计算机通信网提纲

Chapter 8 Network Security

work security problems can be divided roughly into four areas:

monly-used encryption algorithms include and

3.What is digital signature’s functions?

4.What is firewall? Two classes .

Chapter 7 The application layer

1.What is DNS Domain Name System域名系统

2.How to carry out domain name resolution

3.In E-mail, which protocols are used for message transfer and final delivery?

4.If you want to display the selected page, which questions must be solved before?

5. WWW stands for_____

6. Commonly used video compression standards include__________.

7 . What is voice over IP, what is H.323, what is SIP?

Chapter 5/6 network layer and transport layer

1. In the TCP/IP Architecture , there four layers ,they are 应用层、传输层、因特网层and 网络接口层. P573

2. IP Packet consists of header and user data, IP packet header includes fixed 20 byte header and variable options , it will not exceed 60 bytes. How to judge which class an IP address belongs to. How many classes IP addresses are there in IPV4?

IP报文包含报头和用户数据，IP报头包括固定的20字节和可变选项，不超过60字节。IPV4有多少种IP类？0~127A，128~191A，192~223C，224~239D，240~255E

3. In IP packet header, fields related to fragmentation and reassembly include Identification , flags, fragment offset, source IP address and destination IP address. Understanding each field’s meaning of IP header.报头包含的各个部分。

标识：唯一识别一个特定的信息段属于哪个分组

标记：MF置1则还有更多分段，置0则为最后一个分段。DF置1则强制不分段。

段偏移字段：确认一个分段在分组中的位置。

4. In one node , a packet with following header(0x) 4500 0054 0003 0000 0C06 0000 7C81 0E0F 6F7E 0506 is received:

(1)Are there any options in this packet? IHL=5, so header length=20, no option

(2)Is this packet fragmented? Last fragment , offset=0, not fragmented

(3)What is user data length? 5ⅹ16+4-20=64

(4)Source IP address(dotted decimal notation)? (7C 81 0E 0F->124.129. 14.15)

(5)Destination IP address(dotted decimal notation)?(6F 7E 05 06->111.126.5.6)

5. For one of classes A,B and C networks, how many hosts are accommodated respectively? (You should can identify what class IP address is according to some rules) three types of address in internet( mac addr, IP addr, port #)

0XXX:A类，2^24-2台主机16777214

10XX:B类，2^16-2台主机65534

110X:C类，2^8-2台254

6、Subnet Addressing Example on page 439.(In one subnet, please pay attention to subnet addresses range, how to decide subnet mask)

7. How to fragment a packet

8. What characteristics do the UDP and TCP have respectively?

UDP:不可靠，无连接，协议简单，适合短报文，无需传送，面向报文，点到多点也可以TCP：可靠，面向连接，有序传送，提供流控制，拥塞控制，差错控制，协议复杂，只能点到点，面向字节流

9. Understanding the flow control mechanism in TCP.

10. In the TCP segment, what does MSS stands for?

MSS:能接受最大数据段尺寸

MSS=TCP报文段长度-TCP报头长度。MTU=MSS+TCP报头长度+IP报头长度

11. In the TCP congestion control, which three phases are included ? Explain them in detail.

TCP拥塞控制三个阶段

慢启动：拥塞窗口先以指数形式增加，达到拥塞阈值时，进入下一阶段。

拥塞避免：线性地增加拥塞窗口，网络拥塞时，进入下一阶段

拥塞：拥塞阈值变位现在拥塞窗口大小的一半

12. How to judge that congestion has happened?判断发生拥塞

源目之间的中间路由器缓冲区溢出，或多路复用缓冲区填满并且数据包丢失

13. What is three-way handshake and what is a graceful close?

14 How to get its network address, when one host address is known.

知道一个主机地址，确定网络地址：利用子网掩码长度判断，全1部分为网络号

15 For a two-way TCP connection, it is possible that there can be multiple segments exchanged, please pay attention to the parameters used.

16. The segment with SYN set to 1 use up one sequence number(its length is 1), the same with the segment with FIN set to 1.

SYN位置1和FIN位置1的信息都要消耗一个语句号

17. The segment with ACK set to 1 don’t use up sequence number when no data is carried.

ACK置1的ACK语句在没有携带数据情况下，不消耗语句号

18. Please pay attention to Sequence number wraparound problem.

19. IP address’s dotted decimal notation.

20. Designing subnets and deciding the host range of each subnet, given a network address and the number of subnets.