文章导航
计算机网络自顶向下书籍中科大B站课程笔记
习题部分解答
第一章
复习题
R1
![image-20220729223704703](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729223704703.png)
没有区别,都是端系统。
R9
![image-20220729223739943](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729223739943.png)
调制解调器30-50kbps,HFC30M下行、2M上行,DSL24M下行、2.5M上行,FTTH20M
R11
![image-20220729223917305](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729223917305.png)
![image-20220729224036640](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729224036640.png)
电路交换优点:为端到端预留资源保持带宽。FDM需要设备进行载波生成、频率搬移,更复杂去。
R13
![image-20220729224242134](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729224242134.png)
三个以上超过负载,就会等待。
#### R18
![image-20220729224757408](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729224757408.png)
![image-20220729224807030](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729224807030.png)
R19
![image-20220729225005720](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729225005720.png)
最小值500k
4M/500k=64s 注意:k=1000,K=1024,1B=8b
100k,4M/100k=320s
R23
![image-20220729225318700](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729225318700.png)
应用层:实现应用
传输层:多路复用可靠性、拥塞控制
网络层:端到端通信、路由转发
数据链路层:相邻两点传输
物理层:物理介质上传输加载还原数字信号。
R25
![image-20220729225547061](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729225547061.png)
路由器:网络层、链路层、物理层;链路层交换机:链路+物理;主机:所有五个层次。
习题
P2
![image-20220729225700388](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729225700388.png)
![image-20220729225855152](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729225855152.png)
![image-20220729230508800](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729230508800.png)
线路交换更合适,因为产生传输比较稳定,用线路交换可以有性能保证。
不用,直接就可以实现传输。
P6
![image-20220729231238405](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729231238405.png)
刚刚离开发送方
在路上
已经到接收方了
#### P14
![image-20220729231825377](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729231825377.png)
- 转换一下,令L/R=x
x越接近1,t越接近无穷大
P22
![image-20220729232258682](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729232258682.png)
![image-20220729232309037](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729232309037.png)
丢包概率p,不丢概率1-p,n跳不丢概率:
![image-20220729233057832](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729233057832.png)
最大值就是上面的这个值。
在链路上的单向传输数据量(链路容量是它的两倍)
#### P27
![image-20220729233924201](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729233924201.png)
只占1%
P31
![image-20220729234201734](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729234201734.png)
![image-20220729234216871](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729234216871.png)
![image-20220729234228137](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220729234228137.png)
分组交换比报文交换效率要高。
b.c.d.
更大限度利用传输资源。
第二章
复习题
P1
![image-20220909162611468](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909162611468.png)
- 错,四个请求
- 对,同一个服务器下
- 错,非持续TCP连接只能传输一个请求和一个响应报文
- 错,服务器产生并发送该响应报文的日期和时间
- 错,有可能有空的——条件式请求,对象在服务器端未改变,头部代码304,此时报文体是空的
R6
![image-20220909163009973](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163009973.png)
![image-20220909163019779](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163019779.png)
常见难题
P10
![image-20220803153904985](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220803153904985.png)
每次连接先3次握手各自200bit,最后传输内容100kbit,都占用1/10带宽
R=150bps L=100kbit L'=200bit
- 非持久、并行10个
t1=200/150 t2=100k/150
ti=3*t1+t2=3*200/150+100k/150
tii = 3*t1'+t2'=3*200/150/10+100k/150/10
t=ti+tii=7377s 最终T=t+8tp(传播延迟忽略)
![image-20220909163122103](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163122103.png)
- 持久
t1=200/150 t2=100k/150
t = 2t1+t1+t2+10(t1+t2)+24tp=7351+24tp
![image-20220909163145927](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163145927.png)
没有太大差别,因为资源太少了。
![image-20220909163202330](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163202330.png)
![image-20220909163214972](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163214972.png)
P22
![image-20220803155357883](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220803155357883.png)
![image-20220803155407372](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220803155407372.png)
