Bus(总线 Bus(总线) 总线)
Terminator (50 电阻) 电阻)
Host
Host
Host
Terminator (50 电阻) 电阻)
client/server model
client host requests, receives service from server e.g., WWW client (browser)/ server; email client/server
peer-peer model
minimal (or no) use of dedicated servers e.g.: BT,eMule, Skype
communicating hosts
reliable, in-order byte-stream
data transfer
loss: acknowledgements and retransmissions
TCP Connection: like reg. letter
In a very loose mode; Only the end systems is aware(明白的 明白的); 明白的 Virtual Connection: vs. physical connection in circuit switching.
Chapter 1: Computer Network and Internet
puter Network definition and structure
（1）Computer Network ） What is network?—— Human network as an example. What is computer network?
Host Host Host Host
Communication Subnet/network core
Host
Host
Resources Subnet/network edge Host
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Chapter 1: Computer Network and Internet
2. Topological structure of Computer Networks
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App’s using UDP:
streaming media, teleconferencing, Internet telephony
Chapter 1: Computer Network and Internet
1、Computer Network definition and structure 、
计算机网络原理 Computer Network
课程要求
了解计算机网络的体系结构，掌握OSI/RM、TCP/IP体系结构 掌握计算机网络协议的概念、协议层次及各层次的主要协议 掌握主要的网络传输介质、数据交换的主要类型及基本原理 掌握应用层协议原理及典型的应用层协议编程 掌握传送层主要原理，熟练掌握TCP、UDP原理及编程 掌握网络层主要原理，熟练掌握协议地址、路由原理 掌握链路层及局域网主要概念、标准、差错控制等原理 了解多媒体网络原理 了解网络安全的相关问题、主要原理 了解网络管理的基本问题
flow control:
sender won’t overwhelm receiver
congestion control:
senders “slow down sending rate” when network congested
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Chapter 1: Computer Network and Internet
(3) Network edge: connectionless service
Goal: data transfer between
end systems
same as before!
ቤተ መጻሕፍቲ ባይዱ
App’s using TCP:
HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email)
In a computer network, Computer is the element of the set.
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Chapter 1: Computer Network and Internet
1、Computer Network definition and structure 、
（2）internet and Internet ） What is internet?
（4）The Network Core ） mesh of interconnected routers
the fundamental question: how is data transferred
through net? circuit switching: a dedicated circuit per call as telephone net packet-switching: data sent thru net in discrete “chunks”
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Chapter 1: Computer Network and Internet
(3) Network edge: connection-oriented service
Goal:
data transfer between end systems.
TCP service [RFC 793] TCP - Transmission Control Protocol
receiving of messages
e.g., TCP, IP, HTTP, FTP, PPP
router
Hosts workstation server mobile local ISP
Switch
Internet: “network of networks”
loosely hierarchical public Internet versus private Intranet
Internet是一个特定的、实际运行的internet，是国际互 What is Internet? 连网的简称。 Internet is one special internet;
Internet is a world-wide computer network;
What support the internet and Internet to run well: Various communication protocols
UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service no handshaking no flow control no congestion control unreliable data transfer
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Chapter 1: Computer Network and Internet
What’s the Internet: “nuts and bolts(具体细节 view 具体细节)” 具体细节
millions of connected computing devices: hosts, end-systems pc’s, workstations, servers PDA’s, phones, toasters (烘炉 烘炉) 烘炉 running network applications local ISP[1] router Hosts workstation server mobile
the internet is the interconnection of “Computer Network” internet是指多个网络相互连接构成的网络，并更多地代 Can be seen as the collection of computer networks, i.e. 表网络互连技术； Network of networks.
Switch
routers: forward packets (chunks)
of data thru network Other net devices, e.g. switches regional ISP
communication links
fiber, copper, radio, satellite
Internet’s connection-oriented service
handshaking: setup (prepare for)
data transfer ahead of time
Hello, hello back human protocol
set up “state” in two
Computer Network——the collection of computers: Connected Via communication links With the target to share resources Resources include: computer hardware, software, information (data) and something useful to others
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Chapter 1: Computer Network and Internet
puter Network definition and structure
（5）Another view of computer Network ）
Computer Network = Communication subnet + Resources subnet or Communication subnet + User subnet or Network core + Network edge