H.323 Overview
Demystifying Multimedia Conferencing Over the Internet
Using the H.323 Set of Standards
Numbers to know:
• H.225 - call setup, establishment, tear-down
• H.245 - media capability negotiation
• H.261 & H.263 - video codecs
• G.7xx - audio codecs
H.323 Architecture
Audio and Video codecs
H.225 Layer
H.245 Q.931 RASAudio and Video I/O
How does all this work?
( the signaling example )
How does all this work?
Calling party opens H.323 client
How does all this work?
Q.931 Setup
Setup
How does all this work?
Q.931 Alerting (ringing)
Alerting
How does all this work?
Q.931 Connect
Connect
How does all this work?
H.245 terminal capabilities
termCapSet
How does all this work?
H.245 terminal capabilities
termCapAck
How does all this work?
H.245 determine Master/Slave
mSDet
How does all this work?
H.245 determine Master/Slave
mSDetAck
How does all this work?
H.245 determine Master/Slave
mSDetConfirm
How does all this work?
H.245 open channel (RTP)
openReq
How does all this work?
H.245 open channel (RTP)
openAck
How does all this work?
RTP connection
connected
How does all this work?
H.245 End Session
endSession
How does all this work?
Q.931 Release Complete
ReleaseComplete
Gatekeeper
• Purpose is to manage resources in a zone
• Uses RAS signaling
• Provides address resolution
• Alias Address Modification
• Approves calls based on bandwidth
• Dialed Digit Translation (PSTN)
• Directory Services
Advanced Features
• Interoperability with PSTN
• Centralized, decentralized, and hybrid multicast conferences through MCU
• Datastream and multicast encryption (H.235)
• Cascading MC’s for large conferences
• FastStart connection (similar to SIP)
H.323 Issues
• Interoperability issues between clients
• Massive, monolithic, closed specification
• Not designed to be readily extensible
• Competition from simpler, open, IETF standards (SIP, SDP, RTP)
Why is this important?
• Stress test of real latency sensitive data
• H.323 central to QoS issues
• Authentication carried out through CiNIC?