Chapter 17. TCP Urgent Data
TCP is fundamentally stream based. Data placed by the sending process into the operating system's TCP transmit buffer is received by the other end and read by the receiving process in exactly the same order in which it was sent. But what if the sending process detects some exceptional condition and it needs to alert the receiver immediately? Vanilla TCP can't handle this well because all data has equal priority, and the urgent message will have to wait its turn behind all the data sent before it. This is where TCP "urgent" data fits in. This facility, more commonly known as "out-of-band" data, makes it possible, in a limited and highly qualified manner, to send and receive TCP messages that are delivered ahead of ...
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