计算机网络课件 chapter1-1 Introduction

2020/12/20
Computer Networks -1-Part 1
6
Internet History
2007: • ~500 million hosts • Voice, Video over IP • P2P applications: BitTorrent (file
sharing) Skype (VoIP), PPLive (video) • more applications: YouTube, gaming • wireless, mobility
(2) computer progress facilitates telecommunication
Computer Network = computer + communication
• Why networking?
The needs for efficiently collecting, storing, processing, distributing and managing information
2020/12/20
Computer Networks -1-Part 1
11
Important conclusion
• The Internet is not a single network but a network of networks and the Web is a distributed system that runs on top of the Internet.
• 1976: Ethernet at Xerox PARC
• early 70’s: proprietary architectures: DECnet, SNA, XNA
• late 70’s: switching fixed length packets (ATM precursor)
• 1979: ARPAnet has 200 nodes
2020/12/20
Computer Networks -1-Part 1
10
Important conclusion
• In effect, a distributed system is a software system build on top of network. The software gives it a high degree of cohesiveness and transparency. Thus the distinction between a network and a distributed system lies with the software (especially the operating system) rather than with the hardware.
2020/12/20
Computer Networks -1-Part 1
12
1.1 Use of Computer Networks
• Before we start to examine the technical
issues in detail, it is worth devoting some
effectiveness of packetswitching
• 1964: Baran - packetswitching in military nets
– NCP (Network Control Protocol) first host-host protocol
– first e-mail program – ARPAnet has 15 nodes
1972-1980: Internetworking, new and proprietary nets
• 1970: ALOHAnet satellite network in Hawaii
• 1974: Cerf and Kahn architecture for interconnecting networks
Late 1990’s – 2000’s:
• more killer apps: instant messaging, P2P file sharing
• network security to forefront
• est. 50 million host, 100 million+ users
• backbone links running at Gbps
of them would be built. We will start with
traditional uses at companies, then move
on to home networking and recent
developments regarding mobile users,
2020/12/20
Computer Networks -1-Part 1
9
Differences between computer networks and distributed system
• Key distinction is that in a distributed system, the existence of multiple autonomous computers is transparent to users. It looks like a virtual machine with uniprocessor.
– decentralized control define today’s Internet
architecture
2020/12/20
Computer Networks -1-Part 1
4
Internet History
1980-1990: new protocols, a proliferation of networks
The needs for changing manner of using computers
The needs for changing manner of using networks
2020/12/20
Computer Networks -1-Part 1
8
What is a computer network?
Cerf and Kahn’s internetworking principles:
– minimalism, autonomy - no internal changes required to interconnect networks
– best effort service model
– stateless routers
• Tanenbaum’s definition
Computer network - Interconnected collection of autonomous computers
• Our definition:
A sysonomous computers in different locations with communication equipment, trunks, and communication software(OS, protocols, etc.), for resource sharing, is so called computer network.
• With a network, users must explicitly log on to one machine, explicitly submit jobs remotely, explicitly move files around and handle network personally.
• 1983: deployment of TCP/IP
• 1982: smtp e-mail protocol defined
• 1983: DNS defined for name-to-IP-address translation
• 1985: ftp protocol defined
• 1988: TCP congestion control
• 1967: ARPAnet conceived by Advanced Research Projects Agency
• 1969: first ARPAnet
node operational
2020/12/20
Computer Networks -1-Part 1
3
Internet History
network for advanced research project agent of defense department, USA. • Internet: 1986 • National Information Infrastructure: 1993 • Commercialized Internet: 1995 • NGI: 1995, next generation internet • I2: 1996, Internet2 • CNGI: Cernet2 + …
COMPUTER NETWORKS
Chapter 01 Introduction (1)
2020/12/20
Computer Networks -1-Part 1
1
Historic Review
• ENIAC: 1946, the very first computer • ARPANET: 1969, the very first computer
time to pointing out why people are