F=15Gb 服务器上载Us=30Mbps 客户端下载di=2Mbps,N=10、100、1000下客户端上载300k、700k、2Mbps
- C/S模式
带入不同的N,N小的时候,瓶颈在客户端,N很大的情况下非常慢,瓶颈在服务器,NF/us很大,等待时间线性增加。
N | 10 | 100 | 1000 |
---|---|---|---|
300k | 7680 | 51200 | 512000 |
700k | 7680 | 51200 | 512000 |
2M | 7680 | 51200 | 512000 |
- P2P模式
N | 10 | 100 | 1000 |
---|---|---|---|
300k | 7680 | 25600 | 46454 |
700k | 7680 | 15300 | 21041.4 |
2M | 7680 | 7680 | 7680 |
N小的时候,受限于客户端,所以仍然是7680。P在起作用,随着各个peer节点上载能力的增加,下载时间减少很明显,在2M时增加N时间也不会变。
习题
P9
![image-20220908175424193](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220908175424193.png)
![image-20220908175546570](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220908175546570.png)
L=850kbit R=15Mbps 16个/秒 响应平均时间3秒,hit=0.4,内网平均传播延迟t'=10ms
- 没有缓存
- 有缓存
平均速度更快、远程服务器压力更小
P23
![image-20220908181445628](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220908181445628.png)
Us dn N F dmin=min{di}
- Us/N≤dmin 服务器是瓶颈——下载时间NF/Us
服务器向每个客户端提供的带宽都是Us/N即可满足
- Us/N≥dmin 客户端是瓶颈——下载时间F/dmin
服务器向每个客户端分配的带宽都是dmin,总共Ndmin(服务器没有全部出力)
- 两种情况都有,去最大值——最差的情况,即为最小分发时间
P24
![image-20220908182536595](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220908182536595.png)
忽略F/dmin
- Us ≤ (us+u1+...+uN)/N 服务器是瓶颈——下载时间F/Us
按比例把Us、F按照上载能力u1,u2……非等间隔进行划分,节点把自己收到的数据均分到所有其他节点,带宽和服务器提供给它的相同即可满足——可以推出每个节点上载能力完全可以满足
- Us ≥ (us+u1+...+uN)/N 客户端是瓶颈——下载时间NF/ (us+u1+...+uN)
服务器把文件非等间隔分成N+1份,向客户端提供的服务带宽为ui/N-1,发送对应的第i块和N+1块 Ri=ui/N-1,RN+1=(Us-U/N-1)/N——刚好服务器带宽占满了Us。每个客户端以ui/N-1向其他节点发送第i块。
- 两种情况都有,取最大值——最差的情况,即为最小分发时间
第三章
复习题
R3
![image-20220909000120394](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909000120394.png)
源端口y,目的端口x
R7
![image-20220909102532775](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909102532775.png)
会被描述成相同的套接字,UDP socket只绑定自己的端口+IP。socket API里面有receive from字段可以判断不同的源IP、源端口。
R9
![image-20220909102752784](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909102752784.png)
区分新旧、在接收方进行排序
R10
![image-20220909102840333](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909102840333.png)
PDU发送过程中可能丢掉,启动超时重发进程
R14
![image-20220909102925978](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909102925978.png)
- 没有数据捎带也要发送确认,错
- 会变化,根据上层应用层是否取完而变化,错
- 不会超过空闲buffer,更不会超过整个buffer,对
- 序号为m+TCP报文中字节数,确认是以字节为单位的,错
- TCP段头有一个receive window,对
- 指数移动加权平均,以前的值可能小于1秒,不一定大于等于,也可能小于1秒,错
- 不一定能收到,可能是ACK 38,错
R15
![image-20220909103624420](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909103624420.png)
![image-20220909103636725](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909103636725.png)
- 110-90=20
- ACK 90 TCP累计确认
R17
![image-20220909103836010](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909103836010.png)
TCP公平性,每一个R/2.大致的公平性,往返延迟少,抢到的带宽多,和UDP没有可比性。
R18
![image-20220909104204767](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909104204767.png)
当前拥塞窗口的一半ssth=cwnd/2 cwnd=ssth+3(三个冗余ACK)ssth=cwnd/2 cwnd=1(超时)
习题
P1
![image-20220909104920782](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909104920782.png)
Telnet服务器使用的端口是23
- 源x,目的23
- 源y,目的23
- 源23,目的x
- 源23,目的y
- 可以,用不同IP区分即可
- 不可以,IP相同时必须用端口号区分
P3
![image-20220909105214519](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909105214519.png)
简版checksum计算
求和、进位回滚,再取反码。
接收方加和与校验位相加直接判断是否全1——更快更方便
1bit可以,2bit不行
![image-20220909163249752](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163249752.png)
P8
![image-20220909105445008](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909105445008.png)
——状态机,多了超时重传机制
超时所带来的重复问题已经被2.2序号机制搞定,参照2.2即可
![image-20220909105711807](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909105711807.png)
P15
![image-20220909105755436](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909105755436.png)
![image-20220909105930020](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909105930020.png)
传播延迟15ms
Ttrans=L/R=1500*8/10^9=12us
假设处理时间为0
效率=nTtrans/(Ttrans+30ms)>0.9 ——n=2251
P23
![image-20220909110336008](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909110336008.png)
![image-20220909110404885](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909110404885.png)
GBN n ——2^n - 1
SR n —— 2^(n-1)
使用反证法证明
P24
![image-20220909111006661](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909111006661.png)
