Computer Networks fall 2006

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1 Computer Networks fall Introduction, Internet, reference models 1

2 Organisation Web page Lecture Wendesday, 2-4 pm, place: Mogyoródi terem (South bld ) Practice Will be published in the web page Exercises Every Friday in the web page Not obligated Base for the exam They will be discussed on next week 2

3 Exam Written exam Prerequisite for the exam: successful practice grade Content of the exam PDF-slides of the lecture cann be downloaded from the web page of the lecture References on the web page 3

4 Content 1. Introduction Recommended literature Examples Reference models 2. Physical layer 3. Data Link Layer 4. Medium Access Control Sublayer MAC 5. Network Layer 6. Transport Layer 7. Application Layer 8. Network security 4

5 Motivation 5

6 Examples for computer networks 6

7 Recommended literature (I) 1. recommended book: Computer Networks, 4. edition, Andrew S. Tannenbaum, Prentice Hall price: 49,90 Euro (amazon) 7

8 Recommended literature (II) 2. recommended book: Computer Networking - A Top-Down Approach Featuring the Internet, James F. Kurose, Keith W. Ross, Prentice Hall price: 71,64 Euro (amazon) 8

9 Recommended literature (III) L. L. Peterson & B. S. Davie, Computer Networks A Systems Approach, 2003, 3rd edition, Morgan Kaufman price: 53,30 EUR (amazon) 9

10 Recommended literature (IV) Fred Halsal, Data Communications, Computer Networks and Open Systems, Addison-Wesley,

11 Further literature (V) Further literature: TCP/IP Illustrated, Volume - The Protocols, W. Richard Stevens, Addison-Wesley 11

12 The Internet Open word wide WAN (wide area network) System independent Connects LANs (local area networks) with each other Without central control NOT the World Wide Web (WWW) 12

13 Comparation of network structures Hierarchical phone network The Internet 13

14 Network, which is open for every architecture Concept by Robert Kahn (DARPA 1972) Each (local) network is open Works autonomously Without proper configuration for WAN Communication is based on best effort principle If a packet does not arrive to the destinataion, it will be deleted The application resend it Black Box approach for the connections Black Boxes later have been renamed for gateways and routers Packet informations are not stored No flow control No global control That are the principles of the Internet 14

15 History of the Internet 1961: Packet Switching Theory Leonard Kleinrock, MIT, Information Flow in Communication Nets 1962: A Galactic Network concept J.C.R. Licklider and W. Clark, MIT, On-Line Man Computer Communication 1965: First predecessor of the Internet Analog Modem connection between two computers in the USA 1967: Concept of ARPANET Larry Roberts draft paper 1969: First node of the ARPANET UCLA (Los Angeles) End of 1969: connects four computers Az ős-internet eredeti diagrammja 15

17 Architecture of the Internet 17

18 NSFNET

19 The National Academic Backbone Network (MBONE) 19

20 The Internet Autonomous Systems source: netdimes.org (lanet-vi) 20

21 Routers of the Internet source: netdimes.org 21

22 Protokol Layers Networks are complex! hosts, routers, switches, many link mediums protokols operation systems applications hardware, software application protokol SW links router SW (several protocols) application network interface op. system op. system computer switch router HW bridge HW computer 22

23 Protokol Layers How to organize the network? WEB FTP Telnet Phone Video Tw. Pair Coax. Optical WiFi Satellit 23

24 Protokol Layers Try again: How to organize the network? WEB FTP Telnet Phone Intermediate layer(s) Tw. Pair Coax. Optical WiFi Satellit 24

25 Layers of the Internet - TCP/IP Layers Application Telnet, FTP, HTTP, SMTP ( ), DNS,... Transport TCP (Transmission Control Protocol) UDP (User Datagram Protocol) Network IP (Internet Protocol) + ICMP (Internet Control Message Protocol) + IGMP (Internet Group Management Protoccol) Host-to-network LAN (z.b. Ethernet, Token Ring etc.) 25

26 TCP/IP Layer Model 26

27 Interoperation of the Layers 27

28 TCP/IP Layers 1. Host-to-network Not specified LAN dependent 2. IP Internet Protocol Special packet format Route detection, routing-protokoll Packet forwarding 3. Transport TCP (Transport Control Protocol) Reliable, bidirectional byte stream transmission service Fragmentation flow control, multiplexing UDP (User Datagram Protocol) Handing over the packets to the IP Not reliable, no flow control 4. Application Large variety of services: Telnet, FTP, SMTP, HTTP, NNTP, DNS, 28

29 Data Encapsulation 29

30 ISO/OSI Reference Model 7. Application , Terminal, Remote login 6. Presentation System dependent presentation of data (EBCDIC/ASCII) 5. Session Establishment, termination, checkpoints (for restart) 4. Transport Segmentation congestion control 3. Network Packet forwarding, routing 2. Data Link Check sum, flow control 1. Physical Electrical, mechanical, optical devices 30

31 ISO/OSI Reference Model ISO (International Standards Organisation), OSI (Open Systems Interconnections) 1. Physical Layer Transmission of bits (bits in the wire ) Electronics, light, etc Physical details (modulation, wavelength 2. Data Link Layer Cleaning bit transmission errors Collects date into frames and puts control information into frames (e.g. checksum) Sends acknowledgement of frames Deletes duplicated frames Determination of transmission rate (fast source, slow receiver) (flow control) Solves Broadcast problems Controls shared medium access (Medium Access Control MAC) 31

32 ISO/OSI Reference Model 3. Network Layer Packet forwarding Route detection Control of bottlenecks for routing Accounting of packets Transport Layer Dividing the data of session layer into smaller units (into packets) Typically one transport connection per connection Also more transport connections are allowed for optimized throughput Type of connections Reliable point-to-point (e.g. TCP) Non reliable unidirectional (e.g. UDP) Multicasting (one-to-many) Broadcasting (one-to-all) Multiplexing (which connection a packet belongs to) Flow control: how many packet can/must be sent (whithout overloadaing the network) 32

33 ISO/OSI Reference Model 5. Session Layer Determines the type of session E.g. file transfer, remote login Dialog control E.g. if the direction of the communication alternates, the session layer controls the direction Token management If two operations must not be performed in both sides at the same time, the session layer prohibits that Synchronisation Checkpoints for continuing/restart broken connections (e.g. file transfer) 33

34 ISO/OSI Reference Model 6. Presentation Layer matching of coding, e.g. character sets, names, adress fields, etc 7. Application Layer Large variety of functions, e.g. Virtual terminal File transfer (FTP) 34

35 OSI versus TCP/IP 35

36 Hybrid Model We use Tanenbaum s hybrid model 36

Data Communication Networks Introduction

Data Communication Networks Introduction M. R. Pakravan Department of Electrical Engineering Sharif University of Technology Data Networks 1 Introduction The course introduces the underlying concepts and