QoS Reference Guide - (DDS) Community RTI Connext Users
Contents
1. You can use this QoS policy to ensure applications don t receive or act on data commands or messages that are too old and have expired Liveliness Configures the mechanism that allows DataReaders to detect when matching DataWriters become disconnected or dead In a connectionless communications model the only way a DataReader can know if it is able to receive data from a DataWriter is if it actually receives a message from the DataWriter This message can either be real data sent by user code or a message that indicates that the DataWriter is indeed alive and that all elements of the communications link between the DataWriter and DataReader applications is working network cards switches routers etc By using the Liveliness QoS the user configures how the DataWriter application maintains liveliness with the DataReader application and how fast the DataReader application is able to detect when the DataWriter is unable to send data to the DataReader because the sending application has died or perhaps the link between the two applications has broken You can use this to ensure that important messages can be received if they are sent For example if a command message like Emergency Stop is never sent unless the situation is encountered Liveliness can be used to periodically send a message to test the end to end connectivity of the system so that when an Emergency Stop message is sent it will likely be received by all subscrib2. 2012 Real Time Innovations Inc RTI Connext Comprehensive Summary of QoS Policies QoS Policy Description Chng RxO Entities Ext AsynchronousPublisher Configures mechanism that sends user data in an external middleware thread BC P Y Availability Configures Collaborative DataWriters and Durable Subscriptions A R Batch Configures mechanism for collecting multiple data samples to be sent in a single network packet BE WwW Y Database Configures threads amp resource limits that control internal RTI Connext database BC D Y DataReaderProtocol SEEN ENA Configures DDS on the wire protocol RTPS along with WireProtocol QoS for Reliable Topics BC R W DataWriterProtocol g p g Q k DataReaderResourceLimits Confi i i i BC R W Y Dataren our elini igures how Readers Writers allocate and use physical memory for internal resources Deadline Maximum time between data samples A Y T R W See Controls how RTI deals with data from multiple DataWriters f ic i i enreronader f t i p riters for the same topic by reception timestamp BE Y TRW a a or by source timestamp Discovery DiscoveryConfig Configures how automatically discover and connect with new remote DomainParticipants BC D Y DomainParticipantResourceLi fs alee Configures how DomainParticipants allocate and use p
3. By default the UDPv4 and on platforms that support it shared memory transports are enabled Most applications will not need to change this default You may want to disable the shared memory transport if you do not want applications to use shared memory to communicate when running on the same node This may be the case in a lab environment for example where some users kill their applications ungracefully leaving shared memory regions orphaned and unable to be cleaned up by other users of the same machines Be aware that the availability of the shared memory transport should be set in the same way for all applications running on the same machine in the same domain Otherwise discovery will not complete See also Property Used to install external that is not built in transports 42 TransportMulticast Specifies the multicast address on which a DataReader is to receive its data By default DataWriters will send individually addressed packets to each DataReader that subscribes to the topic of the DataWriter this is known as unicast delivery One copy of the data is sent for each DataReader This configuration is the simplest to configure and the easiest to manage However the network bandwidth used by a DataWriter increases linearly with the number of DataReaders Multicast addressing on UDP IP transports allows a DataWriter to send a single network packet that will be received by many DataReaders Thus the network bandwidth usage will be nea
4. Specifies strength used to arbitrate among multiple Writers of same instance A WwW Partition Adds string identifiers for matching DataWriters and DataReaders for the same Topic A P S Presentation Controls how Connext presents data received by an application to the DataReaders of the data BE Y P S Profile Configures how DomainParticipantFactory loads XML documents containing QoS profiles BC F Property Specifies name value pairs used to configure parameters not exposed via formal QoS policies A D R W PublishMode Specifies whether data samples will be sent in the application thread or a middleware thread BC WwW ReaderDataLifecycle Controls how a DataReader manages the lifecycle of the data that it has received A R ReceiverPool Configures threads used to receive and deliver data from network transports for example UDP BC D Y Reliability Indicates whether samples lost by the network should be repaired by the middleware BE Y T R W ResourceLimits Limits amount of memory allocated for cached data BE T R W SystemResourceLimits Configures process level resources independent of particular entities BC F Y TimeBasedFilter Sets minimum time period before new data for an instance is provided to a DataReader A R TransportBuiltin Specifies which built in transports are used BC D Y Sets the multicast address on which Reader will receive data port numbers transports on which to receive TransportMulticast p p BC R Y multicast data Specifies the automatic ma
5. and debug your system It also assigns a role name which specifies the Durable Subscription to which the DataReader belongs Often used with Availability if using Durable Subscriptions 2012 Real Time Innovations Inc 18 19 20 21 22 Event Configures the internal thread in a DomainParticipant that handles timed events In a DomainParticipant the Event Thread is dedicated to handling all timed events including checking for timeouts and deadlines and executing internal and user defined timeout or exception handling routines callbacks An example of a timed event is the reliable heartbeat rate If this rate is very high you should use a higher than normal event thread priority This QoS policy allows you to configure thread properties such as priority level and stack size You can also configure the maximum number of events that can be posted to the event thread By default a DomainParticipant will dynamically allocate memory as needed for events posted to the event thread However by setting a maximum value or setting the initial and maximum value to be the same you can either bind the amount of memory allocated for the event thread or prevent a DomainParticipant from dynamically allocating memory for the event thread after initialization ExclusiveArea Configures multi thread concurrency and deadlock prevention capabilities An exclusive area EA is an abstraction of a multi thread safe region Each entity is pro
