Telecomunicazioni

Transcript

Telecomunicazioni

University of
Roma “Sapienza”
Telecomunicazioni
Docente: Andrea Baiocchi
DIET - Stanza 107, 1° piano palazzina “P. Piga”
Sede Facoltà S. Pietro in Vincoli
E-mail: [email protected]
Corso di Laurea in Ingegneria Gestionale
A.A. 2014/2015
About applications and services…
It will be possible for a business man in New York to dictate instructions, and have them
instantly appear in type at his office in London or elsewhere. He will be able to call up, from
his desk, and talk to any telephone subscriber on the globe.... An inexpensive instrument,
not bigger than a watch, will enable its bearer to hear anywhere, on sea or land, music or
song, the speech of a political leader, the address of an eminent man of science, or the
sermon of an eloquent clergyman, delivered in some other place, however distant. In the
same manner any picture, character, drawing, or print can be transferred from one to
another place…
[Nicolas Tesla, 1908]
I do not think that the wireless waves I have discovered will have any practical application.
[Heinrich Hertz, end of XIX century]
That’s an amazing invention, but who would ever want to use one of them?
[President Rutherford B. Hayes to Alexander Graham Bell in 1876 on viewing the telephone
for the first time]
I think there is a world market for maybe five computers.
[Thomas Watson, chairman of IBM, 1943]
There is no reason anyone would want a computer in their home.
[Ken Olson, president, chairman, and founder of Digital Equipment Corp., 1977]
Telecomunicazioni - a.a. 2014/2015 - Prof. Andrea Baiocchi
2
3
Programma
1. SERVIZI E RETI DI TELECOMUNICAZIONE
2. FONDAMENTI DI COMUNICAZIONI
3. ARCHITETTURE DI COMUNICAZIONE E MODI DI
TRASFERIMENTO
4. ACCESSO MULTIPLO
5. STRATO DI COLLEGAMENTO
6. LO STRATO DI RETE IN INTERNET
7. LO STRATO DI TRASPORTO IN INTERNET
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L’ICT è pervasiva…
•
•
•
•
•
•
Multimedia
Green networking
Data & network security
Nano-scale systems/nets
Data mining, big data
Computational
intelligence
• Smart grids
• E-Government
• Aeronautical Tlc Network
(ATN)
• Intelligent Transportation
System (ITS)
– Vehicular communications
• Context awareness, smart
spaces
• Sensors, Internet of Things
(IoT)
• Cloud computing
• Bio-inspired systems/nets
• E-commerce
Communication Networks and
Services
Basic terminology and concepts
6
The big picture
Users
Communication
Communication
Network
Network
Users run applications and interact via a
communication network
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Applications
• Client-server
– Few host (servers) have got information content,
processing power or any needed facility and are ready to
answer to service requests from a much larger number of
hosts (clients)
• Peer-to-peer
– Many hosts (peers) cooperate to create service, with
possibly small help from some centralized servers
• Also:
– Uni/bi-directional
– Interactive or not
Una rete con due client e un server
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Tanenbaum, Wetherall, Reti di calcolatori © Pearson 2012
8
Il modello client-server
comprende richieste e risposte
9
9
Tanenbaum, Wetherall, Reti di calcolatori © Pearson 2012
Sistema peer-to-peer
10 Tanenbaum, Wetherall, Reti di calcolatori © Pearson 2012
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11
Examples: client-server apps
• Email
• FTP
• SSH, Telnet
• WWW
• E-commerce
• Audio & video streaming
• Web 2.0
• Gaming on line
12
Examples: p2p apps
• Telephony
• Instant messaging: WhatsApp, SMS,…
• File sharing: eMule, BitTorrent,…
• Real-time P2P: Skype, IPTV, TeamSpeak,…
• Network interactive games: CoD,…
13
What is a communication network?
Communication
Network
• The equipment (hardware & software) and facilities
that provide the basic communication service
• Equipment
– Routers, servers,
switches, multiplexers,
hubs, modems, …
• Facilities
– Copper wires, coaxial
cables, optical fiber, radio
– Ducts, conduits,
telephone poles …
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The essence of communications
• Transfer of messages made up of
– parseable sequence of symbols (digital information)
– continuously variable physical quantities (analog
information)
• Messages can be transferred by means of
transmission and reception of signals
– Drums, beacons, mirrors, smoke, flags, semaphores,…
– Electromagnetic field
• We focus on electrical communications
15
Multiplexing
• Point-to-point communication systems:
– tx + communication link + rx
• Usually much more capacity available than
useful/affordable for single user pair
• Natural approach: put multiple information flows
of different user pairs onto the same shared
