1. CSC 535 Communication Networks I Chapter 1 Introduction Dr. Cheer-Sun Yang

2. 2 Communication and Networking zWhat are the differences? yCommunication - focuses on the transmission of data from one end, called the source, to another end, called the destination. yNetworking - focuses on the issues involved when connecting more communication hosts together and becoming a network. zCSC535- focuses on point-to-point communications zCSC581- focuses on networking including LAN and WAN

3. 3 Network and Services zA communication network connects many hosts together to provide services. zSome examples: yRadio and television networks yTelephone networks yCable networks yData networks such as the Internet and SOHO networks yTransportation networks - not our focuses but useful for understanding the services provided by a network.

4. 4 Radio and TV Networks zMeans of commuinication: electrical wave with various frequencies zServices: carrying signals that encode some entertaining programs and commercial information. zRequirements: yMany programs being broadcast simultaneously yDelay in the order of seconds can be tolerated

5. 5 Telephone Networks zMeans of commuinication: electrical wave with various frequencies zServices: carrying signals that encode human conversations. zRequirements: yReal-time service: delay in the order of seconds can not be accepted; acceptable delay is around 250 milliseconds yAvailability requirement is higher than TV or radio. The network must be available throughout the conversations. yMore “intelligent services” that users are involved.

6. Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks6 The caller picks up the phone triggering the flow of current in wires that connect to the telephone office. The current is detected and a dial tone is transmitted by the telephone office to indicate that it is ready to receive the destination number. The caller sends this number by pushing the keys on the telephone set. Each key generates a pair of tones that specify a number. (In the older phone sets the user dials a number which in turn generates a corresponding number of pulses.) The equipment in the telephone office then uses the telephone network to attempt a connection. If the destination telephone busy, then a busy tone is returned to the caller. If the destination telephone is idle, then ringing signals are sent to both the originating and destination telephones. The ringing signals are discontinued when the destination phone is picked up and communication can then proceed. Either of the users terminate the call by putting down a receiver. Telephone Office 1. Telephone Office 2. Telephone Office 3. 4. Telephone Office 5. 6. Telephone Office Telephone Office Figure 1.1

7. 7 Data Networks zMeans of commuinication: electrical wave with various frequencies zServices: carrying signals that encode information. zRequirements: yconnectionless (e-mail) vs. connection-oriented (ftp, telnet, www, etc.); yreal-time (audio/video conferencing) vs. Non real- time (video on demand)

8. 8 zFigure 1.2 Retrieving e-mail zFigure 1.3 World Wide Web example generic examples of each type of application

9. Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks9 The user clicks on a link to indicate which document is to be retrieved. The browser must determine the address that contains the document. It does this by sending a query to its local name server. Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections. The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle. The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format. The TCP connection is then closed and the user may view the document. 1. 2. 3. 4. 5. 6. Figure 1.4

10. Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks10 Realplayer example Figure 1.5 Copyright © 1995-2000, RealNetworks, Inc. All rights reserved. RealPlayer is a trademark of RealNetworks, Inc.

11. 11 Network Funcations and Some Design Issues zProvides connectivity between users zSwitching provides a saving on the number of connectivity zMultiplexing provides an efficient way to share connectivity zRouting provides a direction regarding a destination associated with a connection zAddressing identifies source and destinations zTraffic control regulates traffic flowing through a network zNetwork management monitors network status

12. Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks12 t0t0 t1t1 Network Figure 1.6

13. Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks13 Network (a) A switch provides the network to a cluster of users (b) A multiplexer connects two access networks Access network Figure 1.7

14. Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks14 Metropolitan network A consists of access subnetworks a, b, c, d. National network consists of regional subnetworks . Metropolitan network A is part of regional subnetwork . A A Metropolitan 1* a c b d  (a) (b) 2 3 4   Figure 1.8

15. 15 Key Communications Tasks zTransmission system utilization zInterfacing zSignal generation zSynchronization zExchange management zError detection and correction zAddressing and routing zSwitching and multiplexing zMessage formatting zSecurity zNetwork management

16. 16 What happens “In the Cockpit”? Example: ftp zHardware: links between source and destination zHardware: PCs and Network Interface Card zHardware: modem zSoftware: TCP/IP software zSoftware: device driver zSoftware: operating system that ftp(an application program) is running on zLet’s try “ftp -d taz.cs.wcupa.edu”

17. 17 [yang@coyote yang]$ ftp -d taz.cs.wcupa.edu Connected to taz.cs.wcupa.edu. 220 taz.cs.wcupa.edu FTP server (Version wu-2.6.1(1) Wed Aug 9 05:54:50 EDT 2000 ) ready. Name (taz.cs.wcupa.edu:yang): yang ---> USER yang 331 Password required for yang. Password: ---> PASS XXXX 230 User yang logged in. ---> SYST 215 UNIX Type: L8 Remote system type is UNIX. Using binary mode to transfer files. ftp>

18. 18 ftp> cd public/socket ---> CWD public/socket 250 CWD command successful. ftp> get server1.c local: server1.c remote: server1.c ---> TYPE I 200 Type set to I. ftp: setsockopt (ignored): Permission denied ---> PASV 227 Entering Passive Mode (144,26,77,43,87,139) ---> RETR server1.c 150 Opening BINARY mode data connection for server1.c (1639 bytes). 226 Transfer complete. 1639 bytes received in 0.0147 secs (1.1e+02 Kbytes/sec)

19. 19 ftp> put server1.c local: server1.c remote: server1.c ftp: setsockopt (ignored): Permission denied ---> PASV 227 Entering Passive Mode (144,26,77,43,180,246) ---> STOR server1.c 150 Opening BINARY mode data connection for server1.c. 226 Transfer complete. 1639 bytes sent in 0.000157 secs (1e+04 Kbytes/sec) ftp>

20. 20 ftp> quit ---> QUIT 221-You have transferred 3278 bytes in 2 files. 221-Total traffic for this session was 5858 bytes in 5 transfers. 221-Thank you for using the FTP service on taz.cs.wcupa.edu. 221 Goodbye.

