UA Part 7: Profiles - 5.2 Services

5.2 Services

The following tables describe ConformanceUnitsfor the Servicesspecified in OPC 10000-4. The tables correlate with the Service Sets.

A single ConformanceUnitcan reference several Services(e.g. CreateSession, ActivateSession and CloseSession) but can also refer to individual aspects of Services(e.g. the use of ActivateSession to impersonate a new user).

Each table includes a listing of the Profile Categoryto which a ConformanceUnitbelongs, the title and description of the ConformanceUnit. In some cases, a ConformanceUnitwill be derived from another ConformanceUnit. This parent unit will then be specified in the description of each derived unit. In such cases the derived units inherit all of the tests of its parent plus one or more additional TestCases. These TestCases can only further restrict the existing TestCases. An example would be one in which the number of connections is tested, where the TestCase of the parent required at least one connection and the derived ConformanceUnitwould require a TestCasefor at least five connections.

The Discovery ServiceSet is composed of multiple ConformanceUnits(see Table 3). All Serversprovide some aspects of this functionality; see Profilescategorized as Server Profilesfor details. Clientsmay support some aspects of this functionality; see Profilescategorized as Client Profilesfor details.

Table 3– Discovery Services

Category	Title	Description
Server	DiscoveryGet Endpoints	Support the GetEndpoints Serviceto obtain all Endpoints of the Server. This includes filtering based on Profiles.
Server	DiscoveryGet Endpoints SessionLess	Support at least one endpoint for issueing SessionLess Services. Support obtaining such endpoints by accepting the Transport URI as a filter to the GetEndpoints Service with the query string "SL" appended to the Transport URI. E.g. "http://opcfoundation.org/UA-Profile/Transport/https-uajson?SL"
Server	DiscoveryFind ServersSelf	Support the FindServers Serviceonly for itself.
Server	DiscoveryRegister	Call the RegisterServer Serviceto register itself (OPC UA Server) with an external Discovery Servicevia a secure channel with a SecurityMode other than NONE.
Server	DiscoveryRegister2	Call the RegisterServer2 Serviceto register with an external Discovery Servicevia a Secure Channel with a SecurityMode other than "None". This includes passing a list of short capability identifiers. The identifiers and their use are specified in Part 12.
Server	Discovery ServerAnnouncement using mDNS	Provide mDNS functionality to announce a Serverwith its capabilities. The capability identifiers and the use of mDNS records for the purpose of OPC UA Discoveryis specified in Part 12. Note that this functionality is only required for Serversthat do not register with an LDS. The capability identifiers and their use in mDNS records are specified in Part 12.
Server	DiscoveryConfiguration	Allow configuration of the Discovery ServerURL where the Serverwill register itself. Allow complete disabling of registration with a Discovery Server.
Client	Discovery ClientFind ServersBasic	Uses the FindServers Serviceto obtain all Serversinstalled on a given platform.
Client	Discovery ClientFind Serverswith URI	Use FindServers Serviceto obtain URLs for specific ServerURIs.
Client	Discovery ClientFind ServersDynamic	Detect new Serversafter an initial FindServers Servicecall.
Client	Discovery ClientFind Serverson Network	Support one of the options to locate Serverson the network.
Client	Discovery ClientFind Serverson Network using LDS-ME	Use FindServersOnNetwork Serviceto obtain URLs for specific ServerURIs. Note that this Serviceis available via the Local Discovery Serverwith multicast extension (LDS-ME).
Client	Discovery ClientFind Serverson Network using mDNS	Use mDNS based Service Discoveryto locate Serverson the same multicast network. The contents of mDNS records for OPC UA Discoveryare described in Part 12. Note that this functionality is only required for Clientswhen there is no Local Discovery Serverwith multicast extension (LDS-ME). The capability identifiers and their use in mDNS records are specified in Part 12.
Client	Discovery ClientFind Serversin GDS	Use the QueryServers Methodon the GDS Directory Objectto locate Serversthat meet filter criteria specified in the request. This Methodis specified in Part 12.
Client	Discovery ClientFind Applications in GDS	Use the QueryApplications Methodon the GDS Directory Objectto locate Applications that meet filter criteria specified in the request. This Methodis specified in Part 12.
Client	Discovery ClientGet Endpoints Basic	Uses the GetEndpoints Serviceto obtain all Endpoints for a given ServerURI.
Client	Discovery ClientGet Endpoints SessionLess	Uses the GetEndpoints Servicewith a filter to obtain Endpoints that can be used for SessionLess Serviceinvocation. The filter is the Transport URI extended with the query string "SL". E.g. http://opcfoundation.org/UA-Profile/Transport/https-uajson?SL.
Client	Discovery ClientGet Endpoints Dynamic	Detect changes to the Endpoints after an initial GetEndpoints Servicecall.
Client	Discovery ClientConfigure Endpoint	Allow specification of an Endpoint without going through the Discovery ServiceSet.

