重要概念

2. ,,

   cdmaOne和CDMA2000两种标准都使用CDMA技术，cdmaOne已被CDMA2000取代，即CDMA2000是一种新的基于CDMA的标准。
   

3. ,,

   WDM是用在光纤上的FDM；FDM、WDM、TDM、CDMA是都是

4. (虚拟内存)(特别注意第二段)

虚拟内存不是指用来作内存（准确地说：用于保存从内存交换出去的数据或代码）的硬盘；swap file（交换文件）和page file（页文件）才是平衡的概念；特别注意上面链接的第二段，它专门讲到了虚拟内存和page file（即用硬盘来扩展物理内存）的关系

5. 和可靠的服务是什么关系？

   Note that connection-oriented protocols are not necessarily reliable protocols. ATM and Frame Relay, for example, are both examples of a connection-oriented, unreliable protocol. There are also reliable connectionless protocols as well, such as AX.25 when it passes data in I-frames. But this combination is rare, and reliable-connectionless is uncommon in commercial and academic networks.
   

6. circuit switching和Virtual circuit是什么关系？

Virtual circuit communication resembles circuit switching, since both are connection oriented, meaning that in both cases data is delivered in correct order, and signalling overhead is required during a connection establishment phase. However, circuit switching provides constant bit rate and latency, while these may vary in a virtual circuit service due to reasons such as:

• varying packet queue lengths in the network nodes,
• varying bit rate generated by the application,
• varying load from other users sharing the same network resources by means of statistical multiplexing, etc.

Many virtual circuit protocols, but not all, provide reliable communication service, by means of data retransmissions due to error detection and automatic repeat request (ARQ).

7. packet switching和virtual circuit是什么关系？

The service actually provided to the user by networks using packet switching internally to the network can be datagrams (connectionless messages), and/or virtual circuit switching (also known as connection oriented)

Typeface: is the design of the alphabet--the shape of the letters that make up the typestyle. The letters, numbers, and symbols that make up a design of type. So when you say “Arial” or “Goudy” you’re talking about a set of letters in a specific style.

Font: is the digital file that contains/describes the typeface. Think of the font as a little piece of software that tells the computer and printer how to display and print the typeface.

According to Adobe’s type gloassary: “A font is one weight, width, and style of a typeface. Before scalable type, there was little distinction between the terms font, face, and family. Font and face still tend to be used interchangeably, although the term face is usually more correct.”

If you want to get a little deeper:

A typeface family is a group of typefaces that were designed to be used together. For example, Goudy Old Style has Roman (upright or normal), italic (slanted and cursive), bold and bold italic versions. Each of the style and weight combinations is called a face or typeface, and together they are, hopefully, a happy typeface family (rather than a disfunctional typeface family which will probably be more familiar to you).