计网实验data link layer simulation.doc

计算机通信与网络实验 课程实验报告实验二 : 2.data link layer simulation实验名称：2.data link layer simulation1.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. 2.实验结果A=0.1A=1A=10A=100a=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。 3.实验程序Figure7.12a = 0:0.1:1000;W = 1,7,127;for j = 1:3 for i = 1:length(a) if W(j) = 2*a(i)+1 U(i) = 1; else U(i) = W(j)/(2*a(i)+1); end end if j = 1 W1 = U; end if j = 2 W7 = U; end if j = 3 W10 = U; endendplot(a,W1);hold on;plot(a,W7);plot(a,W10);set(gca,xscale,log);axis(0.1 1000 0 1);Figure7.13a = 0:0.1:1000;W = 1,7,127,127;P=10(-3);for j = 1:4 for i = 1:length(a) if W(j) =1 U(i) = (1-P)/(1+2*a(i); end if W(j)=7 if W(2) = 2*a(i)+1 U(i) = 1-P; else U(i) = W(j)*(1-P)/(2*a(i)+1); end end if W(j)=127 if W(j) = 2*a(i)+1 U(i) = (1-P)/(1+2*a(i)*P); Y(i) = 1-P; else U(i) = W(j)*(1-P)/(2*a(i)+1)*(1-P+W(j)*P); Y(i) = W(j)*(1-P)/(2*a(i)+1); end end if j = 1 W1 = U; end if j = 2 W7 = U; end if j = 3 W10 = U; end if j = 4 W = Y; end endendplot(a,W1);hold on;plot(a,W7);plot(a,W10);plot(a,W);set(gca,xscale,log);axis(0.1 1000 0 1);2、Drawfunction 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)+W.*(1-P)./(2.*a+1)./(1-P+W.*P).*(W2*a+1); endfunction 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