H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network. The H.323 standard addresses call signaling and control, multimedia transport and control, and bandwidth control for point-to-point and multi-point conferences. It is widely implemented by voice and videoconferencing equipment manufacturers, is used within various Internet real-time applications such as GnuGK and NetMeeting It is widely deployed worldwide by service providers and enterprises for both voice and video services over IP networks. It is a part of the ITU-T H.32x series of protocols, which also address multimedia communications over ISDN, the PSTN or SS7, and 3G H.323 call signaling is based on the ITU-T Recommendation Q.931 protocol and is suited for transmitting calls across networks using a mixture of IP, PSTN, ISDN, and QSIG over ISDN.

1. Coursework for IP Networks and Protocols
H.323
Packet Based Network
PROTOCOL
Submitted by:
Yatish Bathla
Bruno Iñiguez

2. Introduction
Coursework for IP Networks and Protocols
• H.323* is a multimedia conferencing protocol, which includes voice, video, and
data conferencing, for use over packet networks
• Standard recommended by ITU-T
• Collection of Standards.
• H.323 belongs to the H.32x class of standards for videoconferencing applications.
• H.323 is ITU-T Recommendation Packet-based multimedia communications
systems”
What is H.323?

3. Architecture
Coursework for IP Networks and Protocols
RR
Router
Gatekeeper
MCU
RR
RR
PSTN
Enterprise
Wireless
ISND
Gateway
Terminals
IP Network
• Terminals
• Gateways
• Multipoint Control Units
• Gatekeepers
• Border Elements
Endpoints

4. Terminals
Coursework for IP Networks and Protocols
• H.323 client endpoints
• They could be:
• Telephones
• Voicemail Systems
• “Soft phones” (e.g., NetMeeting®)
• Multimedia PCs
• Any stand-alone device
• Expectation by H.323:
• Must support audio communication.
• Video, data support optional

5. Gateways
Coursework for IP Networks and Protocols
ptional Component of H.323 implementation.
sed as interface between different networks e.g. LAN & PSTN
unctions:
• Data format translation
• Audio/video codec translation
• Call setup, termination from both sides of the network

6. Multipoint Control Unit (MCU)
Coursework for IP Networks and Protocols
ultipoint conferences (two or more endpoints engaged in a conference)
CUs are also optional in a H.323 implementation
eeded only when multiparty conferences are desired
unctions:
• Provides capability of video-conferencing with more than one party.
• Acts as a coordinator of multiparty conferences

7. Gatekeepers
Coursework for IP Networks and Protocols
Brains” of a H.323 network
xpectation by H.323:
• Address translation
• Admissions Control
• Bandwidth Control
• Zone Management
• Routing Capabilities
he Gatekeeper is an optional component in the H.323 system which is primarily used
for admission control and address resolution
he gatekeeper may allow calls to be placed directly between endpoints or it may
route the call signaling through itself to perform functions such as follow-me/find-me
and forward on busy

8. Border Elements and Peer Elements
Coursework for IP Networks and Protocols
• Peer Elements, which are often co-located with a Gatekeeper, exchange
addressing information and participate in call authorization within and
between administrative domains
• Peer Elements may aggregate address information to reduce the volume of
routing information passed through the network
• Border Elements are a special type of Peer Element that exists between two
administrative domains
• Border Elements may assist in call authorization/authentication directly
between two administrative domains or via a clearinghouse

9. Protocol Stack
Coursework for IP Networks and Protocols
H.323
IP
UDP
RTP
RTCP
TCP/UDP TCP UDPUDP TCP
Audio
Codecs
G.711
G.723.1
G.729
..
Video
Codecs
H.261
H.263
H.264
..V.150 T.120
TCP/UDP
T.38
H.225.0
Call
Signaling
H.245
H.225.0
RAS
Terminal Control and Management
Data
Applications
Media Control
Multimedia Applications, User Interface

10. Registration, Admission, and Status - RAS Signaling
Coursework for IP Networks and Protocols
• 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
GatekeeperTerminal Gatekeeper
GRQ
GRJ
GCF
GK discovery
GRQ
GRQ

11. Registration, Admission, and Status - RAS Signaling
Coursework for IP Networks and Protocols
GatekeeperTerminal
RRQ
RCF
URQ
UCF
／／ ／／

