Transcript 1-1_Introduction_07

Introduction
Advanced Computer Networks
2007. 9
What is a Communication Network?
(from end system point of view)
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Network offers a service: move information
 bird, fire, telegraph, telephone, Internet …
 transportation (horse, train, airplane): move objects
What distinguish different types of networks?
 The services they provide
What distinguish the services?
 latency
 bandwidth
 number of end systems
 service interface (how to invoke?)
 other details
 reliability, unicast vs. multicast, real-time,
message vs. byte ...
What is a Communication Network?
(Infrastructure Centric View)
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Electrons and photons as communication
medium
Links: fiber, copper, satellite, …
Switches: mechanical/electronic/optical,
Protocols:
TCP/IP, ATM, MPLS, Sonet, Ethernet, PPP,
X.25, FrameRelay, AppleTalk, IPX, SNA
Functionalities:
routing, switching, error control, congestion
control, QoS
Applications: FTP, Web, X windows, ...
The Internet
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Global scale, general purpose,
heterogeneous-technologies, public,
computer network
Internet Protocol
 open system: Internet Engineering Task
Force (IETF) as standard body
- RFC (Request for Comments)
 technical basis for other types of networks
 Intranet: enterprise IP network
Developed by the research community
History of the Internet (1)
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1961-1972: Early packet-switching principles
1961: Kleinrock – queueing theory shows
effectiveness of packet-switching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived by Advanced Research
Projects Agency (Licklider, Roberts)
1969: first ARPAnet node operational
1972: ARPAnet has 15 nodes
 ARPAnet demonstrated publicly
 NCP (Network Control Protocol) first host-host
protocol
 first e-mail program
History of the Internet (2)
L. Kleinrock (MIT thesis): “Information flow in large
communication nets”, 1961
History of the Internet (3)
History of the Internet (4)
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Sep69 1st IMP in UCLA
Oct69 2nd IMP in SRI
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22:30 29Oct69
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LOGIN from UCLA to
SRI CLA
We sent an “L” - did
you get the “L”? YEP!
We sent a “O” - did you
get the “O”? YEP!
We sent an “G” - did
you get the “G”? Crash!
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History of the Internet (5)
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1972-1980: Internetworking, research networks
1970: ALOHAnet satellite network in Hawaii
(Abramson)
1973: Metcalfe’s PhD thesis proposes Ethernet
1974: Cerf and Kahn - 2004 A.M. Turing Award
-define today’s Internet architecture (TCP/IP)
 minimalism, autonomy –no internal changes
required to interconnect networks
 best effort service model
 stateless routers
 decentralized control
1979: ARPAnet has 200 nodes, 56 kbps
Late 70’s: proprietary architectures: DECnet, SNA
Late 70’s: switching fixed length packets (-> ATM)
History of the Internet (6)
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1980’s new protocols, a proliferation of net
1982: SMTP e-mail protocol defined
1983: DNS defined for name-to-IP-address
translation
mid-1980’s: IETF active
1985: FTP protocol defined
1988: TCP congestion control
new national networks: Csnet, BITnet, Minitel ,
NSFnet (1.5 Mbps,10,000 computers), NSI (NASA),
ESNet(DOE), DARTnet, TWBNet (DARPA),
100,000 hosts connected to confederation of
networks
History of the Internet (7)
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1990’s: commercialization, the WWW
Early 1990’s: ARPAnet decommissioned
1991: NSFnet (45 Mbps) -> commercial use of NSF
(decommissioned, 1995)
Late 1990’s:
 multiple private backbones
 50 million computers on Internet
 100 million+ users
 backbone links running at 1 Gbps
Early 1990s: WWW
 hypertext [Bush 1945, Nelson 1960’s]
 HTML, http: Berners-Lee
 1994: Mosaic, later Netscape
 late 1990’s: commercialization of the WWW
Growth of the Internet
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Today: backbones run at 2.4/10 Gbps,
400 millions computers in 150 countries
Internet 在中国
1993年3月
中科院高能物理所
64 Kbps
 TJU:1995.3.22
 2006年12月
 计算机5940万
 用户 1.4亿
 WWW站 84万
 CN域名 180万
 国际出口带宽 257 Gbps
 连接美国、俄罗斯、法国、英国、德国、日本、
韩国、新加坡等
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Services Provided by the Internet
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Shared access to computing resources
 telnet (1970’s)
Shared access to data / files
 FTP, NFS, AFS (1980’s)
Communication medium over which people interact
 email (1980’s), on-line chat, messaging (1990’s)
 IP Telephony (2000’s) - replacing telephone network?
A medium for information dissemination
 USENET (1980’s)
 WWW (1990’s) - replacing newspaper, magazine?
 Audio, video (2000’s): peer-to-peer systems
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replacing radio, CD, TV?
A medium for self-publishing (blogs, YouTube, etc.)
What’s next?
Internet Physical Infrastructure
Protocol Architecture
A Taxonomy of Communication Networks
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Communication networks can be classified based on
the way in which the nodes exchange information:
Communication
Network
Switched
Communication
Network
Broadcast
Communication
Network
Packet-Switched
Circuit-Switched
Communication Communication Network
Network
Datagram
Virtual Circuit
Network
Network
Telephone
Internet
Timing in Circuit Switching
Host 1
Host 2
Node 1
Node 2
processing delay at Node 1
propagation delay
between Host 1
and Node 1
Circuit
Establishment
propagation delay
between Host 2
and Node 1
Data
Transmission
DATA
Circuit
Termination
Timing of Datagram Packet Switching
Host 1
transmission
time of Packet 1
at Host 1
Node 1
Packet 1
Host 2
Node 2
propagation
delay between
Host 1 and
Node 2
Packet 2
Packet 1
Packet 3
processing
delay of
Packet 1 at
Node 2
Packet 2
Packet 1
Packet 2
Packet 3
Packet 3
Packet-Switching vs. Circuit-Switching
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Most important advantage of packet-switching
over circuit switching: ability to exploit
statistical multiplexing:
Efficient
bandwidth usage; ratio between peek and
average rate is 3:1 for audio, and 15:1 for data traffic
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However, packet-switching needs to deal with
congestion:
More
complex routers
Harder to provide good network services (e.g., delay
and bandwidth guarantees)
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They will be combined
Timing of Virtual-Circuit Packet Switching
Host 1
Node 1
Host 2
Node 2
propagation delay
between Host 1
and Node 1
VC
establishment
Packet 1
Packet 2
Packet 1
Data
transfer
Packet 3
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
VC
termination