EMA consultant

Hi Team,

one of client raised bellow questions about EMA, pls help answer. thx

通信机制：

1、如果ChannelType选择 RSSL_SOCKET：

Channel中CompressionType配置项的作用是什么？推荐怎么配置？
Channel中DirectWrite配置项推荐怎么配置？
Channel中TcpNodelay配置项推荐怎么配置？

2、从文档和例子中看，<Host>标签并没有配置多个地址，且<Host>标签和<Port>是配合使用的，那么如果配置两个ADS的IP，是这种方式 “ <ChannelSet value="Channel_1, Channel_2"/> ”，还是这种方式 “ <Host value="localhost1, localhost2"/> ”

通信流程：

1、Domain Model中Market Price Request 和 Batch Request / Snapshot Request 它们都是属于行情请求，之间有什么关系吗？每种请求都可以单独发送/接收吗？

2、根据行情请求的特性，是否可以这样理解：

Streaming Requests：一次请求，订阅一个RIC，持续推送
Snapshot Request：一次请求，订阅一个RIC，一次反馈
Batch Request：一次请求，订阅一批RIC，持续推送
Views：一次请求，订阅一个RIC中某几个字段域，持续推送

3、消费者向外部发送消息时一般会用到 ReqMsg / PostMsg / GenericMsg 三种消息类型，这三种消息有什么区别？

4、Private Streams 和 Streaming Request / Snapshot Request 是什么关系？发出的请求可以设置是否是私有流吗？

5、privateStream的默认值是false吗？

6、Private Streams / Tunnel Streams 是什么关系？什么场景下需要开启 Private Streams / Tunnel Streams ？

Gang Chen

Find more posts tagged with

ema-api

Accepted answers

wasin.w

Hello @gang.chen1

I have translated the question using Goole translate, but I am not sure if it is correct.

Question 1: What is the function of the CompressionType configuration item in Channel? What is the recommended configuration?

How to configure the DirectWrite configuration item in Channel?

What is the recommended configuration for the TcpNodelay configuration item in the Channel?

Answer:

The CompressionType configuration is for setting a message compression between the API and server. The supported values are as follows:

None (Default)
ZLib
LZ4

The compression type and compression level must be supported on the server side too. I highly recommend the client contact their Market Data team to verify their RTDS server configurations.

About the "DirectWrite" and "TcpNodelay" recommendations, there is no golden number suggestion. I recommend the client test each setting value to find the one that matches their requirements.

Question 2: From the documentation and examples, the <Host> tag is not configured with multiple addresses, and the <Host> tag and <Port> are used together, then if the IPs of two ADSs are configured, this is the way" <ChannelSet value="Channel_1, Channel_2"/> ", or this way " <Host value="localhost1, localhost2"/> "

Answer: The client can set multiple hosts/IPs with the ChannelSet configuration.

Host 1 in Channel_1
Host 2 in Channel_2
Then set Consumer's ChannelSet to Channel_1 and Channel_2

Example:

<ConsumerGroup>
    <ConsumerList>
        <Consumer>
            <Name value="Consumer_2"/>
            <!-- ChannelSet specifies an ordered list of Channels to which OmmConsumer will attempt to -->
            <!-- connect, one at a time, if the previous one fails to connect -->
            <ChannelSet value="Channel_1, Channel_2"/>
            <Dictionary value="Dictionary_2"/>
            <XmlTraceToStdout value="0"/>
        </Consumer>
    </ConsumerList>
</ConsumerGroup>
...
<ChannelGroup>
    <ChannelList>
        <Channel>
            <Name value="Channel_1"/>        
            <ChannelType value="ChannelType::RSSL_SOCKET"/>
            <CompressionType value="CompressionType::None"/>
            <GuaranteedOutputBuffers value="5000"/>
            <TcpNodelay value="1"/>
            <Host value="localhost1"/>
            <Port value="14002"/>
        </Channel>
        <Channel>
            <Name value="Channel_2"/>
            <ChannelType value="ChannelType::RSSL_SOCKET"/>
            <CompressionType value="CompressionType::None"/>
            <GuaranteedOutputBuffers value="5000"/>
            <TcpNodelay value="1"/>
            <Host value="localhost2"/>
            <Port value="14002"/>
        </Channel>
    </ChannelList>
</ChannelGroup>

All comments

wasin.w

Hello @gang.chen1

I have translated the question using Goole translate, but I am not sure if it is correct.

Question 1: What is the function of the CompressionType configuration item in Channel? What is the recommended configuration?

How to configure the DirectWrite configuration item in Channel?

What is the recommended configuration for the TcpNodelay configuration item in the Channel?

Answer:

The CompressionType configuration is for setting a message compression between the API and server. The supported values are as follows:

None (Default)
ZLib
LZ4

The compression type and compression level must be supported on the server side too. I highly recommend the client contact their Market Data team to verify their RTDS server configurations.

About the "DirectWrite" and "TcpNodelay" recommendations, there is no golden number suggestion. I recommend the client test each setting value to find the one that matches their requirements.

Answer: The client can set multiple hosts/IPs with the ChannelSet configuration.

