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Reliable Messaging Protocol version 1.0

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This topic covers Windows Communication Foundation (WCF) implementation details for the WS-Reliable Messaging February 2005 (version 1.0) protocol necessary for interoperation using the HTTP transport. WCF follows the WS-Reliable Messaging specification with the constraints and clarifications explained in this topic. Note that the WS-ReliableMessaging version 1.0 protocol is implemented starting with the WinFX.

The WS-Reliable Messaging February 2005 protocol is implemented in WCF by the ReliableSessionBindingElement.

For convenience, the topic uses the following roles:

  • Initiator: the client that initiates WS-Reliable Message sequence creation

  • Responder: the service that receives the initiator's requests

This document uses the prefixes and namespaces in the following table.

Prefix Namespace
wsrm http://schemas.xmlsoap.org/ws/2005/02/rm
netrm http://schemas.microsoft.com/ws/2006/05/rm
s http://www.w3.org/2003/05/soap-envelope
wsa http://schemas.xmlsoap.org/ws/2005/08/addressing
wsse http://docs.oasis-open.org/wss/2004/01/oasis-200401-wssecurity-secext-1.0.xsd

Messaging

Sequence Establishment Messages

WCF implements CreateSequence and CreateSequenceResponse messages to establish a reliable message sequence. The following constraints apply:

  • B1101: The WCF Initiator does not generate the optional Expires element in the CreateSequence message or, in the cases when the CreateSequence message contains an Offer element, the optional Expires element in the Offer element.

  • B1102: When accessing the CreateSequence message, the WCFResponder sends and receives both Expires elements if they exist, but does not use their values.

WS-Reliable Messaging introduces the Offer mechanism to establish the two converse correlated sequences that form a session.

  • R1103: If CreateSequence contains an Offer element, the Reliable Messaging Responder must either accept the sequence and respond with CreateSequenceResponse that contains a wsrm:Accept element, forming two correlated converse sequences or reject the CreateSequence request.

  • R1104: SequenceAcknowledgement and application messages flowing on converse sequence must be sent to the ReplyTo endpoint reference of the CreateSequence.

  • R1105: AcksTo and ReplyTo endpoint references in the CreateSequence must have address values that match the octet-wise.

    The WCF Responder verifies that the URI portion of the AcksTo and ReplyTo EPRs are identical before creating a sequence.

  • R1106: AcksTo and ReplyTo Endpoint References in the CreateSequence should have the same set of reference parameters.

    WCF does not enforce but assumes that [reference parameters] of AcksTo and ReplyTo on CreateSequence are identical and uses [reference parameters] from ReplyTo endpoint reference for acknowledgements and converse sequence messages.

  • R1107: When two converse sequences are established using the Offer mechanism, SequenceAcknowledgement and application messages flowing on converse sequences must be sent to the ReplyTo endpoint reference of the CreateSequence.

  • R1108: When two converse sequences are established using the Offer mechanism, the [address] property of the wsrm:AcksTo Endpoint Reference child element of the wsrm:Accept element of the CreateSequenceResponse must match byte-wise the destination URI of the CreateSequence.

  • R1109: When two converse sequences are established using the Offer mechanism, messages sent by initiator and acknowledgements to messages by responder must be sent to the same Endpoint Reference.

    WCF uses WS-Reliable Messaging to establish reliable sessions between the Initiator and Responder. WCF's WS-Reliable Messaging implementation provides reliable session for one-way, request-reply and full duplex messaging patterns. The WS-Reliable Messaging Offer mechanism on CreateSequence/CreateSequenceResponse lets you establish two correlated converse sequences, and provides a session protocol that is suitable for all message endpoints. Because WCF provides a security guarantee for such a session including end-to-end protection for session integrity, it is practical to ensure messages intended to the same party are arriving at the same destination. This also allows piggy-backing of sequence acknowledgements on application messages. Therefore, constraints R1104, R1105, and R1108 apply to WCF.

An example of a CreateSequence message.

