3.2.4 Message Processing Events and Sequencing Rules

The DSS MUST perform the following sequential steps (phases) every time it synchronizes with the USS:

1. Authorization

   The DSS provides credentials to the USS to obtain a Cookie from the USS during this step.

2. Metadata Synchronization

   The DSS uses the Cookie from the Authorization phase and gets information about new updates from the USS during this step.

3. Deployments Synchronization

   This step is applicable only if the DSS is configured as a replica server. The DSS gets the list of target groups and deployments from the USS during this step.

4. Content Synchronization

   The DSS downloads the content files associated with the updates from the USS during this step. This is performed asynchronously. This step is applicable only if the CatalogOnlySync flag in the Server Configuration for this DSS is set to FALSE.

5. Reporting Data Synchronization

   During this step, the DSS sends (to the USS) information on the update servers that synchronize from it and on the client computers that get updates from it.

   This step is performed only if both the USS and DSS support version 1.3 or higher of the protocol.

The following sequence diagram shows the details of the message exchange. The content download step is carried out asynchronously. For simplicity, it is shown in sequence.

Figure 3: Message exchange

If the DSS receives a SOAP fault in response to a web service (2) call, it MUST attempt to parse the SOAP fault using the format specified in section 2.2.9, and then extract the ErrorCode value. If an ErrorCode value is available, the DSS MUST react to the error, as specified in section 2.2.9.3. If no ErrorCode value is available, the DSS MUST stop the protocol.

The following table summarizes the WSDL operations as defined by this specification.

Operation	Description
Authorization	Provides credentials to the USS.
Metadata Synchronization	Synchronizes metadata.
Deployments Synchronization	Synchronizes deployments for replica servers.
Content Synchronization	Synchronizes content.
Reporting Data Synchronization	Synchronizes reporting data.