- 对,接收方ACK滞留了,超时重发,确认到达之后发送窗口前移,又收到旧的ACK
- 对,接收方ACK滞留了,超时重发,确认到达之后发送窗口前移,又收到旧的ACK
- 对,退化成了停止等待协议(比特交替协议)
- 对,退化成了停止等待协议(比特交替协议)
P27
![image-20220909111425101](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909111425101.png)
- 序列号207,源端口302,目的端口80
- 确认号207,源端口80,目的端口302
- 确认号127,在请求127及以后的报文
- 画图即可
P32
![image-20220909111759812](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909111759812.png)
![image-20220909111810705](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909111810705.png)
EstimatedRTT=(1-α)·EstimatedRTT+α·SampleRTT
DEV=β|SRTT-ERTT|+(1-β)DEV
RTO=ERTT+4DEV
- 迭代计算即可
- 算出迭代公式ERTT=x(1-x)^0SRTT1+x(1-x)^1SRTT2+x(1-x)^2SRTT3+...+(1-x)^(n-1)SRTTn
- 最后一项忽略,求极限
![image-20220909112658894](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909112658894.png)
P40
![image-20220909112934913](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909112934913.png)
![image-20220909113929171](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909113929171.png)
- 慢启动:1-6,23-26
- 拥塞避免:6-15,16-22
- 3个冗余ACK,cwnd降到一半+3
- 超时,cwnd降为1
- 32MSS
- 42的一半,21MSS
- 29的一半,14MSS(下取整)
- 累加算一下,什么时候把70号放进去——第七轮
- 窗口本来为8,ssthreh=4,cwnd=4+3=7
- 窗口本来是42,ssthreh=21,cwnd=1(Tahoe3个冗余ACK以后也慢启动),19-16=3:1、2、4——cwnd=4
- 17:1;18:2;19:4;20:8;21:16;22:21(不能大于21)——再线性增加,加起来发送了52个分组
P45
![image-20220909114159898](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909114159898.png)
- 窗口按照锯齿形增长,吞吐量=3/4 * W/RTT
按照每次+1线性增加计算,得到总共预计发送的分组数N为分母,丢失率用1除以它
- 用丢失率算窗口,忽略窗口的一次项,反推出窗口
- 用丢失率算窗口,忽略窗口的一次项,反推出窗口
代入吞吐量公式,得到速率公式
![image-20220909163350961](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163350961.png)
P53
![image-20220909114937965](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909114937965.png)
根据上一题得到的吞吐量和丢失率对应公式
L=2.14×10^-12——此时丢失极大可能是出错造成的,丢失是由拥塞造成的假设不成立了:不使用与高吞吐的情况、也不适合于无线通信的场景。我们的拥塞控制机制需要相应地改变。
第四章
复习题
R2
![image-20220909115434814](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909115434814.png)
![image-20220909135232428](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909135232428.png)
R3
![image-20220909135317092](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909135317092.png)
![image-20220909135332171](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909135332171.png)
R10
![image-20220909135407122](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909135407122.png)
- 内存
- 总线
- 互联网络 fabric——并行转发
R11
![image-20220909135512566](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909135512566.png)
- 输入:进入很快交换结构交换慢,队列满了就会丢失。(头端阻塞)
- 输出:交换机构的到达速度比传输速率快,队列满了也会丢失。
——交换速度n倍于输入限速消除分组消失。
R17
![image-20220909135825731](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909135825731.png)
IP数据报内有个字段upper layer,决定了交给上层的协议实体类型。
R30
![image-20220909135950342](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909135950342.png)
- 版本号-版本号
- 服务类型-流量类型
- 数据报长度-载荷长度
- 协议-下一个首部(next head)
- TTL-跳限制(hop limmit)
R33
![image-20220909140149852](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909140149852.png)
传统方式只匹配目的IP,最长字段匹配,动作只有转发。
SDN方式匹配字段很多,动作也很多:组播、单播、泛洪、block、修改……
习题
P5
![image-20220909140410654](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909140410654.png)
![image-20220909140427142](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909140427142.png)
- 11100000 00 —— 0
- 11100000 01000000 —— 1
- 11100000 —— 2
- 11100001 0 —— 2
- 其他 —— 3
- 3、2、3
P6
![image-20220909140815796](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909140815796.png)
00000000-00111111 —— 0——64
01000000-01011111 —— 1——32
01100000-01111111 —— 2——32
10000000-10111111 —— 2——64
11000000-11111111 —— 3——64
0:64;1:32;2:64+32=96;3:64
P10
![image-20220909141147411](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909141147411.png)
- 11100000 00 (224.0/10)—— 0
- 11100000 01000000 (224.64/16)—— 1
- 11100000 (224/8)—— 2
- 11100001 0 (225.0/9)—— 2
- 其他 —— 3
P14
![image-20220909141704591](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909141704591.png)
MTU=700B:最大传输单元;分组大小=2400B
头部20字节:分成20和2380;
每次传输20+680,20+680……
2380/680=4
标识号422,偏移分别为0、85、170、255(8字节-64bit为单位),标志分别为1、1、1、0
P15
![image-20220909142006808](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909142006808.png)
