(1), the term substantially
Node (node):
网络中的结点可以是计算机，集线器，交换机或路由器等。Link (link):
从一个结点到另一个结点的一段物理线路。中间没有任何其他交点。Host (host):
连接在因特网上的计算机
ISP（Internet Service Provider）：
因特网服务提供者（提供商）.IXP（Internet eXchange Point）：
互联网交换点IXP的主要作用就是允许两个网络直接相连并交换分组，而不需要再通过第三个网络来转发分组。.RFC(Request For Comments)
意思是“请求评议”，包含了关于Internet几乎所有的重要的文字资料。WAN WAN (Wide Area Network)
任务是通过长距离运送主机发送的数据MAN MAN (Metropolitan Area Network)
用来讲多个局域网进行互连Local area network LAN (Local Area Network)
学校或企业大多拥有多个互连的局域网Personal Area Network PAN (Personal Area Network)
在个人工作的地方把属于个人使用的电子设备用无线技术连接起来的网络 End system (end system):
处在因特网边缘的部分即是连接在因特网上的所有的主机.
Packet (packet):
因特网中传送的数据单元。由首部header和数据段组成。分组又称为包，首部可称为包头。
Store and Forward (store and forward):
路由器收到一个分组，先存储下来，再检查其首部，查找转发表，按照首部中的目的地址，找到合适的接口转发出去。Bandwidth (bandwidth):
在计算机网络中，表示在单位时间内从网络中的某一点到另一点所能通过的“最高数据率”。常用来表示网络的通信线路所能传送数据的能力。单位是“比特每秒”，记为b/s。
Throughput (throughput):
表示在单位时间内通过某个网络（或信道、接口）的数据量。吞吐量更经常地用于对现实世界中的网络的一种测量，以便知道实际上到底有多少数据量能够通过网络。吞吐量受网络的带宽或网络的额定速率的限制。(2), summarizes the important points
1, a computer network (the Internet) connecting a number of computers connected together, and the Internet to a number of networks together, is a network of networks.
2, internet is a lowercase I (the Internet) is a general term which refers to a network by a plurality of interconnected computer networks formed. In the communication protocol between the network (i.e., communication rules) may be arbitrary.
I begin with a capital letter Internet (the Internet) is a technical term, it refers to the world's largest, open Internet by a specific number of network connections from each other, and using TCP / IP as the communication protocol rules, formerly the ARPANET. - Translation of the Internet is the Internet, called the Internet now generally popular.
3, the router is a key component to achieve packet switching, packet forwarding its mission is to receive, which is the core part of the network's most important functions. Packet switching using store and forward techniques, a represents the packet (data block to be transmitted) is divided into several packets and then transmitted. Before sending the message, the first long message is divided into a number of smaller segments of equal length. After the necessary header plus some control information composed of the front end of each data, it constitutes a packet. Grouping also known as packets. Packet data units are transmitted in the Internet, it is precisely because the packet header contains important control information such as destination address and source address, each packet to a transmission path independent of the Internet, and to correctly deliver the packet transmission It ends.
4, Internet according to work can be divided into an edge portion and the core part. In the edge portion of the host network, whose role is to process the information. By a large number of networks and routers connecting the edge portion composed of a network, its role is to provide communication and exchange.
5, the communication is a communication between the computer processes the computer (i.e., a running program). Computer communication network uses a client - server mode (C / S mode) and peer connection (P2P mode)
6, client and server communications refer to the application process involved. Customer service requester, the server is a service provider.
7, according to the different scope, the computer network is divided into the WAN wide area network, metropolitan area network MAN, the LAN local area network, personal area network PAN.
8, the most common computer network performance metrics are: speed, bandwidth, throughput, latency (transmission delay, processing delay, queuing delay), delay-bandwidth product, the round trip time and channel utilization.
9, i.e. protocol network protocol, a rule data exchange network established. The layers computer network and its set of protocols, referred to as a network architecture.
10, five-layer architecture by the application layer, transport layer, network layer (Internet layer), a data link layer, physical layer. The main transport layer protocol is TCP and UDP protocols, the most important network layer protocol is IP protocol.
Two physical layer
(1), the term substantially
Data (data):
运送消息的实体。
Signal (signal):
数据的电气的或电磁的表现。或者说信号是适合在传输介质上传输的对象。Symbol (code):
在使用时间域（或简称为时域）的波形来表示数字信号时，代表不同离散数值的基本波形。Simplex (simplex):
只能有一个方向的通信而没有反方向的交互。Half-duplex (half duplex):
通信的双方都可以发送信息，但不能双方同时发送(当然也就不能同时接收)。
Full-duplex (full duplex):
通信的双方可以同时发送和接收信息。
Nyquist criterion:
在任何信道中，码元的传输的效率是有上限的，传输速率超过此上限，就会出现严重的码间串扰问题，使接收端对码元的判决（即识别）成为不可能。Baseband signal (baseband signal):
来自信源的信号。指没有经过调制的数字信号或模拟信号。
Bandpass (band) signal (bandpass signal):
把基带信号经过载波调制后，把信号的频率范围搬移到较高的频段以便在信道中传输（即仅在一段频率范围内能够通过信道），这里调制过后的信号就是带通信号。Modulation (modulation):
对信号源的信息进行处理后加到载波信号上，使其变为适合在信道传输的形式的过程。
The SNR (signal-to-noise ratio):
指信号的平均功率和噪声的平均功率之比，记为S/N。信噪比（dB）=10*log10（S/N）