6. for matching DataWriters and DataReaders for the same Topic Specified for Publishers and Subscribers the Partition QoS policy can be used to add additional identifiers in the form of strings that Connext will used to match DataWriters and DataReaders Normally DataWriters are connected matched to DataReaders of the same Topic assuming that their QoS settings are mutually compatible However by using the Partition QoS policy additional criteria is used to decide if a DataWriter s data is allowed to be sent to a DataReader Referred to as partitions one or more strings can be added to the DataWriter s Publisher or DataReader s Subscriber parent When the Partition QoS policy is used then a DataWriter is only connected matched to a DataReader for the same Topic only if their Publisher and Subscribers have a common partition intersecting partitions Direct comparison of partition strings of the Publisher and Subscriber is the nominal way to determine if there is a common partition However one can also use strings that contain wildcards actually regular expressions as defined by the POSIX fnmatch API as partitions In that case as long as one of the wildcard partitions matches one of the concrete partition strings on the other side then the DataWriter and DataReader are connected 2012 Real Time Innovations Inc 30 31 32 The set of partitions of a Publisher or Subscriber can be dynamically changed This can be used to
7. quickly control which DataWriters and which DataReaders are allowed to connect This facility is useful for creating temporary separation groups among entities that would otherwise be connected to and exchange data each other Therefore if sometimes you want an application or individual DataWriter or DataReader to be connected to another application or DataReader or DataWriter respectively and at other times you don t then you can use the Partition QoS policy to dynamically configure the connection topology without stopping starting or destroying re creating applications or Entities Presentation Controls how Connext presents data received by an application to the DataReaders of the data Usually DataReaders receive data in the order it was sent by a DataWriter When using the Reliability QoS policy samples which arrive out of order will be buffered until all previous samples arrive Once in order data is presented to the DataReader immediately Sometimes you may want a set of data for the same topic to be presented to the receiving DataReader only after ALL of the elements of the set have been received but not before You may also want the data to be presented in a different order than it was received Specifically for keyed data you may want Connext to present the data grouped by instance same key value Thus this QoS policy allows you to specify different scopes of presentation within a topic across instances of a topic and across
8. that the data being sent has a different priority than other data Provides a priority value to the underlying transport protocol for those that can use it Some transport protocols have a concept of user settable priorities that may be used by operating system network stacks and switching hardware in between the publisher and the subscriber For such transports and on supported OSs RTI Connext will pass this value to the transport for its use For other transports and other OSs the middleware will ignore this value For more information about whether RTI Connext can preserve this value for your transports and OSs please consult the Platform Notes 45 TransportSelection Selects which transports a DataWriter or DataReader may use to send or receive its data This QoS policy is used in the advanced case where multiple transports have been installed and only a subset of them are to be used with a particular DataReader or DataWriter For example suppose that transports for UDP IP shared memory Infiniband and VME transports are available and a DataReader should only receive data over Infiniband See also e TransportBuiltin Identifies the available built in transports e Property Used to install external that is not built in transports 46 TransportUnicast Specifies a subset of transports and a port number that can be used by an Entity to receive data RTI Connext may send data to a variety of Entities not just DataReaders Fo
9. with lower OwnershipStrength will be dropped by Connext when received at the subscribing application An arbitrary but deterministic method is used to select a single DataWriter among multiple DataWriters with the same highest OwnershipStrength so all DataReaders will receive the data from the same DataWriter even when the OwnershipStrength is the same value When the DataWriter with the highest Ownership strength loses its liveliness as controlled by the Liveliness QoS policy or misses a deadline as controlled by the Deadline QoS policy or whose application quits dies or otherwise disconnects Connext will change ownership of the Topic instance to the DataWriter with the highest OwnershipStrength from the remaining DataWriters This QoS policy can help you build systems that have redundant elements to safeguard against component or application failures When systems have active and hot standby components the Ownership QoS policy can be used to ensure that data from standby applications are only delivered in the case of the failure of the primary Ownership QoS policy can also be used to create data channels or Topics designed to be taken over by external applications for testing or maintenance Often used with e Liveliness to detect when DataWriters are dead and change ownership e Deadline to detect when DataWriters have not sent data in time so that lower strength data is accepted Partition Adds additional string identifiers
10. 6 64 KB is a good choice as this is the largest packet that can be sent received via UDP Note that RTI Connext does not currently share threads among the different transport plugins Instead each transport plugin is automatically allocated a single thread by default depending on the transport plugin it may request a separate thread for each receive port Often used with e Property configures the maximum message size of individual transports e TransportUnicast TransportMulticast RTI uses a separate receive thread per port per transport plug in by default To force RTI Connext to use a separate thread to process the data for a DataReader set a unique port in the DataReader s Transport Unicast or Transport Multicast QoS policy 10 2012 Real Time Innovations Inc 36 Reliability Enables reliability protocol for a DataWriter DataReader connection This QoS policy turns on the RTPS reliability protocol between those DataWriters and DataReaders that set this QoS policy to the RELIABLE value When the reliability protocol is used Connext will attempt to repair samples that were not successfully received by reliable DataReaders By itself the Reliability policy does not set the level of reliability for a connection between a DataWriter and DataReader Instead the level of reliability is controlled in conjunction with other policies such as History and ResourceLimits to determine which data remains relevant and therefore el
11. ABILITY or TRANSIENT_DURABILITY an external service RTI Persistence Service is used to store and possibly forward the data sent by the DataWriter to DataReaders that are created after the data was initially sent This QoS policy configures certain parameters of RTI Persistence Service when it operates on behalf of the DataWriter such as how much data to store Often used with Durability to specify the level of durability for the data EntityFactory Controls an Entity s behavior as a factory for other entities such as whether child entities are created in the enabled state This QoS policy is useful to synchronize the initialization of Entities For example when a DataReader is created in an enabled state its existence is immediately propagated for discovery and the DataReader s listener is called as soon as data is received The initialization process for an application may extend beyond the creation of the DataReader so you may not want for the DataReader to start to receive or process any data until the initialization process is complete By creating readers in a disabled state you can make sure that no data is received until the rest of the application initialization is complete EntityName Assigns a name to a DomainParticipant amp associates a DomainParticipant with a Durable Subscription This QoS policy assigns a name to a DomainParticipant this name will be visible during discovery and in RTI tools to help you visualize
