Tlc p01 network_services_2012

Telecomunicazioni

Docente: Andrea BaiocchiDIET - Stanza 35, 1° piano palazzina “P. Piga”

Sede Facoltà S. Pietro in Vincoli

E-mail: [email protected]

University of Roma

“La Sapienza”

Corso di Laurea in Ingegneria Gestionale

A.A. 2011/2012

Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi

2

Programma

1. SERVIZI E RETI DI TELECOMUNICAZIONE (KR-Cap. 1; GW-Cap. 1)

2. FONDAMENTI DI COMUNICAZIONI

3. ARCHITETTURE DI COMUNICAZIONE

4. SERVIZI DI RETE E MODI DI TRASFERIMENTO

5. STRATO DI COLLEGAMENTO E ACCESSOMULTIPLO

6. TECNOLOGIE DI STRATO DI COLLEGAMENTO

7. LO STRATO DI RETE IN INTERNET

8. LO STRATO DI TRASPORTO IN INTERNET

9. CENNI SUI PROTOCOLLI APPLICATIVI

Communication Networks andServices

Basic terminology and concepts


4

Communication

Network

The big picture

Communication

Network

Users

Users run applications and interact via acommunication network


5

Applications

• Client-server

– Few host (servers) have got information content,processing power or any needed facility and are ready toanswer to service requests from a much larger number ofhosts (clients)

• Peer-to-peer

– Many hosts (peers) cooperate to create service, withpossibly small help from some centralized servers

• Also:

– Uni/bi-directional

– Interactive or not


6

Examples: client-server apps

• Email

• FTP

• SSH, Telnet

• WWW

• E-commerce

• Audio & video streaming

• Web 2.0


7

Examples: p2p apps

• Telephony, Voice/Telephony-over-Internet

• Instant messaging: messenger, SMS

• File sharing: eMule, BitTorrent,…

• Real-time P2P: Skype, IPTV

• Network interactive games


8

What is a communication network?

• The equipment (hardware & software) and facilitiesthat provide the basic communication service

• Virtually invisible to the user; represented by acloud

Communication

Network

• Equipment

– Routers, servers,switches, multiplexers,hubs, modems, …

• Facilities

– Copper wires, coaxialcables, optical fiber, radio

– Ducts, conduits,telephone poles …


9

Analogies

• A communication network provides services

– This is like utilities, e.g. water supply, electric supply,…

• Flexible connectivity

– This is like transportation systems

Goods / people

information


10

Approaches to long-distancecommunications

• Transfer of messages made up of

– parseable sequence of symbols (digital information)

– continuously variable physical quantities (analoginformation)

• Courier: physical transport of the message

– Messenger pigeons, pony express, FedEx,…

• Messages can be transferred by means oftransmission and reception of signals

– Drums, beacons, mirrors, smoke, flags, semaphores,…

– Electromagnetic field

• We focus on electrical communications


11

• Morse code converts text message into sequenceof dots and dashes

• Use transmission system designed to convey dotsand dashes

— — — — —0! — — — —1! — !R! !I

— — — — !9— — ! !Z— — ! —Q! ! ! !H

— — — ! !8— ! — —Y! — — !P— — !G

— — ! ! !7— ! ! —X— — —O! ! — !F

— ! ! ! !6! — —W— !N!E

! ! ! ! !5! ! ! —V— —M— ! !D

! ! ! ! —4! ! —U! — ! !L— ! — !C

! ! ! — —3—T— ! —K— ! ! !B

! ! — — —2! ! !S! — — —J! —A

MorseCode

MorseCode

MorseCode

MorseCode

Example of digital communications


12

Digital Transmission Evolution

1.0E+00

1.0E+02

1.0E+04

1.0E+06

1.0E+08

1.0E+10

1.0E+12

1.0E+14

1850 1875 1900 1925 1950 1975 2000

Morse

T-1 Carrier

SONET

Optical

Carrier

Info

rma

tio

n t

ran

sfe

r

pe

r se

co

nd

Wavelength

Division

Multiplexing

Baudot


13

Multiplexing

• Point-to-point communication systems:

– tx + communication link + rx

• Usually much more capacity available thanuseful/affordable for single user pair

• Natural approach: put multiple information flowsof different user pairs onto the same sharedcommunication system

• Generalizable to point-to-multipointcommunications


14

The N2 Problem

• For N users to be fullyconnected directly

– Requires N(N – 1)/2connections, i.e. scaleswith square of number ofusers

– Requires too muchcommunication resources,often underutilized:inefficient & costly

• Basic idea to improve:resource sharing

N = 1000

N(N – 1)/2 = 499500

1

2

34

N

. . .


