计算机网络 胥正川( XU Zhengchuan) 管理学院信息管理与信息系统系 办公室:思源楼708室,电话:25011237 Email:zexu@fudan.edu.cn
1 计算机网络 胥正川（XU Zhengchuan） 管理学院 信息管理与信息系统系 办公室：思源楼708室，电话：25011237 Email: zcxu@fudan.edu.cn
First Chapter Topics Covered
First Chapter Topics Covered
Network Elements: Recap Applications( the only element that users care about) Computers Clients Never talk about an Servers innovation"reducing cost, increasing speed, etc · Switches and routers without specifying Transmission lines Which element is cheaper or faster Trunk lines Access Lines For example, multiplexing Messages(Frames) only reduces the cost of trunk lines: other Wireless access points costs are not decreased
3 Network Elements: Recap • Applications (the only element that users care about) • Computers – Clients – Servers • Switches and Routers • Transmission Lines – Trunk lines – Access Lines • Messages (Frames) • Wireless Access Points Never talk about an innovation “reducing cost,” “increasing speed,” etc. without specifying which element is cheaper or faster. For example, multiplexing only reduces the cost of trunk lines; other costs are not decreased
Recap: LANs and WANs LANs transmit data within corporate sites WANS transmit data between corporate sites · Each lan or wan is a single network WAN LAN coSts are low and speeds are high WaN coSts are high and speeds are lower
4 Recap: LANs and WANs • LANs transmit data within corporate sites • WANs transmit data between corporate sites • Each LAN or WAN is a single network • LAN costs are low and speeds are high • WAN costs are high and speeds are lower WAN
Recap: Internets Most firms have multiple LANs and WANs They must create internets An internet is a collection of networks connected by routers so that any application on any host on any single network can communicate with any application on any other host on any other network in the internet Application Application LAN WAN LAN Router Router 5
5 LAN WAN LAN Recap: Internets • Most firms have multiple LANs and WANs. • They must create internets – An internet is a collection of networks connected by routers so that any application on any host on any single network can communicate with any application on any other host on any other network in the internet. Application Application Router Router
I Recap: Internets Elements of an Internet Computers connected to the internet are called hosts Both servers and client pcs are hosts Routers connect the networks of the internet together In contrast switches forward frames within individual networks Router Router LAN WAN LAN Client Pc host Server Host 6
6 LAN WAN LAN Recap: Internets • Elements of an Internet – Computers connected to the internet are called hosts • Both servers and client PCs are hosts – Routers connect the networks of the internet together • In contrast, switches forward frames within individual networks Router Client PC Host Server Host Router
Recap: Internets Hosts have Two Addresses ·| P Address This is the hosts official address on its internet 32 bits long Expressed for people in dotted decimal notation( e.g 128,171,17.13) Single Network Addresses This is the host's address on its single network Ethernet addresses, for instance, are 48 bits long Expressed in hexadecimal notation, e.g., AF-23-9B E8-67-47
7 Recap: Internets • Hosts Have Two Addresses • IP Address – This is the host’s official address on its internet – 32 bits long – Expressed for people in dotted decimal notation (e.g., 128, 171, 17.13) • Single Network Addresses – This is the host’s address on its single network – Ethernet addresses, for instance, are 48 bits long – Expressed in hexadecimal notation, e.g., AF-23-9BE8-67-47
Recap: Internets Switches versus routers Switches move frames through a single network(lan or Wan Routers move packets through internets Messages Messages in single networks are called frames Messages in internets are called packets Packets are encapsulated within(carried inside rames 8
8 Recap: Internets • Switches versus Routers – Switches move frames through a single network (LAN or WAN) – Routers move packets through internets • Messages – Messages in single networks are called frames – Messages in internets are called packets – Packets are encapsulated within (carried inside) frames
i Quality of Service It is not enough that networks work They must work we!∥ Quality of Service(Qos) defines quantitative measures of service quality peed S 速度 Delay( Latency 延迟 Reliability 可靠性 Security(not a Qos measure but crucial)
9 Quality of Service • It is not enough that networks work – They must work well • Quality of Service (QoS) defines quantitative measures of service quality – Speed 速度 – Delay (Latency) 延迟 – Reliability 可靠性 • Security (not a QoS measure but crucial)
I Figure 1.9: Quality of Service(Qos) Speed Bits per second(bps) Multiples of 1, 000(not 1,024) Kilobits per second(kbps)<Note the Lower-case"k Megabits(兆位) per second(Mbps) Gigabits〔千兆位) per second(Gbps) erabits(兆兆位) per second(Tbps) Petabits(千兆兆位) per second(Pbps) 10
10 Figure 1.9: Quality of Service (QoS) • Speed – Bits per second (bps) – Multiples of 1,000 (not 1,024) – Kilobits per second (kbps)—Note the Lower-case “k” – Megabits（兆位）per second (Mbps) – Gigabits （千兆位）per second (Gbps) – Terabits （兆兆位）per second (Tbps) – Petabits（千兆兆位）per second (Pbps)