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Computer Networking


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Computer Networking

  1. 1. Computer Networking — — A Top-Down Approach Featuring the Internet By Shaowen Yao Shaowen Yao, School Of Software, YNU 1
  2. 2. Foreword: Before The lecture begin  Lecturer and tutorial assistant:  Dr. Yao Shaowen (姚绍文), Mr. Tian Kebin(田克斌)  Prof. Of School of Software  Tel: 5038650(O),5032263(L),Email:  Text Book and Reference Books:  Computer Network -- James F. Kurose  Computer Networks -- Andrew S. Tannenbaum - 3rd Edition  Internetworking with TCP/IP, Volume 1; Protoco1s, and Architecture -2nd Edition  Operating Systems -Internals and Design Principles - William Stallings  计算机网络 –谢希仁 –2nd and 3rd Edition(In Chinese)  Etc.  Assessment Procedure:  Exam — — 70%  Middle-term examination — — 20%  Exercise — — 10%  Some Experiment, Practice and Exercise will be assigned during the tutorial hours Shaowen Yao, School Of Software, YNU 2
  3. 3. Foreword: Before The lecture begin  Some Requirements:  Not necessary to present but must keep silent.  Questions and good suggestions are encouraged to be given out in time during lecturing hours.  Self-study with the help of Internet are greatly encouraged. After tutorial hours, you can find and learn some useful protocols, such as HTTP, LDAP, SOAP, IIOP of CORBA, NAT and something else. section 1.1.3 list some useful hyperlinks.  Experiment and Practice:  Experiment: to configure network and some network equipments, such as Firewall, Switch;  Practice: Programming in Java, C++ or ANSI C to implement core protocols, and analyzing the implementation of some protocols with free source codes.  Lecture Notes Download:  URL:  Username: seinetwork(password:seiynu) Shaowen Yao, School Of Software, YNU 3
  4. 4. After the course, you should:  Learn architecture of computer network, Master TCP/IP suite;  Master computer network protocol, network layering and key protocols of each layer;  Master typical transmission media, data switch principle;  Master protocols of application layer and programming of some typical application layer protocols;  Master functionality of transport layer, particularly TCP and UDP programming;  Master functionality of network layer, particularly IP address and routing;  Master functionality of DLL and LAN, focusing on some basic concepts, protocol, error control and IEEE standard for LAN;  Learn multi-media transmission;  Learn core concepts, key issues and foundation of network information security;  Learn other key issues of computer network, such as Network Management, C/S computing, Distributed computing, PKI and so on. Shaowen Yao, School Of Software, YNU 4
  5. 5. Chapter 1— — Computer Networks and the Internet Shaowen Yao, School Of Software, YNU 5
  6. 6. Goal: Overview:  get context, overview,  what’ the Internet s “feel” of networking  what’ a protocol? s  more depth, detail  network edge later in course  network core  approach:  access net, physical media  performance: loss, delay  descriptive  protocol layers, service models  use Internet as  backbones, NAPs, ISPs example  history  ATM network Shaowen Yao, School Of Software, YNU 6
  7. 7. Computer Network, internet and Internet 1、 What is network?— — Human network as an example. 2、What is computer network? 3、What is internet? 3、What is Internet?  Computer Network: the collection of computers:  Via communication links  With the target to share resource  Resource include: hardware/software/ information/data and something useful to others Shaowen Yao, School Of Software, YNU 7
  8. 8. internet and Internet 1、In computer network— — Computer is the element of the set. 2、What is internet?  the internet is the interconnection of “Computer Network”, internet can be seen as: the collection of computer networks, i.e. Network of networks. 3、What is Internet?  Internet is one special internet;  Internet is a world-wide computer network; 4、What support the network and Internet to run well:  Various protocols; Shaowen Yao, School Of Software, YNU 8
  9. 9. What’ the Internet: “nuts and bolts” view s  millions of connected computing devices: hosts, router workstation end-systems server mobile  pc’ workstations, servers s, local ISP  PDA’ phones, toasters s, running network apps regional ISP  communication links  fiber, copper, radio, satellite  routers: forward packets (chunks) of data thru company network network Shaowen Yao, School Of Software, YNU 9
  10. 10. What’ the Internet: “nuts and bolts” view s  protocols: control sending, router workstation receiving of msgs server  e.g., TCP, IP, HTTP, FTP, PPP mobile local ISP  Internet: “network of networks”  loosely hierarchical  public Internet versus private regional ISP intranet  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task company Force network Shaowen Yao, School Of Software, YNU 10
  11. 11. Some concepts 1、Hosts or end systems: the computing devices hooked up to the Internet. 2、TCP/IP: TCP/IP suite are the Internet principal protocols. 3、ISP: Internet Service Provider.  The topology of the Internet;  Access network;  Regional ISP;  National and international ISP; Shaowen Yao, School Of Software, YNU 11
