MultiChannelQosPolicy Class Reference

Configures the ability of a DataWriter to send data on different multicast groups (addresses) based on the value of the data. More...

Inheritance diagram for MultiChannelQosPolicy:

Public Attributes
final ChannelSettingsSeq	channels
	A sequence of com.rti.dds.infrastructure.ChannelSettings_t used to configure the channels' properties. If the length of the sequence is zero, the QoS policy will be ignored.
String	filter_name
	Name of the filter class used to describe the filter expressions of a MultiChannel DataWriter.
Public Attributes inherited from QosPolicy
final QosPolicyId_t	id
	The ID of this QoS policy.
final String	policy_name
	The name of this QoS policy.

Additional Inherited Members
Public Member Functions inherited from Struct
abstract boolean	equals (Object obj)
abstract int	hashCode ()
String	toString ()
Protected Member Functions inherited from Struct
	Struct ()
abstract void	pull_from_nativeI (long native_status)
abstract void	push_to_nativeI (long native_status)

Detailed Description

Configures the ability of a DataWriter to send data on different multicast groups (addresses) based on the value of the data.

This QoS policy is used to partition the data published by a com.rti.dds.publication.DataWriter across multiple channels. A channel is defined by a filter expression and a sequence of multicast locators.

Entity:

com.rti.dds.publication.DataWriter

Properties:

RxO = N/A
Changeable = NO

Usage

By using this QoS, a com.rti.dds.publication.DataWriter can be configured to send data to different multicast groups based on the content of the data. Using syntax similar to those used in Content-Based Filters, you can associate different multicast addresses with filter expressions that operate on the values of the fields within the data. When your application's code calls com.rti.ndds.example.FooDataWriter.write, data is sent to any multicast address for which the data passes the filter.

Multi-channel DataWriters can be used to trade off network bandwidth with the unnecessary processing of unwanted data for situations where there are multiple DataReaders that are interested in different subsets of data that come from the same data stream (Topic). For example, in Financial applications, the data stream may be quotes for different stocks at an exchange. Applications usually only want to receive data (quotes) for only a subset of the stocks being traded. In tracking applications, a data stream may carry information on hundreds or thousands of objects being tracked, but again, applications may only be interested in a subset.

The problem is that the most efficient way to deliver data to multiple applications is to use multicast, so that a data value is only sent once on the network for any number of subscribers to the data. However, using multicast, an application will receive all of the data sent and not just the data in which it is interested, thus extra CPU time is wasted to throw away unwanted data. With this QoS, you can analyze the data-usage patterns of your applications and optimize network vs. CPU usage by partitioning the data into multiple multicast streams. While network bandwidth is still being conserved by sending data only once using multicast, most applications will only need to listen to a subset of the multicast addresses and receive a reduced amount of unwanted data.

Your system can gain more of the benefits of using multiple multicast groups if your network uses Layer 2 Ethernet switches. Layer 2 switches can be configured to only route multicast packets to those ports that have added membership to specific multicast groups. Using those switches will ensure that only the multicast packets used by applications on a node are routed to the node; all others are filtered-out by the switch.

Member Data Documentation

final ChannelSettingsSeq channels

A sequence of com.rti.dds.infrastructure.ChannelSettings_t used to configure the channels' properties. If the length of the sequence is zero, the QoS policy will be ignored.

A sequence length of zero indicates the com.rti.dds.infrastructure.MultiChannelQosPolicy is not in use.

The sequence length cannot be greater than com.rti.dds.infrastructure.DomainParticipantResourceLimitsQosPolicy.channel_seq_max_length.

[default] Empty sequence.

String filter_name

Name of the filter class used to describe the filter expressions of a MultiChannel DataWriter.

The following builtin filters are supported: com.rti.dds.domain.DomainParticipant.SQLFILTER_NAME and com.rti.dds.domain.DomainParticipant.STRINGMATCHFILTER_NAME.

[default] com.rti.dds.domain.DomainParticipant.STRINGMATCHFILTER_NAME