Computer Networks

1
????? Computer
Networks
????? ? ????????
???????????? ??III? 112
Tel [phone]
Emailpengy_at_xidian.edu.cn
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• References
• ?????(???),??,2004, Andrew S. Tanenbaum
• ?????(???)
• ???
• Computer Networks , A System Approach(3rd)
• Larry L. Peterson
• Computer Networks and Internets,
• D. Comer

3

• ????????
• ???????,??????????????????????
• ????????????
• ????????,?????
• ???,???,????

4
Roadmap
??
???
?????
??????(MAC)
???
???
???
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1 ?? 1.1 ???????? 1.2 ???? 1.3 ???? 1.4
???? 1.5 ???? 1.6 ????? 1.7 ??
6
1       ??

• ??????????????????????????????
• Internet,WWW?????????
• ??????????????
• ??
• ???????????????????
• ????????????,????????????
• ???????????????

7
1.1 ????????

• 1.1.1 ????
• ???? ??, ?????
• ??1 ?????????
• CS??(The client-server model)

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• CS????????????
• ??2????????????????,??Email,E-meeting
• ??3???? (B2B, B2C)

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• 1.1.2 ????
• ?????? ??(??), ?????, ????
• ????(P2P)BT.

?? ???????????
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• ??????, VOD.
• ???????.
• ?????

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• 1.1.3 ????
• ????????
• ?????
• ????
• ?????????
• ????.

12

• 1.1.3 ????
• ??????
• ????
• ??

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• 1.2 ????
• ????
• ???????
• ?????????

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??( Multicast )???(Unicast)
Sending Device
A
15
?????
Receiving Devices
Sending Device
A
16
?????
Receiving Devices
Sending Device
A
Broadcast
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?????
Receiving Devices
Sending Device
A
Broadcast Everyone
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?????
Receiving Devices
Sending Device
A
Multicast
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?????
Receiving Devices
Sending Device
A
Multicast Some of the Group
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?????
Receiving Devices
Sending Device
A
Unicast
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?????
Receiving Devices
Sending Device
A
Unicast Just One
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• ??

Storage area network

• lt 1m

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• 1.2.1 ??? (Local area networks)
• ?? ?????,???, ???????
• ???? 10 to 100 Mbps, 1Gbps, 10Gbps
• ?? ???????

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LAN ????(??)
CSMA/CD
Bus Topology - Ethernet
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LAN ????(??)
Carrier Sense / Multiple Access / Collision
Detection
CSMA/CD
Bus Topology - Ethernet
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LAN ????(??)
CSMA/CD
Bus Topology - Ethernet
How It Works!
27
LAN ????(??)
One Broadcast Domain
Bus Topology - Ethernet
28
LAN ????(??)
One Broadcast Domain
Bus Topology - Ethernet
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LAN ????(??)
So, What Happens When Two Data Transmissions Are
Sent At The Same Time?
30
LAN ????(??)
So, What Happens When Two Data Transmissions Are
Sent At The Same Time?
31
LAN ????(??)
Collision
Bus Topology - Ethernet
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LAN ????(??)
Back Off Jamb Signal
Bus Topology - Ethernet
What Happens After the Collision?
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LAN ????(??)
Back-off and Re-send
Re-send 5 µs.
Bus Topology - Ethernet
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LAN ????(??)
One Broadcast Domain One Collision Domain
Re-send 9 µs.
Bus Topology - Ethernet
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LAN ????(???)
Ring Topology Token Ring
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LAN ????(???)
An electrical signal (Token) is circling the LAN
Ring Topology Token Ring
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LAN ????(???)
Message to Send to PC E
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
One Broadcast Domain
Ring Topology Token Ring
39
LAN ????(???)
Not for me
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
Not for me
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
Or me
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
Not for me either!
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
One Broadcast Domain
Its for me!
Ring Topology Token Ring
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LAN ????(???)
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
Message was delivered!
One Broadcast Domain
Ring Topology Token Ring
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LAN ????(???)
No Collisions! Only One Transmission at a Time
Ring Topology Token Ring
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LAN ????(???)
Ring Speed 4 or 16 mbps
Ring Topology Token Ring
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LAN ????(??)
Central Device
Star Topology
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LAN ????(??)
Message to Send to PC E
Central Device
Star Topology
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LAN ????(??)
Central Device
Star Topology
54
LAN ????(??)
Central Device
Star Topology
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• 1.2.2 ???(Metropolitan area networks)
• ???/????, ???LAN?????????
• ???MAN??RPR (2.540Gbps)

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• 1.2.3 ???(Wide area networks)
• ?????????????????
• ???????
• ???? ????????(fig 1-5),???????????????

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• ??-??/?????
• ????

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• 1.2.4 ????(Wireless networks)
• ??????
• ????(personal area network)
• ??LANs
• ??MANs
• ??WANs (?????????)
• ?? ??????

