計算機網(wǎng)絡(luò)第一周作業(yè)(編輯修改稿)
2024-07-15 00:12 本頁面
【文章內(nèi)容簡介】 e from Host Ato Host B over a packetswitched network (VoIP). Host Aconverts analog voice to a digital 64 kbps bit stream on the fly. Host Athen groups the bits into 48byte packets. There is one link between Hosts Aand B。 its transmission rate is 1 Mbps and its propagation delay is 2 msec. As soon as Host Agathers a packet, it sends it to Host B. As soon as Host B receives an entire packet, it converts the packet’s bits to an analog signal. How much time elapses from the time a bit is created (from the original analog signal at Host A) until the bit is decoded (as part of the analog signal at Host B)?答：考慮包中的第一個bit,在這個比特被傳輸之前，包中的所有比特都必須被生成。這需要傳輸數(shù)據(jù)包所需的時間是56*864*103sec=7 msec傳播延遲為2 msec。解碼之前的延遲是56*8500*103sec=896 μsec7 msec + 896μsec + 2msec= msec。 Consider the discussion in Section of packet switching versus circuit switching in which an example is provided with a 1 Mbps link. Users are generating data at a rate of 100 kbps when busy, but are busy generating data only with probability p = . Suppose that the 1 Mbps link is replaced by a 1 Gbps link. a. What is N, the maximum number of users that can be supported simultaneously under circuit switching? b. Now consider packet switching and a user population of M users. Give a formula (in terms of p, M, N) for the probability that more than N users are sending data.答：a).10000 b). Cnm * P^n *(1q)^(mn))9. In the above problem, suppose R1 = R2 = R3 = R and dproc = 0. Further suppose the packet switch does not storeandforward packets but instead immediately transmits each bit it receives before waiting for the entire packet to arrive. What is the endtoend delay?答：由于bits是立即傳輸?shù)?，包交換不引入任何延遲。因此不引入傳輸延遲。D（endend） = L/R + d1/s1 + d2/s28 + 24 + 12 = 44 msec。10. Consider the queuing delay in router buffer (preceding an outbound link). Suppose all packets are L bits, the transmission rate is R bps, and that N packets simultaneously arrive at the buffer every LN/R seconds. Find the average queuing delay of a packet. (Hint:The queuing delay for the first packet is zero。 for the second packet L/R。 for the third packet 2L/ Nth packet has already been transmitted when the second batch of packets arrives.)答：總延遲=(0+1+…+ n 1) L/R平均延遲= (n 1)L/2R11. Suppose N packets arrive simultaneously to a link at which no packets are currently being transmitted or queued. Each packet is of length L and the link has transmission rate R. What is the average queuing delay for the N packets?答 (L/R + 2L/R + ....... + (N1)L/R)/N = L/(RN) * (1 + 2 + ..... + (N1)) = L/(RN) * N(N1)/2 = LN(N1)/(2RN) = (N1)L/(2R) 12. Consider a packet of length L which begins at end system A, travels over one link to a packet switch, and travels from the packet switch over a second link to a destination end system. Let di, si, and Ri denote the length, propagation speed, and the transmission rate of link i, for i = 1, 2. The packet switch delays each packet by dproc. Assuming no queuing delays, in terms of di, si, Ri, (i = 1, 2), and L, what is the total endtoend delay for the packet? 答：第一個端系統(tǒng)需要L/R1時間將
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