Title: H.323: Multimedia Conferencing for Packet Switched Networks
1H.323 Multimedia Conferencing for Packet
Switched Networks
- Dave Lindbergh
- Manager, Technical Standards Group
- PictureTel
2Contents
- What is H.323?
- H.323 Components
- Protocol Stack
- Call Setup
- Current H.323 Standards Work
3What 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
4History 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
5H.323 Components
- Terminals
- Gatekeepers
- Gateways (H.323 to H.320/H.324/POTS)
- MCUs
- Multipoint Controller (MC)
- Multipoint Processor (MP)
6H.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
7H.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
8Gatekeeper Functions (cont.)
- Management of gateway
- H.320, H.324, POTS, etc.
- Call Signaling
- May route calls in order to provide supplementary
services or to provide Multipoint Controller
functionality - Call Management/Reporting/Logging
9H.323 Gateways
- Provide world wide connectivity and
interoperability from LAN - H.320, H.324, regular POTS telephones
- Map 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)
10Multipoint MCMP
- MC - Multipoint Controller portion of a
traditional MCU - Manage common modes, capabilities
- MP - Multipoint Processor
- Portion of traditional MCU mixing or switching
audio. Not necessarily co-resident with MC. (e.g.
MC running multicast conference with each
terminal mixing audio)
11MCU 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 Hoc multipoint calls
- Join, invite, control of conference modes
- Traditional MCU applications
- Multiprotocol via Gateways
12H.323 Protocol Stack
Control
Data
Audio
Video
A/V Cntl
Control
Gate- keeper Reg, Adm, Status (RAS)
G.7xx
H.26x
RTCP
H.225. 0
T.120
H.245
RTP
TCP
UDP
IP
13H.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)
- RTCP - Real-time Transport Control Protocol (IETF)
14Call 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
15Call Initiation
GK
(2a) GK resolves Bob to IP address through
H.323 registration or external name service
(e.g. DNS, ULS, etc..) (2b) Admission
Policy Applied
(1) ARQ Can I call Bob?
(3) ACF Yes, use this IP Address
Bob
Bill
16Call Connection
GK
(5) ARQ May I answer?
(6) ACF Yes
(4) SETUP (Create)
(7) ALERTING
(8) CONNECT (User answers)
Bob
Bill
17H.245 Connection
(9) H.245 connection established
- Capability Exchange
Bob
- Master/Slave Determination
Bill
- Open Logical Channels - audio, video
For this example, assume Bill wins the
Master/Slave determination and becomes the
Multipoint Controller (MC) of the conference
18Bill invites Ross
GK
(13) ARQ May I Join?
(10) ARQ Invite Ross
(11) ACF Resolved Rosss IP Address
(14) ACF Yes
(12) SETUP (Invite)
(15) ALERTING (16) CONNECT
Ross
(17) H.245 CONNECTION
19Work 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)
20Work In Progress (Continued)
- H.245 Version 3
- To 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
21H.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
22H.235 (H.Secure)
- Privacy (encryption)
- A big issue on packet networks
- Authentication
- Key Exchanges (RSA DSS)
- Encryption per media stream
- Signaling procedures
23H.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)
24H.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
25H.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
26For More Information
- Please visit the PictureTel Standards Page
- http//standards.pictel.com