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• Wireless LAN ???????????IEEE 802.11(tens of
  meters)
• LMDS( local multipoint distribution service )
  ????(kilometers) ?IEEE 802.16
• ??????3??????????????????
• 1.2.5 ???(Internetworks)
• ????????????
• ????????WAN????LAN?????
• ?????????????????????????????

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1.3 ????

• ????
• ???????
• ???????????
• ????
• ????????

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• 1.3.1 ????
• ??
• ??????????, ??????????????????,???????????????
  ,???????????,????????????????????
• ??
• ??????????????????

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?????

• Human
  Network

TCP connection request
Hello
TCP connection reply
Hello
SNTP request
Got the time?
SNTP response
Its 1030
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64

?? ??????
Receiver
Sender
Peer to Peer Communications
Layer 7
Layer 7
Layer 6
Layer 6
Layer 5
Layer 5
Inter-Layer Communications
Inter-Layer Communications
Layer 4
Layer 4
Layer 3
Layer 3
Layer 2
Layer 2
Layer 1
Layer 1
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• ??? ??????????????,???????
• ?????????????????????
• ?????????????
• ?????????????????
• ????????????

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• ??

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NO. NAME ENCAPS / PDU DEVICES PROTOCOLS NOTES 1 NOTES 2
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Crayons, Pictures, Writing, Sound .doc .xls
.midi .ppt .jpg .bmp .gif .mp3 .ascii
.ebcdic NFS SQL NetBios RPC TCP UDP
IP IPX OSPF, RIP, BGP, EIGRP, RIP v2,
IGP FR, TR, ATM, FDDI, Ethernet, SDLC,
SNA Cables, Connectors, NIC Cards, ISDN
Checks availability with comm. Partner Syntax,
Compression, Formatting Establish, manage and
terminate sessions Windowing, Buffering,
Reassembly Logical Addressing, Best path BIA
address, Flow Control Like Morse Code
Ideas, Thoughts Standardized format 1
Connection establishment, 2 Data transfer,
3 Connection release Reliable or
Unreliable, 3-way Handshake Routed or routing
protocols, IP Address ARP, MAC Address
Raw Data Segment Packet Frame Bits
Routers, PCs Bridges,
Switches Hubs, Repeaters
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• 1.3.2 ???????
• ????
• ????????????????
• ???????????,ack,??????
• ?? ??(ARQ)
• ???????
• ????????
• ?????????

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• 1.3.4 ??????????
• ?????????????????,???????????????????????????.
• ?????????????????????,??????????????????????????
  ??????
• ????(Quality of service)???

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71

• 1.3.5 ????(Service Primitives)
• ????(??)??????????????
• ????????????,????????????????????
• ?????????,?????????????

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????(CS??)
5?????,????????????????
73
????

• ?????-?????????????

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• 1.3.5 ????????
• ???? layer k1
• ????? layer k
• ?k ??????

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• 1.4 ????
• OSI,TCP/IP????
• 1.4.1 OSI ????
• ISO???????
• OSI??????
• 1.???2.?????3.???4.???
• 5.???6.???7.???

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• ????????????????,????? ??????????,??????????????
  ???
• ???????????????????????????????????????????MAC?
  
• ????????????????????????????????,????????????
• ??? ??????????,?????????,??????????,?????????????
  ????????

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• ???????????????????,??????????????????
• ??? ????????????,????????????
• ??? ?????????,??????????????????HTTP ,FTP?

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• 1.4.2 TCP/IP ????
• ARPANET ? Internet
• ??????????, ???????????????,??????????????(??????
  ?????)? ???????,??IP??.

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• ???
• ??????(Transmission Control Protocol,TCP)
• ???????(User Datagram Protocol,UDP)
• ???
• ?????? TELNET
• ?????? FTP
• ?????? SMTP
• ???? DNS
• ???????? HTTP
• ??????
• ??,?????????????????????

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• ???????????

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• 1.4.3 OSI?????TCP/IP???????
• OSI??????????? ?TCP/IP ?????????????
• OSI ?????,?????TCP/IP?????
• OSI ?????????????????(??????????????),?TCP/IP?????
  ??????,???????????????????

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1.4.4 OSI????????

• ???OSI???????????
• ?????
• ?????
• ?????
• ?????

84
?????

• ???????

85
?????

• OSI??????????????
• ????????????,??????????????
• OSI?????????????????,??????
• ????????,???

86
?????

• ??????,???????????
• ?????
• TCP/IP???!

87
?????

• OSI????????????????
• ??????
• TCP/IP??UNIX??????????

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1.4.5 TCP/IP???????

• ??
• ??????????????????
• ????????
• ???????????????
• ?????????????
• ??????????????

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• ????(????)

