VoIP PRESENTATION BY HÜSEYİN SAVRAN

OUTLINE PSTN an brief history of telephone

PSTN ( Public Switched Telephone Network ) Known structure of conventional telephone network. Call Direction PSTN İstanbul, yeditepeAnkara, METU

PSTN history Since the telephone was invented in the late 1800s, telephone communication has not changed substantially.

Telephony A Change of Perspective Data Cable Broadcast Wireless Traditional View

Telephony A Change of Perspective Data Current View Cable Broadcast Wireless

Data Voice A Change of Perspective Web Reality Video File Transfer Content Cable Wireless Satellite Fiber Devices Apps Users

These Count as Phones?

MOTIVATION

What is VoIP IP TELPHONY (VOICE overIP) Transmission of voice telephone calls using internet infrastructure.

Why need to IP Telephony? Economic (uses internet, IP routers...) Economic (uses internet, IP routers...) Further savings. Because underlying 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. Not only voice but also video is transmitted using similar concepts. Spreads at a fast pace. Spreads at a fast pace. For instance there isnt any internet cafe which doesnt have tiny video cameras over their monitors. For instance there isnt any internet cafe which doesnt 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. 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:

Broadband Network Call Direction IP Protocol VoIP VoIP to VoIP

Internet/Broadband PSTN Server/Gateway India İstanbul, yeditepe New Delhi Call Direction IP Protocol VoIP VoIP to POTS with Internet

PSTN Server/Gateway COMiami İstanbul, kayışdağıMiami, FL LATA Call Direction IP Protocol VoIP VoIP to POTS without Internet

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.

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) 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. 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: UDP Offerrs best-effort delivery. to handle duplication, delay, out-of-order delivery, each RTP message contains: A sequence number A sequence number A real-time clock value 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.

Signaling Protocols IETF Session Initiation Protocol (SIP) ITU H.323 Aboves must be able to interact with SS7 Internet/Broadband PSTN Server/Gateway India İstanbul, yeditepe New Delhi Call Direction IP Protocol VoIP

A Basic IP Telephone System Two basic components interconnected by an IP internet. *IP telephone *Media Gateway Controller IP telephone INTERNET Media Gateway Controller

IP telephone Analog telephone INTERNET Media Gateway Controller PSTN Media gateway handles voice Signaling gateway handles setup