Network Essay

445 Words2 Pages
Problem 1: 1. Access net: digital subscriber line (DSL) [pic] Use existing telephone line to central office DSLAM -data over DSL phone line goes to Internet -voice over DSL phone line goes to telephone net -< 2.5 Mbps upstream transmission rate (typically < 1 Mbps) -< 24 Mbps downstream transmission rate (typically < 10 Mbps) 2. Access net: cable network [pic] -HFC: hybrid fiber coax ♣ asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate -network of cable, fiber attaches homes to ISP router ♣ homes share access network to cable headend ♣ unlike DSL, which has dedicated access to central office 3. Access net: home network [pic] Problem 2: Propagation delay= 2500000m/250000000 =0.01s Transmission delay= 8000bits/2000000bps (since 1bytes=8 bits) =0.004s Because of this the transmission delay is 0.004s, is 2/5 of the propagation delay, the transmission delay cannot be ignored and so that the delay is depends on both propagation and the transmission delay. Problem 3: a. packetization time = 48x8bits/64000bps =0.006s b. transmission delay = 64000bps x 0.006s / 1000000bps =0.384ms c. total time = 6ms + 0.384ms + 2ms =8.384ms Problem 4: a. 3Mbps / 150kbps = 20 users can be supported and 150kbps dedicated. b. Because each user can only transmits 10% of the time So, probability = 0.1 c. Probability = Cn120 x 0.1n x 0.9120-n Problem 5: a. [pic] 2 traceroutes with their appropriate averages and standard deviations. b. The paths may be changed over the hours. c. The largest delays are likely to occur between adjacent ISPs. d. [pic] By comparing the intra-continent and inter-continent results, to connect to other countries outside HK need more traceroutes. Problem 6: a. 8 x 106 / 2 x 106 = 4s Total time = 4 x 3 = 12s b. Time to move the first packet from

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