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4.3. Discussions
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## 4.3. Discussions

While both ebMS and WS-ReliableMessaging support the STAR Delivery Assurance profiles, there are some significant differences in approach.

The key differences are the approach to Message Sequencing and whether message receipt is confirmed per message or per a sequence of messages.

### 4.3.1. Message Sequencing

ebMS views sequencing as an optional feature, separate and distinct from ReliableMessaging, while WS-ReliableMessaging requires the sequencing of messages. ebMS uses sequencing to order messages. An ebMS sender expects that the first message will be processed before the second message. WS-ReliableMessaging uses sequencing generally to enable performance management of the flow control of messages that carry reliability artifacts such as Acknowledgments.

### 4.3.2. Per Message or Per Sequence

ebMS guarantees delivery of individual messages. WS-ReliableMessaging guarantees delivery of a group of messages based on their common SequenceIdentifier. A WS-ReliableMessaging Acknowledgment gives you information about one or more messages that were sent as a sequence.

### 4.3.3. WS-Policy Framework

To implement ReliableMessaging, parties MUST make out-of-band agreements on many parameters including which Delivery Assurance Profile is in use.

The WS-Policy framework is the stated direction for establishing agreements between parties for Reliable Messaging using STAR Web Services Guideline. WS-Policy and related specifications are relatively new and best practices are probably yet to emerge using these capabilities. Some of the capabilities are detailed below under “WS-ReliableMessaging Implementation”, but STAR anticipates that parties may use implementation specific or manual out-of-band agreements for the time being, and future releases of these guidelines will leverage industry experience to clarify best practices around Policy.

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