15

Switching

• Since information flows share same link, there is aneed of intermediate dispatching

– Analogous to railway or bus stations

• A system where more links converge (input) andfrom which more links depart (output) is definedas a switching node if it has the task of decidingand actuating the correct output for each piece ofinformation coming from an input

– In Internet context known as router;

– in telephone circtui networks known as exchange;

– in LAN or ATM contexts known as switch.


16

Switching: telephony example

• Patchcord panel switch invented in 1877

• Operators connect users on demand

– Establish circuit to allow electrical current to flow frominlet to outlet

• Only N connections required to central office

1

23

N – 1

N


17

Circuit switching0

1

62

0

1

31

2

2

0

1

62

0

1

31

0

1

62

0

1

31

0

1

62

0

1

31

3161

0

1

62 31

0

1

0

1

31

0

1

62

A1

B1C1

A2

B2C2

0

1

62

C261

B

C

AA3

B3

C3


18

Telephone subscribers connected to local CO (central office)

Tandem & Toll switches connect COs

Hierarchical Network Structure

Tandem

CO

Toll

CO COCO

CO

Tandem

CO = central office


19

1

2

3

Routing

Store&Forward

Input

lines

Output

lines

Packet switching


20

Communications modes

• With connection

– Two or more parties

– Stateful

– Three phases: Set up, Data transfer, Tear down

• Connectionless

– Two or more parties

– Stateless

– Single phase: Data transfer

Network selects route;

Sets up connection;

Called party alerted

Telephone

network

Pick up phone

Dial tone.

Dial number

Exchange voice

signals

1.

2.

3.

4.

5.

Telephone

network

Telephone

network

Telephone

network

Telephone

network

Hang up.6.

Connection

set up

Information

transfer

Connection

release

Telephone

network

Example: telephone call


22

Communication Network Architecture

• Network architecture: the plan that specifieshow the network is built and operated

– Architecture is driven by network services and relieson available technology

• Overall communication process is complex:therefore network architecture partitions overallcommunication process into separate functionalareas called layers

– E.g. physical layer, end-to-end layer,…


23

Architecture layer view

• Given a layer of the network architecture, thecommunication network can be modeled by a graph

– Vertices are nodes that cooperate with neighboring nodes tosupport upper layer service

– Edges define (logical) direct communication links used bynodes to cooperate

• Network topology

• Interface (node-to-node)

• Protocol (layer)


24

Network topology

• Refers to a givenarchitecture layer viewof the system

• Specifies connectivity,i.e. capability of directinteraction betweenpeer entities

• Topology model: agraph


25

Connections of all Internetsub-networks in the world


26

What is an interface?• Contact point between two entities at a given level of

abstraction (layer)

– In the graph model of the layer, an edge between two nodescorresponds to an interface

• Entity: piece of sw/hw able to perform a task by co-operating with other remote, peer entities

• An interface is defined by specification of thefollowing aspects:

– Mechanical (only for physical interfaces)

– Electrical (only for physical interfaces)

– Functional (role played by any part of the interface)

– Procedural (sequence of events that involve one or morefunctions of the i/f: protocol)


27

Example: ITU-T V.24

!

!

Composizione

numero

telefonico

DTR ON

RI ON

RTS ON

CTS ON

Tono

Audio

Cifre di

selezione

T x D

RTS OFF

CTS OFF

Toni Audio

(Dati)

Toni Audio

(OFF)

Toni Audio

(Dati)R x D

RTS OFF

CTS OFF

CD OFFCD OFF

CTS OFF

RTS OFF

T x D

CTS ON

Breve

Ritardo

Breve

Ritardo

RTS ON

CD OFF

R x D

DSR ON

DTR ON

Modalità

Dati

CD ON

Fase d

i

trasfe

rim

ento

dati

Fase d

i

Insta

ura

zio

ne

Fase d

i

abbattim

ento

Toni Audio

(OFF)

DCE

(Modem)

DTE

(Terminale)

DCE

(Modem)

DTE

(Terminale)

Interfaccia

DTE/DCE

Interfaccia

DTE/DCE

Linea

telefonica

commutata

! Spia luminosa accesa Spia luminosa spenta

DCE

Ring Indication

Data Terminal Ready

Carrier Detect

Signal Ground

Data Set Ready

Clear To Send

Request To Send

Receive Data

Transmit Data

Shield Ground

22

20

8

7

6

5

4

3

2

1

DTE

Connettore 25 pinISO 2110

RI

DTR

CD

SIG

DSR

CTS

RTS

RxD

TxD

SHG

25 24 23 22 21 20 19 18 17 16 15 14

47.17 mm

13 12 11 10 9 8 7 6 5 2 134


28

Example: Ethernet

• Specification of electrical quantities (current, voltage) andwaveforms (sync pulse trains, pulse shape)

• Specification of access procedures: Medium Access Control (MAC)protocol


29

What’s a protocol?

a human protocol and a computer network protocol:

Hi

Hi

Got thetime?