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OSI Model vs TCP/IP (DoD) Model
TCP/IP (in detail)
OSI (7 Layers)
TCP/IP (4 Layers)
Application
Application
User Process
User Process
User Process
User Process
User Process
Presentation
Host-To-Host Transport (TCP)
Session
UDP
TCP
ICMP
Transport
IP
Internetwork (IP)
Network
ARP RARP
Datalink
Network
Ethernet, FR, TR, FDDI PPP, SLIP, etc
Physical
Media
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• 1.5 ????
• 1.5.1 ARPANET
• ????50????, ????,??????????????????,?????????????
  (???)?
• ARPA ??????????????????
• ?????TCP/IP ????????????
• (ARPA, the Advanced Research Projects Agency
  )

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The ARPANET

• (a) ??????.
• (b) Baran??????????.

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The ARPANET (2)
IMPs (Interface Message Processors) link
rate56k

• ???ARPANET??.

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The ARPANET (3)
NAP (Network Access Point).

• ARPANET?? (a) December 1969. (b) July 1970.
• (c) March 1971. (d) April 1972. (e)
  September 1972.

95

• 1.5.2 NSFNET
• 1984????????? ????ARPANET?????,??????????
• ???TCP/IP WAN, ?????56kbps????
• 1990?,??????1.5Mbps
• NSF ??IBM??????????????ANS (Advanced Networks and
  Services). In 1990, ANS ?? NSFNET
  ??ANSNET,??????45M.
• ??????????????ARPANET?NSFNET??(Internet???)

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• 1.5.3 Internet
• 1983?1?,TCP/IP ??ARPANET?????????
• 20??80????,???????????????,??????????
• Internet ???????????
• ???? Email, news, remote login and file
  transfer.
• ???(World Wide Web)??????????????????Internet
• Internet?????????ISPs (Internet Service
  Providers)?ISP??????????
• ???ICP?? ICP?ISP????

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• Internet?????. NAP (Network Access Point). POP
  (Point of Presence),

??
??
98

• 1.5.2 ???????
• ?????????
• ???????????????.
• 1. ?????? 2 ????
• ??????????X.25,???,ATM

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X.25 ????
X.25 20??70????,?????????????????
??64kbps,??????3???????128???????? ????? ???
20??80????X.25??,??????????????????????
??1.5Mbps
100

• ??????(ATM)
• ATM ??????????????,???????????????????(everything)
  ?????????????,???????????????
• ?OSI??,??????????(nothing is happen!)
• ????ATM??????,?????,????????,?????????????,???????
  ???IP???

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ATM ???
????155.52Mbps ? 622.08Mbps(?SDH??)

• ??????

102
ATM ??? (2)

• ATM ??.

103

• ATM ????

104

• ?????????.
• ??????????.
• ???????????????????????.
• ATM??????????
• AAL ???????????

105
(No Transcript)
106
???(Ethernet)

• ??????????

(Metcalfe and Boggs, Xerox PARC ,1976)
107
LANs

• Ethernet (IEEE 802.3 standard in 1983 )
• DEC, Intel, and Xerox (DIX standard )
• ????(Token bus) (IEEE 802.4)
• General Motors
• ???(Token ring) (IEEE 802.5).
• IBM

108
?? LANs - WiFi (802.11)

• (a) ?????.
• (b) ?????.

109
?? LANs (2)

• ????????????????????

110
?? LANs (3)

• ???????802.11??

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?? LANs (4)

• 802.11?????
• 802.11 (1997) 1Mbps, 2Mbps
• 802.11a (1999) 54Mbps (wider frequency)
• 802.11b 11Mbps(same freq with 802.11, diff
  modulation technique)
• 802.11g 54Mbps (same modulation with 11a
  and same freq with 802.11b)

112
1.6 ?????

• ??????????????
• ??????????????
• ??Internet ????????????

De facto and De jure From the fact by
law
113
???? ITU(International Telecommunication Union)

• ??????
• ITU-R ??????
• ITU-T ???????
• ITU-D ????
• ??
• ?? (National governments)
• ????(Sector members)
• ????(Associate members)
• ????(Regulatory agencies)

114
??????

• ISO (International Standards Organization)
• ANSI (American National Standards Institute)
• NIST (National Institute of Standards and
  Technology)
• IEEE (Institute of Electrical and Electronics
  Engineering)

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IEEE 802 Standards
http//standards.ieee.org/reading/ieee/std/lanman/
The 802 working groups. The important ones are
marked with . The ones marked with ? are
hibernating. The one marked with gave up.
116
???????

• ??????????(IAB)
• IETF Internet Engineering Task Force
• RFC Request for comments
• http//www.ietf.org/rfc
• IRTF (Internet Research Task Force)
• Internet Society
• http//www.isoc.org

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1.7 ????

• ??????