12. You can also use this QoS policy to select a Flow Controller to shape the flow of data onto the network Shaping a data flow usually means limiting the maximum data rates that Connext will use to send data for a DataWriter The flow controller will buffer data sent by the DataWriter faster than the maximum rate configured for the Flow Controller and then only send the excess data when the send rate drops below the maximum rate The Asynchronous publish mode must also be used to send large data with RELIABLE reliability Large data is any data that exceeds the maximum message packet size that a transport plugin is configured to send between 9 and 64 KB in the case of UDP transports depending on the configuration Note that a single thread will be used to send data for all of the asynchronous DataWriter s of a Publisher If you want to have different threads to send data asynchronously you must use multiple Publishers Often used with e LatencyBudget controls the scheduling of asynchronously published data onto the network across DataWriters e Property configures maximum size of available transport plug ins e AsynchronousPublisher lower level settings pertaining to asynchronous publication like thread priority and options See also Flow Controllers must be configured via the API see the User s Manual ReaderDataLifecycle Controls how a DataReader manages the lifecycle of the data that it has received When a Da
13. al memory holding data samples can be provided to user code as well as others DataWriters must allocate internal structures to handle the simultaneously blocking of threads trying to call write on the same DataWriter for the storage used by batched DataWriters and for filters for content based filtering DataReaders Most of these internal structures start at an initial size and by default will grow as needed by dynamically allocating additional memory You may set fixed maximum sizes for these internal structures if you want to bind the amount of memory that can be used by a DataReader DataWriter Setting the initial size to the maximum size will prevent RTI Connext from dynamically allocating any memory after the DataReader DataWriter is created Deadline For DataReaders specifies the maximum expected elapsed time between arriving data samples For DataWriters specifies a commitment to publish samples with no greater than this elapsed time between them Can be used during system integration to ensure that applications have been coded to meet design specifications Can be used at run time to detect when systems are performing outside of design specifications Receiving applications can take appropriate actions to prevent total system failure when data is not received in time For topics on which data is not expected to be periodic the deadline period should be set to an infinite value Loss of Deadline results in loss of ownership for topic
14. al middleware thread Must be used to send large data reliably Large means data that cannot be sent as a single packet by a transport For example to send data larger than 63K reliably using UDP IP you must configure Connext to send the data using asynchronous publishers Can reduce the amount of time spent in the user thread to send data For small samples can reduce bandwidth consumption Using an asynchronous publisher provides aggregation of samples collecting many RTPS data samples into 1 network packet since samples written for the same topic to the same destination are coalesced within the same UDP packet which reduces bandwidth For bandwidth reduction see also Batch QoS However for aggregation the preferred mechanism is Batch Often used with e PublishMode activates asynchronous publishing a prerequisite for the use of this policy e LatencyBudget controls the scheduling of asynchronously published data onto the network across Data Writers 2 Availability Configures Collaborative DataWriters and Durable Subscriptions For a Collaborative DataWriter specifies the group of DataWriters expected to collaboratively provide data and the timeouts that control when to allow data to be available that may skip samples For a Durable Subscription configures a set of Durable Subscriptions for a DataWriter Supported in release 4 5e and 4 6a and higher 3 Batch Configures mechanism for collecting multiple user data samp
15. different Topics of a Publisher although this last option is not currently supported by RTI It also controls whether or not a set of changes within the scope is delivered at the same time or can be delivered as soon as each element is received See also DestinationOrder also impacts the order in which samples will be delivered by the middleware to the application Profile Configures how XML documents containing QoS profiles are loaded by the DomainParticipantFactory QoS values for Entities can be configured in QoS profiles defined in XML documents The XML documents that define QoS profiles can be passed to RTI Connext as a string in XML format or loaded through XML files found on a file system The Profile QoS policy for the DomainParticipantFactory configures RTI Connext to load XML documents via 3 independent mechanisms that may be used together or individually disabled e Environment variable the value of the environment variable NDDS_QOS_PROFILES can be used to set the locations of files on the file system that contain XML documents to be loaded automatically by Connext You can also set a XML formatted string as a value for the environment variable You can disable the use of the environment variable using the Profile QoS policy e Default XML files there are default locations where Connext will look for XML files to load QoS profiles These include the current working directory from where an application is started and a file in the di
16. eaders You must use KEEP_ALL History for both the DataWriter and DataReader if you want strict reliability the DataReader must receive all of the data sent by the DataWriter Using KEEP_LAST on either side Connext will only guarantee the reliability of the last N depth values sent Often used with e Reliability using the KEEP_LAST kind for History depth the level of reliability can be tuned e Durability for the DataWriter side to specify how much data need to be stored and sent to new DataReaders who request previously published data using the non VOLATILE Durability settings See also ResourceLimits LatencyBudget Suggests how much time is allowed to deliver data This is an optional QoS its implementation and usage may be determined by the implementer RTI uses this QoS policy to help schedule data to be sent by an asynchronous thread with a Flow Controller Data with low latency requirements can be sent ahead of data that is not latency sensitive when using this QoS policy and the asynchronous publishing mode for a DataWriter The default value is 0 which implies you want to send with minimum latency If using this QoS policy then all DataWriters whose data is sent by the same Flow Controller must set the value for this QoS policy accordingly The data of any DataWriter that uses the default value for this QoS policy will always be sent ahead of DataWriters with non zero values for this QoS policy Only used with e Publi