2:00

TCP connection request

TCP connectionresponse

Get http://net.infocom.uniroma1.it

<file>

time


30

Protocol elements

• A protocol is a set of rules that governs how two ormore parties communicating over an interface areto interact

• Examples

– Internet Protocol (IP), Transmission Control Protocol(TCP), HyperText Transfer Protocol (HTTP), Simple MailTransfer Protocol (SMTP)

• Key elements of a protocol

– Syntax

– Semanthics

– Timing


31

Protocols• A protocol can be described by means of state

machines

• State is the set of variables whose value issufficient to decide next transition given input andinternal events

– E.g. message receipts, timer expiration

• Given state at time t, X(t)=a, any event occurringin the interface at a subsequent time t+h makesthe state evolve to b

• Actions are associated to transition a->b.

Protocols define format, order of msgs sent and receivedamong network entities, and actions taken on msg send/rcv


Internet at large


33

Packet Switching

• Internet is but one example of a packet switchednetwork

• Basic ideas:

– Information is segmented into “small”, self-containedchunks (smaller than typical amount of information to betransferred) -> PACKETS

– Packets hop from one node to another until they find theirway to the destination -> STORE & FORWARD

– Hop can be realized by ANY underlying communicationtechnology -> INTERNETWORKING

– Improvement of QoS demanded to end-to-end protocols(e.g. error recovery, flow/congestion control)


34

High-level view of Internet• Hosts, routers and inter-networking

G

G

G

G

G

G

Net 1

Net 5

Net 3

Net 4Net 2

H

HH

H


35

First packet switching ideasPaul Baran, 1964


36

A closer look at network structure:

• network edge

– applications and hosts

• access networks

– wired/wirelesscommunication links

– large number of “small”routers

• network core

– interconnected routers

– network of networks


37

Q: How to connect end systems to edge router?

• residential access nets

• institutional access networks (school, company)

• mobile access networks

Dialup modem

xDSL - Digital Subscriber Line

wirelessaccess point

wirelesslaptops

router/firewall

modemto/from

CO

Access networks


38

Q: How to connect end systems to edge router?

• residential access nets

• institutional access networks (school, company)

• mobile access networks

LAN - Local Area NetworkWireless

basestation

mobilehosts

router

Access networks


39

Internet structure: network of networks

• roughly hierarchical

• at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cableand Wireless), national/international coverage

– treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1providersinterconnect(peer)privately


40

Tier-1 ISP: e.g., Sprint

…

to/from customers

peering

to/from backbone

…

.

………

POP: point-of-presence


41


• “Tier-2” ISPs: smaller (often regional) ISPs

– Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP paystier-1 ISP forconnectivity torest of Internet! tier-2 ISP iscustomer oftier-1 provider

Tier-2 ISPsalso peerprivately witheach other.


42


• “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 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier-3 ISPs arecustomers ofhigher tierISPsconnectingthem to restof Internet


43


• a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP


44

Hourglass model (H. Schulzrinne)


Outlook


46

Trends in Network Evolution

• It’s all about services

– Building networks involves huge investment

– Services that generate revenues drive the networkarchitecture

• Current trends and issues

– Multimedia applications

– Info-centric communications

– End of trust

– Legal issues (laws are local, network is global)

– Overlay networks

– Nano-networks

– E-government, e-business, e-commerce


47

Declination on Internet

• Internet of Communities: organization of people activitiesthrough the Internet, on the basis of common interests andlikings.

• Internet of Services: interconnection of providers andconsumers of any type of service that can be accessedthrough the Internet.

• Internet of Media: network supporting media search,delivery, and integration, regardless their format, providingsuitable storage and quick access.

• Internet of Things: pervasive network, capable ofconnecting all devices that can generate, transmit, or receivecontents, including sensors, cameras, wearable devices.


48

Evolution of services

Yesterday,call switching…

…today,call center


49

Network models:intelligent vs dumb

Source: M. Dècina, 2006


50

Network models: flat• Mesh, ad hoc networks

– IEEE 802.11 e 802.16

• Pervasive andubiquitous computing

– Domotics,embedded/wearablecomputing

– event-driven, context-aware, communicating,networked smart objects

• Wireless sensornetworks

– ZigBee, RFID Source: M. Dècina, 2006


51

End of Trust

• Security Attacks

– Spam, Phishing, Pharming

– Denial of Service, DDoS

– Viruses

– Impersonators

• Firewalls & Filtering

– Control flow of traffic/data from/to Internet

• Confidentiality, integrity and authentication;authorization; traffic monitoring

• Anonymity, privacy


52

ICT security attributes


53

TCP/IP stack & security


54

Operations, Administration,Maintenance, and Billing

• Communication like transportation networks

– Traffic flows need to be monitored and controlled, QoSand security must be guaranteed, possibly at differentlevels

– Tolls have to be collected

– Roads have to be maintained

– Need to forecast traffic and plan network growth

• Highly-developed in telephone network

– Entire organizations address OAM & Billing

– Becoming automated for flexibility & reduced cost

• Under development for IP networks


55

Success Factors for New Services

• Technology not only factor in success of a newservice

• Three factors considered in new telecom services

TechnologyMarket

Regulation

Can it be

implemented cost-

effectively?