The Session ServiceSet is composed of multiple ConformanceUnits(see Table 4). The CreateSession, ActivateSession, and CloseSession services are supported as a single unit. All Serversand Clientsprovide this functionality.

Table 4– Session Services

Category	Title	Description
Server	SessionGeneral ServiceBehaviour	Implement basic Servicebehaviour. This includes in particular: – checking the authentication token – returning the requestHandle in responses – returning available diagnostic information as requested with the 'returnDiagnostics' parameter – respecting a timeoutHint
Server	SessionBase	Support the Session ServiceSet (CreateSession, ActivateSession, CloseSession) except the use of ActivateSession to change the Sessionuser. This includes correct handling of all parameters that are provided. Note that for the CreateSession and ActivateSession services, if the SecurityMode = None then: 1) The Application Certificateand Nonce are optional. 2) The signatures are null/empty. The details of this are described in Part 4.
Server	SessionChange User	Support the use of ActivateSession to change the Sessionuser.
Server	SessionCancel	Support the Cancel Serviceto cancel outstanding requests.
Server	SessionMinimum 1	Support minimum 1 Session(total).
Server	SessionMinimum 2 Parallel	Support minimum 2 parallel Sessions (total for all Clients).
Server	SessionMinimum 50 Parallel	Support minimum 50 parallel Sessions (total for all Clients).
Server	Session Sessionless Invocation	Defines the support of the SessionlessInvoke Service defined in UA Part 4 to process any of the Services (like Read/Write, Browse, or Call) that are designated for Session-less invocation.
Client	Session ClientGeneral ServiceBehaviour	Implement basic Servicebehaviour. This includes in particular: – including the proper authentication token of the Session – creating a requestHandle if needed – requesting diagnostic information with the 'returnDiagnostics' parameter – evaluate the serviceResult and operational results
Client	Session ClientBase	Use the Session ServiceSet (CreateSession, ActivateSession, and CloseSession) except the use of ActivateSession to change the Sessionuser. This includes correct handling of all parameters that are provided Note that for the CreateSession and ActivateSession services, if the SecurityMode = None then: 1) The Application Certificateand Nonce are optional. 2) The signatures are null/empty.
Client	Session ClientMultiple Connections	Support unlimited connections (client side) with multiple Servers. Any limit on numbers of connections is from server side. May have a memory based limit, but not a software constraint limit.
Client	Session ClientRenew NodeIds	This ConformanceUnitapplies to Clientsthat allow persisting NodeIds. Verify that the Namespace Table has not changed for NodeIds that the Clienthas persisted and is going to re-use beyond a Sessionlifetime. If changes occurred the Clienthas to recalculate the Namespace Indices of the respective NodeIds.
Client	Session ClientImpersonate	Uses ActivateSession to change the Session user (impersonation).
Client	Session ClientKeepAlive	Make periodic requests to keep the Sessionalive.
Client	Session ClientDetect Shutdown	Read or monitor the ServerStatus/State Variable to recognize a potential shutdown of the Server and clean up resources.
Client	Session ClientCancel	Use the Cancel Serviceto cancel outstanding requests.
Client	Session ClientAuto Reconnect	Automatic Clientreconnect including: – ActivateSession with new SecureChannel if SecureChannel is no longer valid but Sessionis still valid – Creation of a new Sessiononly if Sessionis no longer valid
Client	Session ClientSingle Session	The Clientshall interoperate with Serversthat only support one Session.
Client	Session ClientSessionLess ServiceCalls	Defines the use of the SessionlessInvoke Servicedefined in UA Part 4 to request one of the Services(like Read or Browse) that are allowed for sessionless invocation. UA Part 6 specifies which transports may be used and how.