<s:Envelope>
  <s:Header>
    <a:Action s:mustUnderstand="1">
      http://schemas.xmlsoap.org/ws/2005/02/rm/CreateSequence
    </a:Action>
    <a:ReplyTo>
      <a:Address>
         http://Business456.com/clientA
      </a:Address>
    </a:ReplyTo>
    <a:MessageID>
      urn:uuid:addabbbf-60cb-44d3-8c5b-9e0841629a36
    </a:MessageID>
    <a:To s:mustUnderstand="1">
      http://Business456.com/clientA
    </a:To>
  </s:Header>
  <s:Body>
    <wsrm:CreateSequence>
      <wsrm:AcksTo>
       <wsa:Address>
         http://Business456.com/clientA
       </wsa:Address>
     </wsrm:AcksTo>
     <wsrm:Offer>
      <wsrm:Identifier>
        urn:uuid:0afb8d36-bf26-4776-b8cf-8c91fddb5496
      </wsrm:Identifier>
     </wsrm:Offer>
   </wsrm:CreateSequence>
  </s:Body>
</s:Envelope>

An example of a CreateSequenceResponse message.

<s:Envelope>
  <s:Header>
    <a:Action s:mustUnderstand="1">
      http://schemas.xmlsoap.org/ws/2005/02/rm/CreateSequenceResponse
    </a:Action>
    <a:RelatesTo>
      urn:uuid:addabbbf-60cb-44d3-8c5b-9e0841629a36
    </a:RelatesTo>
    <a:To s:mustUnderstand="1">
      http://Business456.com/clientA
    </a:To>
  </s:Header>
  <s:Body>
   <wsrm:CreateSequenceResponse>
    <Identifier>
     urn:uuid:eea0a36c-b38a-43e8-8c76-2fabe2d76386
    </Identifier>
    <Accept>
    <AcksTo>
      <a:Address>
        http://BusinessABC.com/serviceA
      </a:Address>
    </AcksTo>
    </Accept>
   </wsrm:CreateSequenceResponse>
  </s:Body>
</s:Envelope>

Sequence

The following is a list of constraints that apply to sequences:

  • B1201:WCF generates and accesses sequence numbers no higher than xs:long’s maximum inclusive value, 9223372036854775807.

  • B1202:WCF always generates an empty-bodied last message with the action URI of http://schemas.xmlsoap.org/ws/2005/02/rm/LastMessage.

  • B1203: WCF receives and delivers a message with a Sequence header that contains a LastMessage element as long as the action URI is not http://schemas.xmlsoap.org/ws/2005/02/rm/LastMessage.

An example of a Sequence Header.

<wsrm:Sequence>
  <wsrm:Identifier>
    urn:uuid:addabbbf-60cb-44d3-8c5b-9e0841629a36
  </wsrm:Identifier>
  <wsrm:MessageNumber>
    10
  </wsrm:MessageNumber>
  <wsrm:LastMessage/>
 </wsrm:Sequence>

AckRequested Header

WCF uses AckRequested Header as a keep-alive mechanism. WCF does not generate the optional MessageNumber element. Upon receiving a message with an AckRequested header that contains the MessageNumber element, WCF ignores the MessageNumber element’s value, as shown in the following example.

<wsrm:AckRequested>
  <wsrm:Identifier>
    urn:uuid:addabbbf-60cb-44d3-8c5b-9e0841629a36
  </wsrm:Identifier>
</wsrm:AckRequested>

SequenceAcknowledgement Header

WCF uses piggy-back mechanism for sequence acknowledgements provided in WS-Reliable Messaging.

  • R1401: When two converse sequences are established using the Offer mechanism, the SequenceAcknowledgement header may be included in any application message transmitted to the intended recipient.

  • B1402: When WCF must generate an acknowledgement prior to receiving any sequence messages (for example, to satisfy an AckRequested message), WCF generates a SequenceAcknowledgement header that contains the range 0-0, as shown in the following example.

    <wsrm:SequenceAcknowledgement>
  <wsrm:Identifier>
    urn:uuid:addabbbf-60cb-44d3-8c5b-9e0841629a36
  </wsrm:Identifier>
  <wsrm:AcknowledgementRange Upper="0" Lower="0"/>
</wsrm:SequenceAcknowledgement>

  • B1403: WCF does not generate SequenceAcknowledgement headers that contain a Nack element but supports Nack elements.

WS-ReliableMessaging Faults

The following is a list of constraints that apply to the WCF implementation of WS-Reliable Messaging faults:

  • B1501: WCF does not generate MessageNumberRollover faults.

