telefonia, adsl voice over ip · voice over ip. 2 telefonia ... workgroup switch 5. distribuzione...
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Telefonia, ADSL Voice over IP
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Telefonia
Il servizio telefonico e’ costoso
Le LAN utilizzano i cavi utilizzati dalle reti telefoniche negli edifici
La tecnologia telefonica è alla base della maggior parte delle WAN
Le regolamentazioni e i fornitori di servizi telefonici hanno un influenza sulle WAN
Tendenza a far convergere i due servizi: gestione integrata di reti per la voce e I dati
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Cavi telefonici in edifici
EdificiA piu’ piani
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Rete telefonica interna basata su PBX
1. Stanza delle apparecchiature (Di solito nel semi-interrato)
2. ToTelcos
3.EntranceFacility
5. PBXSwitch
Telefonico internoPrivate branch exchange
6. fasciodi cavi
(Molti doppini)
7. VerticalRiserSpace4. Termination
Equipment
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Rete telefonica interna basata su PBX
3. TelecommunicationsCloset on Floor
2. Fasci di cavi
4. Cross-Connect Device
5. Distribuzione orizzontale
1. distribuzioneverticale
Doppini UTP
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Patch Panel
19”Equipment
Rack
PatchPanel
Rack-MountedSwitches
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Rete telefonica interna basata su PBX
1. Distribuzione orizzontaleUn doppino UTP
2. Distribuzione finaleLungo o attraverso una parete
3. Patch Cord
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Cablaggio di una LAN in un edificio
1. Stanza delle apparecchiature (Di solito nel semi-interrato)
2. ToWAN
3. EntranceFacility withTerminationEquipment
5. Switchcentrale
(Chassis)
6. VerticalRiserSpace
4. Router
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Cablaggio di una LAN in un edificio
3. TelecommunicationsCloset on Floor 2. Fibre ottiche
Una coppia in ogni soffitto
4. Workgroup Switch
5. Distribuzione orizzontale
1. distribuzioneverticale
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WorkgroupSwitch inTelecoms
Closet
Cablaggio di una LAN in un edificio
1. Distribuzione orizzontaleDoppino UTP
Le distribuzioni orizzontali e quella finaleSono le stesse della telefonia
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Public Switched Telephone Network (PSTN)
Proprieta’ del cliente(Residenza privata)
Proprieta’ del cliente(Azienda)
Switching OfficeCentral Office
End OfficeLinea di accessoLocal Loop
Doppino unicoDi bassa qualita’
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Public Switched Telephone Network (PSTN)
Gerarchia diSwitching
Trunk LineDigital
Class 4
Class 3
Class 5End
Office
Class 5End
Office
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Elements of the Public Switched Telephone Network (PSTN)
1. Customer Premises Equipment 1. Customer Premises Equipment
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Switching di Circuito
3. Switching di circuito:Un circuito e’ riservato
Per tutta la durata di una chiamata
2. Attraversamolti switch,
linee di accesso, eLinee di collegamento
1. CircuitoConnessione End-to-End
Abbonato-Abbonato
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Switching di Circuito
A circuit is anend-to-end connection
between two subscribers.Capacity is reserved on all trunk lines
and switches along the way.
