Download H323 Overview

H323 Overview
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Agenda
1. What is H.323?
2. H323 components
3. Protocols Specified by H.323
4. Terminal Characteristics
5. Gatekeeper Characteristics
6. Connection Procedures
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What is H.323?
 The H.323 standard is cornerstone technology for the
transmission of real-time audio, video and data
communications over packet-based networks.
 It specifies communication over packet-based
networks(IP-based) or Internet packet(IPX) exchangebased local area networks(LANS), enterprise
networks(ENs), metropolitan-area networks(MANs), and
wide-area networks(WANs)
 Be applied in a variety of mechanisms – IP telephpony,
videotelephony, etc..
 Be applied to multipoint-multimedia communications.
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Interoperability of H.323 Terminals
Scope of
H.323
H.323
Terminal
H.323
MCU
Non-Guaranteed QoS LAN
(Note)
H.323
Gatekeeper
H.323
Gateway
Guaranteed
GSTN
H.323
Terminal
N-ISDN
H.323
Terminal
B-ISDN
QOS
LAN
H.310 terminal
operating in
H.321 mode
V.70
Terminal
H.324
Terminal
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Speech
Terminal
H.322
Terminal
Speech
Terminal
H.320
Terminal
H.321
Terminal
Note: A gateway may support one or more of the GSTN,
N-ISDN and/or B-ISDN connections.
H.321
Terminal
H.323 components
Terminal
MCU
Gateway
H.323
Terminal
Terminal
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H.323 components -Terminals
Used for real-time bidirectional multimedia
communications.
Can be a PC or stand-alone device, running an
H.323 and the multimedia applications.
Supports audio communications and can
optionally support video or data communications.
(basic service provided by an H.323 terminal is
audio comm, an H.323 terminal plays a key role
in IP-telephony services.)
The primary goal of H.323 is to interwork with
other multimedia terminals.
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H.323 components - Gateways
Connects two dissimilar networks.
Provides connectivity between an H.323 network
and a non-H.323 network.
Can connect and provide comm between H.323
terminal and SCN(switched telephony networks
e.g., public switched telephone network(PSTN)).
This connectivity of dissimilar networks is
achieved by translating protocols for call setup
and release, converting media formats between
different networks, and transferring information
between the networks connected by the gateway.
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H323 components - Gatekeepers
Can be considered the brain of the H.323
network.
Provide important services such as
addressing, authorization and
authentication of terminals and gateways.
Provide bandwidth management,
accounting, billing, and charging.,
May also provide call-routing services.
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H.323 components - MCU
Multipoint Control Unit
Provide support for conferences of three
or more H.323 terminals.
All terminals participating in the
conference establish a connection with the
MCU.
The MCU manages conference resources,
negotiates between terminals for the
purpose of determining the audio or video
coder/decoder to use.
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Protocols Specified by H.323 (1)
Audio Codecs
Video Codecs
H.225 registration, admission, and
status(RAS)
H.225 call signaling
H.245 control signaling
Real-time transfer protocol(RTP)
Real-time control protocol(RTCP)
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Protocols Specified by H.323 (2)
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Terminal Characteristics(1)
H.225 Registration, Admission, and Status


RAS is the protocol between endpoints (terminals and
gateways) and gatekeepers.
RAS is used to perform registeration, admission
control, bandwidth changes, status, and disengage
procedures between endpoints and gatekeepers.
H.225 Call signaling


Be used to establish a connection between two H.323
endpoints.
Be achieved byu exchanging H.225 protocol message
on the call signaling channel.
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Terminal Characteristics(2)
 H.245 Control Signaling




Capabilities exchange
Opening and closing of logical channels used to carry media
streams
Flow-control messages
General commands and indications.
 RTP/RTCP




Provides end-to-end delivery services of realtime audio and
video.
Be typically used to transport data via the user datagram
protocol(UDP).
Provides payload-type, sequence numbering, timestamping and
delivery monitoring.
Function of RTCP is to provide feedback on the quality of data
distribution.
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Gatekeeper Characteristics(1)
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Gatekeeper Characteristics(2)
 Address Translation

Calls originating within an H.323 network may use an alias to address
the destination terminal.
 Admission Control


Control the admission of the endpoints into the H.323
Uses RAS messages, ARQ, ACF, ARJ
 Bandwidth Control

Provides support for bandwidth control by using the RAS message,
BRQ, BCF, BRJ.
 Call-control Signaling (opt.)

Route call-signaling message between H.323 endpoints.
 Call Authorization (opt.)


GK may accept or reject the call.
The reasons for rejection may include access-based or time-based
restrictions, to and from particular terminals or gateways,
 Call Management (opt.)

Maintain information about all active H.323 calls.
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Connection Procedures(1)
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Connection Procedures(2)
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Both Gatekeepers Routing Call
Endpoint 1
Gatekeeper 2
Gatekeeper 1
Endpoint 2
ARQ(1)
ACF(2)
Setup(3)
Setup(4)
Call Proceeding(5)
Call Proceeding(5)
ARQ(6)
ARJ(7)
Facility(8)
Release Complete(9)
Setup(10)
Setup(11)
Call Proceeding(5)
Call Proceeding(5)
ARQ(12)
ACF/ARJ(13)
Alerting(14)
Alerting(14)
Alerting(14)
Connect(15)
Connect(17)
RAS Messages
Call Signalling Messages
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Connect(16)
Question ?
H.323
H.225
H.245
RTP/RTCP
Gatekeeper
Gateway
Terminal
MCU
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