Transcript H.323 – A closer look

A Presentation on H.323
Deepak Bote
Email, IM, blog…
Important events of 1996!!

Bill Clinton was re-elected.

Dolly, the cloned sheep,
was born.

Prince Charles and Diana were divorced…

Emergence of VoIP & Internet Telephony
We are interested in the last one!
What about H.323???
VoIP products were proprietary.
 Hence incompatible.
 A standard for interoperability
 H.323 v1 was already existing for
LANs.
 V2 was developed to solve the
incompatibility issue.
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What exactly is H.323?
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Standard recommended by ITU-T
Defines real-time MM communications over
packet based networks.
Collection of Standards.
H.323 belongs to the H.32x class of standards
for videoconferencing applications.
H.323 – A Closer Look

Terminals (what people see/hear)
E
N
D
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Gateways (control and ‘routing’ )
P
O
I
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Multipoint Control Units (provides
conference capabilities )
Gatekeepers (access to other
environments)
N
T
S
Terminals
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H.323 client endpoints
They could be:
 Multimedia
PCs
 Any stand-alone device
 A simple telephone
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Expectation by H.323:
 Must
support audio communication.
 Video, data support optional
Gateways
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Optional Component of H.323
implementation.
Used as interface between different
networks e.g. LAN & PSTN
Functions:
 Data
format translation
 Audio/video codec translation
 Call setup, termination from both sides of the
network
Multipoint Control Units
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MCUs are also optional in a H.323
implementation
Needed only when multiparty conferences are
desired
Functions:
 Provides
capability of video-conferencing with more
than one party.
 Acts as a co-ordinator of multiparty conferences
Gatekeepers
“Brains” of a H.323 network
 Expectation by H.323:

 Address
translation
 Admissions Control
 Bandwidth Control
 Zone Management
 Routing Capabilities
Gatekeeper Zones
The Internet
Zone B
Gatekeeper
Gateway
Zone A
Gatekeeper
Router
Gateway
Phone
MCU
Gatekeeper
Gateway
H.323 terminal
H.323 terminal
ISDN videophone
The Protocols!!
The Protocols (cont)
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H.323 recommendation is a “framework” document that
describes how the various pieces fit together
H.225.0 defines the call signaling between endpoints and
the Gatekeeper
RTP/RTCP (RFC 3550) is used to transmit media such as
audio and video over IP networks
H.225.0 define the procedures and protocol for
communication within and between Peer Elements
H.245 is the protocol used to control establishment and
closure of media channels within the context of a call and
to perform conference control
The Protocols (cont)
H.450.x is a series of supplementary service
protocols
 H.460.x is a series of version-independent
extensions to the base H.323 protocol
 T.120 specifies how to do data conferencing
 T.38 defines how to relay fax signals
 V.150.1 defines how to relay modem signals
 H.235 defines security within H.323
systems
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The Protocols (cont)
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Audio:
 G.711
(popular codec for telephone n/ws)
 G.723.1 – more efficient
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Video
 H.261
codec (for channels with bandwidths
p*64 kb/s)
 H.263 codec (for low bit rate transmission
without loss of quality )
Typical H.323 Stack
Multimedia H.323
Applications, User Interface
Data
Applications
V.150
T.120
Media Control
T.38
Audio
Video
Codecs
Codecs
G.711
H.261
G.723.1
H.263
G.729
H.264
..
..
Terminal Control and Management
H.225.0
RTCP
Call
H.245
Signaling
H.225.0
RAS
RTP
UDP
TCP
TCP/UDP
UDP
IP
TCP/UDP
TCP
UDP
An H.323 Stack
H.323 Application
H.245
RAS
H.225.0
Call Signaling
Packet Network
RTP /
RTCP
H.323 Call Setup and Tear Down
Future
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Users want mobility - “Internet Phone
Numbers” that follow them anywhere
Enhancements for billing
 Enhancements to fax
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More interoperability
Concluding Remarks
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H.323 is a protocol that leverages the strength of
the packet-switched protocols from the IETF
H.323 offers excellent integration with the PSTN
H.323 enables voice, video, and data conferencing
H.323 provides a solid foundation for new
services and the continued growth of Multimedia
over IP
References
www.h323forum.org
 http://www.packetizer.com/voip/h323/
 Intel Tutorial site
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Registration, Admission, and
Status - RAS
Defined in H.225.0
 Allows an endpoint to request authorization
to place or accept a call
 Allows a Gatekeeper to control access to
and from devices under its control
 Allows a Gatekeeper to communicate the
address of other endpoints
 Allows two Gatekeepers to easily exchange
addressing information
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