12. Registration, Admission, and Status - RAS Signaling
Coursework for IP Networks and Protocols
ARQ
ACF
Setup
ACF
／／ ／／ ／／
ARQ
DRQ
DCFDCF
DRQ
TerminalTerminal Gatekeeper

13. H.225.0 Call Signaling
Coursework for IP Networks and Protocols
Terminal
Setup
Call Proceeding
Connect
Release Complete
Terminal
Alerting
H.245 Session Establishment
H.245 Session Release
Media Exchange
Allows an endpoint to initiate and terminate a call with another endpoint

14. Coursework for IP Networks and Protocols
H.245 Call Control
• Provide more extensive control over the conference.
• H.245 provides capabilities such as capability
negotiation, master/slave determination, opening and closing of "logical channels"
(i.e., audio and video flows), flow control, and conference control.
Capability Negotiation
• Enables devices to communicate without having prior knowledge of the capabilities
of the remote entity.
Master/Slave Determination
• Once capabilities are exchanged, the endpoints negotiate master and slave roles.
• The master in a point to point conference really only has the power to indicate when
channels are in conflict (e.g., when one the other terminal tries to open a channel
that is not compatible)
• The slave device must yield to the requests of the master device and reconfigure
channels appropriately

15. Coursework for IP Networks and Protocols
H.245 Call Control
Logical Channel Signaling
•Once capabilities are exchanged and master/slave determination steps have completed,
devices may then open "logical channels" or media flows. This is done by simply sending
an Open Logical Channel (OLC) message and receiving an acknowledgement message.
Upon receipt of the acknowledgement message, an endpoint may then transmit audio or
video to the remote endpoint.
Fast Connect
•Fast Connect (also improperly referred to as “fast start”, after the name of the
associated field) is a means of establishing an H.323 call with as few as two messages
•With the use of Fast Connect, there is no need to open an H.245 channel, as long as all
needed media can be negotiated via Fast Connect

16. Coursework for IP Networks and Protocols
H.245 Call Control

17. Coursework for IP Networks and Protocols
Use Cases
H.323 and Voice over IP services
ITU-T Recommendation H.323 is one of the standards used in VoIP.
H.323 and Videoconference services
Supports advanced videoconferencing features, including:
•Cascading MCUs
•MCU control over audio and video mixing
•Chair control
•Far-end camera control

18. Coursework for IP Networks and Protocols
On to Next Generation Network
• Scalability
H.323 allows calls to be routed directly between endpoints without the need for an
intermediate entity that maintains call state Ability to utilize network services for
address resolution, including ENUM, LDAP, and DNS.
• Gateway Decomposition
H.248.1 defines how to decompose an H.323 gateway into a Media Gateway Controller
and one or more Media Gateways
• Robustness
• Alternate gatekeepers
• Mechanisms for “failing over” to an alternate softswitch or other
routing entity

19. Coursework for IP Networks and Protocols
On to Next Generation Network
• Re-Routing Active Calls (H.460.15)
• Useful to allow “session border controllers” to participate in initial call setup (e.g.,
manipulate source or destination addresses) and then exit the call signaling path
• Allows devices to participate in signaling only when there is a need to exchange messages
during a call (often only the beginning and the end of a call)
• Flexibility
• Support for T.120 data conferencing
• Support for real-time text communication
• Support for fax and modem relay
• Multimedia
• The most important aspect of the Next Generation Network is the ability to communicate
in new ways.
• H.323 has very strong support for video
• H.323 and T.120 allow users to work side by side on a document using voice, video, text,
and application sharing technologies

20. Coursework for IP Networks and Protocols
Summary
• H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T)
that defines the protocols to provide audio-visual communication sessions on any packet
network.
• The H.323 standard addresses call signaling and control, multimedia transport and control, and
bandwidth control for point-to-point and multi-point conferences.
• It is widely implemented by voice and videoconferencing equipment manufacturers, is used
within various Internet real-time applications such as GnuGK and NetMeeting
• It is widely deployed worldwide by service providers and enterprises for both voice and video
services over IP networks.
• It is a part of the ITU-T H.32x series of protocols, which also address multimedia
communications over ISDN, the PSTN or SS7, and 3G
• H.323 call signaling is based on the ITU-T Recommendation Q.931 protocol and is suited for
transmitting calls across networks using a mixture of IP, PSTN, ISDN, and QSIG over ISDN.

21. Thank You!