden?ty and permissions documents – Proxy DDS DomainPar?cipant are exclusive to a single Client ©2017 Real-Time Innova?ons, Inc.
- 37. Other points • Reuses CDR (XTYPES) serializa?on • Serialized Resource format described in IDL • Data serialized using CDR. Data can be relayed serialized • Supports fragmenta?on • Supports mul?ple concurrent sessions • Full “DDS reachability” – Any Qos available in DDS – Any data type available in DDS-XTYPES ©2017 Real-Time Innova?ons, Inc.
- 39. RFP mandatory requirements ©2017 Real-Time Innova?ons, Inc. RFP requirement Submission DDS-XRCE protocol between a Client and an Agent YES DDS-XRCE clients to be perceived by DDS Par?cipants as at least minimum profile DDS Par?cipants YES, the can full DDS Par?cipants, not limited to minimum profile DDS-XRCE protocol overhead, when sending or receiving user data, shall not exceed 24 bytes per packet YES, less than 20 bytes Address clients opera?ng with sleep/wakeup periods YES, state maintained by Agent, “stateless” messages DDS-XRCE protocol for the UDP/IP transport. DDS-XRCE protocol for the TCP/IP transport YES, protocol is independent from transport.