1 Computer Networks and Communications [Δίκτυα Υπολογιστών και Επικοινωνίες] Lectures 2&3: What is the Internet? Univ. of the Aegean Financial and Management Engineering Dpt Petros KAVASSALIS

2 What you will learn in this course A set of fundamental concepts for understanding Data Networks and the Internet A set of fundamental concepts for understanding Data Networks and the Internet  What is the Internet?  Internet architecture and layers  Internet applications and services  New concepts in the evolution of the Internet  The Internet goes Wireless… Familiarization with the structure and organization of Digital Networks Familiarization with the structure and organization of Digital Networks  Business and Social Networks  Electronic Markets and Online Feedback Mechanisms

3 Who am I? PhD in Economics and Management (Univ. Paris Dauphine & Ecole polytechnique) PhD in Economics and Management (Univ. Paris Dauphine & Ecole polytechnique) Research experience Research experience  Ecole polytechnique, Paris  MIT Center of Technology Policy and Industrial Development, MIT CTPID (MIT Internet Telecommunications Convergence Consortium) Current positions Current positions  Univ. of the Aegean (FME): Assoc. Professor  RACTI: Director of ATLANTIS Group

4 Communication tools pkavassalis [at] atlantis-group.gr pkavassalis [at] atlantis-group.gr Course web site: see fme website Course web site: see fme website

5 Course Textbook [ z64SJRBAC&dq=tanenbaum+networks&printsec=frontcover&source=bn&hl=el&ei=ml- dSfH9L4S2jAeJ5L3ZBQ&sa=X&oi=book_result&resnum=4&ct=result]

Supplementary Texts & References William Stallings, Computer Networking with Internet Protocols, Prentice Hall, 2004 William Stallings, Computer Networking with Internet Protocols, Prentice Hall, 2004 William Stallings, Computer Networking with Internet Protocols, Prentice Hall, 2004 William Stallings, Computer Networking with Internet Protocols, Prentice Hall, 2004 James F. Kurose and Keith W. Ross, Computer Networking: A Top-Down Approach, Addison-Wesley, 2008 James F. Kurose and Keith W. Ross, Computer Networking: A Top-Down Approach, Addison-Wesley, 2008 James F. Kurose and Keith W. Ross, Computer Networking: A Top-Down Approach, Addison-Wesley, 2008 James F. Kurose and Keith W. Ross, Computer Networking: A Top-Down Approach, Addison-Wesley,

7 Students evaluation Class Participation (20%) Class Participation (20%)+ Assignments (20%) Assignments (20%)+ Final Exam (60%) Final Exam (60%)

What is a network? A hardware and software communications system formed by the interconnection of three or more devices A hardware and software communications system formed by the interconnection of three or more devices Devices may include: Devices may include:  Telephones  PCs  Routers  Other communications devices (please give examples) 8

The geography of the Internet 9

Internet in a nutshell Protocols control sending, receiving of msgs Protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, IM, Ethernet Composition: “network of networks” Composition: “network of networks”  loosely hierarchical  public Internet versus private intranet Standards Standards  RFC: Request for comments  IETF: Internet Engineering Task Force 10 Home network Institutional network Mobile network Global ISP Regional ISP

Overview of the Internet 11 The structure of the Internet is roughly hierarchical

A multilevel structure: Tier 1 At center: “Tier-1” ISPs (e.g., Verizon, France Telecom, Deutche Telecom etc.), national/international coverage At center: “Tier-1” ISPs (e.g., Verizon, France Telecom, Deutche Telecom etc.), national/international coverage  Treat each other as equals / interconnect privately 12 Tier 1 ISP Tier-1 providers interconnect (peer) privately

A multilevel structure: Tier 2 Tier-2” ISPs: smaller (regional) ISPs (OTEnet, Forthnet) Tier-2” ISPs: smaller (regional) ISPs (OTEnet, Forthnet)  Connect to one or more tier-1 ISPs, possibly other Tier 2 ISPs 13

A multilevel structure: Tier 3 “Tier-3” ISPs and local ISPs “Tier-3” ISPs and local ISPs  Last hop (“access”) network (closest to end systems) 14 Tier 1 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet

