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H.323: Multimedia
Conferencing for Packet
Switched Networks
Dave LindberghManager, Technical Standards Group
PictureTel
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 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
H.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)
Multipoint: MC+MP
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)
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 Hoc multipoint calls Join, invite, control of conference modes
Traditional MCU applications Multiprotocol via Gateways
H.225. 0
G.7xx H.26x
RTP
RTCP
Gate-keeper
Reg,Adm,Status(RAS)
Control Data Audio Video A/V Cntl Control
TCP UDP
IP
H.323 Protocol Stack
T.120 H.245
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) RTCP - Real-time Transport Control 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
PictureTel
PictureTel
PictureTel
(1) ARQCan I call“Bob”?
(2a) GK resolves “Bob”to IP address through H.323registration or externalname service (e.g. DNS, ULS, etc..)(2b) Admission PolicyApplied(3) ACF
Yes, use thisIP Address
Bill Bob
GK
Call Connection
PictureTel
PictureTel
PictureTel
(4) SETUP (Create)
Bill Bob
GK
(5) ARQMay I answer?
(6) ACFYes
(7) ALERTING
(8) CONNECT (User answers)
H.245 Connection
PictureTel
PictureTel
PictureTel
Bill Bob
(9) H.245 connection established- Capability Exchange- Master/Slave Determination- Open Logical Channels
- audio, video
For this example, assume Bill wins the Master/Slave determinationand becomes the Multipoint Controller (MC) of the conference
Bill invites Ross
PictureTel
PictureTel
PictureTel
Ross
GK
(10) ARQInviteRoss (11) ACF
Resolved Ross’sIP Address
(12) SETUP (Invite)
(13) ARQMay IJoin?
(14) ACFYes
(15) ALERTING(16) CONNECT
(17) H.245 CONNECTION
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 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
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 (encryption) A big 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