The NodeManagement ServiceSet is composed of multiple ConformanceUnits(see Table 5). Serversmay provide some aspects of this functionality; see Profilescategorized as Server Profilesfor details. Clientsmay support some aspects of this functionality; see Profilescategorized as Client Profilesfor details.

Table 5– Node Management Services

Category	Title	Description
Server	NodeManagement Add Node	Support the AddNodes Serviceto add one or more Nodesinto the OPC UA AddressSpace.
Server	NodeManagement Delete Node	Support the DeleteNodes Serviceto delete one or more Nodesfrom the OPC UA AddressSpace.
Server	NodeManagement Add Ref	Support the AddReferences Serviceto add one or more Referencesto one or more Nodesin the OPC UA AddressSpace.
Server	NodeManagement Delete Ref	Support the DeleteReferences Serviceto delete one or more Referencesof a Nodein the OPC UA AddressSpace.
Client	NodeManagement Client	Uses NodeManagement Servicesto add or delete Nodesand to add or delete Referencesin Server's OPC UA AddressSpace.

The View ServiceSet is composed of a multiple ConformanceUnits(see Table 6). All Serverssupport some aspects of this conformance group. Clientsmay support some aspects of this functionality; see Profilescategorized as Client Profilesfor details.

Table 6– View Services

Category	Title	Description
Server	View Basic	Support the View ServiceSet (Browse, BrowseNext).
Server	View TranslateBrowsePath	Support TranslateBrowsePathsToNodeIds Service.
Server	View RegisterNodes	Support the RegisterNodes and UnregisterNodes Servicesas a way to optimize access to repeatedly used Nodesin the Server's OPC UA AddressSpace.
Server	View Minimum Continuation Point 01	Support minimum 1 continuation point per Session.
Server	View Minimum Continuation Point 05	Support minimum 5 continuation points per Session. This number has to be supported for at least half of the minimum required sessions.
Client	View ClientBasic Browse	Uses Browse and BrowseNext Servicesto navigate through the Server's OPC UA AddressSpace. Make use of the referenceTypeId and the nodeClassMask to specify the needed References.
Client	View ClientRemote NodesBrowse	The Clientcan browse to nodes that have an extended NodeID that reference a Serverdifferent than the originating Server. This includes automatic connection to the remote Server. It is acceptable that the Serverconfiguration information be pre-configured on the Clientand / or that the user is prompted to connect.
Client	View ClientBasic ResultSet Filtering	Makes use of the resultMask parameter to optimize the result set to be returned by the Server.
Client	View ClientTranslateBrowsePath	Uses the TranslateBrowsePathsToNodeIds Serviceto identify the NodeIds for Nodeswhere a starting Nodeand a BrowsePath is known. Makes use of bulk operations rather than multiple calls whenever possible.
Client	View ClientRemote NodesTranslate Browse	The Clientcan translate browse paths that include nodes with extended NodeID that reference a Serverdifferent than the originating Serverand return them as part of the TranslateBrowsePathsToNodeIds Service. It is acceptable that the Serverconfiguration information be pre-configured on the Client.
Client	View ClientRegisterNodes	Uses the RegisterNodes Serviceto optimize access for Nodesthat are used repeatedly. Use UnregisterNodes when Nodesare not used anymore.

The Attribute ServiceSet is composed of multiple ConformanceUnits(see Table 7). The majority of the Attributeservice set is a core functionality of OPC UA and as such is supported by most Servers. Most Clientswill also support some aspects of the Attribute ServiceSet.