17. ered strictly reliable For strict reliability use the KEEP_ALL setting for the History QoS policy for both the DataWriter and DataReader along with the RELIABLE setting for the Reliability QoS policy RELIABLE DataWriters may send data to both BEST_EFFORT and RELIABLE DataReaders but RELIABLE DataReaders can only receive data from RELIABLE DataWriters The RTPS reliability protocol is highly configurable using the DataWriterProtocol and DataReaderProtocol QoS policy Most users will need to configure the reliability protocol to meet their real time requirements since the default configuration is not designed for speedy packet loss detection and repair In the examples directory of the RTI Connext installation you should find an example QoS configuration for the reliability protocol that is better suited for many applications To maintain reliability in the face of component or system failures you can use RTI Persistence Service to store sent data on other nodes or even to disk elsewhere on the network using the Durability and DurabilityService QoS policies Often used with e History governs how many previously written samples remain relevant set history kind to KEEP_ALL for TCP like reliability over connectionless transports like UDP e _Lifespan governs how long previously written samples remain relevant data with an expired lifespan will not be repaired even if lost e ResourceLimits governs the total sizes of DataWrite
18. ers You can use it at run time to detect when systems are performing outside of design specifications Receiving applications can take appropriate actions in response to disconnected DataWriters Logging Configures the logging feature Allows users to configure various aspects associated with logging via XML profile files verbosity category print format and output file MultiChannel Configures DataWriter to send data using different multicast groups addresses based on data value Data published by a DataWriter can be divided into different channels within the same topic This is useful when the total volume is data is large perhaps even larger than the capacity of a single network link and the number of DataReaders is large but each DataReader is interested in only a subset of the available data A channel is defined by a filter expression and a set of multicast addresses groups When data is sent it is passed through the filter expressions for all defined channels to see if it will be sent on a particular channel The filter expressions are applied on the value of the data contents of the data structure It is possible for the same data value to be sent on multiple channels When sent on a channel Connext will send the data on all of the multicast addresses defined for the channel A DataWriter using the MultiChannel QoS policy will ignore the DataReader s Transport Unicast and Transport Multicast QoS settings It wi
19. etween applications These QoS policies control configurable portions of the protocol including configuration of the reliable data delivery mechanism of the protocol on a per DataWriter DataReader basis These parameters control timing and timeouts and give you the ability to tradeoff between speed of data loss detection and repair versus the network and CPU bandwidth used to maintain reliability It is important to tune the reliability protocol on a per DataWriter and DataReader basis to meet the requirements of the end user application so that data can be sent between DataWriters and DataReaders in an efficient and optimal manner in the presence of data loss You can also use these QoS policies to control how Connext responds to slow reliable DataReaders or ones that disconnect or are otherwise lost See the Reliability QoS policy for more on configuring per DataReader DataWriter reliability The History and ResourceLimits QoS also play an important role in the reliable protocol 2012 Real Time Innovations Inc 7 8 DataReaderResourceLimits DataWriterResourceLimits Configures how DataReaders DataWriters allocate and use 10 11 physical memory for internal resources DataReaders must allocate internal structures to handle the maximum number of DataWriters that may connect to it whether or not a DataReader handles data fragmentation and how many data fragments that it may handle how many simultaneous outstanding loans of intern
20. hysical memory for internal resources BC D Y Durability Specifies if Connext will store and deliver previously published data to new late joining Readers BE Y T R W DurabilityService Configures external Persistence Service for Writers with PERSISTENT or TRANSIENT Durability BE T W EntityFactory Controls Entity behavior as a factory for other entities i e if child entities are created enabled A F D P S EntityName Assigns a name to a DomainParticipant pairs DomainParticipant with a Durable Subscription BE D R W Y Event Configures the internal thread in a DomainParticipant that handles timed events BC D Y ExclusiveArea Configures multi thread concurrency and deadlock prevention capabilities BC P S Y History Controls how much data to store and how stored data is managed for the DataWriter Reader BE T R W LatencyBudget Suggests to the middleware how much time is allowed to deliver data A Y T R W Lifespan Specifies how long Connext considers data sent by a user application to be valid A T W Liveliness Controls mechanism that allows Readers to detect when matching Writers become disconnected dead BE Y T R W Loggin Configures the Logging feature A F Y MultiChannel Configures DataWriter to send data using different multicast groups addresses based on data value BC WwW Y Specifies if a DataReader can receive new samples for an inst i i Gunes p p n instance of data from multiple DataWriters at the BE Y TRW wnersnip same time OwnershipStrength
21. igible for repair For example as a tradeoff for less memory CPU and network usage you can choose a reduced level of reliability where only the last N values are guaranteed to be delivered reliably to DataReaders N is configurable With the reduced level of reliability there are no guarantees that data sent before the last N are received only the last N data packets are monitored and repaired if necessary A connection between a DataWriter and DataReader may be configured for BEST_EFFORT Reliability which means Connext will not use any resources to monitor or guarantee that the data sent by a DataWriter is received by a DataReader For some use cases such as the periodic update of sensor values to a GUI displaying values to a person best effort delivery is often good enough It is the fastest most efficient and least resource intensive CPU and network bandwidth method of getting the newest latest value for a topic from DataWriters to DataReaders However there is no guarantee that the data sent will be received It may be lost due to a variety of factors including data loss by the physical transport such as wireless RF or even Ethernet For some data streams topics you need to be assured that all data from the DataWriter is received reliably by the DataReaders Connext will ensure data was received and repair any lost data by resending a copy as many times as needed until the DataReader receives it This level of reliability is consid
