RTI Connext Modern C++ API  Version 6.1.1
rti::core::policy::MultiChannel Class Reference

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

#include <rti/core/policy/CorePolicy.hpp>

Public Member Functions

 MultiChannel ()
 Creates the default policy. More...
 
 MultiChannel (const rti::core::ChannelSettingsSeq &the_channels, const std::string &the_filter_name=rti::topic::stringmatch_filter_name())
 Creates an instance with the specified channels and filter name. More...
 
MultiChannelchannels (const rti::core::ChannelSettingsSeq &the_channels)
 A sequence of rti::core::ChannelSettings used to configure the channels' properties. If the length of the sequence is zero, the QoS policy will be ignored. More...
 
rti::core::ChannelSettingsSeq channels () const
 Getter (see the setter with the same name) More...
 
MultiChannelfilter_name (const std::string &the_filter_name)
 Name of the filter class used to describe the filter expressions of a MultiChannel DataWriter. More...
 
std::string filter_name () const
 Getter (see the setter with the same name) More...
 

Detailed Description

<<extension>> 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 dds::pub::DataWriter across multiple channels. A channel is defined by a filter expression and a sequence of multicast locators.

Entity:
dds::pub::DataWriter
Properties:
RxO = N/A
Changeable = NO

Usage

By using this QoS, a dds::pub::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 dds::pub::DataWriter::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.

Constructor & Destructor Documentation

◆ MultiChannel() [1/2]

rti::core::policy::MultiChannel::MultiChannel ( )
inline

Creates the default policy.

◆ MultiChannel() [2/2]

rti::core::policy::MultiChannel::MultiChannel ( const rti::core::ChannelSettingsSeq the_channels,
const std::string &  the_filter_name = rti::topic::stringmatch_filter_name() 
)
inline

Creates an instance with the specified channels and filter name.

Member Function Documentation

◆ channels() [1/2]

MultiChannel& rti::core::policy::MultiChannel::channels ( const rti::core::ChannelSettingsSeq the_channels)

A sequence of rti::core::ChannelSettings 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 rti::core::policy::MultiChannel is not in use.

The sequence length cannot be greater than rti::core::policy::DomainParticipantResourceLimits::channel_seq_max_length.

[default] Empty sequence.

◆ channels() [2/2]

rti::core::ChannelSettingsSeq rti::core::policy::MultiChannel::channels ( ) const

Getter (see the setter with the same name)

◆ filter_name() [1/2]

MultiChannel& rti::core::policy::MultiChannel::filter_name ( const std::string &  the_filter_name)

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

The following builtin filters are supported:

[default] rti::topic::stringmatch_filter_name

◆ filter_name() [2/2]

std::string rti::core::policy::MultiChannel::filter_name ( ) const

Getter (see the setter with the same name)