WebSphere brand IBM WebSphere Premises Server, Version 6.1.x

What is QoS?

QoS stands for Quality of Service. It consists of several parameters that control message communication behavior between the Data Capture and Delivery controller and WebSphere® Premises Server.

QoS for messages from the Data Capture and Delivery controller

The default configuration for the Data Capture and Delivery controller is QoS level: QOS 1 and QoS persistence: memory only. This means that messages, including tag reads, are assured to flow from the Data Capture and Delivery controller to WebSphere Premises Server, except when the Data Capture and Delivery controller has been turned off, the Data Transformation has been stopped during network outages, or WebSphere Premises Server is down.

Reasons for these default settings:

Tag reads eventually flow to the back end, as long as the Data Capture and Delivery controller is not rebooted or restarted, regardless of network communications between the Data Capture and Delivery controller and WebSphere Premises Server. Tags cannot be read or queued at all when the network between the tag reader and the Data Capture and Delivery controller is down because there is no quality of service supported by the tag reader protocols.

QoS levels

At the Data Capture and Delivery controller, there are three QoS levels at which messages can be configured to be delivered from the Data Capture and Delivery controller to WebSphere Premises Server:

QOS 0
Messages are delivered at most once. If there is a disruption in the network or on the Data Capture and Delivery controller software, the message may not be delivered.
QOS 1
Messages are delivered at least once. It is possible that a message could be delivered more than once, but they are always delivered at least once.
QOS 2
Messages are delivered once and only once.

QoS persistence

Persistence is configured through the persistence property key in the MicroBroker agent. The values for the persistence property align with the QoS levels 0, 1, and 2.

There are two ways to configure persistence on the Data Capture and Delivery controller:

Memory only
Messages are stored in memory until they can be delivered at the above quality of service.
File Persistence
Messages are persisted in a file until they can be delivered at the above quality of service. The file is saved only when there is a clean "shutdown" of the Data Transformation service.

Setting the QoS level

The configurations for each individual agent are set in the Data Capture and Delivery configuration XML file, which is generated from the agent settings in the WebSphere Premises Server database. Use the WebSphere Premises Server Administrative Console to modify the QoS values. The qos value defines what QoS level a particular agent will use for publication. For example:
<property key="qos" value="1" required="false" default="1" name="QoS" 
description="Messaging Quality of Service: 0-at most once, 1-at least once, 
2-exactly once."/>
In addition, a qos.cutoff value can be set that is specific to the Alert agent. This value sets the lowest alert level that will be published for QoS. Any level that is below the value specified for qos.cutoff publishes at qos=0. For example:
<property key="qos.cutoff" value="warning" default="warning" name="QoS Threshold Cutoff" 
description="Lowest threshold level before assuming QoS=0. Threshold levels that are equal 
to or higher than this value will be published at the agent-defined QOS level."/>
Since the value is set to warning, all alerts of level warning and above (for example, warning and error alerts) will be published at the QoS level defined for the alert agent. Levels below warning (for example, info and debug alerts) will be published at the qos=0 level.

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