1. Computer Networking II Course Outline - introduction -Network Layer -Wireless and Mobile Networks -Multimedia Networking -Network Management -Network Security Computer Networking: A Top Down Approach, 5 th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2009 Communications and Networking, 3rd edition, Behrouz A Forouzan, McGraw-Hill. مترجم ها : 1 - دکتر بهزاد اکبری 2 - دکتر حسین حاج رسولی ها بسم الله الرحمن الرحیم

2. A Communications Model  Source  generates data to be transmitted  Transmitter  Converts data into transmittable signals  Transmission System  Carries data  Receiver  Converts received signal into data  Destination  Takes incoming data

3. Communications Tasks Transmission system utilizationAddressing InterfacingRouting Signal generationRecovery SynchronizationMessage formatting Exchange managementSecurity Error detection and correctionNetwork management Flow control

4. Communications Tasks  Ways to transfer information on a link Signal format  Addressing Identify sender and receiver  Routing Find a path between sender and receiver  Buffering Compensate for differences in speed Variations in traffic load  Error detection and control If data is lost or corrupted  Congestion control To protect the network from being overloaded  Management and network operations

5. Signals

6. Sine Wave

7. Time and Frequency Domains

8. Bandwidth  Important property of a medium Difference between highest and lowest frequency that can pass through the medium Measured in Hertz [Hz] Limits the channel’s capaci

9. Simplified Data Communications Model

10. Requirements on Communication

11. Introduction 1-11 1:What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data) local ISP company network regional ISP router workstation server mobile

12. Introduction 1-12 What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, FTP, PPP  Internet: “network of networks”  loosely hierarchical  public Internet versus private intranet  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force local ISP company network regional ISP router workstation server mobile

13. Introduction 1-13 What’s the Internet: a service view  communication infrastructure enables distributed applications:  Web, email, games, e- commerce, file sharing  communication services provided to apps:  Connectionless unreliable  connection-oriented reliable

14. Introduction 1-14 What’s a protocol? human protocols:  “what’s the time?”  “I have a question”  introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

15. Introduction 1-15 2:A closer look at network structure:  network edge: applications and hosts  network core:  routers  network of networks  access networks, physical media: communication links

16. Introduction 1-16 The network edge:  end systems (hosts):  run application programs  e.g. Web, email  at “edge of network”  client/server model  client host requests, receives service from always-on server  e.g. Web browser/server; email client/server  peer-peer model:  minimal (or no) use of dedicated servers  e.g. Gnutella, KaZaA, Skype

17. Introduction 1-17 Network edge: connectionless service Goal: data transfer between end systems  same as before!  UDP - User Datagram Protocol [RFC 768]:  connectionless  unreliable data transfer  no flow control  no congestion control App’s using TCP:  HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP:  streaming media, teleconferencing, DNS, Internet telephony

18. Introduction 1-18 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”

19. Introduction 1-19 Network Core: Circuit Switching End-end resources reserved for “call”  link bandwidth, switch capacity  dedicated resources: no sharing  circuit-like (guaranteed) performance  call setup required

20. Introduction 1-20 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces”  pieces allocated to calls  resource piece idle if not used by owning call (no sharing)  dividing link bandwidth into “pieces”  frequency division  time division

21. Introduction 1-21 Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:

22. Introduction 1-22 Numerical example  How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?  All links are 1.536 Mbps  Each link uses TDM with 24 slots/sec  500 msec to establish end-to-end circuit Let’s work it out!

23. Introduction 1-23 Another numerical example  How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?  All links are 1.536 Mbps  Each link uses FDM with 24 channels/frequencies  500 msec to establish end-to-end circuit Let’s work it out!

24. Introduction 1-24 Network Core: Packet Switching each end-end data stream divided into packets  user A, B packets share network resources  each packet uses full link bandwidth  resources used as needed resource contention:  aggregate resource demand can exceed amount available  congestion: packets queue, wait for link use  store and forward: packets move one hop at a time  Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation

25. Introduction 1-25 Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. A B C 10 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

26. Introduction 1-26 Packet switching versus circuit switching  1 Mb/s link  each user:  100 kb/s when “active”  active 10% of time  circuit-switching:  10 users  packet switching:  with 35 users, probability > 10 active less than.0004 Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value 0.0004?

27. Introduction 1-27 Packet-switching: store-and-forward  Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps  Entire packet must arrive at router before it can be transmitted on next link: store and forward  delay = 3L/R (assuming zero propagation delay) Example:  L = 7.5 Mbits  R = 1.5 Mbps  delay = 15 sec R R R L more on delay shortly …

28. Introduction 1-28 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Delay & loss in packet-switched networks 1.6 Protocol layers, service models 1.7 History

29. Introduction 1-29 How do loss and delay occur? packets queue in router buffers  packet arrival rate to link exceeds output link capacity  packets queue, wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers

30. Introduction 1-30 Four sources of packet delay  1. nodal processing:  check bit errors  determine output link A B propagation transmission nodal processing queueing  2. queueing  time waiting at output link for transmission  depends on congestion level of router

31. Introduction 1-31 Delay in packet-switched networks 3. Transmission delay:  R=link bandwidth (bps)  L=packet length (bits)  time to send bits into link = L/R 4. Propagation delay:  d = length of physical link  s = propagation speed in medium (~2x10 8 m/sec)  propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!

32. Introduction 1-32 Nodal delay  d proc = processing delay  typically a few microsecs or less  d queue = queuing delay  depends on congestion  d trans = transmission delay  = L/R, significant for low-speed links  d prop = propagation delay  a few microsecs to hundreds of msecs

33. Introduction 1-33 Queueing delay (revisited)  R=link bandwidth (bps)  L=packet length (bits)  a=average packet arrival rate traffic intensity = La/R  La/R ~ 0: average queueing delay small  La/R -> 1: delays become large  La/R > 1: more “work” arriving than can be serviced, average delay infinite!

34. Introduction 1-34 Packet loss  queue (aka buffer) preceding link in buffer has finite capacity  when packet arrives to full queue, packet is dropped (aka lost)  lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all

35. Network Models

36. LAYERED TASKS We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office. Sender, Receiver, and Carrier Hierarchy Topics discussed in this section:

37. TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to- network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. Physical and Data Link Layers Network Layer Transport Layer Application Layer Topics discussed in this section:

38. TCP/IP and OSI model

39. ADDRESSING Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific. Physical Addresses Logical Addresses Port Addresses Specific Addresses Topics discussed in this section:

40. Addresses in TCP/IP

41. Relationship of layers and addresses in TCP/IP