As a result, packet passes through many network infrastructures Which networks? Let’s discover the Internet… Which networks? Let’s discover the Internet… 15 Tier 1 ISP Tier-2 ISP

The essential of Internet: infrastructures but also applications… Communication infrastructure enables various distributed applications Communication infrastructure enables various distributed applications  , Web browsing, Skypying, file sharing, online games Communication applications are supported by Communication applications are supported by  reliable data delivery from source to destination  “best effort” (unreliable) data delivery 16 Home network Institutional network Mobile network Global ISP Regional ISP

… “separated” in two blocks IP (spanning-layer) separates information bitways from applications IP (spanning-layer) separates information bitways from applications Applications may work over multiple substrates (network techs) and these substrates do not pre- specify the development of new applications Applications may work over multiple substrates (network techs) and these substrates do not pre- specify the development of new applications [I will come back!] [I will come back!] 17

What is a protocol? Human protocols Human protocols  “what’s the time?”  “I have a question”  Introductions (“this is…”)  Specific msgs sent  Specific actions taken when msgs received, or other events Machine protocols Machine protocols  Machines “talk each other” (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 18

Human and Computer protocols Make possible a series of interactions Make possible a series of interactions 19

The Internet path of a communication (defined with the use of a protocol) : end-core-end Internet end and core Internet end and core  mesh of interconnected routers how is data transferred through net? how is data transferred through net?  circuit switching: dedicated circuit per call: telephone net  packet-switching: data sent thru net in discrete “chunks 20

Transmission speed Measured in bits per second (bps) Measured in bits per second (bps)  Increasing factors of 1,000 …  Not factors of 1,024  Kilobits per second (kbps) - note the lowercase k  Megabits per second (Mbps)  Gigabits per second (Gbps)  Terabits per second (Tbps) The rule for writing speeds (and metric numbers in general) in proper form is that there should be 1 to 3 places before the decimal point The rule for writing speeds (and metric numbers in general) in proper form is that there should be 1 to 3 places before the decimal point  Mbps is correct (2 places before the decimal point).\  2,300 Mbps has four places before the decimal point, so it should be rewritten as 2.3 Gbps (1 place) 21

Circuit-switching (1) End-end resources reserved for “call” End-end resources reserved for “call”  Link bandwidth, switch capacity  Dedicated resources: no sharing  Circuit-like (guaranteed) performance  Call setup required 22

Circuit-switching (2) Network resources (e.g., bandwidth) divided into “pieces” 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 “service lines” o Frequency division (FDM) o Time division (TDM) 23 FDM frequency time TDM frequency time 4 users Example:

Packet-switching (1) Each end-end data stream divided into packets 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: Resource contention:  Aggregate resource demand can exceed amount available  Congestion: packets queue, wait for link use  Mechanism: store and forward: packets move one hop at a time o Node receives complete packet before forwarding 24

Packet-switching (2): statistical sharing Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand 25 A B C 100 Mb/s Ethernet 1.5 Mb/s D E statistical multiplexing queue of packets waiting for output link

Packet-switching (3): store-and-forward Takes L/R seconds to transmit (push out) packet of L bits on to link at R bps Takes L/R seconds to transmit (push out) packet of L bits on to link at R bps  Store and forward: entire packet must arrive at router before it can be transmitted on next link  Delay = 3L/R (assuming zero propagation delay)  Example: o L = 7.5 Mbits, R = 1.5 Mbps o Transmission delay = 15 sec 26 R R R L

Packet-switching v. Circuit-switching 27 N users 1 Mbps link 1 Mb/s link 1 Mb/s link Each user: Each user:  100 kb/s when “active”  active 10% of time Circuit-switching: 10 users Circuit-switching: 10 users Packet switching: more users can share the network Packet switching: more users can share the network

Packet-switching: pros and cons Great for bursty data Great for bursty data  Resource sharing  Simpler, no call setup Excessive congestion: packet delay and loss Excessive congestion: packet delay and loss  Protocols needed for reliable data transfer, congestion control How to provide circuit-like behavior? How to provide circuit-like behavior?  Bandwidth guarantees needed for audio/video apps  (Still) a not fully unsolved problem 28