计算机网络试验报告.doc

计算机网络试验报告槐玲 黄海凤 程磊一 实验名称 仿真滑动窗口协议。二、实验要求模拟停等协议、回退n协议及选择重传协议的发送过程。三、实验环境硬件环境：windowsXP系统四、实验目的: 1 熟练掌握滑动窗口的状态变化。 2 模拟停等协议、回退n协议及选择重传协议的发送过程。 3 进一步加深对停等协议、回退n协议及选择重传协议的机理的了解。五、实验步骤 1、停等协议的发送过程： 发送端与接受端的窗口大小均为一，发送端一次只能发送一个数据帧，等待接受方接收到数据帧然后发送确认帧后，在发送下一帧。程序界面：（1） 首先设置发送帧数和丢包率设置后如图：发送帧数为3，对保率为56%，即每个帧有56%的几率丢失点击确定后开始发送第一帧：如下图第一帧发送完，接受方接收第一帧完毕后，发送确认帧：如下图开始发送第二帧：第二帧丢失：计时器超时后重发三帧发送完毕：2回退n协议发送过程：发送端的窗口大小为1，接收端窗口大小为1。发送端一次可发送多个数据，而接受端一次只能接受1个数据帧。当发送帧出错时，之后的所有帧延时重发，接受端重新接受。当确认帧出错时，延时重发，接受端不接受，但重发确认帧。首先设置重发定时，如图：开始发送数据帧： 第四帧丢失： 发送丢失帧之前的确认帧： 计时器超时后重发第四帧以及之前的帧 发送完毕3、选择重传协议发送过程： 发送端窗口与接受端窗口都大于1，当发送帧出错时，接受端可以接受此数据帧以下的数据帧，但不提交给接受端。只是放入接受缓冲区。首先设置重发定时：开始发送：第四帧丢失 发送确认帧： 计时器超时后重发第四帧： 发送第四帧的确认帧： 发送完毕：六、源程序模块中的变量：Public Rcapable% 接受方的处理能力Public sendnum% 发送帧数Public dropnum% 丢包率Public num% 纪录发送帧数Public biaoji As Boolean 丢包标记Public timer% 计时器Public ztimer% 总用时计时器Public bj(5) As Integer 回退n中的发送帧与确认帧标记Public diu(5) As Integer 丢包标记Public chongfa 重发定时Public s(5) As BooleanPublic T As IntegerPublic x As Integer 第几帧丢Public q As Boolean 重发标记Form1上的代码：Dim i%Private Sub Command1_Click()Form2.ShowEnd SubPrivate Sub Command2_Click()Text1.Text = Text2.Text = Text3.Text = For sw = 0 To 5Shape1(sw).Visible = TrueNextTimer2.Interval = 300timer = 0ztimer = 0chongfa = Int(InputBox(重发定时：（毫秒）)x = Int(5 * Rnd + 0)diu(x) = 1 丢包标记End SubPrivate Sub Command3_Click()Text1.Text = Text2.Text = Text3.Text = For sw = 0 To 5Shape1(sw).Visible = TrueNextTimer3.Interval = 300timer = 0ztimer = 0chongfa = Int(InputBox(重发定时：（毫秒）)x = Int(5 * Rnd + 0)diu(x) = 1 丢包标记End SubPrivate Sub Form_Load()i = 0timer = 0ztimer = 0For r = 0 To 5bj(r) = 0diu(r) = 0s(r) = TrueNextq = TrueEnd SubPrivate Sub Timer1_Timer()Dim drop%Dim lent%If num = 0 Then 发送帧数If i = 0 Thenzhen.FillColor = &H8000000FIf zhen.Left = 0 ThenIf num 0 Thenzhen.Visible = TrueText1.Text = Text1.Text & Chr(13) & Chr(10) & Time() & 发送方开始第 & sendnum - num + 1 & 帧发送timer = 0End IfIf num = 0 Then 发送完所有的帧得到平均延迟Text1.Text = Text1.Text & Chr(13) & Chr(10) & 平均延迟： & ztimer / sendnumEnd Ifnum = num - 1drop = Int(100 * Rnd + 1) 产生随机数If drop dropnum Then 设置丢包标记biaoji = FalseElsebiaoji = TrueEnd IfEnd IfIf zhen.Left = 100 Thenzhen.FillColor = &HFFzhen.Left = zhen.Left - 100If zhen.Left = 0 ThenIf zhen.Visible = True ThenText1.Text = Text1.Text & Chr(13) & Chr(10) & Time() & 发送方得到第 & sendnum - num & 帧确认帧End Ifi = 0End IfEnd IfEnd IfElse 发送完所有的帧Timer1.Interval = 0End Iftimer = timer + 1ztimer = ztimer + 1 Text2.Text = timer Text3.Text = ztimer End SubPrivate Sub Timer2_Timer()timer = timer + 1ztimer = ztimer + 1Text2.Text = timerText3.Text = ztimerIf (timer = 1) And bj(0) 2 Then s(0) = startgo(Shape1(0), 1, bj(0), diu(0)End IfIf (timer = 4) And bj(1) 2 Thens(1) = startgo(Shape1(1), 2, bj(1), diu(1)End IfIf (timer = 7) And bj(2) 2 Thens(2) = startgo(Shape1(2), 