MTU=1500B,总大小5MB=5×10^6B
IP头部20B、TCP头部20B,后面1460B
N=5×10^6B/1460向上取整3425
若MB按2^20算,3592
P16
![image-20220909142510012](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909142510012.png)
![image-20220909142655214](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909142655214.png)
- 192.168.1.1、192.168.1.2、192.168.1.3,路由器192.168.1.4
NAT转换表为
第五章
复习题
R1
![image-20220909143223061](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909143223061.png)
路由算法在每个路由器中运行,受限于每个路由器的资源和能力。
每个路由器都作为一个整体独立地工作,既有数据平面也有控制平面。——垂直集成
R4
![image-20220909143413737](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909143413737.png)
LS:全局、集中式、一次性计算
DV:局部、分布式、迭代收敛
![image-20220909143539141](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909143539141.png)
R7
![image-20220909143559871](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909143559871.png)
AS内不关心策略只关心性能,自治区之间要进行控制(政策性、经济型)
- AS内不用考虑规模,AS间要考虑
AS内要考虑性能,AS间不考虑
R8
![image-20220909143835683](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909143835683.png)
错误,在自治区内进行泛洪——LS算法,所有节点都要获得链路状态信息
习题
P3
![image-20220909144001902](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144001902.png)
搞清楚源节点是什么(x),给出源节点到所有节点的最短路径,生成最小生成树。
![image-20220909144213146](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144213146.png)
P5
![image-20220909144236661](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144236661.png)
给定z节点判断其距离矢量的变化
![image-20220909144336937](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144336937.png)
![image-20220909144425756](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144425756.png)
![image-20220909144446415](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144446415.png)
![image-20220909144457144](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144457144.png)
P7
![image-20220909144556938](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144556938.png)
![image-20220909144607207](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909144607207.png)
- Dx(w)=2,Dx(y)=5,Dx(u)=7
- c(x,w)增到6以上,c(x,y)减到1以下
- c(x,w)增到6及以下,c(x,y)减到1及以上
P14
![image-20220909145031670](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909145031670.png)
- eBGP
- iBGP
- eBGP
- iBGP
P15
![image-20220909145220655](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909145220655.png)
![image-20220909145228780](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909145228780.png)
- I1,因为I1距离1c更近
- I2,都需要两大跳(AS-PATH相同),而距离最近的网关1b(NEXT-HOP),I2更近
- I1,经过1c需要两大跳而1b需要三大跳
第六章
复习题
R2
![image-20220909151843978](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909151843978.png)
不是多余的,IP协议不是可靠的。逐跳可靠不等于整个链路可靠,IP数据报可能会被丢弃。同时不同的IP数据报经过不同的路径,其延迟可能不同,到达接收方可能会乱序。
R6
![image-20220909152048727](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152048727.png)
i=5,窗口=2^5=32——概率1/32
t=K*512位时 R=10Mbps,位时=1/R,代入求得延时=204.8us
R11
![image-20220909152330631](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152330631.png)
查询时事先不知道IP和mac的对应关系,应答以后就知道了源mac和源IP。——注意仅涉及同一子网。
R12
![image-20220909152456601](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152456601.png)
不可以:全球任何一个网卡有唯一一个mac地址
映射表定期保存、删除
习题
补充
![image-20220909163600610](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163600610.png)
![image-20220909163619996](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909163619996.png)
P2
![image-20220909152631013](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152631013.png)
![image-20220909152700420](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152700420.png)
![image-20220909152713998](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152713998.png)
行列综合即可判断哪一位出错
![image-20220909152811132](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152811132.png)
同一行两列出错,可以判断两列有错,但无法定位
![image-20220909152847093](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152847093.png)
对偶出错,无法检测、无法定位
P8
![image-20220909152923858](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909152923858.png)
P15
![image-20220909153608271](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909153608271.png)
- 不用经过路由器,在一个子网内部,源:E IP 端口;目的:F IP 端口。
- 不会,因为不在一个子网,查询连接路由器R1的mac地址。源:E IP 端口;目的:B IP R1端口.