22. les to be sent in a single network packet This allows you to take advantage of the efficiency of sending larger packets and thus increase effective throughput Can dramatically increase the effective throughput for small data packets Usually throughput for small packets data lt 2048 bytes is limited by CPU capacity not by network bandwidth Batching many smaller data packets so they are sent in 1 large packet increases network utilization and thus throughput in terms of user data packets per second For Reliable topics batching reduces the Reliable RTPS traffic because the Reliable entity is the batch not the sample 4 Database Configures threads and resource limits that control the internal RTI Connext database Essentially a list of lists RTI uses an internal database to store information about entities created locally as well as remote entities of other participants found during the discovery process This QoS configures how RTI manages its database including how often it cleans up priority of the database thread and limits on resources that may be allocated by the database You may be interested in modifying the shutdown_timeout and shutdown_cleanup_period parameters to decrease the time it takes to delete a DomainParticipant when your application is shutting down 5 6 DataReaderProtocol DataWriterProtocol Configures DDS on the wire protocol RTPS Connext uses a standard protocol for packet user and meta data exchange b
23. ll only send the data on the multicast addresses set for its channels DataReaders are expected to subscribe to Content Filtered Topics and will automatically subscribe to data using the configured multicast addresses of a multi channel DataWriter for the channels whose filter intersects the Content Filtered Topic of the DataReader Usually the data of different instances within a topic are grouped together into different channels Since there are usually more objects than multicast addresses that can be practically used a single multicast address assigned to a single channel will usually carry the data for more than one instance So using multi channel DataWriters will greatly reduce but probably not eliminate the undesired delivery and discarding of unwanted data by the subscribing machine Users must analyze the data usage across all applications machines in their system and map out the data topology to create an optimal mapping channel filters of objects instances independent substreams to minimize network bandwidth usage as well as the CPU usage for dropping unwanted data 2012 Real Time Innovations Inc Besides using Content Filtered Topics to configure the substream of data desired there is no additional configuration that is needed for DataReaders See also ContentFilteredTopics in the User s Manual not a QoS policy 27 28 Ownership OwnershipStrength Specifies if a DataReader can receive new samples for an instance of data fro
24. m 29 multiple DataWriters at the same time By default DataReaders for a given topic can receive data from any matching DataWriter for the same topic this is the shared setting for the Ownership QoS policy You can also configure an application to use exclusive Ownership for a topic so that DataReaders only receive data from one DataWriter at a time Ownership applies on a per key value instance basis for Topics that are keyed Thus with exclusive Ownership DataReaders will only receive data from a single DataWriter for a particular instance unique value for the key of a Topic This implies that a DataReader may receive data from multiple DataWriters as long as the DataWriters are sending data for different instances The value of Ownership must be the same for a DataWriter to be connected to a DataReader Either both sides must be shared or both sides must be exclusive Mismatched DataWriter and DataWriter pairs are not connected and will never exchange data The OwnershipStrength QoS policy is used to determine which DataWriter is allowed to send data or updates for instances for keyed Topics to DataReaders when Ownership is exclusive and there are multiple DataWriters all sending data for the same instance The DataWriter with the highest value for the OwnershipStrength QoS policy will be considered the owner of the instance of the Topic and whose data is delivered to DataReaders Data for the instance sent by all other DataWriters
25. omatically discover and connect with new remote DomainParticipants This QoS specifies the identifiers used by the DomainParticipant to discover other DomainParticipants with which to communicate This is done via an initial peers list The middleware will periodically send network packets to these locations announcing itself to any remote applications that may be present and will listen for announcements from those applications This QoS policy also controls the extent of and the transports used for discovery Often used with DiscoveryConfig to tune timeliness and reliability related parameters for the discovery process 2012 Real Time Innovations Inc 12 13 14 15 16 17 DiscoveryConfig Configures timeliness and reliability settings for discovery This QoS policy controls how often discovery data is sent as well as the reliability settings used for discovery topics The amount of network traffic required by the discovery process can vary widely based on how your application has configured the middleware s network addressing e g unicast vs multicast multicast TTL etc the system s size whether all applications are started at the same time or at staggered times and other factors Your application can use this policy to make tradeoffs between discovery completion time and network bandwidth utilization You can also introduce random back off periods into the discovery process to decrease the probability of netw
26. on the information passed in via the object pointer Note RTI generally recommends that users treat generated source files as compiler outputs analogous to object files and that users not modify them RTI cannot support user changes to generated source files Furthermore such changes would make upgrading to newer versions of RTI Connext more difficult as this generated code is considered to be a part of the middleware implementation and consequently does change from version to version This QoS policy should be considered a back door only to be used after careful design consideration testing and consultation with your RTI representative 48 UserData GroupData TopicData Attaches arbitrary application data a buffer of bytes to discovery meta data These QoS policies attach extra data that you want propagated at discovery time This extra data is interpreted by the end user application and is not used by the middleware itself e UserData attaches discoverable meta data at the DataWriter DataReader level e GroupData attaches discoverable meta data at the Publisher Subscriber level e TopicData attaches discoverable meta data at the Topic level Use cases for these policies include application to application identification authentication authorization and encryption purposes For example applications can use these policies to send security certificates to each other for RSA type security See also e DomainParticipantResourceLimits Se