Table 7– Attribute Services

Category	Title	Description
Server	AttributeRead	Supports the Read Serviceto read one or more Attributesof one or more Nodes. This includes support of the IndexRange parameter to read a single element or a range of elements when the Attributevalue is an array.
Server	AttributeRead Complex	Supports reading and encoding Values with structured DataTypes.
Server	AttributeWrite Values	Supports writing to values to one or more Attributesof one or more Nodes.
Server	AttributeWrite Complex	Supports writing and decoding Values with structured DataTypes.
Server	AttributeWrite StatusCode & Timestamp	Supports writing of StatusCode and Timestamps along with the Value.
Server	AttributeWrite Index	Supports the IndexRange to write a single element or a range of elements when the Attributevalue is an array and partial updates is allowed for this array.
Server	AttributeAlternate Encoding	Supports alternate Data Encoding when reading value Attributes. By default, every Serverhas to support the Data Encoding of the currently used Stack Profile(i.e. binary with UA Binary Encoding and XML with XML Encoding). This ConformanceUnit- when supported - specifies that the other Data Encoding is supported in addition.
Server	AttributeHistorical Read	Supports the HistoryRead Service. The details of what aspects of this service are used are listed in additional ConformanceUnits, but at least one of ReadRaw, ReadProcessed, ReadModified, ReadAtTime or ReadEvents must be supported.
Server	AttributeHistorical Update	Supports the HistoryUpdate service. The details of the supported features of this service are described by additional ConformanceUnits, but at least one of the following must be supported: InsertData, InsertEvents, ReplaceData, ReplaceEvents, UpdateData, UpdateEvents, DeleteData, DeleteEvents or DeleteAtTime.
Client	Attribute ClientRead Base	Use the Read Serviceto read one or more Attributesof one or more Nodes. This includes use of an IndexRange to select a single element or a range of elements when the Attributevalue is an array. Clientsshall use bulk operations whenever possible to reduce the number of Serviceinvocations.
Client	Attribute ClientRemote Nodes AttributeAccess	The Clientcan retrieve attributes of nodes that have an extended NodeID that reference a Serverdifferent than the originating Server. This requires a connection to the remote Serverfor access (not necessarily displayed as a connection). It is acceptable that the Serverconfiguration information be pre-configured on the Client.
Client	Attribute ClientRead with proper Encoding	This ConformanceUnitrefers to the ability of a Clientto discover the available encodings and choose a specific one when calling the Read Service.
Client	Attribute ClientRead Complex	Read and decode Values with structured DataTypes.
Client	Attribute ClientWrite Base	Use the Write Serviceto write values to one or more Attributesof one or more Nodes. This includes use of an IndexRange to select a single element or a range of elements when the Attributevalue is an array. Clientsshall use bulk operations whenever possible to reduce the number of Serviceinvocations.
Client	Attribute ClientWrite Complex	Write and Encode Values with structured DataTypes.
Client	Attribute ClientWrite Quality & Timestamp	Use the Write Serviceto also write StatusCode and/or Timestamps along with a Value.
Client	Attribute ClientHistorical Read	The Clientmakes use of the HistoryRead service. The details of which aspect of this service are used are provided by additional ConformanceUnits, but at least one or more of the following is used ReadRaw, ReadAtTime, ReadProcessed, ReadModified or ReadEvents.
Client	Attribute ClientHistorical Updates	The Clientmakes use of the HistoryUpdate service. The details of this usage are provided by additional ConformanceUnits, but at least one or more of the following must be provided InsertData, InsertEvents, ReplaceData, ReplaceEvents, UpdateData, UpdateEvents, DeleteData or DeleteEvents or DeleteAtTime.

The Method ServiceSet is composed of ConformanceUnits (see Table 8). The primary ConformanceUnits provide support for the call functionality. Serversmay provide some aspects of this functionality; see Profilescategorized as Server Profilesfor details. Clientsmay support some aspects of this functionality; see Profilescategorized as Client Profilesfor details.

Table 8– Method Services

Category	Title	Description
Server	MethodCall	Support the Call Serviceto call (invoke) a Methodwhich includes support for MethodParameters.
Client	Method ClientCall	Use the Call Serviceto call one or several Methods.

The MonitoredItem ServiceSet is composed of multiple ConformanceUnits(see Table 9). Serversmay provide some aspects of this functionality; see Profilescategorized as Server Profilesfor details. Clientsmay support some aspects of this functionality; see Profilescategorized as Client Profilesfor details.

