CSC 535 Communication Networks I Chapter 1 Introduction

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

Communication and Networking z What are the differences? y. Communication - focuses on the transmission of data from one end, called the source, to another end, called the destination. y. Networking - focuses on the issues involved when connecting more communication hosts together and becoming a network. z CSC 535 - focuses on point-to-point communications z CSC 581 - focuses on networking including LAN and WAN 2

Network and Services z A communication network connects many hosts together to provide services. z Some examples: y. Radio and television networks y. Telephone networks y. Cable networks y. Data networks such as the Internet and SOHO networks y. Transportation networks - not our focuses but useful for understanding the services provided by a network. 3

Radio and TV Networks z Means of commuinication: electrical wave with various frequencies z Services: carrying signals that encode some entertaining programs and commercial information. z Requirements: y. Many programs being broadcast simultaneously y. Delay in the order of seconds can be tolerated 4

Telephone Networks z Means of commuinication: electrical wave with various frequencies z Services: carrying signals that encode human conversations. z Requirements: y. Real-time service: delay in the order of seconds can not be accepted; acceptable delay is around 250 milliseconds y. Availability requirement is higher than TV or radio. The network must be available throughout the conversations. y. More “intelligent services” that users are involved. 5

1. 2. 3. 4. 5. 6. Telephone Office The caller picks up the phone triggering the flow of current in wires that connect to the telephone office. 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. Telephone Office 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. ) Telephone Office 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. Telephone Office The ringing signals are discontinued when the destination phone is picked up and communication can then proceed. Telephone Office Either of the users terminate the call by putting down a receiver. Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks Figure 1. 1 6

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

z Figure 1. 2 Retrieving e-mail z Figure 1. 3 World Wide Web example generic examples of each type of application 8

1. 2. 3. 4. 5. 6. 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. Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks Figure 1. 4 9

Realplayer example Copyright © 1995 -2000, Real. Networks, Inc. All rights reserved. Real. Player is a trademark of Real. Networks, Inc. Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 10 Figure 1. 5

Network Funcations and Some Design Issues z Provides connectivity between users z Switching provides a saving on the number of connectivity z Multiplexing provides an efficient way to share connectivity z Routing provides a direction regarding a destination associated with a connection z Addressing identifies source and destinations z Traffic control regulates traffic flowing through a network z Network management monitors network status 11

t 1 t 0 Network Copyright 2000 Mc. Graw-Hill Leon-Garcia and Widjaja Communication Networks 12 Figure 1. 6

(a) A switch provides the network to a cluster of users Network Access network (b) A multiplexer connects two access networks Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 13 Figure 1. 7

1* a (a) 2 3 b 4 A c Metropolitan network A consists of access subnetworks a, b, c, d. d Metropolitan (b) A g National network consists of regional subnetworks , , g. Metropolitan network A is part of regional subnetwork . Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 14 Figure 1. 8

Key Communications Tasks z Transmission system utilization z Interfacing z Signal generation z Synchronization z Exchange management z Error detection and correction z Addressing and routing z Switching and multiplexing z Message formatting z Security z Network management 15

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

[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: L 8 Remote system type is UNIX. Using binary mode to transfer files. ftp> 17

ftp> cd public/socket ---> CWD public/socket 250 CWD command successful. ftp> get server 1. c local: server 1. c remote: server 1. 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 server 1. c 150 Opening BINARY mode data connection for server 1. c (1639 bytes). 226 Transfer complete. 1639 bytes received in 0. 0147 secs (1. 1 e+02 Kbytes/sec) 18

ftp> put server 1. c local: server 1. c remote: server 1. c ftp: setsockopt (ignored): Permission denied ---> PASV 227 Entering Passive Mode (144, 26, 77, 43, 180, 246) ---> STOR server 1. c 150 Opening BINARY mode data connection for server 1. c. 226 Transfer complete. 1639 bytes sent in 0. 000157 secs (1 e+04 Kbytes/sec) ftp> 19

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. 20

PS = packet switch C PS C C = computer PS PS PS C Copyright 2000 Mc. Graw-Hill Leon -Garcia and Widjaja Communication Networks 21 Figure 2. 7

