Petros KAVASSALIS

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

<[email protected]> 2

What you will learn in this course

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

Business and Social Networks Electronic Markets and Online Feedback Mechanisms


Who am I?

PhD in Economics and Management (Univ. Paris Dauphine & Ecole polytechnique)

Research experience Ecole polytechnique, Paris MIT Center of Technology Policy and Industrial Development, MIT

CTPID (MIT Internet Telecommunications Convergence Consortium)

Current positions Univ. of the Aegean (FME): Assoc. Professor RACTI: Director of ATLANTIS Group


Communication tools

e-mail: pkavassalis [at] atlantis-group.gr Course web site: see fme website


Course Textbook[http://books.google.gr/books?id=Pd-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

James F. Kurose and Keith W. Ross, Computer Networking: A Top-Down Approach, Addison-Wesley, 2008


http://www.pearsonhighered.com/educator/academic/product/0,3110,0131410989,00.html






Students evaluation

Class Participation (20%)

+ Assignments (20%)

+ Final Exam (60%)

What is a network?

A hardware and software communications system formed by the interconnection of three or more devices

Devices may include: Telephones PCs Routers Other communications devices (please give examples)


The geography of the Internet


Internet in a nutshell

Protocols control sending, receiving of msgs

e.g., TCP, IP, HTTP, IM, Ethernet

Composition: “network of networks” loosely hierarchical public Internet versus private

intranet

Standards RFC: Request for comments IETF: Internet Engineering Task

Force


Home network

Institutional network

Mobile networkGlobal ISP

Regional ISP

Overview of the Internet


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

Treat each other as equals / interconnect privately


Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately


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



“Tier-3” ISPs and local ISPs Last hop (“access”) network (closest to end systems)


Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISPTier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet

As a result, packet passes through many network infrastructures

Which networks? Let’s discover the Internet…


Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISPTier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

The essential of Internet: infrastructures but also applications…

Communication infrastructure enables various distributed applications

E-mail, Web browsing, Skypying, file sharing, online games

Communication applications are supported by

reliable data delivery from source to destination

“best effort” (unreliable) data delivery


Home network

Institutional network

Mobile networkGlobal ISP

Regional ISP

… “separated” in two blocks

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

[I will come back!]


What is a protocol?

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 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


Human and Computer protocols

Make possible a series of interactions


http:www.atlantis-group.gr

The Internet path of a communication (defined with the use of a protocol): end-core-end

Internet end and core mesh of interconnected

routers how is data transferred

through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks


Transmission speed

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

23.72 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)


Circuit-switching (1)

End-end resources reserved for “call” Link bandwidth, switch

capacity Dedicated resources: no

sharing Circuit-like (guaranteed)

performance Call setup required


Circuit-switching (2)

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)


FDM

frequency

time

TDM

frequency

time

4 users

Example:

Packet-switching (1)

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: 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


Packet-switching (2): statistical sharing

Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand


A

B

C100 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting 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

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 Mbpso Transmission delay = 15 sec


R R RL

Packet-switching v. Circuit-switching


N users1 Mbps link

1 Mb/s link Each user:

100 kb/s when “active” active 10% of time

Circuit-switching: 10 users Packet switching: more users can share the network

Packet-switching: pros and cons

Great for bursty data Resource sharing Simpler, no call setup

Excessive congestion: packet delay and loss Protocols needed for reliable data transfer, congestion control

How to provide circuit-like behavior? Bandwidth guarantees needed for audio/video apps (Still) a not fully unsolved problem


Petros KAVASSALIS

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