[心平气和读经典]The TCP/IP Guide(005)

Posted 2020-10-12 veli

The TCP/IP Guide

[Page 44, 45, 46]

Structure and Organization of The TCP/IP Guide | TCP/IP指南的组织结构

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You may have already noticed that the TCP/IP Guide is organized in a way that is very different from most books. I believe this structure will help you not only find the information you need easily, it will even assist you in understanding the content. However, because it is unorthodox, I want to take a few moments to explain what I have done and why.
你可能已经注意到TCP/IP指南的组织方式跟很多别的书都有所不同。 我相信这一组织结构不但能够帮助你很容易地找到你所需要的信息，而且可以帮助你理解内容本身。然而，由于这一结构安排是反传统的，所以我想多说几句，解释一下我做了什么和为什么这么做。

In reviewing other networking books and materials before I wrote this Guide, I was consistently disappointed -- not in the descriptions of the various subjects, but in the way they were organized. Invariably, these resources would cover a lot of material, but it would be presented as a poorly-structured set of seemingly unrelated chapters -- "subject salad" as I sometimes call it. A typical networking book would have dozens of little chapters cobbled together and presented almost as if they were independent of each other. The reader had to figure out how they all connected, and also had to wade through several repeated descriptions of similar concepts, due to aspects that were common between certain technologies. This was all exacerbated by the inability to hyperlink between related topics in a print book.
在我写本指南之前，我阅读了其他的网络书籍和材料，总是感到失望。 -- 我对各种主题的描述并不失望，但是对材料的组织方式感到失望。 总的来说，这些素材涵盖了很多材料，但是作为一个结构不合理的看似不相关的章节出现，我有时称呼之为"主题沙拉"。一本典型的网络书籍将很多小的章节拼凑在一起，仿佛它们是独立存在的。读者必须弄清楚它们是如何联系在一起的，同时也必须仔细研究几个具有相似性的概念的重复描述，因为某些技术之间存在着共性。印刷书籍中相关主题之间没有超链接，这一切都使得阅读变得更加困难。

TCP/IP is a complex topic largely because so many of the concepts and technologies are closely related. TCP/IP as a whole consists of a number of defining concepts and a large number of individual protocols, many of which interact in a specific way. Many of those protocols in turn consist of either subprotocols or descriptive elements that are related to each other in a particular fashion. For example, you can‘t easily describe IP datagram formatting without making reference to IP addressing, which in turn is related to IP routing, which is of course related to IP routing protocols, and so forth.
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For this reason, I didn‘t want to just make this book consist of several dozen chapters slapped together as peers and leave you to figure out how they fit together. So, I spent several weeks just trying to come up with a way to describe TCP/IP technologies in a coherent, organized way that made sense. My primary goal was to come up with a structure that would clearly show how all the various protocols, concepts and technologies were interrelated, to help you understand the subject as a whole, and not just as a collection of parts.
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The result of this effort is that rather than using a set of dozens of chapters all at the same level, this Guide uses a hierarchical structure with many levels. The Guide contains several sections on various high-level subjects, which we will explore in a moment. Most of these contain subsections that describe components or more detailed elements within the higher-level subject. These in turn can contain their own subsections and so on, possibly going down several layers in detail.
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The Guide is formatted so that each section header and section starts at the top of a page. This facilitates printing small sections of information (for use as handouts in a classroom setting, for example) and also helps make navigating using hyperlinks easier. A special horizontal divider graphic is used to clearly mark the end of each section.
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Another organizational feature of this Guide is that I have made extensive use of overview topics. Most sections that include multiple individual topics begin with an overview topic that provides a high-level look at the contents of that section. These serve two purposes. First, they introduce the subject and provide a context for understanding the detailed discussions that follow it, for those who want to read about the protocol or technology in detail. Second, they serve as a "short cut" for those who do not wish to read an entire section. Some large sections containing subsections will have an overview for the section as a whole, and an overview for some of the subsections as well. This is by design, to provide you with flexibility in choosing what you want to read.
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Some of you might find that this all of this takes a bit of getting used to, but it has advantages compared to a "flat" set of chapters. The hierarchical structure itself helps you understand how the many protocols, concepts and other bits and pieces of TCP/IP fit together. It shows you what aspects of TCP/IP are closely and more distantly related. The hierarchy and the use of overview topics allows you to explore a particular subject of interest in the manner you choose, by enabling you to easily choose some subsections to delve into while skipping others that you may already understand or simply not wish to know.
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So, where to begin in exploring this large Guide? Well, you can just read the entire thing from cover to cover, but most people lack the time and patience to do that! The key to taking advantage of this Guide‘s hierarchical structure is to make use of the nested bookmarks that should appear on the left side of your Adobe PDF reader. These let you clearly see the structure of each part of the Guide and let you instantly jump to any topic of interest. The next two topics describe in more detail features of the Guide and how to optimize your use of Adobe Acrobat Reader.
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Chapters of the TCP/IP Guide | TCP/IP指南的章节安排

Due to the hierarchical structure just described, there are only six "top-level" sections in this Guide, which I sometimes called chapters. You will probably find that it usually makes the most sense to begin with these higher-level sections and work your way down to the more detailed topics they contain. Here is a brief description of each, to get you started:
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• Introduction and "Guide To The Guide": You‘r reading it! :-)
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• Networking Fundamentals: This is a background chapter that provides lots of useful general information on networks for those who may be very new to the entire subject. It has subsections that explain what networking is, discuss key networking characteristics, describe networking standards, provide information on binary mathematics and much more. If you are experienced with networks and computers in general you may wish to skip this (or at least, skim it and only read the topics that interest you).
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• The Open System Interconnection (OSI) Reference Model: A description of the important OSI Reference Model, which is used extensively to explain networking architectures and protocol layering concepts. Unless you already know and understand the OSI model, this section is worth reading before getting into the "meat" of the Guide.
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• TCP/IP Protocol Suite and Architecture: This is the first section that is specifically about TCP/IP; it introduces the protocol suite and discusses it in general terms. This includes a look at its history, a description of the TCP/IP architectural model and an overview of key protocols. It should be the place to start reading about TCP/IP for virtually everyone using this Guide, as it provides necessary background information and a context for understanding the more detailed chapters below.
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• TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4): This large chapter describes all of the TCP/IP protocols that operate at layers 2 through 4 of the OSI model, and is organized by layer for easier reference by function. This chapter encompasses about half the entire Guide; it includes all of the most important “core” TCP/IP protocols, including IP, IPv6, ICMP, UDP, TCP and much more.
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• TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7): This chapter is also very large, as it covers all the TCP/IP application protocols and services that correspond to the upper three layers of the OSI Reference Model. This includes protocols such as DNS, DHCP, SNMP, FTP and HTTP, as well as applications such as electronic mail, the World Wide Web and diagnostic utilities.
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As you can see, most of this Guide is actually contained in the last two chapters, since TCP/IP is primarily defined by the functions of its various protocols.
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