📜  门| GATE-CS-2015(套装3)|第 65 题

📅  最后修改于: 2021-09-25 04:31:58             🧑  作者: Mango

考虑连接两个相距 8000 公里的系统的网络。网络带宽为每秒 500 × 10 6位。媒体的传播速度为每秒 4 × 10 6米。需要为此网络设计一个Go-Back-N滑动窗口协议。平均数据包大小为 10 7位。网络将被充分利用。假设节点处的处理延迟可以忽略不计。那么,序列号字段的最小比特大小必须是________。
(一) 2
(乙) 4
(三) 8
(四) 16答案: (C)
解释:

Propagation time = (8000 * 1000)/ (4 * 10^6)
                 = 2 seconds

Total round trip propagation time = 4 seconds

Transmission time for one packet = (packet size) / (bandwidth)
                                 = (10^7) / (500 * 10^6)
                                 = 0.02 seconds

Total number of packets that can be transferred before an 
acknowledgement comes back = 4 / 0.02 = 200

Maximum possible window size is 200.  

In Go-Back-N, maximum sequence number should be one more than
window size.

So total 201 sequence numbers are needed. 201 different sequence
numbers can be represented using 8 bits.

这个问题的测验