VoIP
Content
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
Ankara, METU
Call Direction
PSTN history
Since the telephone was invented in the late 1800s, telephone communication has not changed substantially .
A Change of Perspective
Traditional View
Data
Cable
Broadcast
Telephony
Wireless
A Change of Perspective
Current View
Data
Cable
Broadcast
Telephony
Wireless
A Change of Perspective
Reality
Web
Voice
Data
Video
Email
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
Internet/Broadband
New Delhi
İstanbul, yeditepe
PSTN
VoIP
Server/Gateway India Call Direction IP Protocol
VoIP to POTS without Internet
Server/Gateway
İstanbul, kayışdağı Miami, FL
PSTN
VoIP
CO
Call Direction
LATA
Miami
IP Protocol
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) 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.
Signaling Protocols
IETFSession Initiation Protocol (SIP) ITUH.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
Analog telephone
Signaling gateway handles setup
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
Ankara, METU
Call Direction
PSTN history
Since the telephone was invented in the late 1800s, telephone communication has not changed substantially .
A Change of Perspective
Traditional View
Data
Cable
Broadcast
Telephony
Wireless
A Change of Perspective
Current View
Data
Cable
Broadcast
Telephony
Wireless
A Change of Perspective
Reality
Web
Voice
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
Internet/Broadband
New Delhi
İstanbul, yeditepe
PSTN
VoIP
Server/Gateway India Call Direction IP Protocol
VoIP to POTS without Internet
Server/Gateway
İstanbul, kayışdağı Miami, FL
PSTN
VoIP
CO
Call Direction
LATA
Miami
IP Protocol
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) 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.
Signaling Protocols
IETFSession Initiation Protocol (SIP) ITUH.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
Analog telephone
Signaling gateway handles setup
