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)