Download Chapter03

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project

Document related concepts

SIP extensions for the IP Multimedia Subsystem wikipedia , lookup

Recursive InterNetwork Architecture (RINA) wikipedia , lookup

Lag wikipedia , lookup

Internet protocol suite wikipedia , lookup

Multiprotocol Label Switching wikipedia , lookup

Serial digital interface wikipedia , lookup

Asynchronous Transfer Mode wikipedia , lookup

List of wireless community networks by region wikipedia , lookup

Cracking of wireless networks wikipedia , lookup

RapidIO wikipedia , lookup

Wake-on-LAN wikipedia , lookup

IEEE 1355 wikipedia , lookup

Net bias wikipedia , lookup

Quality of service wikipedia , lookup

Deep packet inspection wikipedia , lookup

Transcript
Voice Over Internet Protocol (VoIP)
Presentation 3 – VoIP: An
Overview
Copyright © 2006 Heathkit Company, Inc. All Rights Reserved
Objectives
At the end of this presentation,
you will be able to:
2
 Define
signaling, encoding, transport, and
gateway control as they apply to VoIP.
 Identify
the protocols associated with
signaling, encoding, transport, and gateway
control in VoIP.
 Define
jitter, latency, and packet loss.
Describe techniques designed to overcome
these problems.
3
Levels of VoIP
to Computer – One softphone
connects to another directly over the
Internet.
 Computer
 Via
a VoIP Service Provider
System – An organization acts
as its own VoIP Service provider
 Enterprise
4
Computer to Computer VoIP
 VoIP over
Instant Messaging
– MSN Messenger and Windows
Messenger
 Microsoft
 AOL – AIM
 Yahoo!
– Yahoo! Messenger
 Google
– Google Talk
5
6
VoIP via a Service Provider
 Great
for homes and small businesses.
 Monthly
fee or per call fee.
 Provide
services which are not
available or cost extra through PSTN.
 Generally
better quality than IM.
7
VoIP Providers

AT&T

Comcast Communications

Cablevision

Time Warner

Vonage

Cox Communications

Verizon

SBC Communications

EarthLink

Bell South

Nortel

Quest Communications
8
Typical Services Provided

Connect to PSTN

Call Waiting

Select your Area
Code

Call Forwarding

Caller ID

Voice Mail

Online Account
Management

Unlimited long
Distance

Conference Calls
9
Vonage
 The
largest VoIP Service provider
 Requires
a broadband connection to
the Internet.
 Signaling
Protocol is SIP.
10
Soft-phone
11
Analog Telephone
Adapter
IP Phone
Analog Phone
12
Enterprise System
Proxy
Server
IP Phones
Internet
IP
PBX
Admin
Server
PSTN
VoIP to PSTN
Gateway
13
Major VoIP Issues
 Signaling
 Voice
Coding
 Packet
Delivery
 Gateway
Control
14
Signaling
 Find
the called party.
 Determine
the status of the called party
– busy or not.
 Create
and manage calls.
15
Voice Coding

Voice is inherently analog.

Microphones produce an analog signal.

Speakers require an analog signal to reproduce
voice.

The Internet requires digital data packets.

The conversion of voice to digital data packets
at the transmitting end and the conversion of the
digital data packets back into voice at the
receiving end.
16
Packet delivery

Moving the voice data packets to their
intended recipient while ensuring
acceptable voice quality.

Rearranging the order of the received data
packets back to the order in which they
were transmitted.

Controlling the rhythm of the packets.
17
Gateway Control
 A gateway
is a device that converts
from one protocol to another.
 Common
 H.323
gateway conversions include:
to SIP and vice versa
 VoIP to
PSTN
 VoIP to ATM
 VoIP to
ISDN
18
VoIP creates two paths within the
IP network.
Path – Carries information
needed to establish and maintain the
media path.
 Signaling
Path – The path used by the
voice packets.
 Media
19
VoIP Protocols
Path protocols – SIP, H.323,
MGCP, and Megaco/H.248
 Signaling
Path protocol – Real Time
Protocol (RTP)
 Media
20
VoIP Challenges
 Latency
 Jitter
 Packet
loss
21
Latency

The delay between the instant a voice
fragment is produced and the later instant at
which the listener hears it.

The amount of time that the packet spends
in the network.

Latency greater than 150 milliseconds
becomes noticeable and may degrade voice
quality.
22
Contributors to Latency
 Encoder
delay
 Transport
 Jitter
delay
Buffer delay
 Decoder
delay
23
Jitter
 Changes
in latency from one packet to
the next.
 Packets
may take different paths with
different overall delays.
24
Packet Jitter
B
Internet
A
25
Jitter
Buffer
26
Lost Packets

Ignore the problem – “transmit” an instant
of silence.

Repeat the last packet transmitted.

Predict the contents of the lost packet by
examining the contents of previous packets.

Insert an instant of noise.
27
Voice Over Internet Protocol (VoIP)
End
Copyright © 2006 Heathkit Company, Inc. All Rights Reserved