Table 9– Monitored Item Services

Category	Title	Description
Server	Monitor Basic	Support the following MonitoredItem Services: CreateMonitoredItems, ModifyMonitoredItems, DeleteMonitoredItems and SetMonitoringMode.
Server	Monitor Value Change	Support creation of MonitoredItemsfor Attributevalue changes. This includes support of the IndexRange to select a single element or a range of elements when the Attributevalue is an array.
Server	Monitor Complex Value	Supports monitoring and encoding Values with structured DataTypes.
Server	Monitored Items Deadband Filter	Supports an absolute Deadband filter as a DataChangeFilter for numeric data types.
Server	Monitor Aggregate Filter	Support for Aggregate filters for MonitoredItems. The result of this ConformanceUnitincludes a list of Aggregates that are supported as part of the Profile Certificate.
Server	Monitor Alternate Encoding	Support alternate encoding when monitoring value Attributes. By default, every Serverhas to support the encoding of the currently used Stack Profile(i.e. binary with UA Binary Encoding and XML with XML Encoding). This ConformanceUnit- when supported - specifies that the other encoding is supported in addition.
Server	Monitor Items 2	Support at least 2 MonitoredItemsper Subscriptionwhere the size of each MonitoredItemis at least equal to size of Double.
Server	Monitor Items 10	Support at least 10 MonitoredItemsper Subscriptionwhere the size of each MonitoredItemis at least equal to size of Double.
Server	Monitor Items 100	Support at least 100 MonitoredItemsper Subscription. This number has to be supported for at least half of the required Subscriptions for half of the required Sessions.
Server	Monitor Items 500	Support at least 500 MonitoredItemsper Subscription. This number has to be supported for at least half of the required Subscriptions for half of the required Sessions.
Server	Monitor QueueSize_1	This ConformanceUnitdoes not require queuing when multiple value changes occur during a "publish period". I.e. the latest change will be sent in the Notification.
Server	Monitor MinQueueSize_02	Support at least 2 queue entries for MonitoredItems. Serversoften will adapt the queue size to the number of currently MonitoredItems. However, it is expected that Serverssupport this minimum queue size for at least one third of the supported MonitoredItems.
Server	Monitor MinQueueSize_05	Support at least 5 queue entries for MonitoredItems. Serversoften will adapt the queue size to the number of currently MonitoredItems. However, it is expected that Serverssupport this minimum queue size for at least one third of the supported MonitoredItems.
Server	Monitor QueueSize_ServerMax	This ConformanceUnitis for events. When the Clientrequests queuesize=MAXUInt32 the Serveris to return the maximum queue size that it can support for event notifications as the revisedQueueSize.
Server	Monitor Triggering	Support the SetTriggering Serviceto create and/or delete triggering links for a triggering item.
Server	Monitor Events	Support creation of MonitoredItemsfor an "EventNotifier Attribute" for the purpose of Event Notification. The subscription includes supporting a filter that includes SimpleAttribute Operands and a select list of Operators. The list of Operators includes: Equals, IsNull, GreaterThan, LessThan, GreaterThanorEqual, LessThatorEqual, Like, Not, Between, InList, And, Or, Cast, BitwiseAnd, BitwiseOr.
Server	Monitor Complex EventFilter	Support for the 'TypeOf' complex Eventfilter operator.
Client	Monitor ClientValue Change	Use the MonitoredItem ServiceSet to register items for changes in Attributevalue. Use CreateMonitoredItems to register the Node/Attributetuple. Set proper sampling interval, Deadband filter and queuing mode. Use disabling / enabling instead of deleting and re-creating a MonitoredItem. Use bulk operations rather than individual service requests to reduce communication overhead.
Client	Monitor ClientComplex Value	Monitor and decode Values with structured DataTypes.
Client	Monitor ClientDeadband Filter	Uses Absolute Deadband filters for subscriptions.
Client	Monitor Clientby Index	Use the IndexRange to select a single element or a range of elements when the Attributevalue is an array.
Client	Monitor ClientAggregate Filter	Uses Aggregate filters for Subscriptions.
Client	Monitor ClientEvents	Use the MonitoredItem ServiceSet to create MonitoredItemsfor Eventnotifications.
Client	Monitor Client EventFilter	Use the Eventfilter when calling CreateMonitoredItems to filter the desired Events and to select the columns to be provided for each Event Notification.
Client	Monitor ClientComplex EventFilter	Use of the 'TypeOf' complex Eventfilter operator.
Client	Monitor ClientModify	Use ModifyMonitoredItems Serviceto change the configuration setting. Use SetMonitoringMode Serviceto disable / enable sampling and / or publishing.
Client	Monitor ClientTrigger	Use the Triggering Model if certain items are to be reported only if some other item triggers. Use proper monitoring mode for these items. Use SetTriggering Serviceto link these items to the trigger item.