27. ork contention when many applications start simultaneously Often used with Discovery to define the discovery peers DomainParticipantResourceLimits Configures how DomainParticipants allocate and use physical memory for internal resources including maximum sizes of various properties This QoS policy sets size limits on variable length parameters used by the participant and its contained entities It also controls the initial and maximum sizes of data structures used by the Domain Participant to store information about locally created and remotely discovered entities such as DataWriters DataReaders as well as parameters used by the internal database to size the hash tables it uses Durability Specifies whether Connext will store and deliver previously published data to new late joining DataReaders Durability controls whether or not new DataReaders get data which was written by DataWriters previously The Durability can vary from not at all the default to persistent stored to disk This QoS policy helps insulate system from startup dependencies and can increase system tolerance to failure conditions Often used with e DurrabilityService to configure the external service parameters e History to specify how much historical data is to be kept DurabilityService Configures external Persistence Service used for DataWriters with PERSISTENCE TRANSIENT Durability When a DataWriter s Durability QoS is set to PERSISTENT _DUR
28. pping between a list of topic e i i TransportulticastMapping p ppi g o p c xpressions and a multicast address that can be BC D y used by a DataReader to receive data for a specific topic TransportPriority Specifies on a per DataWriter basis that the data sent by that DataWriter is of a different priority A T W TransportSelection Selects which transports a DataWriter DataReader may use to send or receive its data BC R W Y TransportUnicast Specifies a subset of transports and a port number that can be used by an Entity to receive data BC D RW Y Attaches application specific values to a Writer Reader that are passed to the serialization deserialization TypeSupport y A R W Y routine of the associated data type UserData GroupData k MEFS R W ears Souen Attaches arbitrary application data a buffer of bytes to discovery meta data A TopicData PS T WireProtocol Configures properties for the DDS wire protocol RTPS BC D Y WriterDataLifecycle Controls how a DataWriter handles the lifecycle of the instances that it is registered to manage A WwW F DomainParticipantFactory T Topic P Publisher W DataWriter Y Yes Chng Changeable BE Before Enable A Always D DomainParticipant S Subscriber R DataReader Blank No Ext Extension to DDS standard BC Before Creation 2012 Real Time Innovations Inc DomainParticipant Publisher DataWriter QoS Policies per Entity Type UserData EntityFactory WireProtocol TransportBuiltin TransportUnicas
29. r History and Durable Reader State for high reliability in the face of component or system failures see the User s Manual s chapter on Mechanisms for Achieving Information Durability and Persistence e Allows you to attach additional information to entities such as for identification authentication authorization Often used with e TransportBuiltin TransportSelection TransportUnicast TransportMulticast configures aspects of built in and dynamically loaded transports 2012 Real Time Innovations Inc 33 34 35 e DomainParticipantResourceLimits configures maximum size of discoverable properties e Availability Durability DurabilityService also relevant to highly reliable and available systems See also UserData GroupData TopicData these QoS policies also attach discoverable meta data to entities PublishMode Specifies the mechanism that sends user data in an external middleware thread By default data is sent in the context of the user thread that calls write this is typically the lowest latency approach However there are times when you may want an internal middleware thread to send the data asynchronously instead Thus when the user thread calls write the data is only serialized and copied to an internal buffer A thread owned by the Publisher is responsible for sending the data when it is scheduled This QoS policy configures this behavior It may be SYNCHRONOUS default or ASYNCHRONOUS
30. r example reliable DataWriters may receive ACK NACK packets from reliable DataReaders During discovery each Entity announces to remote applications a list of up to 4 unicast addresses to which the remote application should send data either user data packets or reliable protocol meta data such as ACK NACKs and heartbeats 13 2012 Real Time Innovations Inc By default the list of addresses is populated automatically with values obtained from the enabled transport plug ins that are allowed to be used by the Entity see the TransportBuiltin and TransportSelection QoS policies The associated ports are automatically determined This default behavior is appropriate for most applications Use this QoS policy to manually select a subset of the available receive addresses for an Entity or to specify a non default receive port See also e TransportBuiltin Specifies the available built in transports at the DomainParticipant level e Property Used to install additional external transports at the DomainParticipant level e TransportSelection Specifies a subset of the available built in and external transports available for a particular DataWriter or DataReader 47 TypeSupport Attaches application specific values to a DataWriter DataReader that are passed to the serialization deserialization routine of the associated data type You can modify the rtiddsgen generated code so that the de serialization routines act differently depending
31. r sample caches used to maintain commitments if a finite reliability send window has not been set see DataWriterProtocol e Availability Durability DurabilityService configure additional data sources to maintain reliable delivery in the face of partial or total system failure e DataWriterProtocol a variety of parameters for controlling the RTPS reliability protocol for a reliable DataWriter including the size of the reliability send window and the rate at which heartbeats are sent This also controls whether reliability will be maintained only by means of negative acknowledgments or by a combination of positive and negative acknowledgments the default e DataReaderProtocol includes corresponding parameters for controlling the reliability protocol for the reliable DataReader Among other things this controls whether reliability will be maintained only by means of negative acknowledgments or by a combination of positive and negative acknowledgments the default 11 2012 Real Time Innovations Inc 37 ResourceLimits Controls amount of physical memory is allocated for middleware entities if dynamic allocations are allowed and how they occur and memory usage among different instance values for keyed topics Configures the amount of memory a DataWriter or DataReader may allocate to store data in a local cache also referred to as send or receive queues respectively The max_samples parameter in this policy also has a
