网络实验报告一.doc

网络实验报告一数据链路层协议的设计与实现 计 83 班 981361 同志强 实验目的计算机网络的数据链路层协议保证通信双方在有差错的通信线路上进行无差错的数据传输，是计算机网络各层协议中通信控制功能最典型的一种协议。本实验实现一个数据链路层协议的数据传送部分，目的在于使学生更好地理解数据链路层协议中的“滑动窗口”技术的基本工作原理，掌握计算机网络协议的基本实现技术。实验内容在一个数据链路层的模拟实现环境中，用C 语言实现下面两个数据链路层协议。（1）“退回到N 重发”的滑动窗口协议（参考文献1第四章的协议5）；（2）“选择重发”的滑动滑动窗口协议（参考文献1第四章的协议6）；实验原理，过程以及分析 首先，我们来分析一下试验原理和所得到的数据，从以下的数据我们不难分析出以下的结论：Protocol 5. Events: 10000 Parameters: 100 20 30Process 1: Total data frames sent: 802 Data frames lost: 162 Data frames not lost: 640 Frames retransmitted: 679 Good ack frames recd: 0 Bad ack frames recd: 0 Good data frames recd: 429 Bad data frames recd: 201 Payloads accepted: 129 Total ack frames sent: 0 Ack frames lost: 0 Ack frames not lost: 0 Timeouts: 97 Ack timeouts: 0Process 0: Total data frames sent: 807 Data frames lost: 177 Data frames not lost: 630 Frames retransmitted: 672 Good ack frames recd: 0 Bad ack frames recd: 0 Good data frames recd: 444 Bad data frames recd: 193 Payloads accepted: 117 Total ack frames sent: 0 Ack frames lost: 0 Ack frames not lost: 0 Timeouts: 96 Ack timeouts: 0Efficiency (payloads accepted/data pkts sent) = 15%End of simulation. Time=10000Protocol 6. Events: 10000 Parameters: 100 20 30Process 1: Total data frames sent: 539 Data frames lost: 119 Data frames not lost: 420 Frames retransmitted: 296 Good ack frames recd: 13 Bad ack frames recd: 8 Good data frames recd: 302 Bad data frames recd: 132 Payloads accepted: 202 Total ack frames sent: 34 Ack frames lost: 6 Ack frames not lost: 28 Timeouts: 296 Ack timeouts: 34Process 0: Total data frames sent: 557 Data frames lost: 123 Data frames not lost: 434 Frames retransmitted: 315 Good ack frames recd: 20 Bad ack frames recd: 8 Good data frames recd: 300 Bad data frames recd: 120 Payloads accepted: 206 Total ack frames sent: 25 Ack frames lost: 4 Ack frames not lost: 21 Timeouts: 315 Ack timeouts: 25Efficiency (payloads accepted/data pkts sent) = 37%End of simulation. Time=10000Protocol 5. Events: 10000 Parameters: 200 20 30Process 1: Total data frames sent: 415 Data frames lost: 89 Data frames not lost: 326 Frames retransmitted: 343 Good ack frames recd: 0 Bad ack frames recd: 0 Good data frames recd: 237 Bad data frames recd: 101 Payloads accepted: 73 Total ack frames sent: 0 Ack frames lost: 0 Ack frames not lost: 0 Timeouts: 49 Ack timeouts: 0Process 0: Total data frames sent: 415 Data frames lost: 77 Data frames not lost: 338 Frames retransmitted: 336 Good ack frames recd: 0 Bad ack frames recd: 0 Good data frames recd: 218 Bad data frames recd: 108 Payloads accepted: 65 Total ack frames sent: 0 Ack frames lost: 0 Ack frames not lost: 0 Timeouts: 48 Ack timeouts: 0Efficiency (payloads accepted/data pkts sent) = 16%End of simulation. Time=10000Protocol 5. Events: 10000 Parameters: 200 20 30Process 1: Total data frames sent: 415 Data frames lost: 89 Data frames not lost: 326 Frames retransmitted: 343 Good ack frames recd: 0 Bad ack frames recd: 0 Good data frames recd: 237 Bad data frames recd: 101 Payloads accepted: 73 Total ack frames sent: 0 Ack frames lost: 0 Ack frames not lost: 0 Timeouts: 49 Ack timeouts: 0Process 0: Total data frames sent: 415 Data frames lost: 77 Data frames not lost: 338 Frames retransmitted: 336 Good ack frames recd: 0 Bad ack frames recd: 0 Good data frames recd: 218 Bad data frames recd: 108 Payloads accepted: 65 Total ack frames sent: 0 Ack frames lost: 0 Ack frames not lost: 0 Timeouts: 48 Ack timeouts: 0Efficiency (payloads accepted/data pkts sent) = 16%End of simulation. Time=10000Protocol 6. Events: 10000 Parameters: 200 40 30Process 1: Total data frames sent: 253 Data frames lost: 115 Data frames not lost: 138 Frames retransmitted: 171 Good ack frames recd: 7 Bad ack frames recd: 6 Good data frames recd: 116 Bad data frames recd: 38 Payloads accepted: 80 Total ack frames sent: 7 Ack frames lost: 2 Ack frames not lost: 5 Timeouts: 171 Ack timeouts: 7Process 0: Total data frames sent: 262 Data frames lost: 108 Data frames not lost: 154 Frames retransmitted: 170 Good ack frames recd: 5 Bad ack frames recd: 0 Good data frames recd: 97 Bad data frames recd: 41 Payloads accepted: 69 Total ack frames sent: 19 Ack frames lost: 6 Ack frames not lost: 13 Timeouts: 170 Ack timeouts: 19Efficiency (payloads accepted/data pkts sent) = 28%End of simulation. Time=10000Protocol 6. Events: 10000 Parameters: 200 20 70Process 0: Total data frames sent: 217 Data frames lost: 44 Data frames not lost: 173 Frames retransmitted: 190 Good ack frames recd: 2 Bad ack frames recd: 10 Good data frames recd: 46 Bad data frames recd: 131 Payloads accepted: 27 Total ack frames sent: 13 Ack frames lost: 1 Ack frames not lost: 12 Timeouts: 190 Ack timeouts: 13Process 1: Total data frames sent: 218 Data frames lost: 41 Data frames not lost: 177 Frames retransmitted: 186 Good ack frames recd: 4 Bad ack frames recd: 8 Good data frames recd: 44 Bad data frames recd: 129 Payloads accepted: 22 Total ack frames sent: 14 Ack frames lost: 2 Ack frames not lost: 12 Timeouts: 186 Ack timeouts: 14Efficiency (payloads accepted/data pkts sent) = 11%End of simulation. Time=100001 由两协议的原理我们也可分析出不同之处：1)由于协议6要存储后续的帧，所以它要用的buffer也就要多一些。2)协议5的接受窗口为1，而协议6的窗口则为：（max_seq+1）/2.2 在一般的情况下，协议6的效率要比协议5的效率高。这个我们可以从原理上来分得到此结论：1）对于协议5，当出现错误时，接受过程直接抛弃所有后续的帧,当发送过程时间到，在重发后续的未经确认的帧；但是对于协议6，当出现错误时，接受方的数据连路层存储后续所有正确的帧，第二次之重发出现错误的帧。重发的帧就少了，所以效率也就上去了。2） 协议6多了一个辅助计时器，当一个按序列号发的数据帧到达后，启动它，如当超时前无反向的通讯后，发送一个