communication system
• Generalizable to point-to-multipoint
communications
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Digression: graphs
• Let V be a finite set. We call an element of V
“node” or “vertex”
– E.g., V={1,2,…,n}.
• Let A be a subset of the cartesian product VxV. We
call an element of A “arc” or “edge”
– The ordered couple (i,j) is an arc from node i to node j.
• A graph is a couple G={V,A}
– Undirected graph: if (i,j) belongs to A, then (j,i) belongs
to A as well.
– Directed graph: the condition above does not hold.
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The N2 Problem
• For N users to be fully
connected directly
– Requires N(N – 1)/2
connections, i.e., it scales
with square of number of
users
– Requires too much
communication resources,
often underutilized:
inefficient & costly
1
N
..
2
.
• Basic idea to improve:
resource sharing
4
3
N = 1000
N(N – 1)/2 = 499500
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Switching
• Since information flows share same link, there is a
need of intermediate dispatching
– Analogous to railway or bus stations
• A system where more links converge (input) and
from which more links depart (output) is defined
as a switching node if it has the task of deciding
and actuating the correct output for each piece of
information coming from an input
– In Internet context known as router;
– in telephone circuit networks known as exchange;
– in LAN context known as switch.
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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
Example: telephone call
Connection
set up
1.
Telephone
network
2.
Telephone
network
3.
Telephone
network
Pick up phone
Dial tone.
Dial number
Network selects route;
4.
Telephone
network
Sets up connection;
Called party alerted
Information
transfer
Connection
release
5.
Telephone
network
6.
Telephone
network
Exchange voice
signals
Hang up.
Operations, Administration,
Maintenance, and Billing
• Communication like transportation networks
– Traffic flows need to be monitored and controlled, QoS
and security must be guaranteed, possibly at different
levels
– Tolls have to be collected
– Roads have to be maintained
– Need to forecast traffic and plan network growth
• Highly-developed in tlc networks
– Entire organizations address OAM & Billing
– Becoming automated for flexibility & reduced cost
Services
Internet at large
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Packet Switching
• Internet is but one example of a packet switched
network
• Basic ideas:
– Information is segmented into “small”, self-contained
chunks (smaller than typical amount of information to be
transferred) -> PACKETS
– Packets hop from one node to another until they find their
way to the destination -> STORE & FORWARD
– Hop can be realized by ANY underlying communication
technology -> INTERNETWORKING
– Improvement of QoS demanded to end-to-end protocols
(e.g., error recovery, flow/congestion control)
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High-level view of Internet
• Hosts, routers and inter-networking
H
H
G
Net 1
Net 3
G
G
G
H
Net 2
Net 5
G
Net 4
G
H
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A closer look at network structure:
• network edge
– applications and hosts
• access networks
– wired/wireless
communication links
– large number of “small”
routers
• network core
– interconnected routers
– network of networks
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Access networks
Q: How to connect end systems to edge router?
• residential access nets
• institutional access networks (school, company)
• mobile access networks
xDSL - Digital Subscriber Line
to/from
CO
modem
wireless
laptops
router
wireless
access
point
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Access networks
Q: How to connect end systems to edge router?
• residential access nets
• institutional access networks (school, company)
• mobile access networks
Wireless / Cellular
LAN - Local Area Network
router
router
switch
Base station
mobile
hosts
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Internet structure: network of networks
• roughly hierarchical
• at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable
and Wireless), national/international coverage
– treat each other as equals
Tier-1
providers
interconnect
(peer)
privately
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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Tier-1 ISP: e.g., Sprint
POP: point-of-presence
to/from backbone
peering
…
…
.
…
…
…
to/from customers
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•
“Tier-2” ISPs: smaller (often regional) ISPs
–
Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier-2 ISP pays
tier-1 ISP for
connectivity to
rest of Internet
! tier-2 ISP is
customer of
tier-1 provider
Tier-2 ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
Tier 1 ISP
Tier-2 ISP
Tier-2 ISPs
also peer
privately with
each other.
Tier-2 ISP
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•
“Tier-3” ISPs and local ISPs
–
last hop (“access”) network (closest to end systems)
local
ISP
Local and tier3 ISPs are
customers of
higher tier
ISPs
connecting
them to rest
of Internet
Tier 3
ISP
local
ISP
Tier-2 ISP
local
ISP
local
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
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• a packet passes through many networks!
local
ISP
Tier 3
ISP
Tier-2 ISP
local
ISP
local
ISP
local
ISP
Tier-2 ISP
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-2 ISP
local
local
ISP
ISP
Tier-2 ISP
local
ISP
Tier-2 ISP
local
ISP
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Schema dell’architettura di Internet
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Il progetto originale di ARPANET
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Crescita di ARPANET
(a) Dicembre 1969. (b) Luglio 1970. (c) Marzo
1971. (d) Aprile 1972. (e) Settembre 1972.
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Internet statistics
• ~908 million hosts (July 2012)
• ~2.4 billion users (June 2012)
• As of Feb. 27rd, 2012: 138,143,921 Top Level Domains
• As of Feb. 1st, 2012: 3,479,770,880 IP addresses assigned in 246
countries
End of 2009:
• 234 million websites
• 247 billion emails sent daily on the average (~90% is spam!)
• Facebook serves 260 billion page views per month (6 millions per
min)
• YouTube serves 1 billion videos per day
http://www.internetworldstats.com/stats.htm
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Host count
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Log-scale host count
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Fixed broadband Internet
2012 - Subscriptions as a percentage of population
Services
Outlook
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Trends in Network Evolution
• It’s all about services
– Building networks involves huge investment
– Services that generate revenues drive the network
architecture
• Current trends and issues
– Multimedia applications
– Info-centric communications
– Security and legal issues (laws are local, network is
global)
– Overlay networks
– Nano-networks
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Declinations of Internet
• Internet of Communities: organization of people activities
through the Internet, on the basis of common interests and
likings.
• Internet of Services: interconnection of providers and
consumers of any type of service that can be accessed
through the Internet.
• Internet of Media: network supporting media search,
delivery, and integration, regardless their format, providing
suitable storage and quick access.
• Internet of Things: pervasive network, capable of
connecting all devices that can generate, transmit, or receive
contents, including sensors, cameras, wearable devices.
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Example of IoT: V2V
Feb 4, 2014
• The U.S. Department of Transportation's (DOT) National
Highway Traffic Safety Administration (NHTSA) announced
today that it will begin taking steps to enable vehicle-tovehicle (V2V) communication technology for light vehicles.
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Evolution of services
Yesterday,
call switching…
…today,
call center
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Success Factors for New Services
• Technology not only factor in success of a new
service
• Three factors considered in new telecom services
New
Service
Market
Technology
Can it be
implemented costeffectively?
Can there be
demand for the
service?
Regulation
Is the service
allowed/somehow
constrained?
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Role of regulation
• Public regulation is fundamental as communication
services become a commodity
• Minimum service access to be guaranteed
– Universal service
• Digital divide
• Also fundamental for
– unique resources (e.g., radio spectrum)
– protection of public interests (e.g., health)
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Standards
• New technologies very costly and risky
• Standards allow players to share risk and benefits
of 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
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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
49
Prefissi metrici principali

Telecomunicazioni

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