3, bj(2), diu(2)End IfIf (timer = 10) And bj(3) 2 Thens(3) = startgo(Shape1(3), 4, bj(3), diu(3)End IfIf (timer = 13) And bj(4) 2 Thens(4) = startgo(Shape1(4), 5, bj(4), diu(4)End IfIf (timer = 16) And bj(5) 2 Thens(5) = startgo(Shape1(5), 6, bj(5), diu(5)End IfIf s(x) = False And q = True Then 丢包处理bj(x) = 2 此帧不再继续传For sk = x To 5 此后的帧也不再继续返回确认帧If bj(sk) = 1 ThenShape1(sk).Visible = Falsebj(sk) = 2If sk = 5 Then 最后一帧收到q = FalseEnd IfEnd IfNextT = timerEnd IfIf ztimer = T + chongfa Then 重发timer = 0For sk = x To 5Shape1(sk).Left = 0Shape1(sk).Visible = Truediu(sk) = 0bj(sk) = 0Nextx = 5End IfEnd IfNextIf ztimer T + chongfa ThenIf bj(0) = 2 And bj(1) = 2 And bj(2) = 2 And bj(3) = 2 And bj(4) = 2 And bj(5) = 2 ThenTimer2.Interval = 0Text1.Text = Text1.Text & Chr(13) & Chr(10) & 平均延迟 & ztimer / 6End IfEnd IfEnd SubPrivate Function startgo(sp As Shape, num As Integer, i As Integer, diu As Integer) As BooleanIf i = 0 Thensp.FillColor = &HFFFF80If sp.Left = 0 Thensp.Visible = TrueText1.Text = Text1.Text & Chr(13) & Chr(10) & Time() & 发送方开始第 & num & 帧发送timer = 0If num = 0 Then 发送完所有的帧得到平均延迟Text1.Text = Text1.Text & Chr(13) & Chr(10) & 平均延迟： & ztimer / sendnumEnd Ifdrop = Int(100 * Rnd + 1) 产生随机数If drop dropnum Then 设置丢包标记biaoji = FalseElsebiaoji = TrueEnd IfEnd IfIf sp.Left 5000 Thensp.Left = sp.Left + 100If diu = 1 ThenIf sp.Left = 2500 Then 此帧丢失sp.Visible = FalseText1.Text = Text1.Text & Chr(13) & Chr(10) & 第 & num & 帧丢失num = num + 1startgo = FalseExit FunctionEnd IfEnd IfEnd IfIf sp.Left = 5000 ThenIf sp.Visible = True And num = 100 Thensp.FillColor = &HFFsp.Left = sp.Left - 100If sp.Left = 0 And sp.Visible = True ThenText1.Text = Text1.Text & Chr(13) & Chr(10) & Time() & 发送方得到第 & num & 帧确认帧i = 2End IfEnd IfEnd Ifstartgo = TrueEnd FunctionPrivate Sub Timer3_Timer()timer = timer + 1ztimer = ztimer + 1Text2.Text = timerText3.Text = ztimerIf (timer = 1) And bj(0) 2 Then s(0) = startgo(Shape1(0), 1, bj(0), diu(0)End IfIf (timer = 4) And bj(1) 2 Thens(1) = startgo(Shape1(1), 2, bj(1), diu(1)End IfIf (timer = 7) And bj(2) 2 Thens(2) = startgo(Shape1(2), 3, bj(2), diu(2)End IfIf (timer = 10) And bj(3) 2 Thens(3) = startgo(Shape1(3), 4, bj(3), diu(3)End IfIf (timer = 13) And bj(4) 2 Thens(4) = startgo(Shape1(4), 5, bj(4), diu(4)End IfIf (timer = 16) And bj(5) 2 Thens(5) = startgo(Shape1(5), 6, bj(5), diu(5)End IfIf s(x) = False And q = True Then 丢包处理bj(x) = 2 此帧不再继续传For sk = x To 5 此后的帧也不再继续返回确认帧If bj(sk) = 1 ThenShape1(sk).Visible = Falsebj(sk) = 2If sk = 5 Then 最后一帧收到q = FalseEnd IfEnd IfNextT = timerEnd IfIf ztimer = T + chongfa Then 重发timer = 0Shape1(x).Left = 0Shape1(x).Visible = Truediu(x) = 0bj(x) = 0x = 5End IfEnd IfNextIf ztimer T + chongfa ThenIf bj(0) = 2 And bj(1) = 2 And bj(2) = 2 And bj(3) = 2 And bj(4) = 2 And bj(5) = 2 ThenTimer3.Interval = 0Text1.Text = T