TCP传输协议专题（03）：TCP Header/Segment

开垦者

本文主要介绍的是TCP协议的Header和Segment，介绍TCP Header和Segment位于以太网数据帧的位置，介绍TCP Header中可用的一些选项。其中文章的一些详细且易于理解的图标可以方便我们去理解。

This article shows the TCP Header and Segment. We explain where the TCP Header and Segment are located in an Ethernet frame and also briefly view the available options in the TCP Header. Our easy-to-understand detailed diagrams help ensure all information provided is easily understood.

所以系好安全带，做好准备开始我们的内容，这一切都非常简单，你只需要理清思路，尝试以最简单的形式看待事物，你会发现TCP是多么容易和友好。只有了解某件事，你才能对它感到舒适。

So buckle up and get ready. It's all really simple, you just need to clear your mind and try to see things in the simplest form and you will discover how easy and friendly TCP really is. You can only feel comfortable with something once you get to know it.

TCP HEADER AND TCP SEGMENT

如果我们想更准确地使用我们使用的术语，那么也许我们会将此页面命名为“分析 TCP 的 Segment”。因为这就是它在网络世界中的称呼，所以我们需要通过正确的术语来了解它。这就是TCP Segment的定义：TCP软件到计算机之前的传输单元称为TCP Segment。

If we wanted to be more accurate with the terms we use, then perhaps we would title this page as "Analysing A TCP Segment". Why? Well, that's what it's called in the networking world so we need to know it by the correct term.This of course leads us to another new definition, a TCP segment:

"The unit of transfer between the TCP software on to machines is called a TCP segment."

如果你对这个定义有些疑问，不要担心，继续往下看，在阅读定义时，这个术语其实并不难理解，可以参考下面的图片来帮助你理解：

If your expression has transformed itself to resemble a confused person, then don't worry, just keep reading...Understanding this term is easier than you thought when reading the definition, just take a good look at the diagram below:



现在你看到TCP段基本上是TCP Header加上它后面的数据，当然，数据属于ISO的上层（5，6，7层）。

数据内容可以是文件传输的一部分，也可以是来自http请求的响应，事实是我们真的对数据的内容不感兴趣，而只对它是TCP Segment 的一部分这一事实感兴趣。

下面的屏幕截图取自数据包的解析，它显示了属于TCP Header的DATA部分：

Now you see that a TCP segment is basically the TCP header plus the data that's right behind it and, of course, the data belongs to the upper layers (5,6,7).

The data contents could be part of a file transfer, or the response from a http request, the fact is that we really are not interested in the data's contents, but only in the fact that it's part of the TCP segment.

The screen shot below was taken from my packet sniffer, and it shows the DATA portion belonging to the TCP Header:



如果您尝试从其他数据包解析类似的数据包，则更有可能在 TCP Header中显示“数据”部分，就像上面的截图一样。所以问题是TCP Header和TCP Segment是否基本上是一回事。尽管在大多数情况下，当引用TCP Header时，我们谈论的是没有数据的Header，而TCP Segment包含数据。

If you tried to capture a similar packet from any packet sniffer, it is more likely to display the Data portion within the TCP header, just as the screen shot on the above. So the question is whether a TCP header and a TCP segment are basically the same thing.Even though it might seem they are, in most cases, when referring to the TCP header, we are talking about the header without the data, whereas a TCP segment includes the data.

准备分析TCP Header的内容
GETTING READY TO ANALYSE THE TCP HEADER

现在，我们已准备好开始分析 TCP Header的结构。但是，请务必记住，“TCP Header”与“TCP Segment”是一回事，这意味着它是 TCP Header信息加上数据，如上图所示。最后一个屏幕截图当然提供了相当多的信息，但仍有很多尚未透露的信息，更不用说尚未真正分析的任何内容:)

后面的文章我们将继续深入分析。

We are now ready to begin examining the structure of the TCP header. However, be sure to keep in mind that the 'TCP Header' is the same thing as a 'TCP Segment', meaning it's the TCP header information plus the Data, just as the diagrams above show.The last screen shot certainly gives out a fair bit of information, but there is still much that hasn't been revealed, not to mention nothing's really been analysed as yet :)

cengjili

这篇关于TCP传输协议专题的文章很具有专业性和指导性。文章清晰地阐述了TCP Header和Segment在以太网数据帧中的位置，并介绍了TCP Header中可用的选项。内容详实，结合图标解释，有助于读者更深入地理解TCP协议的工作原理。期待文章能深入探讨TCP的传输机制、拥塞控制等高级特性，为读者提供更全面的知识。建议采用更多直观的方式，如流程图、图表等，以增强文章的可读性和理解性。总体而言，文章质量高，值得期待后续的深入解析。