计算机通信与网络
实验报告
姓名：徐一得
学号：15081525
班级：通信五班
上课时间：周四3-5
实验名称：Simulation on Performance of Data Link Control Protocols
一、实验目的
1.Realizing the principles of Data Link Control Protocols.
eing the software called matalab to simulate the
Performance of Data Link Control Protocols.
二．实验原理
流量控制实际上是对发送方数据流量的控制，使其发送率不致超过接收方所能承受的能力。这个过程需要通过某种反馈机制使发送方知道接收方是否能跟上发送方，也即需要有一些规则使得发送方知道在什么情况下可以接着发送下一帧，而在什么情况下必须暂停发送，以等待收到某种反馈信息后继续发送。
二、实验内容与要求
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.
三、实验程序与结果
Project(1)
a=0:0.1:1000;
U=utilization(a,1); //when length of window is 1
semilogx(a,U,'b'); //using function to depict line
hold on
U=utilization(a,7); //when length of window is 7
semilogx(a,U,'k');
hold on
U=utilization(a,127); //when length of window is 127
semilogx(a,U,'m');
title('figure 7.12 slind-wind utilization as a function of a')
ylabel('utilization')
xlabel('a')
text(0.7,0.5,'\leftarrow w=1'); //noting arrow to
show what the line is text(8,0.6,'\leftarrow w=7');
text(130,0.8,'\leftarrow w=127');
function U=utilization(a,w)
U=1.*(w>=2*a+1)+w./(2*a+1).*(w<2*a+1);
End //formula for utilization U=1/(1+2a)
Project(2)
a=0:0.1:1000;
p=1/1000;
U=stopandwait(a,p); //using the formula to
calculate the U semilogx(a,U,'r'); //using function to depict line hold on
U=selective_reject(a,7,p); //using the formula to
calculate the U
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,1277,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,'stopwait\rightarrow ');
text(0.23,0.7,'w=7 Go-back-N & \newline w=7 selective_reject\rightarrow w=7');
text(10,0.8,'w=127\newline Go-back-N \rightarrow');
text(110,0.7,'\leftarrow w=127');
function U=stopandwait(a,p)
U=(1-p)./(1+2*a); //U=(1-p)/(1+2a)
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 //U=1-p when w>=2a+1
U=W(1-p)/(2a+1) when w<2a+1
