H.323: Multimedia
Conferencing for Packet
Switched Networks
Dave Lindbergh
Manager, Technical Standards Group
PictureTel
Contents
 What
is H.323?
 H.323 Components
 Protocol Stack
 Call Setup
 Current H.323 Standards Work
What is H.323?
 ITU-T
standard for multimedia
videoconferencing on packet-switched
networks
 LANs
and corporate intranets
 Internet (limited by Internet performance)
Basis
for IMTC VoIP Internet Telephony
 On
LAN, typical video call uses 100-300
kbit/s of LAN capacity
 LAN
traffic can be managed and controlled
History of H.323
 May
1995 - H.323 work started
 June 1996 - Decided by ITU-T
 January 1998 - Version 2 planned for
ITU-T approval (added functions)
 ITU
is learning to work on “Internet time”
H.323 Components
 Terminals
 Gatekeepers
 Gateways
(H.323 to
H.320/H.324/POTS)
 MCUs
 Multipoint
Controller (MC)
 Multipoint Processor (MP)
H.323 Terminal
 Two
Versions
 Corporate
Network (high quality)
 Internet (optimized for low bandwidth
28.8/33.6 - G.723.1 and H.263)
 Built
in Multipoint capability for Ad Hoc
conferences
 Multicast (multi-unicast) allows 3-4
people in call without centralized mixing
or switching
H.323 Gatekeeper
 Address
Translation
 H.323
Alias to transport (IP) address based
on terminal registration
 “email-like” names possible
 “phone number like” names possible
 Admission
control
 Permission
to complete call
 Can apply bandwidth limits
 Method to control LAN traffic
Gatekeeper Functions (cont.)
 Management
 H.320,
 Call
of gateway
H.324, POTS, etc.
Signaling
 May
route calls in order to provide
supplementary services or to provide
Multipoint Controller functionality
 Call
Management/Reporting/Logging
H.323 Gateways
 Provide
world wide connectivity and
interoperability from LAN
 H.320,
 Map
H.324, regular POTS telephones
Call Signaling (Q.931 to H.225.0)
 Map Control (H.242/H.243 to H.245)
 Media Mapping (FEC, multiplex, rate
matching, audio transcoding, T.123
translation)
Multipoint: MC+MP
 MC
- Multipoint Controller portion of a
traditional MCU
 Manage
 MP
common modes, capabilities
- Multipoint Processor
 Portion
of traditional MCU mixing or
switching audio. Not necessarily coresident with MC. (e.g. MC running
multicast conference with each terminal
mixing audio)
MCU Functions
 Media
Distribution
 Unicast
- send media to one terminal
(centralized in MP; traditional model)
 Multicast - send to each receiver directly
 Hybrid - some of each
 Manage Ad
 Join,
Hoc multipoint calls
invite, control of conference modes
 Traditional
MCU applications
 Multiprotocol via Gateways
H.323 Protocol Stack
Control
Data
Audio
Video
A/V Cntl Control
Gatekeeper
G.7xx H.26x
RTCP
H.225. 0 H.245 T.120
RTP
TCP
UDP
IP
Reg,
Adm,
Status
(RAS)
H.323 Protocol Components
 H.323
- System Document
 H.225.0 - Call Signaling, Packetization
 Gatekeeper
Registration, Admission, and
Status
 H.245
- Control (also used in H.324,
H.310)
 T.120 - Data and Conference Control
 RTP - Real-time Transport Protocol
(IETF)
Call Setup
A Call Setup Example
 a point to point call
 3rd terminal invited into call (Ad hoc
multipoint)
 One Gatekeeper using the Direct Call
Model
Call Initiation
GK
(1) ARQ
Can I call
“Bob”?
(3) ACF
Yes, use this
IP Address
Bill
(2a) GK resolves “Bob”
to IP address through H.323
registration or external
name service
(e.g. DNS, ULS, etc..)
(2b) Admission Policy
Applied
PictureTel
Bob
Call Connection
GK
(5) ARQ
May I answer?
(6) ACF
Yes
(4) SETUP (Create)
(7) ALERTING
PictureTel
(8) CONNECT (User answers)
Bill
Bob
H.245 Connection
PictureTel
Bill
(9) H.245 connection established
- Capability Exchange
- Master/Slave Determination
Bob
- Open Logical
Channels
- audio, video
For this example, assume Bill wins the Master/Slave determination
and becomes the Multipoint Controller (MC) of the conference
Bill invites Ross
GK
(10) ARQ
Invite
Ross
(13) ARQ
May I
Join?
(11) ACF
(14) ACF
Resolved Ross’s
Yes
IP Address
(12) SETUP (Invite)
(15) ALERTING
(16) CONNECT
(17) H.245 CONNECTION
PictureTel
Ross
Work in progress
 H.323
 Implementors
Guide
 Version
2
 Supplementary Services
 H.225.0
 Version
2
 Annex E - Video Packetization (w/IETF)
 Annex F - Audio Packetization (w/IETF)
Work In Progress (Continued)
 H.245
 To
Version 3
support H.323 version 2
 H.246
(“H.Interworking”) - Gateway
 Annex A.1
- H.323-H.320
 Annex A.2 - H.323-H.324
 H.235
(“H.Secure”) - Encryption
 H.332 (“H.Loosely Coupled”) Broadcast
 H.MediaMIB
H.323/H.225.0 Version 2
 Enhanced
procedural descriptions
 Gateway registration and selection
procedures, registration capabilities
 Authentication and Security
 MC Cascading and transfer of MC
 Relationship to T.120 and T.130
 RAS Retry/Time-out
 Additional audio and video
packetizations
H.235 (“H.Secure”)
 Privacy
 A big
(encryption)
issue on packet networks
 Authentication
 Key
Exchanges (RSA & DSS)
 Encryption per media stream
 Signaling procedures
H.246 (“H.Interworking”)
 “Interworking
of H-Series of Multimedia
Terminals” - Standard for gateways
 Interworking between H.323, H.320,
H.324, H.310, regular POTS telephones
 Initial Focus:
 H.323
to H.320 (Annex A.1)
 H.323 to H.324 (Annex A.2)
H.332 (“H.Loose Multipoint”)
 “Loosely
coupled” multipoint
conferences
 Potentially
thousands of participants
 Primarily broadcast
 Procedures
for one to many or panel
type conferences
 Similar to H.331(for H.320):

No capability exchange in conference
H.MediaMIB
 Management
Information Database
(MIB) definitions for H.323 entities
(terminals, Gatekeepers, Gateways, and
MCUs)
 Possible MIB definitions for other
H.series endpoints
 IETF coordination required
For More Information
 Please
visit the PictureTel Standards
Page:
 http://standards.pictel.com