Can there be

demand for the

service?

Is the service

allowed/somehow

constrained?

New

Service


56

Role of regulation

• Public regulation is fundamental as communicationservices become a commodity

• Minimum service access to be guaranteed

– Universal service

• Digital divide

• Also fundamental for

– unique resources (radio spectrum)

– protection of public interests (e.g. health)


57

Standards

• New technologies very costly and risky

• Standards allow players to share risk and benefitsof a new market

– Reduced cost of entry

– Interoperability and network effect

– Compete on innovation

– Completing the value chain

• Chips, systems, equipment vendors, service providers

• Example

– 802.11 wireless LAN products


58

Standards Bodies• Internet Engineering Task Force (IETF)

– Internet standards development

– Request for Comments (RFCs): www.ietf.org

• International Telecommunications Union (ITU)

– International telecom standards

• International Standardization Organization (ISO)

• IEEE 802 Committee

– Local area and metropolitan area network standards

• Regional bodies (ETSI, ANSI)

• Industry Organizations and Fora

– 3GPP, MPLS Forum, WiFi Alliance, World Wide Web Consortium,Bluetooth


History


60

Computer Network Evolution Overview

• 1950s: Telegraph technology adapted to computers

• 1960s: Dumb terminals access shared host computer

– SABRE airline reservation system

• 1970s & 1980s: Computers connect directly to each other

– ARPANET packet switching network

– TCP/IP based internetworking

– Ethernet local area network

• 1990s & 2000s: New applications and Internet growth

– Commercialization of Internet

– E-mail, file transfer, web, P2P, streaming . . .

– Internet traffic surpasses voice traffic


61

Internet History (1/5)

• 1961: Kleinrock - queueing theory shows effectiveness ofpacket-switching

• 1964: Baran - packet-switching in military nets

• 1967: ARPAnet conceived by Advanced Research ProjectsAgency

• 1969: first ARPAnet node operational

• 1972:

– ARPAnet public demonstration

– NCP (Network Control Protocol) first host-host protocol

– first e-mail program

– ARPAnet has 15 nodes

1961-1972: Early packet-switching principles


62

ARPANET - September 1971


63


• 1970: ALOHAnet satellite network in Hawaii

• 1974: Cerf and Kahn - architecture for interconnecting nets

• 1976: Ethernet at Xerox PARC

• Late 70’s: proprietary architectures: DECnet, SNA, XNA

• Late 70’s: switching fixed length packets (ATM precursor)

• 1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworking principles:

– minimalism, autonomy - no internal changes required to interconnect nets

– best effort service model

– stateless routers

– decentralized control

1972-1980: Internetworking, new and proprietary nets


64


• 1983: deployment of TCP/IP

• 1982: smtp e-mail protocol defined

• 1983: DNS defined for name-to-IP-address translation

• 1985: ftp protocol defined

• 1988: TCP congestion control

• new national networks: Csnet, BITnet, NSFnet, Minitel

• 100,000 hosts connected to confederation of networks

1980-1990: new protocols, a proliferation of networks


65


• Early 1990’s: ARPAnet decommissioned

• 1991: NSF lifts restrictions on commercial use of NSFnet(decommissioned, 1995)

• Early 1990s: Web

– hypertext [Bush 1945, Nelson 1960’s]

– HTML, HTTP: Berners-Lee, 1989

– 1993: Mosaic, later Netscape

• Late 1990’s

– commercialization of the Web

– network security to forefront

– estimated 50 million host, 100 million+ users

– backbone links running at Gbps

1990, 2000’s: commercialization, the Web, new apps


66


• 2000’s

– more killer apps:

• instant messaging

• P2P applications (BitTorrent - file sharing; Skype - VoIP;PPLive - video)

• YouTube

• Gaming

• E-commerce

– wireless, mobility

– tens/hundreds Gbps backbone


67

The Internet gotha


68

Internet statistics

• ~769 million hosts (July 2010)

• ~2 billion users

• As of Feb. 27rd, 2012: 138,143,921 Top Level Domains

• As of Feb. 1st, 2012: 3,479,770,880 IP addresses assigned in 246countries

End of 2009:

• 234 million websites

• 247 billion emails sent daily on the average

• Facebook serves 260 billion page views per month (6 millions permin)

• YouTube serves 1 billion videos per day


69

Host count