bài thuyết trình về Voip

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PSTN vs. INTERNET
PSTN

Voice network use circuit
switching.

Dedicated path between
calling and called party.

Bandwidth reserved in
advance.

Cost is based on distance
and time.
INTERNET

Data network use packet
switching.

No dedicated path between
sender and receiver.

It acquires and releases
bandwidth, as it needed.

Cost is not based on
distance and time.
PBX
Yesterday’s Networks
Circuit Switched Networks (Voice)
CO
PBX
CO
CO
Packet Switched Networks (Data)
Router
Router
Router
Router
Router
• Separated networks
• Separated applications/services
PBX
IP Phone
Converged Network
PSTN
CO
Gateway
Router
Router
Router
Router
• Converged network
• Separated or integrated applications
PBX
IP Phone
VoIP – How does it work?

Converting the voice signal

ADC (analog to digital)

DAC (digital to analog)
Voice (source) - - ADC - - - Internet - - - DAC - - Voice (dest)

Transmission of voice traffic in packets
VoIP – How does it work?

The 1-2-3s of VoIP

1. Compression – voice is compressed
typically with one of the following codecs,
G7.11 64k, G7.29AB 8k, G723.1 6.3k

2. Encapsulation – the digitized voice is
wrapped in an IP packet

3. Routing – the voice packet is routed thru
the network to its final destination
LT
S
©Telcordia Technologies, Inc.
Slide 10
IP Network
Multimedia
PC
Multimedia
PC
Initially, PC to PC
voice calls over the
Internet
VoIP Architecture?
PSTN
(DC)
Gateway
PSTN
(NY)
Gateway
Public Switched
Telephone Network
Gateways allow PCs
to also reach phones
…or phones to reach
phones
Components

VoIP Protocols

VoIP Gateway

VoIP Codecs
VoIP Network Model
SIP
RTP, RTCP, RTSP
Transport Layer (UDP, TCP)
Network Layer (IP, IP Multicast)
Data Link Layer
Physical Layer
PURC 2004
IP Protocol Layering
IP Protocol Layering
Physical Transport (e.g, Cable Modem)
IP (Internet Protocol)
TCP UDP
Applications (e.g., email, web pages)
Email Data (1000 bytes)
TCP Header
(20 bytes)
IP Header
(20 bytes)
A Typical IP Datagram
VoIP SIP