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
PSTN
Call Direction
Ankara, METU
PSTN history

Since the telephone was invented
in the late 1800s, 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
Reality
Web
Voice
Email
Data
Video
File
Transfer
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?


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:
VoIP to VoIP
Broadband Network
VoIP
VoIP
Call Direction
IP Protocol
VoIP to POTS with Internet
İstanbul, yeditepe
Internet/Broadband
New Delhi
PSTN
VoIP
Server/Gateway
India
Call Direction
IP Protocol
VoIP to POTS without Internet
Server/Gateway
İstanbul, kayışdağı
Miami, FL
PSTN
VoIP
CO
LATA
Call Direction
IP Protocol
Miami
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.
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.
Signaling Protocols
IETFSession Initiation Protocol (SIP)
 ITUH.323
Aboves must be able to interact with SS7

Internet/Broadband
New Delhi
İstanbul, yeditepe
PSTN
VoIP
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
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