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9.3. Meeting STAR Guidelines Requirements
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## 9.3. Meeting STAR Guidelines Requirements

The STAR Transport Guidelines establish the overall requirements for Reliable Messaging. To meet these requirements and to ensure that the terminology that is applied correctly maps to comparable Web Services features, follow the specifications below.

### 9.3.1. Message Assurance Profiles

Best-Effort

To enable Best-Effort, a message is sent without using any of the WS-ReliableMessaging features:

- Parties have no WS-Policies related to reliable messaging for the messages

- No WS-ReliableMessaging headers are present in the messages

- Only applies to messages without reliability requirements

Best-Effort is the implementation supported by the STAR Level 1 interoperability rules. A STAR Level 2 implementation must support STAR Level 1.

At-Least-Once

To enable At-Least-Once with WS-ReliableMessaging:

- Reliable messaging requirements SHOULD be specified with WS-Policy on the message.

| STAR Level 2 Requirement
STAR 2003: "At-Least-Once" requires the sending party to uniquely identify a message and the receiving party to acknowledge the receipt of the message, giving the sender an auditable record stating that the message has been received. If the sender does not receive an acknowledgment of receipt in a reasonable amount of time (Time-Out), it MUST retry the message send.

At-Most-Once

To enable At-Most-Once with WS-Reliable Messaging

- Reliable messaging requirements SHOULD be specified with WS-Policy.

- A durable policy store is required, in memory storage is not sufficient for detecting duplicate messages.

| STAR Level 2 Requirement
STAR 2005: "At-Most-Once" requires a sending party to uniquely identify messages, to retry failed messages and requires the receiving party to identify and ignore any duplicate messages. In order to know which messages to ignore, it is REQUIRED that the receiving party persist received messages in a durable store.

Once-And-Only-Once / Exactly Once

To enable Once-And-Only-Once / Exactly Once with WS-Reliable Messaging

- Reliable messaging requirements should be specified with WS-Policy.

- A durable policy store is required, in memory storage is not sufficient for detecting duplicate messages.

| STAR Level 2 Requirement
STAR 2006: "Once-And-Only-Once / Exactly-Once" requires the sender to uniquely identify each message and to retry any message that the receiver fails to acknowledge. The receiver must acknowledge receipt of messages and ignore duplicate messages. It is REQUIRED that the receiver persist messages in a durable store to enable duplicate elimination.

### 9.3.2. WS-ReliableMessaging Delivery Assurance Features

Message Routing

Message Routing in WS-ReliableMessaging is accomplished through a combination of the underlying Transfer protocol and WS-Addressing data elements in the messages themselves. Full behavior is detailed under the WS-Addressing section.

| Note
Message Routing Most WS-ReliableMessaging v1.1 frameworks have configuration options on how message routing should be handled. In some cases they may also use the WS-MakeConnection specification to handle those situations where an end-point is not always addressable.

| STAR Level 2 Requirement
STAR 2007: For indicating Routing information, STAR requires the use of WS-Addressing or WS-MakeConnection if the end point is not directly addressable.

Acknowledgment of Receipt

Receipt of an acknowledgment indicates that an original message reached its destination. In other words, an acknowledgment signifies only that a message has been received securely and intact, it is not a business level acknowledgment.

| STAR Level 2 Requirement
STAR 2008: Acknowledgement of Receipts MUST be enabled during the use of At-Most-Once and Once and Only Once reliability.

WS-ReliableMessaging clearly defines the format and content of Acknowledgment messages. Acknowledgment messages may be stand-alone messages or could be returned as part of another message.

A WS-ReliableMessaging SequenceAcknowledgment is an acknowledgment of receipt of one or more messages associated with a unique sequence. The message contains the exact Sequence Identifier as sent in the original messages and one or more AcknowledgmentRange elements, which specify exactly which messages, by range of MessageNumbers, have been received.

| STAR Level 2 Requirement
STAR 2009: STAR requires that the messages be sequenced to ensure proper delivery and processing of related messages.

### 9.3.3. WS-ReliableMessaging Message Integrity

Content Integrity

WS-ReliableMessaging strongly recommends that messages by secured by WS-Security, specifically that Content Integrity be validate by applying a digital signature to messages. Full behavior is detailed in the Security Section. STAR Level 2 implementations must use Certificate based security when using WS-Reliable Messaging.

TimeToLive

WS-ReliableMessaging implements TimeToLive like functionality via the Sequence Expiration policy assertion or the wsu:expires element on the sequence. This is detailed under the WS-Reliable Messaging specification.

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