voip presentation by hÜseyİn savran 220702044. outline pstn an brief history of telephone
TRANSCRIPT
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VoIP PRESENTATION
BYHÜSEYİN SAVRAN220702044
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OUTLINE
PSTN an brief history of telephone
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PSTN ( Public Switched Telephone Network)
Known structure of conventional telephone network.
Call Direction
PSTNİstanbul, yeditepe Ankara, METU
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PSTN history
Since the telephone was invented
in the late 1800s, telephone communication has not changed substantially .
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Telephony
A Change of Perspective
Data
Cable
Broadcast
Wireless
Traditional View
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Telephony
A Change of Perspective
Data
Current ViewCable
Broadcast
Wireless
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DataVoice
A Change of Perspective
Web
Reality
Video
File Transfer
Content
Cable
Wire
less
Satellit
e
Fiber
Devices
Apps
Users
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These Count as Phones?
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MOTIVATION
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What is VoIP
IP TELPHONY (VOICE over IP) Transmission of voice telephone calls
using internet infrastructure.
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Why need to IP Telephony?Why need to IP Telephony?
EconomicEconomic (uses internet, IP routers...) (uses internet, IP routers...) Further savingsFurther savings. Because underlying. Because underlying
network infrastructure can be shared.network infrastructure can be shared.a single set of equipment, wiring, network a single set of equipment, wiring, network connection enough.connection enough.
Example: a company with reduced Example: a company with reduced telephone costs.telephone costs.
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Why need to IP Telephony? Why need to IP Telephony? Cont.Cont.
Not only voice but also videoNot only voice but also video is transmitted using similar is transmitted using similar concepts.concepts.
Spreads at a fast paceSpreads at a fast pace.. For instance there isn’t any For instance there isn’t any internet cafe which doesn’t have internet cafe which doesn’t have tiny video cameras over their tiny video cameras over their monitors.monitors.
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Why need to IP Telephony? Why need to IP Telephony? Cont.Cont.
IndependentIndependent. Much larger . Much larger selection of service providers to selection of service providers to provide voice and video provide voice and video communication services .communication services .
No geographical restriction!No geographical restriction!Located virtually anywhere Located virtually anywhere
in the in the world! world!
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Keep in mind!
IP Telephony must be backward compatible with existing PSTN.
There are several communication schemes:
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Broadband Network
Call Direction
IP Protocol
VoIP VoIP
VoIP to VoIP
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Internet/Broadband
PSTN
Server/Gateway India
İstanbul, yeditepe New Delhi
Call Direction
IP Protocol
VoIP
VoIP to POTS with Internet
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PSTN
Server/Gateway
CO Miami
İstanbul, kayışdağı Miami, FL
LATA
Call Direction
IP Protocol
VoIP
VoIP to POTS without Internet
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Basic Idea Behind VoIP
Continuously sample audio.Convert each sample to digital form.Send the resulting digitized stream
accross an IP network in packets.Convert the stream back to analog for
playback.Before the procedure above, the system
must handle call setup. Phnumber to IP.
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Encoding, Transmission, and Playback
Two groups have introduced standards for IP telephonyInternational Telecommunications Union(ITU),
controls telephone standards.
Internet Engineering Task Force(IETF),
controls TCP/IP standards.
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Encoding Pulse Code Modulation (PCM) TransmissionReal-Time Transport
Protocol (RTP)Note: RTP is not a tranport-layer protocol. It is a
tranfer protocol that operates at Layer 5.
Each RTP message is encapsulated in UDP datagram, which is then encapsulated in an IP datagram for transmission.
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Why UDP instead of TCP?Why UDP instead of TCP?
Higher overhead of TCP does not Higher overhead of TCP does not make sense for telephone call. make sense for telephone call. Because audio must stream! No wait Because audio must stream! No wait for missing packets. Play missing for missing packets. Play missing part as silence.part as silence.
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Why UDP instead of TCP?Why UDP instead of TCP?
UDP Offerrs best-effort delivery. to UDP Offerrs best-effort delivery. to handle duplication, delay, out-of-order handle duplication, delay, out-of-order delivery, each RTP message contains:delivery, each RTP message contains:
A sequence numberA sequence number A real-time clock valueA real-time clock value
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What does real-time clock value do?
• Allows a receiver to construct the axact temporal sequence of the data.– İf a packet is missing , the receiver
knows exactly how long to wait before starting to play the next packet
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Signaling Systems and Protocols
Signaling: The process of establishing and terminating a call. Includes:– Mapping a phone number to location– Finding a route to the called party– Handling other details such as call forwarding
Signaling System 7 (SS7) for traditional telephone system.
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Signaling Protocols
IETFSession Initiation Protocol (SIP) ITUH.323
Aboves must be able to interact with SS7
Internet/Broadband
PSTN
Server/Gateway India
İstanbul, yeditepeNew Delhi
Call Direction
IP Protocol
VoIP
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A Basic IP Telephone System
Two basic components interconnected by an IP internet.
*IP telephone
*Media Gateway Controller
IP telephone IP telephoneINTERNET
Media Gateway Controller
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IP telephone
Analog telephoneINTERNET
Media Gateway Controller
PSTN
Media gateway handles voice
Signaling gateway handles setup