G net 1 net 3 G G G net 2 net 5 G net 4 G G = gateway/router Copyright 2000 Leon-Garcia and Widjaja Communication Networks 22 Figure 2. 8

(a) (1, 1) (2, 1) s Ethernet (2, 2) router PPP (1, 3) r w (1, 2) (b) Server HTTP PC HTTP TCP Router IP IP IP Net Interface Ethernet TCP PPP Copyright 2000 Leon-Garcia and Widjaja Communication Networks 23 Figure 2. 13

User Interface Server PI Server DTP Server FTP Control Connection Data User PI User DTP Connection User FTP PI = Protocol interpreter DTP = Data transfer process Copyright 2000 Leon-Garcia and Widjaja Communication Networks 24 Figure 2. 19

Communication Protocols z A set of rules that is used for “governing” how a source and a destination communicates. z Must speak the same language z Entities y. User applications ye-mail facilities yterminals z Systems y. Computer y. Terminal y. Remote sensor 25

Key Elements of a Protocol z Syntax y. Data formats y. Signal levels z Semantics y. Control information y. Error handling z Timing y. Speed matching y. Sequencing 26

Examples of Protocols z Applications: y. HTTP(p. 45) y. SMTP(p. 48) y. FTP(p. 82) z Transportation: TCP z Networking: IP z many 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) 27

TCP/IP Protocol Architecture z Developed by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET) z Used by the global Internet z No official model but a working one. y. Application layer y. Host to host or transport layer y. Internet layer y. Network access layer y. Physical layer 28

TCP/IP Protocol Architecture Model 29

Protocol Data Units (PDU) z At each layer, protocols are used to communicate z Control information is added to user data at each layer z Transport layer may fragment user data z Each fragment has a transport header added y. Destination SAP y. Sequence number y. Error detection code z This gives a transport protocol data unit 30

Application A data Application Layer data Transport Layer data Network Layer Physical Layer data dt Presentation Layer ph data Session Layer Application Layer ah data Presentation Layer Data Link Layer Application B data sh Session Layer th Transport Layer Network Layer nh dh bits Copyright 2000 Leon-Garcia and Widjaja Communication Networks Data Link Layer Physical Layer 31 Figure 2. 9

Physical Layer z Physical interface between data transmission device (e. g. computer) and transmission medium or network z Characteristics of transmission medium z Signal levels z Data rates z etc. 32

Network Access Layer z Exchange of data between end system and network z Destination address provision z Invoking services like priority 33

Internet Layer (IP) z Systems may be attached to different networks z Routing functions across multiple networks z Implemented in end systems and routers 34

Transport Layer (TCP) z Reliable delivery of data z Ordering of delivery 35

Application Layer z Support for user applications z e. g. http, SMPT 36

OSI Model z Open Systems Interconnection z Developed by the International Organization for Standardization (ISO) z Seven layers z A theoretical system delivered too late! z TCP/IP is the de facto standard 37

Application A Application B Application Layer Presentation Layer Session Layer Transport Layer Communication Network Transport Layer Network Layer Data Link Layer Physical Layer Electrical and/or Optical Copyright 2000 Leon-Garcia and. Signals Widjaja Communication Networks 38 Figure 2. 6

OSI Layers z Application z Presentation z Session z Transport z Network z Data Link z Physical 39

OSI v TCP/IP 40

Standards z Required to allow for interoperability between equipment z Advantages y. Ensures a large market for equipment and software y. Allows products from different vendors to communicate z Disadvantages y. Freeze technology y. May be multiple standards for the same thing 41

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

What have they defined? z ISO: Open Systems Interconnection(OSI) z ANSI: represents USA in ISO z ITU-T: X. 25, X. 400, X. 500; e-mail; ISDN z IEEE: IEEE 802. 2, 802. 3, 802. 4, 802. 5, 802. 11 z ISOC and IETF: TCP/IP, SNMP, routing protocols (RIP, OSPF, BGP) z IETF: maintains Request for Comments(RFCs) z ATM: ATM related standards 43

Further Reading z Sections 1. 1, 1. 2, (skip pp. 14 -pp 32) z Sections 2. 1, 2. 2, 2. 3 44