  • B1502:WCF endpoint may generate CreateSequenceRefused faults as described in the specification.

  • B1503:When the service endpoint reaches its connection limit and cannot process new connections, WCF generates an additional CreateSequenceRefused fault subcode, netrm:ConnectionLimitReached, as shown in the following example.

    <s:Envelope>
  <s:Header>
    <wsa:Action>
      http://schemas.xmlsoap.org/ws/2005/08/addressing/fault
    </wsa:Action>
  </s:Header>
  <s:Body>
    <s:Fault>
      <s:Code>
        <s:Value>
          s:Receiver
        </s:Value>
        <s:Subcode>
          <s:Value>
            wsrm:CreateSequenceRefused
          </s:Value>
          <s:Subcode>
            <s:Value>
              netrm:ConnectionLimitReached
            </s:Value>
          </s:Subcode>
        </s:Subcode>
      </s:Code>
      <s:Reason>
        <s:Text xml:lang="en">
          [Reason]
        </s:Text>
      </s:Reason>
    </s:Fault>
  </s:Body>
</s:Envelope>

WS-Addressing Faults

Because WS-Reliable Messaging uses WS-Addressing, WCF WS-Reliable Messaging implementation may generate WS-Addressing faults. This section covers the WS-Addressing faults that WCF explicitly generates at the WS-Reliable Messaging layer:

  • B1601:WCF generates the fault Message Addressing Header Required when one of the following is true:

    • A message is missing a Sequence header and an Action header.

    • A CreateSequence message is missing a MessageId header.

    • A CreateSequence message is missing a ReplyTo header.

  • B1602:WCF generates the fault Action Not Supported in reply to a message that is missing a Sequence header and has an Action header that is not a recognized in the WS-Reliable Messaging specification.

  • B1603:WCF generates the fault Endpoint Unavailable to indicate that the endpoint does not process the sequence based upon examination of the CreateSequence message’s addressing headers.

Protocol Composition

Composition with WS-Addressing

WCF supports two versions of WS-Addressing: WS-Addressing 2004/08 [WS-ADDR] and W3C WS-Addressing 1.0 Recommendations [WS-ADDR-CORE] and [WS-ADDR-SOAP].

While the WS-Reliable Messaging specification mentions only WS-Addressing 2004/08, it does not restrict the WS-Addressing version to be used. The following is a list of constraints that apply to WCF:

  • R2101:Both WS-Addressing 2004/08 and WS-Addressing 1.0 can be used with WS-Reliable Messaging.

  • R2102:A single version of WS-Addressing must be used throughout a given WS-Reliable Messaging sequence or a pair of converse sequences correlated by using the wsrm:Offer mechanism.

Composition with SOAP

WCF supports use of both SOAP 1.1 and SOAP 1.2 with WS-Reliable Messaging.

Composition with WS-Security and WS-SecureConversation

WCF provides protection for WS-Reliable Messaging sequences by using secure Transport (HTTPS), composition with WS-Security, and composition with WS-Secure Conversation. The following is a list of constraints that apply to WCF:

  • R2301:To protect the integrity of a WS-Reliable Messaging sequence in addition to the integrity and confidentiality of individual messages, WCF requires that WS-Secure Conversation must be used.

  • R2302:AWS-Secure Conversation session must be established prior to establishing WS-Reliable Messaging sequence(s).

  • R2303: If the WS-Reliable Messaging sequence lifetime exceeds the WS-Secure Conversation session’s lifetime, the SecurityContextToken established by using WS-Secure Conversation must be renewed by using the corresponding WS-Secure Conversation Renewal binding.

  • B2304:WS-Reliable Messaging sequence or a pair of correlated converse sequences are always bound to a single WS-SecureConversation session.

    The WCF source generates the wsse:SecurityTokenReference element in the element extensibility section of the CreateSequence message.

  • R2305:When composed with WS-Secure Conversation, a CreateSequence message must contain the wsse:SecurityTokenReference element.

WS-Reliable Messaging WS-Policy Assertion

WCF uses WS-Reliable Messaging WS-Policy Assertion wsrm:RMAssertion to describe endpoints capabilities. The following is a list of constraints that apply to WCF:

  • B3001: WCF attaches wsrm:RMAssertion WS-Policy Assertion to wsdl:binding elements. WCF supports both attachments to wsdl:binding and wsdl:port elements.