32. rly constant independent of the number of DataReaders Coordinating the multicast address specified by DataReaders can help optimize network bandwidth usage in systems where there are multiple DataReaders for the same Topic Note that you can also specify a port number as well as a subset of the available transports with which to receive the multicast data These settings multicast address port number and transports do not need to be set uniformly for all DataReaders of the same Topic A DataWriter will automatically detect which DataReaders can be reached at the same network location and which other DataReaders need to be addressed separately See also e TransportBuiltin Identifies the available built in transports e Property Used to install external that is not built in transports 43 TransportMulticastMapping Specifies the automatic mapping between a list of topic expressions and multicast addresses that can be used by a DataReader to receive data for a specific topic This QoS policy provides an easy way to configure and assign multicast addresses to DataReaders based on the names of their associated Topics You can specify an automatic mapping between a list of topic expressions and a multicast address that can be used by the DataReader to receive the data To have a DataReader use this QoS policy to select its multicast address its own TransportMulticast QoS Policy must be set accordingly 44 TransportPriority Tells Connext
33. role in throttling the send rate of reliable DataWriters although starting in version 4 5 using the send window properties of the DataWriterProtocol QoS policy is the recommended way to configure this behavior This QoS policy can limit how much system memory can be allocated by the middleware For embedded real time systems and safety critical systems predetermination of maximum memory usage is often required In addition dynamic memory allocation may introduce non deterministic latencies in time critical paths By setting the initial and maximum settings to the same values for different parameters of this QoS policy you can be assured that an entity will not dynamically allocate more memory after its initialization phase Often used with e History configures the window of relevant previously written samples which must fit within the limits set by the ResourceLimits policy e Reliability the physical data storage limits of the DataWriter and DataReader caches can affect the performance of the protocol for reliable connections See also DataWriterProtocol recommended for taking over the role of reliability throttling from the ResourceLimits policy as of version 4 5 38 SystemResourceLimits Configures DomainParticipant independent resources Within a single process or address space for some supported real time operating systems applications may create and use multiple DomainParticipants This QoS policy governs resource
34. s at the process level across DomainParticipants This QoS policy places an effective limit on the number of DomainParticipants that can be created in a single process You may need to modify this QoS policy if you need to create more than 10 DomainParticipants in a process 39 TimeBasedFilter Sets a minimum time period before new data for an instance is provided to a DataReader excess data sent faster than the period set are not sent or otherwise discarded DataWriters may send data faster than needed by a DataReader For example a DataReader of sensor data that is displayed to a human in a GUI application often does not need data updates faster than a human can reasonably perceive changes in data values The period between updates is often measured in tenths 0 1 of a second up to several seconds However a sensor information DataWriter may have DataReaders that are processing the sensor information to control parts of the system and thus need new data updates with periods of hundredths 0 01 or thousandths 0 001 of a second This policy allows you to optimize resource usage CPU and possibly network bandwidth by only delivering the required amount of data to different DataReaders and filtering out samples that arrive faster than a rate you specify in terms of a period of time between data arrival You can use this QoS policy reduce the amount of data received by a DataReader in order to avoid overwhelming a potentially slow consumer Yo
35. s with Exclusive Ownership DestinationOrder Controls how Connext deals with data sent by multiple DataWriters for the same topic When multiple DataWriters send data for the same Topic the order in which data from different DataWriters is received by the applications of different DataReaders may be different So different DataReaders may not receive the same last value when DataWriters stop sending data If set to by reception timestamp e Data will be delivered by a DataReader in the order in which it was received which may lead to inconsistent final values If set to by source timestamp e Data will be delivered by a DataReader in the order in which it was sent If data arrives on the network with a source timestamp later than the source timestamp of the last data delivered the new data will be dropped This ordering therefore works best when system clocks are relatively synchronized among writing machines e Not all data sent by multiple DataWriters may be delivered to a DataReader and not all DataReaders will see the same data sent by DataWriters However all DataReaders will see the same final data when DataWriters stop sending data Can be used to create systems that have eventual consistency Thus intermediate states across multiple applications may be inconsistent but when DataWriters stop sending changes to the same topic all applications will end up having the same state Discovery Configures mechanism used to aut
36. shMode specifically when using DDS_ASYNCHRONOUS_ PUBLISH _MODE_QoS and a flow controller e DDSFlowController specifically the DDS_EDF_FLOW_CONTROLLER_SCHED_POLICY for DDS_FlowControllerProperty_t 2012 Real Time Innovations Inc 23 24 25 26 Lifespan Specifies how long Connext should consider data sent by a user application to be valid Connext will timestamp all data sent and received When a finite Lifespan is specified for a DataWriter or DataReader Connext will check to see how long the data has been stored in the DataWriter s send queue or the DataReader s receive queue and remove any data that has exceeded its Lifespan duration Connext will always compare times from the same local clock when checking Lifespan Thus the Lifespan for data in the DataReader uses the time as stamped by the local clock when the data was received as the start time for the Lifespan calculation You can use this QoS policy to limit how much data is stored by Connext Even if configured for KEEP_ALL History Qos data may be dropped by Connext due to the use of the Lifespan QoS May interact with the Reliability QoS Due to expired Lifespan data in the DataWriter that has not yet been acknowledged as have been received in a reliable connection may be dropped and thus never repaired if the initial sample was lost Data in the DataReader that has not yet been accessed by the user code may also be removed due to an expired Lifespan
37. stribution directory for RTI Connext You may disable any or all of these default locations using the Profile QoS policy e The locations of files as well as strings containing XML formatted QoS profiles can be specified directly via the Profile QoS policy Property Specifies name value pairs used to configure parameters not exposed via formal QoS policies The Property QoS policy allows name value pairs in the form of strings to be attached to the QoS of different entities These strings are often used to add configuration parameters to an entity without having to change formal QoS policies Behaviors configured by means of this policy are often not known a priori for example dynamically loaded network transport plug ins or are provided on a provisional basis You may also add your own name value pairs to the Property QoS policy of an Entity and direct RTI Connext to propagate this information with the Entity s discovery information so it can be accessed in other applications This allows you to add meta information about an Entity for application specific use e Used to configure the property of builtin transports before DomainParticipant creation e Used to specify dynamic loading of extension transports such as RTI Secure WAN Transport e Used to specify multiple instances of the built in transports e Allows full pluggable transport configuration for non C C languages Java C etc e Used to select a clock e Configures Durable Write
