12081220+金雨鑫+实验2

杭 州 电 子 科 技 大 学

实 验 报 告

学生姓名：金雨鑫 学 号：12081220 指导教师：吴端坡 实验地点：1教108 一、实验室名称：

二、实验项目名称：2.data link layer simulation 三、实验学时：3 四、实验内容：

1.Draw Figure7.12 and 7.13.

2.Simulation on Performance of Data Link Control Protocols

Using the same assumptions that are used for Figure 7.13 in Appendix 7A, plot line utilization as a function of P, the probability that a single frame is in error for the following error-control techniques: a. Stop-and-wait b. Go-back-N with w=7 c. Go-back-N with w=127 d. Selective reject with w=7 e. Selective reject with w=127

Do all of the preceding for the following values of a: 0.1, 1, 10, 100. Draw conclusions about which technique is appropriate for various ranges of a.

实验时间：周二晚上

七、实验器材（设备、元器件）：

PC机一台，装有matlab。

八、实验步骤：

（1）a=0:0.1:1000;

U=utilization(a,1); semilogx(a,U); hold on

U=utilization(a,7); semilogx(a,U); hold on

U=utilization(a,127); semilogx(a,U);

title('Figure 7.12 Sliding-Window Utilization as a Function of a') ylabel('Utilization') xlabel('a')

text(0.7,0.5,' \\leftarrow W=1'); text(8,0.6,' \\leftarrow W=7'); text(130,0.8,' \\leftarrow W=127'); 自编函数代码：

function U=utilization(a,W)

U=1.*(W>=2*a+1)+W./(2*a+1).*(W<2*a+1); end

(2)

a=0:0.1:1000; P=1/1000;

U=stopandwait(a,P); semilogx(a,U,'r'); hold on

U=selective_reject(a,7,P); semilogx(a,U,'g'); hold on

U=gobackn(a,7,P); semilogx(a,U,'b'); hold on

U=selective_reject(a,127,P); semilogx(a,U,'k'); hold on

U=gobackn(a,127,P); semilogx(a,U,'y');

title('Figure 7.13 ARQ Utilization as a Function of a (P = 10-3)') ylabel('Utilization') xlabel('a')

text(0.2,0.2,' Stop-and-wait \\rightarrow');

text(0.23,0.7,' W=7 Go-back-N & \\newline W=7 Selective-reject \\rightarrow');

text(10,0.8,' W=127 \\newline Go-back-N \\rightarrow '); text(110,0.7,' \\leftarrow W=127 \\newline Selective-reject'); 自编函数代码：

function U=stopandwait(a,P) U=(1-P)./(1+2*a); End

function U=selective_reject(a,W,P)

U=(1-P).*(W>=2*a+1)+W.*(1-P)./(2.*a+1).*(W<2*a+1); end

function U=gobackn(a,W,P)

U=(1-P)./(1+2.*a.*P).*(W>=2*a+1)+W.*(1-P)./(2.*a+1)./(1-P+W.*P).*(W<2*a+1); end

(3) figure

set (gcf,'Position',[300,0,800,800], 'color','w') a=[0.1, 1, 10, 100]; for i = 1:4 subplot(2,2,i) lab2_draw(a(i))

title(strcat('a=',num2str(a(i)))) end

自编函数代码：

function lab2_draw(a) P=0:0.1:1000; U=stopandwait(a,P); semilogx(P,U,'r'); hold on

U=selective_reject(a,7,P); semilogx(P,U,'g'); hold on

U=gobackn(a,7,P); semilogx(P,U,'b'); hold on

U=selective_reject(a,127,P); semilogx(P,U,'k'); hold on

U=gobackn(a,127,P); semilogx(P,U,'y'); ylabel('Utilization') xlabel('P')

legend('Stop-and-wait','Go-back-N with w=7 ','Go-back-N with w=127 ','Selective reject with w=7 ','Selective reject with w=127 ',3) end

九、实验数据及结果分析：

。a=0.1时，W=7或者127都是大于2a+1；

a=1时，W=7或者127都是大于2a+1；

a=10时，则选择拒绝和返回N都是一个分段函数。

a=100时，则选择拒绝和返回N都是一个分段函数。

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