A closer look at network structure: ▣network edge: applications and hosts ▣network core: routers network of networks ▣access networks, physical media: communication links (通信链路) Introduction 1-11
Introduction 1-11 A closer look at network structure: ❑ network edge: applications and hosts ❑ network core: ❖ routers ❖ network of networks ❑ access networks, physical media: communication links （通信链路）
The network edge: ▣end systems(hosts): run application programs e.g.Web,email at "edge of network" ▣client/,server model client host requests,receives service from always-on server e.g.Web browser/server; email client/server 口peer-peer(对等网络)model:: minimal (or no)use of dedicated(专用的)servers e.g.Skype,BitTorrent,KaZaA Introduction 1-12
Introduction 1 -12 The network edge: ❑ end systems (hosts): ❖ run application programs ❖ e.g. Web, email ❖ at “edge of network” ❑ client/server model ❖ client host requests, receives service from always -on server ❖ e.g. Web browser/server; email client/server ❑ peer -peer （对等网络 ）model: ❖ minimal (or no) use of dedicated （专用的） servers ❖ e.g. Skype, BitTorrent, KaZaA
Network edge:connection-oriented service Goal:data transfer TCP service_[RFC 793] between end systems reliable,in-order byte- ▣handshaking:setup stream data transfer (prepare for)data ÷loss:acknowledgements(确认 transfer ahead of time and retransmissions Hello,hello back human ▣flow control: protocol sender won't overwhelm *set up "state"in two 没)receiver communicating hosts ▣congestion control:. 口TCP-Transmission senders "slow down sending Control Protocol rate"when network *Internet's connection- congested(拥塞、拥挤、阻塞) oriented service Introduction 1-13
Introduction 1-13 Network edge: connection-oriented service Goal: data transfer between end systems ❑ handshaking: setup (prepare for) data transfer ahead of time ❖ Hello, hello back human protocol ❖ set up “state” in two communicating hosts ❑ TCP - Transmission Control Protocol ❖ Internet’s connectionoriented service TCP service [RFC 793] ❑ reliable, in-order bytestream data transfer ❖ loss: acknowledgements（确认 ） and retransmissions ❑ flow control: ❖ sender won’t overwhelm（淹 没） receiver ❑ congestion control: ❖ senders “slow down sending rate” when network congested（拥塞、拥挤、阻塞）
Network edge:connectionless service Goal:data transfer App's using TCP: between end systems ▣HTTP(Web),FTP(file same as before! transfer),Telnet 口UDP-User Datagram (remote login),SMTP Protocol [RFC 768]: (email) connectionless *unreliable data App's using UDP: transfer 口streaming media, no flow control teleconferencing,DNS, *no congestion control Internet telephony Introduction 1-14
Introduction 1-14 Network edge: connectionless service Goal: data transfer between end systems ❖ same as before! ❑ UDP - User Datagram Protocol [RFC 768]: ❖ connectionless ❖ unreliable data transfer ❖ no flow control ❖ no congestion control App’s using TCP: ❑ HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: ❑ streaming media, teleconferencing, DNS, Internet telephony
Chapter 1:roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay loss in packet-switched networks 1.7 Protocol layers,service models 1.8 History Introduction 1-15
Introduction 1-15 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History