Computer Networks fall 2006 1. Introduction, Internet, reference - PowerPoint PPT Presentation

Computer Networks fall 2006 1. Introduction, Internet, reference models Hálózatok, 2006 Lukovszki Tamás 1

Organisation � Web page � http://people.inf.elte.hu/lukovszki/Courses/NWI/ � Lecture � Wendesday, 2-4 pm, place: Mogyoródi terem (South bld. 0.822) � 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 Hálózatok, 2006 Lukovszki Tamás 2

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 Hálózatok, 2006 Lukovszki Tamás 3

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 Hálózatok, 2006 Lukovszki Tamás 4

Motivation Hálózatok, 2006 Lukovszki Tamás 5

Examples for computer networks Hálózatok, 2006 Lukovszki Tamás 6

Recommended literature (I) � 1. recommended book: � Computer Networks, 4. edition, Andrew S. Tannenbaum, Prentice Hall � price: 49,90 Euro (amazon) Hálózatok, 2006 Lukovszki Tamás 7

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) Hálózatok, 2006 Lukovszki Tamás 8

Recommended literature (III) � L. L. Peterson & B. S. Davie, Computer Networks – A Systems Approach, 2003, 3rd edition, Morgan Kaufman � price: 53,30 EUR (amazon) Hálózatok, 2006 Lukovszki Tamás 9

Recommended literature (IV) � Fred Halsal, Data Communications, Computer Networks and Open Systems, Addison-Wesley, 1995 Hálózatok, 2006 Lukovszki Tamás 10

Further literature (V) � Further literature: � TCP/IP Illustrated, Volume - The Protocols, W. Richard Stevens, Addison-Wesley Hálózatok, 2006 Lukovszki Tamás 11

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) Hálózatok, 2006 Lukovszki Tamás 12

Comparation of network structures The Internet Hierarchical phone network Hálózatok, 2006 Lukovszki Tamás 13

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 Hálózatok, 2006 Lukovszki Tamás 14

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 Az „ � s-internet” � 1967: Concept of “ARPANET” eredeti diagrammja � Larry Roberts draft paper � 1969: First node of the “ARPANET” � UCLA (Los Angeles) � End of 1969: connects four computers Hálózatok, 2006 Lukovszki Tamás 15

The ARPANET Growth of ARPANET (a) 1969 december (b) 1970 july (c) 1971 march. (d) 1972 april. (e) 1972 september. Hálózatok, 2006 Lukovszki Tamás 16

Architecture of the Internet Hálózatok, 2006 Lukovszki Tamás 17

NSFNET 1988 Hálózatok, 2006 Lukovszki Tamás 18

The National Academic Backbone Network (MBONE) Hálózatok, 2006 Lukovszki Tamás 19

The Internet – Autonomous Systems source: netdimes.org (lanet-vi) Hálózatok, 2006 Lukovszki Tamás 20

Routers of the Internet source: netdimes.org Hálózatok, 2006 Lukovszki Tamás 21

Protokol Layers Networks are complex! � hosts, routers, switches,… � many link mediums � protokols � operation systems � applications � hardware, software router SW application links (several protocols) application protokol SW network interface op. system op. system computer switch router HW bridge HW computer Hálózatok, 2006 Lukovszki Tamás 22

Protokol Layers � How to organize the network? WEB FTP Email Telnet Phone Video Tw. Pair Coax. Optical WiFi Satellit Hálózatok, 2006 Lukovszki Tamás 23

Protokol Layers � Try again: How to organize the network? WEB FTP Email Telnet Phone Intermediate layer(s) Tw. Pair Coax. Optical WiFi Satellit Hálózatok, 2006 Lukovszki Tamás 24

Layers of the Internet - TCP/IP Layers Application Telnet, FTP, HTTP, SMTP (E-Mail), DNS, ... TCP (Transmission Control Protocol) Transport UDP (User Datagram Protocol) IP (Internet Protocol) Network + ICMP (Internet Control Message Protocol) + IGMP (Internet Group Management Protoccol) Host-to-network LAN (z.B. Ethernet, Token Ring etc.) Hálózatok, 2006 Lukovszki Tamás 25

TCP/IP Layer Model Hálózatok, 2006 Lukovszki Tamás 26

Interoperation of the Layers Hálózatok, 2006 Lukovszki Tamás 27

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, … Hálózatok, 2006 Lukovszki Tamás 28

Data Encapsulation Hálózatok, 2006 Lukovszki Tamás 29

ISO/OSI Reference Model 7. Application E-Mail, 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 Hálózatok, 2006 Lukovszki Tamás 30

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) Hálózatok, 2006 Lukovszki Tamás 31

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) Hálózatok, 2006 Lukovszki Tamás 32

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) Hálózatok, 2006 Lukovszki Tamás 33

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) � Email � … Hálózatok, 2006 Lukovszki Tamás 34

OSI versus TCP/IP Hálózatok, 2006 Lukovszki Tamás 35

Hybrid Model � We use Tanenbaum’s hybrid model Hálózatok, 2006 Lukovszki Tamás 36