Vo. IP PRESENTATION BY HÜSEYİN SAVRAN 220702044
OUTLINE l PSTN an brief history of telephone
PSTN ( Public Switched Telephone Network) l Known structure of conventional telephone network. İstanbul, yeditepe PSTN Call Direction Ankara, METU
PSTN history l Since the telephone was invented in the late 1800 s, telephone communication has not changed substantially.
A Change of Perspective Traditional View Cable Data Broadcast Telephony Wireless
A Change of Perspective Current View Data Cable Broadcast Telephony Wireless
A Change of Perspective t en t on C s ce i ev D s pp A Reality Web Voice Email l ab e C W e el ir ss t Sa te li el F r be i r se U Data Video File Transfer s
These Count as Phones?
MOTIVATION
What is Vo. IP n n IP TELPHONY (VOICE over IP) Transmission of voice telephone calls using internet infrastructure.
Why need to IP Telephony? n n 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. n Spreads at a fast pace. For instance there isn’t any internet cafe which doesn’t have tiny video cameras over their monitors. n
Why need to IP Telephony? Cont. n 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! n n IP Telephony must be backward compatible with existing PSTN. There are several communication schemes:
Vo. IP to Vo. IP Broadband Network Vo. IP Call Direction IP Protocol
Vo. IP to POTS with Internet İstanbul, yeditepe Internet/Broadband New Delhi PSTN Vo. IP Server/Gateway India Call Direction IP Protocol
Vo. IP to POTS without Internet Server/Gateway İstanbul, kayışdağı Vo. IP Miami, FL PSTN CO LATA Call Direction IP Protocol Miami
Basic Idea Behind Vo. IP l Continuously sample audio. l Convert each sample to digital form. l Send the resulting digitized stream accross an IP network in packets. l Convert the stream back to analog for playback. l Before the procedure above, the system must handle call setup. Phnumber to IP.
Encoding, Transmission, and Playback l 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) Transmission Real-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 l Signaling: The process of establishing and terminating a call. Includes: – – – l Mapping a phone number to location Finding a route to the called party Handling other details such as call forwarding Signaling System 7 (SS 7) for traditional telephone system.
Signaling Protocols IETF Session Initiation Protocol (SIP) l ITU H. 323 Aboves must be able to interact with SS 7 l Internet/Broadband İstanbul, yeditepe New Delhi PSTN Vo. IP Call Direction Server/Gateway India IP Protocol
A Basic IP Telephone System Two basic components interconnected by an IP internet. *IP telephone *Media Gateway Controller IP telephone INTERNET IP telephone
Media Gateway Controller Media gateway handles voice IP telephone INTERNET PSTN Signaling gateway handles setup Analog telephone
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