The Subscription ServiceSet is composed of multiple ConformanceUnits(see Table 10). Serversmay provide some aspects of this functionality; see Profilescategorized as Server Profilesfor details. Clientsmay support some aspects of this functionality; see Profilescategorized as Client Profilesfor details.

Table 10– Subscription Services

Category	Title	Description
Server	SubscriptionBasic	Support the following Subscription Services: CreateSubscription, ModifySubscription, DeleteSubscriptions, Publish, Republish and SetPublishingMode.
Server	SubscriptionMinimum 1	Support at least 1 Subscriptionper Session. This number has to be supported for all of the minimum required sessions.
Server	SubscriptionMinimum 02	Support at least 2 Subscriptions per Session. This number has to be supported for at least half of the minimum required sessions.
Server	SubscriptionMinimum 05	Support at least 5 Subscriptions per Session. This number has to be supported for at least half of the minimum required sessions.
Server	SubscriptionPublish Min 02	Support at least 2 Publish Servicerequests per Session. This number has to be supported for all of the minimum required sessions. Support of a NotificationMessage retransmission queue is not required; if not available the Republish Servicereturns Bad_MessageNotAvailable.
Server	SubscriptionPublish Min 05	Support at least 5 Publish Servicerequests per Session. This number has to be supported for at least half of the minimum required sessions. Support, as a minimum, the number of Publish requests per session as the size of the NotificationMessage retransmission queue for Republish.
Server	SubscriptionPublish Min 10	Support at least 10 Publish Servicerequests per Session. This number has to be supported for at least half of the minimum required sessions. Support, as a minimum, the number of Publish requests per session as the size of the NotificationMessage retransmission queue for Republish.
Server	SubscriptionPublish Discard Policy	Respect the specified policy for discarding Publish Servicerequests. If the maximum number of Publish Servicerequests has been queued and a new Publish Servicerequest arrives, the "oldest" Publish request has to be discarded by returning the proper error.
Server	SubscriptionTransfer	Support TransferSubscriptions Serviceto transfer a Subscriptionfrom one Sessionto another.
Server	SubscriptionDurable	Support setting Subscriptions in durable mode. This mode requires that collected data and events are stored and delivered even if a Clientwas disconnected for a longer time or the Serverwas restarted. Support one of the “SubscriptionDurable StorageLevel nnn” ConformanceUnits.
Server	SubscriptionDurable StorageLevel Small	Support at least 20 monitored items with a queue size of 10000 for each item and where the size of each MonitoredItemis at least equal to size of Double. This requires storage capacity for 200 thousand values of DataType Double.
Server	SubscriptionDurable StorageLevel Medium	Support at least 100 monitored items with a queue size of 50000 for each item and where the size of each MonitoredItemis at least equal to size of Double. This requires storage capacity for 5 million values of DataType Double.
Server	SubscriptionDurable StorageLevel High	Support at least 2000 monitored items with a queue size of 200000 for each item and where the size of each MonitoredItemis at least equal to size of Double. This requires storage capacity for 400 million values of DataType Double.
Client	Subscription ClientBasic	Use the Subscriptionand MonitoredItem ServiceSet as an efficient means to detect changes of Attributevalues and / or to receive Eventoccurrences. Set appropriate intervals for publishing, keep alive notifications and total Subscriptionlifetime. Supply a sufficient number of Publish requests to the Serverso that Notificationscan be sent whenever a publish timer expires. Acknowledge received Notificationswith subsequent Publish requests.
Client	Subscription ClientFallback	The Clientshall interoperate with Serversthat do not support Subscriptions, or have exhausted Subscriptionlimits, for Monitoring by using Read Service.
Client	Subscription ClientRepublish	Evaluate the sequence number in Notificationsto detect lost Notifications. Use Republish to request missing Notifications.
Client	Subscription ClientModify	Allow modification of the Subscriptionconfiguration using the ModifySubscription Service.
Client	Subscription ClientTransferSubscriptions	The Clientsupports transferring Subscriptionfrom other Clients. This ConformanceUnitis used as part of redundant Clients.
Client	Subscription ClientMultiple	Use multiple Subscriptions to reduce the payload of individual Notifications.
Client	Subscription ClientPublish Configurable	Send multiple Publish Servicerequests to assure that the Serveris always able to send Notifications. The number of parallel Publish Servicerequests per Sessionshall be configurable.
Client	Subscription ClientDurable	Use durable Subscriptions.