Outlines requirements and time allocation 1.4.2 Physical Media Protocols 10分钟 Physical Media physical link:transmitted data bit propagates across link guided media:signals propagate in solid media:copper,fiber unguided media:signals propagate freelye.g.,radio Twisted Pair (TP).Coaxial cable,fiber.radio (通过当前家庭及单位接入因特网情况，讲解网络接入方式，网络传输介质，用讨论 式教学方式教学。) 1.5 Intemet Bachbones,NAPs,and ISPs(ISP和因特网主干) 10分钟 Roughly hierarchical National/intemational backbone providers (NBPs) Local ISP.company:connect into regional ISPs (了解网络主干网也是分层次结构的，用讨论式教学方式教学。) .6 Delay and Loss in Packet-.Switched Network(分组交换网络中的时延和分组丢失) 1.6.1 Types of Delay Delay in packet-switched networks 10分钟 Nodal Processing delay: check bit errors determine output link Transmission delay: R=link bandwidth(bps) 10分钟 L=packet length(bits) time to send bits into link =L/R s=propagation speed in medium(~2x108 m/sec) propagation delay=d/s Queuing delay: R=link bandwidth(bps) 10分钟 L=packet length (bits) a=average packet arrival rate traffic intensity=La/R La/R~0:average queuing delay small La/R->1:delays become large La/R>1:more"work"arriving than can be serviced,average delay 重点讲解Queuing delay,用启发、讨论式教学方式教学，) 复习本次课的主要内容。 5分钟4 Outlines, requirements and time allocation 1.4.2 Physical Media Protocols Physical Media physical link: transmitted data bit propagates across link guided media: signals propagate in solid media: copper, fiber unguided media: signals propagate freelye.g., radio Twisted Pair (TP), Coaxial cable, fiber, radio （通过当前家庭及单位接入因特网情况，讲解网络接入方式，网络传输介质，用讨论 式教学方式教学。） 1.5 Internet Bachbones, NAPs, and ISPs（ISP 和因特网主干） Roughly hierarchical National/international backbone providers (NBPs) interconnect (peer) with each other privately, or at public Network Access Point (NAPs) Regional ISPs：connect into NBPs Local ISP, company：connect into regional ISPs （了解网络主干网也是分层次结构的，用讨论式教学方式教学。） 1.6 Delay and Loss in Packet-Switched Network（分组交换网络中的时延和分组丢失） 1.6.1 Types of Delay Delay in packet-switched networks Nodal Processing delay: check bit errors determine output link Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s Queuing delay: R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R La/R ~ 0: average queuing delay small La/R -> 1: delays become large La/R > 1: more “work” arriving than can be serviced, average delay infinite! （重点讲解 Queuing delay，用启发、讨论式教学方式教学。） 复习本次课的主要内容。 10 分钟 10 分钟 10 分钟 10 分钟 10 分钟 5 分钟