38. t Discovery DomainParticipantResourceLimits Event ReceiverPool Database DiscoveryConfig Property EntityName TypeSupport TransportMulticastMapping Presentation Partition GroupData EntityFactory AsynchronousPublisher ExclusiveArea Durability DurabilityService Deadline LatencyBudget Liveliness Reliability DestinationOrder History ResourceLimits TransportPriority Lifespan UserData Ownership OwnershipStrength WriterDataLifecycle DataWriterResourceLimits DataWriterProtocol TransportSelection TransportUnicast PublishMode Property EntityName Batch MultiChannel TypeSupport Subscriber DataReader DomainParticipantFactory TopicData Durability DurabilityService Deadline LatencyBudget Liveliness Reliability DestinationOrder History ResourceLimits TransportPriority Lifespan Ownership Presentation Partition GroupData EntityFactory ExclusiveArea Durability Deadline LatencyBudget Liveliness Reliability DestinationOrder History ResourceLimits UserData Ownership TimeBasedFilter ReaderDataLifecycle DataReaderResourceLimits DataReaderProtocol TransportSelection TransportUnicast TransportMulticast Property Availability EntityName TypeSupport EntityFactory SystemResourceLimits Profile Lo 2012 Real Time Innovations Inc QoS Policy Highlights 1 AsynchronousPublisher Configures the mechanism that sends user data in an extern
39. taReader receives data it caches that data for your application Your application may either take the data from the cache or leave it there This QoS policy controls when the middleware will automatically remove the stored data for a particular instance of the Topic from the cache such that the data is no longer accessible by the application when it detects that there are no more DataWriters alive for a specific instance or when a DataWriter has disposed the instance For Topics without keys this applies when there are no DataWriters alive for the Topic or if the Topic has been disposed by a DataWriter You can use this QoS policy to specify a delay in which the data removal will occur when the middleware detects one of the two states described earlier By default the delays are specified to be infinite which configures Connext not to remove any data from the DataReader s cache ReceiverPool Configures threads used to receive and process data from transports for example UDP sockets Configures the properties of the receive threads that the middleware uses to receive and process data from its installed transports This includes setting thread properties such as priority level and stack size for these threads as well as the size of the buffer used to store packets received from a transport This buffer size limits the largest single packet of data that a DomainParticipant will accept from a transport For many applications the value 65 53
40. tected by one and only one EA although a single exclusive area may be shared by multiple entities Conceptually an EA is a mutex or monitor with additional deadlock protection features Note one only gets into exclusive area violations because entity creation modifications are done in callbacks If these operations are one in user threads exclusive violations cannot occur Creating shared EA s is generally not a good practice since it decreases concurrency GroupData Attaches arbitrary application data to discovery meta data at the publisher subscriber level See UserData History Controls how much data to store and how stored data is managed for a DataWriter or DataReader Controls how Connext manages data sent by a DataWriter or received for a DataReader Two settings are available KEEP_ALL or KEEP_LAST with a value depth KEEP_ALL does not imply that Connext will store infinite data How much data can actually be stored and thus memory allocation is controlled by the ResourceLimits QoS When using the KEEP_LAST setting the value of depth number of data samples to keep applies on a per instance basis unique key value for Topics that are keyed For example for a Topic that provides data about the positions of aircraft and using the aircraft ID as a key a KEEP_LAST setting of 1 will tell Connext to keep the last value for each unique aircraft ID The major use of history is to help tune the reliability between DataWriters and DataR
41. ts the maximum length of the extra data that can be attached default 256 bytes e Property an alternative means of attaching discoverable meta data to entities 49 WireProtocol Configures the DDS on the wire protocol RTPS Configures some global RTPS properties The DataWriterProtocol and DataReaderProtocol QoS policies configure RTPS and reliability properties on a per DataWriter or DataReader basis 50 WriterDataLifecycle Controls how a DataWriter handles the lifecycle of the instances that it is registered to manage The behavior controlled by this QoS policy applies on a per instance key basis for keyed Topics so that when a DataWriter unregisters an instance RTI Connext can automatically also dispose that instance This is the default behavior In cases where the ownership of a Topic is exclusive see the Ownership QoS policy DataWriters may want to relinquish ownership of a particular instance of the Topic to allow other DataWriters to send updates for the value of that instance regardless of how the OwnershipStrength QoS policy is set In that case you may only want a DataWriter to unregister an instance without disposing the instance Disposing an instance is a statement that an instance no longer exists User applications may be coded to trigger on the disposal of instances thus the ability to unregister without disposing may be useful to properly maintain the semantic of disposal 14
42. u can also use it to reduce the amount of data placed on the network by a DataWriter to avoid overwhelming network resources Different DataReaders for the same Topic are allowed to set their own time based filters so that data published faster than the period set by a DataReader will be dropped by the middleware and not delivered to the DataReader without perturbing other DataReaders This time based data filtering does not depend on any DataWriter settings However it also does not force the DataWriter to send at a specific rate How fast a DataWriter updates new data is entirely under the control of the user code See also ContentFilteredTopics Not a QoS policy but a feature in which you can create DataReaders that receive data that are filtered based on the value of the data in addition to time See the User s Manual 40 TopicData Attaches arbitrary application data to discovery meta data at the topic level See UserData 41 TransportBuiltin Specifies which built in transports are used Three transport plug ins are built into the core RTI Connext libraries UDPv4 shared memory and UDPv6 This is true for most supported target platforms However on certain embedded platforms shared memory and or UDPv6 may not be supported Please consult the Platform Notes for more information This QoS policy controls which of these built in transport plug ins are to be used by a DomainParticipant 12 2012 Real Time Innovations Inc
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