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VoIP PRESENTATION. BY HÜSEYİN SAVRAN 220702044. OUTLINE. PSTN an brief history of telephone. PSTN ( Public Switched Telephone Network ). Known structure of conventional telephone network. İstanbul , yeditepe. Ankara , METU. PSTN. Call Direction. PSTN history.
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VoIP PRESENTATION BY HÜSEYİN SAVRAN 220702044
OUTLINE • PSTN an brief history of telephone
PSTN ( Public Switched Telephone Network) • Known structure of conventional telephone network. İstanbul, yeditepe Ankara, METU PSTN Call Direction
PSTN history • Since the telephone was invented in the late 1800s, telephone communication has not changed substantially .
A Change of Perspective Cable Traditional View Broadcast Telephony Data Wireless
A Change of Perspective Cable Current View Data Broadcast Telephony Wireless
A Change of Perspective Content Data Reality Web Devices Apps Voice Users Video Email File Transfer Cable Wireless Satellite Fiber
What is VoIP • IP TELPHONY (VOICE over IP) • Transmission of voice telephone calls using internet infrastructure.
Why need to IP Telephony? • Economic (uses internet, IP routers...) • Further savings. Because underlying network infrastructure can be shared. a single set of equipment, wiring, network connection enough. Example: a company with reduced telephone costs.
Why need to IP Telephony? Cont. • Not only voice but also video is transmitted using similar concepts. • Spreads at a fast pace. For instance there isn’t any internet cafe which doesn’t have tiny video cameras over their monitors.
Why need to IP Telephony? Cont. • Independent. Much larger selection of service providers to provide voice and video communication services . No geographical restriction! Located virtually anywhere in the world!
Keep in mind! • IP Telephony must be backward compatible with existing PSTN. • There are several communication schemes:
Call Direction IP Protocol VoIP to VoIP Broadband Network VoIP VoIP
Call Direction IP Protocol VoIP to POTS with Internet Internet/Broadband İstanbul, yeditepe New Delhi PSTN VoIP Server/Gateway India
Call Direction IP Protocol VoIP to POTS without Internet Server/Gateway İstanbul, kayışdağı Miami, FL PSTN CO Miami VoIP LATA
Basic Idea Behind VoIP • Continuously sample audio. • Convert each sample to digital form. • Send the resulting digitizedstream 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.
Encoding, Transmission, and Playback • Two groups have introduced standards for IP telephony International Telecommunications Union(ITU), controls telephone standards. Internet Engineering Task Force(IETF), controls TCP/IP standards.
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.
Why UDP instead of TCP? • Higher overhead of TCP does not make sense for telephone call. Because audio must stream! No wait for missing packets. Play missing part as silence.
Why UDP instead of TCP? • UDP Offerrs best-effort delivery. to handle duplication, delay, out-of-order delivery, each RTP message contains: • A sequence number • A real-time clock value
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
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.
Call Direction IP Protocol Signaling Protocols • IETFSession Initiation Protocol (SIP) • ITUH.323 Aboves must be able to interact with SS7 Internet/Broadband New Delhi İstanbul, yeditepe PSTN VoIP Server/Gateway India
A Basic IP Telephone System Two basic components interconnected by an IP internet. *IP telephone *Media Gateway Controller Media Gateway Controller IP telephone IP telephone INTERNET
Media gateway handles voice Media Gateway Controller IP telephone Analog telephone INTERNET PSTN Signaling gateway handles setup