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Time Division Multiplexing (TDM)
Used Used Used Used Used
Frame 1 Frame 2 Frame 3
Slot 1for
Circuit A
Slot 3for
Circuit C
Slot 2for
Circuit B
TDM reserves capacityfor each circuit in each frame;assures speed but is wasteful
Time
Slot 1for
Circuit A
Slot 1for
Circuit A
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PSTN: Inizialmente tutta analogica
Vecchia rete telefonica: tutta analogica
LocalLoop
(Analog)
ResidentialTelephone(Analog)
Switch(Analog)
Switch(Analog)
Switch(Analog)
LocalLoop
(Analog)
BusinessTelephone(Analog)
Trunk Line(Analog)
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PSTN: per la maggior parte digitale con alcuni loop locali analogici
LocalLoop
(Analog)
ResidentialTelephone(Analog)
Switch(Digital)
Switch(Digital)
Switch(Digital)
LocalLoop
(Digital)
PBX(Digital)
Trunk Line(Digital)
Attuale rete telefonica: Per la maggior parte digitale
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Codec presso lo switch all’End Office
La linea di accesso all’abbonato è analogicaLo Switch è digitale Il Codec converte i segnali trasmessi tra di
loro
Codec
SegnaleInternoDigitale
SwitchDigitale
Loop localeLinea di accesso
End Office
AnalogSubscriber
Signal ADC
DAC
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Campionamento per effettuare conversioni da Analogico-a-Digitale (ADC)
IL Codec in primo luogo filtra la banda del segnale vocale Taglia tutte l’energia sotto i 300 Hz Taglia tutta l’energia sopra i 3,400 Hz Passa segnale filtrato da 300 Hz a 3.4 kHz
Segnale
Distribuzione di energia perLa voce umana
O Hz 300 Hz ~3,400 Hz 20 kHz
Filtro Bypass
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Campionamento per effettuare conversioni da Analogico-a-Digitale (ADC)
Codec Campiona il segnale della voce Divide ciascun secondo in 8,000 periodi di
campionamento Ciascun periodo di campionamento e’ 1/8,000 di
secondo
Sample
1/8,000 sec Periodo di campionamento
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Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
PCM
0
SignalAmplitude
TimeSample
Duration of Sample(1/8000 sec.)
AnalogSignal
A signal must be sampled at twice its highest frequency (4 kHz) for adequate quality. In PCM, there are 8,000 samples per second
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Campionamento per effettuare conversioni da Analogico-a-Digitale (ADC)
Codec Misura l’intensita’ dei segnali Misura l’intensita’ della voce in ogni periodo di
campionamento come una frazione di un valore massimo (255). Ad esempio in figura e’ 210/255.
Converte il valore decimale 210 nel valore binario di 8-bit, 11010010
Campione
1/8,000 sec Periodo di campionamento
Valore diIntensita’210/255
(1010010)
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Campionamento per effettuare conversioni da Analogico-a-Digitale (ADC)
Codec8,000 campioni/sec * 8 bit/campione = 64
kbpsQuesto e’ il motivo per cui le linee telefoniche
hanno la velocita’ di 64 kbpsSviluppate per la voce digitalizzataSpesso i fornitori (Carrier) “rubano” 8 kbps per
segnali di supervisione, sui 56 kbps
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Conversione Digitale-da-Analogica (DAC)
00000100 00000011 00000111
Segnale digitale in arrivoDa uno Switch telefonico
(8,000 campioni/Sec)
Segnale analogicogenerato
Per la linea dell’abbonatoDAC
1/8000Secondo(8 bits)
E’ di buona qualita’ se ci sono abbastanza
campioni per secondo
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Digital Subscriber Lines (DSLs)
Le linee DSLs danno la possibilita' di trasmettere dati su doppini esistenti (1-pair voice-grade access lines), quelli tipicamente utilizzati e gia' presenti per il normale collegamento telefonico.
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Digital Subscriber Lines (DSLs)
Asymmetric DSL (ADSL) Asymmetrical throughput
Downstream speed of 512 kbps to 1.5 MbpsUpstream speeds of 90 kbps to 384 kbpsGood for Web access with large downloadsSufficiently fast for e-mail
Aimed at residential customersThroughput is NOT guaranteedDSLAM (DSL access multiplexer) often
oversubscribed, slowing access
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Digital Subscriber Lines (DSLs), Continued
Symmetric DSL Services Speed is symmetric
Same upstream and downstream Aimed at business customers
Throughput IS guaranteed Several Types of Symmetric DSL
HDSL (768 kbps): Half of a T1 private line (later)HDSL2 (1.544 kbps): Full T1 private line speedSHDSL: Flexible (384 kbps to 2.3 Mbps)
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Fiber to the Home (FTTH)
Single-pair voice-grade copper running to residences is limited in the speed it can provide for data transmission
Fiber to the home (FTTH) will bring optical fiber to each home
Higher speeds for data transmission, video, etc.
