In this section, I'll introduce terms and abbreviations that are going to be used extensively in this book.
本节里，会介绍那些在这本书里广泛应用到的术语和缩写词。
Eight-bit quantities are normally called octets in the networking literature. In this book, however, I use the more familiar term byte. After all, the book describes the behavior of the kernel rather than some network abstraction, and kernel developers are used to thinking in terms of bytes .
网络著作中Eight-bit常常被称作是octets。然而我更倾向于byte，毕竟我们要讨论的是内核功能而不是一些抽象的网络概念，而内核工程师们更喜欢把它称为bytes.
The terms vector and array will be used interchangeably.
术语vector和array 将常常被互换使用
When referring to the layers of the TCP/IP network stack, I will use the abbreviations L2, L3, and L4 to refer to the link, network, and transport layers, respectively. The numbers are based on the famous (if not exactly current) seven-layer OSI model. In most cases, L2 will be a synonym for Ethernet, L3 for IP Version 4 or 6, and L4 for UDP, TCP, or ICMP. When I need to refer to a specific protocol, I'll use its name (i.e., TCP) rather than the generic Ln protocol term.
讲解到TCP/IP网络层结构的时候，我将会用缩写词L2, L3, 和 L4来分别代替连接层，网络层和传输层。这些数字的定义基于著名的7层OSI（open systom interconnection）模型,大多数时间 L2是以太网的同义词，L3跟ＩＰv4 或者是IPV6，L4和UDP，TCP或ICMP 同意。但是当涉及某个特定协议的时候，我将会用它自己的名字而不是Ln 协议。
In different chapters, we will see how data units are received and transmitted by the protocols that sit at a given layer in the network stack. In those contexts, the terms ingress and input will be used interchangeably. The same applies to egress and output. The action of receiving or transmitting a data unit may be referred to with the abbreviations RX and TX, respectively.
不同章节里，我们会看到不同网络层的协议是怎么实现数据报收发和传输。在这些讲解中，术语ingress 和 input 是可以互换的，egress和output也一样。接受和传输一个数据报的动作有可能涉及到RX（Reception）和TX（Transmission）
A data unit is given different names, such as frame, packet, segment, and message, depending on the layer where it is used (see Chapter 13 for more details). Table 1-1 summarizes the major abbreviations you'll see in the book.
一个数据单元依赖于不同的网络层有像frame, packet, segment, and message等不同的名字。