  • B3002: WCF supports the following optional properties of WS-Reliable Messaging assertion and provides control over them on the WCFReliableMessagingBindingElement:

    • wsrm:InactivityTimeout

    • wsrm:AcknowledgementInterval

    The following is an example.

    <wsrm:RMAssertion>
  <wsrm:InactivityTimeout Milliseconds="600000" />
  <wsrm:AcknowledgementInterval Milliseconds="200" />
</wsrm:RMAssertion>

Flow Control WS-Reliable Messaging Extension

WCF uses WS-Reliable Messaging extensibility to provide optional additional tighter control over sequence message flow.

Flow control is enabled by setting the ReliableSessionBindingElement.FlowControlEnabled property to true. The following is a list of constraints that apply to WCF:

  • B4001: When Reliable Messaging Flow Control is enabled, WCF generates a netrm:BufferRemaining element in the element extensibility of the SequenceAcknowledgement header.

  • B4002: When Reliable Messaging Flow Control is enabled, WCF does not require a netrm:BufferRemaining element to be present in SequenceAcknowledgement header, as shown in the following example.

    <wsrm:SequenceAcknowledgement>
  <wsrm:Identifier>
    http://fabrikam123.com/abc
  </wsrm:Identifier>
  <wsrm:AcknowledgementRange Upper="1" Lower="1"/>
  <netrm:BufferRemaining>
    8
  </netrm:BufferRemaining>
</wsrm:SequenceAcknowledgement>

  • B4003: WCF uses netrm:BufferRemaining to indicate how many new messages the Reliable Messaging Destination can buffer.

  • B4004:The WCF Reliable Messaging Service throttles the number of messages transmitted when the Reliable Messaging destination application cannot receive messages quickly. The Reliable Messaging destination buffers messages and the element’s value drops to 0.

  • B4005: WCF generates netrm:BufferRemaining integer values between 0 and 4096 inclusive, and reads integer values between 0 and xs:int’s maxInclusive value 214748364 inclusive.

Message Exchange Patterns

This section describes WCF's behavior when WS-Reliable Messaging is used for different Message Exchange Patterns. For each Message Exchange Pattern the following two deployments scenarios are considered:

  • Non-Addressable Initiator: Initiator is behind firewall; Responder can deliver messages to Initiator only on HTTP responses.

  • Addressable Initiator: Initiator and Responder both can be sent HTTP requests; in other words, two converse HTTP connections can be established.

One-way, Non-addressable Initiator

Binding

WCF provides a one-way message exchange pattern using one sequence over one HTTP channel. WCF uses the HTTP requests to transmit all messages from the RMS to the RMD and the HTTP response to transmit all messages from the RMD to the RMS.

CreateSequence Exchange

The WCF Initiator generates a CreateSequence message with no offer. The WCF Responder ensures the CreateSequence has no offer before creating a sequence. The WCF Responder replies to the CreateSequence request with a CreateSequenceResponse message.

SequenceAcknowledgement

The WCF Initiator processes acknowledgements on the reply of all messages except the CreateSequence message and fault messages. The WCF Responder always generates a stand-alone acknowledgement in the response to both sequence and AckRequested messages.

TerminateSequence message

WCF treats TerminateSequence as a one-way operation, meaning the HTTP response has an empty body and HTTP 202 status code.

One Way, Addressable Initiator

Binding

WCF provides a one-way message exchange pattern using one sequence over an inbound and an outbound Http channel. WCF uses the HTTP requests to transmit all messages. All HTTP responses have an empty body and HTTP 202 status code.

CreateSequence Exchange

The WCF Initiator generates a CreateSequence message with no offer. The WCF Responder ensures that the CreateSequence has no offer before creating a sequence. The WCF Responder transmits the CreateSequenceResponse message on an HTTP request addressed with the ReplyTo endpoint reference.

Duplex, Addressable Initiator

Binding

WCF provides a fully asynchronous two-way message exchange pattern using two sequences over an inbound and an outbound HTTP channel. WCF uses the HTTP requests to transmit all messages. All HTTP responses have an empty body and HTTP 202 status code.

