A brief summary of message-oriented persistent communication and stream-oriented communication

One, message-oriented persistent communication

The Message Queuing system provides multiple support for durable asynchronous communication, essentially providing the intermediary storage of the message , so that the message sender and receiver are not required to remain active during the message transmission.

Message Queuing model

An application can communicate by inserting messages into a particular queue. Messages are forwarded by a series of communications Servers, which are eventually delivered to the destination. The message can be sent even if the receiver's machine is not running during message delivery.

One of the important characteristics of Message Queuing systems is that it is usually only ensured that the message sent by the sender can eventually be inserted into the receiver's queue , not guaranteeing the time the message arrives, or even that the message must be read, which is entirely up to the receiver.

　　

Message converters can be as simple as a message format Orchestration tool . For example, suppose the input small cell contains a table in the database, where the records are split by a special delimiter that represents the end of the record, and the length of the field in the record is known and fixed. If the destination application wants to use a different delimiter to split the record, and you want the field to be variable length, you need to use a message converter to convert the message format to the format acceptable to the destination application.

The goal of the ordinary Message Queuing system is not only to provide support to the end user, but the important problem to be solved is to provide support for persistent communication between processes , whether the process is running user programs, processing access to the database, or computing, etc. Must be able to support its communications. For example, a design of several database queries may need to be split into several sub-queries and then forwarded to the appropriate database. In this process, each subquery is packaged into a message using the basic methods provided by the Message Queuing system, and then the message is sent to the appropriate database.

Second, flow-oriented communication

1. Support for continuous media

　　media refers to the means by which information is transmitted, including storage and transmission media . The important type of media is how information is represented, that is, the way information is encoded in the computer system. For example, text is usually encoded in ASCII or Unicode. Images can be expressed in GIF or JPEG format. The audio stream in the computer can be encoded using a 16-bit sample such as a PCM.

2. Data Flow

　　for continuous data flow , synchronization is extremely critical. To capture the synchronization situation, make a distinction between different transmission modes. In asynchronous transfer mode, data items in a stream are transmitted one by one, but there is no further restriction on when an item is transferred. For example, a file can be transmitted as a data stream, but it is usually irrelevant that each data item is transmitted in the time it is completed.

　　in synchronous transfer mode , each cell in the data flow defines an end-to-end maximum delay time. For example, the sensor samples the temperature value at a specific sample rate and then transmits the sample results over the network to the operator.

　　wait for the transmission mode , in this mode the data unit must be transmitted on time, that is, the end-to-end delay time of data transmission must be constrained by both upper and lower limit, end-to-end delay time upper and lower limit is also called boundary delay jitter. This transmission mode is extremely useful for distributed multimedia systems.

A simple stream contains only a single data sequence, and a complex stream consists of several related simple streams----sub-streams . An example of a complex stream is about the transmission of the film. This stream consists of a single video stream, and two audio streams used to transmit sound in a movie in stereo. The fourth stream is used to transmit text that is self-touching or translated into other languages. Synchronization between the sub-flows is still important. If you can't sync, you won't be able to reproduce the movie completely.

3. Synchronization mechanism

So how exactly does synchronization happen? Contains two aspects, (1) two basic mechanisms of stream synchronization (2) distributed versions of these mechanisms in a networked environment

　　

A brief summary of message-oriented persistent communication and stream-oriented communication