VoIP PRESENTATION

BYHÜSEYİN SAVRAN220702044

OUTLINE

PSTN an brief history of telephone

PSTN ( Public Switched Telephone Network)

Known structure of conventional telephone network.

Call Direction

PSTNİstanbul, yeditepe Ankara, 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 ViewCable

Broadcast

Wireless

DataVoice

A Change of Perspective

Web

Email

Reality

Video

File Transfer

Content

Cable

Wire

less

Satellit

e

Fiber

Devices

Apps

Users

These Count as Phones?

MOTIVATION

What is VoIP

IP TELPHONY (VOICE over IP) Transmission of voice telephone calls

using internet infrastructure.

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.

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.

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!

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

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

CO Miami

İstanbul, kayışdağı Miami, 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 telephonyInternational 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?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.

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

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

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

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

IP telephone

Analog telephoneINTERNET

Media Gateway Controller

PSTN

Media gateway handles voice

Signaling gateway handles setup