Being held back by high installation costs, which require provable strong demand
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Leased Line Networks
Digital Subscriber Lines (DSLs) Velocita’ a banda larga (Broadband) su un singolo
doppino voice-grade UTP in rame
Non funzionano sempre: limiti di distanze, etc.
Dove funzionano sono meno care delle linee affittate basate su trunk line
Voice-Grade UTP esistenti
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ADSL con Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
Proprietàabbonato
Compagnia telefonicaEnd Office Switch
1.Esistente coppia di
Voice-GradeUTP Wires
PC
3. 4.2.
Voice andData
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ADSL con Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
Proprietàabbonato
Compagnia telefonicaEnd Office Switch
PC
1.Data
256 kbps to1.5 Mbps
2.64 kbps to256 kbps
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ADSL con Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
Proprietàabbonato
Compagnia telefonicaEnd Office Switch
PC
1.Servizio telefonico
ordinario
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Leased Line Networks
Asymmetric DSL (ADSL) Sommario Velocita’ asimmetrica
Downstream (verso il cliente): 256 kbps fino a piu’ di 1.5 Mbps
Upstream (dal cliente): 64 kbps o migliore Servizi dati e telefonici simultanei DSL access multiplexer (DSLAM) all end telephone
office Progettate come un servizio per i clienti, non ci
sono garanzie sulla velocita’ dei dati
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Telefonia Cellulare
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Telefonia cellulare
B
E
H
D
I
G
L
K
F
C
M
A
J
N
P
O
PSTN
Mobile TelephoneSwitching Office
Cellsite
1. Divide un AreaIn celle
2. Un cellulareComunica
Via Cellsites,Con il MTSO
(Mobile ThelephonSwitching Office)
3. ToPSTN
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Telefonia cellulare
B
E
H
D
I
G
L
K
F
C
M
A
J
N
P
O
3. riutilizzaIl canale 47 in
D e F
PSTN
Cellsite
1. TECNOLOGIA TRADIZIONALESi riutilizzano canali in celle
Non adiacenti
2. UsaIl canale 47Nella cella A
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Telefonia cellulare
B
E
H
D
I
G
L
K
F
C
M
A
J
N
P
O
PSTN
Cellsite
1.Usa il canale 47
In A, D, e F
2.In quali altre
CelleRiutilizza ilcanale 47?
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Telefonia cellulare
B
E
H
D
I
G
L
K
F
C
M
A
J
N
P
HandoffO
PSTNMobile TelephoneSwitching Office
1.Handoff automatico
tra Cellsites da O a P nelMomento in cui
Il cellulare viaggiaTra le due celle
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Handoffs vs Roaming
Handoff Per muoversi tra le celle di un singolo sistema
telefonico cellulare Telefonia cellullare 802.11 wireless LANs
Roaming Muoversi tra sistemi Telefonia cellulare: per utilizzare un telefono
cellulare in un altra citta’
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Generazioni di servizi cellulari
Generation First 2nd 2.5G 3G
Tecnologia Analogica Digitale Digitale Digitale
Data TransferRate
Data TransferIs Difficult 10 kbps* 20 kbps to
144 kbps144 kbpsto 2 Mbps
Canali ~800 ~800 +2,500
~800 +2,500 ?
Celle/ canaliRiutilizzo
Largo/Medio
Piccolo/Alto
basatoSu 2G ?