CreateSequence Exchange

The WCF Initiator generates a CreateSequence message with an offer. The WCF Responder ensures that the CreateSequence has an offer before creating a sequence. WCF sends the CreateSequenceResponse on the HTTP request addressed to the CreateSequence’s ReplyTo endpoint reference.

Sequence Lifetime

WCF treats the two sequences as one fully duplex session.

Upon generating a fault that faults one sequence, WCF expects the remote endpoint to fault both sequences. Upon reading a fault that faults one sequence, WCF faults both sequences.

WCF can close its outbound sequence and continue to process messages on its inbound sequence. Conversely, WCF can process the close of the inbound sequence and continue to send messages on its outbound sequence.

Request-Reply, Non-Addressable Initiator

Binding

WCF provides a one-way and request-reply message exchange pattern using two sequences over one HTTP channel. WCF uses the HTTP requests to transmit the request sequence’s messages and uses the HTTP responses to transmit the reply sequence’s messages.

CreateSequence Exchange

The WCF Initiator generates a CreateSequence message with an offer. The WCF Responder ensures that the CreateSequence has an offer before creating a sequence. The WCF Responder replies to the CreateSequence request with a CreateSequenceResponse message.

One-way Message

To complete a one-way message exchange protocol successfully, the WCF Initiator transmits a request sequence message on the HTTP request and receives a standalone SequenceAcknowledgement message on the HTTP response. The SequenceAcknowledgement must acknowledge the message transmitted.

The WCF Responder can reply to the request with an acknowledgement, a fault, or a response with an empty body and HTTP 202 status code.

Two Way Messages

To complete a two way message exchange protocol successfully, the WCF Initiator transmits a request sequence message on the HTTP request and receives a reply sequence message on the HTTP response. The response must carry a SequenceAcknowledgement acknowledging the request sequence message transmitted.

The WCF Responder can reply to the request with an application reply, a fault or a response with an empty body and HTTP 202 status code.

Because of the presence of one-way messages and the timing of application replies, the request sequence message’s sequence number and the response message’s sequence number have no correlation.

Retrying Replies

WCF relies on HTTP request-reply correlation for two-way message exchange protocol correlation. Because of this, the WCF Initiator does not stop retrying a request sequence message when the request sequence message is acknowledged but rather when the HTTP response carries an acknowledgement, user message, or fault. The WCF Responder retries replies on the HTTP request leg of the request to which the reply is correlated.

LastMessage Exchange

The WCF Initiator generates and transmits an empty bodied last message on the HTTP request leg. WCF requires a response but ignores the actual response message. The WCF Responder replies to the request sequence’s empty-bodied last message with the reply sequence’s empty-bodied last message.

If the WCF Responder receives a last message in which the action URI is not http://schemas.xmlsoap.org/ws/2005/02/rm/LastMessage, WCF replies with a last message. In the case of a two-way message exchange protocol, the last message carries the application message; in the case of a one-way message exchange protocol, the last message is empty.

The WCF Responder does not require an acknowledgement for the reply sequence’s empty-bodied last message.

TerminateSequence Exchange

When all requests have received a valid reply, the WCF Initiator generates and transmits the request sequence’s TerminateSequence message on the HTTP request leg. WCF requires a response but ignores the actual response message. The WCF Responder replies to the request sequence’s TerminateSequence message with the reply sequence’s TerminateSequence message.

In a normal shutdown sequence, both TerminateSequence messages carry a full range SequenceAcknowledgement.

Request/Reply, Addressable Initiator

Binding

WCF provides a request-reply message exchange pattern using two sequences over an inbound and an outbound HTTP channel. WCF uses the HTTP requests to transmit all messages. All HTTP responses have an empty body and HTTP 202 status code.

CreateSequence Exchange

The WCF Initiator generates a CreateSequence message with an offer. The WCF Responder ensures that the CreateSequence has an offer before creating a sequence. WCF sends the CreateSequenceResponse on the HTTP request addressed to the CreateSequence’s ReplyTo endpoint reference.

Request/Reply Correlation

The WCF Initiator ensures all application request messages bear a MessageId and a ReplyTo endpoint reference. The WCF Initiator applies the CreateSequence message’s ReplyTo endpoint reference on each application request message. The WCF Responder requires that incoming request messages bear a MessageId and a ReplyTo. The WCF Responder ensures that the endpoint reference’s URI of both the CreateSequence and all application request messages are identical.