21. Copyright 2000 McGraw-Hill Leon-Garcia and Widjaja Communication Networks21 C PS C C C C PS = packet switch C = computer Figure 2.7

22. Copyright 2000 Leon-Garcia and Widjaja Communication Networks22 G G G G G net 1 net 2 net 3 net 4 net 5 G = gateway/router G Figure 2.8

23. Copyright 2000 Leon-Garcia and Widjaja Communication Networks23 Net Interface IP TCP HTTP Net Interface IP Net Interface IP TCP HTTP EthernetPPP Router router (1,1) s (1,2) w (2,1) (1,3) r (2,2) PPP Ethernet (a) (b) Server PC Figure 2.13

24. Copyright 2000 Leon-Garcia and Widjaja Communication Networks24 User Interface User PI User DTP PI = Protocol interpreter DTP = Data transfer process User FTP Server PI Server DTP Server FTP Control Connection Data Connection Figure 2.19

25. 25 Communication Protocols zA set of rules that is used for “governing” how a source and a destination communicates. zMust speak the same language zEntities yUser applications ye-mail facilities yterminals zSystems yComputer yTerminal yRemote sensor

26. 26 Key Elements of a Protocol zSyntax yData formats ySignal levels zSemantics yControl information yError handling zTiming ySpeed matching ySequencing

27. 27 Examples of Protocols zApplications: yHTTP(p.45) ySMTP(p. 48) yFTP(p.82) zTransportation: TCP zNetworking: IP zmany others....almost too many z(skip sections 1.2.2, 1.2.3, 1.2.4,1.2.5, 1.2.6, 1.3.1)

28. 28 TCP/IP Protocol Architecture zDeveloped by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) zUsed by the global Internet zNo official model but a working one. yApplication layer yHost to host or transport layer yInternet layer yNetwork access layer yPhysical layer

29. 29 TCP/IP Protocol Architecture Model

30. 30 Protocol Data Units (PDU) zAt each layer, protocols are used to communicate zControl information is added to user data at each layer zTransport layer may fragment user data zEach fragment has a transport header added yDestination SAP ySequence number yError detection code zThis gives a transport protocol data unit

31. Copyright 2000 Leon-Garcia and Widjaja Communication Networks31 Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application A Application B data ah ph sh th nh dh bits dt Figure 2.9

32. 32 Physical Layer zPhysical interface between data transmission device (e.g. computer) and transmission medium or network zCharacteristics of transmission medium zSignal levels zData rates zetc.

33. 33 Network Access Layer zExchange of data between end system and network zDestination address provision zInvoking services like priority

34. 34 Internet Layer (IP) zSystems may be attached to different networks zRouting functions across multiple networks zImplemented in end systems and routers

35. 35 Transport Layer (TCP) zReliable delivery of data zOrdering of delivery

36. 36 Application Layer zSupport for user applications ze.g. http, SMPT

37. 37 OSI Model zOpen Systems Interconnection zDeveloped by the International Organization for Standardization (ISO) zSeven layers zA theoretical system delivered too late! zTCP/IP is the de facto standard

38. Copyright 2000 Leon-Garcia and Widjaja Communication Networks38 Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Network Layer Electrical and/or Optical Signals Application A Application B Data Link Layer Physical Layer Network Layer Data Link Layer Physical Layer Communication Network Figure 2.6

39. 39 OSI Layers zApplication zPresentation zSession zTransport zNetwork zData Link zPhysical

40. 40 OSI v TCP/IP

41. 41 Standards zRequired to allow for interoperability between equipment zAdvantages yEnsures a large market for equipment and software yAllows products from different vendors to communicate zDisadvantages yFreeze technology yMay be multiple standards for the same thing

42. 42 Who defines standards? zInternational: The International Standards Organization(ISO) zThe American National Standards Institute(ANSI) zThe International Telecommunications Union- Telecommunication Standards Sector (ITU-T, formally the CCITT) zThe Institute of Electrical and Electronics Engineers (IEEE) zInternet Society (ISOC) and Internet Engineering Task Force (IETF) zATM Forum

43. 43 What have they defined? zISO: Open Systems Interconnection(OSI) zANSI: represents USA in ISO zITU-T: X.25, X.400, X.500; e-mail; ISDN zIEEE: IEEE 802.2, 802.3, 802.4, 802.5, 802.11 zISOC and IETF: TCP/IP, SNMP, routing protocols (RIP, OSPF, BGP) zIETF: maintains Request for Comments(RFCs) zATM: ATM related standards

44. 44 Further Reading zSections 1.1, 1.2,(skip pp.14-pp32) zSections 2.1, 2.2, 2.3