  12. 12. Some concepts 4、Communication links: to connect every kinds of end system together.  Links are made up of different types of physical media, including coaxial cable, copper wire, fiber optics, radio spectrum;  Link bandwidth: the link transmission rate in bits/sec. 5、With protocols, how can the information or data be sent on network or Internet: Voice communication vs. packet switching.  Tele-communication: before transmission, a physical link connection is established;  The Internet and Network employ a technique named as “packet switching” instead of a dedicated path, e.g., IP packet  Packet switching allows multiple communicating end systems to share a path, even parts of a path at the same time. Shaowen Yao, School Of Software, YNU 12
  13. 13. Some concepts 6、Who take the responsible to standardize the protocol for network.  There are many organizations with high reputation to produce protocols: IEEE, ITU-T(CCITT), ISO, IETF… … 7、Intranet.  Private Networks;  Use the same Internet Technology (the same types of host, routers, links, protocols, and standards).  Packet switching allows multiple communicating end systems to share a path, even parts of a path at the same time. Shaowen Yao, School Of Software, YNU 13
  14. 14. IETF and RFC documentations  Internet Engineering Task Force (IETF)  Open organization - anyone may join  Primarily dedicated to development of the Internet protocols.  Ideas are presented as RFCs and go through a review process  RFC standards described in RFC 1602  Proposed  Draft  Standard Shaowen Yao, School Of Software, YNU 14
  15. 15. IETF and RFC documentations  Requests For Comment (RFC) Describe formally (and sometimes not so formally) everything about the Internet; Actually, RFCs are really a form of Memo; All RFC docs are available on-line:; We use RFCs to learn about SMTP (821), HTTP (2616), for example. Shaowen Yao, School Of Software, YNU 15
  16. 16. What’ the Internet: a service view s  Communication infrastructure enables distributed applications:  WWW, email, games, e- commerce, databases, voting,  more?  To enable distributed apps., the Internet must provide one or more services to make distributed apps. transparent across the underlied physical network. Shaowen Yao, School Of Software, YNU 16
  17. 17. What’ the Internet: a service view s  communication services provided:  Connection-Oriented: to guarantee Quality of Service (QOS) of data transmission between two peers. Peer can be host, component, computing entity like process or object.  connectionLess: without any guarantees on QOS of data transmission.  Do you give some examples in real life like the services? Shaowen Yao, School Of Software, YNU 17
  18. 18. What’ the Internet: a service view s  Internet and applications:  Internet is an infrastructure to allow various applications to be invented and deployed, e.g., early email, ftp, and etc.  Advance and new development is the eventual power to make the Internet grow up. Shaowen Yao, School Of Software, YNU 18
  19. 19. What’ a protocol? s human protocols: network protocols:  “what’ the time?” s  machines rather than humans  “I have a question”  all communication activity  Run different protocols, in Internet governed by e.g., different languages. protocols … specific msgs sent protocols define format, order … specific actions taken of msgs sent and received when msgs received, or among network entities, and other events actions taken on msg … Without protocol, without transmission, receipt communication. Shaowen Yao, School Of Software, YNU 19
  20. 20. What’ a protocol? s a human protocol and a computer network protocol: Hi TCP connection req. Hi TCP connection Got the reply. time? Get 2:00 time <file> Q: Other human protocol?  Protocol is very important, learning computer network is focused on learning network protocols, to understanding the what, why, and how of networking protocols. Shaowen Yao, School Of Software, YNU 20
  21. 21. Shaowen Yao, School Of Software, YNU 21
  22. 22. A closer look at network structure: network edge: applications and hosts network core:  routers  network of networks access networks, physical media: communication links Shaowen Yao, School Of Software, YNU 22
  23. 23. Another view of computer Network  Computer Network = Communication subnet + Resources subnet or Communication subnet + User subnet Host Host Host Host Communication Communication Subnet Subnet Host Resources Host Subnet Host Shaowen Yao, School Of Software, YNU 23
  24. 24. The network edge:  end systems (hosts):  run application programs  e.g., WWW, email  at “edge of network”  client/server model  client host requests, receives service from server  e.g., WWW client (browser)/ server; email client/server  peer-peer model:  host interaction symmetric  e.g.: teleconferencing Shaowen Yao, School Of Software, YNU 24
  25. 25. Network edge: connection-oriented service Goal: data transfer between end TCP service [RFC 793] sys.  TCP - Transmission Control  handshaking: setup (prepare Protocol for) data transfer ahead of  Internet’ connection-oriented s time service  Hello, hello back human  reliable, in-order byte-stream protocol data transfer  set up “state” in two  loss: acknowledgements and communicating hosts retransmissions  TCP Connection: like reg. letter  flow control:  In a very loose manner;  sender won’ overwhelm receiver t  Only the end systems is aware;  congestion control:  Virtual Connection: vs. physical  senders “slow down sending rate” connection in circuit switching. when network congested Shaowen Yao, School Of Software, YNU 25