- S1收到会向所有其他端口转发广播,R1不会转发——ARP广播不跨子网
响应时向A发送单播即可,因为请求里面携带了A的mac地址。
S1会进行全端口转发——它的作用就是全端口转发,在一个碰撞域内
P17
![image-20220909154236485](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909154236485.png)
![image-20220909154315190](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909154315190.png)
P21
![image-20220909154346496](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909154346496.png)
IP始终是源:A;目标:F
mac地址:
- 源:A;目标:R2
- 源:R2;目标:R1
- 源:R1;目标:F
P26
![image-20220909154703562](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909154703562.png)
核心思想:交换表自学习不断累积——软状态关系,可以定期删除增加
![image-20220909154939728](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909154939728.png)
![image-20220909155020448](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909155020448.png)
![image-20220909155034201](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909155034201.png)
R16
![image-20220909155119194](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909155119194.png)
两两相连,各自出一个端口,连完以后就都在一块了,总共(N-1)*2
P31
![image-20220909155346805](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909155346805.png)
![image-20220909155420883](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909155420883.png)
![image-20220909160200641](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909160200641.png)
路由器的MAC帧,根据路由选择协议对其中的IP数据报进行转发……
P28
![image-20220909160338186](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909160338186.png)
物理上一个、逻辑上两个:一个mac两个IP
每次发IP数据报都要封装为以太网帧,发送到上层路由器解封装后查路由表,再封装成以太网帧下发到对应VLAN
——VLAN把同一交换机的不同端口捆绑为不同的虚拟局域网。
第八章
复习题
R1
![image-20220909160744109](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909160744109.png)
![image-20220909161021198](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161021198.png)
可能,密文取一块就是机密但不完整,未加密的完整报文就是完整而不机密。通常公开密钥下完整性和源端可认证性捆绑。
R3
![image-20220909161041153](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161041153.png)
![image-20220909161058547](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161058547.png)
R13
![image-20220909161137748](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161137748.png)
计算更快、保证反向计算困难
![image-20220909161233919](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161233919.png)
R14
![image-20220909161248807](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161248807.png)
![image-20220909161258940](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161258940.png)
CA私钥对证书散列(报文摘要)进行加密
R16
![image-20220909161450448](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161450448.png)
防止重放攻击
习题
P8
![image-20220909161533561](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161533561.png)
- n=5*11=55 z=4*10=40
- e=3,e<n,且与z没有公因数
- d=27
- m=8,m^e=512,密文c=m^e mod n = 17
P17
![image-20220909161908909](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909161908909.png)
![image-20220909162144470](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909162144470.png)
![image-20220909162207386](/2022/09/09/%E8%AE%A1%E7%AE%97%E6%9C%BA%E7%BD%91%E7%BB%9C%E8%87%AA%E9%A1%B6%E5%90%91%E4%B8%8B/%E4%B9%A0%E9%A2%98%E9%83%A8%E5%88%86%E8%A7%A3%E7%AD%94/image-20220909162207386.png)
先用自己的私钥解出对称式密钥Ks,解出明文m和数字签名,明文m算报文摘要,通过发送方公钥解报文摘要,一样的话就说明通过了机密性校验、完整性校验和身份校验。