笔试一共5个部分，其中第一部分是C语言的，选择，改错，什么都有，有4页纸那么多，没法抄。把后边4部分抄回来了，如下。
Part 2. Network
1. please enumerate all TCP/IP protocols for every layer as many as possible based on TCP/IP 5-layer reference model.
2. what is vlan? why we need it?
3. please describe the PPP protocols.
4. please describe the difference between Hub, Switcher and Router.
Part 3. Operating System
1. please describe the difference between process and thread.
2. please list the scheduling mechanisms of a real time OS as you know, and describe their characteristics, respectively.