Host 1 in Channel_1
Host 2 in Channel_2
Then set Consumer's ChannelSet to Channel_1 and Channel_2

Example:

<ConsumerGroup>
    <ConsumerList>
        <Consumer>
            <Name value="Consumer_2"/>
            <!-- ChannelSet specifies an ordered list of Channels to which OmmConsumer will attempt to -->
            <!-- connect, one at a time, if the previous one fails to connect -->
            <ChannelSet value="Channel_1, Channel_2"/>
            <Dictionary value="Dictionary_2"/>
            <XmlTraceToStdout value="0"/>
        </Consumer>
    </ConsumerList>
</ConsumerGroup>
...
<ChannelGroup>
    <ChannelList>
        <Channel>
            <Name value="Channel_1"/>        
            <ChannelType value="ChannelType::RSSL_SOCKET"/>
            <CompressionType value="CompressionType::None"/>
            <GuaranteedOutputBuffers value="5000"/>
            <TcpNodelay value="1"/>
            <Host value="localhost1"/>
            <Port value="14002"/>
        </Channel>
        <Channel>
            <Name value="Channel_2"/>
            <ChannelType value="ChannelType::RSSL_SOCKET"/>
            <CompressionType value="CompressionType::None"/>
            <GuaranteedOutputBuffers value="5000"/>
            <TcpNodelay value="1"/>
            <Host value="localhost2"/>
            <Port value="14002"/>
        </Channel>
    </ChannelList>
</ChannelGroup>

wasin.w

Hello @gang.chen1

Before I continue, I highly recommend the client check the following resources that might help them understand the Refintiv Real-Time and RTSDK betters:

10 important things you need to know before you write a Refinitiv Real-Time application article that gives all the basic detail about the Refinitiv Real-Time concept for the client.
EMA API step-by-step tutorials (Java, C/C++)

Communication process:

Question 1. Market Price Request and Batch Request / Snapshot Request in Domain Model are all market requests. Is there any relationship between them? Can each request be sent/received individually?

Answer: The normal request message, batch request, and snapshot request message are types of the request message that the API sends to the server. There is no relationship between them and the API can send-receive each request individually.

Question 2: According to the characteristics of the market request, can it be understood as follows:

Streaming Requests: One request, one RIC subscription, continuous push
Snapshot Request: One request, one RIC subscription, one feedback
Batch Request: One request, subscribe to a batch of RICs, and push continuously
Views: One request, subscribe to certain fields in a RIC, and push continuously

Answer: The client's understanding is correct. Please note that the Batch and View requests can be used together too.

Example:

consumer  = EmaFactory.createOmmConsumer(EmaFactory.createOmmConsumerConfig().host("localhost:14002").username("user"));


//Batch
OmmArray arrayBatch = EmaFactory.createOmmArray();
arrayBatch.add(EmaFactory.createOmmArrayEntry().ascii("FB.O"));
arrayBatch.add(EmaFactory.createOmmArrayEntry().ascii("CSCO.O"));


//View
OmmArray arrayView = EmaFactory.createOmmArray();
arrayView.fixedWidth(2);
arrayView.add(EmaFactory.createOmmArrayEntry().intValue(22)); //BID
arrayView.add(EmaFactory.createOmmArrayEntry().intValue(25)); //ASK


//ElementList
ElementList batchView = EmaFactory.createElementList();
batchView.add(EmaFactory.createElementEntry().array(EmaRdm.ENAME_BATCH_ITEM_LIST, arrayBatch));
batchView.add(EmaFactory.createElementEntry().uintValue(EmaRdm.ENAME_VIEW_TYPE, 1));
batchView.add(EmaFactory.createElementEntry().array(EmaRdm.ENAME_VIEW_DATA, arrayView));
            
consumer.registerClient(EmaFactory.createReqMsg().serviceName("ELEKTRON_DD").payload(batchView), appClient);

Question 3: When consumers send messages to the outside world, they generally use three message types: ReqMsg / PostMsg / GenericMsg. What is the difference between these three messages?

ReqMsg: Request Message. The application sends this message to the server to request something.
PostMsg: Post Message. The application sends this message to the server to push content upstream. The upstream can be that RTDS Server, ATS, or even Refinitiv Real-Time (through RCC).
GenericMsg: Generic Message, a bi-directional message without any implicit interaction semantics associated with it, hence the name generic. It is used by some customized data domains for a specific purpose.

wasin.w

Hello @gang.chen1

Question 4: What is the relationship between Private Streams and Streaming Requests/Snapshot Requests? Can the made request be set to be a private stream?

Answer: A private stream is a stream that contains data this is not to be aggregated, stored, or recovered by the infrastructure (i.e. RTDS). Data exchanged on private streams are exclusively between only two endpoints; Provider and Consumer and have not been shared with other Consumers or Providers.

This virtual private connection can be either a direct connection, through the RTDS, or via a cascaded set of platforms.

All types of requests, functionality, and Domain Models can flow across a private stream including (but not limited to):

Streaming Requests
Snapshot Requests
Posting
Generic Messages
Batch Requests
Views
All Refinitiv Domain Models & Custom Domain Models

Question 5: Is the default value of privateStream false?

Answer: The request message is not a private stream by default. The application can set the ReqMsg.privateStream() to enable a private stream.

Please note that the Provider application needs to support a private stream too.

Example from EMA ex220_MBP_PrivateStream example.

consumer.registerClient(EmaFactory.createReqMsg().domainType(EmaRdm.MMT_MARKET_BY_PRICE)
    .serviceName("DIRECT_FEED").name("BBH.ITC")
    .privateStream(true), appClient);

Question 6: What is the relationship between Private Streams / Tunnel Streams? In what scenarios do I need to enable Private Streams / Tunnel Streams?

Answer: A tunnel stream is a private stream with additional behaviors, such as end-to-end line of sight for authentication and guaranteed delivery.

The normal streaming consumer applications with the deployed RTDS connection scenario do not use Private Stream and Tunnel Stream.

In general, the use case of the private stream is to allow the provider and consumer to target content to one another directly. The content can be only specific for only a user/client; for example, only data that a user has permission to access.
The Tunnel Stream is currently used when connecting the consumer application to the Refinitiv Real-Time over secure internet such as Refinitiv Real-Time -- Optimized (RTO) or Refinitiv Real-Time Contribution (RCC).

Hope this helps.

EXPLORE OUR SITES