*Sufficienti per Short Message Service (SMS) e wireless Web accessUtilizzando il Wireless Access Protocol (WAP) o i-mode
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Velocita’ 3G
ITU Speed Requirements for 3G 2 Mbps per dispositivi fissi 384 kbps per persone che camminano 144 kbps per utenti in auto
Tutto il resto e’ 2.5 G Attenzione alcuni tra I produttori 2.5G dicono di
essere 3G ma non forniscono le prestazioni adeguate
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Generazioni di servizi cellulari
Generation First 2nd 2.5G 3G
WorldStandardization(and therefore
roaming)Poor Good
(GSM)Basedon 2G
? (W-CDMA,CDMA-2000,
and othersystems
may compete)
U.S.Standardization
Good(AMPS)
Poor (GSM,CDMA, TDMA,
& CDPD)
Basedon 2G ?
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Figure 6-17: Cellular Standards Families (Study Figure)
GSM Family GSM (Global System for Mobile communications)
Dominates 2G service worldwide200 kHz channels shared by up to eight users
via TDMData transmission speed of approximately 10
kbps
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Figure 6-17: Cellular Standards Families (Study Figure), Continued
GSM Family General Packet Radio Service (GPRS)
Upgrade to GSMUses GSM channelsProvides several TDM time slots per user in each
frame for greater throughput2.5G: Typical throughput of 20 kbps to 30 kbpsComparable to telephone modems
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Figure 6-17: Cellular Standards Families (Study Figure), Continued
GSM Family EDGE
Upgrade to GSM beyond GPRSAlso uses GSM channels with multiple time slots
per user2.5G: Typical throughput of 80 kbps to 125 kbps
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Figure 6-17: Cellular Standards Families (Study Figure), Continued
GSM Family W-CDMA
Wideband CDMAFull 3G serviceThroughput comparable to DSL and cable
modemsDeveloped in Europe and Japan
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Figure 6-17: Cellular Standards Families (Study Figure), Continued
Qualcomm CDMA Family CDMAone (IS-95)
2G system used widely in the United States Used by about 70% of cellphones in the U.S.
Uses CDMA
125 MHz channel shared by multiple simultaneous users
10 kbps data transmission
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Figure 6-17: Cellular Standards Families (Study Figure), Continued
Qualcomm CDMA Family CDMA2000 (IS-2000) Upgrades
1x: 30 kbps to 50 kbps throughput in a 1.25 MHz channel
Only modem throughput Considered to be 3G because rated speed is
144 kbps
1xEV-DO: 100 kbps to 300 kbps throughput DSL/Cable modem throughput
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Perspective
2G Service (Dominant Today) Only 10 kbps data transfer
Telephone Modem Throughput (2.5 G) GPRS and Edge in GSM Family 1x in Qualcomm CDMA Family
DSL/Cable Modem Throughput WCDMA in GSM Family 1x EV-DO in Qualcomm CDMA Family
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IP Telephony (VoIP)
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Figure 6-18: IP Telephony
IPInternet
PSTN
IP Telephonewith
Codec andIP Functionality
PC withIP Telephony
Software
User either has…PC with IP telephony software
OrIP telephone with built-in
codec and IP functionality;Plugs directly into an IP network
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Figure 6-18: IP Telephony, Continued
IPInternet
PSTN
MediaGateway
Media Gateway
Connects IP telephony system to the PSTN.Does signaling and transport format
conversion.
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Figure 6-20: IP Telephony Protocols
IPHdr
UDPHdr
RTPHdr
Codec DataStream
Transport(Voice Transmission)
IP Telephone(Can connect
directly to wall jack)
Signaling: H.323 or SIP(Call setup, breakdown, etc.)
PC with IPTelephony Software
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IP Telephony Transport
UDP (User Datagram Protocol) Used at the transport layer instead of TCP Efficient
No opens, closes, ACKsSo creates less delay, load on the network
UnreliableNo error correctionOK because there is no time to retransmit voice
packetsReceiver “interpolates” between received packets
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IP Telephony Transport, Continued
RTP (Real Time Protocol) RTP Header is used to improve voice signal
Contains a sequence number so that voice packets can be put in order even if unreliable IP and UDP deliver them out of order
Contains a time stamp so that the spacing of sounds in adjacent packets can be handled wellReduces “jitter” (variability in latency)