Out of band data

Out-of-band data, also known as expedited data ),

This means that one of the two parties has an important event and wants to notify the other party quickly.

This notification is sent before any "normal" (sometimes called "in band") data that has been queued for sending.

Out-of-band data is designed to have a higher priority than normal data.

The out-of-band data is mapped to an existing connection, rather than a connection between the client and the server.

In the byte stream service, because there is no message boundary, a user process can read or write any number of bytes at a certain time point. Cache is required to ensure correct transmission or use of a stream control protocol. However, for some special requirements, such as interactive applications, such cache needs to be canceled.

A type of information that you want to process in a timely manner without passing through the conventional transmission mode during data transmission, such as the UNIX system interrupt key (delete or control-C) control-s and control-q are called out-of-band data. Logically, it seems that the user process uses an independent channel to transmit the data. This channel is associated with each connected stream. Because the implementation of out-of-band data in Berkeley Software Distribution is inconsistent with the host agreement specified in RFC 1122, to minimize the problems in interoperability, it is recommended that the application writer not use the out-of-band data unless it is required for interoperability with existing services.

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The out of band Statement on the network:

Out-of-band data, also known as expedited data ),
This means that one of the two parties has an important event and wants to notify the other party quickly. This notification is sent before any "normal" (sometimes called "in band") data that has been queued for sending. Out-of-band data is designed to have a higher priority than normal data. The out-of-band data is mapped to an existing connection, rather than a connection between the client and the server.
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A type of information that you want to process in a timely manner without passing through the conventional transmission mode during data transmission, such as the UNIX system interrupt key (delete or control-C) control-s and control-q are called out-of-band data. Logically, it seems that the user process uses an independent channel to transmit the data. This channel is associated with each connected stream. Because the implementation of out-of-band data in Berkeley Software Distribution is inconsistent with the host agreement specified in RFC 1122, to minimize the problems in interoperability, it is recommended that the application writer not use the out-of-band data unless it is required for interoperability with existing services.

Http://www.cic.tsinghua.edu.cn/sys/book2/twosocket.htm

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The Middleware on the out-of-band data platform makes it clear that an exception event occurs in the application in time outside the normal data flow, the implementation of out-of-band data generally uses the BSD emergency Data Pointer mode, that is, TCP only ensures that all data before the emergency data is returned to the application together, however, it is entirely up to you to decide how your applications handle this event. You can even consider it as common data rather than special treatment. Therefore, for some poorly designed programs, for example, if you do not judge the read return value, it will not be affected by OOB.
Because emergency data is usually caught in the normal data stream, and your network interception program generally obtains packets from the connected slave, there is no concept of emergency data (on the TCP layer ), of course, it can be captured.

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Additionally, sending and receiving out-of-band data: Send (sockfd, "A", 1, MSG_OOB); Recv (sockfd, & outofband, 1, MSG_OOB );

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What I can add is only one explanation of TCP/IP.

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TCP determines that the method for sending data is a kind of traffic-oriented metadata.

That is to say, the data is sent from the local host to the local host in sequence.

On the other hand, the primary machine extracts data from the data stream in sequence and sends it to the application for processing.

However, in some cases, some resources must be processed first. When the receiving end finds that there is an emergency packet in the data,

It must handle traffic first. At this time, the receiver enters the urgent mode and starts to receive urgent data,

Pass it to the application, while URGent pointer in the header of the emergency packet table points out

Halted point (position in the receiver buffer). After the URGent data is digested,

TCP tells the application to return to the normal receiving queue. The packets of this type are sorted in sequence,

It is like a voice that suddenly pops up when a player is playing in the atmosphere. Therefore, it is regarded as an out of band (out of band) resource.

Based on the preceding information, the TCP/IP traffic destined for "fang Ying" is fixed-Inbound and applied.

http://bit.kuas.edu.tw/~cjtu/project/cjtu/oobd.html