  26. 26. Network edge: connectionless service Goal: data transfer App’ using TCP: s between end systems  HTTP (WWW), FTP  same as before! (file transfer), Telnet  UDP - User Datagram (remote login), SMTP Protocol [RFC 768]: (email) Internet’ connectionless s service - no handshaking App’ using UDP: s  unreliable data transfer  streaming media,  no flow control teleconferencing,  no congestion control Internet telephony Shaowen Yao, School Of Software, YNU 26
  27. 27. Shaowen Yao, School Of Software, YNU 27
  28. 28. The Network Core  mesh of interconnected routers  the fundamental question: how is data transferred through net?  circuit switching: dedicated circuit per call: telephone net  packet-switching: data sent thru net in discrete “chunks” Shaowen Yao, School Of Software, YNU 28
  29. 29. Network Core: Circuit Switching End-to-end resources reserved for “call”  link bandwidth, switch capacity  dedicated resources: no sharing  circuit-like (guaranteed) performance  call setup required Shaowen Yao, School Of Software, YNU 29
  30. 30. Visualized circuit switching: illustration Switching in Telephone network:  Relay circuit-based circuit switching  Time-slot-based circuit switching 1 RAM buffering i 2 Input time-slot queue buffer ... 3 Output time-slot queue buffer j 1 2 3 Circuit Switch Time-slot Switching Shaowen Yao, School Of Software, YNU 30
  31. 31. Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces”— — Multiplexing  pieces allocated to calls  resource piece idle if not used by owning call (no sharing)  dividing link bandwidth into “pieces”  frequency division:FDM  time division:TDM  some examples:cable TV, satellite communication… … Shaowen Yao, School Of Software, YNU 31
  32. 32. Network Core: Packet Switching each end-end data stream divided resource contention: into packets  aggregate resource  Why we need packet; demand can exceed  user A, B packets share network amount available resources;  congestion: packets  each packet uses full link queue, wait for link use bandwidth;  store and forward:  resources used as needed, packets move one hop at a time Bandwidth division into “pieces”  transmit over link Dedicated allocation  wait turn at next link Resource reservation Shaowen Yao, School Of Software, YNU 32
  33. 33. Network Core: Packet Switching 10 Mbs A Ethernet statistical multiplexing C 1.5Mbps B queue of packets waiting 45 Mbs for output link Primary Rate Interface (PRI): E1:2.048Mbps; D E T1:1.544Mbps. Packet-switching versus circuit switching: human restaurant analogy  other human analogies? Shaowen Yao, School Of Software, YNU 33
  34. 34. Packet switching vs. circuit switching Packet switching allows more users to use network!  1 Mbit link (1Mbps)  each user:  100Kbps when “active”  active 10% of time  circuit-switching: N users  10 users 1 Mbps link  packet switching:  with 35 users, probability > 10 active less that .0017 Shaowen Yao, School Of Software, YNU 34
  35. 35. Packet switching vs. circuit switching Is packet switching a “slam dunk winner?”  Great for bursty data  resource sharing  no call setup  Excessive congestion: packet delay and loss  protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior?  bandwidth guarantees needed for audio/video apps  still an unsolved problem (chapter 6) Shaowen Yao, School Of Software, YNU 35
  36. 36. Message switching Do you wonder:  All kinds of messages are segmented into smaller on the source host, and the receiver reassembles the packets back into original message. Why do we need packet instead of app. message?  The segmentation and reassembly may be an extra burden, is such burden worthy of the advantage from doing that?  One comparison between packet switching and message switching:  Assume: message with 7.5Mbits,  between source and destination are 2 packet switches and 3 links with 1.5Mbps.  No congestion in the network Shaowen Yao, School Of Software, YNU 36
  37. 37. Packet switching vs. Message switching  Message switching costs: 5sec. in each hop, totally takes 15sec.  Packet switching:  Segment into 5000 packets;  One packet cost 1ms;  Two switches works (in store and forward behavior) simultaneously;  Totally takes 5.002sec. Message Shaowen Yao, School Of Software, YNU 37
  38. 38. The advantages and disadvantages of Packet switching  With obvious smaller end-to-end delays;  When bit errors occur, even only one bit is error, the whole packet is corrupted and will be discarded, the advantage of PS over MS is very obvious.  Sth. like FTP with “Resume” vs. traditional FTP.  Another potential advantage is that different message with different size, and packet can be specified with uniformed length, the PS and end- system can process packets much simpler than msg.  packet switching’ disadvantage: overhead. Both s packets and msg need additional data as their header. Shaowen Yao, School Of Software, YNU 38
  39. 39. Have a Try !  On page 42 before subsection 1.4.2;  Download one Java Applet and try it;  Examine the effect of additional propagation delays Shaowen Yao, School Of Software, YNU 39